Evaluation of the first web-space narrowing in congenital anomalies with Z-deformity

In patients with congenital anomalies of the thumb, the metacarpophalangeal joint often undergoes radial deviation to compensate for a narrow first web space. In this study, we evaluated the relationship between the thumb and index finger in patients with arthrogryposis multiplex congenita (AMC), by measuring the thumb-index angle on radiographs taken while the patient held a styrene foam cone.

Investigation was carried out on nine patients (13 cases: four bilateral and five unilateral) with AMC. The average patient age was 4.4 years (range, 2.6-7.2 years). Overhead radiographs were obtained while the patient held a styrene foam cone. The radiographs were used to evaluate the apparent thumb-index web angle, the thumb to index finger metacarpal angle (1-2MCA), and the first metacarpophalangeal angle (1MPA).

In the five unilateral cases, significant differences were seen on the affected versus unaffected sides in 1-2MCA and 1MPA. All 13 cases were treated surgically, and significant differences were observed between the groups before surgery and 2 years after surgery in the 1-2MCA and 1MPA. In addition, the mean postoperative 1MPA in the bilateral cases was significantly smaller compared with the unilateral cases.

This radiographic technique enabled us to evaluate the severity of the thumb-index web-space narrowing and the radial instability of the thumb metacarpophalangeal joint in patients with AMC. The bilateral cases tended to show better rehabilitative improvement compared with the unilateral ones, probably because the latter patients could use their unaffected hand.