Abstract
Background This study purposed to compare the partial- threaded cannulated screws (PTCS) and the double-threaded cannulated screws (DTCS) in vertical shear femoral neck fractures both clinically and biomechanically. Methods Clinally, the radiographs of 81 patients with Pauwels Ⅲ femoral neck fractures, including 54 fractures fixed with PTCS and 27 fractures fixed with DTCS were analyzed. Complications consist of fixation failure (nail withdrawal, obvious fracture displacement, varus deformity or femoral neck shortening), bony nonunion and avascular necrosis (AVN) were determined. Biomechanically, twenty femur synthetic bones were equally divided and made to a vertical femoral neck fracture model, then fixed with three parallel PTCSs or DTCSs respectively. All specimens were tested for axial stiffness and a maximum load to failure with a loading rate of 2 mm/min. Results Clinically , 22 fractures in the PTCS group experienced fixation failure, including 19 nail withdrawal, 18 femoral neck shortening, 14 varus deformity and 8 obvious fracture displacement; while only 5 fractures showed up with fixation failure in the DTCS group, including 3 nail withdrawal, 4 femoral neck shortening, 4 varus deformity and 1 obvious fracture displacement. Additionally, 11 fractures in the PTCS group had nonunion while only 3 in the DTCS group and 9 fractures with AVN in the PTCS group while only 2 in the DTCS group. Biomechanically, The axial stiffness of DTCS was 152.89±22.74 N/mm, greater than PTCS (134.68±26.61), moreover, the failure load in DTCS was significantly greater than PTCS (1148.11±124.80 vs 795.88±162.50). Conclusion DTCS may exert more advantages than PTCS for vertical femoral neck fractures, including stronger fixation stability, lower rate of fixation failure and nonunion.
Biomechanical analysis of two medial buttress plate fixation methods to treat Pauwels type III femoral neck fractures
