Introduction. Post-operative gait abnormalities are recognized following total hip arthroplasty (THA). Despite global improvement in functional outcome, gait abnormality persists for a decade or more. In this study 3-dimensional gait analysis (3DGA) was performed using a portable system with Inertial Measurement Units (IMUs) to quantify this abnormality. Methods. The gait of 55 patients with monarthrodial hip arthrosis was measured pre-operatively and at one year post-surgery. Patients with medical co-morbidity or other conditions affecting their gait were excluded. Six IMUs were aligned at the level of the anterior superior iliac spines, mid-thigh and mid-leg. Data was analysed using proprietary software. Each patient underwent a conventional THA using a posterolateral approach. 92 healthy individuals were assessed for comparison. Results. Pre-operative movement in the sagittal plane of the ipsilateral hip (mean range 20.4) and the contra-lateral non-diseased hip (35.3 degrees) was reduced compared to the control group (40.5 degrees), (P<0.001). The pre-operative movement of both knees was reduced compared with normal (P<0.001). Pelvic movement on the ipsilateral side was increased. After one year ipsilateral hip movement significantly improved (Mean range 28.9 deg SD 6.6) but did not reach normal values (P<0.001). Movement measured in the contralateral hip was further reduced with a mean difference of −5.25 degrees (95% CI −8.06 to −2.43). Knee movement on both sides increased but not to normal values (p<0.001). There was increased coronal movement bilaterally at the thigh and calf one year after surgery. Discussion and Conclusion. Gait after routine THA does not return to normal. Unilateral hip pathology causes bilateral gait abnormality affecting the entire
