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  • Journal article
    Parkes M, Cann P, Jeffers J, 2017,

    Real-time observation of fluid flows in tissue during stress relaxation using Raman spectroscopy

    , Journal of Biomechanics, Vol: 60, Pages: 261-265, ISSN: 1873-2380

    This paper outlines a technique to measure fluid levels in articular cartilage tissue during an unconfined stress relaxation test. A time series of Raman spectrum were recorded during relaxation and the changes in the specific Raman spectral bands assigned to water and protein were monitored to determine the fluid content of the tissue. After 1000 s unconfined compression the fluid content of the tissue is reduced by an average of 3.9% ± 1.7%. The reduction in fluid content during compression varies between samples but does not significantly increase with increasing strain. Further development of this technique will allow mapping of fluid distribution and flows during dynamic testing making it a powerful tool to understand the role of interstitial fluid in the functional performance of cartilage.

  • Journal article
    Kittl C, Williams A, Amis AA, 2017,

    Biomechanical Role of Lateral Structures in Controlling Anterolateral Rotatory Laxity: The lliotibial Tract

    , OPERATIVE TECHNIQUES IN ORTHOPAEDICS, Vol: 27, Pages: 96-101, ISSN: 1048-6666

    Recent research, focusing on rotatory knee laxity, has intrigued the whole orthopaedic knee community. First popularized by Hughston et al, peripheral knee injuries at the time of cruciate ligament rupture have regained more and more recognition, which has led to a better understanding of these injuries. Recent research has been focused on anterolateral rotatory instability, especially regarding those structures that are responsible for the high-grade anterior subluxation of the lateral tibial plateau when damaged. Work at Imperial College London showed that the iliotibial tract (ITT) was the primary restraint to internal tibial rotation, especially the capsulo-osseous layer of the ITT, which contributed almost 25% of controlling a 5-Nm internal rotation torque at early flexion angles. However, due to the complex fiber arrangement, the functional anatomy of the ITT is difficult to understand. Thus, this article focuses on the involvement of the internal tibial rotation in restraining internal rotation and the pivot-shift phenomenon.

  • Journal article
    Amis A, Zaffagnini S, Musahl V, 2017,

    The anterolateral aspect of the knee: the state of play.

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 25, Pages: 989-990, ISSN: 0942-2056
  • Journal article
    Sopher RS, Amis AA, Calder JD, Jeffers JRTet al., 2017,

    Total ankle replacement design and positioning affect implant-bone micromotion and bone strains

    , MEDICAL ENGINEERING & PHYSICS, Vol: 42, Pages: 80-90, ISSN: 1350-4533
  • Journal article
    Geraldes DM, Hansen U, Amis AA, 2017,

    Parametric analysis of glenoid implant design and fixation type

    , Journal of Orthopaedic Research, Vol: 35, Pages: 775-784, 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.

  • Journal article
    Williams A, Ball S, Stephen J, White N, Jones M, Amis Aet al., 2017,

    The scientific rationale for lateral tenodesis augmentation of intra-articular ACL reconstruction using a modified 'Lemaire' procedure

    , KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY, Vol: 25, Pages: 1339-1344, ISSN: 0942-2056

    PurposeThe purpose of this work was to develop the rationale for adding a lateral extra-articular tenodesis to an ACL reconstruction in a knee with an injury that included both the ACL and anterolateral structures, and to show the early clinical picture.MethodsThe paper includes a review of recent anatomical and biomechanical studies of the anterolateral aspect of the knee. It then provides a detailed description of a modified Lemaire tenodesis technique. A short-term clinical follow-up of a case and control group was performed, with two sequential groups of patients treated by isolated ACL reconstruction, and by combined ACL plus lateral tenodesis.ResultsThe anatomical and biomechanical literature guide the surgeon towards a procedure based on the ilio-tibial band. The clinical study found a reduction in pivot-shift instability in the group of patients with the combined procedure.ConclusionThe evidence suggests that it should be appropriate to add a lateral extra-articular procedure to an ACL reconstruction in selected cases, but it was concluded that further data are required before definitive guidelines on the use of a lateral tenodesis can be established.Level of evidenceIII.

  • Journal article
    Iranpour F, Merican AM, Teo SH, Cobb JP, Amis AAet al., 2017,

    Femoral articular geometry and patellofemoral stability

    , KNEE, Vol: 24, Pages: 555-563, ISSN: 0968-0160

    Background:Patellofemoral instability is a major cause of anterior knee pain. The aim of this study was to examine how the medial and lateral stability of the patellofemoral joint in the normal knee changes with knee flexion and measure its relationship to differences in femoral trochlear geometry.Methods:Twelve fresh-frozen cadaveric knees were used. Five components of the quadriceps and the iliotibial band were loaded physiologically with 175 N and 30 N, respectively. The force required to displace the patella 10 mm laterally and medially at 0°, 20°, 30°, 60° and 90° knee flexion was measured. Patellofemoral contact points at these knee flexion angles were marked. The trochlea cartilage geometry at these flexion angles was visualized by Computed Tomography imaging of the femora in air with no overlying tissue. The sulcus, medial and lateral facet angles were measured. The facet angles were measured relative to the posterior condylar datum.Results:The lateral facet slope decreased progressively with flexion from 23° ± 3° (mean ± S.D.) at 0° to 17 ± 5° at 90°. While the medial facet angle increased progressively from 8° ± 8° to 36° ± 9° between 0° and 90°. Patellar lateral stability varied from 96 ± 22 N at 0°, to 77 ± 23 N at 20°, then to 101 ± 27 N at 90° knee flexion. Medial stability varied from 74 ± 20 N at 0° to 170 ± 21 N at 90°. There were significant correlations between the sulcus angle and the medial facet angle with medial stability (r = 0.78, p < 0.0001).Conclusions:These results provide objective evidence relating the changes of femoral profile geometry with knee flexion to patellofemoral stability.

  • Journal article
    Amis AA, 2017,

    Anterolateral knee biomechanics

    , KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY, Vol: 25, Pages: 1015-1023, ISSN: 0942-2056

    This article reviews the evidence for the roles of the anterolateral soft-tissue structures in rotatory stability of the knee, including their structural properties, isometry, and contributions to resisting tibial internal rotation. These data then lead to a biomechanical demonstration that the ilio-tibial band is the most important structure for the restraint of anterolateral rotatory instability.

  • Journal article
    Ma S, Goh EL, Jin A, Bhattacharya R, Boughton O, Patel B, Karunaratne A, Vo NT, Atwood R, Cobb J, Hansen U, Abel Ret al., 2017,

    Long-term effects of bisphosphonate therapy: perforations, microcracks and mechanical properties

    , Scientific Reports, Vol: 7, ISSN: 2045-2322

    Osteoporosis is characterised by trabecular bone loss resulting from increased osteoclast activation and unbalanced coupling between resorption and formation, which induces a thinning of trabeculae and trabecular perforations. Bisphosphonates are the frontline therapy for osteoporosis, which act by reducing bone remodelling, and are thought to prevent perforations and maintain microstructure. However, bisphosphonates may oversuppress remodelling resulting in accumulation of microcracks. This paper aims to investigate the effect of bisphosphonate treatment on microstructure and mechanical strength. Assessment of microdamage within the trabecular bone core was performed using synchrotron X-ray micro-CT linked to image analysis software. Bone from bisphosphonate-treated fracture patients exhibited fewer perforations but more numerous and larger microcracks than both fracture and non-fracture controls. Furthermore, bisphosphonate-treated bone demonstrated reduced tensile strength and Young’s Modulus. These findings suggest that bisphosphonate therapy is effective at reducing perforations but may also cause microcrack accumulation, leading to a loss of microstructural integrity and consequently, reduced mechanical strength.

  • Journal article
    Colaco H, Lord BR, Back DL, Davies AJ, Amis AA, Ajuied Aet al., 2017,

    Biomechanical properties of Bovine tendon xenografts treated with a modern processing method

    , Journal of Biomechanics, Vol: 53, Pages: 144-147, ISSN: 1873-2380

    Xenograft tendons have been used in few human studies, with variable results. With the advent of novel tissue processing techniques, which may mitigate against an immune-mediated rejection response without adversely affecting mechanical properties, there maynowbe a clinical role for xenograft tendons, particularly in knee ligament reconstruction. We hypothesize that‘BioCleanse®’processed bovine extensor digitorum medialis(EDM) tendons exhibit favorable time-zero pre-implantation biomechanical characteristics when compared to both unprocessed bovine EDM tendons and BioCleanse® processed human cadaveric allograft tibialis anterior tendons.In this in vitrocase controlled laboratory study, three groups of tendons underwent a 5-stage static loading test protocol: 15 BioCleanse® bovine (BCB), 15 fresh frozen unprocessed bovine (FFB), and 12 BioCleanse® human allograft (BCA) tendons. Cross-sectional area of the grafts was measured using an alginate molding technique, and tendons were mounted within an Instron® 5565 Materials Testing System using cryogenic clamps. BCB tendons displayed a higher ultimate tensile stress (p<0.05), with equivalent ultimate failure load, creep, and modulus of elasticity when compared to the FFB tendons (p>0.05). BCB tendons had an equivalent cross-sectional area to the BCA tendons (p>0.05) whilst exhibiting a greater failure load, ultimate tensile stress, less creep and a higher modulus of elasticity (p<0.05).The BioCleanse® process didnot adversely affect the time-zero biomechanical roperties of bovine xenograft EDM tendons. BioCleanse® processed bovine xenograft EDM tendons exhibitedsuperior biomechanical characteristics when 3compared with BioCleanse® processed allograft tibialis anterior tendons

  • Conference paper
    Boughton OR, Zhao S, Arnold M, Ma S, Cobb JP, Giuliani F, Hansen U, Abel RLet al., 2017,

    Measuring bone stiffness using microindentation

    , British Orthopaedic Research Society (BORS) 2016 Conference, Publisher: British Editorial Society of Bone and Joint Surgery, Pages: 31-31, ISSN: 2049-4416
  • Journal article
    van Arkel RJ, Jeffers JRT, Amis AA, 2017,

    Editorial Commentary: Anatomical Vandalism of the Hip? Hip Capsular Repair Seems a Sound Adjunct to Hip Arthroscopic Surgery

  • Book chapter
    Kittl C, Inderhaug E, Stephen J, El-Daou H, Williams A, Amis AAet al., 2017,

    Scientific basis and surgical technique for iliotibial band tenodesis combined with ACL reconstruction

    , Controversies in the Technical Aspects of ACL Reconstruction: An Evidence-Based Medicine Approach, Pages: 393-404, ISBN: 9783662527405

    © ISAKOS 2017. Anatomy: Due to the complexity of the lateral side of the knee, it may be best to describe these structures in terms of three tissue layers from superficial to deep. The distal part of the fascia lata - (1) the superficial layer of the iliotibial band (ITB) - is tethered to the distal femur by the (2) deep and capsulo-osseous fibres of the ITB. Removal of these ITB layers exposes the (3) anterolateral capsule and other deeper structures, which has been described as including the anterolateral ligament (ALL) with differing interpretations. Biomechanics: The anterior cruciate ligament (ACL) and the ITB have been shown to be the primary restraints to anterior tibial translation and internal tibial rotation, respectively. An injury of the ACL and the anterolateral structures may therefore result in a combined translatory and rotatory instability, called anterolateral rotatory instability (ALRI). As a logical rationale, a surgical intervention would include an intra-articular ACL reconstruction alongside a reconstruction of the anterolateral structures. This has been shown to restore normal knee kinematics in a simulated ALRI-injured knee. Conclusion: The anatomy of the anterolateral side is complex and yet not fully understood. Thus, there is an urgent need for a standardised nomenclature/terminology for these structures. A combined ALRI injury may be treated with an intra-articular ACL reconstruction and a nonanatomic ITB tenodesis.

  • Journal article
    Inderhaug E, Stephen JM, Williams A, Amis AAet al., 2016,

    Biomechanical Comparison of Anterolateral Procedures Combined With Anterior Cruciate Ligament Reconstruction

    , American Journal of Sports Medicine, Vol: 45, Pages: 347-354, ISSN: 0363-5465

    Background: Anterolateral soft tissue structures of the knee have a role in controlling anterolateral rotational laxity, and they maybe damaged at the time of anterior cruciate ligament (ACL) ruptures.Purpose: To compare the kinematic effects of anterolateral operative procedures in combination with intra-articular ACL reconstructionfor combined ACL plus anterolateral–injured knees.Study Design: Controlled laboratory study.Methods: Twelve cadaveric knees were tested in a 6 degrees of freedom rig using an optical tracking system to record the kinematicsthrough 0 to 90 of knee flexion with no load, anterior drawer, internal rotation, and combined loading. Testing was firstperformed in ACL-intact, ACL-deficient, and combined ACL plus anterolateral–injured (distal deep insertions of the iliotibial bandand the anterolateral ligament [ALL] and capsule cut) states. Thereafter, ACL reconstruction was performed alone and in combinationwith the following: modified MacIntosh tenodesis, modified Lemaire tenodesis passed both superficial and deep to thelateral collateral ligament, and ALL reconstruction. Anterolateral grafts were fixed at 30 of knee flexion with both 20 and 40 Nof tension. Statistical analysis used repeated-measures analyses of variance and paired t tests with Bonferroni adjustments.Results: ACL reconstruction alone failed to restore native knee kinematics in combined ACL plus anterolateral–injured knees (P\.05 for all). All combined reconstructions with 20 N of tension, except for ALL reconstruction (P 5 .002-.01), restored anteriortranslation. With 40 N of tension, the superficial Lemaire and MacIntosh procedures overconstrained the anterior laxity in deepflexion. Only the deep Lemaire and MacIntosh procedures—with 20 N of tension—restored rotational kinematics to the intactstate (P . .05 for all), while the ALL underconstrained and the superficial Lemaire overconstrained internal rotation. The sameprocedures with 40 N of tension

  • Journal article
    van Arkel RJ, Jeffers JRT, 2016,

    In vitro hip testing in the International Society of Biomechanics coordinate system

    , JOURNAL OF BIOMECHANICS, Vol: 49, Pages: 4154-4158, ISSN: 0021-9290
  • Journal article
    Athwal K, El Daou, Lord B, Davies AJ, Manning W, Rodriguez y Baena, Deehan DJ, Amiset al., 2016,

    Lateral soft-tissue structures contribute to cruciate-retaining total knee arthroplasty stability.

    , Journal of Orthopaedic Science, Vol: 35, Pages: 1902-1909, ISSN: 0949-2658

    Little information is available to surgeons regarding how the lateral structures prevent instability in the replaced knee. The aim of this study was to quantify the lateral soft‐tissue contributions to stability following cruciate‐retaining total knee arthroplasty (CR TKA). Nine cadaveric knees were tested in a robotic system at full extension, 30°, 60°, and 90° flexion angles. In both native and CR implanted states, ±90 N anterior–posterior force, ±8 Nm varus–valgus, and ±5 Nm internal–external torque were applied. The anterolateral structures (ALS, including the iliotibial band), the lateral collateral ligament (LCL), the popliteus tendon complex (Pop T), and the posterior cruciate ligament (PCL) were transected and their relative contributions to stabilizing the applied loads were quantified. The LCL was found to be the primary restraint to varus laxity (an average 56% across all flexion angles), and was significant in internal–external rotational stability (28% and 26%, respectively) and anterior drawer (16%). The ALS restrained 25% of internal rotation, while the PCL was significant in posterior drawer only at 60° and 90° flexion. The Pop T was not found to be significant in any tests. Therefore, the LCL was confirmed as the major lateral structure in CR TKA stability throughout the arc of flexion and deficiency could present a complex rotational laxity that cannot be overcome by the other passive lateral structures or the PCL. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1902–1909, 2017.

  • Journal article
    Cheong VS, Karunaratne A, Amis AA, Bull AMJet al., 2016,

    Strain rate dependency of fractures of immature bone

    , Journal of the Mechanical Behavior of Biomedical Materials, Vol: 66, Pages: 68-76, ISSN: 1751-6161

    Radiological features alone do not allow the discrimination between accidental paediatric long bone fractures or those sustained by child abuse. Therefore, there is a clinical need to elucidate the mechanisms behind each fracture to provide a forensic biomechanical tool for the vulnerable child. Four-point bending and torsional loading tests were conducted at more than one strain rate for the first time on immature bone, using a specimen-specific alignment system, to characterise structural behaviour at para-physiological strain rates. The bones behaved linearly to the point of fracture in all cases and transverse, oblique, and spiral fracture patterns were consistently reproduced. The results showed that there was a significant difference in bending stiffness between transverse and oblique fractures in four-point bending. For torsional loading, spiral fractures were produced in all cases with a significant difference in the energy and obliquity to fracture. Multiple or comminuted fractures were seen only in bones that failed at a higher stress or torque for both loading types. This demonstrates the differentiation of fracture patterns at different strain rates for the first time for immature bones, which may be used to match the case history given of a child and the fracture produced.

  • Conference paper
    Ma S, Goh EL, Patel B, Jin A, Boughton O, Cobb J, Hansen U, Abel RLet al., 2016,

    Are the cracks starting to appear in bisphosphonate therapy?

    , British Orthopaedic Research Society (BORS) 2016 Conference, Publisher: British Editorial Society of Bone and Joint Surgery, Pages: 53-53, ISSN: 2049-4416
  • Journal article
    Lord BR, El-Daou H, Sabnis BM, Gupte CM, Wilson AJ, Amis AAet al., 2016,

    Erratum to: Biomechanical comparison of graft structures in anterior cruciate ligament reconstruction (vol 25, pg 559, 2017)

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 25, Pages: 988-988, ISSN: 0942-2056

    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 remained similar to the nativ

  • Journal article
    Amirthanayagam TD, Amis AA, Reilly P, Emery RJHet al., 2016,

    Rotator cuff-sparing approaches for glenohumeral joint access: an anatomic feasibility study

    , Journal of Shoulder and Elbow Surgery, Vol: 26, Pages: 512-520, ISSN: 1058-2746

    BackgroundThe deltopectoral approach for total shoulder arthroplasty can result in subscapularis dysfunction. In addition, glenoid wear is more prevalent posteriorly, a region difficult to access with this approach. We propose a posterior approach for access in total shoulder arthroplasty that uses the internervous interval between the infraspinatus and teres minor. This study compares this internervous posterior approach with other rotator cuff–sparing techniques, namely, the subscapularis-splitting and rotator interval approaches.MethodsThe 3 approaches were performed on 12 fresh frozen cadavers. The degree of circumferential access to the glenohumeral joint, the force exerted on the rotator cuff, the proximity of neurovascular structures, and the depth of the incisions were measured, and digital photographs of the approaches in different arm positions were analyzed.ResultsThe posterior approach permits direct linear access to 60% of the humeral and 59% of the glenoid joint circumference compared with 39% and 42% for the subscapularis-splitting approach and 37% and 28% for the rotator interval approach. The mean force of retraction on the rotator cuff was 2.76 (standard deviation [SD], 1.10) N with the posterior approach, 2.72 (SD, 1.22) N with the rotator interval, and 4.75 (SD, 2.56) N with the subscapularis-splitting approach. From the digital photographs and depth measurements, the estimated volumetric access available for instrumentation during surgery was comparable for the 3 approaches.ConclusionThe internervous posterior approach provides greater access to the shoulder joint while minimizing damage to the rotator cuff.

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