Patent Application
20070260321
This invention relates to prosthetic glenoid components, more particularly, a conically-shaped glenoid implant for holding a prosthetic glenoid insert used in total shoulder arthroplasty wherein the device is conical in shape to provide a larger amount of surface area and to convert sheer force into compressive force. A special tool is also provided to assist in the process.
Arthritis or other injuries to the shoulder typically cause a patient to seek cures for shoulder stiffness and pain. Although not required, total shoulder arthroplasty is often the most effective method for restoring movement and comfort to shoulders damaged by arthritis, injury or other surgeries.
In total shoulder arthroplasty, the surfaces of the humeral head of the humerus (commonly referred to as “the ball”) and the glenoid (commonly referred to as “the socket”) are resurfaced with metal and plastic implants, thereby restoring movement and comfort to the patient. The humeral prosthesis is usually press fit into the humerus; alternatively, it may be cemented into the shaft of the humerus. Then, the glenoid bone shape and orientation are corrected using a circular reamer and a polyethylene glenoid insert is inserted into the glenoid. A small amount of bone cement is used to hold the polyethylene glenoid insert in place. Thus, the prosthetic humeral head and glenoid are now correctly aligned so as to provide maximum movement without pain.
However, although the results obtained from undergoing total shoulder arthroplasty are initially positive, the prosthetic polyethylene glenoid insert does not remain in a permanent position due to glenoid fixation, thus necessitating additional surgeries to replace the prosthetic polyethylene glenoid insert. The glenoid fixation problem is, in large part, due to the joint being in constant sheer due to the upward and downward movement of the deltoid, thus being non-conducive to bone ingrowth. Although there have been many attempts to stabilize the prosthetic glenoid using keels, screws, etc., the sheer overcomes these stabilizing means, thereby eliminating the possibility of bone ingrowth. In addition, the secondary “rocker horse” eccentric loads placed on the glenoid creates an environment that is not conducive to bone ingrowth.
Furthermore, previous glenoid designs have minimal bone-prosthetic interface surface area to allow for adequate bone ingrowth. Thus, the need for bone ingrowth is of great importance in achieving total shoulder arthroplasties that have long-lasting, positive results.
Although sheer force is not conducive to bone ingrowth, compressive force is conducive to bone ingrowth. Thus, rather than having sheer force acting upon the shoulder, it would be most beneficial to have compressive forces acting on the glenoid in order to promote boney ingrowth.
Thus, a need exists for a conical prosthetic glenoid device and method that converts sheer force into compressive force and also increases the surface area at the bone-prosthetic interface to promote bone ingrowth.
The relevant prior art includes the following references:
The primary object of the present invention is to provide a conically-shaped glenoid implant and method that converts sheer force to compressive force.
A further object of the present invention is to provide a conically-shaped glenoid implant and method that promotes bone ingrowth.
An even further object of the present invention is to provide a conically-shaped glenoid implant and method that has a large surface area for boney ingrowth to occur.
Another object of the present invention is to provide a conically-shaped glenoid implant and method that can remain in the glenoid for a long length of time.
The present invention fulfills the above and other objects by providing a conically-shaped glenoid implant having a fastening means for the acceptance of a conventional prosthetic glenoid insert and a hole located thereon for the acceptance of a locking means. The fastening means are preferably notches while the locking means is reverse barbs. An optional cannulated screw or keels may be located on the exterior surface of the cone for additional securement of the conically-shaped glenoid implant and to prevent rotation of the conically-shaped glenoid implant in the glenoid. The conically-shaped glenoid implant is preferably coated and porous so as to permit boney ingrowth to occur.
To install the conically-shaped glenoid implant of the present invention, a surgeon first drills a central guide wire into the glenoid. Then, using a cannulated drill, he or she begins drilling a hole in the glenoid. The hole is then reamed using progressively larger reamers so as to create a conical hole smaller than the prosthesis. A cone punch is then used to perfect the shape of the hole into a conically-shaped hole that is slightly smaller than the device. A cannulated inserter is then inserted through the screw hole of the conically-shaped glenoid implant and into the glenoid itself. The conically-shaped glenoid implant is then tapped into place in the glenoid to achieve a press fit. The use of reverse barbs may also assist in retaining the implant in the glenoid. Further locking means, preferably a locking screw, is threaded through the screw hole of the conically-shaped glenoid implant. Finally, the guide wire is removed and a conventional prosthetic glenoid insert is impacted onto the fastening means, which are preferably notches, although current locking mechanism are also acceptable.
The above and other objects, features and advantages of the present invention should become even more readily apparent to those skilled in the art upon a reading of the following detailed description in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.
In the following detailed description, reference will be made to the attached drawings in which:
For purposes of describing the preferred embodiment, the terminology used in reference to the numbered components in the drawings is as follows:
1. conically-shaped glenoid
2. cone exterior surface
3. screw
4. humeral head
5. humerus
6. glenoid
7. prosthetic glenoid insert
8. coneapex
9. hole for fastening means
10. cone base
11. notches
12. cone interior surface
13. barb
14. cannulated drill
15. site for insertion of conically-shaped implant, generally glenoid implant
16. center of glenoid
17. reamer
18. cone punch
19. keel
20. cannulated inserter
21. height of cone
22. width of cone base
23. width of cone apex
24. retractor
25. central guide wire
26. deltoid muscle
27. cone
28. compressive force
29. sheer force
Referring to
Although the prosthetic glenoid insert 7 is installed in the glenoid 6, most likely the patient will require another surgery to replace the prosthetic glenoid insert 7 due to up and down movement of the deltoid muscle, also known as sheer force 29. This sheer force 29 eventually leads to loosening at the bone-cement interface and, ultimately, failure of the glenoid implant. In previous attempts at ingrowth, glenoid designs have failed to overcome this sheer force 29, thereby preventing the prosthetic glenoid insert 7 from achieving bone ingrowth within the glenoid and failing to become a permanent fixture in the glenoid 6.
On the other hand, the use of the conically-shaped glenoid implant 1 of the present invention in conjunction with the prosthetic glenoid insert 7 does promote bone ingrowth as the conically-shaped glenoid implant 1 includes a porous coat. In addition, because the surface area of the conically-shaped glenoid implant 1 is markedly larger than the surface area of the ovular prosthetic glenoid insert 7, the likelihood of achieving bone ingrowth is much greater. For example, a conically-shaped glenoid implant 1 with a 28 millimeter diameter would have a surface area of 1,457 mm2 as determined by the formula for surface area of a cone being IIrs where s equals slant height and slant height is the square root of r2+h2. On the other hand, a standard ovular prosthetic glenoid insert 7 having a size of 40 mm by 28 mm would have a surface area of only 879 mm2 as determined by the formula II(L×W/2). Therefore, because the conically-shaped glenoid implant 1 has a larger surface area when compared to the prosthetic glenoid insert 7, the chances of bone ingrowth occurring are greater. Thus, the conically-shaped glenoid implant 1 would, at least theoretically, last forever in the glenoid 6 without the need for additional surgeries.
Specifically focusing on the conically-shaped glenoid implant 1 of the present invention, with reference to
In
With reference to
Next,
In
With regards to
A cannulated drill 14 is then positioned on the center of the glenoid 16 in order to begin drilling a hole for the location for placement of the conically-shaped glenoid implant 15. Progressively larger cone reamers 17 are then used to enlarge the site for insertion of the conically-shaped glenoid implant 15 so as to be sized slightly smaller in diameter than the diameter of the conically-shaped glenoid implant 1. It is most advantageous to use the reamers 17 to enlarge the site for insertion of the conically-shaped glenoid implant 15 as it is a quicker and cleaner alternative for shaping and sizing the site 15. However, the surgeon should stop using the reamers 17 as soon as he or she is near a predetermined site size slightly smaller than the conically-shaped glenoid implant 1. Reaming should be carried out to the anterior and posterior inside edge of the cortical glenoid vault.
Next, a cone punch 18 may be used to punch a shape and size in the glenoid 6 slightly smaller than the size of the conically-shaped glenoid implant 1. By using the cone punch 18, a surgeon can shape the exact size of the site 15 if desired.
A cannulated inserter 20 is then inserted into the hole for fastening means 9 in the conically-shaped glenoid implant 1 and is used for the insertion of the conically-shaped glenoid implant 1 into the site for insertion 15. The conically-shaped glenoid implant 1 is then tapped into place within the glenoid 6. A fastening means, such as a cannulated screw 3, is then secured within the hole for fastening means 9 in the conically-shaped glenoid implant 1 to further aid in the securement of the conically-shaped glenoid implant 1 within the glenoid 6.
Finally, the guide wire 25 is removed and the polyethylene glenoid insert 7 is impacted or snapped onto the conically-shaped glenoid implant 1 via the locking means, which is preferably notches 11. It is important to realize that while the embodiment shown here is on a cannulated system for easier installation, its function and efficacy do not rely on the cannulation and is not necessary.
With respect to
In addition, because the prosthetic device of the present invention is conically-shaped, a surgeon may use both a retractor 24 and a cannulated reamer 17 to ream a location for the conically-shaped glenoid implant 15 that is less than the width of the glenoid 6. Without the use of the present invention, it was difficult for a surgeon to use both instruments at once as the retractors blocked the use of the reamers.
Finally, because the glenoid cortical vault is preserved, a surgeon may revisit the glenoid 6 in the future if necessary to revise the glenoid 6.
The use of the present invention will convert sheer force to compressive force and greatly increase the prosthetic-bone surface area interface, thereby aiding in the promotion of bone ingrowth.
It is to be understood that while a preferred embodiment of the invention is illustrated, it is not to be limited to the specific form or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not be considered limited to what is shown and described in the specification and drawings.
