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DEFORMITIES OF THUMB JOINTS


DEFORMITIES OF THUMB JOINTS
The thumb is the most important digit of the hand. All three joints of the thumb are important in functional adaptations, and each may be affected primarily or secondarily by imbalances of the other joints (e.g., boutonnière and swan-neck deformities). Thus, reconstructive surgery of the thumb must consider the entire thumb (radial) ray; the balance of its musculotendinous system; and the position, mobility, and stability of all its joints. The joints of the thumb may be impaired as a result of osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis. Thumb deformities can be classified as (1) postural, including longitudinal collapse (boutonnière, swan-neck) and fixed positional (adducted retroposed thumb) deformities; (2) unstable, stiff, or painful inter-phalangeal, metacarpophalangeal, or carpometacarpal joints; and (3) tendon deformities, including contracture, displacement, or rupture of the flexor pollicis longus, extensor pollicis longus or brevis, abductor pollicis longus, or intrinsic tendons.


DEFORMITIES OF THUMB JOINTS

POSTURAL DEFORMITIES
The boutonnière deformity is caused primarily by arthritic involvement of the metacarpophalangeal joint. Although it is found in 57% of patients with hands affected by rheumatoid arthritis, boutonnière deformity does not usually occur in osteoarthritis. Initially, the capsule and extensor apparatus around the metacarpophalangeal joint are stretched by synovitis. The extensor pollicis longus tendon and adductor expansions are displaced ulnarly, and the lateral thenar expansions are displaced radially. The extensor pollicis brevis tendon attachment to the base of the proximal phalanx is lengthened, and the ability to extend the metacarpophalangeal joint is decreased, causing a flexion deformity of the proximal phalanx. The extensor pollicis longus tendon and extensor insertions of the intrinsic muscles apply all their power to the distal phalanx and produce secondary hyperextension of the interphalangeal joint. Pinch movements further aggravate the deformity. As contractures develop, the deformity becomes fixed. Destructive articular changes compound the deformity, and disorganization and subluxation of the joint may occur.
Swan-neck deformity, in contrast, is far more common in osteoarthritis than in rheumatoid arthritis. It is usually initiated by destructive changes at the carpometacarpal joint, followed by stretching of the joint capsule and radial subluxation of the base of the metacarpal. As motion at the trapeziometacarpal joint during abduction becomes painful, the patient avoids abduction, using the distal joints to compensate for lack of motion at the base of the thumb. An increasing adduction deformity with contracture of the adductor pollicis muscle develops. Effusion in the joint further loosens the capsule, permitting a proximal radial subluxation of the metacarpal. Subluxation may result in hyperextension of the interphalangeal joint, but more frequently, it causes hyperextension of the metacarpophalangeal joint and adduction of the first metacarpal. Further adduction contracture of the metacarpal aggravates the hyperextension of the metacarpophalangeal joint and permits collapse of the thumb ray. The interphalangeal joint becomes flexed, as in a swan-neck deformity of the finger.
In the adducted retroposed thumb, the first metacarpal is retropositioned, adducted, and externally rotated. The deformity is probably initiated by synovitis of the carpometacarpal joint and aggravated by awkward positioning of the thumb, as on a flat surface during acute illness. There seems to be a contracture of the extensor pollicis longus muscle, with adduction and external rotation of the metacarpal and with palmar and radial subluxation of the metacarpal base off the trapezium.

TENDON DEFORMITIES
In rheumatoid arthritis, tendon deformities are related to muscle contracture, tendon displacement, adhesions, or tendon rupture. Rupture of the extensor pollicis longus tendon is most common, usually occurring within the third extensor compartment in the area of the distal tubercle of the radius. Sudden rupture of the tendon results in a sudden drop of the metacarpophalangeal joint of the thumb and, in some cases, loss of extensor power at the distal phalanx.
Rupture of the flexor pollicis longus tendon usually occurs in the carpal area and must be considered in the diagnosis of hyperextension deformity of the interphalangeal joint of the thumb. Rupture of the abductor pollicis longus and extensor pollicis brevis tendons is rare.
Synovial invasion and stretching of the dorsal hood of the metacarpophalangeal joint may result in displacement and secondary contractures of the tendons of the intrinsic muscles.


SURGERY FOR INTERPHALANGEAL JOINT
Arthrodesis is usually the preferred treatment for instability of the interphalangeal joint of the thumb; bone grafting is necessary if bone resorption is severe.

SURGERY FOR METACARPOPHALANGEAL JOINT
Arthrodesis is indicated in joint destruction and collapse deformities to simplify the articular system of the thumb ray, providing the distal and basal joints have adequate mobility. This can be achieved by a traditional tension band wire technique or more modern intra- medullary locked-screw technology that provides a reproducible 25 degrees of flexion and more rapid return to function.
Capsulodesis is the treatment of choice in hyperextension deformities of more than 20 degrees with good flexion, lateral stability, and intact articular surfaces. The palmar aspect of the joint is exposed through a straight volar incision, and the central third of the proximal membranous insertion of the palmar plate is incised (alternatively all is incised if using a bone anchor). The sesamoids and their tendon attachments are left intact. The periosteum is stripped from the palmar aspect of the metacarpal neck and the joint is pinned at 30 degrees of flexion with a Kirschner wire, which is removed 6 weeks after surgery. The central third of the plate is sutured to the radial and ulnar thirds (or the whole plate is sewn to a bone anchor placed in the metacarpal neck).


SURGERY FOR BASAL JOINTS
The problems presented at the basal joints of the thumb differ in osteoarthritis and rheumatoid arthritis. Accurate diagnosis and evaluation of the location of the arthritic involvement and alignment of adjacent bones are essential in selecting the appropriate treatment. The pathologic changes may involve the trapeziometacarpal joint alone or also affect the peritrapezial or other carpal bone articulations, with or without resorption or displacement of adjacent carpal bones. Treatment must be selected from several options, including resection arthroplasty of the trapezium, with or without tendon interposition and with or without ligament reconstruction (the most typical procedure is ligament reconstruction and tendon interposition [LRTI]), arthrodesis of the carpometacarpal joint, or, less commonly, prosthetic arthroplasty. In some patients, the distal articulations of the thumb must be stabilized or fused.
Resection arthroplasty for the basal joints of the thumb helps maintain a smooth articulating joint space with improved joint mobility, pain relief, and strength. Meticulous reconstruction of the capsuloligamentous structures and correction of associated deformities of the thumb ray are essential for a good result.
In osteoarthritis, the destructive changes are usually present in all articulations around the trapezium and, in most patients, total trapeziectomy is necessary to relieve all arthritic pain. In rheumatoid arthritis, frequently the trapezium is fused to the scaphoid or the scaphoid is resorbed or shifted ulnarly. Therefore, a simple resection, with or without soft tissue interposition, can be used. In certain patients, severe resorptive changes of the metacarpal base and the trapezium produce a result not unlike a resection arthroplasty. If the joint is reasonably stable, mobile, and pain free, surgery is not indicated.
Resection arthroplasty for the trapezium is indicated for surgery when there is (1) localized pain and crepitation during passive circumduction, with axial compression of the thumb (grind test); (2) loss of motion, with decreased pinch and grip strength; (3) radiographic evidence of arthritic changes of the trapeziometacarpal, trapeziotrapezoid, trapezioscaphoid, and trapeziumsecond metacarpal joints; and (4) unstable, stiff, or painful distal joints of the thumb or a swan-neck deformity.
The trapezium is sectioned with an osteotome and removed piecemeal, with care not to injure the underlying flexor carpi radialis tendon. The radial artery must be carefully protected throughout the procedure. Then a tendon (typically the flexor carpi radialis longus either whole or half thickness) is passed through the base of the metacarpal and then sewn back onto itself snugly to re-create the volar beak ligament. The remaining tendon is sewn into a bundle and anchored to the floor trapezial space, thus creating an interposition arthroplasty. Thumb abduction is now restored and, if necessary, a volar capsulodesis of a hyperextended nonarthritic metacarpophalangeal joint is performed or arthrodesis in 25 degrees of flexion is done if painful arthritis is present.
After suture of the dorsal capsular flaps, the first dorsal compartment is loosely closed over the abductor pollicis longus and extensor pollicis brevis tendons. The extensor pollicis longus tendon is left subcutaneous. The incision is closed, with care to avoid the branches of the superficial radial nerve. A conforming hand dressing, including a thumb spica plaster splint, is applied. The limb is kept elevated, and a thumb spica short-arm cast or thermoplastic splint is applied after 4 to 6 days and worn for 4 to 6 weeks. Guarded motion and pinch and grasp activities using various exercise devices are then started.
Special considerations in reconstruction of the basal joints of the thumb include the following.
Hyperextension of the metacarpophalangeal joint of the thumb contributes to the adduction tendency of the metacarpal and prevents proper abduction of the meta- carpal and seating of the implant. If hyperextension is less than 10 degrees, a cast is applied postoperatively so that the metacarpal, but not the proximal phalanx, is abducted. If the hyperextension ranges from 10 to 20 degrees, temporary fixation with a Kirschner wire is indicated; if it is greater than 20 degrees, stabilization with either palmar capsulodesis or arthrodesis is essential.
Adduction of the first metacarpal, if severe and untreated, unbalances the thumb and seriously affects the result of resection arthroplasty. If the angle of abduction between the first and second metacarpals is not at least 45 degrees, the origin of the adductor pollicis muscle must be released and likely the metacarpophalangeal joint arthrodesed.