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United States Patent m
[ii] Patent Number: 5,358,524  Date of Patent: Oct. 25, 1994
 ADJUSTABLE LENGTH PROSTHETIC IMPLANT
 Inventor: Marc E. Richelsoph, Cordova, Tenn.
 Assignee: Wright Medical Technology, Inc., Arlington, Tenn.
 Appl. No.: 17,567
 Filed: Feb. 16,1993
 Int CI.* A61F 2/28
 U.S. CI 623/16; 623/18;
623/38; 403/109; 403/46
 Field of Search 403/26, 43, 46, 118,
403/296, 106, 107, 109; 623/16, 38, 18; 606/63
 References Cited
U.S. PATENT DOCUMENTS
1,934,910 11/1933 Buhr 403/118 X
2,395,332 2/1946 Layman 403/118 X
2,955,854 10/1960 Musser 403/107
3,947,897 4/1976 Owens 623/16
4,216,550 8/1980 Thompson 623/38 X
4,227,518 10/1980 Aginsky 606/63
4,502,160 3/1985 Moore etal. .
4,611,944 9/1986 Larson 403/118 X
4,892,546 1/1990 Kotz et al 623/18
4,988,361 1/1991 Cooper 623/38
5,116,335 5/1992 Hannon et al 606/62
FOREIGN PATENT DOCUMENTS
0212192 3/1987 European Pat. Off. .
2827092 1/1980 Fed. Rep. of Germany 403/46
1237192 6/1986 U.S.S.R 623/16
1325228 7/1987 U.S.S.R 403/43
Primary Examiner—David H. Willse
An adjustable length prosthetic implant includes a stem having a threaded portion and an end portion adapted for mounting with a bone. A barrel includes an end portion adapted for mounting with a bone and a sleeve portion extending therefrom and including an elongated chamber defining an axial dimension. The sleeve portion overlies at least a portion of the threaded portion of the stem. A connecting mechanism is mounted on the barrel for interconnecting the barrel and stem and for controlling the axial extension and retraction of the stem from the barrel.
2 Claims, 2 Drawing Sheets
ADJUSTABLE LENGTH PROSTHETIC IMPLANT
The present invention relates to a surgically implant- 5 able prosthesis and more particularly is directed to a prosthesis suitable for femoral or humeral components in juvenile patients which provides for adjustment as the patient grows.
BACKGROUND OF THE INVENTION
Many types of skeletal implants and skeletal joint prostheses are available as substitutes for natural skeletal components and joints. Such prostheses are used when the natural skeletal component has been damaged 15 by disease or trauma. However, a problem exists in the case of juvenile patients or other patients where natural growth would otherwise be occurring. As the patient grows, the limb having the prosthesis implanted will not grow at the same rate as the opposing limb unless the 20 prosthesis allows for growth along its length.
The U.S. Pat. 4,892,546 to Kotz et al. issued Jan. 9, 1990 discloses an adjustable prosthesis for a bone joint including a joint component, an elongated rod having a distal end and proximal end, a drive trunion connected 25 to the rod through an angular gear, an elongated inner sleeve and outer sleeve, and means for preventing rotation of the inner sleeve within the outer sleeve. The elongated rod includes a threaded spindle and the inner sleeve includes a threaded spindle nut which cooperates 30 with the threaded spindle to provide extension and retraction adjustment of the rod relative to the inner sleeve. The European patent application EP 86109228, assigned to Waldemar Link GMBH, discloses an endoprosthesis replacing bone middle sections including a 35 tubular spacer with a collar at each end and a solid bone nail extending from one collar. A sliding nail fits in a bore of the tubular spacer and can be locked in any required position by a lock screw.
A joint implant is disclosed in the U.S. Pat. 4,502,160 40 to Moore et al, issued Mar. 5, 1985, and assigned to the assignee of the present invention. The Moore et al. patent discloses an implant including a stem for bone implantation including a threaded portion for adjusting axially with respect to an overlying sleeve which 45 carries an articulating component of the joint. A pin in the sleeve and an elongated slot in the stem restrain relative rotation but allow axial relative movement as the stem is urged into or out of the sleeve by the rotation of a nut coacting with the threads on the stem while 50 being axially restrained by the sleeve. The nut acts as a ring gear.
Although the Moore et al. patent discloses a very useful embodiment for the prosthetic joint implant, there are several problems that have been encountered 55 with its use. First, the nut interconnecting the stem with the sleeve or barrel is held on the sleeve by two pins which engage an annular slot disposed about the outer surface of the sleeve. This connection fixes the nut axially relative to the sleeve while allowing rotation of the 60 nut, the rotation extending or retracting the stem member. However, the two pins provide a limited two point contact area between the nut and the barrel about which the nut is rotating. There is a torquing force on the pins which results in friction, thereby increasing the 65 torque necessary to rotate the nut. Further, the round pin ends on the flat surface of the groove on the sleeve causes further friction. A second problematic area re
suits from the end of the barrel contacting an inner surface of the nut. Again, this creates a force or friction which must be overcome. Since these parts are generally made out of biocompatable titanium and titanium is susceptible to galling, such metal to metal contact and the resulting friction should be avoided. However, the juxtaposition of the inner surface of the nut and end of the barrel is necessary since there is only a two point contact between the means retaining the nut on the barrel and the barrel itself.
An additional problem is galling of the threads of the stem caused by the threaded engagement and forces with the threaded inner surface of the nut. These strains can result in increased wear of the unit.
The present invention provides an improvement over the implant disclosed in the Moore et al. patent by providing means for reducing and minimizing the relative friction between the nut member and the sleeve as well as increasing fatigue strength of threaded areas of the device thereby decreasing wear of the parts.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a adjustable length prosthetic implant including a stem having a threaded portion and an end portion adapted for mounting with a bone. A barrel includes an end portion adapted for mounting with a bone and a sleeve portion extending therefrom. The barrel includes an elongated chamber defining an axial dimension and overlying at least a portion of the threaded portion of the stem. Connecting means mounted on the barrel interconnects the barrel and stem and controls the axial extension and retraction of the stem from the barrel. Bearing means connects the connecting means to the barrel to prevent relative axial movement therebetween while allowing relative rotation therebetween about the axis and spacing the connecting means from the barrel to minimize relative friction therebetween the relative rotation.
An enhanced bearing surface, such as ball bearings, ceramic disk, other low friction material, or surface treated to enhance anti-galling properties is positioned between the connecting means and end of the barrel.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. 1 is an exploded view of a preferred embodiment of the invention;
FIG. 2 is a side view in elevation, partially broken away of the invention; and
FIG. 3 is a cross sectional view of the stem member disposed within and locked from rotation within the barrel of the invention.
DESCRIPTION OF THE PREFERRED
An adjustable length prosthetic implant constructed in accordance with the present invention is generally indicated at 10 in the Figures. More specifically, the prosthesis includes a stem generally shown at 12 including a threaded portion 14 and an end portion 16. The end portion is adapted for mounting with a bone. For example, the stem may be in the form of an elongated