TRIGGER FINGER

Either the middle or ring finger is usually involved. Flexion of the finger feels normal but extension is accompanied by a painful snap (see video) . For unknown reasons, a nodular thickening forms in the long flexor tendon just proximal to the metacarpal head; the nodule is pulled out of the sheath during flexion, but during extension the constricted mouth of the sheath momentarily resists the pull of the weaker extensor muscles. The nodule eventually snaps back into the sheath.