Do component position and muscle strength affect the cup-head translation during gait after total hip arthroplasty?

Introduction: This study examined whether the component position or muscle strength affects the cup-head translation under in vivo weight-bearing conditions after total hip arthroplasty (THA). We hypothesized that there was a correlation between the hip offset or abductor strength and cup-head translation during gait. Materials and methods: We prospectively evaluated 31 patients undergoing unilateral cementless primary THA. The cup height, cup/stem offset, and limb length discrepancy were measured on anterior–posterior bilateral hip radiographic images. The isometric muscle strength of the lower limbs was quantified using a handheld dynamometer. Continuous radiographic images were recorded during gait, and cup-head translation was analysed using a computer-assisted method. Results: The average cup height, cup/stem offset, and limb length discrepancy were − 3.8 ± 5.1 mm, 1.2 ± 5.2 mm/− 0.7 ± 7.7 mm, and − 2.1 ± 5.2 mm, respectively. The average hip abductor/flexor and knee extensor strength were 86% ± 18%/85% ± 17% and 88% ± 17% of the contralateral healthy hip, respectively. The average cup-head translation during swing phase of gait was − 0.003 ± 0.31 mm. Multiple regression analyses found no significant independent predictors of cup-head translation (p > 0.05). Conclusions: The component position or muscle strength did not significantly influence cup-head translation during gait after well-positioned primary THA.