Preclinical testing of implants considers THR patients a homogenous group; in reality, patients are heterogeneous and previous large cohort studies have explored stratification and identified that THR patients function differently [1]. The wide- spread failure of the ASR hip highlighted the potential importance of patient characteristics [2], and a more robust pre- clinical testing procedure may have improved prediction of outcome. Therefore this study aimed to identify differences in hip contact force (HCF) in THR patients stratified by their functional ability. 133 THR patients, >12 months post-surgery, underwent 3D kinematic (Vicon, UK) and kinetic (AMTI, USA) analysis whilst walking at self-selected speed. HCF's, normalized by body weight, were computed through multibody modeling (AnyBody Technology, Denmark) during gait and a mean for each patient was calculated from three to five walking trials. Patients were stratified into three functionality groups by distribution around the mean gait speed for the full cohort of 1.1m/s. The low functioning group (LF) comprised cases with a gait speed ≤0.93 m/s (i.e. 1.1m/s ≤1SD), the mid functioning group (MF) comprised cases with a gait speed between 0.94 m/s and 1.25 m/s (cohort mean ± 1SD), while the high functioning group (HF) included cases walking ≥1.26 m/s. Differences between groups were analyzed using one- dimensional statistical parametric mapping [3]. Linear regression was used to test for significant differences across groups. The test statistic SPM{t} was evaluated at each point in the normalized time series, and a critical threshold corresponding to an error rate of α= 0.05 was calculated based on random field theory. Supra-threshold clusters with their associated p-values were then identified.Introduction
Methods
