[Carpal instability]

Traumatic carpal instability implies that the normal relationships of the radiocarpal and mid carpal joint are distorted either statically or during dynamic stress. Normal kinematics of the carpus are dysfunctional. The causes of carpal instability are dissociation of the intercarpal ligaments on either side of the lunate, a so-called scapholunate dissociation or a luno-triquetral dissociation. Carpal instability nondissociative is generally due to a laxity or attenuation of the intrinsic ligaments of the carpus and are associated with deformity of the distal radius. Ulnar translation of the carpus on the distal radioulnar articular surfaces occurs with shear stretching of the origins of the radiocarpal ligaments. The radial styloid attenuation of the ligaments may result in abnormal motions of the carpal bones going from ulnar to radial deviation at which time a catch-up click may occur. Carpal instabilities are usually associated with malalignment of the lunate with respect to the longitudinal axes of the radius and capitate and tends to assume an extended position with scaphoid fractures or injuries to the scapholunate ligament, a palmar flexed position with injuries to the luno-triquetral area or the ulnar capsule.