The patients history, examination, and images are consistent with thumb CMC (basilar) joint arthritis with associated MCP joint arthritis. At the MCP joint there is hyperextension of the thumb metacarpophalangeal (MCP) joint and adduction involving the first web space of the hand (Z deformity). Arthrodesis of the MCP joint is the treatment of choice when thumb MCP hyperextension exceeds 40°, the deformity is not passively correctable, or advanced degenerative changes are noted to affect the articulation.
The review article by Armbruster and Tan state that when MCP joint hyperextension is:
0° to 10°= Surgical intervention is not necessary when MCP hyperextension is less than 10°.
10° to 20°= Percutaneous pinning of the MCP joint in 25° to 35° of flexion for 3-4 weeks may be performed independently or as an adjunct to EPB transfer.
20° to 40°= Capsulodesis of the volar aspect of the MCP joint is recommened to provide a check rein for hyperextension and Sesamoidesis has also been investigated as an adjunctive procedure.
Cooney et al performed a Level 4 review of their CMC arthroplasty patients and found 15 patients with 17 revision arthroplasties in the treatment of mechanical pain related to instability or bone impingement. The revisions included soft-tissue interposition alone or soft-tissue interposition with ligament reconstruction and found that this provided satisfactory patient outcomes in more than 75% of the cases.
Illustration A depicts the forces accounting for the observed adduction and hyperextension deformities. The arrowhead indicates the direction of subluxation of the base of the thumb metacarpal (due to incompetent volar beak ligament). The arrow represents the force vector of the EPB potentiating the MCP hyperextension deformity
Armbruster EJ, Tan V. Carpometacarpal joint disease: addressing the metacarpophalangeal joint deformity. Hand Clin. 2008 Aug;24(3):295-9, vii. Review.
PMID:18675721 (Link to Abstract)
Cooney WP 3rd, Leddy TP, Larson DR. Revision of thumb trapeziometacarpal arthroplasty. J Hand Surg Am. 2006 Feb;31(2):219-27.
PMID:16473682 (Link to Abstract)