Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-12-16
2001-10-23
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023150, C623S023470
Reexamination Certificate
active
06306174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention related to a femoral component of a replacement hip joint of the “Exeter” type which has a collarless stem including a shoulder for fixing in a medullary canal by cement.
2. Discussion of Prior Art
The “Exeter” type femoral component of the kind shown in British Patent No. 1 409 054 is well known and comprises a neck which carries a ball head for cooperation with an acetabular socket. The neck is connected to a tapered collarless stem. Thus, there is no collar for resting either on the bone or the cement in the area where the stem joins the neck of the implant. This type of stem has evolved so that the stem can be given a highly polished finish to help it slide down inside the bone cement and the present invention relates to this type of femoral component.
In certain circumstances, it can be difficult to locate the femoral component in the medullary socket with the neck and ball at the precise height and angle required. This can be caused by the bone which are structurally imperfect or by difficulties in reaming a suitable cavity. It is particularly pronounced when cavities have to be lined with bone fragments prior to cementing or when there are irregularities and the present invention is intended to overcome some of the difficulties experienced.
It is known from U.S. Pat. No. 5,931,871 to provide a femoral component with a separate proximal component but in this application, the angle of the proximal component with regard to the stem about a proximal/distal axis is fixed and there is no provision for adjustment.
U.S. Pat. No. 4,051,559 also shows the use of a separate proximal component and this is provided to allow it to be placed in position on a cylindrical stem which is intended to be screwed directly into the bone. The proximal component is provided with a collar which is intended to rest against the cut and prepared bone and there is no provision for a stem to slide down inside bone cement as is required by the Exeter type hip stem. Moreover, the angular adjustment about a proximal/distal axis may be too coarse to allow final accurate adjustment with an Exeter type component.
SUMMARY OF THE INVENTION
According to the present invention, a femoral component of a replacement hip joint has a stem for fixing in cement in a medullary cavity by cement and having a separate proximal component provided with a neck for a ball head, and including an attachment system for securing the proximal component to the stem which allows selection of an infinite number of angularly displaced positions about a proximal/distal axis, and adapted to allow fixation of the two parts after insertion of the stem into the prepared medullary cavity and causing minimal torsional loads on the stem. The stem extends proximally to the level of the bone cut which allows the proximal component to rotate after the stem is implanted. The attachment system includes a vernier coupling.
Thus, with the component according to the present invention, it is possible to insert the stem into a prepared medullary cavity and subsequently add the proximal component at the precise angle about the proximal/distal axis and then complete fixation of the two parts without causing torsional loads on the stem which might cause the stem to move in the cement and create cavities or cause other damage. This also prevents the stem from being twisted about the proximal/distal axis which might alter the precisely prepared angle of the proximal component.
If an infinite number of positions is unnecessary, the use of a Vernier coupling in the attachment system enables a very large number of positions to be used and provides a simple and inexpensive method of manufacture. In one preferred embodiment, the boss and cavity are tapered and in another they are cylindrical.
Preferably, the attachment system include a male element on the stem adapted to cooperate with the female structure on the proximal component. Thus, the male element may comprise a boss on the proximal portion of the stem and the female structure can be provided by a cavity to receive and cooperate with the boss, and a release or locking element can be provided for preventing axial movement after initial fixing.
In one embodiment, the boss can be tapered to engage a tapered cavity on the proximal component and the release element may comprise an axially extending locking screw extending from the proximal component into the tapered boss.
Alternatively, the release or locking element may comprise a cotter pin adapted to locate on a boss extension, the pin extending tangentially to the extension.
In another construction, the release can be provided by a circumferential groove in the boss which can be engaged by a radially extending lock pin or screw in the proximal component.
According to another preferred construction, the boss can be cylindrical and with this arrangement, the release element can again be provided by a tangentially extending cotter pin located in the proximal component. If desired, the cotter pin can be located in a groove in the boss.
With these arrangements, the release element may comprise a radially extending pin or screw in the proximal component which can engage a peripheral groove in the boss.
In another alternative construction, the boss can be cylindrical or tapered and be provided with a peripheral groove and the release element can comprise a locking plate with means to move it radially to engage said groove. The corresponding cavity is also cylindrical or tapered to match the boss.
In yet another embodiment, the proximal member and stem can each be provided with a predetermined number of openings arranged at the same radius about an axis substantially parallel to the long axis of the prosthesis, one ring of openings having one more opening than the other, and a locking member adapted to enter one of each ring of holes to provide a Vernier coupling. Thus, one ring of holes can be provided in the male element and the other in the proximal component.
REFERENCES:
patent: 3067740 (1962-12-01), Haboush
patent: 4051559 (1977-10-01), Pifferi
patent: 5002578 (1991-03-01), Luman
patent: 5201882 (1993-04-01), Paxson
patent: 5286260 (1994-02-01), Bolesky et al.
patent: 5702479 (1997-12-01), Schawalder
patent: 5858020 (1999-01-01), Johnson et al.
patent: 5931871 (1999-08-01), Baur et al.
patent: 6083263 (2000-07-01), Draenert et al.
patent: 1 409 054 (1975-10-01), None
Gie Graham Allan
Ling Robin Sydney Mackwood
Storer John Andrew
Timperley Andrew John
Benoist Girard SAS
Lerner David Littenberg Krumholz & Mentlik LLP
Snow Bruce
LandOfFree
Femoral component does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Femoral component, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Femoral component will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2594095