Functional outcomes differ between direct lateral and posterior surgical approaches in total hip arthroplasty during higher demanding activities of daily living

Abstract Background: This study investigated the effect of posterior and direct lateral (modified Hardinge) approach total hip arthroplasty on post-operative hip function compared to healthy, control participants. This study aimed to use a combination of motion analysis, strength measurements and imaging to investigate the effect of surgical approach on post-operative hip function in posterior approach and direct lateral approach cases.Methods: Twenty-eight total hip arthroplasty patients (15 direct lateral approach; 13 posterior approach) and 11 control participants underwent motion capture analysis at two walking speeds (normal and fast walking) and whilst standing from a seated position; hip joint strength and patient reported outcomes were also obtained. Muscle cross-sectional area was measured in a sub-set (N=5) using a novel magnetic resonance imaging sequence incorporating encoding for metal artefact correction.Results: The posterior approach group tended not to achieve full hip extension post-surgically, whereas the direct lateral approach patients tended to extend the hip during the fast walk, similar to control participants. The posterior approach group were weaker in all muscle groups excluding hip abductors, compared to the direct lateral approach patients and control group. In both surgical groups the muscle cross sectional area was reduced in all muscles disrupted during surgery, compared to the contralateral limb. Both surgical groups’ perceived hip function and physical health to be superior compared to the control group.Conclusions: Our findings suggest during sit to stand and fast walking the posterior approach group were functionally poorer and demonstrated weaker hip strength compared to the direct lateral approach group. Furthermore, surgical muscle disruption in our subset of patients is still apparent up to five years post-surgery, as reflected by reduced muscle cross sectional area.