Search Results (362)

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. Full article

Background/Objectives: Surgical repair of the rotator cuff tendons can lead to unsatisfactory results and the requirement for further surgical treatment. Development of repair techniques is limited by a lack of appropriate functional pre-clinical testing, especially over extended motion cycles. The purpose of this study was to demonstrate the efficacy of a novel shoulder simulator by assessing changes in internal muscle forces following a rotator cuff tear and double-row surgical repair. Methods: The developed shoulder simulator used motors to apply controlled movements/displacements to tendons (supraspinatus, infraspinatus, subscapularis, teres minor, anterior deltoid and middle deltoid) of a cadaveric human shoulder to produce cyclic abduction motion representative of normal shoulder function. The required displacement for each muscle was determined using a musculoskeletal model. The resultant force applied to each tendon during the cycles was measured using a compression load cell. Results: The developed simulator in this proof-of-concept study enabled the contribution of the different muscles involved in the shoulder during abduction to be assessed for the intact shoulder. The shoulder was also tested with a 50% supraspinatus tear and a double row surgical repair of the supraspinatus to assess the change in internal muscle forces. Conclusions: The study indicated that successful cyclic testing of cadaveric samples could be achieved using the simulator and changes in the internal muscle forces of the shoulder were identified following a supraspinatus tear and double-row surgical repair. Full article

Background: Injuries to the knee joint usually involve ligament or tendon structures. Most of these injuries are traumatic in origin. To better understand the structures and the associated failure mechanisms, a specific understanding of the biomechanical properties of the individual structures is necessary. Objectives: The aim of this study was to biomechanically analyze the tendon and ligament structures around the knee joint in order to acquire tissue-specific mechanical characteristics of these anatomical structures. Methods: Five knee joints (fresh frozen) from three donors were thawed over the course of three days. The respective ligaments and tendons of the knee were separated, removed and cut into a dogbone shape for uniaxial tensile tests. The specimens were clamped in the testing machine using 3D-printed specimen holders. Results: A total of 57 samples from 15 different ligaments and tendons were successfully tested. The tensile strengths were in the range of 0.67–67.99 MPa (patellar tendon vs. biceps femoris tendon) and the moduli of elasticity between 2.1 and 316.9 MPa. A range of 6.2–47.2% was determined for the failure strains. Similar fluctuation ranges were also found in intra-individual comparisons. Conclusions: The results show a clear tissue-specific variation in the strength and elastic modulus. Full article

Background/Objectives: Fracture of ceramic femoral heads in total hip arthroplasty is a rare but catastrophic complication requiring urgent revision surgery. Most finite element studies are limited to static loading and do not capture dynamic behavior under impact conditions from stumbling or falling. The objective was to determine impact fracture thresholds of alumina (Al₂O₃) and yttria-stabilized zirconia (ZrO₂, Y-TZP) femoral heads using explicit dynamic finite element analysis. Methods: A parametric explicit dynamic analysis was performed using LS-DYNA (version 960) on an axisymmetric model of a 32 mm ceramic femoral head articulating with a ceramic liner within a Ti-6Al-4V acetabular shell. Ceramic behavior was described by the Johnson–Holmquist JH-2 damage model, validated against published impact and retrieval data. Bone stock viscoelasticity was a Winkler foundation (stiffness 50–500 N/mm, damping 0–1.0 N·ms/mm). Impact velocity ranged from 0.01 to 0.45 mm/ms, consistent with implant telemetry during stumbling. Fracture criteria were plastic strain, principal stress, and energy inflection. A sensitivity analysis of estimated ZrO₂ parameters was performed. Results: For Al₂O₃, the critical fracture velocity was 0.08 mm/ms under rigid fixation and 0.05 mm/ms with a viscoelastic foundation. The ZrO₂ head did not fracture at any velocity tested; at V ≥ 0.20 mm/ms, the neck deformed plastically while the head remained intact. Foundation stiffness and damping had no influence on outcome. Conclusions: These findings indicate inertia-dominated fracture mechanics for Al₂O₃ at realistic velocities, and suggest a material-dependent shift in critical failure location toward the taper junction for ZrO₂, a tendency warranting experimental confirmation. Full article

Background: Team sports often involve high-intensity unilateral actions that can lead to neuromuscular asymmetries, increasing injury risk and reducing performance, particularly in young female athletes. Methods: This study quantified and compared inter-limb asymmetries in single-leg countermovement jumps (slCMJ) across sexes and sports in 96 youth elite athletes (16.42 ± 1.03 years; 1.83 ± 0.09 m; 74.36 ± 8.69 kg) from basketball, handball, and volleyball. Using a force plate, asymmetries were assessed, and statistical analyses (t-test, ANOVA) identified differences. Results: Females showed greater asymmetry in jump height (9.64 ± 6.43% vs. 6.48 ± 4.87%, p = 0.01, d = 0.59), whereas males exhibited higher asymmetry in time to take-off (10.32 ± 7.5% vs. 6.4 ± 4.7%, p = 0.003, d = 0.63). Volleyball players displayed the lowest asymmetry in jump height (7.05 ± 4.9%) compared to basketball (8.73 ± 7.2%) and handball (11.88 ± 9.7%, p = 0.05), and in relative maximum power (4.63 ± 3.7%) compared to basketball (7.75 ± 5.3%, p = 0.04) and handball (6.51 ± 4.7%). Conclusions: These findings highlight sex- and sport-specific neuromuscular asymmetry patterns, emphasizing their relevance for injury prevention and performance strategies. However, asymmetries are highly variable, influenced by multiple factors. Full article

Background/Objectives: The morphology of the glenoid cavity is increasingly recognized as a key factor influencing joint mechanics and clinical outcomes, particularly in the context of shoulder instability. However, the specific effects of glenoid shape on the contact pressure distribution and humeral head displacement remain insufficiently explored. This study examined the impact of five glenoid morphotypes—pear, oval, teardrop, calabash, and inverted comma—on contact pressure patterns and humeral head displacement. Methods: Using three-dimensional models of the glenoid cavity derived from anatomical landmarks, we simulated cartilage compression and computed pressure fields using an elastic foundation model under a 700 N joint reaction force applied in various orientations. Results: Our results demonstrate that the glenoid morphology significantly influences both the magnitude and spatial distribution of contact pressures, particularly under eccentrically directed loads. Notably, pressure and humeral displacement were more pronounced when the force was inclined in the antero-posterior direction compared with the supero-inferior axis. Discussion: Among the morphotypes, the pear-shaped glenoid, the most prevalent in the general population, exhibited the greatest susceptibility to variations in glenohumeral loading. This suggests a potential evolutionary trade-off in shoulder morphology, favoring increased mobility at the expense of joint stability. Conclusions: These findings underscore the biomechanical relevance of patient-specific glenoid anatomy and advocate for its consideration in diagnostic and therapeutic strategies targeting shoulder instability and cartilage degeneration. Full article

Background/Objectives: Hamstring tendon (HT) autografts are commonly used for anterior cruciate ligament reconstruction (ACLR), traditionally combining semitendinosus and gracilis (ST + GR) tendons to achieve adequate graft length and diameter. More recently, four-strand semitendinosus (ST-only) constructs have been adopted to avoid gracilis harvest and reduce donor-site morbidity when sufficient ST tendon length is available. However, to our knowledge, the intrinsic biomechanical properties of four-strand ST-only and ST + GR grafts have not been directly compared. Methods: Twenty-five hamstring allografts (17 ST, 8 GR) from a single provider were prepared into two four-strand configurations: ST-only (n = 9) and ST + GR (n = 8). Manufacturer-reported folded tendon diameters were used to estimate four-strand graft diameters. Grafts underwent preconditioning, cyclic loading (80–250 N), and load-to-failure testing using a servomechanical testing apparatus. Ultimate failure load, stiffness, cyclic elongation, and elongation at failure were recorded. Groups were compared using the Mann–Whitney U test. Results: Mean donor age was 55.8 years (range, 27–72 years). Estimated mean graft diameter was significantly greater for ST-only constructs compared with ST + GR constructs (8.88 ± 0.62 mm vs. 7.70 ± 0.38 mm; p < 0.001). ST-only constructs demonstrated greater stiffness than ST + GR constructs (458.99 ± 54.51 vs. 364.67 ± 57.18 N/mm; p = 0.007) and lower elongation at failure (5.67 ± 1.25 vs. 7.42 ± 0.86 mm; p = 0.01). Cyclic elongation (0.259 ± 0.045 vs. 0.256 ± 0.049 mm; p = 0.89) and ultimate load to failure (1689.84 ± 121.36 vs. 1626.59 ± 324.92 N; p = 0.64) did not differ between groups. Conclusions: When tested in isolation, four-strand ST-only grafts are not biomechanically inferior to ST + GR grafts and demonstrate greater stiffness and larger estimated diameter. When sufficient semitendinosus length is available, ST-only grafts represent a biomechanically viable option for ACLR without the need for gracilis harvest. Full article

Background/Objectives: Trabecular bone exhibits brittle behaviour governed by microscale deformation and damage, yet quantifying crack progression is difficult because classical fracture-mechanics approaches do not apply to architecturally discontinuous porous tissue. This pilot study evaluates whether synchrotron X-ray computed tomography (XCT) combined with digital volume correlation (DVC) can provide a practical, geometry-normalised approach for quantifying crack-opening behaviour in human trabecular bone. Methods: Semicylindrical specimens from femoral heads of hip-fracture donors (n = 5) and non-fracture controls (n = 5) underwent stepwise three-point bending during XCT imaging. Full-field displacement maps were used to measure crack mouth opening displacement (CMOD), crack length (a), and their ratio CMOD/a, used here as a geometry-normalised comparative descriptor of brittle response rather than an intrinsic material property. Automated phase-congruency crack detection (PCCD) was compared with manual measurement. Results: XCT–DVC resolved three-dimensional displacement discontinuities during crack initiation and propagation in all specimens. Hip-fracture donors exhibited significantly lower critical crack-opening ratios (CMOD/a)* than Controls (median 0.31 vs. 0.47; p = 0.008) and reached instability at lower applied loads. Total crack extension (Δa*) was similar between groups. Automated crack tracking using phase-congruency-based segmentation showed excellent agreement with manual measurements (r² = 0.98), supporting reliable extraction of crack geometry from DVC displacement fields. Conclusions: In this small pilot sample, XCT–DVC provided a feasible, geometry-normalised approach for comparing crack-opening behaviour where classical fracture-mechanics parameters cannot be applied. The close agreement between automated and manual crack measurements supports the reproducibility of the displacement-based measurement pipeline. The lower critical CMOD/a in hip-fracture specimens may indicate a more brittle comparative response. However, given the small sample, differing sex distribution, and lower bone volume fraction in the hip-fracture group, these findings are preliminary and require confirmation in larger cohorts. Establishing whether the observed difference reflects intrinsic tissue brittleness, architectural factors, or both is an important objective for future work in microstructure-matched cohorts. Full article

Background/Objectives: Ankle dorsiflexion plays a fundamental role in gait stability, impact absorption, and the stance-to-swing transition, and its impairment is a major limitation in transtibial prostheses. This study proposes and evaluates a lightweight two-stage pipeline for generating ankle-dorsiflexion references using a single shank-mounted inertial measurement unit (IMU). Methods: In the first stage, a deep neural network (DNN) estimates the shank pitch waveform from raw three-axis accelerations and angular velocities. In the second stage, the estimated shank pitch is transformed into an ankle-dorsiflexion waveform using a temporal mapping model. The approach was evaluated on a multisubject subset of the NONAN GaitPrint database comprising 35 healthy young adults, 598 walking trials, and approximately 122,468 gait cycles, using a strict subject-held-out protocol. Results: A feature-based Random Forest baseline showed limited performance, whereas the waveform-based DNN achieved high accuracy for shank pitch estimation, with test R² values up to 0.97. A conventional polynomial mapping between shank pitch and dorsiflexion yielded weak performance, whereas a temporal mapping model substantially improved the estimation of ankle dorsiflexion, with test R² values up to 0.85. The resulting ankle reference was integrated into a Gazebo/Robot Operating System 2 (ROS 2) simulation of a transtibial prosthesis, where the generated trajectories were executed in a software integration test under open-loop position control, confirming stable and consistent trajectory execution. Conclusions: These results indicate that combining accurate shank pitch estimation with temporal mapping enables feasible ankle-dorsiflexion reference generation from a single sensor in able-bodied gait, offering a preliminary, simulation-based pathway for single-sensor artificial intelligence (AI) pipelines in prosthetic development. The framework supports waveform-level feasibility, not clinical readiness or functional prosthetic control. Full article

Background/Objectives: The Dynamic Strength Index (DSI) has been proposed as an indicator of the ability to dynamically express maximum available strength; however, its practical significance remains unclear. This study examined the associations of the DSI with dynamic and isometric strength measures, as well as sprint performance, in female professional soccer players. Methods: Eighteen female professional soccer players were assessed during pre-season. The DSI was calculated from peak force obtained in the countermovement jump (CMJ) and the isometric mid-thigh pull (IMTP). Spearman’s correlations were analysed alongside bootstrap confidence intervals, false discovery rate (FDR) adjustment, dependent correlation comparisons, and partial correlations controlling for body mass. Results: The DSI showed moderate unadjusted associations with relative CMJ peak force (ρ = 0.59) and relative CMJ peak yank (ρ = 0.56). However, no associations remained statistically significant after FDR correction. Despite this, the overall pattern of effect sizes and confidence intervals suggested a tendency towards stronger associations with dynamic rather than isometric variables. No meaningful associations were observed with IMTP-derived variables or sprint performance. Conclusions: In this exploratory sample, the DSI showed a tendency towards stronger associations with relative dynamic force variables than with isometric measures. However, given the lack of statistical significance after correction for multiple comparisons, these findings should be interpreted cautiously. The DSI may be better considered as a complementary metric within a broader neuromuscular assessment framework rather than as a standalone indicator. Full article

Background/Objectives: This study investigated kinetic performance, leg stiffness and gastrocnemius muscle (GM) activity during shod and barefoot two-legged hopping in female court athletes, while also assessing potential sport specialization-by-footwear interactions. Methods: Forty-two elite female Volleyball, Basketball, and Handball athletes (n = 14 per group) performed two-legged hopping at 130 bpm under both shod and barefoot conditions. Vertical ground reaction force (Fz) (Kistler forceplate sampling at 1000 Hz) was recorded in synchronization with GM vibromyographic intensity (TSD250, Biopac Systems, sampling at 2000 Hz). Kinetic metrics, kleg and GM activation were analyzed via repeated-measures ANOVA (alpha = 0.05, PSS 30.0). For all metrics, results indicated no significant sport-by-footwear interaction (p > 0.05). Results: Footwear significantly altered hopping kinematics; while absolute contact durations remained constant, relative total and effective contact durations were elongated and shortened, respectively. In the shod condition, kleg increased (+6.1%, p < 0.05) alongside a reduction in GM activation (−7.7%, p < 0.05). Additionally, Fz peak increased (+4.3%, p < 0.05) and occurred relatively earlier in the contact phase (−0.7%, p < 0.05). Conclusions: These findings indicate that footwear acts as a mechanical buffer, enabling a stiffer leg spring and reduced neuromuscular demand. The earlier timing of Fz peak suggests a facilitated eccentric-to-concentric transition, most likely allowing athletes to maintain efficient energy return despite the compliance of the footwear interface. Full article

Background/Objectives: Image-based finite element analysis (FEA) is increasingly used in dental biomechanics; however, its reliability is often limited by insufficient experimental benchmarking and a lack of standardized workflows. This study aimed to quantitatively benchmark a Cone beam computed tomography-based (CBCT) finite element pipeline using experimentally measured strain in restored human molars. Methods: Extracted human mandibular molars were restored using a total-etch adhesive system and bulk-fill composite resin. Specimen-specific finite element models were generated from CBCT data using a standardized segmentation and meshing workflow. Numerical simulations were compared with experimentally measured strain obtained during mechanical loading using Digital Image Correlation. Agreement between numerical and experimental data was assessed using regression analysis, Bland–Altman analysis, and equivalence testing. Results: A total of 304 spatially clustered paired measurements nested within 16 specimens were analyzed. FEM predictions showed strong correlation with experimental data (r = 0.91–0.97; R² up to 0.937) and low relative error (~5–6%). The model systematically overestimated deformation by approximately 10–15%. Equivalence was confirmed within ±15% for dentin and composite, and within ±20% for enamel. Bland–Altman analysis revealed proportional bias and heteroscedasticity, particularly in dentin. Conclusions: The proposed CBCT-based finite element workflow demonstrates strong benchmarking agreement with experimental measurements and provides reproducible estimates of mechanical behavior within defined tolerance limits under controlled experimental conditions. Despite systematic overestimation, the model exhibits stable and reproducible behavior under controlled conditions. These findings support the use of experimentally benchmarked, image-based FEA workflows in dental biomechanical research. Full article

Background/Objectives: Accurate and accessible assessment of upper-limb motion is essential for rehabilitation research, ergonomic evaluation, human–machine interaction, and limb exercise. This work presents a comparative evaluation of upper-limb joint angle estimation obtained from wearable inertial measurement units (IMUs) using a Kinect-based practical benchmark during synchronized data acquisition. Methods: The main variables analyzed were shoulder and elbow joint angles, together with IMU-derived acceleration and surface electromyography (sEMG) signals acquired as complementary physiological information during task execution. Ten healthy adult participants performed predefined upper-limb movements while data from both sensing modalities were recorded simultaneously. Joint angles were estimated independently from IMU and Kinect measurements and compared using Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and Two One-Sided Tests (TOST) equivalence analysis. Results: For upper- limb motion, IMU-derived estimates showed practical equivalence within the predefined ±10° acceptance margin with small MAE and RMSE values and significant TOST equivalence results (p < 0.001), supporting reliable proximal joint tracking under controlled conditions. Tested elbow motion exhibited large estimation error and large variability, and although the TOST analysis was significant, the equivalence interval slightly exceeded the predefined acceptance bound, indicating comparatively weak agreement between sensing modalities. The presented results should be interpreted as proof-of-concept evidence derived from a comparative benchmark rather than as definitive validation for unrestricted or clinical implementation. The synchronized acceleration and sEMG signals provided complementary temporal information regarding movement execution but were not treated as primary comparative outputs. Conclusions: These findings support the feasibility of wearable IMU-based upper-limb joint angle estimation as a proof-of-concept comparative framework rather than definitive clinical validation. The presented findings support the feasibility of the proposed IMU-based sensing approach for upper-limb joint angle estimation, particularly at the shoulder level, while also highlighting the greater complexity of elbow-related measurements. Further investigation in larger samples, more functionally diverse tasks, and broader populations is required to extend the applicability of the proposed approach. Full article

Background: Walking a dog on-leash is a common activity for a large portion of our society. Many dogs consistently pull on the leash, which transmits potentially dangerous forces to the human body. The purpose of this in silico study was to determine the effects of dog-leash tension and human posture on lumbar compression, and how comparable the effects of dog walking on lumbar compression are to lifting, an activity known to contribute to low back pain. Methods: Dog-leash simulations were performed with 50–300 N directed along the arm segment of a static three-dimensional musculoskeletal model across a range of trunk segment and shoulder joint angles. Lifting simulations were performed across a range of test postures with the model holding a 50–300 N weight close to the ground. Lumbar compression was computed for each simulation using McGill’s polynomial equation and compared with the 3400 N cutoff used to develop occupational safety guidelines. Results: Lumbar compression increased as trunk segment flexion increased for all simulation conditions. With 200 N of leash tension, lumbar compression exceeded 3400 N for all postures with 25° or more of trunk segment flexion. When lifting 150 N, lumbar compression exceeded 3400 N for all postures with shank segment angle of 80° or greater and knee flexion angle of 100° or less. Conclusions: Our in silico results suggest that dog owners should seek intervention if their dog routinely pulls on the leash with a force of 200 N or greater and should attempt to lean backward when resisting leash pulling to reduce lumbar compression and injury risk. Full article

Objective: To examine lower-body stretch–shortening cycle (SSC) indicators across chronological age categories and playing positions in elite male youth soccer players. Methods: In a cross-sectional design, 984 male players from Slovakia (U15–U19) completed Squat Jumps (SJ), Countermovement Jumps (CMJ), and Drop Jumps (DJ) using the OptoJump photocell system. Outcomes included Eccentric Utilization Ratio (EUR), Reactive Strength Index (RSI), DJ Ground Contact Time (DJ GCT), and Jump Heights (JH). Differences were tested using factorial ANCOVA (age category × playing position) adjusted for height and weight, followed by Tukey-adjusted post hoc comparisons (p < 0.05). Results: Significant age-category main effects were observed for DJ RSI, DJ JH, CMJ JH, SJ JH, and DJ GCT. The largest effects were for DJ JH, CMJ JH, and SJ JH (ηp² = 0.096–0.112), whereas the DJ GCT effect was statistically significant but small (ηp² = 0.013). EUR showed no significant differences across age categories (p = 0.586). Positional differences were limited overall and mainly evident in selected U19 outcomes, particularly jump-height variables and DJ GCT. Conclusions: Lower-body SSC performance increased across chronological age categories, with the largest separation in jump-height and reactive strength outcomes. These differences likely reflect a combination of maturation, training exposure, and selection rather than chronological age alone. EUR remained stable across age categories and playing positions, although the JH-based ratio has limited sensitivity in the present test configuration. Positional separation emerged mainly at U19, supporting broad SSC development across earlier youth categories and position-sensitive interpretation in the oldest cohort. Full article