They are frequent in sports (ski, handball, basketball, rugby, etc.) and are mostly the result of valgus-dominant traumas in 90% of the cases (damage of the medial collateral ligament). Varus-dominant traumas damage the lateral collateral ligament, and those in hyper-extension damage the volar plate. Combined injuries of various elements are frequent. In serious sprains (rupture of the medial collateral ligament), surgery is needed because the proximal extremity of the ligament passes above the adductor expansion towards the extensor pollicis longus, making the healing impossible: it is the Stener effect. Even if it is rare, the same phenomenon can be observed at a radial level with the expansion of the external thenar muscles. The varus deformity is more spectacular in injuries of the radial collateral ligament than the valgus deformity in injuries of the ulnar collateral ligament. This is because the external thenar muscles have a longitudinal orientation and the adductor pollicis has a transversal orientation, which will cause a more important varus in injuries of the radial collateral ligament. The metacarpophalangeal joint of the thumb is a stability joint, so the rehabilitation goal will be to improve the active stability of the joint, especially in the muscles protecting the damaged ligament. Techniques to gain amplitude must be used cautiously during the healing phase in order not to weaken the passive stabilization structures.