Metacarpophalangeal arthroplasty

Indications

• Metacarpophalangeal (MCP) arthroplasty is indicated in patients with chronic pain, deformity, or functional loss. Arthrodesis is poorly tolerated at the MCP level because the arc of motion starts at this joint. Implant arthroplasty is the preferred surgical treatment for arthritic MCP joints.

• There are two common implant options for MCP joints: silicone and pyrocarbon. Silicone implants act as spacers. They are hinged and rely on the formation of a capsule around the implant for stability. Pyrocarbon implants are unconstrained (two parts) and must be supported by normal bone stock and intact surrounding soft tissues. Both types of implants provide excellent pain relief, maintain joint motion, improve hand appearance, and have high levels of patient satisfaction.

• Silicone implants are indicated for rheumatoid arthritis (RA) patients because the construct provides stability. Pyrocarbon should not be used in RA patients because ligament laxity will lead to subluxation of the joints.

• Pyrocarbon arthroplasty is suitable for patients with posttraumatic arthritis or osteoarthritis (OA). Strong ligaments provide structural support for this unconstrained implant.

Clinical examination

• The MCP joint is examined for edema, deformity, and areas of tenderness. Active and passive range of motion (ROM) is measured. The joint is stressed in radial and ulnar deviation to assess collateral ligament stability. The skin is evaluated for integrity and healing potential.

In patients with inflammatory arthritis:

• Ulnar subluxation of the extensor tendons is noted when present ( Fig. 41.1 ).

  

• Overall finger posture (including presence of swan-neck or boutonniere deformity) and the condition of surrounding joints are evaluated.

• Volar subluxation of the proximal phalanx on the metacarpal head and ulnar drift of the fingers is common in RA patients. If this deformity is passively correctable, extensor tendon centralization with cross-intrinsic transfer is considered. Arthroplasty is indicated when passive correction is not possible because the supporting ligament and tendon structures are contracted, which makes soft-tissue releases untenable to maintain joint alignment. Joint resection provides relative lengthening of these contracted structures, thus makes realignment of the digit more predictable ( Fig. 41.2A–B ).

  

• The wrist is carefully evaluated; deformity at the radiocarpal or distal radioulnar joint (DRUJ) affects distal joints and must be treated first, even if the patient is asymptomatic at the proximal joint. Radial deviation at the radiocarpal joint leads to compensatory ulnar drift at the MCP joints. DRUJ instability can result in attritional extensor tendon ruptures. Failure to correct wrist instability and deformity affects outcomes in MCP arthroplasty.

Imaging

• Three views (posteroanterior [PA], oblique, and lateral) of radiographs of the hand are obtained to evaluate articular congruity and bone stock ( Fig. 41.3A–C ).

  

• Implant size can be estimated using measurement tools and templates.

Surgical anatomy

• The MCP is an asymmetric condylar joint; the ovoid articular surface of the metacarpal fits into an elliptical cavity at the base of the proximal phalanx. Motion is permitted in two planes: flexion-extension and radio-ulnar deviation.

• The joint is stabilized by the volar plate, collateral ligaments, and extensor mechanism. The sagittal bands centralize the extensor tendon over the MCP joint and prevent bowstringing during hyperextension ( Fig. 41.4 ).

  

• The intrinsic tendons insert onto the lateral bands, which are volar to the axis of rotation of the MCP joint and act as flexors ( Fig. 41.5 ).

  

• The metacarpal head is sloped ulnarly and volarly. In RA patients, synovitis attenuates the supporting ligaments and the proximal phalanges slide ulnarly and volarly on the metacarpal heads. The extensor tendons subluxate into the intermetacarpal space and contribute to ulnar drift of the digits.

• Chronic MCP subluxation and ulnar drift leads to fibrosis of the intrinsic muscles. When present, this requires release and cross-intrinsic transfer at the time of MCP arthroplasty.

• In scleroderma patients, sclerosis of the skin, collateral ligaments, joint capsules, and tendons results in attenuation of the central slip and volar displacement of the lateral bands. Flexion at the proximal interphalangeal (PIP) joint leads to compensatory hyperextension at the MCP joint, resulting in a boutonniere deformity ( Fig. 41.6A–C ).

  

Positioning and equipment

• The patient is positioned supine with the arm extended and hand pronated on a hand table.

• The operation is performed under tourniquet control.

• A rolled towel is placed in the palm for support.

• Implants, implant-sizers, an oscillating saw, and intraoperative fluoroscopy are required.

Exposures

• A dorsal longitudinal or lazy-S incision centered at the joint is used to access a single MCP ( Fig. 41.7 ).

  

• Multiple arthroplasties are performed through a single, dorsal, transverse incision, which provides ease of access through the same single incision when revision arthroplasty is needed in the future. Care is taken to preserve the dorsal veins to reduce postoperative swelling ( Fig. 41.8 ).

  

Indications

Indications include:

• Painful destruction or subluxation of the MCP joint that cannot be passively corrected

• RA patients with greater than 15 degrees of ulnar drift and/or greater than 20 degrees of extensor lag

• Loss of function because of joint deformity

• Low-demand patients with OA