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  • JOURNAL ARTICLE
    Ghouse S, Babu S, Nai K, Hooper P, Jeffers Jet al., 2018,

    The influence of laser parameters, scanning strategies and material on the fatigue strength of a stochastic porous structure

    , Additive Manufacturing, Vol: 22, Pages: 290-301, ISSN: 2214-8604

    Additive manufactured (AM) porous materials behave quantitatively and qualitatively differently in fatigue than bulk materials, and the relationships normally used for the fatigue design of continuous bulk materials are not applicable to AM porous materials particularly for low stiffness applications.This study investigated how the manufacturing methods and the material used during powder bed fusion affects the compressive strength and high cycle fatigue strength of a stochastic porous material for a given stiffness. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing) and 4 materials. The materials investigated were two titanium alloys: commercially pure grade 2 (CP-Ti) and Ti6Al4V ELI, commercially pure tantalum (Ta) and a titanium-tantalum alloy (Ti-30Ta).The trends observed during fatigue testing for monolithic metals and statically for solid and porous AM materials were not always indicative of the high cycle fatigue behaviour of porous AM materials. Unlike their solid counterparts, porous tantalum and the titanium-tantalum alloy had the greatest fatigue strength for a given stiffness, 8% greater than CP-Ti and 19% greater than Ti6Al4V ELI. Optimisation of the laser parameters and scan strategies was found to also increase the fatigue strength for a given stiffness of porous AM materials by 7–8%.

  • JOURNAL ARTICLE
    Halewood C, Athwal KK, Amis AA, 2018,

    Pre-clinical assessment of total knee replacement anterior-posterior constraint.

    , J Biomech, Vol: 73, Pages: 153-160

    Pre-clinical, bench-top assessment of Total Knee Replacements (TKR) can provide information about the inherent constraint provided by a TKR, which does not depend on the condition of the patient undergoing the arthroplasty. However little guidance is given by the ASTM standard on test configurations such as medial-lateral (M:L) loading distribution, flexion angle or restriction of secondary motions. Using a purpose built rig for a materials testing machine, four TKRs currently in widespread clinical use, including medial-pivot and symmetrical condyle types, were tested for anterior-posterior translational constraint. Compressive joint loads from 710 to 2000 N, and a range of medial-lateral (M:L) load distributions, from 70:30% to 30:70% M:L, were applied at different flexion angles with secondary motions unconstrained. It was found that TKA constraint was significantly less at 60 and 90° flexion than at 0°, whilst increasing the compressive joint load increased the force required to translate the tibia to limits of AP constraint at all flexion angles tested. Additionally when M:L load distribution was shifted medially, a coupled internal rotation was observed with anterior translation and external rotation with posterior translation. This paper includes some recommendations for future development of pre-clinical testing methods.

  • JOURNAL ARTICLE
    Hoogeslag RAG, Brouwer RW, Huis In 't Veld R, Stephen JM, Amis AAet al., 2018,

    Dynamic augmentation restores anterior tibial translation in ACL suture repair: a biomechanical comparison of non-, static and dynamic augmentation techniques.

    , Knee Surg Sports Traumatol Arthrosc

    PURPOSE: There is a lack of objective evidence investigating how previous non-augmented ACL suture repair techniques and contemporary augmentation techniques in ACL suture repair restrain anterior tibial translation (ATT) across the arc of flexion, and after cyclic loading of the knee. The purpose of this work was to test the null hypotheses that there would be no statistically significant difference in ATT after non-, static- and dynamic-augmented ACL suture repair, and they will not restore ATT to normal values across the arc of flexion of the knee after cyclic loading. METHODS: Eleven human cadaveric knees were mounted in a test rig, and knee kinematics from 0° to 90° of flexion were recorded by use of an optical tracking system. Measurements were recorded without load and with 89-N tibial anterior force. The knees were tested in the following states: ACL-intact, ACL-deficient, non-augmented suture repair, static tape augmentation and dynamic augmentation after 10 and 300 loading cycles. RESULTS: Only static tape augmentation and dynamic augmentation restored ATT to values similar to the ACL-intact state directly postoperation, and maintained this after cyclic loading. However, contrary to dynamic augmentation, the ATT after static tape augmentation failed to remain statistically less than for the ACL-deficient state after cyclic loading. Moreover, after cyclic loading, ATT was significantly less with dynamic augmentation when compared to static tape augmentation. CONCLUSION: In contrast to non-augmented ACL suture repair and static tape augmentation, only dynamic augmentation resulted in restoration of ATT values similar to the ACL-intact knee and decreased ATT values when compared to the ACL-deficient knee immediately post-operation and also after cyclic loading, across the arc of flexion, thus allowing the null hypotheses to be rejected. This may assist healing of the ruptured ACL. Therefore, this study would support further clinical evaluation of dyna

  • JOURNAL ARTICLE
    Junaid S, Gregory T, Fetherston S, Emery R, Amis AA, Hansen Uet al., 2018,

    Cadaveric study validating in vitro monitoring techniques to measure the failure mechanism of glenoid implants against clinical CT.

    , J Orthop Res

    Definite glenoid implant loosening is identifiable on radiographs, however, identifying early loosening still eludes clinicians. Methods to monitor glenoid loosening in vitro have not been validated to clinical imaging. This study investigates the correlation between in vitro measures and CT images. Ten cadaveric scapulae were implanted with a pegged glenoid implant and fatigue tested to failure. Each scapulae were cyclically loaded superiorly and CT scanned every 20,000 cycles until failure to monitor progressive radiolucent lines. Superior and inferior rim displacements were also measured. A finite element (FE) model of one scapula was used to analyze the interfacial stresses at the implant/cement and cement/bone interfaces. All ten implants failed inferiorly at the implant-cement interface, two also failed at the cement-bone interface inferiorly, and three showed superior failure. Failure occurred at of 80,966 ± 53,729 (mean ± SD) cycles. CT scans confirmed failure of the fixation, and in most cases, was observed either before or with visual failure. Significant correlations were found between inferior rim displacement, vertical head displacement and failure of the glenoid implant. The FE model showed peak tensile stresses inferiorly and high compressive stresses superiorly, corroborating experimental findings. In vitro monitoring methods correlated to failure progression in clinical CT images possibly indicating its capacity to detect loosening earlier for earlier clinical intervention if needed. Its use in detecting failure non-destructively for implant development and testing is also valuable. The study highlights failure at the implant-cement interface and early signs of failure are identifiable in CT images. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 9999:XX-XX, 2018.

  • JOURNAL ARTICLE
    Kanca Y, Milner P, Dini D, Amis AAet al., 2018,

    Tribological properties of PVA/PVP blend hydrogels against articular cartilage

    , JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 78, Pages: 36-45, ISSN: 1751-6161
  • JOURNAL ARTICLE
    Kanca Y, Milner P, Dini D, Amis AAet al., 2018,

    Tribological evaluation of biomedical polycarbonate urethanes against articular cartilage

    , JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 82, Pages: 394-402, ISSN: 1751-6161
  • JOURNAL ARTICLE
    Kittl C, Inderhaug E, Williams A, Amis AAet al., 2018,

    Biomechanics of the Anterolateral Structures of the Knee

    , CLINICS IN SPORTS MEDICINE, Vol: 37, Pages: 21-+, ISSN: 0278-5919
  • JOURNAL ARTICLE
    Lord BR, Colaco HB, Gupte CM, Wilson AJ, Amis AAet al., 2018,

    ACL graft compression: a method to allow reduced tunnel sizes in ACL reconstruction.

    , Knee Surg Sports Traumatol Arthrosc

    PURPOSE: A common problem during ACL reconstruction is asymmetry of proximal-distal graft diameter leading to tunnel upsizing and graft-tunnel mismatch. Compression downsizing provides a graft of uniform size, allowing easy passage into a smaller tunnel. The purpose of this study was to quantify the graft compression technique and its effects on graft biomechanics and stability. It was hypothesised that compression downsizing would significantly reduce cross-sectional area (CSA); that no significant changes in graft biomechanics would occur; graft fixation stability would be improved. METHOD: Sixty-eight non-irradiated peroneus longus (PL) tendons were investigated. Twenty were halved and paired into ten four-strand grafts, 20 strands were compressed by 0.5-1 mm diameter and changes in CSA recorded using an alginate mould technique. The following properties were compared with 20 control strands: cyclic strain when loaded 70-220 N for 1000 cycles; stiffness; ultimate tensile load and stress; Young's modulus. 24 PL tendons were quadrupled into grafts, 12 were compressed and all 24 were submerged in Ringer's solution at 37 °C and the CSA recorded over 12 h. Twelve compressed and 12 control quadrupled grafts were mounted in porcine femurs, placed in Ringer's solution for 12 h at 37 °C and graft displacement at the bone tunnel aperture recorded under cyclic loading. RESULTS: Mean decreases in CSA of 31% under a stress of 471 kPa and 21% under a stress of 447 kPa were observed for doubled and quadrupled grafts, respectively. Compressed grafts re-expanded by 19% over 12 h compared to 2% for controls. No significant differences were observed between compressed and control grafts in the biomechanical properties and graft stability; mean cyclic displacements were 0.3 mm for both groups. CONCLUSIONS: No detrimental biomechanical effects of graft compression on allograft PL tendons were observed. Following compression, t

  • JOURNAL ARTICLE
    Marsland D, Stephen JM, Calder T, Amis AA, Calder JDFet al., 2018,

    Strength of Interference Screw Fixation to Cuboid vs Pulvertaft Weave to Peroneus Brevis for Tibialis Posterior Tendon Transfer for Foot Drop.

    , Foot Ankle Int

    BACKGROUND: Tibialis posterior (TP) tendon transfer is an effective treatment for foot drop. Currently, standard practice is to immobilize the ankle in a cast for 6 weeks nonweightbearing, risking postoperative stiffness. To assess whether early active dorsiflexion and protected weightbearing could be safe, the current study assessed tendon displacement under cyclic loading and load to failure, comparing the Pulvertaft weave (PW) to interference screw fixation (ISF) in a cadaveric foot model. METHODS: Twenty-four cadaveric ankles had TP tendon transfer performed, 12 with the PW technique and 12 with ISF to the cuboid. The TP tendon was cycled 1000 times at 50 to 150 N and then loaded to failure in a materials testing machine. Tendon displacement at the insertion site was recorded every 100 cycles. An independent t test and 2-way analysis of variance were performed to compare techniques, with a significance level of P < .05. RESULTS: Mean tendon displacement was similar in the PW group (2.9 ± 2.5 mm [mean ± SD]) compared with the ISF group (2.4 ± 1.1 mm), P = .35. One specimen in the ISF group failed early by tendon pullout. None of the PW group failed early, although displacement of 8.9 mm was observed in 1 specimen. Mean load to failure was 419.1 ± 82.6 N in the PW group in comparison to 499.4 ± 109.6 N in the ISF group, P = .06. CONCLUSION: For TP tendon transfer, ISF and PW techniques were comparable, with no differences in tendon displacement after cyclical loading or load to failure. Greater variability was observed in the PW group, suggesting it may be a less reliable technique. CLINICAL RELEVANCE: The results indicate that early active dorsiflexion and protected weightbearing may be safe for clinical evaluation, with potential benefits for the patient compared with cast immobilization.

  • JOURNAL ARTICLE
    Marsland D, Stephen JM, Calder T, Amis AA, Calder JDFet al., 2018,

    Flexor digitorum longus tendon transfer to the navicular: tendon-to-tendon repair is stronger compared with interference screw fixation.

    , Knee Surg Sports Traumatol Arthrosc

    PURPOSE: To assess whether early rehabilitation could be safe after flexor digitorum longus (FDL) tendon transfer, the current biomechanical study aimed to measure tendon displacement under cyclic loading and load to failure, comparing a traditional tendon-to-tendon (TT) repair with interference screw fixation (ISF). METHODS: 24 fresh-frozen cadaveric below knee specimens underwent FDL tendon transfer. In 12 specimens a TT repair was performed via a navicular bone tunnel. In a further 12 specimens ISF was performed. Using a materials testing machine, the FDL tendon was cycled 1000 times to 150 N and tendon displacement at the insertion site measured. A final load to failure test was then performed. Statistical analysis was performed using two-way ANOVA and an independent t test, with a significance level of p < 0.05. RESULT: No significant difference in tendon displacement occurred after cyclic loading, with mean tendon displacements of 1.9 ± 1.2 mm (mean ± SD) in the TT group and 1.8 ± 1.5 mm in the ISF group (n.s.). Two early failures occurred in the ISF group, none in the TT group. Mean load to failure was significantly greater following TT repair (459 ± 96 N), compared with ISF (327 ± 76 N), p = 0.002. CONCLUSION: Minimal tendon displacement of less than 2 mm occurred during cyclic testing in both groups. The two premature failures and significantly reduced load to failure observed in the ISF group, however, indicate that the traditional TT technique is more robust. Regarding clinical relevance, this study suggests that early active range of motion and protected weight bearing may be safe following FDL tendon transfer for stage 2 tibialis posterior tendon dysfunction.

  • JOURNAL ARTICLE
    Milner PE, Parkes M, Puetzer JL, Chapman R, Stevens MM, Cann P, Jeffers JRTet al., 2018,

    A low friction, biphasic and boundary lubricating hydrogel for cartilage replacement

    , ACTA BIOMATERIALIA, Vol: 65, Pages: 102-111, ISSN: 1742-7061
  • JOURNAL ARTICLE
    Musahl V, Getgood A, Neyret P, Claes S, Burnham JM, Batailler C, Sonnery-Cottet B, Williams A, Amis A, Zaffagnini S, Karlsson Jet al., 2018,

    Erratum to: Contributions of the anterolateral complex and the anterolateral ligament to rotatory knee stability in the setting of ACL Injury: a roundtable discussion (Knee Surgery, Sports Traumatology, Arthroscopy, (2017), 25, 4, (997-1008), 10.1007/s00167-017-4436-7)

    , Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 26, ISSN: 0942-2056

    © 2016, European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA). In the original article, one of the co-authors’ name has been published incorrectly. The correct name should be Jeremy M. Burnham. The original article has been updated accordingly.

  • JOURNAL ARTICLE
    Ridzwan MIZ, Sukjamsri C, Pal B, van Arkel RJ, Bell A, Khanna M, Baskaradas A, Abel R, Boughton O, Cobb J, Hansen UNet al., 2018,

    Femoral fracture type can be predicted from femoral structure: A finite element study validated by digital volume correlation experiments

    , JOURNAL OF ORTHOPAEDIC RESEARCH, Vol: 36, Pages: 993-1001, ISSN: 0736-0266
  • JOURNAL ARTICLE
    van Arkel R, Ng KCG, Muirhead-Allwood S, Jeffers Jet al., 2018,

    Capsular ligament function after total hip arthroplasty

    , Journal of Bone and Joint Surgery, American Volume, ISSN: 0021-9355
  • JOURNAL ARTICLE
    Alidousti H, Giles JW, Emery RJH, Jeffers Jet al., 2017,

    Spatial mapping of humeral head bone density

    , JOURNAL OF SHOULDER AND ELBOW SURGERY, Vol: 26, Pages: 1653-1661, ISSN: 1058-2746
  • JOURNAL ARTICLE
    Amirthanayagam TD, Amis AA, Reilly P, Emery RJHet 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
  • JOURNAL ARTICLE
    Amis A, Zaffagnini S, Musahl V, 2017,

    The anterolateral aspect of the knee: the state of play.

    , Knee Surg Sports Traumatol Arthrosc, Vol: 25, Pages: 989-990
  • JOURNAL ARTICLE
    Amis AA, 2017,

    Anterolateral knee biomechanics

    , KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY, Vol: 25, Pages: 1015-1023, ISSN: 0942-2056
  • JOURNAL ARTICLE
    Arnold M, Zhao S, Ma S, Giuliani F, Hansen U, Cobb JP, Abel RL, Boughton Oet al., 2017,

    Microindentation - a tool for measuring cortical bone stiffness? A systematic review.

    , Bone Joint Res, Vol: 6, Pages: 542-549, ISSN: 2046-3758

    OBJECTIVES: Microindentation has the potential to measure the stiffness of an individual patient's bone. Bone stiffness plays a crucial role in the press-fit stability of orthopaedic implants. Arming surgeons with accurate bone stiffness information may reduce surgical complications including periprosthetic fractures. The question addressed with this systematic review is whether microindentation can accurately measure cortical bone stiffness. METHODS: A systematic review of all English language articles using a keyword search was undertaken using Medline, Embase, PubMed, Scopus and Cochrane databases. Studies that only used nanoindentation, cancellous bone or animal tissue were excluded. RESULTS: A total of 1094 abstracts were retrieved and 32 papers were included in the analysis, 20 of which used reference point indentation, and 12 of which used traditional depth-sensing indentation. There are several factors that must be considered when using microindentation, such as tip size, depth and method of analysis. Only two studies validated microindentation against traditional mechanical testing techniques. Both studies used reference point indentation (RPI), with one showing that RPI parameters correlate well with mechanical testing, but the other suggested that they do not. CONCLUSION: Microindentation has been used in various studies to assess bone stiffness, but only two studies with conflicting results compared microindentation with traditional mechanical testing techniques. Further research, including more studies comparing microindentation with other mechanical testing methods, is needed before microindentation can be used reliably to calculate cortical bone stiffness.Cite this article: M. Arnold, S. Zhao, S. Ma, F. Giuliani, U. Hansen, J. P. Cobb, R. L. Abel, O. Boughton. Microindentation - a tool for measuring cortical bone stiffness? A systematic review. Bone Joint Res 2017;6:542-549. DOI: 10.1302/2046-3758.69.BJR-2016-0317.R2.

  • JOURNAL ARTICLE
    Athwal KK, El Daou H, Inderhaug E, Manning W, Davies AJ, Deehan DJ, Amis AAet 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

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