Background: We hypothesized that hyperextension metacarpophalangeal (MP) thumb deformity may be caused by trapeziectomy alone due to telescoping of the first metacarpal without trapezial support.

Objective: To explore the relationship of trapeziectomy with hyperextension thumb MP joint deformity and contribute novel data on the underlying pathomechanics.

Methods: This basic anatomical research study examined thumb MP joint kinematics at 6 surgical stages in 10 cadaveric specimens: stage 1, baseline; 2, volar plate of the thumb MP joint division; 3, trapeziectomy; 4, Weilby's ligament reconstruction and tendon interposition (LRTI); 5, extensor pollicis brevis (EPB) tenotomy; and 6, MP volar plate reconstruction by tenodesis with EPB. Six infrared cameras were used in a motion capture system to determine three-dimensional angles of the first MP joint during 10 cycles of thumb flexion-extension, measuring angles in maximum flexion and extension and the complete flexion-extension arc.

Results: In comparison to baseline, the angle in extension and MP-ROM were significantly increased after stages 3 (trapezium extraction), 4 (LRTI), and 5 (EPB tenotomy). In comparison to values after stages 3, 4, and 5, the hyperextension was significantly corrected after stage 6 (tenodesis).

Conclusions: In a cadaveric model of trapeziectomy, secondary thumb column shortening favors an MP joint hyperextension deformity that is not corrected by LRTI or EPB tenotomy and requires a stabilization procedure.