[Sprain of the thumb metacarpal-phalangeal with lesion of the ulnar collateral ligament].

The sprain of the thumb metacarpal-phalangeal joint must be treated in an adapted way in order to avoid chronic laxity. The comparative and bilateral clinical exam is the main element that will allow to detect laxity. In the case of non laxity, a conservative treatment with a splint makes sense. In the case of laxity with Stener effect, a surgical procedure is recommended in order to reintegrate the collateral ligament. In the case of laxity without Stener effect, the choice of treatment is contentious. A US or MRI would be useful if the Stener effect could be underlying. For whichever treatment opted, rehabilitation is to be started as soon as at week 4, in order to reduce risks of stiffness. The return to any sport or training will depend on the sprain stage and on the possibility to wear a rigid splint or not.