The importance of accurate cup positioning during total hip arthroplasty (THA) to minimise post- operative complications has been well defined. However it remains unclear if following navigated THA there is a relationship between the active range of movement, the inclination and anteversion of the implant, and the theoretical range of movement as measured intra-operatively using imageless navigation. Fifteen male patients undergoing primary THA using the Orthopilot (Aesculap AG, Tuttlingen, Germany) imageless navigation system were recruited. The Orthopilot system flexion value was recorded. Three months post-THA patients underwent 3D biomechanical analysis (Vicon Motion Systems, Oxford, UK) during which patients performed a standing active hip flexion movement and a sitting task. Inclination and anteversion calculated according to Pradhan’s formula were taken from post-operative radiographs. There was no observed correlation with the theoretical hip flexion and the standing peak active or sitting peak hip flexion values in this series. However, Orthopilot flexion considers only the interaction of the implant components and not the soft tissues surrounding the hip joint which may limit clinical flexion. There does not appear to be any relationship between the inclination and anteversion angles and the range of movement observed post- operatively during a standing active hip flexion task and sitting task. It was observed that peak active hip flexion between the operated and non-operated limbs was not significantly different at three months, which indicates a good level of symmetry at this time point.
Quantitative and individualized assessment of the learning curve in preoperative planning of the acetabular cup size in primary total hip arthroplasty