Douglas W. Van Citters

Background: Glenoid loosening is the primary cause of failure in anatomic Total Shoulder Arthroplasty (aTSA). Current ASTM standards evaluate loosening via standard orthogonal vectors using non-continuous monitoring, which offer limited insight into the temporal evolution of loosening along physiological, off-axis wear vectors. This study demonstrates the feasibility and utility of a novel video-based system for continuous monitoring of glenoid loosening under clinically relevant, off-axis wear vectors and subluxation translation (ST) distances. Methods: A custom electromechanical apparatus cyclically displaced a humeral head against 18 cemented 5-peg glenoids over 150,000 cycles across three orientations: superior-inferior (SI), anterior–posterior (AP), and 45-degree angle (45°), and two ST distances (75% and 105% of maximum translation). Each condition had n = 3 glenoids. A video-based motion tracking system continuously monitored micromotion and relative motion at the bone-implant interface against a 150 µm loosening threshold. Differences were analyzed using Kruskal–Wallis tests and non-parametric effect sizes (η²). Results: The system successfully captured non-linear loosening behaviors. Final relative motion at 105% ST was SI (2476.0 ± 1882.3 µm), 45° (239.6 ± 51.9 µm), and AP (265.2 ± 99.7 µm), with all groups exceeding the 150 µm threshold. At 75% ST, relative motion was SI (175.7 ± 140.7 µm), 45° (24.3 ± 69.3 µm), and AP (33.1 ± 18.4 µm). While Kruskal–Wallis tests showed non-significant differences across orientations due to small sample sizes (p = 0.11), large effect sizes (η² = 0.393) indicated practically meaningful differences, with SI showing the greatest motion. Conclusions: This study demonstrated the feasibility of a novel method of using a video-based system for the continuous monitoring of glenoid loosening under varying mechanical conditions, provides a comprehensive platform for evaluating the biomechanics of implant loosening, and suggests that testing along intermediate axes and at higher subluxation levels may be necessary to accurately predict in vivo performance.

Hemiarthroplasty addresses joint damage confined to one side, preserving native cartilage and bone, but accelerated degeneration of the opposing cartilage can compromise outcomes. This systematic review should clarify whether coefficient of friction (COF) reliably predicts cartilage wear when evaluating hemiarthroplasty bearing materials (HBMs). Thirty in vitro studies reporting both outcomes were identified. Data were extracted on COF, wear, and testing parameters, and wear was standardized using a 0–4 rubric to enable cross-study comparison. Three analytical approaches were applied: linear model fits, Pearson’s correlations, and predictive modeling. Reported COFs increased significantly with testing time, while contact stress and sliding velocity showed variable associations with COF. Predictive models for cobalt–chromium (CoCr), the most studied HBM, showed moderate fit, suggesting that mechanical parameters explain only part of COF variability. For wear, linear models showed poor fit with COF, but correlations indicated positive associations with contact stress. Inconsistent effects of velocity and distance were found. Predictive models explained little variability. Together, these findings suggest that outcomes are strongly influenced by testing conditions, lubricants, and HBM selection, and COF alone is an unreliable predictor of cartilage wear in an experimental setting.

Electrically conductive composites of ultra-high molecular weight polyethylene (UHMWPE) may be of interest as strain sensors for event detection in high-strain scenarios, with potential applications in ballistics or orthopedics. In this study, geometric deformations of electrically conductive composites of UHMWPE were quantified for large plastic strains via physical measurements. These measurements were compared to neat (non-composite) control materials, and to geometrical behaviors predicted under volume conservation assumptions. This study found that material geometry remained close to that predicted by volume conservation at low-to-moderate plastic strains, with differences exceeding 5% only above 100% nominal strain. Materials with higher filler loading experienced a greater increase in measured volume than neat controls, particularly at higher strains. The results suggest that this difference could be due in part to volumetric opening in the composite materials with high filler loading. Finally, necking behavior was observed and quantified in this study, presenting another effect that should be taken into account for future work characterizing the electrical behavior of these materials under large plastic deformations. The results of this study thus lay the foundation for further characterization of these electrically-conductive composites, and to determine their intrinsic electrical properties as a function of strain in particular.

Static and dynamic foot function can be evaluated using easy-to-implement, low-cost measurements like arch height index (AHI) and navicular drop (ND). Connections between AHI/ND and lower-extremity kinematics/kinetics have largely focused on gait. Some studies exist evaluating basketball players; however, these predominantly focus on men. To our knowledge, few studies evaluate female athletes, and none have investigated connections between AHI/ND and lower-extremity biomechanics in elite female basketball players. Thus, we conducted an IRB-approved observational investigation of 10 female, National Collegiate Athletic Association (NCAA) Division 1 basketball players, evaluating connections between AHI/ND and lower-extremity biomechanics during basketball activities. Participants completed one visit wherein bilateral AHI/ND measurements and kinematics/kinetics were captured via optical motion capture and force-instrumented treadmill during basketball activities (walking, running, vertical/horizontal jumping, side shuffles, 45° cuts). No connections existed between the AHI and any variable during any task. Contrastingly, ND was statistically significantly correlated with medial/lateral force maximum and range during left cutting. This implies that individuals with stiffer feet produced more side-to-side force than those with more foot mobility during cutting. This is the first report connecting ND to lower-extremity biomechanics in elite, female basketball players. This could inform novel interventions and technologies to improve frontal kinematics/kinetics.

Despite their emerging use, the in vivo behaviour of dual-mobility (DM) total hip replacements (THRs) is not well understood. Therefore, the purpose of this study was to assess the articulating surfaces of 20 early-retrieved DM polyethylene liners (mean length of implantation 20.0 ± 18.8 months) for damage to improve the current understanding of their in vivo functional mechanisms. The internal and external surfaces of each liner were visually and geometrically assessed, and the material composition of embedded debris particles were further characterized. Scratching and pitting were the most common modes of damage identified on either surface, and a high incidence of burnishing (50%) and embedded debris (65%) were observed on the internal and external surfaces, respectively. Embedded debris particles were commonly titanium- or iron-based, although other materials such as cobalt-chrome and tantalum were also identified. The geometric assessment demonstrated highly variable damage patterns across the liners, with the internal surfaces commonly presenting with crescent-shaped, circumferential, or circular regions of penetration whilst the external surfaces commonly presented with regions of deep pitting or gouging. This study demonstrates that DM-THRs primarily articulate at the head/liner junction, and that polyethylene liners are capable of rotating about the femoral neck axis, although the extent of this may be limited in some cases. Additionally, this study suggests that intra-prosthetic dislocation and edge loading may remain pertinent failure mechanisms of DM implants despite the advent of highly crosslinked polyethylene and design features, thus highlighting the need for enhanced monitoring of these devices.

Background: Modern literature has brought into question if wear of tibial inserts made from conventional or highly-crosslinked polyethylene (HXL PE) is still a factor limiting longevity of total knee arthroplasty (TKA) in the mid- to long-term. It is the objective of this study to determine: 1) most common causes of mid- to long-term TKA failure, 2) the prevalence of delamination, and 3) the medial/lateral linear wear rates of conventional and HXL PE tibial inserts retrieved in the mid- to long-term. Methods: A tibial insert retrieval cohort of 107 inserts (79 conventional, 28 HXL PE) with a minimum time in situ of 6.5 years (mean 11.7±4) was studied. Failure causes were determined from chart-review, delamination presence was assessed microscopically, and medial/lateral linear wear was determined by minimal thickness changes measured with a dial-indicator. Results: The most common mid-to long-term etiologies for failure were instability (44.9%), PE wear 15%), aseptic loosening (14%) and infection (13.1%). Delamination occurred in 70% of inserts (72.1% conventional, 64.3% HXLPE). Gross material loss due to delamination appeared to be the underlying reason for at least 33.3% of cases exhibiting instability. Of the cases removed for infection, 75% exhibited no histopathological hallmarks of acute infection. The medial/lateral wear rates were 0.054/0.051 (conventional) and 0.014/0.011 (HXL) mm/year, respectively. Conclusions: Polyethylene wear still appears to be a major primary and secondary cause for TKA revision in the mid- to long-term. Wear may manifest as destabilizing delamination or as continuous release of fine wear particles potentially resulting in inflammatory responses and subsequent failure.

To develop a computational model of microwave ablation (MWA) with a thermal accelerant gel and apply the model toward interpreting experimental observations in ex vivo bovine and in vivo porcine liver. A 3D coupled electromagnetic-heat transfer model was implemented to characterize thermal profiles within ex vivo bovine and in vivo porcine liver tissue during MWA with the HeatSYNC thermal accelerant. Measured temperature dependent dielectric and thermal properties of the HeatSYNC gel were applied within the model. Simulated extents of MWA zones and transient temperature profiles were compared against experimental measurements in ex vivo bovine liver. Model predictions of thermal profiles under in vivo conditions in porcine liver were used to analyze thermal ablations observed in prior experiments in porcine liver in vivo. Measured electrical conductivity of the HeatSYNC gel was ∼83% higher compared to liver at room temperature, with positive linear temperature dependency, indicating increased microwave absorption within HeatSYNC gel compared to tissue. In ex vivo bovine liver, model predicted ablation zone extents of (31.5 × 36) mm with the HeatSYNC, compared to (32.9 ± 2.6 × 40.2 ± 2.3) mm in experiments (volume differences 4 ± 4.1 cm³). Computational models under in vivo conditions in porcine liver suggest approximating the HeatSYNC gel spreading within liver tissue during ablations as a plausible explanation for larger ablation zones observed in prior in vivo studies. Computational models of MWA with thermal accelerants provide insight into the impact of accelerant on MWA, and with further development, could predict ablations with a variety of gel injection sites.

End-stage hip joint osteoarthritis treatment, known as total hip arthroplasty (THA), improves satisfaction, life quality, and activities of daily living (ADL) function. Postoperatively, evaluating how patients move (i.e., their kinematics/kinetics) during ADL often requires visits to clinics or specialized biomechanics laboratories. Prior work in our lab and others have leveraged wearables and machine learning approaches such as artificial neural networks (ANNs) to quantify hip angles/moments during simple ADL such as walking. Although level-ground ambulation is necessary for patient satisfaction and post-THA function, other tasks such as stair ascent may be more critical for improvement. This study utilized wearable sensors/ANNs to quantify sagittal/frontal plane angles and moments of the hip joint during stair ascent from 17 healthy subjects. Shin/thigh-mounted inertial measurement units and force insole data were inputted to an ANN (2 hidden layers, 10 total nodes). These results were compared to gold-standard optical motion capture and force-measuring insoles. The wearable-ANN approach performed well, achieving rRMSE = 17.7% and R² = 0.77 (sagittal angle/moment: rRMSE = 17.7 ± 1.2%/14.1 ± 0.80%, R² = 0.80 ± 0.02/0.77 ± 0.02; frontal angle/moment: rRMSE = 26.4 ± 1.4%/12.7 ± 1.1%, R² = 0.59 ± 0.02/0.93 ± 0.01). While we only evaluated healthy subjects herein, this approach is simple and human-centered and could provide portable technology for quantifying patient hip biomechanics in future investigations.

Joint arthroplasty, specifically total knee arthroplasty (TKA) and total hip arthroplasty (THA), are two of the highest value surgical procedures. Over the last several decades, the materials utilized in these surgeries have improved and increased device longevity. However, with an increased incidence of TKA and THA surgeries in younger patients, it is crucial to make these materials more durable. The addition of nanoparticles is one technology that is being explored for this purpose. This review focuses on the addition of nanoparticles to the various parts of arthroplasty surgery comprising of the metallic, ceramic, or polyethylene components along with the bone cement used for fixation. Carbon additives proved to be the most widely studied, and could potentially reduce stress shielding, improve wear, and enhance the biocompatibility of arthroplasty implants.

Ultra-High Molecular Weight Polyethylene (UHMWPE) is widely used as a bearing surface in total and partial joint arthroplasty. In addition to medical applicatio