Flexion following hip resurfacing and factors that influence it.
Grammatopoulos G., Philpott A., Reilly K., Pandit H., Barker K., Murray DW., Gill HS.
Flexion following arthroplasty of the hip is important for activities of daily living. Studies have highlighted a possible reduction in flexion following Metal-on-Metal Hip Resurfacing Arthroplasty (MoMHRA) but failed to account for inter-subject variability and the possible etiology for this reduction. This in vivo study aims to determine whether flexion is restored following MoMHRA and identify factors that influence it. Charnley Class A patients (n=112) that underwent MoMHRA were reviewed in a dedicated clinic assessing flexion (resurfaced and contra-lateral hips) and outcome. The difference in flexion between both hips was defined as flexion deficit (δflexion). Various patient (age, gender, BMI) and surgical (component orientation, size, head-neck-ratio, offset) factors were examined in terms of their effect on δflexion. MoMHRA-hips had significantly reduced flexion as compared to the native hips. This flexion-deficit correlated with contra-lateral maximum flexion, component size, head-neck-ratio and component orientation. The findings demonstrate that flexion following MoMHRA is strongly correlated to but is reduced in comparison to the native, disease-free, hip flexion. Surgical practice can minimise flexion-deficit and optimise function.