[A adaptive proximal scaphoid implant]

In this study, the insertion of a pyrocarbon implant (APSI) has been described, which is shaped to allow adaptive mobility during carpal movement in the first row of carpals. This implant replaces the proximal part of the scaphoid; it is designed to treat styloscaphoid arthritis, and to prevent further deterioration and carpal collapse by restoring the first carpal row to its original height, i.e., 'SNAC wrist' after scaphoid pseudoarthritis, and 'SLAC wrist' following scapho-lunate dissociation.

This retrospective series included 25 cases which were examined and analyzed at an average of six years post-surgery (between three and ten years) by an independent observer using the EVAL expert database system: 1) 14 cases involved pseudoarthritis, which developed from the scaphoid ('SNAC wrist'); 2) ten cases were connected with scapho-lunate nonunion ('SLAC wrist'); 3) one case involved carpal collapse with siliconite, which had previously been inserted as a scaphoid silicone partial implant for the treatment of pseudoarthritis involving a stage II fracture.

In all cases, the reason for the preoperative-consultation for degenerative arthritis was the presence of pain, which post-surgery was no longer apparent in 60% of cases, and only persisted during effort in 28% of cases. Thus 88% of the patients were satisfied with the results, and were able to resume their normal professional and sports activities at the same level as before. Strength connected with digitopalmar grip and pinch force were found to have increased compared to the function in the healthy hand. No implant dislocation was detected by radiological investigation. Dynamic X-rays of the implant in flexion, extension, and frontal inclination confirmed this adaptive mobility. Carpal height was in all cases maintained. The radio-lunate angle remained unchanged in 15 cases, was improved in six cases, and was worse in four cases. Two poor results were connected with severe ligament lesions prior to surgery.

The preliminary results regarding the APSI implant seem to be promising for cases of polar pseudoarthritis in which curative treatment is no longer possible. This technique avoids further deterioration and carpal collapse ('SNAC wrist'). However, in cases of scapho-lunate nonunion ('SLAC wrist') where ligament lesions are severe, this method does not resolve the problem of ligament destabilization, which requires further treatment.