Tendon lesions of the gluteus medius muscle require surgical repair if conservative treatment fails. Postoperatively, the success of the therapy is influenced by the loading conditions during follow-up treatment. Excessive loading of the hip joint during walking after surgery - and consequently, potential overload of the repaired gluteal tendon - could jeopardize the success of the therapy. In this controlled laboratory study, six subjects performed an instrumented 3D gait analysis using optoelectronic motion capture under three different loading conditions: full weight-bearing, partial weight-bearing, and full unloading with crutches. Gait data were used in silico in an inverse dynamics multi-body simulation to calculate tendon loading. Peak loads occurred on the gluteal tendons and the hip joint during the stance phase. The force on the gluteus medius tendon during full weight-bearing amounted to Fme = 12.0 ( ± 1.5) N/kg BW, while the force on the gluteus minimus tendon was Fmi = 5.0 ( ± 1.6) N/kg BW. Partial weight-bearing reduced these loads by ≈ 68%, whereas full unloading led to a ≈ 88% reduction compared to full weight-bearing. In the hip joint, the average maximum load during full weight-bearing reached FH = 39.8 ( ± 6.7) N/kg BW. To prevent muscle atrophy after gluteal tendon repair, the highest possible load should be applied without compromising suture integrity. Full unloading should be implemented if the tendon and/or bone integrity is compromised and suture stability is reduced. However, if stability is sufficient, partial weight-bearing is recommended.

The flat, stiff sole of energy-storage-and-return prosthetic feet hinders adaptation to irregular terrains. This is among the causes both of high falling risk and of the consequential arising compensatory mechanisms in prosthetic users. To overcome that, we introduce the SoftFoot Pro, an anthropomorphic and adaptive prosthetic foot featuring a flexible and inextensible sole that passively adapts to obstacles, widening the ground contact area. Experimental comparison to a traditional carbon fibre foot in two unilateral transtibial prosthetic users highlights that the adaptive design reduces stance torque and power consumption at the contralateral knee and at both hips, both on level and uneven grounds. The more even load distribution between the two limbs reduces compensatory strategies and gait asymmetries, resulting in biomechanics closer to that of unimpaired individuals. These findings hold promise for enhancing quality of life for individuals with limb loss, potentially improving stability and reducing fall risk. Irregular terrains challenge users of classic prosthetic feet. Here, the authors introduce an adaptive prosthetic foot that equalizes ground contact pressure and reduces compensatory strategies and gait asymmetries compared with a traditional carbon fibre foot.

Abstract To avoid highly invasive cement extraction during revision of cemented hip stems, we investigated in vitro a concept for refixation of loosened cemented stems using induction heating. The thermoplastic polymeric bone cement is softened by heating the metallic stem above the cement’s glass transition temperature, possibly allowing refixation. In an exploratory study three simplified conical Co28Cr6Mo samples were corundum blasted to simulate the surface roughness of matt cemented stems. Three fixation states were produced by cementing the stem samples within a PMMA cavity: (1) initially implanted stem after cement polymerization; (2) loosened stem retained by taper self-locking; (3) refixated stem. The latter should be achieved by inductive surface heating to 95 °C and applying an axial force of 2 kN. Fixation quality was assessed from relative motions in the stem-cement interface, acoustic emissions during quasistatic torsional loading (7 Nm and 10 Nm), and axial pull-out forces of the stem from the cement mantle. Initial fixation yielded a pull-out force of F PO = 1.99 kN ± 0.26 kN, decreasing to 0.84 kN ± 0.38 kN after loosening. After refixation, pull-out forces reached 0.89 kN ± 0.50 kN. However, in one of the three samples, the pull-out force could be restored by refixation. Therefore, the induction-based refixation concept shows potential as a less invasive alternative to conventional revision surgery but requires further validation in more clinically relevant in vitro models.

BACKGROUND:Motion analysis plays an important role in clinical decision-making and biomechanical research. Conventional assessments rely on laboratory-based motion capture and force plates, which are accurate but resource-intensive. Wearable sensors combined with artificial neural networks offer a promising alternative for use outside the laboratory, but they must be validated against established systems. The aim of this study was to predict important kinetic gait parameters, such as ground reaction forces, knee joint moments and knee power, using wearable sensors and neural networks. Such an approach may support gait assessment in orthopaedic conditions and enable more responsive adjustment of exoprostheses. METHODS:Thirty-two healthy adults provided informed consent and were instrumented. Standard kinematic and kinetic data were captured using a conventional motion analysis setup, while linear accelerations were recorded synchronously using wearable sensors. These acceleration signals were used as inputs for two neural network models (long short-term memory and multilayer perceptron) to predict kinetic parameters. FINDINGS:Both models achieved good to very good agreement with the reference system. Pearson correlation coefficients ranged from 0.79 for the knee joint power to 0.99 for anteroposterior ground reaction force. The normalised root mean square errors between 3.1% and 10.3% further demonstrated promising predictive accuracy. INTERPRETATION:The findings indicate that wearable sensors combined with neural networks can estimate clinically relevant kinetic gait parameters with high accuracy outside a laboratory setting. In the future, such predictions may help standardize dynamic adjustments of exoprostheses, support the diagnosis of orthopaedic conditions and evaluate treatment outcomes.

The current literature remains inconclusive about whether kinematic alignment (KA) is superior to mechanical alignment (MA) in total knee arthroplasty (TKA). Therefore, this randomized controlled trial sought to provide further clarification. 39 MA patients, 33 KA patients, and 9 healthy controls were included. All participants underwent three-dimensional gait analysis on a treadmill one day before surgery and one year postoperatively. A preoperative range of motion (ROM) score was calculated and correlated with the postoperative Forgotten Joint Score (FJS). One year after surgery, no significant kinematic differences were observed between MA and KA. However, in Coronal Plane Alignment of the Knee (CPAK) type 1 patients, KA knees more closely reproduced the gait of healthy controls and showed higher walking speed. Correlation analysis revealed that patients with a higher preoperative ROM achieved better outcomes with KA, whereas female patients with lower ROM benefit more from MA. Although no kinematic differences were detected, the strong trend toward reduced joint space in MA compared to KA in CPAK type 1 patients may result from subtle deviations in joint-line restoration or postoperative soft-tissue tension. Both factors can affect load distribution and joint perception. The present findings support a patient-specific approach to alignment selection in TKA.

Introduction: Gait analysis plays a key role in improving our understanding of joint kinematics during locomotion, often by leveraging marker-based systems. Accessibility to marker-based systems is nevertheless limited, as they are usually associated with high equipment costs, large space requirements, and the need for lengthy data processing. These restrictions have therefore driven the need for tools that facilitate the interpretation and comparison of openly accessible kinematic datasets, even in cases where the data have been collected using distinct equipment and/or protocols.Methods: This study addresses variations in kinematic data arising from the use of different marker sets, focusing specifically on the tibio-femoral joint kinematics of 15 healthy subjects during treadmill walking. By simultaneously capturing joint motion using five distinct marker sets, we were able to confirm the presence of visible differences in the raw kinematic outputs prior to data optimisation, despite their representing the same underlying motion. We subsequently implemented the REference FRame Alignment MEthod (REFRAME) to account for signal differences linked to inconsistent local reference frame orientations.Results and Discussion: After REFRAME optimisation, improved convergence of the kinematic signals was observed, confirming that the differences observed in raw signals stemmed primarily from differing reference frame orientations, rather than genuine variations in joint motion. This study highlights REFRAME's potential to enhance comparability across biomechanical datasets, thus facilitating robust inter-laboratory comparisons and supporting reliable interpretations of data in clinical and research applications.

Traditional mechanical methods for implant and bone cement removal during total hip arthroplasty (THA) revision surgeries typically lead to surrounding tissue damage and increased risk of femoral fractures. Transcutaneous induction heating is a promising new removal approach as it causes softening of the thermoplastic bone cement, and thus prevents damage to the surrounding tissue during removal and increases stability post-revision. However, precise knowledge of the heat transfer between implant and bone cement is necessary to minimize the risk of thermal damage to surrounding tissues. In this context, knowledge of the thermal contact conductance (TCC) at the interface of Co28Cr6Mo hip stems and PMMA-based bone cement is a key issue. The present study addresses the challenge of measuring TCC by proposing an inverse method of determination using infrared thermography measurements of the heating process and a finite element simulation with a variable parameter for the TCC. Results indicate TCC values of 3,125 ± 275 Wm− 2K− 1 for dry interfaces and 5,100 ± 300 Wm− 2K− 1 for wet interfaces. The influence of heat conduction on bone cement surface temperature is significant, impacting the measured surface temperatures by 15–19% for wet and 23–30% for dry interfaces. These findings are crucial for the design of heating procedures and minimization of thermal damage during induction heating assisted THA revisions.

Instrumented motion analysis plays a pivotal role in orthopedic technology, offering unique opportunities to analyze and optimize biomechanical, musculoskeletal and neurological processes. This article highlights several recent studies leveraging motion analysis to explore various aspects of prosthetic development, control, loading and safety. The compiled studies highlight the essential potential of instrumented motion analysis in the field of exoskeletal prosthetics. Beyond improving the quality of life for prosthesis users, this technology plays an indispensable role for advancing the functionality and safety of current and future orthopedic devices.

INTRODUCTION:Although three-dimensional marker-based motion analysis is the gold standard for biomechanical investigations, it is time-consuming and cost-intensive. The conjunction of monocular video recordings with pose estimation algorithms addresses this gap. With the Orthelligent VISION app (OPED GmbH) a commercial and easy-to-use tool is now available for implementation in everyday clinical practice. The study investigates the accuracy of the 2D video-based system in measuring joint kinematics, expressed as range of motion, compared to an optoelectronic 3D motion analysis system as the gold standard. MATERIALS AND METHODS:Its accuracy was determined by synchronously measuring ten healthy subjects with Orthelligent and the optoelectronic 3D motion analysis system Qualisys (Qualisys AB) during level walking and at different treadmill walking speeds (1 m/s; 1.4 m/s; 1.8 m/s). Range of motion (RoM) of lower limb joints and time-distance parameters were compared using Bland-Altman plots, t-tests, and correlations between systems. Kinematic outputs of two subjects with a lower limb amputation were also analyzed. RESULTS:The mean RoM deviation was smaller for the knee (3.8°) and hip joints (3.7°) than for the ankle joint (5.4°), but differed significantly between systems in most conditions. The correlation range was 0.36 ≤ r ≤ 0.83, with best results for 1 m/s treadmill walking (mean r = 0.71 across joints). While the accuracy was affected by high inter-subject variability, individual RoM changes from slow to fast walking did not differ between the systems. The kinematics of the prosthetic and sound leg of individuals with an amputation exhibited characteristic patterns in the video-based system, even though side differences were smaller compared to the optoelectronic measurement. CONCLUSIONS:The rather high inter-subject variability would make future comparisons between individuals challenging. Nonetheless, the app shows potential for intra-subject progress monitoring.

Die instrumentierte Bewegungsanalyse spielt eine zentrale Rolle in der Orthopädietechnik und bietet einzigartige Möglichkeiten, biomechanische, muskuloskeletale und neurologische Prozesse zu analysieren und gezielt zu optimieren. Der Beitrag beleuchtet mehrere aktuelle Studien, die unter dem Einsatz der Bewegungsanalyse verschiedene Aspekte in den Bereichen der Prothesenentwicklung, -steuerung, -belastung und -sicherheit untersuchen. Die vorliegende Zusammenstellung verdeutlicht das mittlerweile essenzielle Potenzial der instrumentierten Bewegungsanalyse in der exoskeletalen Prothetik. Sie trägt nicht mehr nur allein nachhaltig zur Steigerung der Lebensqualität von Prothesennutzern bei, sondern ist mittlerweile unverzichtbar für die Funktionalität und Sicherheit aktueller und zukünftiger orthopädietechnischer Hilfsmittel.

Prosthetic gait differs considerably from the unimpaired gait. Studying alterations in the gait patterns could help to understand different adaptation mechanisms adopted by these populations. This study investigated the effects of induced stiff-knee gait (SKG) on prosthetic and healthy gait patterns and the capabilities of predictive simulation. Self-selected speed gait of two participants was measured: one healthy subject and one knee disarticulation subject using a variable-damping microprocessor controlled knee prosthesis. Both performed unperturbed gait and gait with restricted knee flexion. Experimental joint angles and moments were computed using OpenSim and muscle activity was measured using surface electromyography (EMG). The differences between the conditions were analyzed using statistical parametric mapping (SPM). Predictive models based on optimal control were created to represent the participants. Additionally, a hypothetical unimpaired predictive model with the same anthropometric characteristics as the amputee was created. Some patterns observed in the experimental prosthetic gait were predicted by the models, including increased knee flexion moment on the contralateral side caused by SKG in both participants, which was statistically significant according to SPM. With the exception of the rectus femoris muscle, we also found overall good agreement between measured EMG and predicted muscle activation. We predicted more alterations in activation of the hip flexors than other muscle groups due to the amputation and in the activation of the biceps femoris short head, quadratus femoris, and tibialis anterior due to SKG. In summary, we demonstrated that the method applied in this study could predict gait alterations due to amputation of the lower limb or due to imposed SKG.

Purpose:The objective of this case series was to investigate the effect of ultrasound-guided cement removal devices on operating time and patient safety in the revision of cemented knee and hip arthroplasties. Methods:A total of 11 cases were examined in which ultrasound-guided cement extraction was utilised for implant removal. The primary endpoint of the study was the duration of the surgery. Additionally, the cohort was analysed for the occurrence of intraoperative fractures or postoperative ossification. Postoperative laboratory dynamics of haemoglobin and C-reactive protein levels were also investigated. A matched group of 11 patients who underwent revision arthroplasty using conventional techniques to remove bone cement served as the reference group. Results:Ultrasound-guided removal of cement from the medullary canal was associated with a significantly longer operation time (187.19 min ± 54.4 vs. 121.91 min ± 43.5, (p = 0.0026). Furthermore, there was a significant decrease in haemoglobin drop relative to baseline haemoglobin levels when ultrasound-guided tools were employed for cement removal (2.36 g/dL ± 1.9 vs. 4.54 g/dL ± 1.9, p = 0.0015). Moreover, an intraoperative fracture complication of the femoral shaft was observed when the cement was removed using an ultrasonic cement stripper. Conclusion:A comparison between the two groups reveals a significant increase in surgical duration when cement removal was performed using ultrasound-guided technique. Simultaneously, the use of an ultrasound-assisted system for cement removal did not mitigate the risk of intraoperative bone perforation. Based on the data presented in this study, the authors cannot conclude that the use of ultrasound-guided devices for the removal of cement residues from the medullary canal during revision surgery is superior to conventional techniques. Level of Evidence:Level IV.

AbstractPurposeEffective rehabilitation after orthopaedic surgery is critical. The early post‐operative phase is increasingly managed in outpatient settings, necessitating objective measures such as step counts to monitor rehabilitation progress. However, it remains unclear if commercially available wearables or accelerometers using simple algorithms can accurately count steps in early post‐operative conditions. We hypothesised that only accelerometers could accurately determine the number of steps under these conditions.MethodsThis case series involved 20 healthy subjects, 7 female and 13 males, walking in a circle at varying speeds under partial loading with three different walking aids (forearm crutches, walking frame and rolling walker) and four wearables (Vivofit 4, Fenix 3HR, Fitbit Charge 3 and Omron HJ‐325) and one accelerometer (AX6) worn on the wrist, hip and ankle. The two‐point and modified three‐point gait patterns commonly used post‐operatively were simulated. The primary end point was the relative error (RE), defined as RE = (manual count − automated count)/manual count, of each wearable measurement compared to visual and video step counting, the gold standard.ResultsThe RE of AX6 and Fitbit was less than 0.1 for all walking aids except the rolling walker, with AX6 showing the lowest standard deviation (SD) compared to other wearables. Other wearables had significantly higher RE. Increased gait speed generally improved accuracy, reducing RE in most devices, except for the AX6, which showed the opposite trend. At 0.6 m/s, only AX6 achieved an RE below 0.1. The ankle was identified as the best measuring location.ConclusionDuring the early post‐operative period, commercial wearables can only accurately count steps under specific conditions and should be used cautiously for monitoring steps in the early post‐operative phase. However, accelerometers with appropriate coding appear suitable for this purpose.Level of EvidenceLevel III diagnostic study.

In hip arthroplasty, relative movements between the femoral stem and bone can lead to implant loosening, resulting in extensive bone loss. Acoustic emission (AE) analysis is a promising technique for a nondestructive and noninvasive detection of these relative movements. To develop such a detection method, in vitro investigations using piezoelectric AE sensors on implant stems in artificial or human femora are required to characterize the AE signals induced by loosening. This study aims to identify suitable coupling materials to bridge the gap between the planar AE-sensor surface and the exposed freeform surface of the femur. Four coupling materials, both synthetic and natural, with acoustic properties similar to human soft tissue were investigated for signal attenuation and repeatability between tests. The synthetic materials demonstrated better inter-sample repeatability. One synthetic material exhibited higher flexibility, enabling better adaptation to the sensor and resulting in significantly lower signal attenuation.

Background: The use of tapered fluted revision stems has been shown to be reliable and safe. Primary stability is mandatory for a long-lasting fixation between bone and a prosthesis. Nevertheless, aseptic loosening due to insufficient primary stability occurs and may be related to technically improper preparation of the femoral canal. Instructions of manufacturers are heterogeneous regarding preparation of implant beds. Questions/Purposes: Does speed or the design of the reamer influence the accuracy of the implant bed and, consecutively, primary stability? Materials and Methods: A test foam with an elastic moduli and pressure resistance similar to that of cancellous bone was used. The medullary canal was prepared with the use of reamers of two different straight and tapered femoral revision devices. Three different rotational speeds were used for preparation. After preparation, primary stability was measured and fixating characteristics were derived. Results: Sufficient primary stability was achievable by all three preparation methods but fixating characteristics were different. Significantly higher micro-motions were detected near the tip of the prosthesis compared to those at all more proximal measuring points. Reaming with high velocity resulted in significantly higher micro-motions compared to that with mid- or low-speed burring. Conclusions: Different preparation methods may be one explanation for the range of reported survivorship data of the two devices with aseptic loosening as the end point. The precision of the implant bed and fixating characteristics were best after reaming with lower velocity. Superior but not significantly better fixation characteristics were achieved with the monobloc stem compared to those with the modular device.

Background/Objectives: Minor amputations are increasingly relevant due to a growing proportion of lower limb amputations but remain underrepresented in research. These amputations impair mobility due to altered gait, and biomimetic devices could potentially address this issue. Fundamental research is needed to better understand this pathological gait pattern. The aim of this study is to analyse the holistic gait characteristics of the lower extremity during barefoot walking in individuals with different levels of minor amputations for the first time. Methods: Eight young to middle-aged subjects with minor foot amputations (four × hallux; four × forefoot) underwent instrumented gait analysis. Kinematic and kinetic data were acquired barefoot at self-selected gait speeds. Individual gait characteristics were considered relative to the physiological gait represented by the 95% confidence interval of ten unimpaired volunteers. Results: Subjects with a minor amputation show reduced walking speed and shorter stride length compared to controls. Sagittal ankle moment and ankle power are lower, with greater deficits in subjects with a forefoot amputation. Proximal joints also show variability, notably reduced knee flexion in subjects with a forefoot amputation and a more flexed hip profile in six subjects. Single-subject frontal plane kinetics also vary. Conclusions: Although the subjects with a hallux amputation exhibit smaller deviations in ankle kinetics than the subjects with a forefoot amputation, proximal joint abnormalities are present across cases. These findings highlight the need for a broad range of care to adequately address individual needs.

Abstract Background High-offset stems in cementless primary total hip arthroplasty (THA) have been potentially associated with early aseptic femoral loosening. This study aimed to evaluate the primary and secondary stability of a cementless high-offset femoral component under full weight-bearing conditions using model-based RSA, comparing it with a standard offset stem in patients undergoing THA. Methods In this prospective, observational, single-center study, 42 patients with end-stage hip osteoarthritis underwent cementless primary THA using either a standard (SL-PLUS Standard) or a high-offset (SL-PLUS Lateral) cementless stem. Radiostereometric analysis (RSA) was employed to monitor stem migration at six weeks and three, six, twelve, and twenty-four months. Clinical outcomes were assessed using the modified Harris Hip Score (HHS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Results There were no significant differences in mean stem subsidence between the groups at any follow-up interval, indicating comparable primary and secondary stability. After minimal initial subsidence (SL-PLUS Standard: up to −0.54 mm; SL-PLUS Lateral: up to −0.73 mm), no further progressive migration was observed. A significant difference in stem anteversion was noted between the groups at six months (P = 0.021) and two years (P = 0.001). The SL-PLUS Lateral group had significantly better WOMAC scores at the two-year follow-up (P = 0.027). Conclusions This RSA study demonstrated similar migration patterns for the high-offset and standard-offset cementless stems within the first two years after operation. Both groups exhibited initial subsidence followed by high secondary stability. Based on the results of this study, the SL-PLUS Lateral is a safe alternative for patients with high femoral offset undergoing cementless THA.

Implant loosening remains a primary cause of failure of total hip arthroplasty1 (THA) and is often detected late, when pain occurs. Acoustic emission2 (AE) analysis is a promising method for early loosening detection, on the supposition that relative movements at the bone-implant interface induce detectable AE signals. To distinguish loosening-induced AE signals from those of stable THA components in vitro investigations are necessary. Substituting human with animal bone for such testing could enable simplified and cost-effective sample preparation. The aim of this study was to investigate whether AE signals differ between bone tissues of different species. AE signals generated by relative movements between TiAl6V4 and human, bovine, and porcine cortical bone were investigated. Per species, 125 movements were analyzed, with 26 AE features identified for each movement. The most important time and frequency features of AE signals from human bone differed significantly from those of both animal species. Signals of human origin were longer and exhibited higher rise time. The main frequency components of human AE signals were in a lower frequency range, with a centroid frequency of 113.7 kHz. Based on these differences, it is not advisable to replace human cortical bone with animal bone for AE-related in vitro studies.

Revision surgery for total hip arthroplasties involves removing the endoprosthesis stem from the patient's femur. The conventional method of extraction carries a substantial risk of peripheral bone damage, impeding rehabilitation and reducing stability of the revision endoprosthesis. A promising option for intentional implant removal in revision hip arthroplasty is the use of transcutaneous induction heating to soften the thermoplastic bone cement to reduce extraction forces and increase patient safety. Accurate knowledge of the implant surface temperatures generated during induction heating is essential to avoid thermal damage to surrounding tissues. In this work, an in-silico model for the induction heating of CoCrMo hip endoprostheses was developed and validated using IR thermography. This model allows for the prediction of surface temperature distributions on hip implants in the low temperature ranges required for intentional implant removal and aids in the design of inductor geometries to achieve homogeneous heating of hip endoprostheses.

This study investigated how muscle synergies adapt in response to unexpected changes in object weight during lifting tasks. The aim was to discover which motor control strategies individuals use to maintain their grasping performance. Muscle synergies were extracted from the muscle activity of fifteen healthy participants who lifted objects of identical appearance but varying weights in a randomized order, which introduced artificial perturbations. Reaching and manipulation phases of object lifting were analyzed using constrained non-negative matrix factorization and k-means clustering. Participants exhibited a perturbation-independent and thus consistent recruitment of spatial synergy components, while significant adaptations in muscle synergy activation occurred in response to unexpected perturbations. Perturbations caused by unexpectedly heavy objects led to delayed and gradual increases in muscle synergy activation until the force required to lift the object was reached. In contrast, perturbations caused by lighter objects led to reductions in excess muscle synergy activation occurring later. Sensorimotor control maintains the modularity of muscle synergies. Even when external mechanical perturbations occur, the grasping performance is preserved, and control is adapted solely through muscle synergy activation. These results suggest that using pure spatial synergy components as control signals for myoelectric arm prostheses may prevent them from malfunctioning due to external perturbations.