Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-10-17
2004-02-17
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S062000
Reexamination Certificate
active
06692530
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the medical field of orthopaedics and joint replacement, in particular. Modular artificial joints have several components that must be assembled and placed in the patient to reconstruct a joint. While modular joints provide the ability to custom fit an artificial joint to a patient's anatomy, the connection between the components must be without relative movement after implantation. This invention is directed to a modular artificial joint construction which provides a locking mechanism to secure the components immovably together.
BACKGROUND OF THE INVENTION
Artificial joints or prosthesis have now been constructed for almost every natural joint in the living body. As the medical field gains more understanding of the problems involved in mating inanimate constructions with animate tissue and designing mechanical devices that can duplicate natural movement, the number of implantations will continue to increase. In addition to the major joints, such as the hip, knee, shoulder, elbow, wrist and ankle, better engineering of the prosthesis, accompanied with miniaturization, will permit smaller and smaller natural joints, e.g. vertebrae, phalanges and tarsals, to be reconstructed. Until now, the larger joints have received the most attention mainly because of the larger size of the bones. The prosthesis of this invention may be utilized in all joints.
In replacing a hip joint, the head of the femur is removed along with the ball. The trochanter portion of the femur is shaped and prepared for receiving the prosthesis so that the artificial joint will closely approximate the natural hip.
Earlier artificial hip joints were made of one-piece construction requiring a large inventory of prosthesis to accommodate the various sized patients. The modular artificial joint has two or three or more elements which replace the natural hip. By manufacturing these components with interchangeable connections but different external sizes, inventories may be smaller because of the ability to mix and match components. Also, the modular prosthesis provides more flexibility in customizing the various components of a joint to the various parts of a patient's natural joint.
In a three piece artificial hip joint, the various sized components of the joint that may be selected are the intramedullary rod, the trochanter and the neck. The intramedullary rod is inserted into the end of the femur. The rod acts as a stabilizer in maintaining the artificial joint in the axis of 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.
The natural trochanter is the broadened area offset from the end of the femur. The natural trochanter may be at any radial angle about the axis of the femur. This natural angular relationship must be reproduced by the intramedullary rod and the artificial trochanter. The artificial trochanter is seated on the end of the patient's femur and is the main load bearing element of the prosthesis. It is important that this load, which is mostly compression, is transmitted along the axis of the femur.
A neck element is inserted into the trochanter element and carries an extension onto which the ball joint will be fixed. The horizontal angle between the trochanter and the neck extension is variable to reproduce the anteversion angle of the patient's natural joint. The neck carries cantilevered forces in torque and compression between the acetabulum and the trochanter. It is also important that these forces do not result in relative movement between the trochanter and the neck.
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 emplaced rod during the placement of the prosthesis to more closely reproduce the natural structure of the hip. It has been found that, in some cases, as the intramedullary rod has been inserted into the bone canal, there is rotational movement of the rod. In order to preserve the union between the rod and the bone, there must be a mechanism to accommodate the changed angular orientation of the proximal end of the intramedullary rod so that the prosthesis closely approximates the natural trochanter and ball.
While the above description refers to a modular hip prosthesis, substantially the same considerations must be given to other modular prosthesis, such as a knee prosthesis in which an intramedullary rod is placed in the lower end of the femur and in the upper end of the tibia or the elbow in which an intramedullary rod is placed in the lower end of the humerus and the upper end of the radius or ulna. Because of individual physical anomalies, the functional prosthesis must be capable of angular adjustment to conform to the natural physique.
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 is U.S. Pat. No. 5,876,459 to Powell which discloses a modular hip joint 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.
The Leto patent, U.S. Pat. No. 4,419,026 issued Dec. 6, 1983, discloses a resilient split sleeve camming lock for use with telescoping tubula
Doubler Robert L.
Hammill, Sr. John E.
Blanco Javier G.
Hammill Manufacturing Co.
Willse David H.
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