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  • Journal article
    Munford M, Hossain U, Ghouse S, Jeffers Jet al., 2020,

    Prediction of Anisotropic Mechanical Properties for Lattice Structures

    , Additive Manufacturing, ISSN: 2214-8604
  • Journal article
    Clark J, Garbout A, Rodrigues Mendes Ferreira S, Javaheri B, Pitsillides A, Rankin S, Jeffers J, Hansen Uet al., 2020,

    Propagation phase-contrast micro-computed tomography allows laboratory-based three-dimensional imaging of articular cartilage down to the cellular level

    , Osteoarthritis and Cartilage, Vol: 28, Pages: 102-111, ISSN: 1063-4584

    ObjectiveHigh-resolution non-invasive three-dimensional (3D) imaging of chondrocytes in articular cartilage remains elusive. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) permits imaging cells within articular cartilage.DesignBovine osteochondral plugs were prepared four ways: in phosphate-buffered saline (PBS) or 70% ethanol (EtOH), both with or without phosphotungstic acid (PTA) staining. Specimens were imaged with micro-CT following two protocols: 1) absorption contrast (AC) imaging 2) propagation phase-contrast (PPC) imaging. All samples were scanned in liquid. The contrast to noise ratio (C/N) of cellular features quantified scan quality and were statistically analysed. Cellular features resolved by micro-CT were validated by standard histology.ResultsThe highest quality images were obtained using propagation phase-contrast imaging and PTA-staining in 70% EtOH. Cellular features were also visualised when stained in PBS and unstained in EtOH. Under all conditions PPC resulted in greater contrast than AC (p < 0.0001 to p = 0.038). Simultaneous imaging of cartilage and subchondral bone did not impede image quality. Corresponding features were located in both histology and micro-CT and followed the same distribution with similar density and roundness values.ConclusionsThree-dimensional visualisation and quantification of the chondrocyte population within articular cartilage can be achieved across a field of view of several millimetres using laboratory-based micro-CT. The ability to map chondrocytes in 3D opens possibilities for research in fields from skeletal development through to medical device design and treatment of cartilage degeneration.

  • Journal article
    Ng KC, Jeffers J, Beaule P, 2019,

    Hip joint capsular anatomy, mechanics, and surgical management

    , Journal of Bone and Joint Surgery, American Volume, Vol: 101, Pages: 2141-2151, ISSN: 0021-9355
  • Journal article
    Hoogeslag RAG, Brouwer RW, Huis In 't Veld R, Amis AAet al., 2019,

    Isometric placement of the augmentation braid is not attained reliably in contemporary ACL suture repair.

    , Knee

    BACKGROUND: To assess if during arthroscopic braid-augmented ACL suture repair (ACLSR), the actual positions of the augmentation braids' tunnels corresponded with the positions of their intended and targeted isometric points, and to test the hypothesis that there would be no dispersion in actual positions of the augmentation braids' tunnels compared to their intended and targeted isometric points. METHODS: In 12 human cadaveric knees, the positions of the augmentation braids' tunnels and their intended and targeted isometric points relative to a femoral and tibial grid were analysed. Furthermore, vector length between these positions was calculated to assess the accuracy and precision of the augmentation braids' tunnel placement. RESULTS: There was dispersion for all of the augmentation braids' tunnel positions compared to their intended isometric points. The femoral and tibial vector lengths (mean ± SD (range)) were 2.9 ± 1.0 (1.1-4.1) and 7.1 ± 2.0 (3.2-9.8) mm respectively. CONCLUSION: In augmented ACLSR, with the ruptured ACL in situ, there was dispersion of the positions of the actual small diameter femoral and tibial augmentation braids' tunnels away from their desired isometric points. CLINICAL RELEVANCE: The extent of dispersion of the position of both the femoral and tibial tunnels away from their intended isometric positions may cause cyclic length changes with knee motion. An ACLSR with static braid augmentation will thus be vulnerable to cyclic stretching-out. The difficulty of obtaining an isometric tunnel combination for the small diameter augmentation braid may influence the clinician's choice between non-, static or dynamic augmented ACLSR techniques.

  • 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, Vol: 37, Pages: 2367-2375, 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, Vol: 37, Pages: 2104-2111, 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
    Garner A, van Arkel RJ, Cobb J, 2019,

    Classification of combined partial knee arthroplasty

    , Bone and Joint Journal, Vol: 101B, Pages: 922-928, ISSN: 2049-4394

    AimsThere has been a recent resurgence in interest in combined partial knee arthroplasty (PKA) as an alternative to total knee arthroplasty (TKA). The varied terminology used to describe these procedures leads to confusion and ambiguity in communication between surgeons, allied health professionals, and patients. A standardized classification system is required for patient safety, accurate clinical record-keeping, clear communication, correct coding for appropriate remuneration, and joint registry data collection.Materials and MethodsAn advanced PubMed search was conducted, using medical subject headings (MeSH) to identify terms and abbreviations used to describe knee arthroplasty procedures. The search related to TKA, unicompartmental (UKA), patellofemoral (PFA), and combined PKA procedures. Surveys were conducted of orthopaedic surgeons, trainees, and biomechanical engineers, who were asked which of the descriptive terms and abbreviations identified from the literature search they found most intuitive and appropriate to describe each procedure. The results were used to determine a popular consensus.ResultsSurvey participants preferred “bi-unicondylar arthroplasty” (Bi-UKA) to describe ipsilateral medial and lateral unicompartmental arthroplasty; “medial bi-compartmental arthroplasty” (BCA-M) to describe ipsilateral medial unicompartmental arthroplasty with patellofemoral arthroplasty; “lateral bi-compartmental arthroplasty” (BCA-L) to describe ipsilateral lateral unicompartmental arthroplasty with patellofemoral arthroplasty; and tri-compartmental arthroplasty (TCA) to describe ipsilateral patellofemoral and medial and lateral unicompartmental arthroplasties. “Combined partial knee arthroplasty” (CPKA) was the favoured umbrella term.ConclusionWe recommend bi-unicondylar arthroplasty (Bi-UKA), medial bicompartmental arthroplasty (BCA-M), lateral bicompartmental arthroplasty (BCA-L), and tricompartmental arthroplasty (

  • Journal article
    Lord BR, El-Daou H, Zdanowicz U, Smigielski R, Amis AAet al., 2019,

    The Role of Fibers Within the Tibial Attachment of the Anterior Cruciate Ligament in Restraining Tibial Displacement

  • Journal article
    Devitt BM, Lord BR, Williams A, Amis AA, Feller JAet al., 2019,

    Biomechanical Assessment of a Distally Fixed Lateral Extra-articular Augmentation Procedure in the Treatment of Anterolateral Rotational Laxity of the Knee

    , AMERICAN JOURNAL OF SPORTS MEDICINE, Vol: 47, Pages: 2102-2109, ISSN: 0363-5465
  • 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 &lsquo;optimum&rsquo; 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 &plusmn; 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
    Huber C, Zhang Q, Taylor WR, Amis AA, Smith C, Hosseini Nasab SHet al.,

    Properties and Function of the Medial Patellofemoral Ligament: A Systematic Review.

    , Am J Sports Med, Pages: 363546519841304-363546519841304

    BACKGROUND: As the main passive structure preventing patellar lateral subluxation, accurate knowledge of the anatomy, material properties, and functional behavior of the medial patellofemoral ligament (MPFL) is critical for improving its reconstruction. PURPOSE: To provide a state-of-the-art understanding of the properties and function of the MPFL by undertaking a systematic review and statistical analysis of the literature. STUDY DESIGN: Systematic review. METHODS: On June 26, 2018, data for this systematic review were obtained by searching PubMed and Scopus. Articles containing numerical information regarding the anatomy, mechanical properties, and/or functional behavior of the MPFL that met the inclusion criteria were reviewed, recorded, and statistically evaluated. RESULTS: A total of 55 articles met the inclusion criteria for this review. The MPFL presented as a fanlike structure spanning from the medial femoral epicondyle to the medial border of the patella. The reported data indicated ultimate failure loads from 72 N to 208 N, ultimate failure elongation from 8.4 mm to 26 mm, and stiffness values from 8.0 N/mm to 42.5 N/mm. In both cadaveric and in vivo studies, the average elongation pattern demonstrated close to isometric behavior of the ligament in the first 50° to 60° of knee flexion, followed by progressive shortening into deep flexion. Kinematic data suggested clear lateralization of the patella in the MPFL-deficient knee during early knee flexion under simulated muscle forces. CONCLUSION: A lack of knowledge regarding the morphology and attachment sites of the MPFL remains. The reported mechanical properties also lack consistency, thus requiring further investigations. However, the results regarding patellar tracking confirm that the lack of an MPFL leads to lateralization of the patella, followed by delayed engagement of the trochlear groove, plausibly leading to an increased risk of patellar dislocations. The observed isometric behavior up to

  • 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

  • Journal article
    Athwal K, Milner P, Bellier G, Amis AAet al., 2019,

    Posterior capsular release is a biomechanically safe procedure to perform in total knee arthroplasty

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 27, Pages: 1587-1594, ISSN: 0942-2056

    PurposeSurgeons may attempt to strip the posterior capsule from its femoral attachment to overcome flexion contracture in total knee arthroplasty (TKA); however, it is unclear if this impacts anterior–posterior (AP) laxity of the implanted knee. The aim of the study was to investigate the effect of posterior capsular release on AP laxity in TKA, and compare this to the restraint from the posterior cruciate ligament (PCL).MethodsEight cadaveric knees were mounted in a six degree of freedom testing rig and tested at 0°, 30°, 60° and 90° flexion with ± 150 N AP force, with and without a 710 N axial compressive load. After the native knee was tested, a deep dished cruciate-retaining TKA was implanted and the tests were repeated. The PCL was then cut, followed by releasing the posterior capsule using a curved osteotome.ResultsWith 0 N axial load applied, cutting the PCL as well as releasing the posterior capsule significantly increased posterior laxity compared to the native knee at all flexion angles, and CR TKA states at 30°, 60° and 90° (p < 0.05). However, no significant increase in laxity was found between cutting the PCL and subsequent PostCap release (n.s.). In anterior drawer, there was a significant increase of 1.4 mm between cutting the PCL and PostCap release at 0°, but not at any other flexion angles (p = 0.021). When a 710 N axial load was applied, there was no significant difference in anterior or posterior translation across the different knee states (n.s.).ConclusionsPosterior capsular release only caused a small change in AP laxity compared to cutting the PCL and, therefore, may not be considered detrimental to overall AP stability if performed during TKA surgery.Level of evidenceControlled laboratory study.

  • 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
    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.

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