WO1994014385A1

WO1994014385A1 - A device for use in surgical spinal operations in which vertebrae fixating instruments are used

Info

Publication number: WO1994014385A1
Application number: PCT/SE1993/000704
Authority: WO
Inventors: Sven Olerud
Original assignee: Sven Olerud
Priority date: 1992-12-22
Filing date: 1993-08-25
Publication date: 1994-07-07
Also published as: SE9203883D0; SE470345B; SE9203883L; AU5121793A

Abstract

An adjustable spinal joint for use with fixation instruments intended for fixating lumbal vertebrae to the sacrum, wherein the spinal joint includes a cranial part which is provided with a pin provided with longitudinally extending splines or serrations, and a caudal part which is provided with a bore having corresponding internal, longitudinally extending splines or serrations. These splines or serrations mesh with one another after desired variable adjustment when a screw provided in the caudal part has been tightened. The longitudinal splines or serrations are oriented so that those forces that act on the cranial part are transferred to the caudal part without the splines or serrations meshing with one another prior to tightening the screw.

Description

A DEVICE FOR USE IN SURGICAL SPINAL OPERATIONS IN WHICH VERTEBRAE FIXATING INSTRUMENTS ARE USED

DESCRIPTION OF THE TECHNICAL FIELD

The present invention relates to a device for use in surgical operations on the spine in which the fixation instrument includes spinal joints which are intended to fixate two spinal vertebrae in relation to each other. The device includes a cranial part which includes a pin provided with longitudinally extending splines or serra¬ tions, a caudal part which includes a bore having corre¬ sponding internal, longitudinally extending splines or serrations, wherein the pin is intended to engage in the bore so as to transmit forces from the cranial part to the caudal part, and the respective splines are intended to lock the caudal part firmly to the cranial part subseguent to adjusting the fixation instrument.

DESCRIPTION OF THE PRIOR ART

One problem encountered when performing surgical operations in the lumbar or sacral region of a patient, and particu¬ larly older patients, is that the structure of the bone material is cancellous and often of an osteoporotic nature. Among other things, this may make it difficult to anchor fixation instruments of the aforesaid kind, for instance in or adjacent to bone material. Among other things, the fixation instrument is intended to fixate the vertebrae relative to one another, to relieve load on the vertebrae and possibly also to adjust the distance and the mutual angles therebetween.

In one type of surgical operation of this kind, a so-called spinal joint is attached in the sacrum and in one or more vertebrae. The spinal joint is comprised of fastener devices for attachment to respective vertebrae, and of a length adjustable device, normally in the form of a screw spindle. The fastener devices may have the form of bone screws which are anchored in sacrum, and pairs of jaws or clamps which can be adjusted in relation to one another and which grip a part of respective vertebrae. The clamps or jaws may, of course, be replaced with bone screws.

The screw spindle is provided with spindles and also with journal means in which the screw is journalled for rota- tion. The journal means and the spindles are each provided with a cranial, cylindrical pin which although rotatable can be fixedly journalled in a corresponding caudal, cylindrical bore in respective fasteners.

However, when adjusting the length of the spinal joint, it is essential that spindles and bearing means are able to rotate freely in relation to the fasteners and therewith in relation to the vertebrae, so as to prevent the vertebrae from being subjected to deleterious loads and tensions during and after the adjustment procedure, while it is ensured that no clearance or play is able to cause the adjusted position to be changed when spindles and bearing means are fixed in relation to the fasteners upon comple¬ tion of the adjustment.

A pin-bore combination which solves this problem and which is known from EP-A-91110712.6 (EP-Al-0,469,304) has been described by way of introduction.

These known spinal joints have been found difficult to adjust, however, when under very heavy load. Such adjust¬ ment is also made difficult by the fact that the space available to the surgeon is greatly restricted in the relevant regions of the spine. BRIEF SUMMARY OF THE INVENTIVE CONCEPT

The object of the present invention is to eliminate the aforesaid drawbacks of fixation instruments of the afore- said kind, i.e. to provide a so-called spinal joint which can be easily adjusted even when under high load, and which will retain its adjusted position relative to the vertebrae with regard to angular and transversal positioning.

This object is achieved in that the bore has an eccentric cross-section, preferably composed of two part-circles of mutually different diameters corresponding to two cylindri¬ cal surfaces connected by means of generally rectilinear transition lines corresponding to transition surfaces in the bore, or alternatively of a cylindrical surface having a small radius together with a curved surface which in the use position has a form which corresponds generally to the form of the splined part of said pin, wherein the splines are located in that part of the cross-section of larger radius, wherein the part of larger radius is thin-walled and is separated from the remaining part, the main part, of said cranial part at a first of said transition surfaces by means of a penetrating slot, such as to form a free end, wherein said free end is provided with a first bore which receives a fastener screw and which is oriented generally parallel to said transition line, wherein the thinnest part of the thin-walled part is located in the vicinity of the second of said transition surfaces, thereby enabling said part to function as hinge means, wherein said main part is provided in the vicinity of said fastener receiving bore with a second, internally screw-threaded bore, and wherein in the use position the caudal part is so oriented that all forces which act on the cranial part are transferred to the cylinder surface of smaller radius on said main part. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a fixation instrument having bone screws and caudal and cranial parts included in so-called spinal joints, said instrument being shown from one side and in perspective.

Figure 2 illustrates the fixation instrument with bone screws and caudal and cranial parts included in so-called spinal joints as seen in perspective from the front.

Figure 3 shows the cranial part of the spinal joint from above.

Figure 4 is an enlarged, vertical part-sectional view of the caudal part of the spinal joint.

Figure 5 is an enlarged sectional part-view of the caudal part of the spinal joint in an adjustment position, with the adjustment screw partially screwed-in.

Figure 6 is an enlarged sectioned part-view of the caudal part, and shows the caudal part fixed and locked by means of the adjustment screw.

A DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Figures 1 and 2 illustrate a sacral joint of the fixation instrument, said joint being comprised of a caudal fastener device 2 with associated bone screws 7, 8 (the illustrated instrument is intended for the right side of the spinal column). The cranial part of the sacral joint is referenced 3. The instrument also includes a screw spindle 4 having a spindle jaw 5 on which there is firmly mounted a bone screw jaw 6 in which a bone screw 7 is rotatably journalled. The bone screw jaw is rotatably but fixedly journalled to the spindle jaw 5 and can be locked relative thereto by means of a locking screw 10. The bone screw jaw 6 is fastened around the bone screw 7 by means of a conical screw.

Figure 3 shows the cranial part 3 of the sacral joint from above, and also shows the screw spindle rotatably journal- led in the cranial part. The screw spindle can be locked by means of a locking screw 11 provided in a bore 15. The cranial part is also provided with a cylindrical pin 13, the outer surface of which is provided with splines or serrations 14 around roughly 120 degrees of its circumfer¬ ence. The pin is intended to coact with a complementary bore 22 in the caudal part 2 of the sacral joint.

Figures 4, 5 and 6 are enlarged part-sectional views of the caudal part 2 of the spinal joint. As will be seen from these Figures, the bore cross-section is comprised of two part-circles 25 and 26 of different diameters, correspond¬ ing to two cylinder surfaces which are mutually joined by means of generally rectilinear transition lines 27 and 28 corresponding to transition surfaces in the bore. The bore 22 is also provided with longitudinally orientated, inner splines 19 located in that part of the cross-section that has the larger radius 25. The part of the bore having the larger radius 25 is thin-walled and is separated from the remaining part at the first of said transition surfaces by means of a penetrating slot 29, which thus forms a free end 30. The free end 30 is provided with a first non-threaded, or plain, bore 23 for a fastener screw 12 oriented general- ly parallel with said transition line. The thinnest part 18 of the thin-walled part of the bore is located adjacent the second of said transition surfaces 27, whereby this part is able to function as a hinge means. The main part 20, 21 has in the vicinity of said screw-receiving bore a second bore 32 which is provided with screw-threads 16 and intended to receive the threaded part of the fastener screw. The screw 12 has a conical surface 23 which coacts with a conical surface 24 in the screw-receiving bore in the thinner part 20 of the aforesaid main part. The first plain bore 23 has a slightly larger inner diameter than the outer diameter of the upper part of the fastener screw, so as to provide for limited movement of the part 20 in the radial direction of the screw as the two conical surfaces 23 and 24 slide against one another when tightening the screw 12. In the initial stage, the screw 23 is screwed partly into the thread 16 in the thicker part 20 of the main part 20, 21. As shown in Figures 5 and 6, when the screw is fully tightened so as to lock the pin 13, the thinnest part 18 will function as a hinge. As the pin is locked, the screw 12, by virtue of the conical surfaces, forces the thinner part 20 to pivot on the hinge-like part 18 towards the part 21, so that the serrations or splines 14, 19 on the pin 13 and on the part 20 will mesh with one another. This provides positive fixation and locking between the caudal part and the cranial part. When the pin 13 is secured in the bore 22, a given clearance remains between the parts 20 and 21, due to the respective dimensions of the pin 13 and the bore 22. This clearance is necessary to ensure that the pin is properly secured in the bore.

In the use position, the main part 20, 21, i.e. the caudal part, is intended to be oriented so that those forces that act initially on the caudal part from the cranial part of the spinal joint through the pin 13 are oriented generally parallel with the longitudinal axis of the fastener screw

12. As will be seen from Figure 6, in this regard, the splines or serrations 19 on the inner surface of the bore

22 are swung out of engagement with the serrations on the pin 13 prior to tightening the screw 12. The direction of the transferred forces is such as to press the pin 13 towards the main part 21, away from the serrations 19, therewith enabling the pin 13 to twist freely in the bore

22 without obstruction from the serrations or splines 19.

This enables the caudal part and the cranial part to be swung freely relative to one another while adjusting the spinal joint. As before mentioned, this is a particularly important characteristic of so-called spinal joints.

Although the invention has been described with reference to a preferred embodiment thereof, it will be understood that modifications can be made within the scope of the following Claims.

Claims

CLAIM

1. A spinal joint for use in fixation instruments intended for fixating lumbar vertebrae to sacrum (the lumbosacral transition) comprising a cranial part (3) having a pin (13) provided with longitudinal splines or serrations (14), and a caudal part (2) provided with a bore (22) having corres¬ ponding internal, longitudinal splines or serrations (19), wherein the pin (13) is intended to engage in the bore (22) so as to transfer forces from the cranial part (3) to the caudal part (2), wherein respective splines (14, 19) are intended to lock the caudal part (2) positively to the cranial part (3) subseguent to adjustment of the fixation instrument, characterized in that the bore (22) has an eccentric cross-section which is preferably comprised of two part-circles (25, 26) of different diameters corre¬ sponding to two cylinder surfaces mutually joined by means of generally rectilinear transition lines (27, 28) corre¬ sponding to transmission surfaces in the bore (22), or alternatively of a cylinder surface of smaller radius together with a curved surface which in the use position has a form corresponding generally to the form of the splined part of the pin (13), wherein the splines (19) are located in that part of the cross-section which has the larger radius (20), wherein said part of larger radius (20) is thin-walled and separated from the remainder of the main part (20, 21) of the caudal part at a first of said transition surfaces (28) by a penetrating slot (29) so as to form a free end (30), wherein said free end (30) is provided with a first bore (23) for receiving a fastener screw (12), said bore being oriented generally parallel with said transition line (28), wherein the thinnest part (18) of the thin-walled part (20) of said main part is located adjacent the second of said transition surfaces (27), whereby said part (18) is able to function as a hinge means, wherein said main part (20, 21) is provided adjacent the bore (23) which receives said fastener screw (12) with a second bore (32) provided with internal screw-threads, and wherein in the use position the caudal part (2) is oriented so that all forces acting on the cranial part (3) will be transferred to the cylinder surface of smaller radius (26) located on the main part (20, 21).