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  • Journal article
    Geraldes DM, Modenese L, Phillips ATM, 2015,

    Consideration of multiple load cases is critical in modelling orthotropic bone adaptation in the femur

    , Biomechanics and Modeling in Mechanobiology, Vol: 15, Pages: 1029-1042, ISSN: 1617-7959

    Functional adaptation of the femur has beeninvestigated in several studies by embedding bone remodellingalgorithms in finite element (FE) models, with simpli-fications often made to the representation of bone’s materialsymmetry and mechanical environment. An orthotropicstrain-driven adaptation algorithm is proposed in order topredict the femur’s volumetric material property distributionand directionality of its internal structures within a continuum.The algorithm was applied to a FE model of the femur,with muscles, ligaments and joints included explicitly. Multipleload cases representing distinct frames of two activitiesof daily living (walking and stair climbing) were considered.It is hypothesised that low shear moduli occur in areasof bone that are simply loaded and high shear moduli inareas subjected to complex loading conditions. In addition,it is investigated whether material properties of differentfemoral regions are stimulated by different activities. The loading and boundary conditions were considered to providea physiological mechanical environment. The resultingvolumetric material property distribution and directionalitiesagreed with ex vivo imaging data for the whole femur.Regions where non-orthogonal trabecular crossing has beendocumented coincided with higher values of predicted shearmoduli. The topological influence of the different activitiesmodelled was analysed. The influence of stair climbing onthe properties of the femoral neck region is highlighted. It isrecommended that multiple load cases should be consideredwhen modelling bone adaptation. The orthotropic model ofthe complete femur is released with this study.
  • Journal article
    van Arkel RJ, Amis AA, Jeffers JRT, 2015,

    The envelope of passive motion allowed by the capsular ligaments of the hip

    , JOURNAL OF BIOMECHANICS, Vol: 48, Pages: 3803-3809, ISSN: 0021-9290
  • Journal article
    Athwal KK, Daou HE, Kittl C, Davies AJ, Deehan DJ, Amis AAet al., 2015,

    The superficial medial collateral ligament is the primary medial restraint to knee laxity after cruciate-retaining or posterior-stabilised total knee arthroplasty: effects of implant type and partial release.

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 24, Pages: 2646-2655, ISSN: 0942-2056

    PURPOSE: The aim of this study was to quantify the contributions of medial soft tissues to stability following cruciate-retaining (CR) or posterior-stabilised (PS) total knee arthroplasty (TKA). METHODS: Using a robotic system, eight cadaveric knees were subjected to ±90-N anterior-posterior force, ±5-Nm internal-external and ±8-Nm varus-valgus torques at various flexion angles. The knees were tested intact and then with CR and PS implants, and successive cuts of the deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) quantified the percentage contributions of each structure to restraining the applied loads. RESULTS: In implanted knees, the sMCL restrained valgus rotation (62 % across flexion angles), anterior-posterior drawer (24 and 10 %, respectively) and internal-external rotation (22 and 37 %). Changing from CR TKA to PS TKA increased the load on the sMCL when resisting valgus loads. The dMCL restrained 11 % of external and 13 % of valgus rotations, and the PMC was significant at low flexion angles. CONCLUSIONS: This work has shown that medial release in the varus knee should be minimised, as it may inadvertently result in a combined laxity pattern. There is increasing interest in preserving constitutional varus in TKA, and this work argues for preservation of the sMCL to afford the surgeon consistent restraint and maintain a balanced knee for the patient.
  • Journal article
    Chong DYR, Hansen UN, Amis AA, 2015,

    CEMENTLESS MIS MINI-KEEL PROSTHESIS REDUCES INTERFACE MICROMOTION VERSUS STANDARD STEMMED TIBIAL COMPONENTS

    , Journal of Mechanics in Medicine and Biology, Vol: 16, ISSN: 0219-5194

    Fixation strength of the cementless knee prostheses is dependent on the initial stability of the fixation and minimal relative motion across the prosthesis–bone interface. Broad mini-keels have been developed for tibial components to allow minimally invasive knee arthroplasty, but the effect of the change in fixation design is unknown. In this study, bone–prosthesis interface micromotions of the mini-keel tibial components (consisting of two designs; one is stemless and another with a stem extension of 45mm) induced by walking and stair climbing were investigated by finite element modeling and compared with standard stemmed design. The prosthesis surface area amenable for bone ingrowth for the mini-keel tibial components (both stemmed and unstemmed) was predicted to be at least 67% larger than the standard stemmed implant, thereby reducing the risk of long-term aseptic loosening. It was also found that while different load patterns may have led to diverse predictions of the magnitude of the interface micromotions and the extent of osseointegration onto the prosthesis, the outcome of design change evaluation in cementless tibial fixations remains unchanged. The mini-keel tibial components were predicted to anchor onto the periprosthetic bone better than the standard stemmed design under all loading conditions investigated.
  • Book chapter
    Masouros S, Halewood C, Bull A, Amis Aet al., 2015,

    Biomechanics

    , Expertise orthopadie und unfallchirurgie: Knie, Editors: Kohn, ISBN: 978-3-1317500-1-3
  • Conference paper
    Geraldes D, Hansen U, Amis A, 2015,

    An automated framework for parametric analysis glenoid implant design

    , Bath Biomechanics Symposium 2015
  • Conference paper
    Geraldes D, Hansen U, Amis A, 2015,

    Parametric analysis of glenoid implant design

    , International Society of Biomechanics 2015
  • Journal article
    Simpson RL, Nazhat SN, Blaker JJ, Bismarck A, Hill R, Boccaccini AR, Hansen UN, Amis AAet al., 2015,

    A comparative study of the effects of different bioactive fillers in PLGA matrix composites and their suitability as bone substitute materials: a thermo-mechanical and in vitro investigation

    , Journal of The Mechanical Behavior of Biomedical Materials, Vol: 50, Pages: 277-289, ISSN: 1751-6161

    Bone substitute composite materials with poly(L-lactide-co-glycolide) (PLGA) matrices and four different bioactive fillers: CaCO3, hydroxyapatite (HA), 45S5 Bioglass(®) (45S5 BG), and ICIE4 bioactive glass (a lower sodium glass than 45S5 BG) were produced via melt blending, extrusion and moulding. The viscoelastic, mechanical and thermal properties, and the molecular weight of the matrix were measured. Thermogravimetric analysis evaluated the effect of filler composition on the thermal degradation of the matrix. Bioactive glasses caused premature degradation of the matrix during processing, whereas CaCO3 or HA did not. All composites, except those with 45S5 BG, had similar mechanical strength and were stiffer than PLGA alone in compression, whilst all had a lower tensile strength. Dynamic mechanical analysis demonstrated an increased storage modulus (E') in the composites (other than the 45S5 BG filled PLGA). The effect of water uptake and early degradation was investigated by short-term in vitro aging in simulated body fluid, which indicated enhanced water uptake over the neat polymer; bioactive glass had the greatest water uptake, causing matrix plasticization. These results enable a direct comparison between bioactive filler type in poly(α-hydroxyester) composites, and have implications when selecting a composite material for eventual application in bone substitution.
  • Journal article
    Sukjamsri C, Amis A, Hansen UN, Geraldes DM, Gregory T, Ahmed F, Hollis D, Schenk S, Emery Ret al., 2015,

    Digital volume correlation and micro-CT: an in-vitro technique for measuring full-field interface micromotion around polyethylene implants

    , Journal of Biomechanics, Vol: 48, Pages: 3447-3454, ISSN: 0021-9290

    Micromotion around implants is commonly measured using displacement-sensor techniques. Due to the limitations of these techniques, an alternative approach (DVC-μCT) using digital volume correlation (DVC) and micro-CT (μCT) was developed in this study. The validation consisted of evaluating DVC-μCT based micromotion against known micromotions (40, 100 and 150 μm) in a simplified experiment. Subsequently, a more clinically realistic experiment in which a glenoid component was implanted into a porcine scapula was carried out and the DVC-μCT measurements during a single load cycle (duration 20 min due to scanning time) was correlated with the manual tracking of micromotion at 12 discrete points across the implant interface. In this same experiment the full-field DVC-μCT micromotion was compared to the full-field micromotion predicted by a parallel finite element analysis (FEA). It was found that DVC-μCT micromotion matched the known micromotion of the simplified experiment (average/peak error=1.4/1.7 μm, regression line slope=0.999) and correlated with the micromotion at the 12 points tracked manually during the realistic experiment (R2=0.96). The DVC-μCT full-field micromotion matched the pattern of the full-field FEA predicted micromotion. This study showed that the DVC-μCT technique provides sensible estimates of micromotion. The main advantages of this technique are that it does not damage important parts of the specimen to gain access to the bone–implant interface, and it provides a full-field evaluation of micromotion as opposed to the micromotion at just a few discrete points. In conclusion the DVC-μCT technique provides a useful tool for investigations of micromotion around plastic implants.
  • Journal article
    Aqil A, Sheikh HQ, Masjedi M, Jeffers J, Cobb Jet al., 2015,

    Birmingham Mid-Head Resection Periprosthetic Fracture.

    , Clin Orthop Surg, Vol: 7, Pages: 402-405

    Total hip arthroplasty in the young leads to difficult choices in implant selection. Until recently bone conserving options were not available for younger patients with deficient femoral head bone stock. The novel Birmingham Mid-Head Resection (BMHR) device offers the option of bone conserving arthroplasty in spite of deficient femoral head bone stock. Femoral neck fracture is a known complication of standard resurfacing arthroplasty and is the most common reason for revision. It is unknown whether this remains to be the case for the BMHR neck preserving implants. We report a case of a 57-year-old male, who sustained a periprosthetic fracture following surgery with a BMHR arthroplasty. This paper illustrates the first reported case of a BMHR periprosthetic fracture. The fracture pattern is spiral in nature and reaches to the subtrochanteric area. This fracture pattern is different from published cadaveric studies, and clinicians using this implant should be aware of this as revision is likely to require a distally fitting, rather than a metaphyseal fitting stem. We have illustrated the surgical technique to manage this rare complication.
  • Journal article
    Stephen JM, Dodds AL, Lumpaopong P, Kader D, Williams A, Amis AAet al., 2015,

    The Ability of Medial Patellofemoral Ligament Reconstruction to Correct Patellar Kinematics and Contact Mechanics in the Presence of a Lateralized Tibial Tubercle

    , AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 43, Pages: 2198-2207, ISSN: 0363-5465
  • Journal article
    Tuncer M, Patel R, Cobb JP, Hansen UN, Amis AAet al., 2015,

    Variable bone mineral density reductions post-unicompartmental knee arthroplasty

    , KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY, Vol: 23, Pages: 2230-2236, ISSN: 0942-2056
  • Journal article
    Kittl C, Schmeling A, Amis AA, 2015,

    The patellofemoral joint. Anatomy, biomechanics, and surgical interventions

    , ARTHROSKOPIE, Vol: 28, Pages: 172-180, ISSN: 0933-7946
  • Journal article
    Halewood C, Traynor A, Bellemans J, Victor J, Amis AAet al., 2015,

    Anteroposterior Laxity After Bicruciate-Retaining Total Knee Arthroplasty Is Closer to the Native Knee Than ACL-Resecting TKA: A Biomechanical Cadaver Study.

    , Journal of Arthroplasty, ISSN: 1532-8406

    The purpose of this study was to examine whether a bicruciate retaining (BCR) TKA would yield anteroposterior (AP) laxity closer to the native knee than a posterior cruciate ligament retaining (CR) TKA. A BCR TKA was designed and compared to CR TKA and the native knee using cadaver specimens. AP laxity with the CR TKA was greater than the native knee (P=0.006) and BCR TKA (P=0.039), but no difference was found between the BCR TKA and the native knee. No significant differences were found in rotations between the prostheses and the native knee. BCR TKA was shown to be surgically feasible, reduced AP laxity versus CR TKA, and may improve knee stability without using conforming geometry in the implant design.
  • Journal article
    Ghosh KM, Hunt N, Blain A, Athwal KK, Longstaff L, Amis AA, Rushton S, Deehan DJet al., 2015,

    Isolated popliteus tendon injury does not lead to abnormal laxity in posterior-stabilised total knee arthroplasty

    , KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY, Vol: 23, Pages: 1763-1769, ISSN: 0942-2056
  • Journal article
    Hansen UN, sukjamsri, amis, 2015,

    Digital volumecorrelationandmicro-CT:Anin-vitrotechniquefor measuringfull-field interfacemicromotionaroundpolyethyleneimplants

    , Journal of Biomechanics, ISSN: 1873-2380
  • Book chapter
    Halewood C, Masouros S, Amis AA, 2015,

    Structure and function of the menisci

    , Meniscal Allograft Transplantation. A comprehensive review., Editors: Getgood, Spalding, Cole, Gersoff, Verdonk, ISBN: 978-0-9558873-5-2
  • Book chapter
    Halewood C, Lumpaopong P, Stephen JM, Amis AAet al., 2015,

    Functional Biomechanics with Cadaver Specimens

    , Experimental Research Methods in Orthopedics and Trauma, Editors: Simpson, Augat, Publisher: Thieme Medical Publishers, ISBN: 9783131731111

    This book provides a comprehensive summary of all current research methodologies for translational and pre-clinical studies in biomechanics and orthopedic trauma surgery.
  • Journal article
    Halewood C, Amis AA, 2015,

    Clinically relevant biomechanics of the knee capsule and ligaments

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 23, Pages: 2789-2796, ISSN: 0942-2056

    The paper describes the concepts of primary and secondary restraints to knee joint stability and explains systematically how the tibia is stabilised against translational forces and rotational torques in different directions and axes, and how those vary across the arc of flexion–extension. It also shows how the menisci act to stabilise the knee, in addition to load carrying across the joint. It compares the properties of the natural stabilising structures with the strength and stiffness of autogenous tissue grafts and relates those strengths to the strength of graft fixation devices. A good understanding of the biomechanical behaviour of these various structures in the knee will help the surgeon in the assessment and treatment of single and multi-ligament injuries.
  • Journal article
    van Arkel RJ, Amis AA, Cobb JP, Jeffers JRTet al., 2015,

    The capsular ligaments provide more hip rotational restraint than the acetabular labrum and the ligamentum teres

    , Bone & Joint Journal, Vol: 97B, Pages: 484-491, ISSN: 2049-4394

    In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty.

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