Correction of a Hyperextension Deformity at the Metacarpophalangeal Joint by Arthroplasty for Osteoarthritis of the Thumb Carpometacarpal Joint Followed by External Fixator: A Case Series: Modified Ilizarov Method for Correction of a Collapsed Thumb Deformity Due to Carpometacarpal Osteoarthritis.

A hyperextension deformity in the advanced stages of carpometacarpal (CMC) arthritis of the thumb could affect the outcomes of thumb CMC joint arthroplasty. We introduce the interesting approach for treating severely collapsed thumb deformities with gradual distraction and coordinated correction of the MCP and CMC joints by means of external fixators. We divided 8 cases into 3 groups according to the angle of passive flexion of the hyperextended MCP joint: group 1, 10-20°, group 2a, 20-40°, and group 2b, >40°, retrospectively. We first performed CMC arthroplasty with trapezium excision. In group 1, we corrected the MCP hyperextension deformity by manual passive flexion and fixed the joint with an extension block Kirshner wire (K-wire) for 2 months. However, deformities recurred in 2 of 5 cases after removing the K-wire. These patients received corrective percutaneous osteotomy with external fixators at the metacarpal neck. In groups 2a and 2b, we performed CMC arthroplasty and set external fixators at the same time. All cases in groups 1 and 2a have been without recurrence for more than 2 years, while a deformity recurred in group 2b. The results of this small case series encouraged us to propose an interesting approach for collapsed zigzag thumb deformity. Good outcomes with excellent maintenance of active MCP movement and no recurrence are highly anticipated if the hyperextended thumb has no obvious degenerative changes and can be corrected by <40° of passive flexion. Our results also indicate a risk of recurrence associated with extension block by K-wire.