Imperial College London

Anthony M J Bull .......... .... Professor of Musculoskeletal Mechanics

Faculty of EngineeringDepartment of Bioengineering

Head of Department of Bioengineering



+44 (0)20 7594 5186a.bull Website




Mrs Angela Glyes +44 (0)20 7594 9794




B217Bessemer BuildingSouth Kensington Campus





Publication Type

306 results found

Bin Abd Razak H, Chew D, Kazezian Z, Bull AMJet al., 2021, Autologous Protein Solution - A Promising Solution for Osteoarthritis?, EFORT Open Reviews, ISSN: 2396-7544

Journal article

Berthaume MA, Bull AMJ, 2021, Cyamella (a popliteal sesamoid bone) prevalence: a systematic review, meta-analysis, and proposed classification system., Clin Anat

INTRODUCTION: The cyamella is a rare, generally asymptomatic, knee sesamoid bone located in the proximal tendon of the popliteal muscle. Only two studies have investigated cyamella presence/absence in humans, putting ossified prevalence rates at 0.57-1.8%. We aim to 1) determine cyamella prevalence in a Korean population, 2) examine coincident development of the cyamella and fabella, and 3) perform a systematic review and meta-analysis on the cyamella in humans. MATERIALS AND METHODS: Medical computed tomography scans of 106 individuals were reviewed. A systematic review and meta-analysis were performed following PRISMA guidelines. RESULTS: Cyamellae were found in 3/212 knees (1.4%), and presence/absence was uncorrelated to height, age, and sex. The cyamella was not found coincidentally with the fabella, although the statistical power was low. Our systematic review/meta-analysis revealed cyamellae were generally asymptomatic and ossification could occur at 14 years. Cyamellae were equally likely to be found in both sexes, knees, one or both knees, and there appeared to be no global variation in prevalence rates. Cyamellae were found in three distinct locations. CONCLUSIONS: There is little support for the role of intrinsic genetic and/or environmental factors in cyamella development in humans. However, the apparent phylogenetic signal in Primates suggests genetics plays a role in cyamella development. We propose a cyamella classification system based on cyamella location (Class I, popliteal sulcus; Class II, tibial condyle; Class III, fibular head) and hypothesize locations may correspond to distinct developmental pathways, and cyamella function may vary with location. This article is protected by copyright. All rights reserved.

Journal article

van der Kruk E, Silverman AK, Koizia L, Reilly P, Fertleman M, Bull AMJet al., 2021, Age-related compensation: Neuromusculoskeletal capacity, reserve & movement objectives., J Biomech, Vol: 122

The prevention, mitigation and treatment of movement impairments, ideally, requires early diagnosis or identification. As the human movement system has physiological and functional redundancy, movement limitations do not promptly arise at the onset of physical decline. A such, prediction of movement limitations is complex: it is unclear how much decline can be tolerated before movement limitations start. Currently, the term 'homeostatic reserve' or 'physiological reserve' is used to refer to the redundancy of the human biological system, but these terms do not describe the redundancy in the muscle architecture of the human body. The result of functional redundancy is compensation. Although compensation is an early predictor of movement limitations, clear definitions are lacking and the topic is underexposed in literature. The aim of this article is to provide a definition of compensation and emphasize its importance. Compensation is defined as an alteration in the movement trajectory and/or altering muscle recruitment to complete a movement task. Compensation for capacity is the result of a lack in neuromusculoskeletal reserve, where reserve is defined as the difference between the capacity (physiological abilities of the neuromusculoskeletal system) and the task demand. Compensation for movement objectives is a result of a shift in weighting of movement objectives, reflecting changing priorities. Studying compensation in biomechanics requires altered protocols in experimental set-ups, musculoskeletal models that are not reliant on prescribed movement, and inclusion of alternative movement objectives in optimal control theory.

Journal article

Yeh C, Calder J, Antflick J, Bull A, Kedgley Aet al., 2021, Maximum dorsiflexion increases Achilles tendon force during exercise for midportion Achilles tendinopathy, Scandinavian Journal of Medicine and Science in Sports, ISSN: 0905-7188

Journal article

van der Kruk E, Silverman AK, Reilly P, Bull AMJet al., 2021, Compensation due to age-related decline in sit-to-stand and sit-to-walk., J Biomech, Vol: 122

Capacity is the physiological ability of the neuromusculoskeletal systems; this declines with age. This decline in capacity may result in the inability to stand up (sit-to-stand, sit-to-walk), which is an important movement for independent living. Compensation, as a result of functional redundancy, is key in understanding how much age-related decline can be tolerated before movement limitations arise. Yet, this topic has been underexposed in the biomechanics literature. The purpose of this systematic review was to approach the literature on sit-to-stand and sit-to-walk studies from the perspective of compensation and create an overview of our current understanding of compensation in standing up, identifying the limitations and providing future recommendations. A literature search was performed, using the keywords and their synonyms: strateg*(approach, technique, way)AND, sit-to-walk OR sit-to-stand OR rise (raise, arise, stand, stand-up) AND chair (seat). Inclusion criteria: full articles on biomechanics or motor control on sit-to-stand or sit-to-walk in healthy adults (<60y), healthy or frail elderly adults (>60y), and adults with osteoarthritis. The results show that the experimental set-ups and musculoskeletal models in STS and STW studies generally exclude compensation by using restricted protocols and simplifications. Moreover, factors are mostly analysed in isolation, excluding confounding causes within capacity and/or movement objectives which limits the generalization of the results. Future studies in the standing up task should consider to (1) determine the effect of varying arm push-off strategies, (2) focus on sit-to-walk, (3) determine the biomechanical implications of asymmetry, and (4)incorporate assessments of physical capacity as well as changes in psychological priorities.

Journal article

Ding Z, Jarvis H, Bennett A, Baker R, Bull Aet al., 2021, Higher knee contact forces might underlie increased osteoarthritis rates in high functioning amputees: a pilot study, Journal of Orthopaedic Research, Vol: 39, Pages: 850-860, ISSN: 0736-0266

High functioning military transtibial amputees (TTAs) with well‐fitted state of the art prosthetics have gait that is indistinguishable from healthy individuals, yet they are more likely to develop knee osteoarthritis (OA) of their intact limbs. This contrasts with the information at the knees of the amputated limbs that have been shown to be at a significantly reduced risk of pain and OA. The hypothesis of this study is that biomechanics can explain the difference in knee OA risk. Eleven military unilateral TTAs and eleven matched healthy controls underwent gait analysis. Muscle forces and joint contact forces at the knee were quantified using musculoskeletal modeling, validated using electromyography measurements. Peak knee contact forces for the intact limbs on both the medial and lateral compartments were significantly greater than the healthy controls (P  ≤ .006). Additionally, the intact limbs had greater peak semimembranosus (P  = .001) and gastrocnemius (P  ≤ .001) muscle forces compared to the controls. This study has for the first time provided robust evidence of increased force on the non‐affected knees of high functioning TTAs that supports the mechanically based hypothesis to explain the documented higher risk of knee OA in this patient group. The results suggest several protentional strategies to mitigate knee OA of the intact limbs, which may include the improvements of the prosthetic foot control, socket design, and strengthening of the amputated muscles.

Journal article

Goodwin JE, Bull AMJ, 2021, Novel Assessment of Isometric Hip Extensor Function: Reliability, Joint Angle Sensitivity, and Concurrent Validity., J Strength Cond Res

ABSTRACT: Goodwin, JE and Bull, AMJ. Novel assessment of isometric hip extensor function: reliability, joint angle sensitivity, and concurrent validity. J Strength Cond Res XX(X): 000-000, 2021-Closed-chain hip extension function has not been well examined. The aim of this study was to examine the reliability, joint angle sensitivity, muscle recruitment, and concurrent validity of a force plate-based isometric hip extensor test (isometric hip thrust). All subjects were active men aged 19-29 years. In part 1, bilateral and unilateral hip extensor testing was completed on 4 occasions by 14 subjects to evaluate repeatability of force and torque measures. In part 2, joint angle sensitivity of force, torque, and surface electromyography was assessed by 10 subjects completing testing at 4 hip joint angles in a single test session. In part 3, concurrent validity of joint torque was assessed relative to standing and supine test positions on an isokinetic dynamometer, by 10 subjects in a single test session. The repeatability study found small changes in the mean from sessions 1-2 (mean standardized change d = 0.31) and close to no change in later sessions (mean d = 0.12). Typical error was predominantly low to moderate (mean 0.42), and intraclass correlation coefficient (ICC) was typically high (mean ICC = 0.87). The joint angle sensitivity study showed that increasing the hip flexion resulted in increases in peak extension force (p = 0.001) and gluteus maximus activation (p = 0.003) and a reduction in biceps femoris activation (p < 0.001). There was no change in torque (p = 0.585) and vastus lateralis activation (p = 0.482). The concurrent validity study found that torque was correlated with supine dynamometry (R2 = 0.555) but not with standing dynamometry (R2 = 0.193). In summary, the isometric hip thrust is repeatable, but benefits from familiarization. Force output and muscle recruitment are sensitive to joint position, providing an opportunity to assess different fu

Journal article

Smith SHL, Coppack RJ, Bogert AJVD, Bennett AN, Bull AMJet al., 2021, Review of musculoskeletal modelling in a clinical setting: Current use in rehabilitation design, surgical decision making and healthcare interventions, CLINICAL BIOMECHANICS, Vol: 83, ISSN: 0268-0033

Journal article

Kazezian Z, Bull AMJ, 2021, A review of the biomarkers and in vivo models for the diagnosis and treatment of heterotopic ossification following blast and trauma-induced injuries, Bone, Vol: 143, ISSN: 1873-2763

Heterotopic ossification (HO) is the process of de novo bone formation in non-osseous tissues. HO can occur following trauma and burns and over 60% of military personnel with blast-associated amputations develop HO. This rate is far higher than in other trauma-induced HO development. This suggests that the blast effect itself is a major contributing factor, but the pathway triggering HO following blast injury specifically is not yet fully identified. Also, because of the difficulty of studying the disease using clinical data, the only sources remain the relevant in vivo models. The aim of this paper is first to review the key biomarkers and signalling pathways identified in trauma and blast induced HO in order to summarize the molecular mechanisms underlying HO development, and second to review the blast injury in vivo models developed.The literature derived from trauma-induced HO suggests that inflammatory cytokines play a key role directing different progenitor cells to transform into an osteogenic class contributing to the development of the disease. This highlights the importance of identifying the downstream biomarkers under specific signalling pathways which might trigger similar stimuli in blast to those of trauma induced formation of ectopic bone in the tissues surrounding the site of the injury. The lack of information in the literature regarding the exact biomarkers leading to blast associated HO is hampering the design of specific therapeutics. The majority of existing blast injury in vivo models do not fully replicate the combat scenario in terms of blast, fracture and amputation; these three usually happen in one insult. Hence, this paper highlights the need to replicate the full effect of the blast in preclinical models to better understand the mechanism of blast induced HO development and to enable the design of a specific therapeutic to supress the formation of ectopic bone.

Journal article

Toderita D, Henson D, Klemt C, Ding Z, Bull AMJet al., 2021, An anatomical atlas-based scaling study for quantifying muscle and hip joint contact forces in above and through-knee amputees using validated musculoskeletal modelling, IEEE Transactions on Biomedical Engineering, Pages: 1-1, ISSN: 0018-9294

Journal article

Kazezian Z, Yu X, Ramette M, Macdonald W, Bull Aet al., 2020, Development of a rodent high energy blast injury model for investigating conditions associated with traumatic amputations, Bone and Joint Research, ISSN: 2046-3758

In recent conflicts, most injuries to the extremities are due to blast resulting in a large number of lower limb amputations. These lead to heterotopic ossification (HO), phantom limb pain (PLP), and functional deficit. The mechanism of blast loading produces a combined facture and amputation. Therefore, to study these conditions, in vivo models that replicate this combined effect are required. The aim of this study is to develop a preclinical model of blast-induced lower limb amputation.

Journal article

Kazezian Z, Yu X, Ramette M, Macdonald W, Bull Aet al., 2020, Development of a blast injury model for investigating conditions associated with traumatic amputations, ORS 2021 Annual Meeting

Conference paper

Urbanczyk CA, Prinold JAI, Reilly P, Bull AMJet al., 2020, Avoiding high-risk rotator cuff loading: Muscle force during three pull-up techniques., Scandinavian Journal of Medicine and Science in Sports, Vol: 30, Pages: 2205-2214, ISSN: 0905-7188

Heavily loaded overhead training tasks, such as pull-ups are an effective strength training and rehabilitation exercise requiring high muscle forces maintained over a large range of motion. This study used experiments and computational modeling to examine loading patterns during three different pull-up variants and highlighted risks to vulnerable musculoskeletal structures. Optical motion tracking and a force platform captured kinematics and kinetics of 11 male subjects with no history of shoulder pathology, during performance of three pull-up variants-pronated front grip, pronated wide grip, and supinated reverse grip. UK National Shoulder model (UKNSM) simulated biomechanics of the shoulder girdle. Muscle forces and activation patterns were analyzed by repeated measures ANOVA with post-hoc comparisons. Motor group recruitment was similar across all pull-up techniques, with upper limb depression occurring secondary to torso elevation. Stress-time profiles show significant differences in individual muscle patterns among the three pull-up variants, with the most marked differences between wide grip and reverse grip. Comparing across techniques, latissimus dorsi was relatively more active in wide pull-ups (P < .01); front pull-ups favored activation of biceps brachii and brachialis (P < .02); reverse pull-ups displayed higher proportional rotator cuff activation (P < .01). Pull-ups promote stability of the shoulder girdle and activation of scapula stabilizers and performing pull-ups over their full range of motion is important as different techniques and phases emphasize different muscles. Shoulder rehabilitation and strength & conditioning programs should encourage incorporation of all three pull-up variants with systematic progression to provide greater global strengthening of the torso and upper limb musculature.

Journal article

Bennett AN, Dyball DM, Boos CJ, Fear NT, Schofield S, Bull AMJ, Cullinan P, ADVANCE Studyet al., 2020, Study protocol for a prospective, longitudinal cohort study investigating the medical and psychosocial outcomes of UK combat casualties from the Afghanistan war: the ADVANCE Study., BMJ Open, Vol: 10, Pages: 1-11, ISSN: 2044-6055

INTRODUCTION: The Afghanistan war (2003-2014) was a unique period in military medicine. Many service personnel survived injuries of a severity that would have been fatal at any other time in history; the long-term health outcomes of such injuries are unknown. The ArmeD SerVices TrAuma and RehabilitatioN OutComE (ADVANCE) study aims to determine the long-term effects on both medical and psychosocial health of servicemen surviving this severe combat related trauma. METHODS AND ANALYSIS: ADVANCE is a prospective cohort study. 1200 Afghanistan-deployed male UK military personnel and veterans will be recruited and will be studied at 0, 3, 6, 10, 15 and 20 years. Half are personnel who sustained combat trauma; a comparison group of the same size has been frequency matched based on deployment to Afghanistan, age, sex, service, rank and role. Participants undergo a series of physical health tests and questionnaires through which information is collected on cardiovascular disease (CVD), CVD risk factors, musculoskeletal disease, mental health, functional and social outcomes, quality of life, employment and mortality. ETHICS AND DISSEMINATION: The ADVANCE Study has approval from the Ministry of Defence Research Ethics Committee (protocol no:357/PPE/12) agreed 15 January 2013. Its results will be disseminated through manuscripts in clinical/academic journals and presentations at professional conferences, and through participant and stakeholder communications. TRIAL REGISTRATION NUMBER: The ADVANCE Study is registered at ISRCTN ID: ISRCTN57285353.

Journal article

Villatte G, van der Kruk E, Asim B, Zumstein M, Moor B, Emery R, Bull AMJ, Reilly Pet al., 2020, A biomechanical confirmation of the relationship between critical shoulder angle (CSA) and articular joint loading, Journal of Shoulder and Elbow Surgery, Vol: 29, Pages: 1967-1973, ISSN: 1058-2746

Background: The Critical Shoulder Angle (CSA) has been shown to be correlated with shoulder disease states. The biomechanical hypothesis to explain this correlation is that the CSA changes the shear and compressive forces on the shoulder. The objective of this study is to test this hypothesis by use of a validated computational shoulder model. Specifically, this study assesses the impact on glenohumeral biomechanics of modifying the CSA. Methods: An inverse dynamics three-dimensional musculoskeletal model of the shoulder was used to quantify muscle forces and glenohumeral joint forces. The CSA was changed by altering the attachment point of the middle deltoid into a normal CSA (33°), a reduced CSA of 28°, and an increased CSA of 38°. Subject-specific kinematics of slow and fast speed abduction in the scapular plane, and slow and fast forward flexion measured by a 3D motion capture system were used to quantify joint reaction shear and compressive forces.Results: Increasing the CSA results in increased superior-inferior forces (shearing forces; integrated over the range of motion; p<0.05). Reducing CSA results in increased latero-medial (compressive) forces for both the maximum and integrated sum of the forces over the whole motion; p<0.01).Discussion/Conclusion: Changes in the CSA modify glenohumeral joint biomechanics with increasing CSA producing higher shear forces that would contribute to rotator cuff overuse, whereas reducing the CSA results in higher compressive forces which contribute to joint wear.

Journal article

Foss L, Belli A, Brody D, Brookes M, Bull A, Craner M, Dunkley B, Evangelou N, Furlong P, Gibb I, Goldstone A, Green G, Hettiaratchy S, Hodgetts T, Lee R, Mistlin A, Nader K, Perl D, Reid A, Scadding J, Seri S, Sharp D, Sherwood D, Simms A, Sinclair A, Wessely S, Wilde E, Woods Det al., 2020, Setting a national consensus for managing mild and blast traumatic brain injury: post-meeting consensus report

A meeting was held on Wednesday 15 January 2020 to examine the current evidence for non-routine imaging and for neuroendocrine screening in the management of military personnel with brain injury and overlapping symptom domains. The Summit aimed to specifically address the relative utility of magnetoencephalography (MEG), diffusion tensor imaging (DTI) and susceptibility weighted imaging (SWI) in the UK context. This Consensus Report discusses points of consensus, points for further discussion/points of equipoise and recommendations that arose during, and following, the meeting.


Dimitrov H, Bull AMJ, Farina D, 2020, Real-time interface algorithm for ankle kinematics and stiffness from electromyographic signals, IEEE Transactions on Neural Systems and Rehabilitation Engineering, Vol: 28, Pages: 1416-1427, ISSN: 1534-4320

Shortcomings in capabilities of below-knee (transtibial) prostheses, compared to their biological counterparts, still cause medical complications and functional deficit to millions of amputees around the world. Although active (powered actuation) transtibial prostheses have the potential to bridge these gaps, the current control solutions limit their efficacy. Here we describe the development of a novel interface for two degrees-of-freedom position and stiffness control for below-knee amputees. The developed algorithm for the interface relies entirely on muscle electrical signals from the lower leg. The algorithm was tested for voluntary position and stiffness control in eight able-bodied and two transtibial amputees and for voluntary stiffness control with foot position estimation while walking in eight able-bodied and one transtibial amputee. The results of the voluntary control experiment demonstrated a promising target reaching success rate, higher for amputees compared to the able-bodied individuals (82.5% and 72.5% compared to 72.5% and 68.1% for the position and position and stiffness matching tasks respectively). Further, the algorithm could provide the means to control four stiffness levels during walking in both amputee and able-bodied individuals while providing estimates of foot kinematics (gait cycle cross-correlation >75% for the sagittal and >90% for the frontal plane and gait cycle root mean square error <7.5° in sagittal and <3° in frontal plane for able-bodied and amputee individuals across three walking speeds). The results from the two experiments demonstrate the feasibility of using this novel algorithm for online control of multiple degrees of freedom and of their stiffness in lower limb prostheses.

Journal article

Nolte D, Ko S-T, Bull AMJ, Kedgley AEet al., 2020, Reconstruction of the lower limb bones from digitised anatomical landmarks using statistical shape modelling, Gait & Posture, Vol: 77, Pages: 269-275, ISSN: 0966-6362

BackgroundBone shapes strongly influence force and moment predictions of kinematic and musculoskeletal models used in motion analysis. The precise determination of joint reference frames is essential for accurate predictions. Since clinical motion analysis typically does not include medical imaging, from which bone shapes may be obtained, scaling methods using reference subjects to create subject-specific bone geometries are widely used.Research questionThis study investigated if lower limb bone shape predictions from skin-based measurements, utilising an underlying statistical shape model (SSM) that corrects for soft tissue artefacts in digitisation, can be used to improve conventional linear scaling methods of bone geometries.MethodsSSMs created from 35 healthy adult femurs and tibiae/fibulae were used to reconstruct bone shapes by minimising the distance between anatomical landmarks on the models and those digitised in the motion laboratory or on medical images. Soft tissue artefacts were quantified from magnetic resonance images and then used to predict distances between landmarks digitised on the skin surface and bone. Reconstruction results were compared to linearly scaled models by measuring root mean squared distances to segmented surfaces, calculating differences of commonly used anatomical measures and the errors in the prediction of the hip joint centre.ResultsSSM reconstructed surface predictions from varying landmark sets from skin and bone landmarks were more accurate compared to linear scaling methods (2.60–2.95 mm vs. 3.66–3.87 mm median error; p < 0.05). No significant differences were found between SSM reconstructions from bony landmarks and SSM reconstructions from digitised landmarks obtained in the motion lab and therefore reconstructions using skin landmarks are as accurate as reconstructions from landmarks obtained from medical images.SignificanceThese results indicate that SSM reconstructions can be used to increase the accurac

Journal article

Papi E, Bull AMJ, McGregor AH, 2020, Alteration of movement patterns in low back pain assessed by Statistical Parametric Mapping, Journal of Biomechanics, Vol: 100, Pages: 109597-109597, ISSN: 0021-9290

Changes in movement pattern in low back pain (LBP) groups have been analysed by reporting predefined discrete variables. However, this approach does not consider the full kinematic data waveform and its dynamic information, potentially exposing the analysis to bias. Statistical Parametric Mapping (SPM) has been introduced and applied to 1 dimensional (D) kinematic variables allowing the assessment of data over time. The aims of this study were to assess differences in 3D kinematics patterns in people with and without LBP during functional tasks by using SPM and to investigate if SPM analysis was consistent with standard 3D range of motion (RoM) assessments. 3D joints kinematics of the spine and lower limbs were compared between 20 healthy controls and 20 participants with non-specific LBP during walking, sit-to-stand and lifting. SPM analysis showed significant differences in the 3Dkinematics of the lower thoracic segment, upper and lower lumbar segment and knee joint during walking and lifting mostly observed at the beginning and/or towards the end of the tasks. ROMs differed between groups in the lower thoracic segment (walking/sit-to-stand), upper and lower lumbar segments (walking/sit-to-stand/lifting), hip and knee (sit-to-stand/lifting). Based on these results, the two approaches can yield different data interpretations. SPM analysis allows the identification of differences in movement that occur over time. This adds value to LBP movement analysis as it allows an understanding of the LBP strategies adopted during motion that may not be conveyed by simple discrete parameters such as ROMs.

Journal article

Bull A, Berthaume M, 2020, Human biological variation in sesamoid bone prevalence: the curious case of the fabella, Journal of Anatomy, Vol: 236, Pages: 228-242, ISSN: 0021-8782

The fabella is a sesamoid bone located in the gastrocnemius behind the lateral femoral condyle. In humans, fabellae are 3.5 times more common today than they were 100 years ago, with prevalence rates varying between and within populations. In particular, fabellae have been assumed to be more common in Asians than non-Asians, equally common in men and women, potentially more common in older individuals, and bilateral cases (one per knee) appear to be more common than unilateral ones. The roles of genetic and environmental factors in this phenotypic variation have been hypothesized, but not rigorously investigated. Given its clinical and evolutionary significance (i.e., being associated with several knee ailments, causing medical issues on its own, interfering with medical devices, and being less common in humans compared to other mammals), it is important to comprehensively understand prevalence rate variation, and the roles of genetics and environmental factors in that variation. To address these questions, we performed a meta-analysis on data from a previously published systematic review to investigate possible variation in sexual dimorphic (n = 22 studies, 7,911 knees), ontogenetic (n = 10 studies, 4,391 knees), and global (n = 65 studies, 21,626 knees) fabella prevalence rates. In addition, we investigated what proportion of cases are bilateral (n = 37 studies, 900 individuals), and among unilateral cases (n = 20 studies, 204 individuals), if fabellae are more common in the left or right knee. Our results show that, today, fabellae are 2.47-2.60% more common in men than women, and prevalence rates increase ontogenetically into old age (i.e., 70 years old), implying that fabellae can ossify early (i.e., 12 years old) or late in life. Approximately 72.94% of cases are bilateral, and among unilateral ones, fabellae are equally common in right and left knees. There is marked regional variation in fabella prevalence rates, with rates being highest in Asia, followed by

Journal article

Smith SHL, Reilly P, Bull AMJ, 2020, A musculoskeletal modelling approach to explain sit-to-stand difficulties in older people due to changes in muscle recruitment and movement strategies, Journal of Biomechanics, Vol: 98, ISSN: 0021-9290

By 2050 the proportion of over 65s is predicted to be 20% of the population. The consequences of an age-related reduction in muscle mass have not been fully investigated and, therefore, the aim of the present study was to quantify the muscle and joint contact forces using musculoskeletal modelling, during a sit-to-stand activity, to better explain difficulties in performing everyday activities for older people. A sit-to-stand activity with and without the use of arm rests was observed in ninety-five male participants, placed into groups of young (aged 18-35 years), middle-aged (aged 40-60 years) or older adults (aged 65 years and over). Older participants demonstrated significantly lower knee extensor and joint forces than the young when not using arm rests, compensating through elevated hip extensor and ankle plantarflexor muscle activity. The older group were also found to have higher shoulder joint contact forces whilst using arm rests. This tendency to reorganise muscle recruitment to include neighbouring groups or other parts of the body could make everyday activities more susceptible to age-related functional decline. Reductions in leg strength, via age- or atrophy- related means, creates increased reliance on the upper body and may result in further lower limb atrophy through disuse. The eventual decline of upper body function reduces strength reserves, leading to increased vulnerability, dependence on others and risk of institutionalisation.

Journal article

Ding Z, Gudel M, Smith SHL, Ademefun RA, Bull AMJet al., 2019, A femoral clamp to reduce soft tissue artefact: accuracy and reliability in measuring three-dimensional knee kinematics during gait, Journal of Biomechanical Engineering, Vol: 142, Pages: 044501-1-044501-8, ISSN: 0148-0731

The accurate measurement of full sixdegrees-of-freedom(DOFs) knee joint kinematics is prohibited by soft tissue artifact (STA), which remains the greatest source of error. The purpose of this study was to present and assess a new femoral clampto reduce STA at the thigh. It was hypothesised that the device can preserve the natural knee joint kinematics pattern and outperform a conventional marker mounted rigid cluster during gait. 6Six healthy subjects were askedto walk barefoot on level ground with a cluster marker set (cluster gait) followed by a cluster-clamp-merged marker set (clamp gait) and their kinematics wasmeasured using the clustermethod in clustergait and thecluster and clamp methodssimultaneouslyin clamp gait. Two operators performed the gait measurement. A six DOFs knee joint model wasdeveloped to enable comparison withthe gold standard knee joint kinematics measured using adual fluoroscopic imaging technique. One-dimensional paired t-tests were used to compare the knee joint kinematics waveforms between cluster gait and clamp gait. The accuracy was assessed in terms of the root mean square error, coefficient of determination and Bland-Altman plots. Inter-operatorreliability was assessed15usingthe intra-class correlation coefficient.The result showed that the femoral clamp did not change the walking speed andknee joint kinematicswaveforms. Additionally, clamp gait reduced the rotationand translation errorsin the transverse plane and improved the inter-operator reliabilitywhen compared to the rigid cluster method, suggesting amore accurate and reliable measurement of knee joint kinematics.

Journal article

Ding Z, Tsang C, Nolte D, Kedgley A, Bull Aet al., 2019, Improving musculoskeletal model scaling using an anatomical atlas: the importance of gender and anthropometric similarity to quantify joint reaction forces, IEEE Transactions on Biomedical Engineering, Vol: 66, Pages: 3444-3456, ISSN: 0018-9294

Objective: The accuracy of a musculoskeletal model relies heavily on the implementation of the underlying anatomical dataset. Linear scaling of a generic model, despite being time and cost-efficient, produces substantial errors as it does not account for gender differences and inter-individual anatomical variations. The hypothesis of this study is that linear scaling to a musculoskeletal model with gender and anthropometric similarity to the individual subject produces similar results to the ones that can be obtained from a subject-specific model. Methods: A lower limb musculoskeletal anatomical atlas was developed consisting of ten datasets derived from magnetic resonance imaging of healthy subjects and an additional generic dataset from the literature. Predicted muscle activation and joint reaction force were compared with electromyography and literature data. Regressions based on gender and anthropometry were used to identify the use of atlas. Results: Primary predictors of differences for the joint reaction force predictions were mass difference for the ankle (p<0.001) and length difference for the knee and hip (p≤0.017) . Gender difference accounted for an additional 3% of the variance (p≤0.039) . Joint reaction force differences at the ankle, knee and hip were reduced by between 50% and 67% (p=0.005) when using a musculoskeletal model with the same gender and similar anthropometry in comparison with a generic model. Conclusion: Linear scaling with gender and anthropometric similarity can improve joint reaction force predictions in comparison with a scaled generic model. Significance: The scaling approach and atlas presented can improve the fidelity and utility of musculoskeletal models for subject-specific applications.

Journal article

Smith SHL, Reilly P, Bull AMJ, 2019, Serratus anterior weakness is a key determinant of arm-assisted standing difficulties, Medical Engineering and Physics, Vol: 74, Pages: 41-48, ISSN: 1350-4533

The ageing population has led to recent increases in musculoskeletal conditions, with muscle weakness a major contributor to functional decline. Understanding the early phases of muscle weakness will help devise treatments to extend musculoskeletal health. Little is understood of the effects of muscle weakness on everyday activities such as sit-to-stand, a determinant of mobility that, in the early stages of weakness, requires upper limb compensation. This experimental and computational modelling study investigated the effects of muscle weakness on upper-extremity muscle forces of 27 healthy adults when using arm rests. Weakness of 29 upper limb muscles was simulated by individually removing each from a musculoskeletal model. Serratus anterior weakness was highlighted as detrimental, with the model unable to fully solve the loadsharing redundancy in its absence, and forces at the elbow and glenohumeral joint and in other muscles were found to be profoundly increased. Its large number of fast-twitch muscle fibres, predisposed to atrophy with age, highlight the centrality of the serratus anterior as a key determinant of mobility in this critical task and a potential source of early immobility through its preferential loss of strength and thus point to the requirement for early clinical interventions to mitigate loss.

Journal article

Ding Z, Güdel M, Smith S, Ademefun R, Bull AMJet al., 2019, Measuring Three-dimensional Knee Kinematics Using a Femoral Clamp: Accuracy, Repeatability and Reproducibility in Gait., J Biomech Eng

The ability to measure full six degrees-of-freedom knee joint kinematics is critical in the diagnosis of knee pathology. Soft tissue artifact (STA) remains the greatest source of error in measurement knee kinematics. The purpose of this study is to present a new femoral clamp to reduce STA at the thigh while preserving the natural gait pattern. Knee joint kinematics during gait was measured for six healthy subjects by using the femoral clamp and a rigid cluster-based technique. Performance was assessed in terms of accuracy, repeatability and reproducibility. The result showed that the femoral clamp did not change the walking speed and the natural knee kinematics pattern of the subjects. The clamp-measured kinematics had smaller knee translation in the transverse plane and were closer to data from the literature obtained by dual fluoroscopic imaging. The clamp had improved repeatability and reproducibility compared to the rigid cluster technique, suggesting that this technology is suitable for accurate measurement of gait.

Journal article

Barnes S, Clasper J, Bull A, Jeffers Jet al., 2019, Micromotion and Push‐Out Evaluation of an Additive Manufactured Implant for Above‐the‐Knee Amputees, Journal of Orthopaedic Research, Vol: 37, Pages: 2104-2111, ISSN: 0736-0266

In comparison to through knee amputees the outcomes for above‐the‐knee amputees are relatively poor; based on this novel techniques have been developed. Most current percutaneous implant based solutions for transfemoral amputees make use of high stiffness intramedullary rods for skeletal fixation which can have risks including infection, femoral fractures and bone resorption due to stress shielding. This work details the cadaveric testing of a short, cortical bone stiffness matched subcutaneous implant, produced using additive manufacture, to determine bone implant micromotion and push out load. The results for the micromotions were all less than 20 microns and the mean push out load was 2099 Newtons. In comparison to a solid control, the stiffness matched implant exhibited significantly higher micromotion distributions and no significant difference in terms of push out load. These results suggest that, for the stiffness matched implant at time zero, osseointegration would be facilitated and that the implant would be securely anchored. For these metrics, this provides justification for the use of a short stem implant for transfemoral amputees in this subcutaneous application.

Journal article

Milwood Hargrave J, Pearce P, Mayhew E, Bull A, Taylor Set al., 2019, Blast injuries in children: a mixed-methods narrative review., BMJ Paediatrics Open, Vol: 3, ISSN: 2399-9772

Background and significance. Blast injuries arising from high explosive weaponry iscommon in conflict areas. While blast injury characteristics are well recognised in the adults,there is a lack of consensus as to whether these characteristics translate to the paediatricpopulation. Understanding blast injury patterns in this cohort is essential for providingappropriate provision of services and care for this vulnerable cohort.Methods. In this mixed-method review, original papers were screened for data pertaining topaediatric injuries following blasts. Information on demographics, morbidity and mortality andservice requirements were evaluated. The papers were written and published in English from a range of international specialists in the field. Patient and public involvementstatement: No patients or members of the public were involved in this review.Results. Children affected by blast injuries are predominantly male and their injuries arisefrom explosive remnants of war, particularly unexploded ordinance. Blasts show increasedmorbidity and mortality in younger children, while older children have injury patterns similarto adults. Head and burn injuries represent a significant cause of mortality in young children,while lower limb morbidity is reduced compared to adults. Children have a disproportionaterequirement for both operative and non-operative service resources, and provisions for thisburden are essential.Conclusions. Certain characteristics of paediatric injuries arising from blasts are distinctfrom that of the adult cohort, while the intensive demands on services highlights theimportance of understanding the diverse injury patterns in order to optimise future serviceprovisions in caring for this the child blast survivor.

Journal article

Majed A, Thangarajah T, Southgate DFL, Reilly P, Bull A, Emery Ret al., 2019, The biomechanics of proximal humeral fractures: Injury mechanism and cortical morphology, Shoulder & Elbow, Vol: 11, Pages: 247-255, ISSN: 1758-5732

BackgroundThe aim of this study was to examine the effect of arm position on proximal humerus fracture configuration and to determine whether cortical thinning would predispose to fracture propagation and more complex patterns of injury.MethodsA drop test rig was designed to simulate falls onto an outstretched arm (‘parachute reflex’). Thirty-one cadaveric specimens underwent computer tomography scanning and cortical thicknesses mapping. Humeri were fractured according to one of the two injury mechanisms and filmed using a high-speed camera. Anatomical descriptions of the injuries were made. Areas of thinning were measured and correlated with zones of fracture propagation.ResultsDirect impact simulation resulted in undisplaced humeral head split fractures in 53% of cases, with the remainder involving disruption to the articular margin and valgus impaction. Alternatively, the ‘parachute reflex’ predominantly produced shield-type injuries (38%) and displaced greater tuberosity fractures (19%). A strong correlation was demonstrated between cortical thinning and the occurrence of fracture (odds ratio = 7.766, 95% confidence interval from 4.760 to 12.669, p<0.0001).ConclusionThis study has shown that arm position during a fall influences fracture configuration of the proximal humerus. Correlating fracture pattern and mechanism of injury will allow more appropriate fracture reduction techniques to be devised.

Journal article

Ahmadzadeh SMH, Chen X, Hagemann H, Tang M-X, Bull AMJet al., 2019, Developing and using fast shear wave elastography to quantify physiologically-relevant tendon forces, Medical Engineering and Physics, Vol: 69, Pages: 116-122, ISSN: 1350-4533

Direct quantification of physiologically-relevant tendon forces can be used in a wide range of clinical applications. However, tendon forces have usually been estimated either indirectly by computational models or invasively using force transducers, and direct non-invasive measurement of forces remains a big challenge. The aim of this study was to investigate the feasibility of using Shear Wave Elastography (SWE) for quantifying human tendon forces at physiological levels. An experimental protocol was developed to measure Shear Wave Speed (SWS) and tensile force in a human patellar tendon using SWE and conventional tensile testing to quantify the correlation between SWS and load. The SWE system was customised to allow imaging of fast shear waves expected in human tendons under physiological loading which is outside the normal range of the existing SWE systems. SWS increased from 10.8 m/s to 36.1 m/s with the increasing tensile load from 8 N to 935 N and a strong linear correlation between SWS and load (r = 0.99, p < 0.01) was observed. The findings in this study suggest that SWE can be used as a potential non-invasive method for direct quantification of physiologically-relevant tendon forces, as well as for validating the estimated forces from other methods such as computational models.

Journal article

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