Optimal screw orientation for fixation of coronal shear fractures: a biomechanical comparison

Background: Coronal shear fractures of the capitellum are rare injuries which can be challenging to treat. The aim of this study was to compare the biomechanical properties of different internal screw fixation techniques for Dubberley type IA fractures of the capitellum. Methods: In this biomechanical study, Dubberley type IA fractures of the capitellum were created in 30 human fresh-frozen humeri. The specimens were then divided into 3 groups: fixation was either performed with 3 × 3.0 mm headless cannulated compression screws (HCCSs) in anteroposterior (AP) orientation (AP group), 3 × 3.0 mm HCCSs in posteroanterior (PA) orientation (PA group) or with 2 × 3.0 mm HCCSs in PA orientation and 1 × 3.0 mm HCCS in lateral orientation (LAT) group. Displacement under cyclic loading and ultimate load-to-failure were evaluated in all specimens. Results: There was no significant difference in fragment displacement after 2000 cycles between AP and PA groups (0.8 ± 0.5 mm vs. 0.8 ± 0.6 mm; P = .987) or PA and LAT groups (0.8 ± 0.6 mm vs. 0.8 ± 0.3 mm; P = .966). LAT group showed the highest load-to-failure (548 ± 250 N) without reaching statistically significant difference to AP group (388 ± 173 N; P = .101). There was also no significant difference between AP and PA groups (388 ± 173 N vs. 422 ± 114 N; P = .649). Conclusions: Variations in screw placement had no statistically significant influence on cyclic displacement or load-to-failure in Dubberley Type IA fractures. However, fracture fixation in 2 planes—both the coronal and the sagittal plane—by adding a screw in a lateral to medial direction may be beneficial to increase primary stability.