トラペジオメタカル関節形成術：不均衡の回避と転帰の最適化

Trapeziometacarpal joint osteoarthritis is common and can lead to pain, loss of pinch strength, and progressive deformity, including the classic Z-deformity. Understanding the pathomechanics of the disease progression can help surgeons effectively balance trapeziometacarpal joint arthroplasty.Biomechanics:The disease process begins with resorption of the anterior beak of the thumb metacarpal, weakening the anterior oblique ligament. This alters joint contact mechanics, leading to thumb metacarpal flexion and dorsoradial subluxation. As deformity progresses, the effective excursion of the thenar muscles shortens, reducing grip efficiency. Compensation by the flexor pollicis longus produces distal phalanx flexion, which shifts load dorsally across the metacarpophalangeal joint and promotes hyperextension, culminating in the classic Z-deformity.Arthroplasty:Trapeziometacarpal joint arthroplasty aims to restore thumb column balance by correcting basal joint deformity. Correct component selection and alignment are critical to stability and function. Cup orientation within the trapezium should approximate the flexion-extension axis to reduce dislocation risk. Dual-mobility designs have lowered dislocation rates compared with single-mobility implants. Careful resection of osteophytes, particularly between the thumb and index metacarpals, is essential to prevent bony impingement. Metacarpophalangeal joint hyperextension often improves following TMC arthroplasty through secondary soft-tissue stabilization, reducing the need for adjunctive metacarpophalangeal procedures. Arthrodesis remains an option in selected cases with significant instability or degenerative change.

Modern arthroplasty, particularly with dual-mobility prostheses, provides reliable correction of deformity, improved stability, and durable outcomes in patients with advanced TMC osteoarthritis.

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