Publications
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Kittl C, Inderhaug E, Williams A, et al., 2017, Biomechanics of the Anterolateral Structures of the Knee, Clinics in Sports Medicine, Vol: 37, Pages: 21-31, ISSN: 0278-5919
El Daou H, Lord B, Amis A, et al., 2017, Assessment of pose repeatability and specimen repositioning of a robotic joint testing platform, MEDICAL ENGINEERING & PHYSICS, Vol: 47, Pages: 210-213, ISSN: 1350-4533
This paper describes the quantitative assessment of a robotic testing platform, consisting of an industrial robot and a universal force-moment sensor, via the design of fixtures used to hold the tibia and femur of cadaveric knees. This platform was used to study the contributions of different soft tissues and the ability of implants and reconstruction surgeries to restore normal joint functions, in previously published literature.To compare different conditions of human joints, it is essential to reposition specimens with high precision after they have been removed for a surgical procedure. Methods and experiments carried out to determine the pose repeatability and measure errors in repositioning specimens are presented. This was achieved using an optical tracking system (fusion Track 500, Atracsys Switzerland) to measure the position and orientation of bespoke rigid body markers attached to the tibial and femoral pots after removing and reinstalling them inside the rigs. The pose repeatability was then evaluated by controlling the robotic platform to move a knee joint repeatedly to/from a given pose while tracking the position and orientation of a rigid body marker attached to the tibial fixture.The results showed that the proposed design ensured a high repeatability in repositioning the pots with standard deviations for the computed distance and angle between the pots at both ends of the joint equal to 0.1 mm, 0.01 mm, 0.13° and 0.03° for the tibial and femoral fixtures respectively. Therefore, it is possible to remove and re-setup a joint with high precision. The results also showed that the errors in repositioning the robotic platform (that is: specimen path repeatability) were 0.11 mm and 0.12°, respectively.
Sugita T, Amis AA, 2017, Anatomic and biomechanical study of the lateral collateral and popliteofibular ligaments, AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 29, Pages: 466-472, ISSN: 0363-5465
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Li J, Clarke S, Cobb JP, et 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.
Inderhaug E, Stephen JM, El-Daou H, et 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
Athwal KK, El Daou H, Inderhaug E, et 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.
Athwal KK, El Daou H, Inderhaug E, et 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
Junaid S, Sanghavi S, Anglin C, et 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.
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.
Geraldes D, Hansen U, Jeffers J, et 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.
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
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.
Williams A, Ball S, Stephen J, et 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.
Iranpour F, Merican AM, Teo SH, et 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.
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.
Amirthanayagam TD, Amis AA, Reilly P, et 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.
Colaco H, Lord BR, Back DL, et 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
Sopher R, Amis A, Calder J, et 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.
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.
Kittl C, Inderhaug E, Stephen J, et 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.
Inderhaug E, Stephen JM, Williams A, et 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
Athwal K, El Daou, Lord B, et 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.
Cheong VS, Karunaratne A, Amis AA, et 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.
Lord BR, El-Daou H, Sabnis BM, et 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
Merican AM, Iranpour F, Amis AA, 2016, Iliotibial band tension reduces patellar lateral stability, J Orthop Res
Sopher R, Amis A, Davies D, et 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
Lord BR, El-Daou H, Sabnis BM, et 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
Geraldes D, Hansen U, Jeffers J, et 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
Kittl C, El-Daou H, Athwal KK, et 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
Halewood C, Amis AA, 2016, Physiology: Biomechanics, Surgery of the Meniscus, Pages: 35-45, ISBN: 9783662491867
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