Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-11-27
2004-03-02
Philogene, Pedro (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06699292
ABSTRACT:
This invention relates to a prosthetic joint adapted to replace a human joint and, more specifically, to an improved prosthetic joint adapted to replace an interphalangeal joint of the human finger.
BACKGROUND OF THE INVENTION
The first elongated bone (metacarpal) at the base of each finger is connected to a proximal phalangeal bone through the metacarpal-phalangeal (MCP) joint. The proximal phalangeal bone is connected to the middle phalangeal bone through the proximal interphalangeal (PIP) joint. The PIP joint can be flexed independently of the MCP or the distal interphalangeal (DIP) joint. This variable reciprocal motion, along with the opposability of the thumb, allows for grasping of objects and the performance of daily functions which are of critical importance to humans. Damage to the PIP joint through physical injury or disease can therefore be a severe physiological burden to inflicted humans.
Degenerative joint diseases: osteoarthritis (OA), post-traumatic arthritis, and rheumatoid arthritis (RA) of the PIP joint cause interminable pain and poor function of the finger. Patients who have mild symptoms often respond to rest, immobilization, nonsteroidal anti-inflammatory drugs or intra-articular injections of steroids. However, patients who have more severe forms of arthritis may require total joint replacement of the PIP joint.
The most common deformity in patients suffering from OA is narrowing of the articular cartilage of the PIP joint. OA is a hypertropic arthritis that results in degeneration of the articular cartilage which is often either primary or secondary to trauma or other conditions, and such degeneration of the cartilage causes movement of the joint to be painful. The usual solution is fusion of the joint which eliminates pain but renders the joint nonfunctional. This is particularly true in young patients with normal grip strength. The preferred solution is the installation of a prosthetic PIP joint, however, there has long been a need for a replacement joint which resurfaces the native joint, allows for normal joint motion, and withstands the joint reaction forces produced in patients with normal grip strength.
Various prosthetic joints have been developed to replace finger joints; however, most of these have involved the replacement of the MCP joint where the finger joins the hand. These prosthetic joints have typically involved some type of captive ball-and-socket arrangement for permitting a substantial range of pivoting movement in a vertical plane, while sometimes also permitting limited sideward displacement in an attempt to provide for motion which more closely correlates with the natural joint. Joints of this type are normally not suitable for replacing the proximal or distal interphalangeal joints of the finger because they typically possess a structure which is undesirably large and complex, i.e. interphalangeal joints desirably do not incorporate a capability for sideward or lateral pivoting.
Examples of finger joints which are designed specifically for replacing the human MCP joint are disclosed in U.S. Pat. Nos. 5,782,927, 4,731,087 and 4,231,121, with this latter patented joint being represented as also being suitable for use as a PIP or DIP joint. U.S. Pat. No. 4,725,280 discloses a joint which is designed specifically for use in replacing the human PIP joint or the DIP joint. More recent U.S. Pat. No. 5,728,163 (Mar. 17, 1998) discloses a MCP joint prosthesis which is alleged to also be useful as an interphalangeal joint prosthesis. Work was also done at The Mayo Clinic in the 1970's directed to the PIP joint, and this work is reported in an article by Linscheid, R. L. et al, entitled “Proximal Interphalangeal Joints Arthroplasty with a Total Joint Design”,
Mayo Clin. Proc.,
54, 227-240 (1979). Continuing work on this project was more recently reported in a further article by Linscheid et al. entitled “Development of a Surface Replacement Arthroplasty for Proximal Interphalangeal Joints”,
The Journal of Hand Surgery,
22a, 286-298 (1997).
Although various of these PIP joints have had limited success, they have not gained wide acceptance throughout the medical profession. Accordingly, the search has continued for improved joints particularly suited for the replacement of the PIP joint that are implantable in such a manner as to facilitate its attachment to the phalanges while at the same time providing a vertical range of pivoting movement which closely approximates natural joint movement.
One important design consideration for PIP prosthetic joints is minimizing the wear between the mating articular surfaces. Mating surfaces may conform to such an extent that biological fluids, which would normally provide joint lubrication, are expressed from the PIP prosthetic joint, and the resulting “dry joint” may experience increased friction between the congruent articulating surfaces. Thus, it is now felt that a prosthetic PIP joint should preferably avoid the use of substantially congruent articular surfaces.
Still another important design consideration for prosthetic PIP joints is preserving the structure and function of the ligamentous tissues which surround the joint. The collateral ligaments which run along each lateral side of the PIP joint comprise both fan-like collateral ligaments and cord-like collateral ligaments (see
FIGS. 2
a
and
2
b
). The fan-like collateral ligaments insert at both sides of the distal portion of the proximal phalanx and serve to support the volar plate, thereby forming an important part of the overall PIP joint. The cord-like collateral ligaments, which also insert at both sides of the distal portion of the proximal phalanx, serve to resist subluxation-dislocation of the middle phalangeal bone; because they insert at about the center of rotation of the PIP joint, they do not undergo any dramatic change in tension during flexion/extension of the PIP joint. A prosthetic PIP joint should be designed so as to preferably not require the excision of the attachment sites or disruption of the collateral ligaments and/or the volar or palmar plate. Additionally, a prosthetic PIP joint should preferably not alter the manner in which the collateral ligaments and/or the volar plate wrap around the joint during PIP joint flexion and extension.
The retinacular ligaments cross each lateral side of the PIP joint as seen in
FIGS. 2
c
and
2
d.
On flexing the DIP joint, each retinacular ligament becomes taut and pulls the PIP joint into flexion. Similarly, on extending the proximal joint, the distal joint is pulled by the retinacular ligament into nearly complete extension. A prosthetic joint should preferably not interfere with the function of the retinacular ligaments.
Yet another important design consideration for a prosthetic PIP joint is the preservation of the structure and function of the tendinous tissues which surround and motivate the PIP joint. The PIP joint can only flex and extend for it has just one degree of freedom. The extensor expansion is the extensor mechanism of the finger. The tendons of extensor digitorum form the extensor expansions of all fingers, see
FIGS. 2
a
and
2
b.
The extensor digiti minimi tendon contributes to the extensor expansion of the little finger. The extensor indicis tendon contributes to the extensor expansion of the index finger. The lumbricals and interossei also contribute to the extensor expansions of the fingers. The tendons of flexor digitorum profundus (FDP) and flexsor digitorum superficialis (FDS) form the flexor mechanism of a finger. The FDS tendon crosses the bottom of the PIP joint and attaches to the proximal volar region of the middle phalanx. The FDP tendon crosses the bottoms of both the PIP and DIP joints to attach to proximal volar surface of the distal phalanx.
For any finger, the median band, also referred to as the “central slip”, of the extensor expansion crosses the top of the PIP joint and attaches to the proximal dorsal surface of the middle phalanx. The median band of the extensor expansion wraps around the distal head of the proximal phalanx as
Mumme Charles W.
Ogilvie William F.
Stanley John K.
Ascension Orthopedics, Inc.
Philogene Pedro
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