Dr David Lunn

Objective: To examine hip contact force (HCF), calculated through multibody modelling, in a large total hip replacement (THR)cohort stratified by patient characteristics such as body mass index (BMI), age and function. Method: 132 THR patients undertook one motion capture session of gait analysis at a self-selected walking speed. HCFs were then calculated using the AnyBody Modelling System. Patients were stratified into three BMI groups, five age groups, and finally three functional groups determined by their self-selected gait speed. By means of statistical parametric mapping (SPM), statistical analyses of the 1-dimensional time series were performed to separately evaluate the influence of age, BMI and functionality on HCF. Results: The mean predicted HCFs were comparable to HCFs measured with instrumented prostheses reported in the literature. The SPM analysis revealed a statistically significant positive linear correlation between BMI and HCF, indicating that obese patients are more likely to experience higher HCF during most of the stance phase, while a statistically significant negative correlation with age was found only during the late swing-phase. Patients with higher functional ability exhibited significantly increased peak HCF, while patients with lower functional ability demonstrated lower HCFs overall and a pathological flattening of the typical double hump force profile. Conclusion: HCFs experienced at the bearing surface are highly dependent on patient characteristics. BMI and functional ability were determined to have the biggest influence on contact forces. Current preclinical testing standards do not reflect this.

The current pre-clinical testing standards for total hip replacements (THRs), ISO standards, use simplified loading waveforms that do not fully replicate real-world biomechanics. These standards provide a benchmark of data that may not accurately predict in vivo wear, necessitating the evaluation of physiologically relevant loading conditions. Previous studies have incorporated activities of daily living (ADLs) such as walking, jogging and stair negotiation into wear simulations. However, these studies primarily used simplified adaptations that increased axial forces and applied accelerated sinusoidal waveforms, rather than fully replicating the complex kinematics experienced by THR patients. To address this gap, this study applied patient-derived ADL profiles—jogging and stair negotiation—using a three-station hip simulator, obtained through 3D motion analysis of total hip arthroplasty patients, processed via a musculoskeletal multibody modelling approach to derive realistic hip contact forces (HCFs). The results indicate that jogging significantly increased wear rates compared to the ISO walking gait waveform, with wear increasing from 15.24 ± 0.55 to 28.68 ± 0.87 mm3/Mc. Additionally, wear was highly sensitive to changes in lubricant protein concentration, with an increase from 17 g/L to 30 g/L reducing wear by over 60%. Contrary to predictive models, stair descent resulted in higher volumetric wear (8.62 ± 0.43 mm3/0.5 Mc) compared to stair ascent (4.15 ± 0.31 mm3/0.5 Mc), despite both profiles having similar peak torques. These findings underscore the limitations of current ISO standards in replicating physiologically relevant wear patterns. The application of patient-specific loading profiles highlights the need to integrate ADLs into pre-clinical testing protocols, ensuring a more accurate assessment of implant performance and longevity.

Background: Total hip arthroplasty (THA) implants are routinely tested for their tribological performance through regulatory preclinical wear testing (eg, ISO-14242). The standardized loading conditions defined in these tests consist of simplified waveforms, which do not specifically represent in vivo loads in different groups of patients. The aim of this study is to investigate, through musculoskeletal modeling, patient-specific and activity-related variation in hip contact forces (HCFs) in a large cohort of THA patients during common activities of daily living (ADLs). Methods: A total of 132 THA patients participated in a motion-capture analysis while performing different ADLs, including walk, fast walk, stair ascent, and descent (locomotor); sit to stand, stand to sit, squat, and lunge (nonlocomotor). HCFs were then calculated using the AnyBody Modeling System and qualitatively compared across all activities. The influence of gender on HCFs was analyzed through statistical parametric mapping analysis. Results: Systematic differences were found in HCF magnitudes and individual components in both locomotor and nonlocomotor ADLs. The qualitative analysis of the ADLs revealed a large range and a large variability in forces experienced at the hip during different activities. Significant differences in the 3-dimensional loading patterns were observed between males and females across most activities. Conclusion: THA patients present a large variability in the forces experienced at the hip joint during their daily life. The interpatient variation might partially explain the heterogeneity observed in implant survival rates. A more extensive preclinical implant testing standard under clinically relevant loading conditions has been advocated to better predict and avoid clinical wear problems.

To examine functional differences in total hip replacement patients (THR) when stratified either by age or by functional ability as defined by self-selected walking speed. THR patients and a control group underwent three-dimensional motion analysis under self-selected normal and fast walking conditions. Patients were stratified into five age groups for comparison with existing literature. The THR cohort was also stratified into three functional groups determined by their self-selected gait speed (low function <1SD of total cohort's mean walking speed; high function >1SD; normal function within 1SD). Hip kinematics, ground reaction forces, joint moments and joint powers in all three planes (x-y-z) were analysed. 137 THR and 27 healthy control patients participated. When stratified by age, during normal walking the youngest two age groups walked quicker than the oldest two groups (p < 0.0001) but between-group differences were not consistent across age strata. The differences were diminished under the fast walking condition. When stratified by function, under normal walking conditions, the low function and normal function THR groups had a reduced extension angle (mean = 1.75° SD = ±7.75, 1.26° ± 7.42, respectively) compared to the control group (−6.07° ± 6.43; p < 0.0001). The low function group had a reduced sagittal plane hip power (0.75 W/kg ± 0.24), reduced flexor (0.60 Nm/kg ± 0.85) and extensor moment (0.51 Nm/kg ± 0.17) compared to controls (p < 0.0001). These differences persisted under the fast walking condition. There were systematic differences between patients when stratified by function, in both walking conditions. Age-related differences were less systematic. Stratifying by biomechanical factors such as gait speed, rather than age, might be more robust for investigating functional differences.

Technology has had an increasing influence on our lives for some time, and this was accelerated by the enforced remote way of working five years ago. The first paper in this special topic from Chahin-Inostroza et al. articulates some of the challenges faced during this time as countries across the world enforced distancing measures and remote working to control the spread of COVID-19. Sport was not exempt, and both national and global events were put on standby. However, this not only affected elite athletes, but amateur athletes too had fewer opportunities to socialise with peers and receive feedback and advice. In their cross-section of amateur Chilean athletes, Chahin-Inostroza et al. report how the use of some technologies and training software changed during periods of quarantine, and remained elevated when quarantine ended.

The basic mechanical principles which govern how the hip joint maintains equilibrium and balance during standing and performing activities is explained along with the consequences when this balanced system is compromised. A description of the movements and forces acting around the hip joint that are expected during activities of daily living is offered and also how these movements are affected following total hip replacement, with particular reference to femoral offset and leg length inequality.

The vast majority of total hip arthroplasty (THA) performed in the United Kingdom are undertaken using either a posterior or direct lateral approach. This review describes the functional outcomes of these approaches. Functional outcome can be assessed through motion capture of function, strength testing of muscle groups around the hip, and imaging of anatomical structures. Regardless of surgical approach, THA patients rarely return to the ‘normal’ gait exhibited by healthy age-matched controls. The direct lateral approach is associated with abductor deficiencies whilst the posterior approach may introduce extension and rotation deficits. How long functional differences persist between surgical approaches is unclear. The emergence of improved imaging technologies as well as isokinetic dynamometry (muscle strength testing) and 3D biomechanical modelling provide more comprehensive evaluations than traditional post-operative assessments such as radiology or couch examination. Targeted physiotherapy has been suggested as a possible intervention to counter lasting functional deficits. This review provides a foundation to inform surgeons of the impact of each approach to justify their surgical practice and may inform physical rehabilitation regimens post-surgery.

One of the main causes of implant failure and revision surgery in total hip replacement (THR) is aseptic loosening often caused by the accumulation of wear debris arising between the contact surfaces of the acetabular cup and femoral head during activities of daily living (ADL’s). However, limited information is available regarding the contact force pathways between these two surfaces during specific ADL’s. In this study, through musculoskeletal modelling, we aimed to estimate the orientation of the hip contact force pathway on the acetabular cup. One hundred and thirty-two THR patients underwent motion capture analysis whilst undertaking locomotor and non-locomotor ADL’s. Musculoskeletal simulations were performed to calculate contact force pathways using inverse dynamics analysis. We then qualitatively compared differences in the contact force pathways between patients and between ADL’s. Walking resulted in a typical figure-of-eight pattern, with the peak contact forces occurring in the superior-anterior area of the cup. The non-locomotive activities such as stand up, sit down and squat had a more linear shape, spanning across the superior-posterior quarter of the cup. Our results showed a large inter-patient variability in the shape and location of the contact force pathway. There is a distinct difference in the location and shape of the pathway between locomotor and non-locomotor activities and this could result in different wear accumulations. These results could enhance our understanding why revision rates vary across the population and could inform the development of personalised implant design.

Musculoskeletal models represent a powerful tool to gain knowledge on the internal forces acting at the joint level in a non-invasive way. However, these models can present some errors associated with the level of detail in their geometrical representation. For this reason, a thorough validation is necessary to prove the reliability of their predictions. This study documents the development of a generic musculoskeletal model and proposes a working logic and simulation techniques for identifying specific model features in need of refinement; as well as providing a quantitative validation for the prediction of hip contact forces (HCF). The model, implemented in the AnyBody Modeling System and based on the cadaveric dataset TLEM 2.0, was scaled to match the anthropometry of a patient fitted with an instrumented hip implant and to reproduce gait kinematics based on motion capture data. The relative contribution of individual muscle elements to the HCF and joint moments was analyzed to identify critical geometries, which were then compared to muscle magnetic resonance imaging (MRI) scans and, in case of inconsistencies, were modified to better match the volumetric scans. The predicted HCF showed good agreement with the overall trend and timing of the measured HCF from the instrumented prosthesis. The average root mean square error (RMSE), calculated for the total HCF was found to be 0.298*BW. Refining the geometries of the muscles thus identified reduced RMSE on HCF magnitudes by 17% (from 0.359*BW to 0.298*BW) over the whole gait cycle. The detailed study of individual muscle contributions to the HCF succeeded in identifying muscles with incorrect anatomy, which would have been difficult to intuitively identify otherwise. Despite a certain residual over-prediction of the final hip contact forces in the stance phase, a satisfactory level of geometrical accuracy of muscle paths has been achieved with the refinement of this model.

The dynamic orientation of total hip replacement acetabular cups during walking may vary substantially from their assumed position at surgical implantation and may vary between individuals. The scale of this effect is of interest for both pre-clinical device testing and for pre-operative surgical planning. This work aimed to evaluate (1) patient variation in dynamic cup orientation; (2) whether walking speed was a candidate proxy measure for the dynamic cup orientation; and (3) the relationships between dynamic cup orientation angles and planar pelvic angles. Pelvic movement data for patients with fast (20 patients) and slow (19 patients) self-selected walking speeds were used to calculate acetabular cup inclination and version angles through gait. For aim 1, the range and extremes of acetabular cup orientation angles were analysed for all patients. A large patient-to-patient variation was found in the ranges of both inclination angle (1° to 11°) and version angle (4° to 18°). The version angle was typically retroverted in comparison to the implantation position (greatest deviation 27°). This orientation is substantially different to the static, 0° version, simplifying assumptions in pre-clinical ‘edge loading’ testing. For aim 2, the cup orientation angles were compared between the fast- and slow-walking groups using statistical parametric mapping. The only significant differences observed were for cup version angle, during ~12% of the gait cycle before toe-off (p < 0.05). Therefore, self-selected walking speed, in isolation, is not a sufficient proxy measure for dynamic acetabular orientation. For aim 3, correlations were recorded between the acetabular cup orientation angles and the planar pelvic angles. The cup inclination angle during gait was strongly correlated (Spearman’s coefficient −1) with pelvic obliquity alone, indicating that simple planar assessment could be used to anticipate inclination angle range. The cup version angle was correlated with both pelvic rotation and tilt (Spearman’s coefficient 0.8–1), indicating that cup version cannot be predicted directly from any single pelvic movement. This complexity, along with the interaction between inclination angle and range of version angle, supports the use of computational tools to aid clinical understanding.

A priority, irrelevant of pathology, is to keep patients moving, enabling them to lead an independent life. How a patient moves and how they walk, can provide an insight into disease progression, be a good indicator of overall health and evaluate treatment interventions. In this chapter we introduce methods used to measure movement and gait which can be used in a clinical environment and methods where technology and a level of expertise are required. This chapter will describe variables typically measured during gait analysis, which include temporal-spatial parameters, kinematics, kinetics, and foot pressures. As well as understanding how and what data is typically collected, and how interpreting the outcomes to provide meaningful clinical information to improve care for patients is most important. Data for a healthy population is presented before the final section discusses typical changes in function that would be expected to be observed in patients diagnosed with inflammatory arthritis.

Introduction Total hip replacement (THR) patients are often considered a homogenous group whereas in reality, patients are heterogeneous. Variation in revision rates between patient groups suggest that implants are exposed to different environmental conditions in different patients [1]. Previous reports suggest that for every unit increase of BMI, there is a 2% increased risk of revision of a THR [2]. The aim of this study was to better understand the effect of patient-specific characteristics such as BMI on hip motions and to explore the possible impact on wear. Methods 137 THR patients, at least 12 months post-surgery, underwent 3D kinematic (Vicon, Oxford, UK) and kinetic (AMTI, USA) analysis whilst walking at self-selected walking speed. 3D kinematic data were then mapped onto a modelled femoral cup at 20 pre-determined points to create pathways for femoral head contact, which were then quantified by deriving the aspect ratio (AR). Patients were stratified into three groups determined by BMI scores; healthy weight (BMI ≤25 kg/m2) (n=34); overweight (BMI >25kg/m2 to ≤ 30 kg/m2) (n=66) and obese patients (BMI > 30 kg/m2) (n=37). Comparisons were made using 95% confidence intervals (CI) and one way ANOVAs. Results The healthy weight strata demonstrated a minimum flexion angle of 0.59°(CI −2.15 to 3.32), compared to overweight 1.12°(CI 0.99 to 2.11) and obese strata 1.37°(−0.72 to 3.46). The healthy weight strata exhibited a lower frontal ROM 7.91° (CI 7.02 to 8.80) (p<0.000) compared to the overweight (9.42°, CI 8.76 to 10.08) and obese strata (9.79°; CI 9.08 to 10.50). No differences between strata were observed in the transverse plane. The real-world gait inputs resulted in a lower aspect ratio for all three patient groups compared to the ISO standard AR of 3.86. There was a trend towards a higher AR in patients with a lower BMI. Obese patients had a reduced AR of 3.33 (CI 3.08 to 3.58) compared to the overweight and healthy weight patients, demonstrating AR of 3.36(CI 3.21 to 3.52) and 3.48 (CI 3.25 to 3.70), respectively. Discussion There were few hip kinematic differences between BMI strata, except for a lower frontal ROM in the healthy weight patients. There was a resulting trend towards an increased AR in the healthy weight group. Notwithstanding the effect of contact force which was not modelled in this study, increased AR in the healthy weight group might assist long molecule entrainment and hence reduce risk of polyethylene wear for equivalent levels of activity. These results highlight the conservative nature of the ISO standard ISO-14242 and provide a possible link between kinematics and the observed increased in revision rates in patients with high BMI.

This is the model used in an FP7 European Commission project called Lifelongjoints (https://lifelongjoints.eu/). The model was used to investigate hip loads using a large dataset collect at Leeds Teaching Hospital NHS Trust

In the UK, the posterior approach (PA) and direct lateral approach (DLA) are the most common total hip arthroplasty (THA) procedures. Few studies however, have compared the subsequent functional outcomes. This exploratory study aimed to examine the effect of PA and DLA approaches on post-operative hip kinematics, strength and hip muscle cross-sectional area (CSA), compared to healthy controls.Participants comprised of 15 cases in the DLA group, > 12 month post-operatively, (ten male, age 68.9+/-5.5 years, BMI 26.9+/-3.0), 13 cases in the PA group (six male; age 72.9+/-6.9 years, BMI 27.1+/-3.6) and 11 age/BMI-matched healthy control participants. All participants underwent 3D kinematic (Vicon, Oxford, UK) and kinetic (AMTI, USA) analysis whist performing self-selected and fast walking as well as sit-to-stand and stand-to-sit. Isometric dynamometry was performed (Biodex Medical systems, USA) for all major muscle groups around the operated hip, and a subset of five participants (three DLA v two PA) underwent ?slice encoding for metal artefact correction? (SEMAC) MRI imaging to measure muscle CSA. Patient-reported outcome measures were collected.Both post-operative surgical groups exhibited altered gait, particularly in limited hip extension, compared to the control participants. The DLA group demonstrated forced hip extension matching controls only under fast walking conditions while the PA group did not achieve hip extension. Both surgical approaches achieved high PROMs scores.The PA group were weaker for all strength activities tested, whereas the DLA cases demonstrated similar hip strength to controls. SEMAC imaging revealed reduced CSA for those muscles dissected during surgery, compared to the contralateral side.This exploratory study demonstrated small but measurable differences between surgical approaches for muscle CSA, hip strength of major hip muscle groups and a number of gait variables, although both approaches produce satisfactory functional outcomes for patients after surgery.

Abstract Objectives The importance of cup position on the performance of total hip replacements (THR) has been demonstrated in in vitro hip simulator tests and clinically. However, how cup position changes during gait has not been considered and may affect failure scenarios. The aim of this study was to assess dynamic cup version using gait data. Methods Pelvic movement data for walking for 39 unilateral THR patients was acquired (Leeds Biomedical Research Centre). Patient’s elected walking speed was used to group patients into high- and low-functioning (mean speed, 1.36(SD 0.09)ms−1 and 0.85(SD 0.08)ms−1 respectively). A computational algorithm (Python3.7) was developed to calculate cup version during gait cycle. Inputs were pelvic angles and initial cup orientation (assumed to be 45° inclination and 7° version, anterior pelvic plane was parallel to radiological frontal plane). Outputs were cup version angles during a gait cycle (101 measurements/cycle). Minimum, maximum and average cup version during gait cycle were measured for each patient. Two-sample t-test (p=0.05) was used to compare groups. Results Over a gait cycle the mean minimum, maximum and average version angles for the high-functioning group were −4.5(SD 4.4)°, 5.0(SD 4.3)°, 9.5(SD 4.0)° and for low-functioning group 2.0(SD 3.7)°, 6.2(SD 2.9)°, 8.1(SD 3.2)°. There were no significant differences for the minimum, maximum and average version angles between the two groups. Conclusions The study shows that dynamic acetabular cup version changes substantially during gait and this must be considered clinically and in pre-clinical testing. There was no significant difference between the two groups; however, dynamic cup version was more negative in high-functioning compared to low-functioning patients. Further studies on a larger cohort are required to determine whether patients’ profiles can be stratified to provide enhanced inputs for pre-clinical THR testing. Declaration of Interest (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Introduction One of the known mechanisms which could contribute to the failure of total hip replacements (THR) is edge contact. Failures associated with edge contact include rim damage and lysis due to altered loading and torques. Recent study on four THR patients showed that the inclusion of pelvic motions in a contact model increased the risk of edge contact in some patients. The aim of current study was to determine whether pelvic motions have the same effect on contact location for a larger patient cohort and determine the contribution of each of the pelvic rotations to this effect. Methods Gait data was acquired from five male and five female unilateral THR patients using a ten camera Vicon system (Oxford Metrics, UK) interfaced with twin force plates (AMTI) and using a CAST marker set. All patients had good surgical outcomes, confirmed by patient-reported outcomes and were considered well-functioning, based on elective walking speed. Joint contact forces and pelvic motions were obtained from the AnyBody modelling system (AnyBody Technologies, DK). Only gait cycle regions with available force plate data were considered. A finite element model of a 32mm head on a featureless hemispherical polyethylene cup, 0.5mm radial clearance, was used to obtain the contact area from the contact force. A bespoke computational tool was used to analyse patients’ gait profiles with and without pelvic motions. The risk of edge contact was measured as a “centre proximity angle” between the cup pole and centre of the contact area, and “edge proximity angle” between the cup pole and the furthest contact area point away from the pole. Pelvic tilt, drop and internal-external rotation were considered one at a time and in combinations. Results In eight out of 10 patients, the addition of pelvic motions decreased the risk of edge contact during toe-off. There was up to 6° reduction in the proximity angles when pelvic motions were introduced to the gait cycle. In six out of 10 patients, the addition of pelvic motions resulted in an increase in the risk of edge contact during heel-strike with up to 6° increase in the proximity angles. For all patients where these effects were seen, sagittal pelvic tilt was a substantial contributor. Conclusion The results of this study suggest that pelvic motion play an important role in contact location in THR bearings during loading phase. Both static and dynamic pelvic tilt contribute to the variability in the risk of edge contact. Further tests on larger patient cohorts are required to confirm the trends observed. The outcomes of this study suggest that pre-clinical mechanical and tribological testing of THRs should consider the role of pelvic motion. The outcomes also have implications for establishing surgical positioning safe zones, which are currently based only on risk of dislocation and severe impingement.

Introduction Preclinical testing of implants considers THR patients a homogenous group; in reality, patients are heterogeneous and previous large cohort studies have explored stratification and identified that THR patients function differently [1]. The wide- spread failure of the ASR hip highlighted the potential importance of patient characteristics [2], and a more robust pre- clinical testing procedure may have improved prediction of outcome. Therefore this study aimed to identify differences in hip contact force (HCF) in THR patients stratified by their functional ability. Methods 133 THR patients, >12 months post-surgery, underwent 3D kinematic (Vicon, UK) and kinetic (AMTI, USA) analysis whilst walking at self-selected speed. HCF’s, normalized by body weight, were computed through multibody modeling (AnyBody Technology, Denmark) during gait and a mean for each patient was calculated from three to five walking trials. Patients were stratified into three functionality groups by distribution around the mean gait speed for the full cohort of 1.1m/s. The low functioning group (LF) comprised cases with a gait speed ≤0.93 m/s (i.e. 1.1m/s ≤1SD), the mid functioning group (MF) comprised cases with a gait speed between 0.94 m/s and 1.25 m/s (cohort mean ± 1SD), while the high functioning group (HF) included cases walking ≥1.26 m/s. Differences between groups were analyzed using one- dimensional statistical parametric mapping [3]. Linear regression was used to test for significant differences across groups. The test statistic SPMt was evaluated at each point in the normalized time series, and a critical threshold corresponding to an error rate of α= 0.05 was calculated based on random field theory. Supra-threshold clusters with their associated p-values were then identified. Results Systematic differences were observed between the different functioning groups throughout the gait cycle. Four different supra-threshold clusters reached or exceeded the critical threshold of t=3.244 indicating systematic between-group differences, with the chances of observing similar clusters in repeated random samplings of p<0.001. HCF were linearly increasing with functionality from heel strike to foot flat (1st cluster), from terminal stance to initial swing (3rd cluster), and during terminal swing (4th cluster), while they were decreasing for higher functionality during midstance (2nd cluster). Discussion Stratification of THR patients by functionality showed significant differences in the contact forces that implants have to withstand during gait. The LF patients displayed a pathological HCF, with a flattening of the typical double hump, indicating that differences can be observed between groups of healthy THR patients. Overall, THR patients are functionally heterogeneous and preclinical testing should reflect differences better than currently required by the ISO-14242 implant testing standard.

This dataset contains kinematic and kinetic motion capture data collected on 140 post-operative total hip replacement patients. The data has been stratified into age groups and function groups in order to understand whether function in THR patients is dependent on patient or biomechanical characteristics. This study was supported by the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. GA-310477 LifeLongJoints.

Abstract

Background: This study investigated the effect of posterior and direct lateral (modified Hardinge) approach total hip arthroplasty on post-operative hip function compared to healthy, control participants. This study aimed to use a combination of motion analysis, strength measurements and imaging to investigate the effect of surgical approach on post-operative hip function in posterior approach and direct lateral approach cases.Methods: Twenty-eight total hip arthroplasty patients (15 direct lateral approach; 13 posterior approach) and 11 control participants underwent motion capture analysis at two walking speeds (normal and fast walking) and whilst standing from a seated position; hip joint strength and patient reported outcomes were also obtained. Muscle cross-sectional area was measured in a sub-set (N=5) using a novel magnetic resonance imaging sequence incorporating encoding for metal artefact correction.Results: The posterior approach group tended not to achieve full hip extension post-surgically, whereas the direct lateral approach patients tended to extend the hip during the fast walk, similar to control participants. The posterior approach group were weaker in all muscle groups excluding hip abductors, compared to the direct lateral approach patients and control group. In both surgical groups the muscle cross sectional area was reduced in all muscles disrupted during surgery, compared to the contralateral limb. Both surgical groups’ perceived hip function and physical health to be superior compared to the control group.Conclusions: Our findings suggest during sit to stand and fast walking the posterior approach group were functionally poorer and demonstrated weaker hip strength compared to the direct lateral approach group. Furthermore, surgical muscle disruption in our subset of patients is still apparent up to five years post-surgery, as reflected by reduced muscle cross sectional area.

Research investigating ankle function during walking in a controlled ankle motion (CAM) boot has either placed markers on the outside of the boot or made major alterations to the structure of the CAM boot to uncover key landmarks. The aim of this study was to quantify joint kinematics and kinetics using “in-boot” skin markers whilst making only minimal structural alterations. Seventeen healthy participants walked at their preferred walking speed in two conditions: (1) in standard athletic trainers (ASICS patriot 8, ASICS Oceania Pty Ltd, USA), and (2) using a hard-cased CAM boot (Rebound® Air Walker, Össur, Iceland) fitted on the right foot. Kinematic measurements revealed that CAM boots restrict sagittal plane ankle range of motion to less than 5°, and to ∼3° in the frontal plane, which is a reduction of 85% and 73% compared to standard footwear, respectively (p < 0.001). This ankle restriction resulted in a reduction of ankle joint total limb work contribution from 38 ± 5% in normal footwear to 13 ± 4% in the CAM boot (p < 0.001). This study suggests that CAM boots do restrict the ankle joint’s ability to effectively perform work during walking, which leads to compensatory mechanisms at the ipsilateral and contralateral hip and knee joints. Our findings align with previous research that employed “on-boot” kinematic measurements, so we conclude that in-boot approaches do not offer any benefit to the researcher and instead, on-boot measurements are suitable.

Preferred walking speed (PWS) is lower when wearing a controlled ankle motion (CAM) boot, which can potentially make comparisons between footwear conditions difficult. Standardising walking speed accounts for this but lacks the ecological validity of PWS. The aim of this study was to compare acute biomechanical responses to CAM boot wear when walking is freely chosen and when it is controlled. Twelve healthy participants walked on an instrumented treadmill at their PWS and at three standardised speeds: 3, 4, and 5 km/h. They did so in three footwear conditions: (1) with a Rebound® Air Walker CAM boot on the right leg, (2) with a Rebound® Air Walker on the right leg and an Evenup Shoelift™ on the left, and (3) in normal footwear. Comparisons between footwear conditions were largely similar in the ipsilateral limb at PWS and at the standardised speeds, which included a decrease in total mechanical work and ankle joint work during CAM boot wear (p < 0.001). At the standardised speeds, total mechanical work and hip joint work were lower during CAM boot wear than wearing normal shoes and the Evenup Shoelift™ (p ≤ 0.014), although there were no differences between footwear conditions at PWS (p ≥ 0.095). As such, acute responses to CAM boot wear are different when speed is standardised compared to when speed is freely chosen, meaning conclusions cannot necessarily be transferred between approaches. Based on these differences observed between walking speeds, it would be prudent for future studies to try to maintain ecological validity by using PWS.

Introduction Controlled ankle motion (CAM) boots are a below-knee orthotic device prescribed for the management of foot and ankle injuries to reduce ankle range of motion (RoM) and offload the foot and ankle whilst allowing continued ambulation during recovery. There is a lack of clarity within the current literature surrounding the biomechanical understanding and effectiveness of CAM boots. Aims To summarise the biomechanical effects of CAM boot wear as an orthotic for restricting ankle RoM and offloading the foot. Methods A systematic literature review was conducted in accordance with the PRISMA 2020 guidelines. All papers were independently screened by two authors for inclusion. Methodological quality was appraised using Joanna Briggs Critical Appraisal checklists. A narrative synthesis of all eligible papers was produced. Results Thirteen studies involving 197 participants (113 male and 84 female) were included. All studies were quasi-randomised and employed a within-study design, of which 12 studies included a control group and a range of CAM boots were investigated. CAM boots can be seen to restrict ankle RoM, however, neighboring joints such as the knee and hip do have kinetic and kinematic compensatory alterations. Plantar pressure of the forefoot is effectively redistributed to the hindfoot by CAM boots. Conclusion The compensatory mechanisms at the hip and knee joint during CAM boot wear could explain the secondary site pain often reported in patients, specifically at the ipsilateral knee and contralateral hip. Although CAM boots can be used to restrict ankle motion, this review has highlighted a lack of in-boot kinematic analyses during CAM boot use, where tracking markers are placed on the anatomical structure rather than on the boot, or through video fluoroscopy, urging the need for a more robust methodological approach to achieve this. There is a need for studies to assess the biomechanical alterations caused by CAM boots in populations living with foot and ankle pathologies. Future research, adopting a longitudinal study design, is required to fully understand the effectiveness of CAM boots for rehabilitation.

Hinged controlled ankle motion boots are used to incrementally increase ankle joint range of movement during rehabilitation following Achilles’ tendon rupture. This increased movement should induce mechanical stress on the tendon via cycles of stretching and shortening. However, research has yet to determine how this permitted range of movement influences tendon length change. Eight healthy individuals (age: 23 ± 2 y; stature = 1.70 ± 0.09 m; body mass = 67.7 ± 13.7 kg) walked at a self-selected speed on an instrumented, motorised treadmill in a hinged controlled ankle motion boot with three pre-established ankle ranges of movement: 0, 15, and 30°, which were all compared with walking in normal footwear. Kinematic and kinetic measurements were obtained using motion capture and the treadmill. Triceps surae mechanical characteristics, including Achilles’ tendon stretch, were obtained with B-mode ultrasonography. Achilles’ tendon stretch significantly (p < 0.001) increased as boot range of movement increased and was strongly correlated with measured ankle joint range of movement when the boot was set to a 15 or 30° range of movement (r ≥ 0.84, p ≤ 0.009). Increasing controlled ankle motion boot range of movement also increased ankle joint mechanical work done and total mechanical work done by the boot-wearing limb, which led to an increase in self-selected walking speed (all p < 0.001). These findings provide preliminary evidence that hinged controlled ankle motion boots have the capacity to provide a controlled mechanical stimulus to the Achilles’ tendon when range of movement is increased. This has possible clinical application for the early management of Achilles’ tendon rupture, potentially improving healing and functional outcomes if it can be translated into a patient population.

Background Controlled ankle motion (CAM) boots are often prescribed during the rehabilitation of lower limb injuries and pathologies to reduce foot and ankle movement and loading whilst allowing the patient to maintain normal daily function. Research question The aim of this study was to quantify the compensatory biomechanical mechanisms undergone by the ipsilateral hip and knee joints during walking. In addition, the compensatory mechanisms displayed by the contralateral limb were also considered. Methods Twelve healthy participants walked on an instrumented treadmill at their preferred walking speed. They underwent kinematic and kinetic analysis during four footwear conditions: normal shoes (NORM), a Malleo Immobil Air Walker on the right leg (OTTO), a Rebound® Air Walker on the right leg with (EVEN) and without (OSS) an Evenup Shoelift™ on the contralateral leg. Results CAM boot wear increased the relative joint contribution to total mechanical work from the ipsilateral hip and knee joints (p < 0.05), which was characterised by increased hip and knee abduction during the swing phase of the gait cycle. EVEN increased the absolute work done and relative contribution of the contralateral limb. CAM boot wear reduced walking speed (p < 0.05), which was partially compensated for during EVEN. Significance The increased hip abduction in the ipsilateral leg was likely caused by the increase in effective leg length and limb mass, which could lead to secondary site complications following prolonged CAM boot wear. Although prescribing an even-up walker partially mitigates these compensatory mechanisms, adverse effects to contralateral limb kinematics and kinetics (e.g., elevated knee joint work) should be considered.

Introduction Conventional and functional knee strength ratios, defined using peak joint moment of the flexors and extensors, are used in practice to estimate injury risk (Baroni et al., 2020). Despite literature commonly reporting these values there remains uncertainty regarding their functional value (Kellis et al., 2022). It has been suggested that using a time-series metric from angle-specific joint moments might be more successful at identifying injury risk (Read et al., 2022). Therefore, the aim of this study was to compare discrete strength ratios commonly used in practice with angle-specific ratios to determine differences between the two measures. Method Twenty-eight footballers were recruited from the same English Premier League club (age: 22±4 y; stature: 1.81±0.07 m; body mass: 75.2±6.8 kg). Isokinetic testing was conducted for the knee flexors and extensors in a concentric motion at two angular velocities (60°/s and 240°/s) and in an eccentric motion (for the knee flexors only) at one angular velocity (30°/s) using an isokinetic dynamometer (Biodex Medical Systems). Conventional, discrete H:Q ratio’s (cHQR-D) were calculated as the ratio between peak joint moment in the flexors and extensors at 60°/s. Functional, discrete H:Q ratio’s (fHQR-D) were calculated as the peak joint moment in the flexors during the eccentric condition (30o/s) and the extensors at 240°/s. Angle-specific ratios (cHQR-AS and fHQR-AS) were computed as the ratio between flexor and extensor joint moments for all angles where both muscle groups were in the isokinetic range. Mean absolute residuals were then computed to compare between discrete and angle specific ratios. Results Peak joint moment for flexors and extensors at 60°/s was 129.4±21.6 and 240.9±35.6 Nm, respectively (cHQR-D = 0.54±0.07). Eccentric peak joint moment for the flexors was 165.9±34.6 Nm, and concentric peak moment for the extensors at 240°/s was 145.3±18.4 Nm (fHQR-D = 1.15±0.21). Throughout the isokinetic range, average cHQR-AS ranged from 0.41-0.98 with a mean absolute residual of 0.11±0.11 versus cHQR-D. In comparison, the average fHQR-AS ranged from 0.98-1.33 with a larger mean absolute residual of 0.26±0.14 versus fHQR-D. Conclusion Neither conventional nor functional discrete ratios were fully representative of angle-specific ratios throughout the isokinetic range. However, the average residual for the conventional ratio was lower than the functional ratio, despite a greater range of values for cHQR-AS. Suggesting that discrete conventional ratios are more representative of angle-specific ratios over a greater range of joint angles, compared to discrete functional ratios. Furthermore, discrete functional ratios are not representative of angle specific functional ratios, which could mask athletes who may have fHQR deficits and may be at risk of injury. References Baroni, BM et al. (2020). J Strength Cond Res, 34, 281-293. Kellis, E et al. (2022). J Sport Health Sci. Read, PJ et al. (2022). J Sports Sci, 1-7.

Background Effective management of anterior cruciate ligament (ACL) injuries requires a comprehensive approach, from initial assessment, through treatment, rehabilitation, and discharge, however no gold standard care pathway exists to help guide clinicians. This case series provides an overview of current ACL injury management processes in six National Health Service (NHS) Trusts. Methods This study utilised a retrospective case series design within six NHS Trusts in the Yorkshire region of the United Kingdom. Using a standard operating procedure, each Trust selected ten consecutive ACL injured patients (≥ 16 years), managed either surgically or non-surgically. Data relating to the patient injury journey, patient and injury characteristics, key pathway events, rehabilitation management, outcome measures, and discharge, were collected. Data was anonymised and analysed using descriptive statistics. Results Reviews covered 55 patients, median age 25.5 years, (41 males, 14 females). Median time to specialist assessment from injury was 12 days (Interquartile Range [IQR] 6 to 20 days), with 43 patients managed operatively, and 12 non operatively. The median number of physiotherapy sessions was 21 (IQR 9 to 29.5), with outcome measures being variably used across Trusts. Trusts using patient reported outcome measures (PROMS) consistently with their patients provided more physiotherapy appointments (34.5 and 27) and achieved higher return to sport (RTS) rates. Time from injury to discharge varied with a median of 421 (IQR 249 to 546) days. Discharge criteria were applied inconsistently across Trusts, with 31% of cases not using specific criteria. However, Trusts using standardised discharge criteria showed better RTS outcomes, with 27 (61%) patients successfully returning to sport. Conclusions This case series review highlighted some good practice in initial ACL management across six NHS Trusts in the Yorkshire region. However, from time to MRI diagnosis to discharge, substantial variation in care is observed. Whether treated operatively or non-operatively, for patients aiming to RTS, this was achieved with greater consistency when more physiotherapy appointments were undertaken, outcome measures and PROMs were used, and specific discharge criteria was utilised. Future larger pathway investigation studies incorporating causative and predictive analysis studies on a national scale are required to determine whether similar trends are observed in a wider ACL injured population, which could help to improve national pathways for patients and clinicians working towards ensuring more positive and standardised patient-related ACL injury outcomes.

This study compared angle-specific hamstring:quadricep (H:Q) ratios with their discrete counterparts during strength testing in pro fessional male footballers. Twenty-eight professional English Premier League footballers were recruited for this study (age: 22 6 4 years; stature: 1.81 6 0.07 m; body mass: 75.2 6 6.8 kg). Isokinetic testing of the knee flexors and extensors was conducted concentrically at 2 angular velocities (60˚ and 240˚·s21 ) and eccentrically (for the knee flexors only) at 30˚·s21 . Conventional H:Q ratio was calculated as the ratio between peak joint moment in the flexors and extensors at 60˚·s21 . Functional H:Q ratio was calculated as the peak joint moment in the flexors during the eccentric condition and the extensors at 240˚·s21 . Discrete conventional and functional H:Q ratios were 0.56 6 0.06% and 1.28 6 0.22%, respectively. The residual differences between discrete values and angle-specific residual values were 13.60 6 6.56% when normalized to the magnitude of the discrete value. For the functional ratios, the normalized residual was 21.72 6 5.61%. Therefore, neither discrete ratio was representative of angle-specific ratios, although the conventional ratio had lower error overall. Therefore, practitioners should consider H:Q ratio throughout the full isokinetic range of motion, not just the discrete ratio calculated from peak joint moments, when designing and implementing training programs or monitoring injury risk, recovery from injury, and readiness to return to play

We do not yet understand the concurrent validity of markerless motion capture (MMC) to measure kinematic differences between multiple gait speeds. This study determined the capacity of Theia3D (Theia Markerless Inc.) MMC to detect sagittal-plane kinematic responses to different gait speeds during walking (3 and 5 km/h) and running (10 and 12 km/h). Fourteen participants ambulated on a motorised treadmill, while markerbased motion capture, through optoelectronic cameras (Oqus 7+, Qualisys AB), and MMC, through videos (Miqus, Qualisys AB) were synchronously collected. Sagittal plane changes in pelvis, hip, knee, and ankle kinematics were compared. Mostly excellent waveform similarity was found for joint kinematic changes (coefficient of multiple determination [CMD] ≥ 0.87), but pelvic tilt was less similar (CMD ≤ 0.48). Agreement between outcome measures (joint minima and maxima, range of motion) was mostly good-to-excellent (intraclass correlation coefficient [ICC] = 0.475-0.950) with standard error of measurement values of less than 1°. Pelvis kinematics showed lower agreement between systems (ICC = 0.032-0.776). In this study, Theia3D detected changes in hip, knee, and ankle sagittal-plane joint kinematics between speeds with a similar accuracy to the marker-based approach. Therefore, Theia3D is appropriate for use if interested in lower-limb sagittal joint kinematics, but not pelvic tilt.

INTRODUCTION: Markerless motion capture (MMC) is increasing in popularity among biomechanists because of the reduced data collection time and removal of subjects needing to wear tight, minimalist clothing [1]. However, gait analysis often requires subjects to walk or run at multiple speeds, such as in an incremental exercise test. The sensitivity of MMC to detect kinematic changes across speeds has yet to be thoroughly explored, so the aim of this study was to compare kinematic responses to changes in gait speed when measured with a widely used marker-based system versus a MMC system. METHOD: Fifteen healthy, adult participants walked on an instrumented treadmill (1,000 Hz; Gaitway3D; h/p/cosmos) at 3 and 5 km/h and ran at 10, 11, and 12 km/h. A 14-camera optoelectronic motion capture system (Oqus 7+, Qualisys) was used to collect marker data, where markers were placed according to Cappozzo et al. [2]. Markerless video data were collected synchronously with 12 high-speed video cameras (Miqus, Qualisys). Both systems were sampling at 100 Hz. Markerless data were exported to Theia3D for processing, before being exported to Visual3D for modelling alongside marker data. Gait events were determined using the kinetic data, which was the same for both motion capture systems. Kinematic data were exported to MATLAB to calculate changes in sagittal angular data between gait speeds. RESULTS: For walking (changes between 3-5 km/h), MMC demonstrated the capacity to measure similar changes in joint range of motion (ROM), peak flexion, and peak extension for hip, knee, and ankle joints (ICC[3,1] ≥ 0.892) when compared to marker-based data, and there were no significant differences between the change in joint kinematics between systems (p > 0.05). MMC also displayed moderate-to-excellent agreement for knee and ankle joint kinematics during running (changes between 10-11 and 11-12 km/h), including ROM and peak flexion/extension (ICC ≥ 0.626). However, the hip joint was less consistent, with poor-to-moderate agreement generally being found, especially in peak hip extension (ICC = 0.198 when comparing differences between 11-12 km/h). There were no significant differences between systems during running (p < 0.05). CONCLUSION: MMC was able to measure small changes in joint angles during walking at similar magnitudes to traditional marker-based motion capture, which is promising for clinical biomechanists and gait analysis clinics. However, MMC importantly performs less well when trying to measure joint angle changes during different running speeds, with varying results between lower limb joints. Researchers and practitioners should be cautious when interpreting sagittal-plane kinematic changes during running when employing MMC as the chosen method of motion capture. REFERENCES: [1] Kanko, RM et al. (2021) J Biomech;127:110665 [2] Cappozzo, A et al. (1995) Clin Biomech;10:171-8