The Effects of Extramedullary Reduction in Unstable Intertrochanteric Fracture: A Biomechanical Study Using Cadaver Bone

Purpose: To prevent excessive sliding and subsequent fixation failures in unstable intertrochanteric fractures with posteromedial comminution, extramedullary reduction through overlapping of the anteromedial cortices of both proximal and distal fragments as a buttress has been introduced.The purpose of this study was to compare the biomechanical properties between two reduction methodsintramedullary reduction and extramedullary reduction-in treating unstable intertrochanteric fractures with posteromedial comminution (AO/OTA classification 31-A2.2). Materials and Methods:Eight pairs of frozen human cadaveric femora were used.The femora of each pair were randomly assigned to one of two groups: the intramedullary reduction group or the extramedullary reduction group.A single axial load-destruction test was conducted after cephalomedullary nailing.Axial stiffness, maximum load to failure, and energy absorbed to failure were compared between the two groups.Moreover, the pattern of mechanical failure was identified.Results: The mean axial stiffness in the extramedullary reduction group was 27.3% higher than that in the intramedullary reduction group (422.7 N/mm vs. 332.0N/mm, p=0.017).Additionally, compared with the intramedullary reduction group, the mean maximum load to failure and mean energy absorbed to failure in the extramedullary group were 44.9% and 89.6% higher, respectively (2,848.7 N vs. 1,966.5N, p=0.012 and 27,969.9N•mm vs. 14,751.0N•mm, p=0.012, respectively).In the intramedullary reduction group, the mechanical failure patterns were all sliding and varus deformities.In the extramedullary reduction group, sliding and varus deformities after external rotation were noted in 3 specimens, sliding and varus deformities after internal rotation were noted in 3 specimens, and medial slippage was noted in 2 specimens. Conclusion:In unstable intertrochanteric fractures with posteromedial comminution, the biomechanical properties of extramedullary reduction are superior to those of intramedullary reduction.Anteromedial cortex could be the proper buttress, despite a comminuted posteromedial cortex.It could help enhance the stability of the bone-nail construct.