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  • Journal article
    Li J, Clarke S, Cobb JP, Amis AAet al., 2017,

    Novel curved surface preparation technique for knee resurfacing

    , Medical Engineering and Physics, Vol: 49, Pages: 89-93, ISSN: 1350-4533

    Conventional tools are incapable of preparing the curved articular surface geometry required during cartilage repair procedures. A novel curved surface preparation technique was proposed and tested to provide an accurate low-cost solution. Three shapes of samples, with flat, 30 mm radius and 60 mm radius surfaces, were manufactured from foam bone substitute for testing. Registering guides and cutting guides were designed and 3-D printed to fit onto the foam samples. A rotational cutting tool with an adapter was used to prepare the surfaces following the guidance slots in the cutting guides. The accuracies of the positions and shapes of the prepared cavities were measured using a digital calliper, and the surface depth accuracy was measured using a 3-D scanner. The mean shape and position errors were both approximately ± 0.5 mm and the mean surface depth error ranged from 0 to 0.3 mm, range − 0.3 to + 0.45 mm 95% CI. This study showed that the technique was able to prepare a curved surface accurately; with some modification it can be used to prepare the knee surface for cartilage repair.

  • Journal article
    Ridzwan M, Sukjamsri C, Pal B, van Arkel R, Bell A, Khanna M, Baskaradas A, Abel R, Boughton O, Cobb J, Hansen Uet al., 2017,

    Femoral fracture type can be predicted from femoral structure: a finite element study validated by digital volume correlation experiments

    , Journal of Orthopaedic Research, Vol: 36, Pages: 993-1001, ISSN: 1554-527X

    Proximal femoral fractures can be categorized into two main types: Neck and intertrochanteric fractures accounting for 53% and 43% of all proximal femoral fractures, respectively. The possibility to predict the type of fracture a specific patient is predisposed to would allow drug and exercise therapies, hip protector design, and prophylactic surgery to be better targeted for this patient rendering fracture preventing strategies more effective. This study hypothesized that the type of fracture is closely related to the patient-specific femoral structure and predictable by finite element (FE) methods. Fourteen femora were DXA scanned, CT scanned, and mechanically tested to fracture. FE-predicted fracture patterns were compared to experimentally observed fracture patterns. Measurements of strain patterns to explain neck and intertrochanteric fracture patterns were performed using a digital volume correlation (DVC) technique and compared to FE-predicted strains and experimentally observed fracture patterns. Although loaded identically, the femora exhibited different fracture types (six neck and eight intertrochanteric fractures). CT-based FE models matched the experimental observations well (86%) demonstrating that the fracture type can be predicted. DVC-measured and FE-predicted strains showed obvious consistency. Neither DXA-based BMD nor any morphologic characteristics such as neck diameter, femoral neck length, or neck shaft angle were associated with fracture type. In conclusion, patient-specific femoral structure correlates with fracture type and FE analyses were able to predict these fracture types. Also, the demonstration of FE and DVC as metrics of the strains in bones may be of substantial clinical value, informing treatment strategies and device selection and design.

  • Journal article
    Inderhaug E, Stephen JM, El-Daou H, Williams A, Amis AAet al., 2017,

    The Effects of Anterolateral Tenodesis on Tibiofemoral Contact Pressures and Kinematics.

    , American Journal of Sports Medicine, Vol: 45, Pages: 3081-3088, ISSN: 0363-5465

    BACKGROUND: Anterolateral tenodeses are increasingly popular in combination with intra-articular anterior cruciate ligament reconstructions. Despite the perception of risk of overconstraint and lateral osteoarthritis, evidence is lacking regarding the effect of graft tensioning on knee kinematics and intra-articular compartmental joint pressures. PURPOSE: To investigate tibiofemoral joint contact pressures and kinematics related to an anterolateral lesion and the effectiveness of a MacIntosh tenodesis in restoring these when varying (1) graft tension and (2) tibial rotation during graft fixation. STUDY DESIGN: Controlled laboratory study. METHODS: Eight fresh-frozen cadaveric knees were tested in a customized rig with femur fixed and tibia free to move from 0° to 90° of flexion. The quadriceps and iliotibial band were loaded by means of a weighted pulley system. At 30° intervals of knee flexion, tibiofemoral contact pressures were measured with a Tekscan sensor and tibiofemoral kinematics were recorded by use of an optical tracking system. The knee was tested intact and then with an anterolateral soft tissue transection. MacIntosh tenodeses were then tested in a randomized order with 20 N or 80 N of graft tension, each with the tibia held in neutral intact alignment or free to rotate. RESULTS: Tibial anterior translation and internal rotation were significantly increased and lateral contact pressures significantly reduced compared with the intact knee following anterolateral soft tissue cutting ( P < .05). Contact pressures were restored with fixed neutral tibial rotation combined with 20 N or 80 N of graft tension or by a free-hanging tibia with 20 N of graft tension (all P values > .5). Grafts tensioned with 80 N caused significant overconstraint both when the tibia was fixed and free hanging (all P values < .05). Increases in the lateral tibiofemoral contact pressures were also seen when the tibia was free hanging and 80 N was used for graft

  • Journal article
    Athwal KK, El Daou H, Inderhaug E, Manning W, Davies AJ, Deehan DJ, Amis AAet al., 2017,

    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

    Purpose: The 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.Methods: Eight 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.Results: In 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.Conclusion: There 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
    Athwal KK, El Daou H, Inderhaug E, Manning W, Davies AJ, Deehan DJ, Amis AAet al., 2017,

    Erratum to: 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: 2656-2656, ISSN: 0942-2056
  • Journal article
    Junaid S, Sanghavi S, Anglin C, Bull A, Emery R, Amis AA, Hansen Uet al., 2017,

    Treatment of the Fixation Surface Improves Glenoid Prosthesis Longevity in vitro.

    , Journal of Biomechanics, Vol: 61, Pages: 81-87, ISSN: 0021-9290

    Many commercial cemented glenoid components claim superior fixation designs and increased survivability. However, both research and clinical studies have shown conflicting results and it is unclear whether these design variations do improve loosening rates. Part of the difficulty in investigating fixation failure is the inability to directly observe the fixation interface, a problem addressed in this study by using a novel experimental set-up. Cyclic loading-displacement tests were carried out on 60 custom-made glenoid prostheses implanted into a bone substitute. Design parameters investigated included treatment of the fixation surface of the component resulting in different levels of back-surface roughness, flat-back versus curved-back, keel versus peg and more versus less conforming implants. Visually-observed failure and ASTM-recommended rim-displacements were recorded throughout testing to investigate fixation failure and if rim displacement is an appropriate measure of loosening. Roughening the implant back (Ra>3µm) improved resistance to failure (P<0.005) by an order of magnitude with the rough and smooth groups failing at 8712±5584 cycles (mean±SD) and 1080±1197 cycles, respectively. All other design parameters had no statistically significant effect on the number of cycles to failure. All implants failed inferiorly and 95% (57/60) at the implant/cement interface. Rim-displacement correlated with visually observed failure. The most important effect was that of roughening the implant, which strengthened the polyethylene-cement interface. Rim-displacement can be used as an indicator of fixation failure, but the sensitivity was insufficient to capture subtle effects. LEVEL OF EVIDENCE: Basic Science Study, Biomechanical Analysis.

  • 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
    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
    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
    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, Pages: 1-10, 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
    Amirthanayagam TD, Amis AA, Reilly P, Emery RJHet al., 2017,

    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.

  • 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,

    <i>Editorial Commentary</i>: 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

    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.

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