Pin Configurations for the Treatment of Scaphoid Nonunion: A Biomechanical Study.

Abstract

Kirschner wire (K-wire) fixation is one of many strategies for the treatment of scaphoid fractures. The present study investigated the strength and stiffness of convergent and parallel K-wire configurations in a cadaveric model using a simulated nonunion with a 6-mm defect. Eight pairs of cadaveric scaphoids (N = 16) were harvested. Morphological measurements were made to assess the influence of dimensional differences. A 6-mm defect was created in each specimen to replicate scaphoid nonunion. Two parallel or convergent K-wire orientations were used for fixation, and placements were confirmed with radiographic images. Biomechanical testing was conducted using an eight-degree-of-freedom servohydraulic load frame. Interfragmentary motions, measured by motion tracker flags, and the load applied were measured throughout the duration of the testing. The relative motions of the fragments were used to calculate the average cyclic motion and the stiffness of each construct. The maximum force for the convergent configuration had a median of 36.5 N, and for the parallel configuration, 16.6 N. The median stiffness of the convergent configuration was 81.6 N/mm and that of the parallel configuration was 54.1 N/mm. Scaphoid morphology measurements varied from 5% to 9% between the left and right hands of the same donor. A convergent configuration for treating scaphoid nonunion may be more stable than a parallel configuration when a bony defect and nonunion are present. A convergent K-wire configuration for treating scaphoid nonunion may be more stable than a parallel configuration.