[Scaphoid and lunate palmar divergent dislocation. Apropos of a case]

A case of palmar dislocation of the scaphoid and lunate which where dissociated from each other is reported with a 3.5 years follow up. A 32 years old man fell while reading his motorcycle. He landed on his left hand dorsiflexed. There was no skin dilaceration and neuro-vascular status of his hand was intact. X-rays showed a palmar dislocation of the scaphoid and lunate with a large gap between the two bones. The lunate was also completely dissociated from the triquetrum and the capitate. Distal pole of the scaphoid remained in contact with the trapezium. The patient was taken to the operating room, and after unsuccessful closed reduction, an open reduction through a palmar approach was performed. A complete disruption of the anterior capsule was founded and all perilunate ligaments were completely disrupted. Reduction was easy under direct vision, and the anterior capsule was repaired. A non displaced trapezium fracture seen at surgery was fixed with a Kirschner wire. A long arm cast applied for 6 weeks. At 3.5 years follow-up, the patient had an almost full range of motion and no residual pain. Power grip was 25 per cent reduced in comparison with the opposite side. X-rays showed a palmarflexed scaphoid and Magnetic Resonance imaging showed no evidence of avascular necrosis.

Simultaneous dislocation of scaphoid and lunate as a unit or with a large gap between the two bones are extremely rare injuries. In all cases already reported, results were briefly presented without any available clinical and radiological data because patients were lost for follow-up. In our case report, the anatomy and kinematics of the wrist showed the lack of our initial treatment with a single volar approach, anterior capsular reparation and a long arm cast alone. In fact, at 3.5 years follow up, ligamentous healing was inadequate to control compressive forces across the wrist and the scaphoid volarflexed despite a good alignement in the cast. Although the functional results is good, radiological outcome is far from being good. This case demonstrated that even in early treatment with a good position of carpal bones in the sole cast, healing of the ligamentous system without loosing reduction is difficult.

In such a case, and with a low rate of avascular necrosis in perilunate dislocations treated early we suggest an open reduction and internal fixation (O.R.I.F.) to prevent carpal instability. We recommend combined volar and dorsal approaches for repairing anterior and posterior ligaments (especially interosseous ligaments on both sides of the lunate), associated with a stabilization of the entire carpum by scapho-lunate, triquetro-lunate, and capito-lunate Kirschner wire fixation.