The impact of hip geometrical parameters on muscle and joint biomechanics during normal gait

BACKGROUND: Effective preoperative planning is essential for reducing pain, fatigue, and joint damage following total hip arthroplasty (THA). This study investigates the effects of key geometric parameters - neck-shaft angle (NSA), anteversion angle (AVA), and hip offset (HO) - on muscle mechanics and joint reaction forces during normal walking gait using musculoskeletal simulation. METHODS: A MATLAB-based HO tool combined with a femoral torsion tool was used to generate 45 OpenSim models with systematic variations in NSA, AVA, and HO. All models were evaluated using identical gait kinematics and ground reaction forces to isolate the biomechanical influence of geometric changes. RESULTS: Increases in femoral neck length and HO substantially affect muscle lever arms and joint reaction forces, with peak hip and knee joint loading and associated muscle mechanics increasing by up to approximately 2.5-fold compared to the reference model. Changes in NSA, AVA, and HO significantly altered muscle moment arms, muscle activations, and muscle forces, particularly in hip abductors and flexors. Simultaneous variation of all 3 parameters produced markedly larger effects than isolated changes. CONCLUSIONS: This study highlights the importance of considering prosthesis geometry and implantation parameters during THA planning and biomechanical modelling to optimise gait mechanics and reduce postoperative joint loading.