Patients with scapholunate interosseous ligament (SLIL) injury often report pain with loading in wrist extension, however the etiology of pain in this position is poorly understood. While it is known that without an intact SLIL and secondary stabilizers, dissociation of the scaphoid and lunate results in scaphoid rotatory subluxation, dorsal intercalated segment instability (DISI), and eventually dorsal scaphoid translation (DST), there is limited understanding of carpal pathophysiology in weight-bearing (WB) conditions. The purpose of this study was to evaluate how WB affects carpal bone position in healthy and SLIL-injured wrists using weight-bearing computed tomography (WBCT). Ten healthy controls and 10 participants with arthroscopy (Geisler III or IV) or magnetic resonance imaging (MRI) proven SLIL injury underwent WBCT imaging in 3 positions: 1) non-weight bearing (NWB) neutral; 2) WB push-up bar (WBPUB); and 3) WB in wrist extension (WBE) (Figure 1). Radiographic parameters including scapholunate angle (SLA), radiolunate angle (RLA), radioscaphoid angle (RSA), scapholunate interval (SLI), dorsal scaphoid translation (DST), and capitate-radius index (CRI) were measured by a senior resident and reviewed by consensus by three fellowship-trained hand surgeons. Measurements were compared between positions and groups. Outcome measurements were analyzed in mixed-effects repeated measures ANOVA models, except for DST which we anticipated would be zero in the healthy group, was analyzed using Wilcoxon signed-rank tests. Statistical significance was assessed at a=0.05 significance level. All p-values were two-tailed, and 95% confidence intervals were computed. WB decreased SLA in both healthy and SLIL injury and eliminated the difference between groups (healthy: 63° NWB to 48° WBPUB and 52° WBE, SLIL: 88° NWB to 54° WBPUB and 55° WBE). RLA increased in both groups from NWB to WBE (healthy: 14° to 42°, SLIL: 28° to 45°) and WBPUB to WBE (healthy: 17° to 42°, SLIL: 32° to 45°). RSA decreased in both groups from NWB to both WB positions (healthy: 64° NWB, 22° WBPUB, 11° WBE, SLIL: 48° NWB, 26° WBPUB, 23° WBE). The SLI remained static in WB in SLIL injury (3.95mm NWB, 3.97mm WBPUB, 3.67mm WBE) yet increased in healthy wrists in WBE (1.61mm NWB vs. 2.47mm WBE). WBPUB eliminated DST in SLIL (mean 2.25mm to 0mm), however, both injured and healthy wrists demonstrated some degree of DST in WBE (healthy mean 1.44mm, SLIL mean 1.93mm). Figure 2 demonstrates comparison of SLA, RLA, RSA, SLI, and CRI in all positions between groups. WB affects carpal bone position in both normal and SLIL-injured wrists. This study demonstrates restricted motion of the scaphoid and lunate in weight-bearing as well as reduction of the scaphoid into the scaphoid facet in WBPUB. These findings may explain why SLIL-injured patients can often WB pain-free in neutral position but not in forced extension. Continued WBCT research will contribute to improved diagnostic measures and surgical decision making for clinical conditions affected by load application in the hand and wrist. For any figures or tables, please contact the authors directly.
Ritchie et al. (Wed,) studied this question.