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• Journal article
  Ding Z, Azmi NL, Bull AMJ, 2019,

  Validation and use of a musculoskeletal gait model to study the role of functional electrical stimulation

  , IEEE Transactions on Biomedical Engineering, Vol: 66, Pages: 892-897, ISSN: 0018-9294

  Objective: Musculoskeletal modeling has been used to predict the effect of functional electrical stimulation (FES) on the mechanics of the musculoskeletal system. However, validation of the resulting muscle activations due to FES is challenging as conventional electromyography (EMG) recording of signals from the stimulated muscle is affected by stimulation artefacts. A validation approach using a combination of musculoskeletal modeling and EMG was proposed, whereby the effect on nonstimulated muscles is assessed using both techniques. The aim is to quantify the effect of FES on biceps femoris long head (BFLH) and validate this directly against EMG of gluteus maximus (GMAX). The hypotheses are that GMAX activation correlates with BFLH activation; and the muscle activation during FES gait can be predicted using musculoskeletal modeling. Methods: Kinematics, kinetics, and EMG of healthy subjects were measured under four walking conditions (normal walking followed by FES walking with three levels of BFLH stimulation). Measured kinematics and kinetics served as inputs to the musculoskeletal model. Results: Strong positive correlations were found between GMAX activation and BFLH activation in early stance peak (R = 0.78, p = 0.002) and impulse (R = 0.63, p = 0.021). The modeled peak and impulse of GMAX activation increased with EMG peak (p <; 0.001) and impulse (p = 0.021). Conclusion: Musculoskeletal modeling can be used reliably to quantify the effect of FES in a healthy gait. Significance: The validation approach using EMG and musculoskeletal modeling developed and tested can potentially be applied to the use of FES for other muscles and activities.

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• Journal article
  Nguyen T-T, Pearce AP, Carpanen D, Sory D, Grigoriadis G, Newell N, Clasper J, Bull A, Proud WG, Masouros SDet al., 2019,

  Experimental platforms to study blast injury

  , Journal of the Royal Army Medical Corps, Vol: 165, Pages: 33-37, ISSN: 2052-0468

  Injuries sustained due to attacks from explosive weapons are multiple in number, complex in nature, and not well characterised. Blast may cause damage to the human body by the direct effect of overpressure, penetration by highly energised fragments, and blunt trauma by violent displacements of the body. The ability to reproduce the injuries of such insults in a well-controlled fashion is essential in order to understand fully the unique mechanism by which they occur, and design better treatment and protection strategies to alleviate the resulting poor long-term outcomes. This paper reports a range of experimental platforms that have been developed for different blast injury models, their working mechanism, and main applications. These platforms include the shock tube, split-Hopkinson bars, the gas gun, drop towers and bespoke underbody blast simulators.

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• Journal article
  Klemt C, Toderita D, Nolte D, Di Federico E, Reilly P, Bull AMJet al., 2019,

  The critical size of a defect in the glenoid causing anterior instability of the shoulder after a Bankart repair, under physiological joint loading

  , Bone and Joint Journal, Vol: 101-B, Pages: 68-74, ISSN: 2049-4394

  AIMS: Patients with recurrent anterior dislocation of the shoulder commonly have an anterior osseous defect of the glenoid. Once the defect reaches a critical size, stability may be restored by bone grafting. The critical size of this defect under non-physiological loading conditions has previously been identified as 20% of the length of the glenoid. As the stability of the shoulder is load-dependent, with higher joint forces leading to a loss of stability, the aim of this study was to determine the critical size of an osseous defect that leads to further anterior instability of the shoulder under physiological loading despite a Bankart repair. PATIENTS AND METHODS: Two finite element (FE) models were used to determine the risk of dislocation of the shoulder during 30 activities of daily living (ADLs) for the intact glenoid and after creating anterior osseous defects of increasing magnitudes. A Bankart repair was simulated for each size of defect, and the shoulder was tested under loading conditions that replicate in vivo forces during these ADLs. The critical size of a defect was defined as the smallest osseous defect that leads to dislocation. RESULTS: The FE models showed a high risk of dislocation during ADLs after a Bankart repair for anterior defects corresponding to 16% of the length of the glenoid. CONCLUSION: This computational study suggests that bone grafting should be undertaken for an anterior osseous defect in the glenoid of more than 16% of its length rather than a solely soft-tissue procedure, in order to optimize stability by restoring the concavity of the glenoid.

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• Journal article
  Papi E, Bull A, McGregor A, 2019,

  Spinal segments do not move together predictably during daily activities

  , Gait and Posture, Vol: 67, Pages: 277-283, ISSN: 0966-6362

  Background: Considering the thoracic, lumbar spine or whole spine as rigid segments has been the norm until recent studies highlighted the importance of more detailed modelling. A better understanding of the requirement for spine multi-segmental analysis could guide planning of future studies and avoid missing clinically-relevant information.Research question: This study aims to assess the correlation between adjacent spine segments movement thereby evaluating segmental redundancy in both healthy and participants with low back pain (LBP).Methods: A 3D motion capture system tracked the movement of upper and lower thoracic and lumbar spine segments in twenty healthy and twenty participants with LBP. Tasks performed included walking, sit-to-stand and lifting, repeated 3 times. 3D angular kinematics were calculated for each spine segment. Segmental redundancy was evaluated through cross-correlation (Rxy) analysis of kinematics time series and correlation of range of motion (RROM) of adjacent spine segments.Results: The upper/lower lumbar pairing showed weak correlations in the LBP group for all tasks and anatomical planes (Rxyrange:0.02–0.36) but moderate and strong correlations during walking (Rxy _frontalplane:0.4) and lifting (Rxy _sagittalplane:0.64) in the healthy group. The lower thoracic/upper lumbar pairing had weak correlations for both groups during lifting and sit-to-stand in the frontal plane and for walking (Rxy:0.01) in the sagittal plane only. The upper/lower thoracic pairing had moderate correlations during sit-to-stand in sagittal and transverse plane in patients with LBP (Rxy _sagittalplane:0.41; Rxy _transverse plane:−0.42) but weak in healthy (Rxy _sagittalplane:0.23; Rxy _transverseplane:−0.34); the contrary was observed during lifting.The majority of RROM values (55/72) demonstrated weak correlations.Significance:The results suggest that multi-segmental analysis of the spine is necessary if spine movement characteristics are to be

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• Journal article
  Kedgley AE, Saw TH, Segal NA, Hansen UN, Bull AMJ, Masouros SDet al., 2019,

  Predicting meniscal tear stability across knee-joint flexion using finite-element analysis

  , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 27, Pages: 206-214, ISSN: 0942-2056

  Purpose: To analyse the stress distribution through longitudinal and radial meniscal tears in three tear locations in weight-bearing conditions and use it to ascertain the impact of tear location and type on the potential for healing of meniscal tears. Methods: Subject-specific finite-element models of a healthy knee under static loading at 0°, 20°, and 30° knee flexion were developed from unloaded magnetic resonance images and weight-bearing, contrast-enhanced computed tomography images. Simulations were then run after introducing tears into the anterior, posterior, and midsections of the menisci. Results: Absolute differences between the displacements of anterior and posterior segments modelled in the intact state and those quantified from in vivo weight-bearing images were less than 0.5 mm. There were tear-location-dependent differences between hoop stress distributions along the inner and outer surfaces of longitudinal tears; the longitudinal tear surfaces were compressed together to the greatest degree in the lateral meniscus and were most consistently in compression on the midsections of both menisci. Radial tears resulted in an increase in stress at the tear apex and in a consistent small compression of the tear surfaces throughout the flexion range when in the posterior segment of the lateral meniscus. Conclusions: Both the type of meniscal tear and its location within the meniscus influenced the stresses on the tear surfaces under weight bearing. Results agree with clinical observations and suggest reasons for the inverse correlation between longitudinal tear length and healing, the inferior healing ability of medial compared with lateral menisci, and the superior healing ability of radial tears in the posterior segment of the lateral meniscus compared with other radial tears. This study has shown that meniscal tear location in addition to type likely plays a crucial role in dictating the success of non-operative treatment of the menisci. T

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• Journal article
  Smith SHL, Bull A, 2018,

  Rapid calculation of bespoke body segment parameters using 3D infra-red scanning

  , Medical Engineering and Physics, Vol: 62, Pages: 36-45, ISSN: 1350-4533

  Body segment parameters such as segment mass, centre of mass and moment of inertia, serve as important inputs for musculoskeletal modelling. These parameters are normally derived from regression tables; however, can be poorly representative of the study population with variations of up to 40% recorded between different tables. More recent methods, such as 3D scanning, present a rapid and accurate way to produce subject-specific body segment parameters for use in musculoskeletal models. An infra-red 3D scanner was used to produce full-body scans of 95 males and females. Each was put through an algorithm to calculate bespoke segment mass, centre of mass and inertial properties for each segment of the body, with results comparable to cadaveric data. These methods could be used to increase the specificity of musculoskeletal modelling outputs for individual subjects, improving the accuracy of modelling outputs in biomechanics-related research.

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• Journal article
  Rosenberg N, Bull AMJ, 2018,

  Application of a mechanobiological algorithm to investigate mechanical mediation of heterotopic bone in trans-femoral amputees

  , Scientific Reports, Vol: 8, Pages: 1-11, ISSN: 2045-2322

  Heterotopic ossification (HO) is the process of bone formation in tissues that are not usually osseous. It occurs in 60% of those with blast-related amputations. HO can result in reduced range of motion, pain, nerve impingement and can affect prosthesis fitting and is caused by a combination of mechanical, biological, local and systemic factors. As with normal bone formation and remodelling, it is expected that heterotopic bone responds to mechanical stimuli and understanding this relationship can give insight into the pathology. The objective of this research was to investigate whether a physiological 2D computational model that considers both mechanical and biological factors can be used to simulate HO in the residual limb of a trans-femoral amputee. The study found that characteristic morphologies of HO were reproduced by adjusting the loading environment. Significant effects were produced by changing the loading direction on the femur; this is potentially associated with different initial surgical interventions such as muscle myodesis. Also, initial treatment such as negative pressure through a dressing was found to change the shape of heterotopic bone.

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• Journal article
  Majed A, Thangarajah T, Krekel P, Nelissen R, Reilly P, Bull A, Emery Ret al., 2018,

  Simulation of bone-determined range of motion in proximal humeral fractures.

  , Shoulder Elbow, Vol: 10, Pages: 186-191, ISSN: 1758-5732

  Background: Predicting the outcome following fractures of the proximal humerus is an important consideration when effectively counselling patients and planning treatment. The purpose of the present study was to analyze different proximal humeral fracture configurations, using a computerized simulation model, aiming to predict the range of motion (ROM). Methods: The computer tomography scans of 79 proximal humeral fractures were analyzed using a customized software system that simulated the range of movement at the glenohumeral joint. Four fracture patterns were investigated: (1) head split fractures; (2) greater tuberosity fractures; (3) lesser tuberosity fractures; and (4) combined tuberosity fractures. Results: Intra-articular fractures had the smallest mean (SE) range of abduction and forward flexion [34.3° (6.6°) and 60.7° (12.4°)]. Isolated displaced greater tuberosity resulted in limited abduction but not forward flexion [75.0° (5.9°) and 118.2° (4.9°)]. Isolated lesser tuberosity fractures displayed a ROM comparable to that of healthy subjects [89.3° (3.3°) and 122.6° (3.4°) versus 102.3° (2.8°) and 96.2° (3.8°)]. The reduced head inclination angle was a relatively strong predictor of a limited range of abduction for all fracture types. Conclusions: The present study describes a novel simulation system used to quantify the bone-determined ROM in proximal humeral fractures and may be a useful adjunct in the diagnostic armamentarium for proximal humeral fractures.

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• Journal article
  Papi E, Bull A, McGregor A, 2018,

  Is there evidence to use kinematic/kinetic measures clinically in low back pain patients? A systematic review

  , Clinical Biomechanics, Vol: 55, Pages: 53-64, ISSN: 0268-0033

  BackgroundCurrently, there is a widespread reliance on self-reported questionnaires to assess low back pain patients. However, it has been suggested that objective measures of low back pain patients' functional status should be used to aid clinical assessment. The aim of this study is to systematically review which kinematic /kinetic parameters have been used to assess low back pain patients against healthy controls and to propose clinical kinematic/kinetic measures.MethodsPubMed, Embase and Scopus databases were searched for relevant studies. Reference lists of selected studies and hand searches were performed. Studies had to compare people with and without non-specific low back pain while performing functional tasks and report body segment/joint kinematic and/or kinetic data. Two reviewers independently identified relevant papers.FindingsSixty-two studies were included. Common biases identified were lack of assessor blinding and sample size calculation, use of samples of convenience, and poor experimental protocol standardization. Studies had small sample sizes. Range of motion maneuvers were the main task performed (33/62). Kinematic/kinetic data of different individual or combination of body segments/joints were reported among the studies, commonest was to assess the hip joint and lumbar segment motion (13/62). Only one study described full body movement. The most commonly reported outcome was range of motion. Statistically significant differences between controls and low back pain groups were reported for different outcomes among the studies. Moreover, when the same outcome was reported disagreements were noted.InterpretationThe literature to date offers limited and inconsistent evidence of kinematic/kinetic measures in low back pain patients that could be used clinically.

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• Journal article
  Bull A, Mayhew E, Reavley P, Tai N, Taylor Set al., 2018,

  Paediatric blast injury: challenges and priorities.

  , Lancet Child Adolesc Health, Vol: 2, Pages: 310-311
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