An implant

Abstract

An implant 200 comprising, a mounting portion 202 including a mounting surface (204, fig.2) for mounting the implant on a glenoid neck of a glenohumeral joint, and a plurality of spaced apart fixation holes 210 for attaching the implant to the glenoid neck with bone screws; a support portion 220 comprising a support surface 222 for supporting a humeral head of the glenohumeral joint, and a recessed inner surface 208 extending from the support surface towards the mounting surface to define a gap between the implant and the glenoid neck when the implant is mounted thereon; and a plurality of spaced apart suture holes 224 extending through the implant for drawing a capsule of the glenohumeral joint into the gap by sutures. Also described is an implant comprising, a mounting surface (204, fig.2); a porous region (814, fig.8) comprising a plurality of passageways terminating at the mounting surface; at least one fixation hole (810, fig.8); and at least one location aperture (850, fig.8) extending through the implant from the mounting surface to at least proximal to a one of the passageways and configured to receive a K-wire. The implant minimises time and cost for stabilising the glenohumeral joint.

Description

The present invention relates to an implant and in particular, but not exclusively, to a glenoid implant for stabilising the glenohumeral (shoulder) joint. The shoulder is made up of two joints; the acromioclavicular joint and the glenohumeral joint. The acromioclavicular joint is where the acromion, part of the shoulder blade (scapula) and the collar bone (clavicle) meet. As illustrated in Figure 1, the glenohumeral joint 100 is where the bail 102 (humeral head) and the socket 104 (the glenoid) meet. In Figure t the glenohumeral joint is dislocated anteriorly. The rotator cuff connects the humerus to the scapula and is made up of the tendons of four muscles, the supraspinatus, infraspinatus, teres minor and the subscapularis. Tendons attach muscle to bone. Muscles in turn move bones by pulling on the tendons. The muscles of the rotator cuff keep the humerus tightly in the socket. The socket, or the glenoid, is shallow and flat, it is rimmed with soft tissue called the labrum that creates a deeper socket that moulds to fit the humeral head. The joint capsule surrounds the shoulder joint and is a fluid-filled sac that lubricates the joint, it is made up of ligaments which are soft tissue that holds bone to bone. Shoulder injuries or complications can occur to any part of the shoulder. One such injury / compiication is dislocation of the humerus from the glenoid socket in view of the same being shallow and covering only about a third of the humeral head. Whilst the soft tissue of the labrum and capsule provide some constraint, it cannot provide the same degree of constraint as bone. The chance of dislocation is made worse in the case of anterior bone toss caused by shoulder instability and / or repetitive dislocation. Conventional treatment typically involves attaching a relatively small tissue graft from a donor or directly from the patient to the lesion to restore the bony anatomy. However, a graft directly from the patient, typically from the iliac crest or coracoid, is time consuming for the surgeon and in turn costly, it can cause the patient additional pain and carries the risk of complications including serious nerve and blood vessel injuries. It is an aim of certain embodiments of the present invention to provide a glenoid implant for locating on the glenoid neck and to extend the bearing surface of the glenoid, particularly where bone loss has occurred. It is an aim of certain embodiments of the present invention to provide a glenoid implant for locating on the glenoid neck and configured to allow the soft tissue of the joint capsule to be pulled by sutures between the implant and the glenoid neck to encourage soft tissue to bone healing. It is an aim of certain embodiments of the present invention to provide a glenoid implant configured to adapt to different patient anatomies and / or to allow for some tolerance during preparation of the glenoid neck. It is an aim of certain embodiments of the present invention to provide a glenoid implant that minimises the time and in turn cost for stabilising the glenohumeral joint. It is the aim of certain embodiments of the present invention to allow provisional fixation of the implant with K-wires in slotted holes that allow the implant to be moved when some of the holes have wires in place but be firmly fixed when all of the wires are in place. According to a first aspect of the present invention there is provided an implant comprising: a mounting portion comprising a mounting surface for mounting the implant on a glenoid neck of a glenohumeral joint, and a plurality of spaced apart fixation holes for attaching the implant to the glenoid neck with bone screws; a support portion comprising a support surface for supporting a humeral head of the glenohumeral joint, and a recessed inner surface extending from the support surface towards the mounting surface to define a gap between the implant and the glenoid neck when the implant is mounted thereon; and a plurality of spaced apart suture holes extending through the implant for drawing a capsule of the glenohumeral joint into the gap by sutures. Optionally, the suture holes are located between the fixation holes and the support surface. Optionally, the suture holes extend out of or proximal to the recessed inner surface. Optionally, the suture holes are proximal to or on a line of intersection where the mounting surface meets the recessed inner surface. Optionally, the recessed inner surface is substantially flat or curved. Optionally, the recessed inner surface is angled with respect to the mounting surface by around 5 to 20 degrees. Optionally, the recessed inner surface defines a gap distance between the support surface and a plane of the mounting surface of around 1 to 4 mm. Optionally, the support surface is oriented substantially perpendicular to the mounting surface. Optionally, the support portion extends outwardly with respect to the mounting portion such that the implant comprises a substantially L-shaped cross section. Optionally, the mounting portion comprises a substantially porous structure for allowing bone ingrowth. Optionally, the porous structure extends through the mounting portion and defines a portion of the mounting surface. Optionally, the implant comprises a plurality of K-wire apertures for guiding a respective K-wire through the implant and into the glenoid neck. Optionally, the plurality of K-wire apertures comprises a first pair of slotted K-wire apertures oriented substantially parallel with respect to each other and a second pair of slotted K-wire apertures oriented substantially parallel with respect to each other, and wherein the first pair of slotted K-wire apertures is orientated substantially perpendicularly with respect to the second pair of slotted K-wire apertures. Optionally, the first pair of slotted K-wire apertures are oriented substantially parallel with the support surface of the implant, and wherein a first aperture of the first pair of slotted K-wire apertures is located in an upper region of the implant and a second aperture of the first pair of slotted K-wire apertures is located in a lower region of the implant. Optionally, the first aperture of the first pair of slotted K-wire apertures is located between a pair of the suture holes. Optionally, the K-wire apertures are located and oriented through the implant to terminate at or proximal to the porous structure. Optionally, the plurality of fixation holes comprises two fixation holes and the porous structure is substantially W-shaped to extend from a lower edge region of the implant and partially surround the fixation holes. Optionally, the W-shaped porous structure defines a curved trough region between a central region and each one of a pair of outboard regions. Optionally, the central region is wider than each of the outboard regions. Optionally, a first pair of the suture holes is located proximal to a first one of the fixation holes, and a second pair of the suture holes is located proximal to a second one of the fixation holes. Optionally, the support surface is substantially concave. Optionally, the support portion comprises substantially curved edge regions. Optionally, the implant comprises titanium. According to a second aspect of the present invention there is provided a system for stabilising a glenohumeral joint, comprising an implant according to the first aspect of the present invention and a plurality of sutures. Optionally, the system comprises a plurality of bone screws and / or K-wires. According to a third aspect of the present invention there is provided an implant comprising: a mounting surface for mounting the implant on bone; a porous region comprising a plurality of passageways terminating at the mounting surface for bone ingrowth; and at least one fixation hole for fixing the implant to the bone with at least one bone screw; and at least one location aperture extending through the implant and terminating at the mounting surface and at least proximal to a one of the passageways of the porous region, wherein the at least one location aperture is configured to receive a K-wire to perforate the bone at or proximal to the at least one passageway and allow the implant to be selectively positioned prior to fixation. Optionally, the at least one location aperture comprises a first pair of slotted location apertures oriented substantially parallel with respect to each other and a second pair of slotted location apertures oriented substantially parallel with respect to each other, and wherein the first pair of slotted location apertures is orientated substantially perpendicularly with respect to the second pair of slotted location apertures. Optionally, the first pair of slotted location apertures are oriented substantially parallel with the support surface of the implant, and wherein a first aperture of the first pair of slotted location apertures is located in an upper region of the implant and a second aperture of the first pair of slotted location apertures is located in a lower region of the implant. Optionally, the first aperture of the first pair of slotted location apertures is located between a pair of suture holes extending through the implant. Optionally, the at least one location aperture extends through the implant at an angle towards the mounting surface to communicate with the at least one passageway at the mounting surface. Description of the Drawings Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a glenohumeral joint and anterior bone loss to the glenoid socket with a dislocated humeral head; Figure 2 illustrates an outer side of an implant according to certain embodiments of the present invention with respect to the glenoid neck to which the implant is mountable: Figure 3 illustrates an inner side of the implant of Figure 2 which is mountable to the glenoid neck; Figure 4 illustrates the implant, including preinstalled sutures, located on a prepared glenoid neck using K-wires; Figure 5 illustrates the implant securely attached to the glenoid neck using bone screws and positioned slightly below the glenoid bearing surface; Figure 6 illustrates the implant with bone screws and sutures in situ; Figure 7 illustrates the implant securely attached to the glenoid neck and the joint capsule repaired and pulled into the gap created between the implant and the glenoid bone: Figure 8 illustrates an implant according to an alternative embodiment of the present invention including slotted holes to optionally allow temporary fixation of the implant to bone using K-wires; and Figure 9 illustrates a cross sectional region of the implant of Figure 8. Detailed Description As illustrated in Figures 2 and 3, a glenoid implant 200 according to certain embodiments of the present invention includes a mounting portion 202 defining a substantially fiat mounting surface 204 on a first side of the implant for locating on a pre-prepared glenoid neck of the patient. The mounting surface 204 extends across the full width of the implant and up a major part, i.e. more than 50%, of the first side from a lower edge region 205 thereof towards an upper edge region 206. The upper edge region 206 of the implant defines an angled surface 208 which is angled with respect to the mounting surface 204 to define a gap between the implant and the surface of the glenoid neck when the implant is located thereon. The angled surface may be substantially flat or curved such as concave. Alternatively, the gap may be provided by an offset surface of the upper edge region which is substantially parallel with the mounting surface 204 but which is set back therefrom to define an inwardly extending shoulder surface between the mounting surface and the offset surface, and in turn the gap between the implant and the glenoid neck in use. The inwardly extending shoulder surface may be substantially perpendicular to the mounting surface and the offset surface, or it may define an angle of more than ninety degrees with respect to the offset surface, i.e. it may slope from the offset surface to the mounting surface. A height of the mounting surface 204 in a direction from the lower edge region 205 towards the upper edge region is around 3-4 times greater than a height of the angled surface 208 or the alternative offset surface. A pair of spaced apart fixation holes 210 extend through the mounting portion 202 from the first side to the second side of the Implant, wherein each fixation hole 210 is shaped and sized to receive a bone screw for securely fixing the implant to the glenoid neck (see bone screws referenced 640,650 in Figure 6). Each fixation hole 210 defines a flared / tapered inner surface 212 to allow the screws to be independently oriented into bone in a range of desired angles. A diameter of the relatively narrow end of each fixation hole is around 3.5 mm and a diameter of the relatively wide end of each fixation hole is around 6 mm. The tapered inner surface 212 also acts as a countersink to accommodate the head of the screw and avoid the same protruding beyond the second side of the implant. The fixation holes can also be used to provisionally position the implant on the glenoid neck using K-wires or the like. The mounting portion 202 includes a porous structure 214 extending at least partially through, and preferably as illustrated fully through, the implant from the first side to the second side. The porous structure 214 allows for bone ingrowth to further secure and anchor the implant on the glenoid neck post-operation and during the healing process. The porous structure 214 extends from the lower edge region 205 of the implant and upwardly past the fixation holes 210 to define a W-shape comprising a central region 216 and a pair of outboard regions 218. The central region 216 may be slightly wider and / or longer than the outboard regions 218. The implant 200 illustrated in Figures 2 and 3 further includes a support region 220 defining a support surface 222 for supporting the humeral head of the glenohumeral joint. The support region 220 defines the upper edge region 206 of the implant including the angled or offset inner surface 208 defining the gap between the implant and the glenoid neck in use. A plurality of suture holes 224 extend through the support portion and out of the angled or offset surface 208, and aptly at or proximal to a line of intersection 260 where the mounting surface 204 meets the angled or offset surface 208. There are four spaced apart suture holes in the illustrated embodiment but there could be more or less as desired. A first adjacent pair of the four sutures holes 224 is located directly over a first one of the fixation holes 210 and a second adjacent pair of the four suture holes is located directly over a second one of the fixation holes. Each suture hole 224 is around 1 mm in diameter and at least the inner edge of each suture hole at the angled or offset surface 208 may be curved for the respective suture to smoothly engage with and to prevent compromising the integrity of the suture as it is pulled through the implant to draw the joint capsule into the gap between the implant and the glenoid neck. Aptly, the support portion 220 extends outwardly with respect to the mounting portion to define a shoulder region on the second / outer side of the implant, and such that the implant comprises a substantially L-shaped cross section. This arrangement provides a support structure to replace at least the anterior bone loss which has been caused by shoulder instability and / or repetitive dislocation for example whilst minimising the material needed to provide the mounting portion of the implant, and in turn the overall weight of the implant. The support portion may replace and extend the support surface otherwise provided by the glenoid. The corner and edge regions of the support portion are curved to eliminate any sharp corners or edges and the undersurface thereof is angled to minimise stress concentrations and efficiently transfer loading into the mounting portion. In use, the patient is sat up in a 30 degree beech chair position and optionally a bolster is placed behind the scapula. A 10 cm incision is made starting at the tip of the coracoid process and extending distally. The coracoid process is a hook-shaped bone structure projecting anterolaterally from the superior aspect of the scapular neck. The deltopectoral interval is developed and the cephalic vein is retracted laterally. A Kobal retractor is used to retract the deltoid and pectoralis major muscles. The axillary nerve is palpated behind the conjoined tendon passing under the subscapularis. The conjoined tendon and coracoid are identified. One blade of the Kobal retractor is placed under the conjoined tendon. A subscapularis tendon tenotomy is performed leaving enough tendon on both sides to repair at the end of the procedure. The subscapularis tendon, the glenohumeral capsule and the anterior labrum are elevated as one exposing the anterior glenoid neck. An anterior glenoid retractor is placed onto the glenoid neck and a Fukuda retractor is used to retract the humeral head posteriorly. Holding these retractors will tie up one assistant so a second assistant is useful for this part of the procedure. The glenoid neck is then prepared with a rasp or burr to flat bleeding bone. Minimal bone resection is usually required. A 1,6mm K wire can be used to create bleeding holes through cortical bone of the glenoid neck. Two or three no. 2 ultra-high molecular weight (UHMW) polyethylene sutures are passed through the suture holes 224 of the implant 200 with both suture ends of each suture coming through the angled or offset surface 208, or at the intersection between the mounting surface 204 and the angled or offset surface 208, or through the mounting surface at proximal location to the intersection. The sutures 400 are kept on the articular side of the implant during implant insertion and will be used to repair the capsule, as described further below. As illustrated in Figure 4, the implant 200 is positioned on the anterior glenoid neck 402 and provisionally fixed with 2mm K-wires 404. The implant is flush with, or as shown in Figure 5 (sutures not shown) very slightly below, the glenoid articular surface 406 and should never be proud of the glenoid articular surface. The K-wires 404 could pass through the screw holes 210 in the implant or, as illustrated in Figure 8, the implant 800 according to an alternative embodiment of the present invention could include round or slotted apertures 850 dedicated for K-wires to pass therethrough. The K-wire apertures 850 are orientated so that the implant is moveable with respect to the glenoid neck when some of the K-wire apertures 850 have a respective K-wire passing through them into bone allowing the implant position to be selectively adjusted and optimised before the implant is fixed in the desired position to the glenoid neck by bone screws through the fixation holes 810. When all the K-wire apertures have a K-wire passing through them into bone, the implant is fixed in position with respect to the bone at least in a plane of the bone mounting surface. Aptly, two pairs of slotted K-wire apertures are provided, wherein the slotted apertures of each pair are orientated substantially parallel to each other and the pairs of slotted apertures are oriented substantially perpendicularly with respect to each other. Aptly, each vertically (as illustrated) oriented slotted aperture is located between a respective pair of the suture apertures 824 and the horizontally (as illustrated) oriented slotted apertures are disposed substantially centrally on the implant. Aptly, as illustrated in Figure 9, the K-wire apertures 850 are located and oriented through the implant to terminate on the inner side of the implant at or proximal to the porous bone ingrowth region of the implant such that the K-wire apertures guide the respective K-wire 860 to perforate the bone 900 adjacent to the porous region 814 (only one bone in-growth hole shown for illustration purposes) of the implant 800 where bone grows into the implant. The K-wire apertures are aptly angled into the implant to terminate on the inner side of the implant adjacent to the porous region and so after implant fixation there is a continuous passageway from the perforated bone into the implant for new blood vessels to form in and cells to pass through. After definitive fixation of the implant and the K-wires have been removed, the holes created in the bone by the K-wires allow bleeding from the bone proximal to the porous region of the implant to facilitate and encourage bone ingrowth into the implant. Aptly, the K-wire apertures are around 1.6 - 2mm wide and the holes of the porous bone ingrowth region are around 600pm in diameter. The inferior bone screw 640 (see Figure 6) is measured and inserted loosely so the implant can rotate. The final implant position is determined and the superior bone screw 650 is inserted with bicortical hold and fully tightened. The inferior bone screw 640 is then tightened. The porous structure of the implant, particularly the central region thereof, reduces the material in the centre of the implant and in turn its bending strength about its centre line on which the relatively long and wide central porous region is disposed. This allows the implant to flex slightly about its centre line when the bone screws are tightened to encourage it to conform to a variety of prepared glenoid neck surfaces which desirably provides some tolerance for the surgeon and consistent stability and security for the implant. As illustrated in Figure 7, the joint capsule 408 and labrum (not shown) are repaired using the sutures 400 loaded through the implant 200. The capsule is drawn into the gap between the implant 200 and the glenoid neck 402 by applying a tension to the sutures 400 and pulling them through the suture holes 224 in the implant. The W-shaped porous structure, in combination with the bone screws, help to resist any loading on the implant in that direction. Drawing the medial edge region of the capsule 408 into the gap between the implant and the glenoid neck brings the capsule into contact with the bone to encourage tissue to bone healing. This arrangement makes the implant extraarticular and reconstructs the anterior inferior glenohumeral ligament. Care is taken to ensure only the capsule is repaired and not the subscapularis tendon. The humeral attachments of the anterior glenohumeral ligaments, capsule and subscapularis tendon merge and are repaired as one using No.2 UHMW polyethylene sutures to the cuff of tissue on the lesser tuberosity of the humerus. Post operation, a safe zone of external rotation is provided by the surgeon. Active assisted abduction and flexion are allowed from day one. Combined abduction and external rotation are not introduced until six weeks post operatively. Certain embodiments of the present invention therefore provide a glenoid implant for locating on the glenoid neck and to extend the bearing surface of the glenoid, particularly where bone loss has occurred. The implant is desirably configured to allow the soft tissue of the joint capsule to be pulled by sutures into a gap provided between the implant and the glenoid neck to encourage soft tissue to bone healing. The implant is configured to adapt to different patient anatomies and / or prepared glenoid neck surfaces to allow for some tolerance during preparation of the glenoid neck and mounting of the implant thereon. The glenoid implant according to certain embodiments of the present invention minimises the time and in turn cost for stabilising the glenohumeral joint.

Claims

1. An implant comprising:a mounting portion comprising a mounting surface for mounting the implant on a glenoid neck of a glenohumeral joint, and a plurality of spaced apart fixation holes for attaching the implant to the glenoid neck with bone screws;a support portion comprising a support surface for supporting a humeral head of the glenohumeral joint, and a recessed inner surface extending from the support surface towards the mounting surface to define a gap between the implant and the glenoid neck when the implant is mounted thereon; anda plurality of spaced apart suture holes extending through the implant for drawing a capsule of the glenohumeral joint into the gap by sutures.

2. The implant according to claim 1, wherein the suture holes are located between the fixation holes and the support surface.

3. The implant according to claim 2, wherein the suture holes extend out of or proximal to the recessed inner surface.

4. The implant according to claim 3, wherein the suture holes are proximal to or on a line of intersection where the mounting surface meets the recessed inner surface.

5. The implant according to any preceding claim, wherein the recessed inner surface is substantially flat or curved.

6. The implant according to any preceding claim, wherein the recessed inner surface is angled with respect to the mounting surface by around 5 to 20 degrees.

7. The implant according to any preceding claim, wherein the recessed inner surface defines a gap distance between the support surface and a plane of the mounting surface of around 1 to 4 mm.

8. The implant according to any preceding claim, wherein the support surface is oriented substantially perpendicular to the mounting surface.

9. The implant according to any preceding claim, wherein the support portion extends outwardly with respect to the mounting portion such that the implant comprises a substantially L-shaped cross section.

10. The implant according to any preceding claim, wherein the mounting portion comprises a substantially porous structure for allowing bone ingrowth.

11. The implant according to claim 10, wherein the porous structure extends through the mounting portion and defines a portion of the mounting surface.

12. The implant according to claim 10 or 11, comprising a plurality of K-wire apertures for guiding a respective K-wire through the implant and into the glenoid neck.

13. The implant according to claim 12, wherein the plurality of K-wire apertures comprises a first pair of slotted K-wire apertures oriented substantially parallel with respect to each other and a second pair of slotted K-wire apertures oriented substantially parallel with respect to each other, and wherein the first pair of slotted K-wire apertures is orientated substantially perpendicularly with respect to the second pair of slotted K-wire apertures.

14. The implant according to claim 13, wherein the first pair of slotted K-wire apertures are oriented substantially parallel with the support surface of the implant, and wherein a first aperture of the first pair of slotted K-wire apertures is located in an upper region of the implant and a second aperture of the first pair of slotted K-wire apertures is located in a lower region of the implant.

15. The implant according to claim 14, wherein the first aperture of the first pair of slotted K-wire apertures is located between a pair of the suture holes.

16. The implant according to any of claims 12 to 15, wherein the K-wire apertures are located and oriented through the implant to terminate at or proximal to the porous structure.

17. The implant according to any of claims 10 to 16, wherein the plurality of fixation holes comprises two fixation holes and the porous structure is substantially W-shaped to extend from a lower edge region of the implant and partially surround the fixation holes.

18. The implant according to claim 17, wherein the W-shaped porous structure defines a curved trough region between a central region and each one of a pair of outboard regions.

19. The implant according to claim 18, wherein the central region is wider than each of the outboard regions.

20. The implant according to any preceding claim, wherein a first pair of the suture holes is located proximal to a first one of the fixation holes, and a second pair of the suture holes is located proximal to a second one of the fixation holes.

21. The implant according to any preceding claim, wherein the support surface is substantially concave.

22. The implant according to any preceding claim, wherein the support portion comprises substantially curved edge regions.

23. The implant according to any preceding claim, comprising titanium.

24. A system for stabilising a glenohumeral joint, comprising an implant according to any preceding claim and a plurality of sutures.

25. The system according to claim 24, comprising a plurality of bone screws and / or K-wires.

26. An implant comprising:a mounting surface for mounting the implant on bone;a porous region comprising a plurality of passageways terminating at the mounting surface for bone ingrowth; andat least one fixation hole for fixing the implant to the bone with at least one bone screw; andat least one location aperture extending through the implant and terminating at the mounting surface and at least proximal to a one of the passageways of the porous region, wherein the at least one location aperture is configured to receive a K-wire to perforate the bone at or proximal to the at least one passageway and allow the implant to be selectively positioned prior to fixation.

27. The implant according to claim 26, wherein the at least one location aperture comprises a first pair of slotted location apertures oriented substantially parallel with respect to each other and a second pair of slotted location apertures oriented substantially parallel with respect to each other, and wherein the first pair of slotted location apertures is orientated substantially perpendicularly with respect to the second pair of slotted location apertures.

28. The implant according to claim 27, wherein the first pair of slotted location apertures are oriented substantially parallel with the support surface of the implant, and wherein a first aperture of the first pair of slotted location apertures is located in an upper region of the implant and a second aperture of the first pair of slotted location apertures is located in a lower region of the implant.

29. The implant according to claim 28, wherein the first aperture of the first pair of slotted location apertures is located between a pair of suture holes extending through the implant.

30. The implant according to any of claims 26 to 29, wherein the at least one location aperture extends through the implant at an angle towards the mounting surface to communicate with the at least one passageway at the mounting surface.17

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