Hybrid anteroposterior–posteroanterior headless screw fixation improves biomechanical stability of capitellar coronal shear fractures: a paired cadaveric study

To compare the biomechanical performance of a hybrid headless-screw construct (one anteroposterior [AP] and one posteroanterior [PA]) with a traditional PA-only (two PA screws) construct in a paired cadaveric model of capitellar coronal-shear fractures. Seven pairs of fresh-frozen cadaveric humeri were used. Simulated Bryan–Morrey type I coronal-shear capitellar fractures were created and fixed with Acutrak cannulated headless compression screws. Each pair received either hybrid fixation (one AP and one PA screw) or two PA screws. Constructs underwent cyclic loading followed by load-to-failure testing. Force and displacement were sampled at 100 Hz during selected cycles (cycles 1–10, 100–110 and 491–500). Data were analyzed using paired statistical tests; a p-value < 0.05 was considered significant. Hybrid fixation showed greater initial stiffness than PA-only (277.8 ± 64.6 vs 166.6 ± 51.0 N/mm; p = 0.036). Although stiffness remained higher with hybrid after further cycling, later differences were not statistically significant. Load-to-failure was higher with hybrid (253.7 ± 75.8 vs 151.6 ± 29.9 N; p = 0.014). Failure displacement did not differ (1.21 ± 0.43 vs 1.06 ± 0.35 mm; p = 0.42). Overall, hybrid constructs demonstrated ≈67% greater initial stiffness and ≈67% greater failure load versus PA-only. In this paired cadaveric model of capitellar shear fractures, a hybrid AP–PA screw orientation improved early construct stiffness and increased failure tolerance compared with two PA screws. These biomechanical advantages may support early supervised motion while maintaining construct integrity, however, clinical correlation is required. IV (cadaveric biomechanical study).