Development of a hip wear simulation rig including micro-separation

Currently, hip joint simulation is an important tool in both testing total hip prosthesis and developing new biomaterials with enhanced tribological properties. During total hip arthroplasty (THA), the ligament of the femoral head (LHF) and the cartilage of the acetabulum pelvic cup are often disrupted or degenerated and are surgically removed. Recent studies have reported that one consequence of the absence of LHF and cartilage dissection on THA patients is the micro-separation between the femoral head and the acetabulum in the artificial hip joint during normal gait. In the present work, a new hip joint simulator was developed, integrating mechanical devices and electronic control. This hip simulator provides a dynamic load close to human body conditions during walking and jogging. Also, micro-separation is included and multidirectional motions with the following amplitudes: flexion-extension (FE) ±23°, abduction-adduction (AA) ±23° and internal-external (IER) ±8°. This machine allows flexibility to use different path loads and different micro-separations amplitudes (1–4 mm) through a pneumatic muscle adapted to a springs system. Using this system is possible to measure the combined effect of micro-separation (micro-impact between the contact surfaces), multidirectional motion and the Paul load peak in a similar lubricated system, allowing more accurate replication of in vivo conditions.