Treatment of Scapholunate Dissociation With Palmaris Longus Tendon Graft: A Biomechanical Study

Posttraumatic instability of the wrist, resulting in scapholunate dissociation, is a common injury pattern in the wrist [2]. Mayfield et al. [1] described instability progressing sequentially from a scapholunate interosseous ligament (SLIL) tear to complete ligament failure around the lunate, resulting in lunate dislocation. Linscheid et al. [4] also demonstrated that excision of the dorsal radiocarpal and scapholunate interosseous ligament produced rotary subluxation of the scaphoid. Further sectioning of the volar radiocarpal ligament increased the rotary subluxation. If scapholunate dissociation is left untreated, it may result in degenerative arthritis of the wrist. A survey by Watson and Brenner [3] found that degenerative arthritis was associated with scapholunate advance collapse (SLAC) in 55% of the cases. Viegas et al. [5] have shown that destabilizing the lunate by sectioning ligaments to create a scapholunate dissociation increases the joint contact pressure on the scaphoid and decreases the contact surface area of the scaphoid. There is no single treatment for scapholunate dissociation. Current repair techniques consist of ligament repair, tendon grafting, limited intercarpal arthrodesis, and proximal row carpectomy. Each of the repair techniques has certain advantages. However, none restores the normal motion and stability of the uninjured wrist. For acute scapholunate dissociation without joint arthrosis, most authors advocate direct repair of the SLIL with temporary Kirschner (K) wire fixation [8,9]. Dorsal capsulodesis can augment a direct repair [6] or the capsulodesis can be performed alone [7]. For chronic scapholunate dissociation with arthrosis of the radioscaphoid fossa, the treatment is limited to SLIL reconstruction, a fusion of the capitate, lunate, triquetrum, and hamate with scaphoid excision [10], or proximal row carpectomy [11,15]. The treatment of chronic scapholunate dissociation without degenerative changes of the periscapholunate joints is controversial. Watson et al. [12], Rotman et al. [13], and Pisano et al. [14] have had clinical success with various intercarpal arthrodeses. However, Kleinman and Carroll [17] have noted a high rate of complication with scaphotrapeziotrapezoid (STT) intercarpal fusions. In a cadaveric study of STT fusion, Viegas et al. [18] noted increase contact pressure of the radioscaphoid fossa, which may eventually lead to degenerative arthritis over time. Ligament reconstructions using local tendon weave have been reported by Palmer et al. [8], Linscheid and Dobyns [22], Brunelli and Brunelli [23], and Almquist et al. [19], with good results. However, this treatment has been criticized for being technically difficult [8,19,20] and for having the potential problem of tendon loosening [21]. At our institution, the senior author has been performing a scapholunate ligament reconstruction using the palmaris longus tendon. This is performed through a dorsal and volar approach and the ligament is passed through drill holes in the anteroposterior plane of the scaphoid and the lunate to reconstruct the ligament. This has the advantage of being a simpler operation than the four-bone tendon weave performed by Almquist et al. [19] because only the scaphoid and lunate are included in the reconstruction. Biomechanical studies by Augsburger et al. [21] have shown that a four-bone tendon weave restores the radiocarpal contact characteristic similar to that of the intact wrist versus that of the STT fusion using pressure-sensitive film. Our study is based on the hypothesis that the scapholunate ligament reconstruction will improve the radiocarpal joint forces to that of the intact wrist.