Biomechanical comparison of fixation methods on third-generation femoral composite bone models in Pauwels type 3 femoral neck fractures: Contribution of the medial buttress plate to fixation.

Objective: To compare the use of cannulated screws in an inverted triangular configuration, medial buttress plates, and the combination of these 2 fixation methods in the treatment of Pauwels type 3 femoral neck fractures.
Methods: Twenty-eight anatomical composite third-generation femoral bone models were divided into 4 groups. The control group (group 1) was formed with 7 third-generation intact bone models. The fracture model was created with a 70° cutting block to fit 21 Pauwels type 3 fracture configurations. Seven models were fixed with an isolated 3.5 mm one-third semi-tubular medial buttress plate (group 2), 7 were fixed in an inverted triangular configuration with 6.5 mm cannulated screws (group 3), and 7 were fixed using a combination of 6.5 mm cannulated screws and a medial buttress plate (group 4). Cyclic loading was applied using axial forces ranging from 60 N to 600 N and moments ranging from 0.7 Nm to 7.0 Nm for 500 cycles. Once the cyclic loading stage was completed, the loads were removed from the system, and the quasi-static loading stage was employed to determine the stiffness and failure forces of the system under both axial and torsional forces. Quasi-static tests were performed with an axial speed of 1.8 mm/min and a torsional speed of 4.5°/min. The biomechanical properties of all groups were examined in terms of axial stiffness, torsional stiffness, and maximum axial force parameters.
Results: The stiffness values of groups 1, 2, 3, and 4 were 303 ± 35.8 N/mm, 159.6 ± 25 N/mm, 232 ± 35.9 N/mm, and 366.9 ± 58 N/mm, respectively, under axial forces (P < .01); 2172.7 ± 252.1 Nmm/°, 1225.3 ± 238.6 Nmm/°, 2123 ± 359.4 Nmm/°, and 2721.85 ± 304 Nmm/°, respectively, under torsional moments (P < .01); and 2072.1 ± 256.1 N, 1379.9 ± 290.6 N, 2099.1 ± 454.2 N, and 2648.4 ± 364.6 N, respectively, under the maximum force (P < .01).
Conclusion: This study showed that in the fixation of Pauwels type 3 fractures formed on third-generation bone models, the utilization of half-thread cannulated screws in an inverted triangle configuration, along with a medial buttress plate, provided stronger fixation compared to the remaining implant groups and the control group. According to the evaluation of the parameters, the isolated application of a medial buttress plate had poorer biomechanical properties than other fixation methods.