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  • Journal article
    Doyle R, van Arkel R, Jeffers J, 2019,

    The effect of impaction energy on dynamic bone strains, fixation strength and seating of cementless acetabular cups

    , Journal of Orthopaedic Research, ISSN: 0736-0266

    Seating a cementless acetabular cup via impaction is a balancing act; good cup fixation must be obtained to ensure adequate bone in‐growth and cup apposition, while acetabular fracture must be avoided. Good impaction technique is essential to the success of hip arthroplasty. Yet little guidance exists in the literature to inform surgeons on ‘how hard’ to hit. A drop rig and synthetic bone model were used to vary the energy of impaction strikes in low and high density synthetic bone, while key parameters such as dynamic strain (quantifying fracture risk), implant fixation and polar gap were measured. For high energy impaction (15 J) in low density synthetic bone a peak tensile strain was observed during impaction that was up to 3.4x as large as post‐strike strain, indicating a high fracture risk. Diminishing returns were observed for pushout fixation with increasing energy. 85% of the pushout fixation achieved using a 15 J impaction strike was attained by using a 7.5 J strike energy. Similarly polar gap was only minimally reduced at high impaction energies. Therefore it is suggested that higher energy strikes increase fracture risk, but do not offer large improvements to fixation or implant‐bone apposition. It may difficult be for surgeons to accurately deliver specific impaction energies, suggesting there is scope for operative tools to manage implant seating.

  • Journal article
    Barnes S, Clasper J, Bull A, Jeffers Jet al., 2019,

    Micromotion and push out evaluation of an additive manufactured implant for above-the-knee amputees

    , Journal of Orthopaedic Research, ISSN: 0736-0266

    In comparison to through knee amputees the outcomes for above‐the‐knee amputees are relatively poor; based on this novel techniques have been developed. Most current percutaneous implant based solutions for transfemoral amputees make use of high stiffness intramedullary rods for skeletal fixation which can have risks including infection, femoral fractures and bone resorption due to stress shielding. This work details the cadaveric testing of a short, cortical bone stiffness matched subcutaneous implant, produced using additive manufacture, to determine bone implant micromotion and push out load. The results for the micromotions were all less than 20 microns and the mean push out load was 2099 Newtons. In comparison to a solid control, the stiffness matched implant exhibited significantly higher micromotion distributions and no significant difference in terms of push out load. These results suggest that, for the stiffness matched implant at time zero, osseointegration would be facilitated and that the implant would be securely anchored. For these metrics, this provides justification for the use of a short stem implant for transfemoral amputees in this subcutaneous application.

  • Journal article
    Ghouse S, Reznikov N, Boughton O, Babu S, Ng KCG, Blunn G, Cobb J, Stevens M, Jeffers Jet al., 2019,

    The design and in vivo testing of a locally stiffness-matched porous scaffold

    , Applied Materials Today, Vol: 15, Pages: 377-388, ISSN: 2352-9407

    An increasing volume of work supports utilising the mechanobiology of bone for bone ingrowth into a porous scaffold. However, typically during in vivo testing of implants, the mechanical properties of the bone being replaced are not quantified. Consequently there remains inconsistencies in the literature regarding ‘optimum’ pore size and porosity for bone ingrowth. It is also difficult to compare ingrowth results between studies and to translate in vivo animal testing to human subjects without understanding the mechanical environment. This study presents a clinically applicable approach to determining local bone mechanical properties and design of a scaffold with similar properties. The performance of the scaffold was investigated in vivo in an ovine model.The density, modulus and strength of trabecular bone from the medial femoral condyle from ovine bones was characterised and power-law relationships were established. A porous titanium scaffold, intended to maintain bone mechanical homeostasis, was additively manufactured and implanted into the medial femoral condyle of 6 ewes. The stiffness of the scaffold varied throughout the heterogeneous structure and matched the stiffness variation of bone at the surgical site. Bone ingrowth into the scaffold was 10.73 ± 2.97% after 6 weeks. Fine woven bone, in the interior of the scaffold, and intense formations of more developed woven bone overlaid with lamellar bone at the implant periphery were observed. The workflow presented will allow future in vivo testing to test specific bone strains on bone ingrowth in response to a scaffold and allow for better translation from in vivo testing to commercial implants.

  • Journal article
    Boughton O, Ma S, Cai X, Yan L, Peralta L, Laugier P, Marrow J, Giuliani F, Hansen U, Abel R, Grimal Q, Cobb Jet al., 2019,

    Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties

    , Scientific Reports, Vol: 9, ISSN: 2045-2322

    The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients. Techniques that can potentially be applied in vivo to measure bone stiffness, including computed tomography (CT), bulk wave ultrasound (BWUS) and indentation, were compared against in vitro techniques, including compression testing, density measurements and resonant ultrasound spectroscopy. Porosity, as measured by micro-CT, correlated with femoral neck cortical bone’s elastic modulus and ultimate compressive strength at the millimetre length scale. Large-tip spherical indentation also correlated with bone mechanical properties at this length scale but to a lesser extent. As the elastic mechanical properties of cortical bone correlated with porosity, we would recommend further development of technologies that can safely measure cortical porosity in vivo.Introduction

  • Journal article
    Amis AA, 2019,

    Editorial Commentary: Taking a Wider View During Anterior Cruciate Ligament Reconstruction? The Case for Doing More Than Just Reconstructing the Anterior Cruciate Ligament Itself

    , ARTHROSCOPY-THE JOURNAL OF ARTHROSCOPIC AND RELATED SURGERY, Vol: 35, Pages: 1484-1485, ISSN: 0749-8063
  • Journal article
    Kedroff L, Galea Holmes MN, Amis A, Newham DJet al., 2019,

    Effect of patellofemoral pain on foot posture and walking kinematics.

    , Gait Posture, Vol: 70, Pages: 361-369

    Background Excessive pronation has been implicated in patellofemoral pain (PFP) aetiology and foot orthoses are commonly prescribed for PFP patients. Pronation can be assessed using foot posture tests, however, the utility of such tests depends on their association with foot and lower-limb kinematics. Research questions Do PFP participants compared with healthy participants (1) have a more pronated foot measured with static foot tests and a kinematic multi-segmental foot model and (2) is there an association between static foot posture and foot and lower limb kinematics during walking? Methods A case-control study including 22 participants (n = 11 PFP, 5 females per group, aged 24 ± 3 (mean ± SD) years) was conducted. Foot posture measures included Arch Height Ratio, Navicular Drop (ND), and Foot Posture Index. Between-group comparisons of foot posture, segment and joint angle magnitudes, and associations between foot posture and kinematic data during gait were evaluated. Results There were no group differences in foot posture tests and mean joint angles. PFP participants had greater internal rotation of the shank and rearfoot segments, and adduction of the mid- and forefoot in the transverse plane (all p < 0.05). Greater ND was associated with increased forefoot abduction (rho=-0.68, p = 0.02) in healthy participants but no relationships were found between foot posture and kinematics in PFP participants. Significance Foot posture and kinematic data did not indicate excessive pronation in PFP participants questioning the use of orthoses to correct pronation. Larger studies are needed to determine the utility of foot posture tests as indicators of gait abnormalities in PFP.

  • Journal article
    Logishetty K, van Arkel RJ, Ng KCG, Muirhead-Allwood SK, Cobb JP, Jeffers JRTet al., 2019,

    Hip capsule biomechanics after arthroplasty THE EFFECT OF IMPLANT, APPROACH, AND SURGICAL REPAIR

    , BONE & JOINT JOURNAL, Vol: 101B, Pages: 426-434, ISSN: 2049-4394
  • Journal article
    Reznikov N, Boughton OR, Ghouse S, Weston AE, Collinson L, Blunn GW, Jeffers JRT, Cobb JP, Stevens MMet al., 2019,

    Individual response variations in scaffold-guided bone regeneration are determined by independent strain- and injury-induced mechanisms

    , BIOMATERIALS, Vol: 194, Pages: 183-194, ISSN: 0142-9612
  • Journal article
    Ng KCG, Daou HE, Bankes MJK, Rodriguez y Baena F, Jeffers JRTet al., 2019,

    Hip Joint Torsional Loading Before and After Cam Femoroacetabular Impingement Surgery

    , AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 47, Pages: 420-430, ISSN: 0363-5465
  • Journal article
    Doyle R, Boughton O, Plant D, Desoutter G, Cobb JP, Jeffers JRTet al., 2019,

    An in vitro model of impaction during hip arthroplasty

    , JOURNAL OF BIOMECHANICS, Vol: 82, Pages: 220-227, ISSN: 0021-9290
  • Journal article
    Kedgley AE, Saw TH, Segal NA, Hansen UN, Bull AMJ, Masouros SDet al., 2019,

    Predicting meniscal tear stability across knee-joint flexion using finite-element analysis

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 27, Pages: 206-214, ISSN: 0942-2056

    Purpose: To analyse the stress distribution through longitudinal and radial meniscal tears in three tear locations in weight-bearing conditions and use it to ascertain the impact of tear location and type on the potential for healing of meniscal tears. Methods: Subject-specific finite-element models of a healthy knee under static loading at 0°, 20°, and 30° knee flexion were developed from unloaded magnetic resonance images and weight-bearing, contrast-enhanced computed tomography images. Simulations were then run after introducing tears into the anterior, posterior, and midsections of the menisci. Results: Absolute differences between the displacements of anterior and posterior segments modelled in the intact state and those quantified from in vivo weight-bearing images were less than 0.5 mm. There were tear-location-dependent differences between hoop stress distributions along the inner and outer surfaces of longitudinal tears; the longitudinal tear surfaces were compressed together to the greatest degree in the lateral meniscus and were most consistently in compression on the midsections of both menisci. Radial tears resulted in an increase in stress at the tear apex and in a consistent small compression of the tear surfaces throughout the flexion range when in the posterior segment of the lateral meniscus. Conclusions: Both the type of meniscal tear and its location within the meniscus influenced the stresses on the tear surfaces under weight bearing. Results agree with clinical observations and suggest reasons for the inverse correlation between longitudinal tear length and healing, the inferior healing ability of medial compared with lateral menisci, and the superior healing ability of radial tears in the posterior segment of the lateral meniscus compared with other radial tears. This study has shown that meniscal tear location in addition to type likely plays a crucial role in dictating the success of non-operative treatment of the menisci. T

  • Journal article
    El Daou H, Ng KC, van Arkel R, Jeffers J, Rodriguez y Baena Fet al., 2019,

    Robotic hip joint testing: Development and experimental protocols

    , Medical Engineering and Physics, Vol: 63, Pages: 57-62, ISSN: 1350-4533

    The use of robotic systems combined with force sensing is emerging as the gold standard for in vitro biomechanical joint testing, due to the advantage of controlling all six degrees of freedom independently of one another. This paper describes a novel robotic platform and the experimental protocol used for hip joint testing. An experimental protocol implemented optical tracking and registration techniques in order to define the position of the hip joint centre of rotation (COR) in the coordinate system of the robot's end effector. The COR coordinates defined the origin of the task-related coordinate system used to control the robot, with a hybrid force/position law to simulate standard clinical tests. The axes of this frame were defined using the International Society of Biomechanics (ISB) anatomical coordinate system.Experiments were carried out on two cadaveric hip joint specimens using the robotic testing platform and a mechanical testing rig previously developed and described by our group. Simulated internal-external and adduction/abduction laxity tests were carried out with both systems and the resulting peak range of motion (ROM) was measured. Similarities and differences were observed in these experiments, which were used to highlight some of the limitations of conventional systems and the corresponding advantages of robotics, further emphasising their added value in vitro testing.

  • Journal article
    Correa T, Pal B, van Arkel R, Vanacore F, Amis AAet al., 2018,

    Reduced tibial strain-shielding with extraosseous total knee arthroplasty revision system

    , Medical Engineering and Physics, Vol: 62, Pages: 22-28, ISSN: 1350-4533

    BackgroundRevision total knee arthroplasty (RTKA) has poorer results than primary total knee arthroplasty (TKA), and the prostheses are invasive and cause strain-shielding of the bones near the knee. This paper describes an RTKA system with extracortical fixation. It was hypothesised that this would reduce strain-shielding compared with intramedullary fixation.MethodsTwelve replica tibiae were prepared for full-field optical surface strain analysis. They were either left intact, implanted with RTKA components with cemented intramedullary fixation stems, or implanted with a novel design with a tibial tray subframe supported by two extracortical fixation plates and screw fixation. They were loaded to simulate peak walking and stair climbing loads and the surface strains were measured using digital image correlation. The measurements were validated with strain gauge rosettes.ResultsCompared to the intact bone model, extracortical fixation reduced surface strain-shielding by half versus intramedullary fixation. For all load cases and bone regions examined, the extracortical implant shielded 8–27% of bone strain, whereas the intramedullary component shielded 37–56%.ConclusionsThe new fixation design, which offers less bone destruction than conventional RTKA, also reduced strain-shielding. Clinically, this design may allow greater rebuilding of bone loss, and should increase long-term fixation.

  • Journal article
    Inderhaug E, Stephen JM, Williams A, Amis AAet al., 2018,

    Effect of anterolateral complex sectioning and tenodesis on patellar kinematics and patellofemoral joint contact pressures

    , American Journal of Sports Medicine, Vol: 46, Pages: 2922-2928, ISSN: 0363-5465

    Background:Anterolateral complex injuries are becoming more recognized. While these are known to affect tibiofemoral mechanics, it is not known how they affect patellofemoral joint behavior.Purpose:To determine the effect of (1) sectioning the anterolateral complex and (2) performing a MacIntosh tenodesis under various conditions on patellofemoral contact mechanics and kinematics.Study Design:Controlled laboratory study.Methods:Eight fresh-frozen cadaveric knees were tested in a customized rig, with the femur fixed and tibia free to move, with optical tracking to record patellar kinematics and with thin pressure sensors to record patellofemoral contact pressures at 0°, 30°, 60°, and 90° of knee flexion. The quadriceps and iliotibial tract were loaded with 205 N throughout testing. Intact and anterolateral complex–sectioned states were tested, followed by 4 randomized tenodeses applying 20- and 80-N graft tension, each with the tibia in its neutral intact alignment or left free to rotate. Statistical analyses were undertaken with repeated measures analysis of variance, Bonferroni post hoc analysis, and paired samples t tests.Results:Patellar kinematics and contact pressures were not significantly altered after sectioning of the anterolateral complex (all: P > .05). Similarly, they were not significantly different from the intact knee in tenodeses performed when fixed tibial rotation was combined with 20- or 80-N graft tension (all: P > .05). However, grafts tensioned with 20 N and 80 N while the tibia was free hanging resulted in significant increases in lateral patellar tilt (P < .05), and significantly elevated lateral peak patellofemoral pressures (P < .05) were observed for 80 N.Conclusion:This work did not find that an anterolateral injury altered patellofemoral mechanics or kinematics, but adding a lateral tenodesis can elevate lateral contact pressures and induce lateral patellar tilting if the tibia is pulled into external ro

  • 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
    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
    Merican AM, Iranpour F, Amis AA, 2016,

    Iliotibial band tension reduces patellar lateral stability

    , J Orthop Res
  • 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
    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.

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