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Abstract
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 methods–intramedullary 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. 332.0 N/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. 1,966.5 N, p=0.012 and 27,969.9 N·mm vs. 14,751.0 N·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.
References
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Fig. 1.
Schematic drawing of fracture creation. Unstable intertrochanteric fracture with posteromedial defect including the lesser and greater trochanters (AO/OTA classification 31-A2.2); anterior (A) and posterior (B) views.
Fig. 2.
Intramedullary reduction. The anteromedial cortex of the proximal fragment is positioned inside the distal shaft fragment (anteromedial aspect of femur).
Fig. 3.
Extramedullary reduction. The anteromedial cortex of the proximal fragment is positioned outside the distal shaft fragment (anteromedial aspect of femur).
Fig. 5.
Paired graph showing differences in axial stiffness between the intramedullary (IM) reduction and extramedullary (EM) reduction groups.
Fig. 6.
Paired graph showing differences in maximum load to failure between the intramedullary (IM) reduction and extramedullary (EM) reduction groups.
Table 1.
Axial Stiffness, Maximum Load to Failure, Energy Absorbed to Failure, and Axial Displacement for the Intramedullary Reduction and Extramedullary Reduction Groups
Table 2.
Mechanical Failure Patterns for the Intramedullary Reduction and Extramedullary Reduction Groups
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