Joint fusion for thumb metacarpophalangeal instability

Indications

Thumb metacarpophalangeal (MCP) joint fusion is indicated in patients with symptomatic arthritis or instability.

Clinical examination

• Patients may complain of pain, swelling, stiffness, or decreased grip strength.

• Patients with carpometacarpal joint destruction often have compensatory hyperextension of the thumb MCP joint and will have pain with gripping, twisting, and key pinch.

• A normal thumb has a subtle degree of passive hyperextension at the MCP joint but should not collapse or hyperextend during key pinch, which is a sign of MCP instability ( Fig. 44.1 ).

  

Imaging

Standard three-view radiographs (anteroposterior, oblique, and lateral) are required to evaluate the articular anatomy and bony quality.

Surgical anatomy

• The thumb MCP joint has characteristics of both a condyloid and a hinge joint.

• There is little inherent stability in the bony anatomy; the joint is dependent on soft tissue constraints, including the ligamentous complex and musculotendinous attachments.

• The paired proper and accessory collateral ligaments stabilize the joint on the radial and ulnar aspects. The proper collateral ligaments originate from the lateral condyles of the metacarpal and insert onto the volar third of the proximal phalanx. The accessory collateral ligaments originate from the metacarpal (volar to the proper ligament) and insert onto the volar plate and the sesamoid bones. The proper collateral ligaments are tight in flexion, and the accessory collateral ligaments are tight in extension.

• The adductor pollicis originates from the second and third metacarpals and inserts at the thumb MCP joint. The adductor aponeurosis courses obliquely across the MCP joint and inserts onto the extensor apparatus distal to the sagittal band.

• The fibrocartilaginous volar plate forms the floor of the capsuloligamentous complex.

• The intrinsic muscles of the thumb (flexor pollicis brevis and abductor pollicis brevis) insert onto the radial sesamoid and have attachments to the extensor mechanism to provide dynamic support ( Fig. 44.2 ).