Imageless computer assistance to orientate the cup of total hip arthroplasties: a new system based on joint kinematics

Purpose of the study Most imageless navigation systems for computer-assisted (CAS) total hip arthroplasty (THA) aim at orientating the cup with regard to the anterior pelvic plane (APP). However, these systems have some limitations: 1) the adequate position is not well defined to prevent impingement and dislocation; 2) dynamic variation of the APP according to activities (sitting, climbing stairs, etc.) are not integrated in determining the adequate orientation; 3) intraoperative assessment of the APP is not reliable with conventional tools, requiring ultrasound or two-stage identification. To address these issues, we developed an imageless CAS system without using APP, based on a kinematic approach of the hip joint. This system does not use the APP as the reference plane to orient the cup. The systemhelps the surgeon to orient the cup in relation to the cone describing the hip joint range of motion. The purpose of this study was to detail the technique and to analyze preliminary results.