Dynamical analysis of dislocation-associated factors in total hip replacements by hardware-in-the-loop simulation

Area of Science:

• Orthopaedic Surgery
• Biomechanics
• Biomedical Engineering

Background:

• Total hip replacement (THR) dislocation is a persistent clinical challenge.
• Previous research has limitations in understanding THR instability due to neglecting soft tissues, dynamic processes, and simplified joint mechanics.

Purpose of the Study:

• To systematically analyze the impact of implant positioning, design, and muscle function on THR instability.
• To investigate these factors under physiological loading during dynamic movements using hardware-in-the-loop (HiL) simulation.

Main Methods:

• Utilized a hardware-in-the-loop (HiL) simulation integrating a musculoskeletal multibody model with a six-axis robot.
• Emulated lower extremity biomechanics during a sit-to-stand maneuver with femoral adduction.
• Tested commercial THRs with varying head diameters (28, 36, 44 mm) and offsets (M, XL).

Main Results:

• Specific implant positions (45° cup inclination, 20° cup anteversion, 10° stem anteversion) demonstrated robustness against instability.
• Higher combined anteversion angles of the cup and stem were favorable for flexion motion.
• Larger head diameters (>36 mm) and offsets (8 mm) delayed impingement and increased resisting torques.
• Implant positioning had a greater impact on total hip stability than gluteal or muscle insufficiency.

Conclusions:

• Optimized implant positioning is crucial for enhancing total hip replacement stability.
• Larger femoral head sizes and appropriate offsets can mitigate risks of impingement and dislocation.
• The study highlights the paramount importance of surgical technique and implant selection over muscle function in preventing THR instability.