Patent Application
20110106267
The present invention relates to prosthetic devices particularly shoulder prostheses and, more particularly, to a shoulder prosthesis and method of use for shoulder replacement.
The state of the prosthetic shoulder market has progressed such that a surgeon generally approaches shoulder replacement surgery in one of two strategic ways. One strategic manner is to perform the shoulder replacement surgery in accordance with a manufacturer's shoulder prosthesis or shoulder prosthesis product line. Particularly, a surgeon is provided with instrumentation and technique guidelines for the particular shoulder prosthesis or prosthesis line. The guidelines and/or instrumentation direct or dictate the angle of humeral head resection for the implant (prosthesis). This angle is in relation to the humeral intramedullary (IM) canal and is designed to match an optimum set of angles already present in the prosthetic design.
Another strategic manner is to perform the shoulder replacement surgery in accordance with a patient's anatomy. Particularly, the humeral head is resected according to angles perceived to be “anatomic” in the opinion of the surgeon, not according to angles already present in the prosthetic design. The prosthesis is designed such that the configuration of the prosthesis is intraoperatively adjustable. This allows the prosthesis to be adjustable whereby it can match the boney preparation.
Even with respect to these two divergent manners of surgical strategy, a common problem in shoulder surgery is matching the humeral resection angle to the predetermined angle designed into the prosthesis. This angle may describe the angle between a prosthetic collar and the diaphyseal section of the stem. In the case of a collarless stem, the angle may describe the difference between the long axis of the stem and the inferior surface of the prosthetic head. It is considered optimal for fixation and biomechanics if the resected angle and the angle of the prosthesis are identical—thereby allowing intimate contact between the superior surface of resected bone and the inferior surface of the implant.
Moreover, the angular version in which the prosthesis is implanted will have a significant impact on the biomechanics of the prosthetic joint. Currently, most shoulder prosthesis systems on the market dictate the varus/valgus angle of the bone cut. This strategy does not allow the surgeon to easily alter biomechanics after the prosthesis has been trialed, much less implanted.
There are some known products currently marketed that attempt to resolve at least one of the above-noted issues. First, the Tornier-Aequalis system provides a modular junction within the metaphyseal region of the stem, which allows a small block between the stem and humeral head to be interchanged. This block is available in multiple angles, thus allowing the surgeon to select the block that best fits the boney anatomy as resected. This system, however, has two primary weaknesses. First, the use of modular blocks obviously forces the design to only allow angular adjustments in finite increments. Second, the need to adjust the angle through modular blocks forces the surgeon to remove the stem, change out a component, and reset the stem. This presents inconvenience, as well as risk for interfering with resected bone and compromising fixation.
A second product marketed as a solution to the problems addressed above is the CenterPulse Anatomica (now Zimmer, Inc.). This product provides a humeral head that is infinitely adjustable in varus/valgus and anterior/posterior angles relative to the stem portion of the prosthesis. This is accomplished through a spherical shaped protrusion on the superior surface of the stem that fits into a spherical recess in the humeral head. These mating surfaces allow the head to be articulated about the stem, thus allowing adjustable positioning of the head. The head can be locked in a position relative to the stem. This solution provides adjustment of the neck-shaft angle as well as being able to affect adjustment of the version through flexibility in the anterior/posterior angle. The locking means, however, is sub-optimal. Particularly, the locking mechanism requires the turning of a locking screw that has its head facing lateral and inferior, for which there is no access once the stem has been cemented. This eliminates the ability to adjust head position on the fly, and forces a total revision if articular surfaces ever need to be revised. Lastly, the protrusion on the humeral stem even when the humeral head is not in place limits the surgeon's access to the glenoid in preparation for a glenoid replacement.
In some cases, a spherical ball having a split on the top of the ball was discussed. The split spherical ball would engage a recess in the head. The idea is that the sphere allows the head to be rotated during surgery, but once the proper angle was chosen, the sphere can be expanded and lock into the recess. However, as the sphere expanded, the points of contact with the recesses move outward as the sphere expands. This results in the engagement between the sphere and the recess being unstable.
What is thus needed is a shoulder prosthesis and/or method of use that allows adjustment of the angular position of the humeral head.
What is thus further needed is a shoulder prosthesis and/or method of use that allows almost infinite adjustment of the angular position of the humeral head.
What is thus even further needed is a shoulder prosthesis and/or method of use that allows adjustability during surgery and stability during the life of the device in service.
It is also desirable that there be a shoulder prosthesis that allows the components to lock together once the components are in the appropriate positions.
According to one embodiment of the present invention, a shoulder prosthesis including a head a head having a cavity defined therein is provided. The head further has a first bearing surface configured to mate with a second bearing surface of a glenoid, A stem having a recess defined therein is included and is configured to be received a humerus. The shoulder prosthesis also includes a first connector having a proximal end and a distal end. The first connector also includes a threaded cavity and an outer wall, the outer wall for engaging the recess of the stem. The threaded cavity opens at the proximal end of the first connector. The shoulder prosthesis further includes a second connector having a threaded end sized and shaped to fit in the threaded cavity of the first connector. The second connector also has a head connector end, sized and shaped to fit within the cavity of the head. The outer wall of the first connector is sized and shaped to expand at the proximal end as the second connector is threaded into the threaded cavity.
According to another embodiment, a shoulder prosthesis is provided. The shoulder prosthesis includes a head having a cavity defined therein and a stem having a recess defined therein. The recess has a first open end that is defined in a proximal surface of the stem, a second closed end, and a sidewall extending therebetween. The shoulder prosthesis further includes a neck having a first coupling portion configured to mate in a friction fit manner with the cavity of the head, and a second coupling portion configured to be received in the recess of the stem. The neck includes a locking portion sized and shaped to lock the second coupling portion to the neck. The second coupling portion has a proximal end and a distal end and the locking portion engages the second coupling portion at the proximal end. The proximal end of the second coupling portion of the neck is configured to expand to thereby couple the neck to the stem when the second portion of the locking element is received within the proximal end of the second coupling portion of the neck.
According to yet another embodiment, a method of assembling a shoulder prosthesis for use in shoulder arthroplasty is provided. The method includes using a head having a cavity defined therein and a stem having a recess defined therein. A first connector having a proximal end and a distal end is also used. The first connector also includes a threaded cavity and an outer wall, the outer wall for engaging the recess of the stem. The threaded cavity opens at the proximal end of the first connector. The method also includes using a second connector having a threaded end sized and shaped to fit in the threaded cavity of the first connector. The second connector also has a head connector end, sized and shaped to fit within the cavity of the head. The method further includes inserting the first connector into the recess of the stem and adjusting the first connector to the desired angle. The second connector is then fully threaded into the first connector, causing the proximal end of the first connector to expand. This results in locking the first connector to the stem.
In the drawings:
Corresponding reference characters indicate corresponding parts throughout the several views. Like reference characters tend to indicate like parts throughout the several views.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein by described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Referring now to
As depicted in
Turning now to the head 16, the head is characterized by a body 30 formed as a general partial spheroid. Particularly, the body 30 is shaped to conform to a glenoid. The body 30 has an articulation surface 32 conforming to the general partial spheroid and a bottom surface 34. It should be appreciated that the head 16 represents any size shoulder prosthesis head. The subject invention allows the use of various sized heads with the other components of the present shoulder prosthesis 10. While a head of only one size is ultimately used for the shoulder prosthesis 10 when implanted into the patient, the components of the present shoulder prosthesis 10 allow various sized heads to be trialed and/or used when the stem 12 is implanted into the humerus (i.e. during and/or after the time at which the stem 12 is final stage implanted in the humerus). The various heads may be variously proportioned and/or sized.
The head 16 further includes a recess, cavity or the like 36 defined by an inner surface 37 within the body 30 that is open on the underside or bottom surface 34. The inner surface (wall) 37 and thus the cavity 36 is tapered and will be described more fully below.
Referring now to
The second connector 40 includes a threaded end 50 and a head connector end 52. The head connector end 52 couples the second connector to the head 16. The head connector end 52 is in the shape of a male taper such that when the head connector end 52 is inserted into the cavity 36 of the head 16, the head connector end 52 is taper locked into the cavity 36. In other embodiments, the head connector end 52 may not be tapered and the head connector end 52 may be locked into the cavity 36 of the head 16 using other known methods.
The threaded end 50 of the second connector 40 is sized and shaped to thread into the threaded cavity 46 of the first connector 38. The threaded cavity 46 of the first connector 38 has a diameter that is slightly less than the diameter of the threaded end 50 of the second connector 40. As the threaded end 50 is threaded into the threaded cavity 46, the threaded end 50 forces the proximal end 42 of the first connector 38 to expand.
In the illustrated embodiment, the first connector 38 includes a plurality of slits 54 at the proximal end 42. The slits 54 are defined by a plurality of coupler segments 56. In this embodiment, there are three slits 54 and three coupler segments 56. In other embodiments, there may be other numbers of slits 54 and coupler segments 56. As the threaded end 50 of the second connector 40 is threaded into the threaded cavity 46, the slits 54 allow the coupler segments 56 to separate and expand.
Turning now to
It should be appreciated that
Once the appropriate angular orientation of the stem 12 is determined, a pin 62 is inserted into a pin-receiving aperture 64 (
As depicted in
Turning now to
The shoulder prosthesis 10 may be made of any known biocompatible material. For example, the shoulder prosthesis 10 may be made of titanium, cobalt chrome and/or stainless steel. Other known biocompatible or medical grade implant materials may also be used.
Although the above-described embodiment relates to a shoulder prosthesis, it should be understood that the trials may also be used in lieu of implants.
Although the figures illustrate the use of a long humeral stem, it should be understood that the word “stem” does not require that there be a distal portion that extends into the intramedullary canal. The stem as used herein means a component that extends into the humerus.
There is a plurality of advantages of the subject invention arising from the various features of the shoulder prosthesis described herein. It will be noted that alternative embodiments of the shoulder prosthesis of the subject invention may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a shoulder prosthesis that incorporate one or more of the features of the subject invention and fall within the sprit and scope of the subject invention.
