WO2005084559A1

WO2005084559A1 - An alignment instrument for use with an intramedullary nail

Info

Publication number: WO2005084559A1
Application number: PCT/GB2005/000728
Authority: WO
Inventors: Grant Mellor; Henri Defossez
Original assignee: Depuy International Limited
Priority date: 2004-03-01
Filing date: 2005-02-28
Publication date: 2005-09-15
Also published as: WO2005084560A1

Abstract

An alignment instrument for use with an intramedullary nail includes a nail holder (2) having an engagement fixture (5) towards one end for engaging an intramedullary nail and a bearing portion (6). A frame (4) having a socket (10) received in the bearing portion (6) includes at least one arm (8, 9) extending from the bearing portion (6), the arm defining at least one drilling guide hole (42, 44). The socket (10) can rotate around the bearing portion (6) so that the frame (4) can be rotated around the nail holder (2), in which one of the bearing portion (6) or the socket (10) has at least one deployable locking pin (32) and the other of the bearing portion and the socket has at least a bore (30) in which the locking pin moves so that it locks the frame against rotation or allows its rotation.

Description

AN ALIGNMENT INSTRUMENT FOR USE WITH AN INTRAMEDULLARY NAIL

This invention relates to an alignment instrument for use with an intramedullary nail.

Intramedullary nails are used in the treatment of fractures in long bones such as the femur or the humerus. Intramedullary nails generally have two spaced transverse holes towards the distal end and two spaced transverse holes or holes towards the proximal end. These holes can receive bone screws (or other fasteners) to extend through the nail in order to fix it within the bone.

An intramedullary nail can have holes which extend across it which are not parallel so that the angle at which the fixation screws are inserted into the bone, relative to the plane which contains the axis of the nail, can be selected, for example taking into account the angular alignment of the nail in the intramedullary canal.

Holes for the fixation screws can be prepared in the patient's bone while the nail is implanted in the intramedullary canal. It is important that the holes are located and aligned accurately so that the fixation screws can pass smoothly through the drilled holes in the bone and the holes in the nail which are aligned with the holes. However, it is not possible to align a drill bit with the holes in the nail when the nail is implanted in the canal.

EP-A- 1350479 discloses an instrument for determining the location and alignment of holes which are to be drilled in a bone for fixation screws for an intramedullary nail. The instrument comprises a nail carrier portion to which a nail can be attached, and a drill jig portion having bores in it. The instrument is fastened to a nail which has been or is to be located in the intramedullary canal in a patient's bone. The drill jig portion can be rotated around the nail carrier portion. A drill bit which is inserted through the bores in the drill jig portion so that the holes which are drilled in the bone are appropriately aligned with the holes in the nail.

The instrument disclosed in EP-A- 1350479 suggests that the nail carrier portion should be able to position the intramedullary nail in certain angular or rotational orientations. The present invention provides alignment instruments which can be used with an intramedullary nail, which facilitate the alignment of drill holes with selected fixation holes in the nail.

Accordingly, in one aspect, the invention provides an alignment instrument for use with an intramedullary nail, which comprises: a. a nail holder having an engagement fixture towards one end for engaging an intramedullary nail and a bearing portion, b. a frame which includes a socket in which the bearing portion of the nail holder can be received, the frame including at least one arm which extends from the bearing portion, in a direction generally towards the distal tip of a nail when fitted in the engagement fixture, the arm defining at least one drilling guide hole for defining the location of a hole to be drilled in a patient's bone which intercepts a corresponding hole in the nail,

in which the socket can rotate around the bearing portion so that the frame can be rotated around the nail holder, in which one of the bearing portion and the socket has at least one deployable locking pin, and the other of the bearing portion and the socket has at least one bore, in which the locking pin can be moved in a direction which is generally transverse to the axis of rotation between a retracted position in which the frame can be rotated around the bearing portion and a deployed position in which the pin is received in the bore so as to lock the frame against rotation.

The instrument of the invention provides for positive locking against rotation in either direction (clockwise and anti-clockwise) of the frame relative to the nail holder. The frame can be locked in this way at predetermined angular orientations in which the drilling guide holes are aligned with one or more of the holes in the intramedullary nail, when the nail is fastened to the nail holder by means of the engagement fixture. When the pin is in its retracted position, the frame is able to rotate around the nail holder in at least one direction, preferably in both directions (clockwise and anti-clockwise). The or each pin can be provided in the nail holder and the bore for receiving the nail can be provided in the frame. Preferably, the pin is provided in the frame and the bore is provided in the bearing portion. This has the advantage of simplifying the structure of the nail holder.

Preferably, the bearing portion has a plurality of bores in it which are radially spaced apart around the bearing portion, for receiving the locking pin in predetermined respective angular positions of the frame relative to the bearing portion. For example, when the intramedullary nail has fixation screws arranged in two different planes (each plane containing the axis of the nail) which are angularly separated, there can be two or more angular positions of the frame relative to the bearing portion. The bearing portion will have bores in it for receiving the locking pin when the frame is in each of the angular positions. The bores in the nail holder bearing portion should be arranged so that the angle between the planes containing the holes in the nail is about the same as the angle between the two locations of the frame. For example, when the angle between the planes containing the holes in the nail is 45°, the bores in the nail holder bearing portion will be arranged so that the angle between the two locations of the frame is also 45°.

Preferably, the pin is biassed resiliently towards the deployed position. In this way, the pin will tend to lock the frame against rotation around the nail holder whenever the pin is aligned with one of the bores. When the pin is provided in the frame, a spring can be provided within the frame, arranged coaxially with the pin. The spring can act between a stop on the frame and a stop on the pin. Preferably, the spring is compressed resiliently as the pin is retracted. WTien the pin is provided in the bearing portion of the nail holder, it can be biassed similarly using a spring which is arranged between two stops, on the bearing portion and the pin respectively.

Preferably, the frame includes a trigger which, when squeezed, causes the pin to move in the direction from the deployed position towards the retracted-position. The trigger can be mounted pivotally in the frame. For example, the trigger can be pivotally mounted in the frame, and connected to the pin at a point between the pivot and the button portion at which it is actuated. Preferably, the nail holder includes a grip portion by which it can be gripped to restrict rotation of the nail holder. The grip portion can be configured to be gripped manually; for example the grip portion can comprise a handle. Preferably, the grip portion is configured to be gripped by an instrument. For example, can have the configuration of a hexagonal nut so that it can be received within a control tool which presents a corresponding hexagonal socket.

Preferably, the cross-sectional area of the socket when the opening is in the lock configuration is smaller than the cross-sectional area when the opening is in the unlock configuration.

Preferably, the opening is provided in a plate which can move within the frame between a lock position in which the opening is in the lock configuration and an unlock position in which the opening is in the unlock configuration.

Preferably, the nail holder has a lock portion which has a peripheral surface extending around the nail holder and the socket has an internal surface which is engaged by the peripheral surface when the socket portions are in the closed configuration, in which a first one of the peripheral surface and the internal surface has at least one flat portion and the second one of the peripheral surface and the internal surface has at least two flat portions, and in which the flat on the first surface contacts respective ones of the flat portions on the second surface in the first and second angular positions of the frame and the nail holder.

Preferably, the frame comprises a first limb which extends from the socket generally transversely relative to the axis of the engagement fixture, and a second limb which extends generally parallel to the said axis, and in which the drilling guide hole is provided in the second limb.

Preferably, the frame is made from a material which has a low X-ray absorbance. Certain polymeric materials are preferred, especially when reinforced with fibres. A preferred material is a carbon fibre reinforced epoxy resin. The frame can be made by moulding. It can include one or more bushings (especially of a metal) which define the drilling guide holes. It can include a bushing which defines the socket, in which the bearing portion is received. The provision of a bushing to define the socket has the advantage that it can ensure an accurate fit of the bushing in the socket, with minimum play.

Preferably, the nail holder is made from a metal. Suitable metals will include many stainless steels which are commonly used in the construction of surgical instruments. The use of a metal for the nail holder is that the nail can be engaged positively by the nail holder, with minimum play. Suitable engagement fixtures for use in an intramedullary nail alignment device are known. For example, the engagement can use thread or bayonet features.

The nail holder, and any bushings, can be moulded in place within the frame when the frame is made by moulding.

Other parts of the frame, such as a pin and a trigger, can be provided by subsequent machining steps after a moulding step has been completed, for example by drilling and subsequent assembly.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a side view of an alignment instrument according to the invention.

Figure 2 is an isometric view of an intramedullary nail which can be used with the instrument shown in Figure 1.

Figure 3 is a side view of the alignment instrument shown in Figure 1 , partially cut away.

Figure 4 is an enlarged side view of a part of the alignment instrument shown in Figure 1.

Figure 5 is an exploded view showing the arrangement of the pin, trigger and spring components of the alignment instrument shown in Figure 1. Figure 6 is an isometric view of a pin and nail holder of another alignment instrument according to the invention.

Figure 7 is a side view sectional elevation through an alignment instrument which incorporates the pin and nail holder shown in Figure 6.

Figure 8 is an enlarged view of the first limb and nail holder of the alignment instrument shown in Figure 7.

Referring to the drawings, Figure 1 shows an alignment instrument which comprises a nail holder 2 and a frame 4. The nail holder includes an engagement fixture 5 at its lower end for engaging an intramedullary nail. Suitable engagement features are used in existing intramedullary nail products and associated instruments. The engagement fixture should ensure that the nail and the nail holder have a predetermined angular relationship when assembled, for example using a bayonet arrangement. The nail holder has a bearing portion 6 which is received in a socket which is defined in the frame, as described in more detail below in relation to Figure 3. The nail holder has a hexagonal grip portion 7 at its upper end which can be received in a hexagonal socket in a control tool (not shown) by which the nail holder can be rotated relative to the frame.

The frame is made from fibre reinforced epoxy polymer. It includes a first limb 8 which extends generally perpendicular to the axis defined by the socket and the bearing portion of the nail holder, and a second limb 9 which extends generally parallel to that axis.

The nail holder is made from a stainless steel having characteristics which make it suitable for use in a surgical instrument.

Figure 2 shows an intramedullary nail 10 with which the instrument shown in Figure 1 can be used. The nail has a bore extending through it from its proximal end 12 to its distal end 14. The diameter of the nail is greater in the region towards the proximal end than in the region towards the distal end. The nail which is shown in Figure 2 is essentially straight.

However, the nail with which the instrument of the invention is used can have a kink at a point between its ends, generally in that part of the nail which is towards the proximal end, for example at about or closely below the point where the diameter of the nail changes. The kink will generally be not more than about 25°, preferably not more than about 20°, more preferably not more than about 15°, for example not more than about 10°.

The nail has a plurality of fixation holes extending through it. Proximal fixation holes 16,

18, 20 are provided towards the proximal end 12 in respective planes, each plane including the axis of the hole and the axis of the nail. (When the nail is kinked as discussed above, the axis of the nail is the axis which is defined by the bore in which the fixation holes which are to be aligned are located.) Distal fixation holes 22 are provided towards the distal end. The distal fixation holes are arranged in a single plane. However, the instrument of the invention can be used with a nail which has distal fixation holes arranged in different planes. When the nail is kinked as discussed above, it is then important to ensure that the axis around which the frame rotates around the nail holder is coincident with the axis of the distal part of the nail.

Figures 3 and 4 show the alignment instrument of Figure 1 in more detail. The nail holder

2 has a bearing portion 6 which is circular when viewed in cross-section. The bearing portion is located in a socket 10 at the end of the first limb 8 in the frame. Preferably, the socket is provided by a metal sleeve which is embedded in the polymer of the frame.

The bearing portion 6 of the nail holder 2 has a plurality of bores 30 in it which are arranged radially around its circumference and which are open at the external wall of the bearing portion.

The frame includes a pin 32 which is a close sliding fit in a bore within the first limb 8 the frame. The transverse size of the pin (its diameter if it has a circular cross-section) is slightly smaller than that of the bores in the bearing portion of the nail holder, so that the pin is a tight sliding fit in the bores. The fit of the pin in the bores should be sufficiently tight that the play between the nail holder and the frame, when the pin is received in one of the bores, is minimised, subject to the pin being capable of being withdrawn from the bores for adjustment of the angular orientation. The bore in the frame can be formed by drilling the frame after it has been fabricated (for example by moulding). A spring 34 is provided on the pin 32, compressed between a trigger 36 and a closure cap 38 as described in more detail below. The trigger 36 is located in a slot 50 in the frame and has a button 40 which extends out of the frame by which the trigger can be actuated, to move the pin against the force exerted on it by the spring 34.

The frame has drilling guide holes in its second limb 9 which define axes for drilling a bone to receive fixation screws which can be aligned selected one or more of the holes in the nail. These include guide holes 42 which extend perpendicular to the second limb for intersection with the fixation holes in the nail which are perpendicular to the axis of the nail, and a guide hole 44 which is inclined relative to the second limb for intersection with the fixation holes in the nail which are inclined to the axis of the nail.

Figure 5 shows the trigger arrangement on the pin 32 which is located in the slot in the first limb of the frame (as shown in Figure 4). The first limb has a bore extending along its length, in which the pin is a sliding fit. The trigger 36 is located in a slot in the first limb in which the trigger can slide in a direction along the limb. The slot communicates with the bore in the first limb of the frame. The trigger has a hole 52 extending through it at its upper end in which the pin can slide.

The pin 32 has a flange 56 on it which is sized so that it will not pass through the hole 52 in the trigger. Accordingly, when the flange abuts the hole in the pin, movement of the trigger in a direction towards the flange causes the pin to move in that direction.

The pin has a spring 54 fitted over it at the trigger end 55 remote from the nail holder. The spring abuts the flange 56 on the pin and the hole in the trigger at one end.

The spring abuts an end cap 58 at its other end. The end cap has a hole 60 extending through it through which the pin can slide.

The pin and trigger is assembled by locating the trigger 36 in the slot in the first limb 8 so that the hole 52 in the upper end of the trigger is aligned with the bore. The pin is inserted into the bore so that it extends along the bore, through the hole 52 in the trigger. The pin is passed along the bore until the flange 56 abuts the hole in the trigger.

The spring 54 is located on the pin so that it abuts the flange and the trigger at one end, and the end cap 58 is located on the pin so that it abuts the spring at its other end.

The pin, spring and end cap are retained within the frame by means of a thread 60 on the closure cap 58, which engages a thread at the end of the bore remote from the nail holder.

In use, an intramedullary nail is connected to the nail holder by means of the engagement fixture 4, in a predetermined angular relationship. The nail is then introduced into the intramedullary cavity in the patient's bone. The first limb of the frame will extend away from the bone, generally transverse to the axis of the bone. The second limb of the frame will extend generally parallel to the axis of the bone.

For each rotational position of the nail holder in the first limb (defined by location of the pin 32 in one of the bores 30), one or more of the drilling guide holes 42, 44 is aligned with a corresponding fixation hole 16, 18, 20 in the nail. Different drilling guide holes can be aligned with their corresponding fixation holes in the nail by rotating the frame around the nail holder, allowing the surgeon to select the fixation holes which are most suitable in the procedure which is being performed. The intramedullary nail can be held against rotation using the hexagonal grip portion 7. The frame can be freed for rotation between first and second angular orientations by withdrawing the pin from the bore corresponding to the first orientation (by squeezing the trigger, causing compression of the spring between the flange on the pin and the end cap), and locked in the second orientation by releasing the pin so that it is received in the bore to corresponding to the second orientation. The intramedullary nail can be held against rotation using the hexagonal grip portion 7.

Figure 6 shows a nail holder 100 which has an engagement fixture 102 at one end and a hexagonal grip portion 104 at its other end, as described above in relation to the embodiment shown in Figure 1. The nail holder has cylindrical bearing portions 106. An octagonal portion 1 10 is provided between the cylindrical portions. The hexagonal grip portion can be separated from the remainder of the nail holder to facilitate assembly of the nail holder with the frame.

A pin 120 has a spring 122 located on it and a control button 124 at one end. The pin has a plate 124 at its other end. The plate has an opening in it. The opening is defined by first portion 126 which is shaped as part of an octagon, and a second portion 128 which is shaped as a part of a circle. The side walls of the octagon are sized so that the octagonal portion of the nail holder is a snug fit. The diameter of the second portion is slightly greater than the diameter of the cylindrical bearing portions 106 of the nail holder so that the nail holder can rotate within the second portion of the opening. The first and second portions intersect.

The plate has a threaded bore in it and the pin has a threaded end. These features allow the plate and the pin to be connected to one another.

Figures 7 and 8 show an alignment instrument which includes the nail holder 100 and the pin 120 which are described above in relation to Figure 6. The instrument includes a frame 130 which has a first limb 132 and a second limb 134. The second limb has drilling guide holes in it which can be aligned with six fixation holes in an intramedullary nail, as follows:

The first limb 132 of the frame has a bore 148 extending along its length. The bore communicates with a socket 150 at one end in which the bearing portion of the nail holder can be received. The socket has bearing surfaces which correspond to the cylindrical bearing portions 106, 108. The socket provides a plate-shaped recess between the bearing surfaces in which the plate 124 is received. The bore 148 is enlarged at its other end to accommodate the spring 122 and control button 124. The spring acts between the control button and the end wall of the enlarged portion of the bore to urge the control button (and the pin and plate which are connected to it) out of the bore, so that the axis of first portion (octagonal) 126 of the opening in the plate is aligned with the axis of the socket. The axis of the second portion (circular) 128 of the opening in the plate can be aligned with the axis of the socket by applying force to the button 124 so that the pin is displaced along the bore in the first limb, and the spring is compressed.

The instrument is assembled by locating the plate 124 in the socket and the pin (with the pin and the control button) in the bore in the first limb, and connecting them by means of the thread on the pin received in the threaded bore in the plate. The nail holder is introduced into the socket while force is applied to the control button to cause the pin to be displaced in the bore in the first limb, so that the axis of the circular portion 128 of the opening in the plate is aligned with the axis of the socket. The upper cylindrical bearing portion is then able to pass through the opening in the plate so that each of the cylindrical bearing portions is aligned with a corresponding bearing surface in the socket.

Release of the force applied to the control pin allows the spring to urge the control button out of the bore in the first limb so that the axis of the octagonal portion of the opening in the plate is aligned with the axis of the socket. Provided that the angular orientation of the frame relative to the nail holder (and nail connected to it when the instrument is in use) is appropriate, the octagonal portion 110 of the nail holder is received in the octagonal portion of the opening in the plate. The snug fit of the octagonal portion 110 of the nail holder is received in the octagonal portion of the opening in the plate ensures that the frame is locked against rotation relative to the nail holder. The frame can be released for rotation relative to the nail holder by applying force to the control button.

Claims

CLAIMS:

1. An alignment instrument for use with an intramedullary nail, which comprises: a. a nail holder having an engagement fixture towards one end for engaging an intramedullary nail and a bearing portion, b. a frame which includes a socket in which the bearing portion of the nail holder can be received, the frame including at least one arm which extends from the bearing portion, in a direction generally towards the distal tip of a nail when fitted in the engagement fixture, the arm defining at least one drilling guide hole for defining the location of a hole to be drilled in a patient's bone which intercepts a corresponding hole in the nail,

2. An alignment instrument as claimed in claim 1, in which the pin is provided in the frame and the bore is provided in the bearing portion.

3. An alignment instrument as claimed in claim 2, in which the bearing portion has a plurality of bores in it which are radially spaced apart around the bearing portion, for receiving the locking pin in predetermined respective angular positions of the frame relative to the bearing portion.

4. An alignment instrument as claimed in claim 1, in which the pin is biassed resiliently towards the deployed position.

5. An alignment instrument as claimed in claim 1, in which the frame includes a trigger which, when squeezed, causes the pin to move in the direction from the deployed position towards the retracted position.

6. An alignment instrument as claimed in claim 1 , in which the nail holder includes a grip portion by which it can be gripped to restrict rotation of the nail holder.

7. An alignment instrument as claimed in claim 6, in which the grip portion has the configuration of a hexagonal nut.

8. An alignment instrument as claimed in claim 1 , in which the frame comprises a first limb which extends from the socket generally transversely relative to the axis of the engagement fixture, and a second limb which extends generally parallel to the said axis, and in which the drilling guide hole is provided in the second limb.

9. An assembly for use in surgery, which comprises an alignment instrument as claimed in claim 1 and an intramedullary nail which can be connected to the alignment instrument using the engagement fixture.