Surgically implantable trapezium prosthesis and method of reconstructing the thumb carpometacarpal joint

Abstract

A prosthesis for the trapezium of the thumb carpometacarpal joint comprising an integral elastomeric member configured to include a generally cylindrical portion, having extending from one end thereof an elongated, longitudinally extending tapered portion adapted to be embedded into a reamed out-channel in the thumb metacarpal bone, while the opposite end of said cylindrical portion is slightly concave to conform to the navicular bone, and wherein said cylindrical portion includes a transverse aperture. In the subject method following the step of implanting the tapered projection of the subject prosthesis in the thumb metacarpal bone, the axis of the aperture is aligned perpendicular to the plane of the thumb, and a segment of the flexor carpi radialis tendon is then passed over the cylindrical portion of said prosthesis and down through the aperture, and then fixed to the main portion of said tendon, thereby forming a reinforced structure to inhibit dislocation of the prosthesis.

Description

Freedom from pain is essential for normal thumb function. Although the carpometacarpal joint of the thumb is described as a saddle joint, it is actually formed by apposed saddles, one astride the other, each one's longitudinal axis perpendicular to the other. Such a relationship creates a joint where two primary planes of motion, flexion-extension and adduction-abduction, are perpendicular to one another. With rotatory movement such as opposition and circumduction, the surfaces are twisted into a less congruous relationship, causing tightening of the joint capsule and thereby increasing joint stability, provided all ligaments are competent.

Idiopathic hypermobility of the thumb basal joint is not uncommon, particularly in women, and would seem to be a major factor in producing the arthrosis which so frequently afflicts this joint. Trauma, acute or recurrent, causing partial tears or stretching of the ligaments, likewise will produce varying degrees of hypermobility. Undetected articular damage may also accompany such trauma, thereby compounding the pathological process. When painful hypermobility is present, restoration of ligament stability will not only relieve the pain and stabilize the joint, but, when done prior to the onset of articular damage, may prevent or at least retard subsequent joint degeneration. A new ligament reconstruction procedure for painful, unstable thumb carpometacarpal joint is presented in an article entitled "Ligament Reconstruction for the Painful Carpometacarpal Joint," by applicant, Dr. Richard Eaton, and Dr. J. William Littler, which appears in the Journal of Bone and Joint Surgery, Vol. 55-A, No. 8, pp. 1655-1666, December, 1973.

For more advanced arthrosis, ligament reconstruction is not sufficient. Advanced arthrosis is generally recognized by the obvious dorsal subluxation of the metacarpal base. As the base of the thumb metacarpal subluxates dorsally, there is a reciprocal flexion-abduction of the metacarpal shaft, and frequently flexion-adduction contracture of the entire thumb ray. Carried to the extreme deformity, the metacarpophalangeal joint compensates for the metacarpal flexion-adduction position by hyperextending and the joint may become fixed in this hyperextended position. These sequential compensation deformities must be recognized and corrected at the same time as reconstruction of the basal joint is carried out.

Heretofore, deformities of the carpometacarpal joint have been undertaken utilizing a trapezium prosthesis, and implanting the prosthesis following removal of the diseased trapezium bone. One known prosthesis comprises an integral elastomeric member, preferably of a flexible silicone material, having a cylindrical base portion from one end of which extends a triangular shaped projection adapted to be imbedded into the reamed-out channel in the thumb metacarpal bone. In view of the very slippery, low coefficient surface of the material of the prosthesis, and the fact that the elastomeric material of the prosthesis is difficult to handle and will not hold a stitch, when implanted, the prior art prosthesis has a tendency to slip out of place in that the opposite end of the cylindrical portion of the prosthesis merely rests against the adjacent navicular. Furthermore, when implanted, the amount of force applied by the patient, in a pinching direction of the hand, must be limited in order to prevent inadvertent popping out of the prior art prosthesis. Still further, in order to insure as close a fit as possible, in order to minimize slipping out of position of the prosthesis, several different sizes of prosthesis must be manufactured, and by trial and error implanted into the patient's hand.

Another form of known prosthesis or trapezium prosthesis is of the general shape of the prior art device described above with the addition of several elastomeric tails or extending elements which are looped around a structure of the palmer aspect of the hand in an attempt to keep the prosthesis from dislocating dorsally. As is readily apparent, considering the type of material which must be employed for an implantable prosthesis, the tails or extending elements are extremely fragile, and tend to wear and break thereby losing the fixation sought to be obtained. In addition, it is difficult to firmly secure the elastomeric tails to the hand structure, thereby resulting in the patient having to limit the use of his hand with reference to the application of hand grip forces.

Accordingly, it is the object of the subject invention to provide a new and improved surgically implantable trapezium prosthesis, as well as a new and improved method of reconstructing the thumb metacarpal joint. More particularly, it is an object to provide a new and improved prosthesis and method which will provide the patient with, as close as possible, his original strength and flexibility of the carpometacarpal joint.

Specific details relative to the subject invention will be fully described below with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of the new and improved surgically implantable trapezium prosthesis according to the subject invention;

FIG. 2 is a side view of said prosthesis;

FIG. 3 is a top view of a thumb and the surgically implanted trapezium prosthesis according to the subject invention; and

FIG. 4 schematically illustrates the completed surgically implanted trapezium prosthesis as firmly fixed in place by the use of a portion of the patient's tendon.

Referring to FIGS. 1 and 2, the trapezium prosthesis of the subject invention is generally designated by the numeral 10 and comprises an integral elastomeric member, preferably a silastic material such as silicone rubber, and which is inherently flexible and physiologically inert. The prosthesis 10 includes a generally cylindrical portion 12 having end faces 14 and 16, and integrally formed and projecting from the end face 14 is an elongated, longitudinally extended tapered portion 18. The end 19 of the tapered portion 18 is blunted, and the tapered portion has a generally annular cross-section. The opposite end face 16 of cylindrical portion 12 is slightly concave in order to more effectively cooperate with the navicular or scaphoid bone 40 (see FIGS. 3 and 4), as will be more particularly described hereinafter.

Extending transverse to the longitudinal axis of the prosthesis 10, and more particularly radially through the cylindrical portion 12 is an aperture 20. The diameter of the aperture 20 is suitably dimensioned relative to the size of the cylindrical portion 12 to prevent tearing of the prosthesis 10, and furthermore is large enough to fully accommodate the portion of the tendon which is to be inserted therethrough, as described below.

FIGS. 3 and 4 illustrate steps in the process of applicant's invention. As shown in FIG. 3, in the subject process of reconstructing the thumb carpometacarpal joint 34 following the surgical removal of the diseased trapezium, the surgeon then performs the step of hollowing out the lining of the marrow cavity of the metacarpal bone 36 utilizing conventional techniques and conventional apparatus such as an electric reaming device in order to define any elongated cavity 38 in the metacarpal bone 36. The prosthesis 10, and more particularly the elongated extended portion 18 is inserted into the cavity 38, and the prosthesis is rotated so that the longitudinal axis of the aperture 20 extends orthogonal to the plane of the patient's thumb nail 32 of the thumb 30. The alignment of the aperture is important in reconstructing the metacarpal joint 34, as will be more fully described hereinafter. The base or end face 16 of the prosthesis 10 should fit in good contact circumferentially with the cortex or outer portion of the thumb metacarpal 36 so that it has even pressure around the entire contact surface. Likewise the opposite end face 16, which is slightly concave, should fit in good firm contact with the navicular or scaphoid 40. The next step in the subject process is to obtain a strip of adjacent tendon for which is suggested the use of the flexor carpi radialis tendon. Through conventional technique, two incisions are made above the wrist, and the flexor carpi radialis tendon 50 is partially cut across its width as at 52, and stripped along the longitudinal line 54 to obtain a strip 56 of about 6 centimeters in length. This segment 56 is tunneled under the skin to emerge at the wrist in the vicinity of the metacarpal joint, after which the free end of the tendon strip 56 is directed around the surface of the prosthesis 10 (see FIG. 4) and then penetrated through the residual capsule attached to the metacarpal 36 at a point which again is perpendicular to the plane of the thumb nail 32, and then the tendon strip 56 is passed through the aperture or channel 20 in the prosthesis 10, and then to the remaining flexor radialis, as at point 58, at the palm side of the new reconstructed joint. The strip 56 is fixed, such as by means of two switches, to the flexor radialis tendon 50 on the dorsal side of the hand, at the point where it enters the prosthesis on the dorsal of the wrist, and then likewise the prosthesis is pulled into place by pulling on the ligament, thereby seating it into its socket, and then a second suture is placed between this new ligament and the flexor radialis 50. The free tail 60 usually represents about 4 centimeters, and this free tail is then interwoven across and around the prosthesis to form a new capsule for the metacarpal joint. The use of a tendon as a building material to weave a new capsule provides an extremely strong and durable construction, since it is thicker than the natural capsule, and of course, since it is the patient's own tissue it cannot and won't be rejected. It will adhere to any normal tissue, and it will not adhere to the elastomeric material of the prosthesis 10. Of course, the tendon does not have to adhere to the prosthesis since it passes directly through the prosthesis and therefore becomes incorporated in the prosthesis. As indicated before, suturing of a prosthesis is not possible because of the nature of the substance, and secondly because the prosthesis would be much weaker than using the thick 3 or 4 millimeter tendon which is passed through the center of the prosthesis, as in applicant's process. Furthermore, the tendon cannot tear the prosthesis.

The resulting reconstructed metacarpal joint is significantly stronger and more durable than prior art reconstructed joints using conventional prosthesis. The alignment of the aperture 20 of the prosthesis assures that the passing of the tendon therethrough will hold the prosthesis in the socket that was created by the removal of the diseased trapezium, and provide the necessary reconstructed metacarpal joint to enable the patient to resume his normal activities without fear of slipping of the prosthesis or movement thereof. According to the inventor's experimentation, it has been found that with prior art prosthesis, the patient's grip strength is only restored to the extent of 8 to 10 pounds, and certainly not in excess of 15 pounds, whereas the normal joint strength of a patient is in the area of 40 to 80 pounds grip strength. Utilizing applicant's prosthesis and applicant's process, such grip strengths on the order of 40 to 80 pounds may be restored in the event of a diseased trapezium, when using applicant's device and process.

While the prosthetic device was described with reference to the drawings as being made of silicone rubber it will be realized that other inherently flexible, clinically inert materials having sufficient strength may also be used.

To those skilled in the art to which this invention relates, many changes in construction and widely different embodiments and applications of the subject process and device will suggest themselves without departing from the spirit and scope of the invention. The disclosures and descriptions herein are purely illustrative and are not intended to be in any sense limiting.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A prosthesis for the trapezium of the thumb metacarpal joint comprising an integral, elastomeric member configured to include a generally cylindrical portion, having extending from one end thereof an elongated, longitudinally extending tapered portion, and wherein said cylindrical portion includes a transverse aperture extending through the longitudinal axis of said prosthesis.

2. A prosthesis for the trapezium of the thumb metacarpal joint as in claim 1 wherein said elongated, longitudinally extending tapered portion is annular in cross section and includes a blunt end.

3. A prosthesis for the trapezium of the thumb metacarpal joint as in claim 1 wherein the opposite end of said cylindrical portion is slightly concave to conform to the end of the navicular bone.

4. A prosthesis for the trapezium of the thumb metacarpal joint as in claim 1 wherein said elastomeric is silicone rubber.

5. A method of reconstructing the metacarpal joint of a thumb by surgically implanting an improved trapezium prosthesis having a cylindrical portion to which is integrally connected an elongated tapered portion, and with an aperture extending transversely through said cylindrical portion, comprising the steps of:

a. removing the diseased trapezium;

b. reaming the medullary canal of the thumb metacarpal bone to fit the elongated tapered portion of said prosthesis;

c. inserting the prosthesis elongated tapered portion into said medullary canal, and aligning the aperture in the cylindrical portion of the prosthesis to extend perpendicular to the plane of the thumb nail;

d. stripping away approximately a 6 centimeter portion of the flexor carpi radialis tendon, leaving the distal attachment intact adjacent the prosthesis;

e. extending the split tendon around the surface of the prosthesis then passing the same through the aperture in the prosthesis to a point intersecting the remaining flexor radialis at the palm side of the hand, and suturing said split tendon to the flexor radialis tendon;

f. weaving the remaining free end of the tendon in the vicinity of the prosthesis to form a new capsule securing the prosthesis in place.