Change of carpal alignment under anaesthesia: role of physiological axial loading on carpus

to study the effect of physiological axial loading on the carpal alignment.

Patients with distal radial fracture undergoing general anaesthesia for management of their injury were employed for the present study. The contralateral normal wrist was assessed for any change in carpal alignment following the elimination of the physiological axial load under anaesthesia with complete muscle relaxation.

Axial load across the wrist is known to affect carpal alignment. Axial compression is known to dorsiflex the lunate due to its dorsally thinned wedge shape. However, cadaveric experiments have also shown the axial compression to flex the whole proximal carpal row.

Lateral radiographs of the uninjured wrist joint were performed in twenty patients with distal radial fracture. Radiographs were taken before and after giving general anaesthesia along with muscle relaxants and were repeated after applying the traction in line with the long axis of the radius.

Anaesthesia caused scaphoid and lunate to dorsiflex with no change in scapholunate angle while, traction caused scaphoid to rotate further dorsally.

Physiological axial loading due to the normal tone of the forearm muscles tends to flex the scaphoid and the lunate. This is contrary to the lunate's classical description of its tendency to dorsiflex under axial loading. Our results also failed to support the view that scapholunate interosseous ligament is in continuous tension due to the tendency of the scaphoid and lunate to move in the opposite directions.

A dorsiflexed lunate need not be considered the hallmark for diagnosing the scapholunate dissociation.