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  • Book chapter
    Halewood C, Amis AA, 2016,

    Physiology: Biomechanics

    , Surgery of the Meniscus, Pages: 35-45, ISBN: 9783662491867
  • Journal article
    Stephen JM, Kittl C, Williams A, Zaffagnini S, Marcheggiani Muccioli GM, Fink C, Amis AAet al., 2016,

    Effect of medial patellofemoral ligament reconstruction method on patellofemoral contact pressures and kinematics.

    , American Journal of Sports Medicine, Vol: 44, Pages: 1186-1194, ISSN: 1552-3365

    BACKGROUND: There remains a lack of evidence regarding the optimal method when reconstructing the medial patellofemoral ligament (MPFL) and whether some graft constructs can be more forgiving to surgical errors, such as overtensioning or tunnel malpositioning, than others. HYPOTHESIS: The null hypothesis was that there would not be a significant difference between reconstruction methods (eg, graft type and fixation) in the adverse biomechanical effects (eg, patellar maltracking or elevated articular contact pressure) resulting from surgical errors such as tunnel malpositioning or graft overtensioning. STUDY DESIGN: Controlled laboratory study. METHODS: Nine fresh-frozen cadaveric knees were placed on a customized testing rig, where the femur was fixed but the tibia could be moved freely from 0° to 90° of flexion. Individual quadriceps heads and the iliotibial tract were separated and loaded to 205 N of tension using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film inserted between the patella and trochlea, in conjunction with an optical tracking system. The MPFL was transected and then reconstructed in a randomized order using a (1) double-strand gracilis tendon, (2) quadriceps tendon, and (3) tensor fasciae latae allograft. Pressure maps and tracking measurements were recorded for each reconstruction method in 2 N and 10 N of tension and with the graft positioned in the anatomic, proximal, and distal femoral tunnel positions. Statistical analysis was undertaken using repeated-measures analyses of variance, Bonferroni post hoc analyses, and paired t tests. RESULTS: Anatomically placed grafts during MPFL reconstruction tensioned to 2 N resulted in the restoration of intact medial joint contact pressures and patellar tracking for all 3 graft types investigated (P > .050). However, femoral tunnels positioned proxim

  • Journal article
    Ghosh KM, Manning WA, Blain AP, Rushton SP, Longstaff LM, Amis AA, Deehan DJet al., 2016,

    Influence of increasing construct constraint in the presence of posterolateral deficiency at knee replacement: A biomechanical study

    , JOURNAL OF ORTHOPAEDIC RESEARCH, Vol: 34, Pages: 427-434, ISSN: 0736-0266
  • Journal article
    Stephen JM, Kader D, Lumpaopong P, Deehan DJ, Amis AAet al., 2016,

    The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction (vol 42, pg 364, 2014)

    , AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 44, Pages: NP11-NP11, ISSN: 0363-5465
  • Journal article
    Stephen JM, Urquhart DWJ, van Arkel RJ, Ball S, Jaggard MKJ, Lee JC, Church JSet al., 2016,

    The use of sonographically guided botulinum toxin type A (Dysport) injections into the tensor fasciae latae for the treatment of lateral patellofemoral overload syndrome

    , American Journal of Sports Medicine, Vol: 44, Pages: 1195-1202, ISSN: 1552-3365

    Background: Pain in the anterior and lateral parts of the knee during exercise is a common clinical problem for which current management strategies are often unsuccessful.Purpose: To investigate the effect of an ultrasound-guided botulinum toxin (BT) injection into the tensor fasciae latae (TFL), followed by physical therapy, in patients classified with lateral patellofemoral overload syndrome (LPOS) who failed to respond to conventional treatment.Study Design: Case series; Level of evidence, 4.Methods: A total of 45 patients (mean ± SD age, 32.4 ± 8.6 years) who met the inclusion criteria of (1) activity-related anterolateral knee symptoms, (2) symptoms lasting longer than 3 months, (3) a pathological abnormality confirmed by magnetic resonance imaging, and (4) previous failed physical therapy received an ultrasound-guided injection of BT into the TFL followed by physical therapy. Patient-reported outcomes were collected at 5 intervals: before the injection; at 1, 4, and 12 weeks after the injection; and at a mean 5 years after the injection. In 42 patients, relative iliotibial band (ITB) length changes were assessed using the modified Ober test at the first 4 time points. A computational model was run to simulate the effect of TFL weakening on gluteus medius (GMed) activity. Statistical analysis was undertaken using 1-way analysis of variance and paired t tests with Bonferroni post hoc correction.Results: There was a significant improvement in Anterior Knee Pain Scale scores from before the injection (61 ± 15) to 1 (67 ± 15), 4 (70 ± 16), and 12 weeks (76 ± 16) after the injection and in 87% of patients (39/45 patients available for follow-up) at approximately 5 years (from 62.9 ± 15.4 to 87.0 ± 12.5) after the injection (all P < .010). A significant effect on the modified Ober test was identified as a result of the intervention, with an increase in leg drop found at 1 (3° ± 5°), 4 (4° &

  • Journal article
    Stephen JM, Halewood C, Kittl C, Bollen SR, Williams A, Amis AAet al., 2016,

    Posteromedial Meniscocapsular Lesions Increase Tibiofemoral Joint Laxity With Anterior Cruciate Ligament Deficiency, and Their Repair Reduces Laxity

    , American Journal of Sports Medicine, Vol: 44, Pages: 400-408, ISSN: 0363-5465

    Background:Injury to the posteromedial meniscocapsular junction has been identified after anterior cruciate ligament (ACL) rupture; however, there is a lack of objective evidence investigating how this affects knee kinematics or whether increased laxity can be restored by repair. Such injury is often overlooked at surgery, with possible compromise to results.Hypotheses:(1) Sectioning the posteromedial meniscocapsular junction in an ACL-deficient knee will result in increased anterior tibial translation and rotation. (2) Isolated ACL reconstruction in the presence of a posteromedial meniscocapsular junction lesion will not restore intact knee laxity. (3) Repair of the posteromedial capsule at the time of ACL reconstruction will reduce tibial translation and rotation to normal. (4) These changes will be clinically detectable.Study Design:Controlled laboratory study.Methods:Nine cadaveric knees were mounted in a test rig where knee kinematics were recorded from 0° to 100° of flexion by use of an optical tracking system. Measurements were recorded with the following loads: 90-N anterior-posterior tibial forces, 5-N·m internal-external tibial rotation torques, and combined 90-N anterior force and 5-N·m external rotation torque. Manual Rolimeter readings of anterior translation were taken at 30° and 90°. The knees were tested in the following conditions: intact, ACL deficient, ACL deficient and posteromedial meniscocapsular junction sectioned, ACL deficient and posteromedial meniscocapsular junction repaired, ACL patellar tendon reconstruction with posteromedial meniscocapsular junction repair, and ACL reconstructed and capsular lesion re-created. Statistical analysis used repeated-measures analysis of variance and post hoc paired t tests with Bonferroni correction.Results:Tibial anterior translation and external rotation were both significantly increased compared with the ACL-deficient knee after posterior meniscocapsular sectioning (P <

  • Journal article
    Kittl C, El-Daou H, Athwal KK, Gupte CM, Weiler A, Williams A, Amis AAet al., 2016,

    The role of the anterolateral structures and the ACL in controlling laxity of the intact and ACL-deficient knee

    , AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 44, Pages: 345-354, ISSN: 0363-5465

    Background:Anterolateral rotatory instability (ALRI) may result from combined anterior cruciate ligament (ACL) and lateral extra-articular lesions, but the roles of the anterolateral structures remain controversial.Purpose:To determine the contribution of each anterolateral structure and the ACL in restraining simulated clinical laxity in both the intact and ACL-deficient knee.Study Design:Controlled laboratory study.Methods:A total of 16 knees were tested using a 6 degrees of freedom robot with a universal force-moment sensor. The system automatically defined the path of unloaded flexion/extension. At different flexion angles, anterior-posterior, internal-external, and internal rotational laxity in response to a simulated pivot shift were tested. Eight ACL-intact and 8 ACL-deficient knees were tested. The kinematics of the intact/deficient knee was replayed after transecting/resecting each structure of interest; therefore, the decrease in force/torque reflected the contribution of the transected/resected structure in restraining laxity. Data were analyzed using repeated-measures analyses of variance and paired t tests.Results:For anterior translation, the intact ACL was clearly the primary restraint. The iliotibial tract (ITT) resisted 31% ± 6% of the drawer force with the ACL cut at 30° of flexion; the anterolateral ligament (ALL) and anterolateral capsule resisted 4%. For internal rotation, the superficial layer of the ITT significantly restrained internal rotation at higher flexion angles: 56% ± 20% and 56% ± 16% at 90° for the ACL-intact and ACL-deficient groups, respectively. The deep layer of the ITT restrained internal rotation at lower flexion angles, with 26% ± 9% and 33% ± 12% at 30° for the ACL-intact and ACL-deficient groups, respectively. The other anterolateral structures provided no significant contribution. During the pivot-shift test, the ITT provided 72% ± 14% of the restraint at 45° for th

  • Journal article
    Shah SIMRANA, Jin ANDI, Wilson HANNAHCP, Abel PAULD, Price PATRICIAM, Hansen ULRICHN, Abel RICHARDLet al., 2015,

    Novel Computed Tomography-based Metric Reliably Estimates bone Strength, Offering Potentially Meaningful Enhancement in Clinical Fracture Risk Prediction

    , European Journal of Medicine, Vol: 10, Pages: 214-220, ISSN: 2310-3434

    Osteoporosis with resultant fractures is a major global health problem with huge socioeconomicimplications for patients, families and healthcare services. Areal (2D bone mineraldensity (BMD) assessment is commonly used for predicting such fracture risk, but is unreliable,estimating only about 50% of bone strength. By contrast, computed tomography (CT) basedtechniques could provide improved metrics for estimating bone strength such as bone volumefraction (BVF; a 3D volumetric measure of mineralised bone), enabling cheap, safe and reliablestrategies for clinical application, and to help divert resources to patients identified as most likelyto benefit, meeting an unmet need.Here we describe a novel method for measuring BVF at clinical-CT like low-resolution(550µm voxel size). Femoral heads (n=8) were micro-CT scanned ex-vivo. Micro-CT data weredowngraded in resolution from 30µm to 550µm voxel size and BVF calculated at high and lowresolution. Experimental mechanical testing was applied to measure ex vivo bone strength ofsamples. BVF measures collected at high-resolution showed high correlation (correlationcoefficient r2=0.95) with low-resolution data. Low-resolution BVF metrics showed high correlation(r2=0.96) with calculated sample strength. These results demonstrate that measuring BVF at lowresolution is feasible, which also predicts bone strength. Measures of BVF should be useful for clinically estimating bone strength and fracture risk. The method needs to be validated using clinical CT scans.

  • 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
    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
    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
    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

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