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The collateral ligament system and the flexor and extensor tendons play an important role in maintaining the normal configuration of the proximal interphalangeal joint. The distal interphalangeal joint acts as a simple hinge but is very important for balancing the proximal interphalangeal joint, and hyperextension or flexion (mallet) deformity can cause boutonnière or swan-neck deformities, respectively. The rheumatoid process compromises the normal anatomy of the joint and may lead to joint stiffness, with or without lateral deviation, or to collapse deformities, most notably boutonnière and swan-neck deformities. Mallet finger is not common in rheumatoid arthritis but is common in osteoarthritis. Limited joint movement may result from articular factors (adhesions and disorganization of the joint), periarticular factors (adhesions or laxity of ligaments), or tendinous factors (synovial invasion of the flexor tendons and adhesions).

Collapse deformities of the three-joint system of the digit are characterized by hyperextension of one joint and reciprocal flexion of adjacent joints. The deformity occurs when the balance between the tendon and ligament systems is compromised. Axially applied forces further aggravate the deformity, establishing a cycle of deforming forces.


Boutonnière Deformity
This condition is characterized by flexion of the proximal interphalangeal joint and hyperextension of the distal interphalangeal joint (see Plate 4-31). In rheumatoid arthritis, causes of boutonnière deformity include (1) capsular distention of the proximal interphalangeal joint; (2) lengthening of the central long extensor tendon, with lack of extension in the middle phalanx; (3) lengthening of the transverse fibers; (4) palmar subluxation of the lateral bands, which become flexors of the proximal interphalangeal joint; (5) increased extensor pull on the distal phalanx; (6) self-perpetuating collapse deformity; and (7) soft tissue contracture, joint stiffness, and disorganization.

Swan-Neck Deformity
The term swan-neck deformity refers to hyperextension of the proximal interphalangeal joint and flexion of the distal interphalangeal joint (see Plate 4-31). In rheumatoid arthritis, the deformity may result from (1) synovitis of the flexor tendon sheath, which causes difficulty in initiating or completing flexion of the interphalangeal joint; (2) increased flexor pull at the metacarpophalangeal joint; (3) increased pull of the intrinsic muscles to the central tendon; (4) loosened attachments of the palmar ligament and accessory collateral ligaments of the proximal interphalangeal joint; (5) hyperextension of the proximal interphalangeal joint; (6) stretching of the oblique retinacular ligaments; (7) dorsal subluxation of the lateral bands, which become extensors of the proximal interphalangeal joint; (8) pull of the flexor digitorum profundus tendon, which flexes the distal interphalangeal joint; and (9) joint disorganization and subluxation. Other factors that increase the mechanical advantage of the extensor pull and accentuate the deformity include palmar subluxation of the metacarpophalangeal or wrist joint and contracture of the intrinsic muscles secondary to chronic flexion deformity of the metacarpophalangeal joint. In osteoarthritis, deformity typically starts with a stiff flexion deformity of the distal interphalangeal joint.


Deformities Of Distal Interphalangeal Joint
In osteoarthritis and rheumatoid arthritis, deformities of the distal interphalangeal joint are usually secondary to collapse deformities. Specific deformities resulting from synovial invasion are uncommon; however, loosening of the distal attachment of the extensor tendon may cause a mallet or drop finger. Loosening of the collateral ligaments, erosive changes in the subchondral bone, and cartilage destruction in combination with external forces applied during daily activities may lead to joint instability. Complete joint destruction may also occur secondary to the severe resorptive changes seen in arthritis mutilans.

Surgery For Proximal Interphalangeal Joint
In swan-neck deformity, flexor synovitis is treated first. If the articular surfaces are preserved, hemitenodesis of the flexor digitorum superficialis tendon to the base of the middle phalanx can be done at the same time to check the hyperextension deformity of the proximal interphalangeal joint. Usually, it is not necessary to lengthen the central slip in release of the swan-neck deformity. It is important to obtain adequate release of the dorsal capsule, collateral ligaments, and palmar plate. A 10-degree flexion contracture (or greater) of the proximal interphalangeal joint should be obtained and associated deformities of the contiguous joints corrected.
In a mild flexible deformity in weak hands, dermadesis is indicated: an elliptic wedge of skin (sufficient to create a 20-degree flexion contracture) is removed from the flexor aspect of the proximal interphalangeal joint, preserving the underlying vessels and nerves. If the articular surfaces are inadequate, however, fusion of the proximal interphalangeal joint is preferred. Implant arthroplasty is rarely indicated.

Treatment of arthritic deformities of this joint includes realignment of the longitudinal arch of the digit. The joint can be treated by arthrodesis, resurfacing arthroplasty, or resection implant arthroplasty. Resurfacing of the proximal interphalangeal joint is indicated for painful, degenerative, or posttraumatic deformities with destruction. When subluxation of the joint that cannot be corrected with soft tissue reconstruction alone or significant bone loss exists, implant resection arthroplasty is indicated. For deformities of the proximal interphalangeal joints of both the index and long fingers with osteoarthritis or early rheumatoid arthritis in a young person who performs heavy labor, the proximal interphalangeal joint of the index finger is fused in 20 to 40 degrees of flexion, and resurfacing or resection implant arthroplasty is performed for the proximal interphalangeal joint of the middle finger. The more stable index finger can be used in pinch, and the more flexible long finger can be used in grasp. Flexion of the proximal interphalangeal joints in the ring and little fingers is very important for grasping small objects, and function should be restored if possible.
Good results require adequate release of joint contractures. The collateral ligaments are left intact when-ever possible and if released they should be released on both sides to prevent pivoting instability on the intact side. Rebalancing and postoperative capsuloligamentous healing will stabilize the joint when the postoperative protocol below is utilized. If the joint is severely contracted, more bone is removed, or if too great and the joint cannot reduced, an implant resection arthroplasty is used, allowing for even more bone resection. If the contracture persists, the palmar plate and collateral ligaments may be incised proximally or distally, as needed. The collateral ligaments are not required to be repaired. Resurfacing arthroplasty may be placed either press-fit because they have a bone ingrowth surface or cemented if a tight fit cannot be achieved. Importantly, the central tendon is advanced slightly distal on the middle phalanx, which ensures full extension postoperatively. A coexisting mallet deformity of the distal interproximal joint must be corrected at the time of surgery to prevent a swan-neck deformity.
The hand is dressed as in metacarpophalangeal joint surgery, and 2 or 3 days after surgery, hand-based thermoplastic splints are applied with the finger in 0 degrees of flexion for 3 to 4 weeks. Motion is initiated under supervision, and flexion is gradually increased after 3 weeks as long as full extension can be obtained. The resting splint can be applied slightly to the radial or ulnar side of the digit to correct any residual tendency to deviate; it is worn at night and between exercise periods until adequate healing occurs.
In an alternative approach, the central tendon is pre- served and the exposure is volar, releasing the cruciate pulley, displacing the flexor tendons, releasing the volar plate, and preserving the extensor tendon insertion. Postoperative motion is immediate and preferred for resection implant arthroplasty. However, visualization and correction of soft tissue and bony deformity for resurfacing arthroplasty is more difficult to achieve and may be incomplete.
Implant resection arthroplasty for proximal interphalangeal joints with collapse deformity requires adjustment of the tension of the central tendon and lateral bands as mentioned earlier. Compared with the lateral bands, the central tendon is relatively tight in the swan-neck deformity and must be released, while in the boutonnière deformity, the central tendon is relatively loose and must be tightened.
Implant resection arthroplasty for boutonnière deformity is accompanied by reconstruction of the extensor tendon mechanism. The collateral ligaments are reefed or reattached to bone as needed. After surgery, extension of the proximal interphalangeal joint and flexion of the distal interphalangeal joint must be maintained. The proximal interphalangeal joint is immobilized in extension with a padded aluminum splint for 3 to 6 weeks; the distal joint is allowed to flex freely. Active flexion and extension exercises are started 3 to 4 weeks after surgery, and a splint should be worn at night for about 10 weeks.

Surgery For Distal Interphalangeal Joint
If the distal interphalangeal joint is unstable, subluxated, or deviated or if there is articular damage, arthrodesis is the treatment of choice. Contractures of the joint may be treated with soft tissue release and temporary fixation with a Kirschner wire to allow some useful residual movement. Slight flexion movement of the distal interphalangeal joint is very important in finely coordinated activities, but if movement at the proximal interphalangeal joint is good, fixation in a functional position is acceptable.