Biomechanical comparison of fixation techniques for transverse acetabular fractures – Single-leg stance vs. sit-to-stand loading. Issue 10 (October 2020) - Le Quang, Huy
Highlights: Biomechanical testing aims at mimicking physiological loads in a laboratory environment using predefined loading protocols. Although sit-to-stand (STS) motion results in higher peak pressures of the hip joint, single-leg stance (SLS) loading is commonly used to evaluate acetabular fracture fixation techniques. We directly compared the SLS and STS loading protocol for five transverse acetabular fracture fixation techniques (AFFT). SLS loading overestimates the strength of AFFT. STS loading appeared be more appropriate to provide clinically relevant biomechanical data. Single column plate fixation is inferior while single plate plus column screw fixation is comparable to both column plate fixation. Abstract: Objectives: To biomechanically compare five different fixation techniques for transverse acetabular fractures using both the single-leg stance (SLS) and the sit-to-stand (STS) loading protocols and to directly compare fracture gap motion (FGM) and relative interfragmentary rotation (RIFR). Methods: Transtectal transverse acetabular fractures were created on fourth-generation composite hemipelves in a reproducible manner. Five different fixation techniques were biomechanically assessed using both an SLS and STS loading protocol: anterior plate (AP) only, posterior plate (PP) only, anterior plate plus posterior column screw (AP+PCS), posterior plate plus anterior column screw (PP+ACS) and anterior plus posterior plate (AP+PP). After preconditioning, the specimens were loaded from 50 to 750 N with a ramp of 100 N/s. FGM and RIFR under loads of 750 N were measured using an optical 3D measurement system. Results: In the three groups of fixation techniques addressing both columns, STS loading resulted in higher mean FGM and in RIFR than SLS loading. No construct failure was observed. In the single plate groups (AP only and PP only), STS loading resulted in failure of all specimens before reaching loads of 750 N, while no failure occurred after SLS loading. No significant differences in FGM and RIFR were found between the double plate (AP+PP) and the single plate plus column screw (AP+PCS and PP+ACS) techniques. Conclusion: SLS loading appeared to overestimate the strength of acetabular fracture fixation constructs and STS loading may be more appropriate to provide clinically relevant biomechanical data. Internal fixation of a single column might not provide adequate stability for transverse fractures, while strength of single plate plus column screw fixation and double plate fixation was comparable.