Impact of leg length adjustment, base offset, neck length and neck cross-section variations on hip implant joints and neck mechanics

Geometrical view of the investigated Accolade hip implant model with trunnion and acetabular head-liner joint, (b) eight Accolade hip implant designs with varying offsets, leg length adjustments and neck length, and (c) Accolade hip implant with varying cross-section of neck. • This study investigates the effects of varying base offset, leg-length adjustment, neck length, and neck cross-section on head-neck and head-liner contact mechanics. • Across the designs, variations in neck geometry resulted in only minor deviations in contact stress and micromotion at the head-neck and head-liner. • Larger geometric parameters, including increased neck length, offset, or specific neck cross-sections—lead to higher penetration and implant deformation, despite minimal changes in contact stress and micromotion. • These findings highlight a critical design trade-off and a research opportunity: optimizing neck geometry to enhance mechanical performance and mitigate deformation and penetration. This study examines the influence of base offset, leg-length adjustment, neck length, and neck cross-section on hip implant joints and neck mechanics. Eleven designs (eight geometric variations and three neck cross-sections) were modelled in SolidWorks and analyzed using finite element analysis in ANSYS under walking gait cycle. Across all designs, neck geometry caused only minor variations in trunnion stress and micromotion (max 2.5–35 MPa, micromotion 3.75–4.5 µm), while head–liner stresses remained low (<5 MPa) with negligible changes. Maximum penetration at both interfaces follows the contact pressure pattern. The von Mises stress results show that Designs 1–6, and all neck cross-sections, remain below the yield strength of Ti6Al4V for all load cases, while Designs 7 and 8 exceed the yield limit at loads above 3000 N. Implant deformation increases with neck length, offset, and leg length, from 0.012 mm (Design 1) to 0.56 mm (Design 8), and the rectangular–oval cross-section showing the highest values (0.08 mm). Overall, while contact parameters are minimally affected by neck geometry, von Mises stress and deformation are strongly influenced by neck design, with Designs 1–6 and all cross-sections neck mechanically stable and Designs 7–8 unstable under higher loads.