Locking hip prosthesis

Details Locking hip prosthesis Locking hip prosthesis

2000-03-17

2001-10-09

Isabella, David J (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S022420

Reexamination Certificate

active

06299648

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the surgical field of joint replacement, particularly to a modular artificial joint having three elements which replace the natural hip, and most particularly to the connection between the intramedullary rod and the other parts of the prosthesis.
BACKGROUND OF THE INVENTION
In replacing a hip joint, the head of the femur is removed along with the ball. The femur is shaped and prepared for receiving the prosthesis so that the artificial joint will closely approximate the natural hip.
The modular artificial joint has three elements which replace the natural hip. The intramedullary rod is inserted into the end of the femur. The entire prosthesis is supported by this connection between the rod and the femur. The upper portion of the rod which extends out of the femur is fitted into a trochanter element which is shaped like the removed broad head of the femur which it replaces. This element, along with the rod, is used to adjust the length of the prosthesis to approximate the natural length of the femur. A neck element is inserted into the trochanter element and carries an angular extension onto which the ball joint will be fixed. All these elements have a central bore and are permanently secured together by a bolt which is inserted into the neck element, extends through the trochanter element, and is threaded into the upper end of the rod. In some cases, the intramedullary rod may be attached to the bone with bone cement while, in other cases the cement is omitted.
When the cement is omitted, the placement and fixation of the intramedullary rod becomes more critical to pain free usage of the prosthesis. Further, it is most important that the intramedullary rod not be disturbed after insertion since this would corrupt the union between the rod and the interior of the femur.
In order to maintain the original union between the femur and the intramedullary rod, modular prosthesis have been developed to allow rotational adjustment of the several parts or elements about the rod during the placement of the prosthesis to more closely reproduce the natural structure of the hip. The modular concept also allows the selection of different sized elements, before or during surgery, to more closely approximate the natural joint.
With the advantage of flexibility gained by modular prosthesis, there comes the requirement that there be no movement between the several parts or elements after implantation. These movements may cause misalignment of the joint resulting in increased pain, trauma to the joint and, even, dislocation of the joint.
DESCRIPTION OF THE PRIOR ART
The prior art is replete with artificial prosthesis and hip joints, in particular.
Illustrative of the state of the art are U.S. Pat. No. 5,876,459 and U.S. Pat. No. 5,506,644 to Powell which disclose modular hip joints having a stem, one end of which is inserted in the intramedullary canal. The other end of the stem is tapered to fit within a second, neck, element. The neck ultimately supports the ball joint. A sleeve element is placed over the junction of the first two elements. All three elements are rotationally movable relative to each other. A bolt is driven through the bore of the neck and stem deforming a portion of the interconnected elements for a friction fit between the neck and the stem. These prior art patents disclose that the sleeve may have a polygonal shaped bore with the articulating elements having corresponding shaped portions. The interconnected elements of these hip joints do not form a static lock between each other but require a deformation of one or more elements before a friction fit is established. The deformation and friction fit is between the stem and the neck rather than the sleeve and the stem.
U.S. Pat. No. 5,653,765, to McTighe et al discloses a modular hip joint with a stem, an intermediate shoulder portion, and a proximal shoulder piece which attaches to the ball. The stem and the intermediate shoulder portion have interengaging teeth on the corresponding ends of each by which they are connected. This end-to-end connection allows for rotational movement of the elements relative to each other. The proximal shoulder piece and the intermediate shoulder piece also have an end-to-end toothed connection for rotational adjustment. This construction has two movable end-to-end connections which provide good flexibility for rotation of the elements but have small surface areas of fixation to each other limited to the surfaces of the interengaged teeth.
SUMMARY OF THE INVENTION
In the instant invention a modular prosthesis is taught which has an intramedullary rod element which is to be inserted in a bone. The rod has a shaped proximal portion which is telescoped into one end of a bore in the trochanter element. The mating surfaces of the shaped rod and the trochanter bore form a rotationally immovable connection. A neck element is telescoped into the other end of the trochanter bore permitting rotational adjustment. All the elements are locked together by a bolt through the neck and rod.
In a particularly preferred embodiment of the instant invention a modular prosthesis is taught for use as a hip replacement which comprises an intramedullary rod, a trochanter and a neck, said intramedullary rod having a distal end adapted for insertion into the intramedullary canal of the femur and a proximal end, said proximal end having a circumference with opposite planar surfaces joined by curved surfaces, said proximal end having a screw threaded blind bore along the longitudinal axis of said intramedullary rod, said trochanter having a narrow distal end and a larger proximal end with a through bore from said distal end to said proximal end, said proximal end of said through bore having a smooth circumference, said distal end of said through bore having a circumference with opposite planar sides joined by curved surfaces, said circumference of said trochanter bore and said circumference of said proximal end of said intramedullary rod adapted to telescope together forming a rotationally secure connection, said neck having a distal end adapted to be inserted into the proximal end of said through bore of said trochanter, said distal end of said neck having a smooth circumference, said distal end of said neck and said proximal end of said through bore in said trochanter adapted to telescope together forming a rotationally adjustable connection, said neck having a through bore, said proximal end of said through bore having a countersunk bore, said distal end of said through bore adapted to telescope over the proximal end of said intramedullary rod, and a screw threaded bolt adapted to be disposed in said countersunk bore and threadably engaged with said screw threads in said proximal end of said intramedullary rod forming a locked integral prosthesis.
Accordingly, it is an objective of the instant invention to provide a hip joint with an intramedullary rod element which is connected with the trochanter element in such a manner as to prevent any rotational movement between the elements. Rotational movement, in this context, refers to the turning of either element in a plane normal to the common longitudinal axis of the elements.
It is a further objective of the instant invention to provide a connection between the trochanter element and the intramedullary rod in such a manner as to limit the combined length of the elements.
It is a further objective of the instant invention to provide the intramedullary rod with a fluted exterior surface for increasing the surface area of the junction between the rod and the intramedullary canal of the femur.
It is yet another objective of the instant invention to provide a slot through the end of the intramedullary rod to increase the accommodation of the rod with the interior of the intramedullary canal of the femur.
It is a still further objective of the invention provide a connection between the neck element and the trochanter element that permits rotational adjustment and limits the length of the combined elements.


REFERENCES:
patent:

Affiliated with

Also associated with

Rating

Locking hip prosthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Locking hip prosthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Locking hip prosthesis will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2611074