DEFORMITIES OF THE METACARPOPHALANGEAL JOINTS
Arthritic diseases may affect any joint, but their effect on the hands can be especially devastating. The disease process attacks the joints, ligaments, and tendons, causing painful and disabling deformities. Fortunately, developments in joint reconstruction and replacement have made it possible to restore hands deformed by crippling arthritis to a nearly normal appearance and useful function.
Ideally, arthroplasty should produce a joint that is pain free, mobile, stable, and durable. Four methods of reconstruction for arthritic joints of the hand have emerged: arthrodesis, resection interposition arthroplasty, resurfacing joint replacement, and flexible implant resection arthroplasty.
Arthrodesis works very well for the thumb at the metacarpophalangeal joint level and for the lesser fingers at the proximal and distal interphalangeal joint level, but lack of motion is debilitating in the lesser fingers at the metacarpophalangeal joint level and rarely used.
Resection interposition arthroplasty can improve motion by shortening skeletal structures, lengthening soft parts, providing new gliding surfaces, and allowing the development of a new supportive fibrous joint capsule. The chief disadvantage of the procedure in the metacarpophalangeal joints is the unpredictability of results. Resurfacing joint replacement has proved successful in knee and hip joints, but early results in finger joints have been mixed because of dislocation, bone resorption, and implant loosening. More recently, newer designs are proving useful in patients with osteoarthritis and early rheumatoid arthritis where the soft tissue balance is still relatively normal.
In flexible implant resection arthroplasty, a flexible silicone implant is used as an adjunct to resection arthroplasty. This method was devised in 1962 and has been used successfully in several hundred thousand patients. This discussion emphasizes the techniques of implant resection arthroplasty.
The basic concept of flexible implant resection arthroplasty can be summarized as “bone resection + implant + encapsulation = functional joint.” The flexible implant acts as a dynamic spacer, maintaining internal alignment and spacing of the reconstructed joint and supporting the capsuloligamentous system that develops around it. The joint is thus rebuilt through a healing phenomenon called the “encapsulation process.” Because the capsuloligamentous system around a new joint is adaptable, a functional balance of mobility and stability can be obtained. This allows for realignment of severely dislocated and angulated joints after the significant bony and soft tissue resection needed in severe rheumatoid deformities. Postoperative mobilization is tailored to the amount of instability present after reconstruction; delay in mobilization increases stability. This is typically acceptable as the flexors greatly over- power the extensors and prolonged immobilization in extension is rapidly overcome, giving a stable, mobile grip. Soft tissue balance is key to preventing the recurrence of deformity and to implant breakage, dislocation, and failure.
The candidate for arthroplasty must be in good general condition. Skin cover and neurovascular status must be adequate. The elements necessary to restore a functioning musculotendinous system and sufficient bone stock to receive and support the implant must be available. In certain patients with progressive rheumatoid arthritis who have insufficient bone stock to support the implant, a simple resection arthroplasty or arthrodesis with a bone graft is preferable. Surgery is also contraindicated if postoperative hand therapy is not available or adequate.
Proper staging of the reconstructive procedures is important in planning the treatment program. Procedures in the upper limbs should be delayed in patients who also need lower limb reconstruction that will necessitate the use of crutches. After hand reconstruction, patients should avoid excessive manual labor and awkward hand weight bearing when using crutches. The special platform type of crutch is recommended.
In deformities of the metacarpophalangeal joint associated with severe wrist involvement, the wrist should be treated first. In the patient with rheumatoid arthritis, tendon repair and synovectomy of tendon sheaths must precede arthroplasty of the metacarpophalangeal joints by 6 to 8 weeks. If both metacarpophalangeal and proximal interphalangeal joints are involved, the metacarpophalangeal joint is usually treated first or simultaneously if only operating on one or two metacarpophalangeal joints. In swan-neck deformity, the metacarpophalangeal and proximal interphalangeal joints are reconstructed at the same stage. In boutonnière deformity, the proximal interphalangeal joint is reconstructed first. Tendon imbalances and joint misalignment must be corrected. Implant arthroplasty for both the metacarpophalangeal and proximal interphalangeal joints of the same digit is usually avoided if possible.
Several procedures can be performed during one operation, depending on the time available. Surgery for the thumb, proximal interphalangeal and distal inter-phalangeal joints, wrist, and, occasionally, the elbow joint can often be combined. A limb procedure should be limited to no more than 2 hours, and an axillary or supraclavicular block is recommended if the tourniquet time exceeds 112 hours. Small joints may also be injected with corticosteroids or other agents during surgery.
Deformities Of Finger Joints
In the normal hand, a delicate balance exists among the muscles and tendons and the bones and joints through which they interact. The hand has three functional arches, one longitudinal and two transverse. The proximal transverse arch crosses the carpal area, with its center at the capitate. The distal transverse arch is formed by the metacarpal heads and is centered on the head of the third metacarpal. The digits make up the longitudinal arches, each with its apex at the metacarpophalangeal joint.
In rheumatoid arthritis, this balance among the muscles, tendons, and bones is compromised as the inflammatory synovial membrane grows over the surface of the cartilage, into the ligamentous attachments, and into and around the tendons. The result is capsular distention, destruction of cartilage, subchondral erosions, loosening of ligamentous insertions, impaired tendon function, and, finally, joint dis- organization, subluxation, and dislocation. A break in the longitudinal arch system causes collapse deformities of the multiarticular structure of the hand, disturbing the stability and balance necessary for prehension. Use of the hand in daily activities (functional adaptation) causes further deformity.
Deformities Of Metacarpophalangeal Joint
The metacarpophalangeal joint is a key element in finger function. This joint not only flexes and extends but also abducts and adducts; it also has some passive axial rotation. The index finger can pronate up to 45 degrees.
Rheumatoid arthritis commonly involves the metacarpophalangeal joints, resulting in increased ulnar deviation of the fingers, subluxation of extensor tendons, and palmar subluxation of joints (see Plate 4-21). The flexor tendons enter the fibrous sheath at an angle, exerting an ulnar and palmar pull that is resisted in the normal hand. When the rheumatoid process distends and weakens the capsule and ligaments of the metacarpophalangeal joint, the forces generated by the long flexor tendons across the sheath during flexion may elongate these supporting structures. Resistance to the deforming pull of the tendons is gradually lost, and the sheath inlet and tendons are displaced in distal, ulnar, and palmar directions. Eventually, the base of the proximal phalanx moves ulnarly and palmarly. The intrinsic muscles, which normally form a bridge between the extensor and flexor systems and provide direct flexor power across the metacarpophalangeal joint, can also become deforming elements once the disease has lengthened the restraining structures of the metacarpophalangeal joint.
Increased mobility of the fourth and fifth metacarpals, common in rheumatoid arthritis, results from loosening of ligaments at the carpometacarpal joints and dysfunction of the extensor carpi ulnaris tendon (ulnar head syndrome). Flexion of the metacarpophalangeal joints increases the breadth of the transverse arch of the hand, which pulls the extensor tendons in an ulnar direction through the juncture tendons. The extensor tendon expansions (hoods) are loosely fixed and vulnerable to disruption. Ulnar subluxation of the extrinsic extensor tendons compromises the balance of the intrinsic extensor tendons, which in turn increases the tendency for palmar subluxation and ulnar deviation.
Factors that exacerbate ulnar deviation include (1) the normal mechanical advantage of the ulnar intrinsic muscles, (2) the asymmetry and ulnar slope of the metacarpal heads of the index and middle fingers, (3) the asymmetry of the collateral ligaments, (4) the ulnar forces applied on pinch and grasp, and (5) the postural forces of gravity. Wrist deformities and rupture of the extensor tendons play a secondary role in aggravating the joint disturbances.
Pronation deformity of the index finger is common in the rheumatoid hand. In the normal hand, pinch between the thumb and index finger requires a slight supination of the index finger so that the palmar surfaces can meet. In pronation deformity, the less useful lateral surfaces are opposed. During pinch, pronation deformity is seen in all three digital joints, but it is more pronounced in the metacarpophalangeal joint. Arthroplasty of this joint should include reconstruction of the capsuloligamentous and musculotendinous systems.
Surgery For Metacarpophalangeal Joint
Flexible implant resection arthroplasty of the metacarpophalangeal joints is carried out for deformities due to rheumatoid arthritis and trauma, with radiographic evidence of joint destruction too great to support resurfacing implants or subluxation greater than 25%, ulnar deviation not correctable with soft tissue surgery alone, and contraction of the intrinsic and extrinsic musculature and ligamentous system.
The surgical technique for implant resection arthroplasty for the metacarpophalangeal joint is shown on Plates 4-26 to 4-28. Soft tissue release must be complete to obtain an appropriate joint space. The ulnar collateral ligament is incised at its phalangeal insertion in all fingers; if severely contracted, it is excised with the palmar ligament (plate). The ulnar intrinsic tendon, if tight, is sectioned at its myotendinous junction and the abductor digiti minimi is released.
Reconstruction of the radial collateral ligament is done for index and middle fingers. The radial collateral ligament and related structures are reattached proximally to the metacarpal neck and distally to the proximal phalanx through small drill holes. The radial half of the palmar plate and the preserved radial capsule are included in this repair. The ulnar edge of the capsule is sutured to the distally released ulnar collateral ligament. Sutures are placed before the implant is inserted and tied with the finger held in supination and abduction. Although the procedure seems to slightly limit flexion of the metacarpophalangeal joint, this is out-weighed by increased lateral and vertical stability and better correction of the pronation deformity.
After the procedure, a voluminous conforming dressing, including a palmar splint, is applied with the metacarpophalangeal joints in 30 degrees of flexion and slight radial deviation. During the postoperative period, the limb must be elevated. A meticulous postoperative therapy program is usually started 3 to 5 days after surgery and consists of static splinting of the metacarpophalangeal joints for 4 weeks with free movement of the proximal and distal interphalangeal joints followed by mobilization of the metacarpophalangeal joints in a radial deviation support brace. Full hand night splinting in a slightly overcorrected position is used for 6 months.