Loading of the index metacarpal after trapezial and partial versus complete trapezoid resection

To examine the effects of partial or complete trapezoidectomy in conjunction with trapezium resection on proximal migration of the index metacarpal during axial loading.

Five specimens from below the elbow were obtained from fresh-frozen cadavers. A customized vise was used to position the wrist in 20 degrees extension and 5 degrees ulnar deviation, simulating a power grip. The index metacarpal was instrumented to allow axial loading at 125 N and 250 N. Specimens were tested under 4 experimental conditions: (1) in the intact state, (2) after trapezial resection, (3) after partial trapezoid resection, and (4) after complete trapezoid resection. Specimens were tested 5 times under each experimental condition, displacement was measured with a linear variable differential transformer, and stiffness was calculated.

There was no difference in stiffness between the different treatments at either 125 N or 250 N. Displacement was not significantly different between treatments for loads of 125 N. For loads of 250 N the displacement was approximately 1 mm greater with complete trapezoid resection than with any of the other treatment conditions. Displacement did not differ significantly between the other 3 treatments.

The addition of a partial trapezoid resection performed at the time of trapezial resection does not affect proximal migration of the second metacarpal. When a complete trapezoidectomy is performed at the time of trapezial excision, however, the loading characteristics of the index metacarpal do change statistically significantly, although the magnitude of that change is only approximately 1 mm. Further testing will be necessary to elucidate the biomechanical effects of a partial trapezoid resection in conjunction with a trapezial resection on the second metacarpal in other planes.