Analysis of Three-Dimensional Anatomical Variance and Fit of the Distal Radius to Current Volar Locking Plate Designs

PURPOSE: Distal radius fractures are the most common upper-extremity fracture and are increasingly being treated surgically with precontoured volar locking plates. It is not currently known whether existing implant designs are anatomically accurate and whether this has clinical implications. The objective of this study was to determine whether anatomic alignment of the distal radius corresponds accurately to modern volar locking plate designs, including any sex-linked differences in morphology of the distal radius. It was hypothesized that the 2 plates examined would show differences in watershed line (WSL) overlap and that female specimens would have a larger overlap compared with males owing to a decrease in plate-WSL border distances. METHODS: We used 3-dimensional models of 20 cadaver arms (10 female: mean age, 88.7 ± 4.6 years [range, 82–97 years]; and 10 male: mean age, 86 ± 3.6 years [range, 81–91 years]) to create 3-dimensional computed tomography models of the distal radius. Virtual models of 2 common volar plates were created and were used to place the plate virtually onto the distal radii. Outcome measures included the volar cortical angle of the bone and plate, the definition of the WSL subsequently followed by quantitative distance and overlap measures, and percent contact between the plate and the distal radius. RESULTS: Both sexes showed an decrease (approximately 7°) in average volar cortical angle measure from medial to lateral columns that was statistically significantly smaller on the lateral column (males: 38°; females: 29°) compared with the medial column (males: 45°; females: 36°). Watershed line overlap ranged from 0% to 34.8% with statistically significant differences between sexes. Average border distance for females was 2.7 mm, compared with 3.8 mm for males. Maximum percent contact of 22.0% was observed at a 0.3-mm threshold. CONCLUSIONS: Distal radius fractures are common in elderly female patients, yet clinically available plates have important differences in WSL overlap between sexes, and with minimal contact. Female specimens had more WSL overlap than did males. This indicates the need for volar locking plates to be redesigned to factor in anatomical features of individual patients with a particular focus on sex differences. CLINICAL RELEVANCE: New plate designs should focus on providing smaller head sizes that are more accurately tailored to the natural contours of the volar distal radius. It is recommended that future studies incorporate expertise from multiple surgeons to diversify and further understand plate placement strategies.