In Vitro Hip Biomechanical Positioning Device Integrated with Clinical Imaging

While in vitro hip biomechanics are well-studied, the lack of radiolucent testing platforms makes it difficult to validate joint mechanics at specified positions against gold-standard clinical imaging without introducing metal artifacts. We developed a low-cost, non-ferrous, and radiolucent testing fixture designed to bridge this gap by aligning benchtop loading with International Society of Biomechanics (ISB) recommendations. The testing device and a dedicated drill guide were 3D printed from tough polylactic acid (PLA), enabling controlled flexion-extension and internal-external rotation (IR-ER) with a mountable torque meter to quantify rotational joint loading. To assess reliability, twenty cadaveric hips were mounted onto the fixture and imaged using computed tomography (CT) across various joint positions. The fixture demonstrated high accuracy, with mean positioning errors of 1.8 ± 1.4 % in flexion-extension and 7.3 ± 3.2 % in IR-ER confirmed by CT-based measurements. Intraclass correlation coefficients (ICC) indicated excellent reliability between image-based and device measurements (ICC rotation = 0.98; ICC flexion = 0.99) and exceptional repeatability (ICC ≥ 0.99). Bland-Altman analysis confirmed strong clinical agreement across the range of testing. This imaging-compatible device provides a robust, standardized platform for hip biomechanics, facilitating the quantitative evaluation of joint stability and surgical interventions. The CAD models are provided as supplementary material to facilitate fabrication and setup elsewhere.