Imperial College London

ProfessorAndrewAmis

Faculty of EngineeringDepartment of Mechanical Engineering

Professor
 
 
 
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Contact

 

+44 (0)20 7594 7062a.amis

 
 
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Assistant

 

Ms Fabienne Laperche +44 (0)20 7594 7033

 
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Location

 

713City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

430 results found

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

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

Geraldes D, Hansen U, Jeffers J, Amis Aet al., 2017, The stability of small pegs for cementless implant fixation, Journal of Orthopaedic Research, Vol: 35, Pages: 2765-2772, ISSN: 1554-527X

Most glenoid implants rely on large centrally located fixation features to avoid perforation of the glenoid vault in its peripheral regions. Upon revision of such components there may not be enough bone left for the reinsertion of an anatomical prosthesis. Multiple press-fit small pegs would allow for less bone resection and strong anchoring in the stiffer and denser peripheral subchondral bone. This study assessed the fixation characteristics, measured as the push-in (Pin) and pull-out (Pout) forces, and spring-back, measured as the elastic displacement immediately after insertion, for five different small press-fitted peg configurations manufactured out of UHMWPE cylinders (5 mm diameter and length). A total of 16 specimens for each configuration were tested in two types of solid bone substitute: Hard (40 PCF, 0.64 g/cm3, worst-case scenario of Pin) and soft (15 PCF, 0.24 g/cm3, worst-case scenario of spring-back and Pout). Two different diametric interference-fits were studied. Geometries with lower stiffness fins (large length to width aspect ratio) were the best performing designs in terms of primary fixation stability. They required the lowest force to fully seat, meaning they are less damaging to the bone during implantation, while providing the highest Pout/Pin ratio, indicating that when implanted they provide the strongest anchoring for the glenoid component. It is highlighted that drilling of chamfered holes could minimize spring-back displacements. These findings are relevant for the design of implants press-fitted pegs because primary fixation has been shown to be an important factor in achieving osseointegration and longevity of secondary fixation.

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

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

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

Journal article

Sopher R, Amis A, Calder J, Jeffers Jet al., 2017, Total ankle replacement design and positioning affect implant-bone micromotion and bone strains, Medical Engineering & Physics, Vol: 42, Pages: 80-90, ISSN: 1873-4030

Implant loosening -commonly linked with elevated initial micromotion -is the primary indication for total ankle replacement (TAR) revision. Finite element modelling (FEM) has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning -previously linked with higher failure rates -remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Computational models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjectedto physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.

Journal article

van arkel R, Jeffers J, amis A, 2017, Editorial Commentary: Anatomical vandalism of the hip? Hip capsular repair seems a sound adjunct to hip arthroscopic surgery, Arthroscopy-the Journal of Arthroscopic and Related Surgery, Vol: 33, Pages: 314-316, ISSN: 1526-3231

The study “Contribution of the Pubofemoral Ligament to Hip Stability: A Biomechanical Study” by Martin,Khoury, Schröder, Johnson, Gómez-Hoyos, Campos, and Palmer found that cutting the hip capsular ligament allowed alarge increase in femoral internal rotation, particularly in the flexed hip, causing subluxation to occur. In addition toproviding new data on the role of the pubofemoral ligament, it raises the question of whether hip joint surgeons shouldrepair the capsuledwhat are the likely consequences?dand whether any beneficial effects persist in long-term clinicalfollow-ups. For now, hip capsular repair seems a sound adjunct to hip arthroscopic surgery.

Journal article

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.

Book chapter

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

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.

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.

Journal article

Merican AM, Iranpour F, Amis AA, 2016, Iliotibial band tension reduces patellar lateral stability, J Orthop Res

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

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.

Journal article

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

Conference paper

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

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

Halewood C, Amis AA, 2016, Physiology: Biomechanics, Surgery of the Meniscus, Pages: 35-45, ISBN: 9783662491867

Book chapter

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

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

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

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