Comparison of total hip arthroplasty surgical approaches by Statistical Parametric Mapping

Background: The most common surgical approaches in use for total hip arthroplasty are the lateral and posterior. When comparing these approaches in terms of gait biomechanics, studies usually rely on pre-defined discrete variables related to the events of gait cycle. However, this analysis may miss differences in other parts of the movement pattern that are not explored. We applied Statistical Parametric Mapping to compare hip kinematics between patients who underwent arthroplasty using either a lateral or posterior approach, contrasting these results with discrete variable analysis. Methods: Twenty-two participants (11 lateral, 11 posterior; age between 50 and 80 years) underwent gait analysis before, 3 weeks and 12 weeks after hip arthroplasty. One-dimensional (e.g. time-varying) trajectories and zero-dimensional (e.g. peak extension) discrete variables were used to assess differences between groups in each plane of hip movement (sagittal, frontal, and transverse). Findings: One-dimensional and zero-dimensional analyses found no significant differences between groups. Statistical Parametric Mapping revealed that both groups presented significant changes over time in hip adduction at 11-43% of the gait cycle. Zero-dimensional analysis seems to overstate sagittal plane changes over time since no such changes were found by Statistical Parametric Mapping. Interpretation: Our results agreed with previous studies suggesting that surgical approach do not affect hip kinematics at the early post-operative stage after arthroplasty. However, Statistical Parametric Mapping revealed changes in frontal plane kinematics over time that were underestimated by the zero-dimensional variables. These findings suggest hip adduction impairment up to 12 weeks after arthroplasty.