Effect of head size and rotation on taper corrosion in a hip simulator

Aims This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads. Methods In all, six 28 mm and six 36 mm titanium stem-cobalt chrome head pairs with polyethylene sockets were tested in a novel instrumented hip simulator. Samples were tested using simulated gait data with incremental increasing loads to determine corrosion onset load and electrochemical activity. Half of each head size group were then cycled with simulated gait and the other half with gait compression only. Damage was measured by area and maximum linear wear depth. Results Overall, 36 mm heads had lower corrosion onset load (p = 0.009) and change in open circuit potential (OCP) during simulated gait with (p = 0.006) and without joint movement (p = 0.004). Discontinuing gait’s joint movement decreased corrosion currents (p = 0.042); however, wear testing showed no significant effect of joint movement on taper damage. In addition, 36 mm heads had greater corrosion area (p = 0.050), but no significant difference was found for maximum linear wear depth (p = 0.155). Conclusion Larger heads are more susceptible to taper corrosion; however, not due to frictional torque as hypothesized. An alternative hypothesis of taper flexural rigidity differential is proposed. Further studies are necessary to investigate the clinical significance and underlying mechanism of this finding. Cite this article: Bone Jt Open 2021;2(11):1004–1016.

Validation of a novel hip arthroscopy simulator: establishing construct validity

Hip arthroscopy (HA) is technically demanding and associated with a prolonged learning curve. Recently, arthroscopic simulators have been developed to anatomically model various joints including the knee, shoulder and hip. The purpose of this study is to validate a novel HA simulator. Twenty trainees and one sports medicine fellowship-trained orthopaedic surgeon at a single academic institution were recruited to perform a diagnostic HA procedure using the VirtaMed ArthroS hip simulator. Trainee characteristics, including level of training, general arthroscopy experience and hip specific arthroscopy experience, were gathered via questionnaire. For the purpose of this study, participants were categorized as novice (<25), intermediate (25–74) or experienced (≥75) based on the number of prior arthroscopies performed. Various performance metrics, including composite score, time and camera path length were recorded for each attempt. Metrics were analyzed categorically using ANOVA tests with significance set to P < 0.05. Composite performance score in the novice cohort was 114.5 compared with 146.4 and 151.5 in the intermediate and experienced cohorts (P = 0.0019), respectively. Novice arthroscopists performed the simulated diagnostic arthroscopy procedure in an average time of 321 s compared with 202 s and 181 s in the intermediate and experienced cohorts (P < 0.002), respectively. Cartilage damage and simulator safety score did not differ significantly between groups (P = 0.775). Simulator composite score and procedure time showed strong correlation with year of training (r = 0.65 and −0.70, respectively) and number of arthroscopies performed (r = 0.65 and −0.72). The ArthroS hip simulator shows good construct validity and performance correlates highly with total number of arthroscopic cases reported during training.

Evaluation of Aerosol Electrospray Analysis of Metal-on-Metal Wear Particles from Simulated Total Joint Replacement

Wear is a common cause for aseptic loosening in artificial joints. The purpose of this study was to develop an automated diagnostical method for identification of the number and size distribution of wear debris. For this purpose, metal debris samples were extracted from a hip simulator and then analyzed by the electrospray method combined with a differential mobility analyzer, allowing particle detection ranging from several nanometers up to 1 µm. Wear particles were identified with a characteristic peak at 15 nm. The electrospray setup was successfully used and validated for the first time to characterize wear debris from simulated total joint replacement. The advantages of this diagnostic method are its time- and financial efficiency and its suitability for testing of different materials.

The Influence of Kinematic Conditions and Variations in Component Positioning on the Severity of Edge Loading and Wear of Ceramic-on-Ceramic Hip Bearings

Dynamic separation and direct edge loading of hip replacement bearings can be caused by many factors, including implant positioning, implant design, changes in device over time, surgical variations and patient variations. Such dynamic separation and direct edge loading can lead to increased wear. Different input kinematic conditions have been used for experimental hip simulator studies to produce clinically relevant elliptical contact wear paths between the bearings during gait. The aim of this study was to investigate the influence of input kinematics (two axes of rotation simulation conditions (without abduction/adduction) and three axes of rotation simulation conditions (with abduction/adduction and different loading profiles) and variations in component positioning (different levels of medial-lateral translational mismatch at standard and steep cup inclination angles) on the occurrence, severity of edge loading, dynamic separation and wear of size 36 mm ceramic-on-ceramic hip bearings on an electromechanical hip joint simulator. The results showed that, overall, either of the two axes or three axes input profiles were equally valid in providing a suitable preclinical testing method for assessing the occurrence and severity of edge loading and wear under edge loading conditions. In terms of component positioning, as cup inclination and medial-lateral translational mismatch increased, so did dynamic separation, axial load at the rim, severity of edge loading and wear.