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  • Journal article
    Sopher R, Amis A, Davies D, Jeffers Jet al., 2016,

    The influence of muscle pennation angle and cross-sectional area on contact forces in the ankle joint

    , Journal of Strain Analysis for Engineering Design, Vol: 52, Pages: 12-23, ISSN: 0309-3247

    Data about a muscle’s fibre pennation angle and physiological cross-sectional area are used in musculoskeletal modelling to estimate muscle forces, which are used to calculate joint contact forces. For the leg, muscle architecture data are derived from studies that measured pennation angle at the muscle surface, but not deep within it. Musculoskeletal models developed to estimate joint contact loads have usually been based on the mean values of pennation angle and physiological cross-sectional area.Therefore, the first aim of this study was to investigate differences between superficial and deep pennation angles within each muscle acting over the ankle and predict how differences may influence muscle forces calculated in musculoskeletal modelling. The second aim was to investigate how inter-subject variability in physiological cross-sectional area and pennation angle affects calculated ankle contact forces.Eight cadaveric legs were dissected to excise the muscles acting over the ankle. The mean surface and deep pennation angles, fibre length and physiological cross-sectional area were measured. Cluster analysis was applied to group the muscles according to their architectural characteristics. A previously validated OpenSim model was used to estimate ankle muscle forces and contact loads using architecture data from all eight limbs.The mean surface pennation angle for soleus was significantly greater (54%) than the mean deep pennation angle. Cluster analysis revealed three groups of muscles with similar architecture and function: deep plantarflexors and peroneals, superficial plantarflexors and dorsiflexors. Peak ankle contact force was predicted to occur before toe-off, with magnitude greater than five times bodyweight. Inter-specimen variability in contact force was smallest at peak force.These findings will help improve the development of experimental and computational musculoskeletal models by providing data to estimate force based on both surface and deep

  • Journal article
    Lord BR, El-Daou H, Sabnis BM, Gupte CM, Wilson AM, Amis AAet al., 2016,

    Biomechanical comparison of graft structures in anterior cruciate ligament reconstruction

    , Knee Surgery Sports Traumatology Arthroscopy, Vol: 25, Pages: 559-568, ISSN: 1433-7347

    PURPOSE: Double-bundle (DB) anterior cruciate ligament (ACL) reconstruction may offer kinematic restoration superior to anatomic single bundle (SB), but it remains technically challenging. The femoral attachment site has the most effect on ACL graft isometry, so a simplified three-socket (3S) construct which still uses two sockets to cover the femoral ACL attachment is attractive. It was hypothesised that ACL reconstruction using three- and four-socket techniques would more closely restore native knee kinematics compared to anatomic two-socket (SB) surgery. METHODS: Nine cadaveric knees were used to evaluate the kinematics of ACL-intact, ACL-deficient, anatomic SB, three-socket, and DB arthroscopic ACL reconstructions. Suspensory fixation was used, and grafts were tensioned to match the anterior draw of the intact knee at 20°. A six-degree-of-freedom robotic system measured knee laxity under 90 N anterior tibial force and rotational laxity under 5 N-m torque. Combined moments were applied to simulate the pivot-shift subluxation: 4 N-m internal rotation and 8 N-m valgus. RESULTS: Significant differences between reconstructions were not found during anterior tibial loading, apart from SB being more lax than DB at 60° flexion. All reconstructions produced comparable laxity to the intact state, apart from SB at 60°. Significant differences between reconstructions were not found at any flexion angle during tibial internal/external applied torques. Under combined loading, DB produced significantly less laxity than SB constructs apart from anterior tibial translation at 0° and internal rotation at 45°. 3S and DB were comparable to the native knee throughout. CONCLUSION: Although 3S restored laxities to a similar extent to DB, significant superiority over SB surgery was not observed. Although statistically significant differences were found between SB and DB surgery during anterior tibial and simulated pivot-shift loading, both remain

  • Journal article
    Ma S, Boughton O, Karunaratne A, Jin A, Cobb JP, Hansen U, Abel RLet al., 2016,

    Synchrotron imaging assessment of bone quality

    , Clinical Reviews in Bone and Mineral Metabolism, Vol: 14, Pages: 150-160, ISSN: 1559-0119

    Bone is a complex hierarchical structure and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-Ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen-mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in-vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex-vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in-situ testing in bone research.

  • Journal article
    Hansen UN, 2016,

    Dynamic three-dimensional shoulder MRI during active motion for investigation of rotator cuff diseases

    , PLOS One, Vol: 11, ISSN: 1932-6203

    BackgroundMRI is the standard methodology in diagnosis of rotator cuff diseases. However, many patients continue to have pain despite treatment, and MRI of a static unloaded shoulder seems insufficient for best diagnosis and treatment. This study evaluated if Dynamic MRI provides novel kinematic data that can be used to improve the understanding, diagnosis and best treatment of rotator cuff diseases.MethodsDynamic MRI provided real-time 3D image series and was used to measure changes in the width of subacromial space, superior-inferior translation and anterior-posterior translation of the humeral head relative to the glenoid during active abduction. These measures were investigated for consistency with the rotator cuff diseases classifications from standard MRI.ResultsThe study included: 4 shoulders with massive rotator cuff tears, 5 shoulders with an isolated full-thickness supraspinatus tear, 5 shoulders with tendinopathy and 6 normal shoulders. A change in the width of subacromial space greater than 4mm differentiated between rotator cuff diseases with tendon tears (massive cuff tears and supraspinatus tear) and without tears (tendinopathy) (p = 0.012). The range of the superior-inferior translation was higher in the massive cuff tears group (6.4mm) than in normals (3.4mm) (p = 0.02). The range of the anterior-posterior translation was higher in the massive cuff tears (9.2 mm) and supraspinatus tear (9.3 mm) shoulders compared to normals (3.5mm) and tendinopathy (4.8mm) shoulders (p = 0.05).ConclusionThe Dynamic MRI enabled a novel measure; ‘Looseness’, i.e. the translation of the humeral head on the glenoid during an abduction cycle. Looseness was better able at differentiating different forms of rotator cuff disease than a simple static measure of relative glenohumeral position.

  • Journal article
    Geraldes DM, Hansen U, Amis AA, 2016,

    Parametric analysis of glenoid implant design and fixation type.

    , Journal of Orthopaedic Research, ISSN: 1554-527X

    Common post-operative problems in shoulder arthroplasty such as glenoid loosening and joint instability may be reduced by improvements in glenoid design, shape, material choice and fixation method. A framework for parametric analysis of different implant fixation configurations was developed in order to efficiently sift through potential glenoid component designs and investigate the influence of design factors such as fixation type, component thickness and peg position, number, diameter and length in a multi-factorial design investigation. The proposed method allowed for simultaneous comparison of the performance of 344 different parametric variations of 10 different reference geometries with large central fixation features or small peripheral pegs, undergoing four different worst-case scenario loading conditions, averaging 64.7 seconds per model. The impact of design parameters were assessed for different factors responsible for post-operative problems in shoulder arthroplasty, such as bone volume preservation, stresses in the implant, central displacement or fixation stability, and the worst performing geometries all relied on conventional central fixation. Of the remaining geometries, four peripheral fixation configurations produced von Mises stresses comfortably below the material's yield strength. We show that the developed method allows for simple, direct, rapid and repeatable comparison of different design features, material choices or fixation methods by analyzing how they influence the bone-implant mechanical environment. The proposed method can provide valuable insight in implant design optimization by screening through multiple potential design modifications at an early design evaluation stage and highlighting the best performing combinations according to the failure mechanism to mitigate. This article is protected by copyright. All rights reserved.

  • Conference paper
    Geraldes D, Hansen U, Jeffers J, Amis Aet al., 2016,

    Interference fit optimisation for small press-fitted pegs

    , International Society for Technology in Arthroplasty 2015, Publisher: BRITISH EDITORIAL SOCIETY OF BONE & JOINT SURGERY, Pages: 150-150, ISSN: 2049-4416
  • 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: Response.

    , American Journal of Sports Medicine, Vol: 44, Pages: NP15-NP18, ISSN: 1552-3365
  • Book chapter
    Halewood C, Amis AA, 2016,

    Physiology: Biomechanics

    , Surgery of the Meniscus, Pages: 35-45, ISBN: 9783662491867
  • Journal article
    Athwal KK, El Daou H, Inderhaug E, Manning W, Davies AJ, Deehan DJ, Amis AAet al., 2016,

    An in vitro analysis of medial structures and a medial soft tissue reconstruction in a constrained condylar total knee arthroplasty

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 25, Pages: 2646-2655, ISSN: 0942-2056

    PurposeThe aim of this study was to quantify the medial soft tissue contributions to stability following constrained condylar (CC) total knee arthroplasty (TKA) and determine whether a medial reconstruction could restore stability to a soft tissue-deficient, CC-TKA knee.MethodsEight cadaveric knees were mounted in a robotic system and tested at 0°, 30°, 60°, and 90° of flexion with ±50 N anterior–posterior force, ±8 Nm varus–valgus, and ±5 Nm internal–external torque. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were transected and their relative contributions to stabilising the applied loads were quantified. After complete medial soft tissue transection, a reconstruction using a semitendinosus tendon graft was performed, and the effect on kinematic behaviour under equivocal conditions was measured.ResultsIn the CC-TKA knee, the sMCL was the major medial restraint in anterior drawer, internal–external, and valgus rotation. No significant differences were found between the rotational laxities of the reconstructed knee to the pre-deficient state for the arc of motion examined. The relative contribution of the reconstruction was higher in valgus rotation at 60° than the sMCL; otherwise, the contribution of the reconstruction was similar to that of the sMCL.ConclusionThere is contention whether a CC-TKA can function with medial deficiency or more constraint is required. This work has shown that a CC-TKA may not provide enough stability with an absent sMCL. However, in such cases, combining the CC-TKA with a medial soft tissue reconstruction may be considered as an alternative to a hinged implant.

  • 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.

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