Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-08-31
2004-03-23
Prebllic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06709459
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to prostheses. More specifically, the present invention pertains to prostheses which act as part of an elbow joint in a patient for motions which mimic anatomical movements. The present invention is particularly, but not exclusively, useful as a prosthesis for the radial head in the elbow joint of a patient.
BACKGROUND OF THE INVENTION
Like other joints and anatomical features of the human body, the elbow joint is exceedingly complex in its make-up and function. Also like the other joints and anatomical features of the human body, the elbow joint is unique unto itself and requires specific consideration for its reconstruction or replacement. The complexity and uniqueness of this joint are quite interesting and are, perhaps, best appreciated by considering the skeletal motions which are involved in its movement.
In the transition of the hand and forearm from pronation to supination the radius and ulna of the forearm transition from a crossed relationship to a side-by-side relationship. Thus, in this movement there is a relative rotation of the radius bone about the ulna. Also, but more subtly, during the transition between pronation and supination there is also some relative translational movement between the radius bone and the ulna. The consequence of all this is that from a reference point on the ulna, the radius bone appears to move with a general motion that includes both translation and rotation. The head of the radius interacts with the capitellum and the radial notch of the ulna during pronation and supination, providing elbow and forearm stability during rotation and translation.
In addition to its importance as a component of forearm function, the radial head is an equally important component of normal elbow function. Indeed, elbow function involves bending, lifting and twisting movements, all of which require joint stability. Because motions in the human body require the interaction of various anatomical components, it is crucial that replacement of a component be precise in form, size, and orientation. While the head of the radius bone directly engages the capitellum of the humerus and the radial notch of the ulna, it also relates indirectly to other anatomical components of the arm. Specifically, ligaments surrounding the radial head are essential to elbow stability. Further, misalignment of the radius bone will cause poor radial-capitellar joint contact, leading to subluxation, or poor alignment of the elbow. It follows that the wrist and shoulder joints are also affected by the alignment of the radius bone.
The importance of having a workable prosthesis for the head of the radius bone is underscored by the debilitating effects which commonly result when a joint becomes damaged due to fracture, arthritis, or osteochondrosis. It is well known that radial head resection, as seen in elbow injuries, results in persistent elbow instability. Additionally, forearm axial instability can result from radial head excision if the remaining stabilizers, the supporting ligaments, are compromised. Because this loss of stability affects the interdependent functions of the elbow and forearm, when the radial head is damaged, it is common to see further damage to other components of the radial ulnar joint system, including, but not limited to, the complex system of supporting ligaments that encase the elbow joint. It has been well demonstrated that damage of any one of the components of the radial ulnar joint system leads to pain, weakness, and loss of motion. It is, therefore, of great importance to the patient that damage to the radial head be remedied.
In light of the above, it is an object of the present invention to provide a prosthesis for engaging a radius bone in the forearm of a patient with the capitellum of a humerus bone and the radial notch of the ulna at the elbow of a patient. It is a further object of the present invention to provide a prosthesis that is shaped to establish a secure engagement with the radius bone and is capable of cooperating with the anatomic structure and function of the portion of the radius being replaced. Yet another object of the present invention is to provide a system for implanting the prosthesis which places the forearm in the precise anatomical orientation necessary for implantation of the prosthesis. It is also an object of the present invention to precisely measure the length of the radial bone to be resected, and to precisely measure the size of the prosthesis to be implanted in place of the resected bone. Another object of the present invention to provide a prosthesis that is relatively easy to manufacture, is simple to implant, and is comparatively cost effective.
SUMMARY OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, a prosthesis for replacing the head of a radius bone in the elbow of a patient includes a head and a curved stem which extends therefrom. Specifically, the head is shaped for simultaneous articulation with both the capitellum of the humerus bone and with the radial notch of the ulna. Also, the stem is curved, or arcuate shaped, in order to accommodate the anatomy of the proximal radius after resection of the radial head, and to securely anchor the prosthesis when the stem is inserted into the medullary canal of the radius bone.
In detail, the head of the prosthesis of the present invention has a proximal surface that is formed as a substantially concave recess, and it has a distal surface that is formed with a hole. Preferably, the proximal surface of the head is made of highly polished cobalt chrome or a ceramic material to facilitate articulation of the head with the capitellum and with the radial notch of the ulna bone. More specifically, as envisioned for the present invention this articulation involves a relative sliding motion between the head of the prosthesis and both the capitellum and the radial notch of the ulna.
The stem of the prosthesis has a proximal end and a distal end. Also, the stem is preferably made of a material such as cobalt chrome or titanium. Further, it has an extension at its proximal end that is slightly tapered with a proximally decreasing cross section to facilitate insertion of the extension into the hole in the distal surface of the head. Preferably, the extension is configured as a morse taper. In any event, as intended for the present invention, the proximally decreasing cross section of the extension establishes an interference fit between the extension of the stem and the head that helps to hold the head on the stem.
As indicated above, the stem of the prosthesis is curved in shape and is generally arcuate. Importantly, the configuration of the stem is intended to structurally mimic the shape of the medullary canal of the radius bone. In general, to accomplish this the stem is formed with a first portion and a second portion. Specifically, the first portion is attached to the head and extends distally therefrom substantially along a first axis. The second portion then extends distally from the first portion substantially along a second axis. In their relation to each other, the first axis and the second axis define an angle &agr; therebetween. Preferably, the angle &agr; will be in a range of about 5 degrees to approximately 25 degrees. The curve of the stem that is established by the angle &agr; can be achieved using a radius of curvature that is in a range of about 0.5 inch to approximately 3 inches. Further, as it extends distally along the first and second axes, the stem is tapered with a distally decreasing cross section. This facilitates insertion of the stem into the medullary canal of the radius bone and helps to anchor the prosthesis on the radius bone. The stem also has a roughened or textured surface, which interacts with the medullary canal of the radius bone to help hold the stem on the radius. For purposes of the present invention, the surface of the stem can be coated with a material such as titanium, cobalt-chrome beads or hydroxyapatite. In addition to these structural features,
Cooney, III William P.
Leibel David A.
Linsheid Ronald L.
Morrey Bernard F.
O'Driscoll Shawn W.
Matthew William H.
Mayo Foundation for Medical Education and Research
Patterson Thuente Skaar & Christensen P.A.
Prebllic Paul B.
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