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.
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.
