[Carpal instability with scapho-lunate dissociation treated using the flexor carpi radialis and scaphoid-trapezoid ligament repair: foundations, technique and results of preliminary series].

Carpal instability with scapho-lunate dissociation is still attributed to rupture of the so-called scapho-lunate ligament. Actually, this structure is not a ligament but a loose capsule allowing very different flexion of the scaphoid (92 degrees) and the lunate (20 degrees). As reconstruction of the scapho-lunate "ligament" has often been less than satisfactory we searched for another technique. Sections of the scapho-lunate "ligament" on cadaver specimens never produce scapho-lunate dissociation. This dissociation can not occur because the scaphoid is maintained in the radial facette. It was observed that the only way to produce scapho-lunate dissociation is to section the scapho-trapezo-trapezoid ligament allowing flexion of the scaphoid and dorsal dislocation out of the radial facette. The scapho-trapezo-trapezoid ligament is not well known and is not described in anatomy text books because it is hidden by the flexor carpi radialis tendon. It is confluent with the scaphoid and the trapezoid. This produces a radial (scapho-trapezoid) column which acts like a true external pillar maintaining the height of the carpus and preventing carpal collapse. Finally, dissociation of the proximal pole from the semi-lunate can only occur by posterior displacement. After experimenting the technique on cadaver specimens, we developed a reconstruction method for the palmar scapho-trapezoid ligament using a band of the flexor carpi radialis tendon, applied in 38 patients. The flexor carpi radialis band measured 7 cm and was left attached to the base of the second metacarpal then passed in a tunnel bored anteriorly to posteriorly in the distal pole of the scaphoid. The band was then drawn dorsally while maintaining the scaphoid in place, and sutured to the postero-ulnar border of the radius. The height of the carpus was restored as was scaphoid movement over the lunate. The reduction persisted at mid- and long-term and prevented carpal collapse and joint destruction. Among the 38 operated patients, 33 remained pain free and 5 complained of minor pain under stressful conditions. All were satisfied. Anatomic research and clinical experience has demonstrated that the scapho-trapezoidal ligament is the key to scapho-lunate dissociation and its correction. Currently, this operation is the only way to achieve easy and persistent correction of carpal instability with scapho-lunate dissociation.