Generally resulting from high-energy trauma, simultaneous palmar dislocation of scaphoid and lunate is extremely rare (1-9) and currently classified into two subtypes depending on whether the scapholunate ligament is intact or not: 1) palmar dislocation as a unit; 2) palmar-divergent dislocation (4-7). If residual violence was kept on transmitting other dislocations or fractures might occur in the ipsilateral upper extremity. Prior to our report, one case with ipsilateral radial head fracture and another trapezium fracture were described besides palmar-divergent dislocation of scaphoid and lunate (1, 4). Concomitant ipsilateral fractures or dislocations could be undiagnosed without special attention. To raise our awareness of coexisting dislocations or fractures in ipsilateral upper extremity and avoid missed diagnosis and fully evaluate injuries severity, we proposed this sort injuries should be an additional third subtype of palmar dislocation of scaphoid and lunate, just as Maisonneuve fracture of high fibular in Lauger-Hansen classification of ankle fracture-dislocation (13).
As palmar-divergent dislocation of the scaphoid and lunate is rarely observed, its optimal treatment remains unclear. In this case, the patient showed palmar-divergent dislocation of scaphoid and lunate and homolateral humeroradial dislocation and humeral fracture. This complexity forced us to take a treatment different from those commonly used. We first fixed the humeral shaft fracture and then reduced the dislocation, preventing the radial nerve from iatrogenic damage during manual traction reduction. Among previous reports, only one case developed postoperative avascular necrosis of lunate due to delay diagnosis (3), and one was treated with proximal row carpectomy (PRC) due to the complete absence of scaphoid (6). Although PRC may eliminate avascular necrosis and avoid additional surgery, postoperative range of motion (ROM) and grip strength reach 50～70% and 60～90% of that healthy-side, respectively (10). Therefore, except for special patients needing PCR, we recommend surgical repair as the first choice, especially for active young people and manual workers (4, 6, 9).
The anatomic reduction can protect the scapholunate from further avascular damage and accelerate spontaneous revascularisation (1, 2). Closed reduction is technically difficult and cannot repair carpal interosseous ligaments. Moreover, repeated close reduction could damage the scapholunate's remaining soft tissue attachments, which may contain vessels blood-supplying scaphoid and lunate (3, 9). Meanwhile, just a plaster cast is not enough to fix the scapholunate due to ruptured interosseous ligaments and severe carpal instability (3, 4, 7, 8). Owing to severe carpal instability, scaphoid and lunate still needed to be refixed with Kirschner's wires after successful close reduction and plaster fixation, as reported by Komura (7) and Idrissi (8). In our case, both open reduction and fixation with Kirschner's wires were performed with favourable outcomes, even far from the accurate fixation of scaphoid and lunate.
In a previous report, 4 out of 5 cases without interosseous ligament repair complicated dorsal intercalated segment instability (DISI) (Table1). Recently, the carpal interosseous ligament repair benefits have been recognised in the preventment of late carpal instability, scapholunate dissociation, and avascular osteonecrosis. Short et al. have studied the ligamentous stabilisers of scaphoid and lunate and demonstrated that the scapholunate interosseous ligament is the primary stabiliser, and the others are secondary stabilisers of the scapholunate articulation (11). In our case, we only repaired the stronger palmar scapholunate ligament through single volar approach, even though scaphoid and lunate were not fixed accurately, the patient had no avascular necrosis of carpal bones, which indicated that protection of blood supplies of scapholunate from surrounding soft tissue was effective for the scapholunate revascularisation. Reduction and ligament repair through only a palmar incision have greater advantages, as it is less invasive, easier operation, less damage to the blood supply and lower wrist stiffness. It has already reported that torn ligaments repair with a suture anchor make operation simplify and offer non-space-consuming and permanent fixation (7, 9, 12). Of previous reports, a total of 3 cases undertook fixation of scapholunate or interosseous ligaments repaired by combined palmar and dorsal approaches, limited ROM to different extent occurred in all cases and avascular osteonecrosis or subchondral sclerosis of scapholunate in two cases and flexion deformity of the scaphoid with a break in arc II of Gilula's line in one case, postoperatively (3, 7, 9). By analysis, we speculated that these complications might be closely related to additional dorsal incision and increasing damage to blood supplies or no suture of the stronger palmar scapholunate ligament. In this case, therefore, we renewed the surgical strategy to prevent those complications.