DE102012108151A1 - Method for determining craniocaudal length change and mediolateral change femur offset, involves calculating spatial change of location coordinates and projecting spatial change of location coordinates to craniocaudal reference direction - Google Patents

Abstract

The method involves defining a reference coordinate system using a surgical reference marking device (26,28). The surgical marking device is defined at the femur (12) for defining a primary characteristic point on the femur. The location coordinates of the primary and secondary characteristic points of the femur are determined in the reference coordinate system before and after implantation. The spatial changes of location coordinates of the primary and secondary characteristic points in the reference coordinate system due to the implantation are calculated. The change in length of the femur is determined by projecting the spatial change of the location coordinates of the primary characteristic point to the craniocaudal reference direction. The change of the offset of the femur is determined by projecting the spatial change of the location coordinates of the secondary characteristic point to the mediolateral reference direction. Independent claims are included for the following: (1) a device for determining craniocaudal length change and mediolateral change of the offset of a femur of a patient due to the implantation of an artificial hip joint; and (2) a computer program product with a computer readable medium for storing a computer program for determining craniocaudal length change and mediolateral change of the offset of a femur of a patient due to the implantation of an artificial hip joint.

Description

The invention relates to a method for determining the cranio-caudal change in length of the medio-lateral change in the offset of a femur of a patient as a result of the implantation of an artificial hip joint.

Moreover, the invention relates to an apparatus for carrying out the method.

Furthermore, the invention relates to a computer program product and a computer program.

In the field of hip arthroplasty, navigation systems have been used for some time to assist the surgeon in the insertion of the artificial hip joint, usually consisting of a socket to be anchored in the pelvis and a shaft to be anchored in the femur with a joint ball engaging in the socket. Anatomical conditions of the patient as well as the relative orientation of the components of the hip joint to each other can be recorded with a navigation system and the data thus obtained can be further processed with a data processing system.

In such systems it is known to signal the surgeon the cranio-caudal change in length of the femur and the medio-lateral change in the offset of the femur as a result of the implantation. In the present case, the change in length of the femur is understood in particular to be the difference in the length of the femur, given by the distance of the hip joint center from the knee joint before and after implantation. In particular, the distance of the point of intersection of the axis of the femoral neck and the axis of the femoral canal from the mechanical axis of the femur is considered to be the offset of the femur (also referred to as "offset" of the femur). from a line connecting the hip joint center to the knee joint. As a change of the offset of the femur is accordingly understood the difference of the distance before and after implantation. The above definitions are used in the present case only to illustrate the invention, the scope of which is not limited to this specific definition of the change in length and the change in the offset.

The detection of location coordinates "before implantation" means in this case that the spatial coordinates are detected on the natural hip joint without changing the femur or pelvis, although a removal of the femoral head from the acetabulum is possible. The determination of location coordinates "after implantation" includes the case in which a femoral shaft with joint ball is already anchored in the femur and a joint socket is already anchored in the pelvis, but femur shaft and socket are not yet connected to each other.

Change in length and change in the offset of the femur are important for the surgeon information on insertion of the artificial hip joint, using which he can in particular determine the change in the leg length of the patient as a result of surgery. This is desirable, for example to ensure that the patient has two legs of equal length after implantation. On the basis of the information provided to him, the surgeon can then correct the positioning of the femoral shaft relative to the femur or the socket relative to the pelvis, depending on need before the final implantation of the hip joint, so that the desired leg length results.

It is known that the change in length and the change in the offset of the femur can be calculated by detecting the neutral position of the femur before and after the implantation, which neutral position corresponds to the orientation of the femur relative to the pelvic bone when the patient is standing and the leg extended. For this purpose, the femur is to be transferred to the neutral position before and after the implantation, and a surgical marking device is fixed to the femur at a characteristic point. The determination of the location coordinates of the first characteristic point and the hip joint center in this method takes place in the reference coordinate system of the femur. For a sufficiently accurate determination of the change in length of the long femur, for this reason, the marking device is fixed in the region of the distal end of the femur and close to the mechanical femur axis. However, this leads to an inaccurate calculation of the change in the offset.

Although the method described and the corresponding device have proven successful in practice despite the inaccuracy described above. Nevertheless, it would be desirable to be able to make a more accurate determination of the change in length and the change in the offset of the femur.

The object of the present invention is to provide a method and a device with which the change in length and the change in the offset of the femur due to the implantation of an artificial hip joint can be calculated with increased accuracy.

• – es wird mittels einer chirurgischen Referenzmarkiervorrichtung ein Referenzkoordinatensystem definiert und im Referenzkoordinatensystem eine erste, cranio-caudale Referenzrichtung sowie eine zweite, medio-laterale Referenzrichtung quer zur ersten Referenzrichtung;
• – es wird eine erste chirurgische Markiervorrichtung am Femur festgelegt zur Definition eines ersten charakteristischen Punktes am Femur;
• – es werden vor und nach der Implantation
• – die Ortskoordinaten des ersten charakteristischen Punktes des Femurs im Referenzkoordinatensystem bestimmt durch Detektion des ersten charakteristischen Punktes am Femur sowie
• – die Ortskoordinaten eines zweiten charakteristischen Punktes des Femurs im Referenzkoordinatensystem bestimmt, wobei zumindest vor der Implantation der zweite charakteristische Punkt mittels einer zweiten chirurgischen Markiervorrichtung am Femur detektiert wird;
• – es wird die räumliche Änderung der Ortskoordinaten des ersten charakteristischen Punktes infolge der Implantation im Referenzkoordinatensystem berechnet;
• – es wird die räumliche Änderung der Ortskoordinaten des zweiten charakteristischen Punktes infolge der Implantation im Referenzkoordinatensystem berechnet;
• – es wird die Längenänderung des Femurs am Mittel durch Projektion der räumlichen Änderung der Ortskoordinaten des ersten charakteristischen Punktes auf cranio-caudale Referenzrichtung; und
• – es wird die Änderung des Versatzes des Femurs ermittelt durch Projektion der räumlichen Änderung der Ortskoordinaten des zweiten charakteristischen Punktes auf die medio-laterale Referenzrichtung.

This object is achieved by a method according to the invention for determining the cranio-caudal change in length and the medio-lateral change in the offset of a femur of a patient as a result of the implantation of an artificial hip joint having the following features:

• A reference coordinate system is defined by means of a surgical reference marking device, and a first, cranio-caudal reference direction and a second, medio-lateral reference direction transversely to the first reference direction are defined in the reference coordinate system;
• A first surgical marking device is set on the femur to define a first characteristic point on the femur;
• - it will be before and after implantation
• - The location coordinates of the first characteristic point of the femur in the reference coordinate system determined by detection of the first characteristic point on the femur and
• - determines the location coordinates of a second characteristic point of the femur in the reference coordinate system, wherein at least prior to implantation, the second characteristic point is detected by means of a second surgical marking device on the femur;
• The spatial change of the location coordinates of the first characteristic point as a result of the implantation in the reference coordinate system is calculated;
• The spatial change of the location coordinates of the second characteristic point due to the implantation in the reference coordinate system is calculated;
• - It is the change in length of the femur at the center by projection of the spatial change of the spatial coordinates of the first characteristic point on cranio-caudal reference direction; and
• - The change in the offset of the femur is determined by projection of the spatial change of the position coordinates of the second characteristic point on the medio-lateral reference direction.

In the method according to the invention, a reference coordinate system is defined by means of the reference marking device. The reference coordinate system may, for example, be body-based in a simple and reliable implementation of the method with respect to the patient. It is also conceivable that the reference coordinate system is environment-oriented with respect to an object to which the patient has a fixed spatial relationship during the operation. In particular, the reference coordinate system can be defined by the position and orientation of the operating table on which the patient is fixed during the operation. In the reference coordinate system, a cranio-caudal reference direction and a medio-lateral reference direction are defined, for example as axes or vectorially.

The reference directions are transversely and in particular vertically aligned relative to each other.

By means of the first marking device fixed on the femur, spatial coordinates of the first characteristic point are detected before and after the implantation and their spatial change is calculated vectorially, for example. The projection of the spatial change on the cranio-caudal reference direction is regarded as a change in length of the femur as a result of the implantation. It turns out in practice that this approximation is sufficiently accurate and reliable.

Correspondingly, spatial coordinates of a second characteristic point of the femur are determined, of which at least prior to implantation by detection with a second marking device. The spatial change of the location coordinates of the second characteristic point, for example vectorially, are calculated and projected onto the medio-lateral reference direction. The projection is considered to be a change in the offset of the femur as a result of implantation. It turns out in practice that this approximation is also sufficiently accurate and reliable.

The above-mentioned process steps need not all be carried out in the stated order. For example, the definition of the reference direction in the reference coordinate system can also be carried out only after the determination of the location coordinates of the characteristic points before the implantation. It is also conceivable, for example, that the location coordinates of the second characteristic point are determined before those of the first characteristic point.

Unlike the method described above, according to the invention, a second marking device is used, and location coordinates of a second characteristic point on the femur are determined prior to implantation and after implantation of the artificial hip joint. This makes it possible to base the calculation of the change in length and the calculation of the change in the offset on more data than in the method described above. In carrying out the method, the first characteristic point can be chosen so that the most accurate determination of the change in length can be made, and the second characteristic point can be selected in a corresponding manner so that the most accurate determination of the change in the offset can be made. This allows a more accurate calculation of the change in length and the change in the offset. This allows the surgeon to assess the influence of the implantation of the artificial hip joint on the leg position in a better way.

Furthermore, it proves to be advantageous that it is not necessary to determine spatial coordinates of the hip joint center and to be included in the calculation of the change in length and the change in the offset of the femur. The process according to the invention can thereby be carried out in a simpler manner. Furthermore, a check of the previous calculation method of the change in length and the change in the offset can be made. The results of both methods of determination can be compared. If, for example, the results deviate from each other by a predefinable threshold, an indication can be given to the surgeon, who requests him to re-examine the implantation result. This reduces the risk of incorrect implantation.

It is favorable if the location coordinates of the first characteristic point and the second characteristic point are determined before and / or after the implantation in the neutral position of the femur relative to the pelvic bone. This allows the most accurate determination of the change in length and the change in the offset of the femur by the mechanical femur axis is aligned as parallel as possible to the cranio-caudal reference direction. Ideally, then, the mechanical femur axis is aligned perpendicular to the medio-lateral reference direction, which in turn can be aligned perpendicular to the cranio-caudal reference direction.

Additionally or alternatively it can be provided that the femur is not transferred to the neutral position relative to the pelvic bone and the neutral position of the femur is calculated. This can be done, for example, in the WO 2006/074954 A1 described method.

Preferably, the reference marking device is fixed to the pelvic bone. This gives the possibility to define a body-based reference coordinate system. The determination of location coordinates of the characteristic points in the reference coordinate system is thereby independent of the positioning of the patient relative to its surroundings. This facilitates the implementation of the method.

In the reference coordinate system, a reference plane defined by the two reference directions is preferably defined. Conversely, it can be provided that the reference plane is defined and in this the reference directions are selected.

In an advantageous variant of the method according to the invention, it is favorable if the coordinate coordinates of the left anterior superior iliac spine, the right anterior superior iliac spine and the pubic symphysis (pubis) are respectively detected by the pelvic bone when the medio-lateral reference direction is defined as extending along an imaginary connecting line of the left upper iliac spine to the right upper iliac spine, and if the cranio-caudal reference direction is defined as extending along an imaginary, preferably orthogonal, projection of the pubis onto the imaginary connecting line. The location of the left and right upper iliac spine and the pubis define the so-called pelvic entrance plane (also called the anterior pelvic plane). The pelvic entrance plane is oriented substantially vertically in an upright patient and oriented parallel to the mechanical axis of the femur. Accordingly, the medio-lateral reference direction extends along an imaginary connection of the iliac spine perpendicular to the mechanical axis of the femur in a plane parallel thereto. The cranio-caudal reference direction runs, with advantageous vertical projection of the pubis on the aforementioned imaginary connecting line, parallel to the mechanical axis of the femur. The reference directions thus correspond to the body's preferred directions with particularly advantageous suitability for reliable determination of the change in length and the change in the offset of the femur.

The determination of the location coordinates of the left and right iliac spine and the pubis takes place, for example, by their detection with a marking device in the form of a surgical palpation instrument. The iliac spine and pubis can also be felt extracorporeally.

Preferably, the location coordinates of the second characteristic point after implantation are determined by detecting the second characteristic point on the femur by means of the second surgical marking device. This allows a simple implementation of the method involving the surgeon. After the implantation, the surgeon may pay particular attention to the fact that the second characteristic point is identical to the second characteristic point detected before the implantation.

Alternatively or additionally, it can be provided in another advantageous variant of the method according to the invention that the spatial coordinates of the second characteristic point are determined after the implantation by the spatial distance of the location coordinates of the second characteristic point from the location coordinates of the first characteristic point before Implantation is calculated and the spatial distance is added to the location coordinates of the first characteristic point after implantation. For example, in the reference coordinate system, the spatial distance of the two characteristic points prior to implantation is determined vectorially and the resultant vector is added to the position vector of the first characteristic point after the implantation.

The two last-mentioned variants of the method according to the invention can both be carried out and their plausibility and conformity checked for their results. This allows an even more reliable determination of the change in length and the change in the offset of the femur. If the results deviate from each other by a predefinable threshold, an indication can be given to the surgeon.

Advantageously, the first characteristic point is detected in the region of the distal end of the femur and / or the first characteristic point is detected on or near the mechanical femur axis. This can be achieved in a simple manner by fixing the first marking device in the region of the distal end of the femur and / or on or near the mechanical femur axis on the femur. This allows a more accurate determination of the change in length of the femur.

Preferably, the second characteristic point is detected more proximally at the femur than the first characteristic point. This takes into account the structure of the femur in which the intersection of the axis of the femoral neck with the axis of the femoral canal is located near its proximal end and the distance of the axis of the femoral canal from the mechanical femoral axis increases steadily from the distal end of the femur to the point of intersection. In this variant of the method, a more accurate determination of the change in the offset can be carried out.

It is advantageous if the second characteristic point is detected in the region of the proximal end of the femur in order to allow the most accurate determination possible of the change in the offset.

The most accurate determination of the change in the offset is made possible, in particular, by detecting the second characteristic point on the greater trochanter of the femur. A detection of the second characteristic point on the greater trochanter is also feasible due to its prominent training for the surgeon in a simple manner.

As mentioned earlier, the offset of the femur can be defined as the distance of an intersection of the axis of the femoral neck with the axis of the femoral canal from the mechanical femoral axis. For an accurate determination of the change in the offset, it is therefore advantageous if this distance is maximized as far as possible. For this reason, it is favorable if the second characteristic point is detected laterally at the greater trochanter.

Preferably, the second characteristic point is detected by palpation by means of the second marking device, which is designed for this purpose as a surgical palpation instrument. Thereby, it can be avoided that the second marking device is fixedly attached to the femur, and consequently operated less invasively. Furthermore, a possible obstruction of the surgeon by a permanently attached second marking device can be avoided, in particular if the second characteristic point is detected in the region of the proximal end of the femur.

Advantageously, the second characteristic point is palpated subcutaneously. Thereby, an inaccuracy of the determination of the location coordinates of the second characteristic point can be avoided, as it may result in percutaneous palpation by moving soft tissue surrounding the femur. Overall, therefore, the change in the offset can be determined more accurately.

Preferably, the second characteristic point is marked, for example by means of a bone screw attached to the femur by the surgeon or a notch. In this way, it is possible to ensure that, before and after the implantation, local coordinates of the same second characteristic point are determined in each case in order to be able to determine the change in the offset as precisely as possible.

As mentioned above, the invention also relates to a device for determining the change in length and the change in the offset of a femur.

• – ein chirurgisches Navigationssystem zur Bestimmung der Position und der Orientierung von mindestens einer chirurgischen Markiervorrichtung im Raum;
• – mindestens eine zwei oder mehr Markerelemente umfassende Referenzierungseinrichtung, die an der mindestens einen Markiervorrichtung angeordnet oder mit dieser verbindbar ist;
• – eine Nachweisvorrichtung zum Detektieren von von den Markerelementen ausgesandter oder reflektierter Strahlung;
• – eine Datenverarbeitungsanlage zur Verarbeitung von vom Navigationssystem bestimmbaren Positions- und Orientierungsdaten der Markerelemente im Raum;
• – eine am Femur eines Patienten festlegbare erste chirurgische Markiervorrichtung zur Definition eines ersten charakteristischen Punktes des Femurs, wobei das Navigationssystem und/oder die Datenverarbeitungsanlage so ausgebildet und programmiert ist, dass mittels einer Referenzmarkiervorrichtung ein Referenzkoordinatensystem definierbar ist sowie im Referenzkoordinatensystem eine erste, cranio-caudale Referenzrichtung sowie eine zweite, medio-laterale Referenzrichtung quer zur ersten Referenzrichtung und wobei:
• – Ortskoordinaten des ersten charakteristischen Punktes des Femurs vor und nach der Implantation bestimmbar sind durch Detektion des ersten charakteristischen Punktes am Femur;
• – Ortskoordinaten eines zweiten charakteristischen Punktes des Femurs vor und nach der Implantation bestimmbar sind und hiervon zumindest vor der Implantation durch Detektion des zweiten charakteristischen Punktes am Femur mittels einer zweiten chirurgischen Markiervorrichtung; und wobei die Datenverarbeitungsanlage so ausgebildet und programmiert ist, dass sie:
• – die räumliche Änderung der Ortskoordinaten des ersten charakteristischen Punktes infolge der Implantation im Referenzkoordinatensystem berechnet;
• – die räumliche Änderung der Ortskoordinaten des zweiten charakteristischen Punktes infolge der Implantation im Referenzkoordinatensystem berechnet;
• – die Längenänderung des Femurs ermittelt durch Projektion der räumlichen Änderung der Ortskoordinaten des ersten charakteristischen Punktes auf die cranio-caudale Referenzrichtung; und
• – die Änderung des Versatzes des Femurs ermittelt durch Projektion der räumlichen Änderung der Ortskoordinaten des zweiten charakteristischen Punktes auf die medio-laterale Referenzrichtung.

The object stated at the beginning is solved by a device for carrying out one of the methods explained above, comprising:

• A surgical navigation system for determining the position and orientation of at least one surgical marking device in the room;
• - At least one two or more marker elements comprehensive referencing device, which is arranged on the at least one marking device or connectable to this;
• A detection device for detecting radiation emitted or reflected by the marker elements;
• - A data processing system for processing by the navigation system determinable position and orientation data of the marker elements in space;
• A first surgical marking device which can be fixed on the femur of a patient for defining a first characteristic point of the femur, wherein the navigation system and / or the data processing system is designed and programmed such that a reference coordinate system can be defined by means of a reference marking device and a first cranio-caudal one in the reference coordinate system Reference direction and a second medio-lateral reference direction transverse to the first reference direction and wherein:
• - Location coordinates of the first characteristic point of the femur before and after implantation can be determined by detection of the first characteristic point on the femur;
• Local coordinates of a second characteristic point of the femur can be determined before and after implantation, and thereof at least prior to implantation by detection of the second characteristic point on the femur by means of a second surgical marking device; and wherein the data processing equipment is designed and programmed to:
• - calculates the spatial change of the location coordinates of the first characteristic point as a result of the implantation in the reference coordinate system;
• - calculates the spatial change of the location coordinates of the second characteristic point as a result of the implantation in the reference coordinate system;
• - Determining the change in length of the femur by projection of the spatial change of the location coordinates of the first characteristic point on the cranio-caudal reference direction; and
• - The change in the offset of the femur determined by projection of the spatial change of the location coordinates of the second characteristic point on the medio-lateral reference direction.

With the device according to the invention, the advantages already mentioned in connection with the explanation of the method according to the invention can be achieved. In this regard, reference is made to the above statements.

The detection of the location coordinates of the first characteristic point, which can be defined by fixing the first marking device on the femur, takes place, for example, by the device issuing an instruction to the operator to register the location coordinates of the first characteristic point. For this purpose, the operation of a registration element or input device, such as a foot switch or a manual switch, be provided by the surgeon. A corresponding actuation can also be provided in the detection of the further points mentioned here, for example in the selection of the second characteristic point, the iliac spine and / or the pubis.

It is advantageous if an instruction can be issued with the device to transfer the femur before and / or after implantation in the neutral position relative to the pelvic bone. This allows, as already explained, a more accurate and reliable calculation of the change in length and the change in the offset of the femur.

Preferably, the device can issue an instruction that the first marking device is fixed in the region of the distal end of the femur and / or that the first marking device is fixed on or near the mechanical femur axis. This allows you to determine the change in length of the femur in a more accurate way.

It is advantageous if an instruction can be issued with the device that the reference marking device is fixed to the pelvic bone. This makes it possible to define a body-based reference coordinate system.

In the body-based reference coordinate system, a body-based reference plane spanned from the two reference directions can be defined.

For example, it is favorable if an instruction can be issued with the device, location coordinates of the left anterior superior iliac spine (left upper iliac spine), the right anterior superior iliac spine and the pubic symphysis (pubis) respectively by detection on the pelvic bone and when the navigation system and / or the data processing system is configured and programmed to define the medio-lateral reference direction as extending along an imaginary connecting line of the left upper iliac spine to the right upper iliac spine and defining the cranio-caudal reference direction as running along an imaginary, preferably orthogonal projection of the pubis on the imaginary connecting line. The advantages of registering the pelvic entrance plane, which is spanned by the cranio-caudal and medio-lateral reference directions and by the location of the left upper and right upper iliac spine and the of the pubis is already explained above.

Advantageously, with the device, an instruction can be issued to determine the location coordinates of the second characteristic point after implantation by detection of the second characteristic point on the femur by means of the second surgical marking device.

Alternatively or additionally, it is advantageous if the navigation system and / or the data processing system is designed and programmed such that the location coordinates of the second characteristic point after implantation are determined by the spatial distance of the location coordinates of the second characteristic point from the location coordinates of the first characteristic point is calculated before implantation and the spatial distance is added to the location coordinates of the first characteristic point after implantation.

Preferably, an instruction can be issued with the device that the second characteristic point is detected more proximal to the femur than the first characteristic point. Due to the structure of the femur, this makes it possible to determine the change in the offset of the femur with higher accuracy.

Advantageously, an instruction can be issued with the device that the second characteristic point is detected in the region of the proximal end of the femur in order to allow the most accurate determination of the change in the offset of the femur.

Preferably, an instruction can be output with the device that the second characteristic point on the greater trochanter of the femur is detected. This allows on the one hand the most accurate determination of the change in the offset of the femur due to the relatively large distance that has the greater trochanter to the mechanical axis of the femur. Due to the prominent formation of the trochanter majoris, the detection from the surgeon to the other can be carried out in a simple manner.

In order to minimize possible inaccuracies in the detection and the calculation of the change in the offset, it is advantageous if the second characteristic point is detected laterally at the trochanter major and a corresponding instruction can be output by the device.

It is favorable if an instruction can be output by the device that the second characteristic point is detected by palpation, wherein the second marking device is designed as a navigated feeler instrument. As a result, it can be avoided that the second marking device is firmly attached to the femur. In particular, if the second characteristic point lies in the region of the proximal end of the femur, a possible disturbing influence on the surgeon can also be avoided.

It is advantageous if with the device an instruction can be output that the second characteristic point is scanned subcutaneously, so that its location coordinates can be determined with the highest possible accuracy.

Preferably, an instruction can be output with the device that the second characteristic point is marked. This makes it possible to ensure that the same second characteristic point is detected on the femur before and after the implantation. As a result, an erroneous determination of the location coordinates of the second characteristic point can be largely avoided.

The object stated at the outset is also achieved by a further method according to the invention in which a first surgical marking device on the femur is defined for defining a reference coordinate system, location coordinates of a first characteristic point of the femur in the reference coordinate system before and after the implantation are determined by detection of the first characteristic point on the femur, spatial coordinates of the hip joint center in the reference coordinate system before and after the implantation are determined by detecting the hip joint center and calculating the change in length and the change in the offset of the femur from a data processing system taking into account the location coordinates of the first characteristic point and the location coordinates of the hip joint center, wherein the location coordinates of a second characteristic point of the femur in the reference coordinate system before and after the implantation best By detecting the second characteristic point on the femur by means of a second marking device, the change in length of the femur is calculated by changing the location coordinates of the first characteristic point and the location coordinates of the hip joint center relative to each other before and after the implantation and changing the offset of the femur is calculated by changing the location coordinates of the second characteristic point and the location coordinates of the hip joint center relative to each other before and after the implantation.

Also in this method, a second marking device is used to To determine locational coordinates of a second characteristic point on the femur before and after implantation of the artificial hip joint. This makes it possible to base the calculation of the change in length and the calculation of the change in the offset on more data than in the method mentioned above.

It is advantageous if the change in length and / or the change in the offset of the femur by changing the distance of the location coordinates of the first characteristic point and the location coordinates of the hip joint center each other or by changing the distance of the location coordinates of the second characteristic point and the location coordinates of the hip joint center point be calculated. This allows a calculation of the change in length and / or the change of the offset in a simple manner, which nevertheless has sufficient accuracy of the calculation, for example, with only a small change in length and / or change in the offset.

Preferably, the first characteristic point selected is the origin of the reference coordinate system at which the first marking device is fixed to the femur. This makes it possible to reduce the number of required arithmetic operations.

It is advantageous if the first characteristic point is detected in the region of the distal end of the femur and / or if the first characteristic point is detected on or near a connecting line of the hip joint center and the knee joint (mechanical femur axis). This allows a more accurate determination of the change in length of the femur.

The first characteristic point does not need to be exactly at the distal end of the femur. In practice, it is sufficient to determine the relative change in length of the femur. An absolute determination of the change in length, however, is not required. The same applies to the change in the offset of the femur.

Preferably, the second characteristic point is detected more proximally at the femur than the first characteristic point.

It is favorable if the second characteristic point is detected in the region of the proximal end of the femur.

The most accurate determination of the change in the offset is made possible, in particular, by detecting the second characteristic point on the greater trochanter of the femur.

It is favorable if the second characteristic point is detected laterally at the greater trochanter.

Preferably, the second characteristic point is detected by palpation by means of the second marking device, which is designed for this purpose as a surgical palpation instrument.

Advantageously, the second characteristic point is palpated subcutaneously.

Preferably, the second characteristic point is marked.

So far, it has not yet been mentioned how the location coordinates of the hip joint center can be determined. This is possible, for example, by rotation of the femur relative to the pelvis, with the femur moving on a sphere whose center is formed by the hip joint midpoint.

It is also possible, after removal of the femoral head from the acetabulum to insert a marker in this, with the aid of the hip joint center is detected relative to the pelvis, in addition, the positional relationship of the pelvis relative to the reference coordinate system of the femur can also be determined and thus the location of the hip joint center relative to the femur.

After implantation of the femoral shaft, it is z. B. possible to determine the hip joint center, for example, by detecting the center of the joint ball of the femoral shaft.

Conveniently, the location coordinates of the hip joint center relative to the pelvis before and after implantation are determined by detection and included in the calculation of the change in length of the femur and / or the change in the offset of the femur. This takes into account the fact that not only the length and offset of the femur can change during implantation of the hip joint, but also the orientation of the femur relative to the pelvis, for example by cranio-caudal or medio-lateral offset of the hip joint center relative to the pelvis. By means of a second reference coordinate system of the pelvis, which is defined, for example, by a third pelvic device fixed to the pelvis, it is possible to transfer pelvic loci of the hip joint center into the reference coordinate system of the femur and to take this into account in the calculation. This can be used to calculate the impact of the implanted hip joint on the leg length change and / or the leg displacement change.

The object set out above is also achieved with a further device according to the invention for carrying out the second method according to the invention with a surgical navigation system for determining the position and orientation of at least one surgical marking device in the room, with a reference device comprising at least two marker elements, which at least one Marking device is arranged or connectable to this, with a detection device for detecting radiation emitted by the marker elements or reflected radiation and with a data processing system for processing determinable by the navigation system position and orientation data of the marker elements in space, a first marking device on the femur can be fixed and the Navigation system and / or the data processing system is designed and programmed so that as a reference coordinate system a fixed relative to the femur coordinate system m, with instructions being impartable with the device before and after implantation to determine location coordinates of a first characteristic point of the femur by detecting the first characteristic point on the femur, locating coordinates of the hip joint midpoint by detection of the hip joint midpoint, and wherein with the device taking into account the location coordinates of the first characteristic point and the location coordinates of the hip joint center, the change in length and the change in the offset of the femur can be calculated, whereby instructions can be issued with the device before and after the implantation to determine the location coordinates of a second characteristic point of the femur by detection the second characteristic point on the femur by means of a second marking device, and that the data processing system is designed and programmed such that the change in length of the femur by altering g of the location coordinates of the first characteristic point and the location coordinates of the hip joint center relative to each other before and after the implantation is calculated and that the change in the offset of the femur by changing the location coordinates of the second characteristic point and the location coordinates of the hip joint center relative to each other before and after the implantation calculable is.

It is favorable if by means of the data processing system the change in length and / or the change of the offset of the femur by changing the distance of the location coordinates of the first characteristic point and the location coordinates of the hip joint center from each other or by changing the distance of the location coordinates of the second characteristic point and the location coordinates of the hip joint center are calculated from each other. This makes it possible to determine the change in length and the change in the offset of the femur in a computationally simpler manner. In particular, small changes in length and changes in the offset still sufficient accuracy of the calculation can be achieved.

Advantageously, the navigation system is designed and programmed such that the first characteristic point is selected as the origin of the reference coordinate system at which the first marking device is fixed to the femur. This allows to minimize the number of calculations required.

Preferably, an instruction can be issued with the device that the first characteristic point in the region of the distal end of the femur is detected and / or that the first characteristic point is detected on or near a connecting line of the hip joint center and the knee joint. This allows a more accurate determination of the change in length of the femur.

Preferably, an instruction can be issued with the device that the second characteristic point is detected more proximal to the femur than the first characteristic point.

Advantageously, an instruction can be output with the device that the second characteristic point in the region of the proximal end of the femur is detected.

Preferably, an instruction can be output with the device that the second characteristic point on the greater trochanter of the femur is detected.

It is advantageous if the second characteristic point is detected laterally at the greater trochanter and a corresponding instruction can be issued by the device.

It is favorable if an instruction can be output by the device that the second characteristic point is detected by palpation, wherein the second marking device is designed as a navigated feeler instrument.

It is advantageous if an instruction can be output with the device that the second characteristic point is palpated subcutaneously.

Preferably, an instruction can be output with the device that the second characteristic point is marked.

It is advantageous if by means of the navigation system, the location coordinates of the hip joint center relative to the pelvis before and after the Implantation can be determined by detection and when the data processing system is designed and programmed so that the location coordinates of the hip joint center relative to the pelvis in the calculation of the change in length of the femur and / or the change in the offset of the femur can be included. This makes it possible to determine the position of the femur before and after implantation relative to the pelvis. A possible cranio-caudal and / or medio-lateral displacement of the hip joint center relative to the pelvis can be used to determine the change in length and change in the offset of the leg after implantation with increased accuracy.

The above object is further achieved by a computer program product comprising a computer readable medium and a computer program stored on the computer readable medium having program code means adapted to execute one of the above-described methods upon execution of the computer program on a computer of a navigation system. The program is preferably designed such that instructions are issued to the navigation system computer to detect the first and second characteristic points of the femur and, if appropriate, the right and left upper iliac spine, the pubis or the hip joint center.

Furthermore, the object set out above is achieved by a computer program with program code means which are suitable for executing one of the methods described above when the computer program is executed on a computer of a navigation system. In this case as well, the computer program preferably controls the computer of the navigation system in such a way that it gives instructions in order to guide an operator to carry out one of the methods described above.

The following description of preferred embodiments of the invention is used in conjunction with the drawings for a more detailed explanation of the invention. Show it:

1 a schematic representation of a device for determining the cranio-caudal change in length and the medio-lateral change of the offset of a femur as a result of the implantation of an artificial hip joint in a patient also shown;

2 3 is a schematic view of the femoral pelvic bone and a portion of the patient's lower leg bone, three surgical marking devices used on the patient, and additionally indicating the mechanical femoral axis and pelvic entrance plane prior to implantation of the artificial hip joint;

3 : a representation accordingly 2 after implantation of the artificial hip joint;

4 : A schematic representation of the position of two characteristic points and the hip joint center of a femur relative to each other before and after the implantation of the artificial hip joint and two surgical marking devices.

1 shows by way of example and in schematic form a preferred embodiment of a device according to the invention 10 for determining the change in length and the change in the offset of a femur 12 a patient 14 on an operating table 16 is shown lying. The change in length and the change in the offset results from the implantation of an in 3 partially illustrated artificial hip joint 18 , When implanting a femoral shaft 19 with the condyle arranged thereon 20 replacing the femoral head on the femur 12 anchored. Furthermore, can be on the pelvic bone 22 of the patient 14 an artificial socket 23 of the hip joint 18 be anchored, which serves to accommodate the condyle 20 serves.

The device 10 includes a surgical navigation system 24 for determining the positions of the orientation of surgical marking devices 26 . 28 and 30 in the room. The marking devices 26 . 28 and 30 each have a referencing device 27 . 29 respectively. 31 each having at least two active marker elements 32 or passive marker elements 33 include.

The navigation system 24 further comprises a detection device 34 for detecting radiation coming from the marker elements 32 . 33 is emitted or reflected. This can be done at the detection device 34 a stereo camera 35 be provided, for example, the electromagnetic radiation, in particular infrared radiation, can detect. To deal with passive marker elements 33 can cooperate, the detection device 34 additionally emit electromagnetic and in particular infrared radiation.

In addition, the navigation system includes 24 a data processing system 36 in the form of a computer, operable for example via conventional input devices such as a keyboard 38 or a mouse 39 , Furthermore, a footswitch 40 be provided with the data processing system 36 connected is. The keyboard 38 , the mouse 39 and the footswitch 40 are actuators with which a user an action of the data processing system 36 can trigger, in particular the detection of spatial coordinates of characteristic points. A display device 42 is with the data processing system 36 coupled to indicate data and instruction to an operator.

With the navigation system 24 can in a known manner position and orientation data of the marker elements 32 . 33 and thus the marking device 26 . 28 . 30 be determined in space, to spatial coordinates of characteristic points on the patient's body 14 to determine and perform calculations with it. The calculations can be made in particular by the data processing system 36 and calculation results can be sent to the operator via the display device 42 are displayed.

The marking devices 26 and 28 on the one hand, and 30 on the other hand are designed differently. The marking devices 26 and 28 are active labeling devices with active marker elements 32 and they are each releasably connectable with bone screws, for example, in the pelvic bone 22 and in the femur 12 can be anchored. The marking devices 26 and 28 each define a coordinate system to determine the location coordinates of the characteristic points to be determined on the body of the patient.

The marking device 30 is in contrast in the form of a touch instrument 44 with passive marker elements 33 formed, which is a Tastspitze 46 includes. By the navigation system 24 the position and orientation of the passive marker elements 33 determined, from their position and orientation in the room, the position of the probe tip 46 from the data processing system 36 be calculated. This allows characteristic points of the body of the patient 14 by palpation and spatial coordinates of the palpated points by means of the navigation system 24 to determine.

The location coordinates can, for example, in the respective coordinate system of the marking devices 26 and or 28 being represented. In these coordinate systems, distances of different points in space can be calculated on the basis of the location coordinates.

In the same way it is due to the navigation system 24 stored geometries of the marking devices 26 and 28 possible, those points at which these marking devices on the patient's body 14 are determined by means of the navigation system 24 to determine. For example, and in particular it is possible, spatial coordinates of that point at which the marking device 28 is set in the coordinate system of the marking device 26 to determine. If the location coordinates of this point change, their change in that of the marking device may change 26 defined coordinate system can also be determined.

The change of location coordinates in a given coordinate system can be done by the data processing system 36 be determined in the present case as a spatial change, for example as a vector between the location coordinates resulting from successive determinations of the location coordinates of a point. For example, at a first time, a characteristic point is detected by the stylus tip 46 palpiert and calculated its location coordinates and at a second, later time the same point again by means of Tastspitze 46 palpiert and recalculated its location coordinates. The difference of the location coordinates is then in the data processing system 36 as a spatial change of the location coordinates in vector form in the data processing system 36 in front.

From the data processing system 36 can via the display device 42 Instructions issued to the operator, a particular characteristic point of the patient's body 14 to detect. A detection by means of the palpation instrument 44 For example, the fact that the probe tip 46 held at the characteristic point and by the operator the keyboard 38 , the mouse 39 or in particular the footswitch 40 is actuated, whereupon the position and orientation of the feeler instrument 44 from the navigation system 24 is determined. Are the marking devices 26 and or 28 firmly on the body of the patient 14 set, the detection is done by pressing the keyboard 38 , the mouse 39 and in particular the footswitch 40 , whereupon the position and orientation of the marking devices 26 . 28 from the navigation system 24 is determined.

As mentioned above, the device is used 10 to carry out a procedure in which the change in length and the change in the offset of the femur 12 as a result of implantation of the hip joint 18 be determined in a reliable manner and with sufficient accuracy in practice. The change in length and the change in the offset of the femur 12 is in the 2 and 3 shown schematically before and after implantation, with the femur 12 beyond the pelvic bone 22 , the marking devices 26 . 28 and 30 , a knee joint 48 as well as a part of the lower leg bone 49 are shown.

The inventive method can be carried out as explained below, wherein on the display device 42 Instructions for the operator can be issued below Execute said respective method steps and optionally to detect the location coordinates of characteristic points again. The process steps need not necessarily all be performed in the order described.

First, the marking device 26 on the pelvic bone 22 defined for the definition of a body-based reference coordinate system in which the location coordinates of the characteristic points are determined, ie in the system of the pelvic bone 22 ,

Subsequently, the pelvic entrance level 56 (also called anterior pelvic plane) are registered by three characteristic points of the pelvic bone 22 be detected, in particular by palpation using the palpation instrument 44 , The left iliac spine becomes anterior superior (left upper iliac spine) 50 , the right anterior superior iliac spine (right upper iliac spine) 52 and the pubic symphysis (pubis) 54 detected. From these three points 50 . 52 and 54 calculates the data processing system 36 the location of the pelvic entrance level 56 in the reference coordinate system of the marking device 26 , The pelvic entrance level 56 is in an upright patient 14 oriented substantially vertically.

The data processing system 36 determined from an imaginary connecting line through the iliac spine 50 and 52 a medio-lateral reference direction in the reference coordinate system, indicated by an arrow 58 is symbolized. Furthermore, the data processing system forms 36 mathematically an orthogonal projection of the pubis 54 on the imaginary connecting line of the iliac spine 50 and 52 in the reference coordinate system and determines therefrom a cranio-caudal reference direction, indicated by an arrow 60 is symbolized. The reference directions 58 and 60 are vectorially defined in the reference coordinate system and, for example, as unit vectors, and their absolute position in the reference coordinate system does not matter here.

Subsequently, the operator is instructed to the femur 12 in the neutral position relative to the pelvic bone 22 to convict. In the neutral position is the femur 12 relative to the pelvic bone 22 oriented in a way that he essentially in an upright patient 14 Has. In the neutral position is the mechanical femoral axis 62 essentially parallel to the pelvic entrance level 56 aligned parallel to the cranio-caudal reference direction 60 and perpendicular to the medio-lateral reference direction 58 , The mechanical femur axis 62 is given by an imaginary connecting line of the hip joint midpoint 64 with the center 66 of the knee joint 48 ,

The connection of the hip joint center 64 and knee center 66 Forms the base of a triangle whose tip is formed by an intersection 68 an axis 70 of the neck of the femur 12 and an axis 72 of the canal of the femur 12 , The axis 70 passes through the intersection 68 and the hip joint center 64 , and the axis 72 passes through the intersection 68 and the knee joint center 66 , The distance of the intersection 68 from the mechanical femur axis 62 defines in the present case the so-called "offset of the femur 12 ".

The following will be the active marking device 28 at the femur 12 fixed, preferably near the mechanical axis of the femur 62 and near the knee joint 48 , Of course, this could also be done before setting the marking device 26 on the pelvic bone 22 and / or before the transfer of the femur 12 take place in the neutral position. The marking device 28 becomes at a first characteristic point 74 at the femur 12 established. The first characteristic point 74 is relative to the femur 12 uniquely defined, and whose location coordinates may be in the reference coordinate system of the marking device 26 be determined. Then the location coordinates of the first characteristic point become 74 determined in the reference coordinate system and in the data processing system 36 saved.

Subsequently, a second characteristic point 76 by means of the palpation instrument 44 palpiert and determined its location coordinates in the reference coordinate system. The second characteristic point 76 is preferably more proximal to the first characteristic point 74 detected, in particular in the region of a proximal end of the femur 12 and if possible laterally on the femur 12 , In particular, the greater trochanter 78 of the femur 12 be palpated, as far as possible from the mechanical axis of the femur 62 , The palpation is preferably performed subcutaneously directly on the bone, and preferably the operator marks the palpated second characteristic point 76 by means of a notch on the bone or by means of a bone screw.

As a result, the artificial hip joint 18 be implanted in a known manner.

After implantation of the artificial hip joint 18 becomes the femur 12 again in the neutral position relative to the pelvic bone 22 transferred. Subsequently, the location coordinates of the characteristic points are again 74 and 76 detected in the reference coordinate system, for example, those of the first characteristic point 74 be recorded first.

The location coordinates of the second characteristic point 76 after implantation, for example, by repeated palpation by means of the palpation instrument 44 be recorded. The feeler instrument 44 is again for this purpose at the previously preferably marked point proximal to the femur 12 and laterally on the greater trochanter 78 created and then the location coordinates of the second characteristic point 76 from the navigation system 24 detected.

Alternatively or additionally, it can be provided that the data processing system 36 the spatial distance of the characteristic points 74 and 76 before implantation of the hip joint 18 calculated and this spatial distance, in particular vectorially, the location coordinates of the first characteristic point 74 after implantation adds. This allows the location coordinates of the second characteristic point 76 be determined by calculation after implantation.

The data processing system calculates from the determined data 36 then the spatial change of the location coordinates of the first characteristic point 74 and the second characteristic point 76 in the reference coordinate system of the marking device 26 as a result of the implantation of the hip joint 18 , A change of these location coordinates may result from the fact that the femur 12 extended by the implantation, and / or that its offset changes.

A change in length of the femur is present given by the difference in the distance of the knee joint center point 66 from the hip joint center 64 before and after implantation. The change in the offset of the femur is given here by the difference of the offset of the femur (distance of the intersection 68 from the mechanical femur axis 62 ) before and after implantation.

By means of the method according to the invention and the device according to the invention 10 For example, the change in length and the change in the offset of the femur can be determined fairly accurately using the determined location coordinates of the characteristic points 74 and 76 be calculated. For this purpose, the data processing system calculates 36 in the reference coordinate system, the projection of the spatial change of the location coordinates of the first characteristic point 74 as a result of implantation in the cranio-caudal reference direction 60 , As shown in practice, this projection is largely consistent with the actual change in length of the femur 12 match, because the marking device 28 near the knee joint 64 at a great distance to the pelvic bone 22 and advantageously near the mechanical femoral axis 62 fixed at the femur.

The change of the offset of the femur 12 is decoupled from the data processing system 36 calculated by the spatial changes of the location coordinates of the second characteristic point 76 due to the implantation on the medio-lateral reference direction 58 be projected.

This projection is quite accurate with the actual change in the offset of the femur 12 because the second characteristic point 76 as proximal and lateral to the femur 12 , especially laterally on the greater trochanter 78 , is detected.

In practice, it shows that the actual change in length and the actual change in the offset of the femur 12 only slightly from the length change calculated in the manner described above or change in the offset of the femur 12 different. For an operator, this is a reliable way to effect the implantation of the hip joint 18 on the patient 14 still detectable in the course of the operation and thus also the change in the leg length of the patient. This gives the possibility that the operator corrects the hip joint 18 should make a change in length and / or a change in the offset of the femur 12 result, which exceeds a predetermined threshold.

By means of the device according to the invention 10 It is also possible to carry out a further method according to the invention explained below in which the change in length and the change in the offset of the femur 12 as a result of the implantation of the hip joint 18 be calculated.

The change in length and the change in the offset of the femur 12 is in 4 shown schematically before and after implantation, wherein in principle the same reference numerals as previously used. However, reference is made to the situation after implantation by reference numerals whose numerical value is in each case 100 higher than in the situation before implantation.

The situation before implantation is as follows: The marking device 28 is at the femur 12 in the region of its distal end, ie near the knee center 66 , The marking device 28 thus defines the first characteristic point 74 of the femur 12 , whose location coordinates in the reference coordinate system of the femur 12 are known, because the first characteristic point 74 forms its origin. Its location coordinates are due to the known geometry of the marking device 28 determinable.

In the reference coordinate system of the femur 12 can also before the implantation the Location coordinates of the hip joint center 80 be determined. This is known per se and will not be explained in detail for this reason. It is only pointed out that this, for example, by pivoting the femur 12 relative to the pelvic bone 22 can be done or by inserting a likewise known per se palpation instrument in the exposed acetabulum. Taking into account the position of this palpation instrument relative to the pelvic bone 22 and the relative orientation of the marking devices 28 and 26 then also the position of the hip joint center can be 80 in the reference coordinate system of the femur 12 be determined.

Due to its location at the distal end of the femur 12 is the first characteristic point 74 near the mechanical femur axis 62 arranged.

The second method described here according to the invention now provides that, prior to implantation, that is to say for a still natural hip joint, optionally for femoral heads removed from the acetabulum, spatial coordinates of the second characteristic point 76 of the femur 12 be determined in its reference coordinate system. The second characteristic point 76 is preferably more proximal than the first characteristic point 74 at the femur 12 and in particular in the region of its proximal end. Specifically, the second characteristic point lies 76 especially laterally on the greater trochanter 78 , As a result, he can not only be found by a surgeon in a simple way, but he also has the largest possible distance from the mechanical axis of the femur 62 on to calculate the change in the offset as accurately as possible.

The location coordinates of the second characteristic point 76 are now using the Tastinstrumentes 44 determined by the stylus tip 46 to the second characteristic point 76 held and the data is registered.

The palpation of the second characteristic point 76 is preferably performed subcutaneously with the hip area opened to ensure that in the subsequent further palpation of the second characteristic point 76 with high accuracy can be found again. Preferably, the operator marks the second characteristic point 76 with a bone screw or leaving a notch on the greater trochanter 78 ,

After implantation of the hip joint are from the navigation system 24 again the location coordinates of the characteristic points 74 and 76 , now with reference numerals 174 and 176 referred, as well as the hip center 80 , now with reference numerals 180 referred to, recorded. In the reference coordinate system of the femur 12 The coordinates of the first characteristic point are correct 74 . 174 before and after implantation because they are at their origin. Meanwhile, the representation of the 2 chosen differently, for the sake of clarity of the hip joint center alone 80 . 180 as well as the mechanical femoral axis 62 . 162 before and after implantation are shown lying one above the other.

Because the first characteristic point 74 . 174 before and after implantation the same coordinates in the reference coordinate system of the femur 12 can have its location coordinates from the navigation system 24 following the marking device 28 . 128 be recorded.

The location coordinates of the hip joint center 80 after the implantation can again in the known and therefore not explained ways in the reference coordinate system of the femur 12 be determined.

Furthermore, after implantation, the location coordinates of the second characteristic point 176 in the reference coordinate system of the femur 12 determined, again by palpation. The surgeon places the tip of the probe 146 of the palpation instrument 144 again to the greater trochanter 178 on, namely to the preferably previously marked characteristic second point.

Thus, prior to implantation and after implantation, there are respective location coordinates of the first characteristic point 74 . 174 , the second characteristic point 76 . 176 and the hip center 80 . 180 in the reference coordinate system of the femur 12 to disposal.

Based on this information, the data processing system can now 36 the change in length of the femur 12 due to the implantation of the artificial hip joint. This may take into account the change of the location coordinates of the first characteristic point 74 . 174 and the location coordinates of the hip joint midpoint 80 . 180 before and after implantation relative to each other. The absolute change in length ΔL of the femur 12 given herein by changing the distance of the hip joint midpoint 80 . 180 and knee center 66 . 166 from one another, can for example be approximately calculated by changing the distance of the location coordinates of the first characteristic point 74 . 174 and the location coordinates of the hip joint midpoint 80 . 180 from each other. This is sufficiently accurate in practice, since the marking device 28 in the area of the distal end of the femur 12 near the mechanical femur axis 62 is fixed.

The data processing system can be decoupled from this calculation 36 the change of the offset of the femur 12 due to the implantation, taking into account the change in the location coordinates of the second characteristic point 76 . 176 and the location coordinates of the hip joint midpoint 80 . 180 relative to each other. The offset of the femur 12 is herein defined as the distance of the intersection 68 . 168 the axis of the femoral neck 70 . 170 with the axis of the femoral canal 72 . 172 from the mechanical femur axis 62 . 162 ,

For example, the change ΔV of the offset may be approximated by changing the distance of the location coordinates of the second characteristic point 76 . 176 and the location coordinates of the hip joint midpoint 80 . 180 be determined from each other.

In the typically occurring changes in length and changes in the offset of the femur 12 the accuracy of the calculations explained above is sufficient. In that regard, the presentation of the 2 with their very large relative change in length and change in the offset of the femur 12 , which were chosen so alone so that the geometric conditions before and after implantation are better recognizable.

Furthermore, by utilizing the reference coordinate system of the pelvic bone 22 the leg length change and an offset of the leg are calculated. This can be done by the navigation system 24 the change in the location coordinates of the hip joint center 80 . 180 in the reference coordinate system of the pelvic bone 22 be recorded. An eventual cranio-caudal and / or medio-lateral offset of the spatial coordinates of the hip joint midpoint 80 . 180 as a result of the implantation can then by the data processing system 36 be included. This is possible because of the relative orientation of the marking devices 26 and 28 before and after implantation the position of the femur 12 relative to the pelvic bone 22 is known.

By palpation of the second characteristic point 76 at the greater trochanter 78 Before and after implantation in both methods explained here, the possibility is thus opened of calculating the change in length and the change in the offset of the femur 12 on the one hand to rely on more data, as is the case with known methods, and on the other hand, to perform decoupled from each other. This makes it possible to calculate the change in length and the change in the offset with higher accuracy than has hitherto been possible. The surgeon can thereby make a more reliable assessment of the influence of the implantation on the leg position of the patient.

In addition, the result of a conventional calculation method, which is based on the neutral position of the femur 12 be checked for agreement with the result of the calculation by the method according to the invention. The surgeon thus has a control option available, which allows to reduce the risk of incorrect implantation.

The method described above and advantageous embodiments thereof may also be embodied in a computer program product comprising a computer-readable medium and a computer program with program code means stored thereon. The program code means are adapted to instruct and guide the operator in the performance of one or both of the methods of the invention to perform the steps necessary to perform the method, to locate coordinates of all for calculating the change in length and changing the offset of the femur 12 to detect required points. The computer-readable medium may in particular include a 1 illustrated DVD 82 , a CD or other non-volatile storage medium, such as a USB memory 84 ( 1 ).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2006/074954 A1 [0020]

Claims (24)

Method for determining the cranio-caudal change in length and the medio-lateral change in the offset of a femur of a patient as a result of the implantation of an artificial hip joint, characterized by the following features: A reference coordinate system is defined by means of a surgical reference marking device, and a first cranio-caudal reference direction and a second, medio-lateral reference direction transversely to the first reference direction are defined in the reference coordinate system; A first surgical marking device is set on the femur to define a first characteristic point on the femur; - it will be before and after implantation - The location coordinates of the first characteristic point of the femur in the reference coordinate system determined by detection of the first characteristic point on the femur and - determines the location coordinates of a second characteristic point of the femur in the reference coordinate system, wherein at least prior to implantation, the second characteristic point is detected by means of a second surgical marking device on the femur; The spatial change of the location coordinates of the first characteristic point as a result of the implantation in the reference coordinate system is calculated; The spatial change of the location coordinates of the second characteristic point due to the implantation in the reference coordinate system is calculated; - The change in length of the femur is determined by projecting the spatial change of the spatial coordinates of the first characteristic point to the cranio-caudal reference direction; and - The change in the offset of the femur is determined by projection of the spatial change of the position coordinates of the second characteristic point on the medio-lateral reference direction. A method according to claim 1, characterized in that the location coordinates of the first characteristic point and the second characteristic point are determined before and / or after implantation in the neutral position of the femur relative to the pelvic bone. A method according to claim 1 or 2, characterized in that the reference marking device is fixed to the pelvic bone. Method according to one of the preceding claims, characterized in that in the reference coordinate system spatial coordinates of the left iliac spine anterior superior (left upper iliac spine), the right anterior superior iliac spine (right iliac spine) and the pubic symphysis (pubis) respectively determined by detection on the pelvic bone in that the medio-lateral reference direction is defined as extending along an imaginary connecting line of the left upper iliac spine to the right upper iliac spine, and the cranio-caudal reference direction is defined as extending along an imaginary, preferably orthogonal, projection of the pubis onto the imaginary connecting line. Method according to one of the preceding claims, characterized in that the location coordinates of the second characteristic point after the implantation are determined by detection of the second characteristic point on the femur by means of the second surgical marking device. Method according to one of the preceding claims, characterized in that the location coordinates of the second characteristic point after implantation are determined by calculating the spatial distance of the location coordinates of the second characteristic point from the location coordinates of the first characteristic point prior to implantation and the spatial distance Location coordinates of the first characteristic point after implantation is added. Method according to one of the preceding claims, characterized in that the first characteristic point in the region of the distal end of the femur is detected and / or that the first characteristic point is detected on or near the mechanical femur axis. Method according to one of the preceding claims, characterized in that the second characteristic point is detected more proximally on the femur than the first characteristic point. Method according to one of the preceding claims, characterized in that the second characteristic point is detected at the greater trochanter of the femur. Method according to one of the preceding claims, characterized in that the second characteristic point is detected by palpation by means of the second marking device. A method according to claim 10, characterized in that the second characteristic point is palpated subcutaneously. Apparatus for carrying out the method according to any one of the preceding claims, comprising: - a surgical navigation system ( 24 ) for determining the position and the orientation of at least one surgical marking device ( 26 . 28 . 30 ) in the room; At least one two or more marker elements ( 32 . 33 ) comprehensive referencing device ( 27 . 29 . 31 ) attached to the at least one marking device ( 26 . 28 . 30 ) is arranged or connectable with this; A detection device ( 34 ) for detecting from the marker elements ( 32 . 33 ) emitted or reflected radiation; - a data processing system ( 36 ) for processing from the navigation system ( 24 ) determinable position and orientation data of the marker elements ( 32 . 33 ) in the room; - one on the femur ( 12 ) of a patient ( 14 ) fixable first surgical marking device ( 28 ) for defining a first characteristic point ( 74 ) of the femur ( 12 ), whereby the navigation system ( 24 ) and / or the data processing system ( 36 ) is designed and programmed in such a way that by means of a reference marking device ( 26 ) a reference coordinate system is definable and in the reference coordinate system a first, cranio-caudal reference direction ( 60 ) and a second, medio-lateral reference direction ( 58 ) transverse to the first reference direction ( 60 ) and where: - location coordinates of the first characteristic point ( 74 ) of the femur ( 12 ) can be determined before and after the implantation by detecting the first characteristic point ( 74 ) on the femur ( 12 ); - location coordinates of a second characteristic point ( 76 ) of the femur ( 12 ) can be determined before and after implantation, and of which at least before implantation by detection of the second characteristic point ( 76 ) on the femur ( 12 ) by means of a second surgical marking device ( 30 ); and wherein the data processing system ( 36 ) is designed and programmed to: - spatially change the location coordinates of the first characteristic point ( 74 ) as a result of the implantation in the reference coordinate system; The spatial change of the location coordinates of the second characteristic point ( 76 ) as a result of the implantation in the reference coordinate system; - the change in length of the femur ( 12 ) determined by projection of the spatial change of the location coordinates of the first characteristic point ( 74 ) to the cranio-caudal reference direction ( 60 ); and - the change of the offset of the femur ( 12 ) determined by projection of the spatial change of the location coordinates of the second characteristic point ( 76 ) to the medio-lateral reference direction ( 58 ). Apparatus according to claim 12, characterized in that with the device ( 10 ) an instruction can be issued, the femur ( 12 ) before and / or after implantation in the neutral position relative to the pelvic bone ( 22 ). Apparatus according to claim 12 or 13, characterized in that with the device ( 10 ) an instruction can be issued that the first marking device ( 28 ) in the region of the distal end of the femur ( 12 ) and / or that the first marking device ( 28 ) on or near the mechanical axis of the femur ( 62 ). Device according to one of claims 12 to 14, characterized in that with the device ( 10 ) an instruction can be issued that the reference marking device ( 26 ) on the pelvic bone ( 22 ). Device according to one of claims 12 to 15, characterized in that with the device ( 10 ) an orientation can be output, spatial coordinates of the left anterior superior iliac spine (left upper iliac spine) ( 50 ), the right anterior superior iliac spine (right upper iliac spine) ( 52 ) and the pubic symphysis (pubis) ( 54 ) in each case by detection on the pelvic bone ( 22 ) and that the navigation system ( 24 ) and / or the data processing system ( 36 ) is designed and programmed such that the medio-lateral reference direction ( 58 ) is defined as running along an imaginary connecting line of the left upper iliac spine ( 50 ) with the right upper iliac spine ( 52 ) and that the cranio-caudal reference direction ( 60 ) is defined as running along an imaginary, preferably orthogonal, projection of the pubis ( 54 ) on the imaginary connecting line. Device according to one of claims 12 to 16, characterized in that with the device ( 10 ) an instruction can be output, the location coordinates of the second characteristic point ( 76 ) after implantation by detection of the second characteristic point ( 76 ) on the femur ( 12 ) by means of the second surgical marking device ( 30 ). Device according to one of claims 12 to 17, characterized in that the navigation system ( 24 ) and / or the data processing system ( 36 ) is designed and programmed such that the location coordinates of the second characteristic point ( 76 ) after implantation are determined by the spatial distance of the location coordinates of the second characteristic point ( 76 ) from the location coordinates of the first characteristic point ( 74 ) is calculated before the implantation and the spatial distance is the location coordinates of the first characteristic point ( 74 ) is added after implantation. Device according to one of claims 12 to 18, characterized in that with the device ( 10 ) an instruction can be output that the second characteristic point ( 76 ) more proximal to the femur ( 12 ) is detected as the first characteristic point ( 74 ). Device according to one of claims 12 to 19, characterized in that with the device ( 10 ) an instruction can be output that the second characteristic point ( 76 ) on the trochanter major ( 78 ) of the femur ( 12 ) is detected. Device according to one of claims 12 to 20, characterized in that with the device ( 10 ) an instruction can be output that the second characteristic point ( 76 ) is detected by palpation, wherein the second marking device ( 30 ) as a navigated palpation instrument ( 44 ) is trained. Apparatus according to claim 21, characterized in that with the device ( 10 ) an instruction can be output that the second characteristic point ( 76 ) is palpated subcutaneously. Computer program product with a computer-readable medium ( 82 . 84 ) and a computer program stored on the computer-readable medium with program code means which are suitable for executing the computer program on a computer ( 36 ) of a navigation system ( 24 ) to carry out a method according to one of claims 1 to 11. Computer program comprising program code means adapted to run on a computer when the computer program is run ( 36 ) of a navigation system ( 24 ) to carry out a method according to one of claims 1 to 11.

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