The effect of the dorsal intercarpal ligament on lunate extension after distal scaphoid excision.

PURPOSE

After a distal scaphoid excision, most wrists develop a mild form of carpal instability-nondissociative with dorsal intercalated segment instability. Substantial dysfunctional malalignment is only occasionally seen. We hypothesized that distal scaphoid excision would lead to carpal instability-nondissociative with dorsal intercalated segment instability in cadavers and that the dorsal intercarpal (DIC) ligament plays a role in preventing such complications.

METHODS

We used 10 cadaver upper extremities in this experiment. A customized jig was used to load the wrist with 98 N. Motion of the capitate and lunate was monitored using the Fastrak motion tracking system. Five specimens had a distal scaphoid excision first, followed by excision of the DIC ligament, whereas the other 5 specimens first had excision of the DIC ligament and then had a distal scaphoid excision. Rotation of the lunate and capitate was calculated as a sum of the relative motions between each intervention and was compared with its original location before intervention (control) for statistical analysis.

RESULTS

Distal scaphoid excision and subsequent DIC ligament excision both led to significant lunate extension. DIC ligament excision alone resulted in lunate flexion that was not statistically significant. After DIC ligament excision, distal scaphoid excision led to significant lunate extension. Capitate rotation was minimal in both groups, verifying that the overall wrist position did not change with loading.

CONCLUSIONS

Distal scaphoid excision leads to significant lunate extension through an imbalance in the force couple between the scaphotrapeziotrapezoidal joint and the triquetrum-hamate joint. The DIC ligament may serve as a secondary stabilizer to the lunocapitate joint and prevent further lunate extension with the wrist in neutral position.

CLINICAL RELEVANCE

The development of a clinically symptomatic carpal instability-nondissociative with dorsal intercalated segment instability with lunocapitate subluxation after distal scaphoid excision may be due to an incompetent DIC ligament.