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  • Journal article
    Kohli N, Stoddart J, van Arkel RJ, 2021,

    The limit of tolerable micromotion for implant osseointegration: a systematic review

    , Scientific Reports, Vol: 11, Pages: 1-11, ISSN: 2045-2322

    Much research effort is being invested into the development of porous biomaterials that enhance implant osseointegration. Large micromotions at the bone-implant interface impair this osseointegration process, resulting in fibrous capsule formation and implant loosening. This systematic review compiled all the in vivo evidence available to establish if there is a universal limit of tolerable micromotion for implant osseointegration. The protocol was registered with the International Prospective Register for Systematic Reviews (ID: CRD42020196686). Pubmed, Scopus and Web of Knowledge databases were searched for studies containing terms relating to micromotion and osseointegration. The mean value of micromotion for implants that osseointegrated was 32% of the mean value for those that did not (112 ± 176 µm versus 349 ± 231 µm, p < 0.001). However, there was a large overlap in the data ranges with no universal limit apparent. Rather, many factors were found to combine to affect the overall outcome including loading time, the type of implant and the material being used. The tables provided in this review summarise these factors and will aid investigators in identifying the most relevant micromotion values for their biomaterial and implant development research.

  • Journal article
    Stoddart J, Dandridge O, Garner A, Cobb J, van Arkel RJet al., 2021,

    The compartmental distribution of knee osteoarthritis – a systematic review and meta-analysis

    , Osteoarthritis and Cartilage, Vol: 29, Pages: 445-455, ISSN: 1063-4584

    ObjectivesFor a population with knee osteoarthritis (OA), determine: 1) the prevalence of single compartmental, bicompartmental and tricompartmental OA, 2) the prevalence of isolated medial tibiofemoral, lateral tibiofemoral, or patellofemoral OA, and combinations thereof.MethodsPubMed and Web of Science databases, and reference lists of identified studies, were searched to find studies which reported on the compartmental distribution and prevalence of knee OA. Two independent reviewers assessed studies against pre-defined inclusion criteria and prevalence data were extracted along with subject characteristics. The methodological quality of each included study was assessed. A random-effects model meta-analysis was performed for each OA category to estimate the relative prevalence of OA in the knee compartments amongst people with knee OA.Results16 studies (3,786 knees) met the inclusion criteria. High heterogeneity was measured. Normalised for knees with OA, estimated prevalence rates (95% CI) were: single compartmental 50% (31.5–58.3%), bicompartmental 33% (23.1–37.2%) and tricompartmental only 17% (8.8–24.8%). Isolated medial tibiofemoral OA, isolated patellofemoral OA, and combined medial tibiofemoral and patellofemoral OA were more common than tricompartmental disease, occurring in 27% (15.2–31.1%), 18% (9.9–22.7%) and 23% (14.1–27.3%) of people respectively. Single/bicompartmental patterns of disease involving the lateral tibiofemoral compartment were less common, summing to 15% (8.5–18.7%).ConclusionThree-quarters of people with knee OA do not have tricompartmental disease. This is not reflected in the frequency with which partial and combined partial knee arthroplasties are currently used.Trial registration numberPROSPERO systematic review protocol (CRD42019140345).KeywordsGonarthrosisUnicompartmentalBicompartmentalPrevalenceEpidemiology

  • Journal article
    Hossain U, Ghouse S, Nai K, Jeffers JRTet al., 2021,

    Controlling and testing anisotropy in additively manufactured stochastic structures

    , ADDITIVE MANUFACTURING, Vol: 39, ISSN: 2214-8604
  • Journal article
    Parkes M, Tallia F, Young GR, Cann P, Jones JR, Jeffers JRTet al., 2021,

    Tribological evaluation of a novel hybrid for repair of articular cartilage defects

  • Journal article
    Hall T, Cegla F, van Arkel RJ, 2021,

    Simple smart implants: simultaneous monitoring of loosening and temperature in orthopaedics with an embedded ultrasound transducer

    , IEEE Transactions on Biomedical Circuits and Systems, Vol: 15, Pages: 102-110, ISSN: 1932-4545

    Implant failure can have devastating consequences on patient outcomes following joint replacement. Time to diagnosis affects subsequent treatment success, but current diagnostics do not give early warning and lack accuracy. This research proposes an embedded ultrasound system to monitor implant fixation and temperature – a potential indicator of infection. Requiring only two implanted components: a piezoelectric transducer and a coil, pulse-echo responses are elicited via a three-coil inductive link. This passive system avoids the need for batteries, energy harvesters, and microprocessors, resulting in minimal changes to existing implant architecture. Proof-of-concept was demonstrated in vitro for a titanium plate cemented into synthetic bone, using a small embedded coil with 10 mm diameter. Gross loosening – simulated by completely debonding the implant-cement interface – was detectable with 95% confidence at up to 12 mm implantation depth. Temperature was calibrated with root mean square error of 0.19 °C at 5 mm, with measurements accurate to ±1 °C with 95% confidence up to 6 mm implantation depth. These data demonstrate that with only a transducer and coil implanted, it is possible to measure fixation and temperature simultaneously. This simple smart implant approach minimises the need to modify well-established implant designs, and hence could enable mass-market adoption.

  • Journal article
    Garner A, Dandridge O, Amis A, Cobb J, van Arkel Ret al., 2021,

    The extensor efficiency of unicompartmental, bicompartmental and total knee arthroplasty

    , Bone and Joint Research, Vol: 10, Pages: 1-9, ISSN: 2046-3758

    Aims: Unicompartmental (UKA) and bicompartmental (BCA) knee arthroplasty have been associated with improved functional outcomes compared to Total Knee Arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function. Methods: Extensor function was measured for sixteen cadaveric knees and then re-tested following the different arthroplasties. Eight knees underwent medial UKA then BCA, then posterior-cruciate retaining TKA, and eight underwent the lateral equivalents then TKA. Extensorefficiency was calculated for ranges of knee flexion associated with common 46activities of daily living. Data were analyzed with repeated measures analysis of variance (=0.05). Results: Compared to native, there were no reductions in either extension moment or efficiency following UKA. Conversion to BCA resulted in a small decrease in extension moment between 70-90° flexion(p<0.05), but when examined in the context of daily activity ranges of flexion, extensor efficiency was largely unaffected. Following TKA, large decreases in extension moment were measured at low knee flexion angles(p<0.05), resulting in 12-43% reductions in extensor efficiency for the daily activity ranges. Conclusion: This cadaveric study found that TKA resulted in inferior extensor function compared to UKA and BCA. This may, in part, help explain the reported differences in 58function and satisfaction differences between partial and total knee arthroplasty.

  • Journal article
    Ng KCG, Bankes M, El Daou H, Rodriguez y Baena F, Jeffers Jet al., 2021,

    Cam osteochondroplasty for femoroacetabular impingement increases microinstability in deep flexion: A cadaveric study

    , Arthroscopy: The Journal of Arthroscopy and Related Surgery, Vol: 37, Pages: 159-170, ISSN: 0749-8063

    Purpose: The purpose of this in vitro cadaveric study was to examine the contributions of each surgical stage during cam femoroacetabular impingement (FAI) surgery (i.e., intact cam hip, T8 capsulotomy, cam resection, capsular repair) towards hip range of motion, translations, and microinstability.Methods: Twelve cadaveric cam hips were denuded to the capsule and mounted onto a robotic tester. Hips were positioned in several flexion positions: Full Extension, Neutral 0°, Flexion 30°, and Flexion 90°; and performed internal-external rotations to 5-Nm torque in each position. Hips underwent a series of surgical stages (T-capsulotomy, cam resection, capsular repair) and was retested after each stage. Changes in range of motion, translation, and microinstability (overall translation normalized by femoral head radius) were measured after each stage.Results: For range of motion, cam resection increased internal rotation at Flexion 90° (ΔIR = +6°, P = .001), but did not affect external rotation. Capsular repairs restrained external rotations compared to the cam resection stage (ΔER = –4 to –8°, P ≤ .04). For translations, the hip translated after cam resection at Flexion 90° in the medial-lateral plane (ΔT = +1.9 mm, P = .04), relative to the intact and capsulotomy stages. For microinstability, capsulotomy increased microinstability in Flexion 30° (ΔM = +0.05; P = .003), but did not further increase after cam resection. At Flexion 90°, microinstability did not increase after capsulotomy (ΔM = +0.03; P = .2, d = .24), but substantially increased after cam resection (ΔM = +0.08; P = .03), accounting for a 31% change with respect to the intact stage.Conclusions: Cam resection increased microinstability by 31% during deep hip flexion relative to the intact hip. This suggests that iatrogenic microinstability may be due to separation of the labral seal and resected contour of the femoral head.

  • Journal article
    Ball S, Stephen JM, El-Daou H, Williams A, Amis AAet al., 2020,

    The medial ligaments and the ACL restrain anteromedial laxity of the knee

    , Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3700-3708, ISSN: 0942-2056

    PurposeThe purpose of this study was to determine the contribution of each of the ACL and medial ligament structures in resisting anteromedial rotatory instability (AMRI) loads applied in vitro.MethodsTwelve knees were tested using a robotic system. It imposed loads simulating clinical laxity tests at 0° to 90° flexion: ±90 N anterior–posterior force, ±8 Nm varus–valgus moment, and ±5 Nm internal–external rotation, and the tibial displacements were measured in the intact knee. The ACL and individual medial structures—retinaculum, superficial and deep medial collateral ligament (sMCL and dMCL), and posteromedial capsule with oblique ligament (POL + PMC)—were sectioned sequentially. The tibial displacements were reapplied after each cut and the reduced loads required allowed the contribution of each structure to be calculated.ResultsFor anterior translation, the ACL was the primary restraint, resisting 63–77% of the drawer force across 0° to 90°, the sMCL contributing 4–7%. For posterior translation, the POL + PMC contributed 10% of the restraint in extension; other structures were not significant. For valgus load, the sMCL was the primary restraint (40–54%) across 0° to 90°, the dMCL 12%, and POL + PMC 16% in extension. For external rotation, the dMCL resisted 23–13% across 0° to 90°, the sMCL 13–22%, and the ACL 6–9%.ConclusionThe dMCL is the largest medial restraint to tibial external rotation in extension. Therefore, following a combined ACL + MCL injury, AMRI may persist if there is inadequate healing of both the sMCL and dMCL, and MCL deficiency increases the risk of ACL graft failure.

  • Journal article
    Munford MJ, Ng KCG, Jeffers JRT, 2020,

    Mapping the Multi-Directional Mechanical Properties of Bone in the Proximal Tibia

  • Journal article
    Clark JN, Heyraud A, Tavana S, Al-Jabri T, Tallia F, Clark B, Blunn GW, Cobb JP, Hansen U, Jones JR, Jeffers JRTet al., 2020,

    Exploratory Full-Field Mechanical Analysis across the Osteochondral Tissue-Biomaterial Interface in an Ovine Model

    , MATERIALS, Vol: 13
  • Journal article
    Clark JN, Tavana S, Heyraud A, Tallia F, Jones JR, Hansen U, Jeffers JRTet al., 2020,

    Quantifying 3D Strain in Scaffold Implants for Regenerative Medicine

    , MATERIALS, Vol: 13
  • Journal article
    Athwal KK, Willinger L, Shinohara S, Ball S, Williams A, Amis AAet al., 2020,

    The bone attachments of the medial collateral and posterior oblique ligaments are defined anatomically and radiographically

    , Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3709-3719, ISSN: 0942-2056

    PurposeTo define the bony attachments of the medial ligaments relative to anatomical and radiographic bony landmarks, providing information for medial collateral ligament (MCL) surgery.MethodThe femoral and tibial attachments of the superficial MCL (sMCL), deep MCL (dMCL) and posterior oblique ligament (POL), plus the medial epicondyle (ME) were defined by radiopaque staples in 22 knees. These were measured radiographically and optically; the precision was calculated and data normalised to the sizes of the condyles. Femoral locations were referenced to the ME and to Blumensaat’s line and the posterior cortex.ResultsThe femoral sMCL attachment enveloped the ME, centred 1 mm proximal to it, at 37 ± 2 mm (normalised at 53 ± 2%) posterior to the most-anterior condyle border. The femoral dMCL attachment was 6 mm (8%) distal and 5 mm (7%) posterior to the ME. The femoral POL attachment was 4 mm (5%) proximal and 11 mm (15%) posterior to the ME. The tibial sMCL attachment spread from 42 to 71 mm (81–137% of A-P plateau width) below the tibial plateau. The dMCL fanned out anterodistally to a wide tibial attachment 8 mm below the plateau and between 17 and 39 mm (33–76%) A-P. The POL attached 5 mm below the plateau, posterior to the dMCL. The 95% CI intra-observer was ± 0.6 mm, inter-observer ± 1.3 mm for digitisation. The inter-observer ICC for radiographs was 0.922.ConclusionThe bone attachments of the medial knee ligaments are located in relation to knee dimensions and osseous landmarks. These data facilitate repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion.

  • Journal article
    Williams A, Becker R, Amis A, 2020,

    The medial collateral ligament: the neglected ligament

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 28, Pages: 3698-3699, ISSN: 0942-2056
  • Journal article
    Willinger L, Shinohara S, Athwal KK, Ball S, Williams A, Amis AAet al., 2020,

    Length-change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery

    , Arthroskopie, Vol: 33, Pages: 288-294, ISSN: 0933-7946

    PurposeThe purpose of this study was to define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads.Material and methodsTen cadaveric knees were mounted in a kinematics rig with loaded quadriceps and hamstrings muscles. Length change patterns of the anterior and posterior fibres of the sMCL, dMCL and POL were recorded from 0 to 100° flexion. Length changes were recorded while a 90 N anterior load and a 5 Nm internal and external rotational torque were applied. Length changes were normalized to lengths at 0° flexion.ResultsThe anterior sMCL tightened as the knee was flexed (p < 0.01), and further tensioned under tibial external rotation (p < 0.001). Conversely, the posterior sMCL slackened with flexion (p < 0.001), while internal rotation tightened these fibers between 10 and 100° (p < 0.05). Tibial external rotation significantly lengthened the anterior dMCL fibres by 10% compared to the unloaded condition throughout flexion (p < 0.001). Release of the sMCL caused the dMCL fibres to become taut and increased valgus rotation (p < 0.01). The lengths of the anterior and posterior POL fibres decreased continuously with knee flexion (p < 0.001). Tibial internal rotation significantly increased the length of the POL (p < 0.001).ConclusionThe structures of the medial ligament complex reacted differently to knee flexion and applied loads. Structures attaching proximal and posterior to the medial epicondyle were taut in extension, whereas the anterior sMCL tensioned during flexion. The anterior dMCL was extensively strained by tibial external rotation and after sMCL release.

  • Journal article
    Doyle R, van Arkel RJ, Muirhead-Allwood S, Jeffers JRTet al., 2020,

    Impaction technique influences implant stability in low-density bone model

    , BONE & JOINT RESEARCH, Vol: 9, Pages: 386-393, ISSN: 2046-3758
  • Journal article
    Amis A, Willinger L, Shinohara S, Athwal K, Ball S, Williams Aet al., 2020,

    Length change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery

    , Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3720-3732, ISSN: 0942-2056

    PurposeTo define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads, and to relate these findings to their functions in knee stability and to surgical repair or reconstruction.MethodsTen cadaveric knees were mounted in a kinematics rig with loaded quadriceps, ITB, and hamstrings. Length changes of the anterior and posterior fibres of the sMCL, dMCL, and POL were recorded from 0° to 100° flexion by use of a linear displacement transducer and normalised to lengths at 0° flexion. Measurements were repeated with no external load, 90 N anterior draw force, and 5 Nm internal and 5 Nm external rotation torque applied.ResultsThe anterior sMCL lengthened with flexion (p < 0.01) and further lengthened by external rotation (p < 0.001). The posterior sMCL slackened with flexion (p < 0.001), but was lengthened by internal rotation (p < 0.05). External rotation lengthened the anterior dMCL fibres by 10% throughout flexion (p < 0.001). sMCL release allowed the dMCL to become taut with valgus rotation (p < 0.001). The anterior and posterior POL fibres slackened with flexion (p < 0.001), but were elongated by internal rotation (p < 0.001).ConclusionThe structures of the medial ligament complex react differently to knee flexion and applied loads. Structures attaching posterior to the medial epicondyle are taut in extension, whereas the anterior sMCL, attaching anterior to the epicondyle, is tensioned during flexion. The anterior dMCL is elongated by external rotation. These data offer the basis for MCL repair and reconstruction techniques regarding graft positioning and tensioning.

  • Journal article
    Amis A, Joseph M, Carmont M, Stephen J, Tailor Het al., 2020,

    Total knee arthroplasty reduces knee extension torque in-vitro and patellofemoral arthroplasty does not

    , Journal of Biomechanics, Vol: 104, Pages: 1-6, ISSN: 0021-9290

    Patients often have difficulty recovering knee extension strength post total knee arthroplasty (TKA), and that may reflect alteration of the mechanics including geometry and rollback kinematics, so the purpose of this work was to explore this by comparing the knee extension torque (KET) of the native knee, TKA and patellofemoral arthroplasty (PFA) in response to quadriceps tension. Eight fresh-frozen knees were mounted in a knee extension rig with quadriceps loading and tibial extension torque measurement. Each knee was subject to four conditions: native knee, PFA, cruciate-retaining (CR) and posterior-stabilized (PS) TKA. The KET was measured from 120° to 0° knee flexion. Data were analyzed using one-way ANOVA and post-hoc paired t-tests. The native KET was lowest in terminal extension and 70–100° flexion, and maximal at 20–30° flexion. PFA produced the greatest KET (p < 0.008) compared with native, CR- and PS-TKA, at 30–40° flexion. CR- and PS-TKA had lower KET across 0–50° flexion (p < 0.001 across 0–30°), falling to 25% of the native knee KET or the PFA at full extension. PFA had the highest KET in early flexion possibly due to increased trochlear offset and/or preservation of the cruciate mechanism, so PFA may be more beneficial during the functional range of motion. The claimed benefits of PS- over CR-TKA in deep flexion were not detected. Both CR- and PS-TKAs led to lower KET than the native and PFA knee states across 0–50° flexion. This mechanical effect may help to explain clinical findings of knee extension weakness post-TKA.

  • Journal article
    Ajdari N, Tempelaere C, Masouleh MI, Abel R, Delfosse D, Emery R, Dini D, Hansen Uet al., 2020,

    Hemiarthroplasties: the choice of prosthetic material causes different levels of damage in the articular cartilage

    , Journal of Shoulder and Elbow Surgery, Vol: 29, Pages: 1019-1029, ISSN: 1058-2746

    Background Hemiarthroplasty has clear advantages over alternative procedures and is used in 20% of all shoulder joint replacements. Because of cartilage wear, the clinical outcome of hemiarthroplasty is unreliable and controversial. This paper suggests that the optimal choice of prosthetic material may reduce cartilage degeneration and improve the reliability of the procedure. The specific objectives were to assess 3 materials and assess how the severity of arthritis might affect the choice of prosthetic material. Methods A CoCr alloy, an AL2O3 ceramic, and a polycarbonate urethane polymer (PCU) were mechanically tested against 5 levels of human osteoarthritic cartilage (from intact to severely arthritic, n = 45). A high friction coefficient, a decrease in Young's modulus, an increase in permeability, a decrease in relaxation time, an increase in surface roughness, and a disrupted appearance of the cartilage after testing were used as measures of cartilage damage. The biomaterial that caused minimal cartilage damage was defined as superior. Results The CoCr caused the most damage. This was followed by the AL2O3 ceramic, whereas the PCU caused the least amount of damage. Although the degree of arthritis had an effect on the results, it did not change the trend that CoCr performed worst and PCU the best. Discussion and Conclusion This study indicates that ceramic implants may be a better choice than metals, and the articulating surface should be as smooth as possible. Although our results indicate that the degree of arthritis should not affect the choice of prosthetic material, this suggestion needs to be further investigated.

  • Journal article
    Athwal KK, Willinger L, Manning W, Deehan D, Amis AAet al., 2020,

    A constrained-condylar fixed-bearing total knee arthroplasty is stabilised by the medial soft tissues

    , Knee Surgery Sports Traumatology Arthroscopy, Vol: 29, Pages: 659-667, ISSN: 0942-2056

    PurposeRevision constrained-condylar total knee arthroplasty (CCK-TKA) is often used to provide additional mechanical constraint after failure of a primary TKA. However, it is unknown how much this translates to a reliance on soft-tissue support. The aim of this study was therefore to compare the laxity of a native knee to the CCK-TKA implanted state and quantify how medial soft-tissues stabilise the knee following CCK-TKA.MethodsTen intact cadaveric knees were tested in a robotic system at 0°, 30°, 60° and 90° flexion with ± 90 N anterior–posterior force, ± 8 Nm varus-valgus and ± 5 Nm internal–external torques. A fixed-bearing CCK-TKA was implanted and the laxity tests were repeated with the soft tissues intact and after sequential cutting. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were sequentially transected and the percentage contributions of each structure to restraining the applied loads were calculated.ResultsImplanting a CCK-TKA did not alter anterior–posterior laxity from that of the original native knee, but it significantly decreased internal–external and varus-valgus rotational laxity (p < 0.05). Post CCK-TKA, the sMCL restrained 34% of the tibial displacing load in anterior drawer, 16% in internal rotation, 17% in external rotation and 53% in valgus, across the flexion angles tested. The dMCL restrained 11% of the valgus rotation moment.ConclusionsWith a fully-competent sMCL in-vitro, a fixed-bearing CCK-TKA knee provided more rotational constraint than the native knee. The robotic test data showed that both the soft-tissues and the semi-constrained implant restrained rotational knee laxity. Therefore, in clinical practice, a fixed-bearing CCK-TKA knee could be indicated for use in a knee with lax, less-competent medial soft tissues.

  • Journal article
    Ruiz de Galarreta S, Jeffers JRT, Ghouse S, 2020,

    A validated finite element analysis procedure for porous structures

    , MATERIALS & DESIGN, Vol: 189, ISSN: 0264-1275

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