[Chronic internal metacarpophalangeal sprains of the thumb. Anatomo-clinical classification and therapeutic consequences].

In the light of a physiopathological study of severe medial strain of the metacarpophalangeal joint of the thumb in 20 cadaver hands, the authors propose a correlation between anatomical and clinical findings and a classification derived from it: Stage I: rupture of one fascicle of the collateral ligament. Passive valgus mobility of less than 15 degrees. The ruptured ends of the ligament remain in contact. Stage II: rupture of both fascicles of the ligament. Passive valgus and supination mobility of the metacarpophalangeal joint of 20 to 40 degrees. Interposition of the dorsal digital expansion between the ruptured ends of the ligament. Abnormal movements can be corrected by applying tension to the dorsal digital expansion. Stage III: rupture of both fascicles of the collateral ligament and the dorsal digital expansion. Tension from the thenar muscles causes abnormal movement and produces a fixed flexion of the metacarpophalangeal joint with hyperextension of the interphalangeal joint (Z-shaped thumb). From this the authors determine the operative indications and suggest a palliative ligamentoplasty to restore the anatomy as much as possible.