RESUMO
PURPOSE: This biomechanical study investigates the optimal number of proximal screws for stable fixation of a 2-part proximal humerus fracture model with a locking plate. METHODS: Twenty-four proximal humerus fracture models were included in the study. An unstable 2-part fracture was created and fixed by a locking plate. Cyclic loading and load-to-failure tests were used for the following 4 groups based on the number of screws used: 4-screw, 6-screw, 7-screw, and 9-screw groups. Interfragmentary gaps were measured following cyclic loading and compared. Consequently, the load to failure, maximum displacement, stiffness, and mode of failure at failure point were compared. RESULTS: The interfragmentary gaps for the 4-screw, 6-screw, 7-screw, and 9-screw groups were significantly reduced by 0.24 ± 0.09 mm, 0.08 ± 0.06 mm, 0.05 ± 0.01 mm, and 0.03 ± 0.01 mm following 1000 cyclic loading, respectively. The loads to failure were significantly different between the groups with the 7-screw group showing the highest load to failure. The stiffness of the 7-screw group was superior compared with the 6-screw, 9-screw, and 4-screw groups. The maximum displacement before failure showed a significant difference between the comparative groups with the 4-screw group having the lowest value. The 7-screw group had the least structural failure rate (33.3%). CONCLUSION: At least 7 screws would be optimal for proximal fragment fixation of proximal humerus fractures with medial comminution to minimize secondary varus collapse or fixation failure. LEVEL OF EVIDENCE: Basic science study.
RESUMO
BACKGROUND: Significant discrepancy exists between anatomical plate designs and the anatomy of the native distal radius, which may be attributable to considerable morphometric variations in the volar aspect of the distal radius. We aimed to evaluate the degree of variability in the morphometry of the distal radius and identify factors associated with this variability. METHODS: We measured the volar surface angle (VSA) of the intermediate and lateral columns and the volar surface width (VSW) in the distal radius from three-dimensional computed tomography scans acquired from 81 cadaveric forearms. These morphometric parameters were compared between the lateral and intermediate columns, between males and females, and between Koreans and Caucasians. Caucasian morphometric data were obtained and pooled from the previous studies. The coefficient of variation was used to assess the variability of the parameters and Cohen's d to estimate the effect size of the difference between groups. RESULTS: The average VSA of the lateral column was 22° ± 6°, and that of the intermediate column was 29° ± 8° in Koreans (p < 0.001). The variability was high for both VSAs. The VSA of the intermediate column was significantly larger in males than in females (p < 0.001) and in Caucasians than in Koreans (p < 0.001). The average VSW of distal radius was 30 ± 3 mm at the watershed line, and it became narrower proximally. The VSW was significantly larger in males than in females (p < 0.001) and in Koreans than in Caucasians (p < 0.001). The effect sizes of the difference for the VSA and VSW between sexes, races and columns were medium to large. CONCLUSIONS: Considerable variability exists in the morphometry of the volar distal radius, with sex, race, and column as contributing factors. These results suggest that surgeons should carefully choose an anatomical volar locking plate with appropriate angulation characteristics for each patient to achieve patient-specific alignment of the distal radius.
