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  • Journal article
    Burge TA, Jeffers JRT, Myant CW, 2022,

    Development of an Automated Mass-Customization Pipeline for Knee Replacement Surgery Using Biplanar X-Rays

    , Journal of Mechanical Design, Vol: 144, ISSN: 1050-0472

    <jats:title>Abstract</jats:title> <jats:p>For standard “off-the-shelf” knee replacement procedures, surgeons use X-ray images to aid implant selection from a limited number of models and sizes. This can lead to complications and the need for implant revision due to poor implant fit. Customized solutions have been shown to improve results but require increased preoperative assessment (Computed Tomography or Magnetic Resonance Imaging), longer lead times, and higher costs which have prevented widespread adoption. To attain the benefits of custom implants, whilst avoiding the limitations of currently available solutions, a fully automated mass-customization pipeline, capable of developing customized implant designs for fabrication via additive manufacturing from calibrated X-rays, is proposed. The proof-of-concept pipeline uses convolutional neural networks to extract information from biplanar X-ray images, point depth, and statistical shape models to reconstruct the anatomy, and application programming interface scripts to generate various customized implant designs. The pipeline was trained using data from the Korea Institute of Science and Technology Information. Thirty subjects were used to test the accuracy of the anatomical reconstruction, ten from this data set, and a further 20 independent subjects obtained from the Osteoarthritis Initiative. An average root-mean-squared error of 1.00 mm was found for the femur test cases and 1.07 mm for the tibia. Three-dimensional (3D) distance maps of the output components demonstrated these results corresponded to well-fitting components, verifying automatic customization of knee replacement implants is feasible from 2D medical imaging.</jats:p>

  • Journal article
    Dandridge O, Garner A, Jeffers JRT, Amis AA, Cobb JP, van Arkel RJet al., 2021,

    Validity of repeated-measures analyses of in vitro arthroplasty kinematics and kinetics

    , Journal of Biomechanics, Vol: 129, Pages: 1-5, ISSN: 0021-9290

    In vitro models of arthroplasty enable pre-clinical testing and inform clinical decision making. Repeated-measures comparisons maximise resource efficiency, but their validity without testing order randomisation is not known. This study aimed to identify if there were any large testing order effects for cadaveric models of knee and hip arthroplasty. First, the effect of testing order on total knee arthroplasty (TKA) biomechanics was assessed. Extension moments for TKAs (N=3) implanted into the native knee (TKA-only) were compared to a dataset of TKAs (N=24) tested after different combinations of partial knee arthroplasty (TKA-last). The effect of repeatedly testing the same knee five times over 36 hours on patellofemoral and tibiofemoral kinematics was also quantified. Second, the effect of testing order on capsular ligament function after total hip arthroplasty (THA) was assessed. Randomisation was removed from a previously published dataset to create increasing and decreasing head size groups, which were compared with t-tests.All three TKA-only extension moments fell within the 95% CI of the TKA-last knees across the full range of knee flexion/extension. Repeated testing resulted in root-mean-squared kinematics errors within 1 mm, 1°, or < 5 % of total range of motion. Following THA, smaller head-size resulted in greater laxity in both the increasing (p=0.01) and decreasing (p<0.001) groups. Testing order did not have large effects on either knee or hip arthroplasty biomechanics measured with in vitro cadaveric models.

  • Journal article
    Clark J, Tavana S, Clark B, Briggs T, Jeffers J, Hansen Uet al., 2021,

    High resolution three-dimensional strain measurements in human articular cartilage

    , Journal of The Mechanical Behavior of Biomedical Materials, Vol: 124, ISSN: 1751-6161

    An unresolved challenge in osteoarthritis research is characterising the localised intra-tissue mechanical response of articular cartilage. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) and digital volume correlation (DVC) permit non-destructive quantification of three-dimensional (3D) strain fields in human articular cartilage. Human articular cartilage specimens were harvested from the knee, mounted into a loading device and imaged in the unloaded and loaded states using a micro-CT scanner. Strain was measured throughout the cartilage volume using the micro-CT image data and DVC analysis. The volumetric DVC-measured strain was within 5% of the known applied strain. Variation in strain distribution between the superficial, middle and deep zones was observed, consistent with the different architecture of the material in these locations. These results indicate DVC method may be suitable for calculating strain in human articular cartilage.

  • Journal article
    Ghouse S, Oosterbeek R, Tayub A, Vecchiato F, Dye D, Jeffers Jet al., 2021,

    Vacuum heat treatments of titanium porous structures

    , Additive Manufacturing, Vol: 47, ISSN: 2214-8604

    Additive manufacturing (AM) of Ti-6Al-4V enables rapid fabrication of complex parts, including porous lattices which are of interest for aerospace, automotive, or biomedical applications, however currently the fatigue resistance of these materials is a critical limitation. Engineering the alloy microstructure provides a promising method for increasing fatigue strength, but conventional heat treatment procedures are known to produce atypical results for AM and porous samples, and must therefore be optimised for these materials. Using vacuum heat treatment, microstructures comparable to those observed for conventional wrought and heat treated alloys were achieved with porous AM Ti-6Al-4V. Fine lamellar microstructures were produced using sub-transus heat treatment at 920 °C, while coarse lamellar microstructures were produced using super-transus heat treatment at 1050 °C or 1200 °C. Increasing the heat treatment temperature increased the elastic modulus from 2552 ± 22 MPa to a maximum of 2968 ± 45 MPa, due to strut sintering increasing the effective strut thickness, and removal of prior β-grain orientation. Heat treatment eliminated the brittle α’ martensite phase in favour of an α + β mixture, where the phase boundaries and β-phase provide greater resistance to crack propagation. Super-transus heat treatments increased the α-lath size which typically reduces crack propagation resistance, however strut sintering reduced surface crack initiation sites, increasing the fatigue strength by 75% from 4.86 MPa for the as-built material to a maximum of 8.51 MPa after 1200 °C heat treatment. This work demonstrates that vacuum heat treatment is effective at tuning the micro- and macro-structure of porous AM Ti-6Al-4V, thereby improving the crucial fatigue resistance.

  • Journal article
    Ruiz de Galarreta S, Doyle RJ, Jeffers J, Ghouse Set al., 2021,

    Laser powder bed fusion of porous graded structures: A comparison between computational and experimental analysis

    , Journal of the Mechanical Behavior of Biomedical Materials, Vol: 123, Pages: 1-12, ISSN: 1751-6161

    Functionally graded porous structures (FGPSs) are gaining interest in the biomedical sector, specifically for orthopaedic implants. In this study, the compressive behaviour of seven different FGPSs comprised of Face Centred Cubic (FCC) and the Octet truss unit cells (OCT) were analysed. The porosity of the structures were graded in different directions (radially, longitudinally, laterally and longitudinally & radially) by varying the strut diameters or by combining the two types of unit cells. The structures were manufactured by laser power bed fusion and compression tests were performed. Radially and laterally porous graded structures were found to outperform uniform porous structures with an increase in stiffness of 13.7% and 21.1% respectively. The experimental and finite element analysis (FEA) results were in good agreement with differences in elastic modulus of 9.4% and yield strength of 15.8%. A new FEA beam model is proposed in this study to analyse this type of structures with accurate results and the consequent reduction of computational time. The accuracy of the Kelvin-Voight model and the rule of mixtures for predicting the mechanical behaviour of different FGPSs was also investigated. The results demonstrate the adequacy of the analytical models specifically for hybrid structures and for structures with smooth diameter transitions.

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

    Mechanical and morphological properties of additively manufactured SS316L and Ti6Al4V micro-struts as a function of build angle

    , Additive Manufacturing, Vol: 46, Pages: 1-11, ISSN: 2214-8604

    Additive manufacturing methods such as laser powder bed fusion (PBF) can produce micro-lattice structures which consist of ‘micro-struts’, which have properties that differ from the bulk metal and that can vary depending on the orientation of the strut to the build direction (the strut build angle). Characterising these mechanical and morphological changes would help explain macro-scale lattice behaviour. Individual stainless steel (SS316L) and titanium alloy (Ti6Al4V) laser PBF struts were built at 20°, 40°, 70° and 90° to the build platform, with 3 designed diameters and tested in uniaxial tension (n = 5). Micro-CT was used to quantify changes in surface roughness, eccentricity and cross-section. Average elastic modulus was 61.5 GPa and 37.5 GPa for SS316L and Ti6Al4V respectively, less than the bulk material. Yield strength was uniform over build angle for SS316L, but for Ti6Al4V varied from 40% to 98% of the bulk value from 20° to 90° build angles. All lower angle struts had worse morphology, with higher roughness and less circular cross-sections. These data should help inform micro-lattice design, especially in safety critical applications where lower mechanical performance must be compensated for.

  • Journal article
    Karunaseelan K, Dandridge O, Muirhead-Allwood S, van Arkel R, Jeffers Jet al., 2021,

    The capsular ligaments provide a passive stabilising force to protect the hip against edge loading

    , Bone and Joint Research, Vol: 10, Pages: 594-601, ISSN: 2046-3758

    Aims: In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilising force to protect the hip against edge loading. In this study we quantified the stabilising force vectors generated by capsular ligaments at extreme range of movement (ROM) and examined their ability to prevent edge loading. Methods: Torque-rotation curves of the hip joint were obtained from nine human cadaveric specimens to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line of action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral and pubofemoral ligaments in all positions. The net force vector generated by the capsule was evaluated in each position and functioning ligament forces and stiffness were determined. Results: The medial and lateral arms of the iliofemoral ligament generated the highest net inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest net inbound force in flexion, adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.7° inbound for each Nm of internal capsular 17restraint, preventing edge loading. Conclusion: The hip ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimising complications related to joint instability.

  • Journal article
    Arnold M, Zhao S, Doyle R, Jeffers J, Boughton Oet al., 2021,

    Power tool use in orthopaedic surgery: iatrogenic injury, its detection and technological advances

    , JBJS Open Access, ISSN: 2472-7245

    Background: Power tools are an integral part to orthopaedic surgery but have the capacity to cause iatrogenic injury. This systematic review aimed to investigate the prevalence of iatrogenic injury due to power tools in orthopaedic surgery and discuss the current methods 9that can be used to reduce this. Methods: A systematic review of all English language articles using a keyword search was undertaken in Medline, Embase, PubMed and Scopus databases. Exclusion criteria included injuries related to cast saw, temperature induced damage and complications not clearly related to power tool use. Results: 3694 abstracts were retrieved, and 88studies were included in the final analysis. Only a few studies and individual case reports directly looked at prevalence of injury due to power tools. This included 2 studies looking at frequency of vascular injury during femoral fracture fixation (0.49% and 0.2%),2 studies investigating frequency of vertebral artery injury during spinal surgery (0.5% and 0.08%)and 3 studies investigating vascular injury during total joint arthroplasty (124 vascular injuries involving 138 blood vessels,0.13% and 0.1% incidence)in addition to 1 questionnaire sent electronically to surgeons. There are multiple methods to prevent damage during the use of power tools. These include robotics, Revised Manuscript (Maximum 3000 Words)simulation, specific drill settings and real-time feedback techniques such as spectroscopy and electromyography. Conclusion: Power tools have the potential to cause iatrogenic injury to surrounding structures during orthopaedic surgery. Fortunately, the published literature suggests the frequency of iatrogenic injury using orthopaedic power tools is low. There are multiple technologies available to reduce damage using power tools. In high-risk operations the use of advanced technologies to reduce the chance of iatrogenic injury should be considered. Clinical Relevance: Power tools used during orthopaedic surgery have the potentia

  • Journal article
    Munford M, Xiao D, Jeffers J, 2021,

    Lattice implants that generate homeostatic and remodeling strains in bone

    , Journal of Orthopaedic Research, ISSN: 0736-0266

    Bone remodeling is mediated by several factors including strain. An increase in strain between 1% and 10% compared to homeostasis can trigger bone formation. We aim to create an orthopedic implant using clinically established imaging and manufacturing methods that induces this strain control in human bone. Titanium scaffolds were manufactured with multiaxial apparent modulus tailored to the mechanical properties of bone defined from computed tomography scans of cadaver human tibiae. Five bone cubes were tested with corresponding titanium scaffolds by loading under compression, which is similar to the implanted tibia loading condition. Bone strain was precisely controlled by varying the scaffold modulus, from 0% to 15% bone strain increase. This strain increase is the magnitude reported to invoke bone's positive remodeling. Axial modulus was closely matched between titanium scaffolds and bone, ranging from 48–728 and 81–800 MPa, respectively, whereby scaffold axial modulus was within 2% of nominal target values. Fine control of multiaxial moduli resulted in transverse modulus that matched bone well; ranging from 42–648 and 47–585 MPa in scaffolds and bone respectively. The scaffold manufacturing material and method are already used in the orthopedic industry. This study has significant clinical implications as it enables the design of implants which positively harness bone's natural mechanoresponse and respect bone's mechanical anisotropy and heterogeneity.

  • 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 Jet al., 2021,

    Controlling and testing anisotropy in additively manufactured stochastic structures

    , Additive Manufacturing, Vol: 39, ISSN: 2214-8604

    Additive manufacturing (AM) enables fine control over the architecture and mechanical properties of porous lattice structures. Typical periodic unit cells used in porous structures are inherently anisotropic, may not be suitable for multi-axial applications and cannot reliably create features or struts with low build angle. This study used laser powder bed fusion (PBF) to create isotropic stochastic porous structures in stainless steel (SS316L) and titanium alloy (Ti6Al4V), with modifications that aimed to overcome PBF manufacturing limitations of build angles. The structures were tested in uniaxial compression (n = 5) in 10 load orientations relative to the structure, including the three orthogonal axes. The testing verified that no hidden peaks in elastic modulus existed in the stochastic structure. Modification to the structure reduced the standard deviation of the 10 elastic modulus values from 249 MPa to 101 MPa when made in SS316L and from 95.9 MPa to 52.5 MPa for Ti6Al4V, indicating the structures were more isotropic. These modified stochastic structures have improved stiffness isotropy and could be used for lightweighting and biomaterial applications, reducing the dependence of performance on build orientation, and allowing more flexibility for component orientation on the build platform.

  • 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
    Parkes M, Tallia F, Young G, Cann P, Jones J, Jeffers Jet al., 2021,

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

    , Materials Science and Engineering C: Materials for Biological Applications, Vol: 119, Pages: 1-10, ISSN: 0928-4931

    The friction and wear properties of silica/poly(tetrahydrofuran)/poly(ε-caprolactone) (SiO2/PTHF/PCL-diCOOH) hybrid materials that are proposed as cartilage tissue engineering materials were investigated against living articular cartilage. A testing rig was designed to allow testing against fresh bovine cartilage. The friction force and wear were compared for five compositions of the hybrid biomaterial articulating against freshly harvested bovine cartilage in diluted bovine calf serum. Under a non-migrating contact, the friction force increased and hence shear force applied to the opposing articular cartilage also increased, resulting in minor damage to the cartilage surface. This worse case testing scenario was used to discriminate between material formulations and revealed the increase in friction and damaged area was lowest for the hybrid containing the most silica. Further friction and wear tests on one hybrid formulation with an elastic modulus closest to that of cartilage were then conducted in a custom incubator system. This demonstrated that over a five day period the friction force, cell viability and glucosaminoglycan (GAG) release into the lubricant were similar between a cartilage-cartilage interface and the hybrid-cartilage interface, supporting the use of these materials for cartilage repair. These results demonstrate how tribology testing can play a part in the development of new materials for chondral tissue engineering.

  • 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

    , ADVANCED FUNCTIONAL MATERIALS, Vol: 30, ISSN: 1616-301X
  • Journal article
    Clark J, Heyraud A, Tavana S, Al-Jabri T, Tallia F, Clark B, Blunn G, Cobb J, Hansen U, Jones J, Jeffers Jet al., 2020,

    Exploratory full-field mechanical analysis across the osteochondral tissue– biomaterial interface in an ovine model

    , Materials, Vol: 13, ISSN: 1996-1944

    Osteochondral injuries are increasingly prevalent, yet success in articular cartilage regeneration remains elusive, necessitating the development of new surgical interventions and novel medical devices. As part of device development, animal models are an important milestone in illustrating functionality of novel implants. Inspection of the tissue-biomaterial system is vital to understand and predict load-sharing capacity, fixation mechanics and micromotion, none of which are directly captured by traditional post-mortem techniques. This study aims to characterize the localised mechanics of an ex vivo ovine osteochondral tissue–biomaterial system extracted following six weeks in vivo testing, utilising laboratory micro-computed tomography, in situ loading and digital volume correlation. Herein, the full-field displacement and strain distributions were visualised across the interface of the system components, including newly formed tissue. The results from this exploratory study suggest that implant micromotion in respect to the surrounding tissue could be visualised in 3D across multiple loading steps. The methodology provides a non-destructive means to assess device performance holistically, informing device design to improve osteochondral regeneration strategies.

  • Journal article
    Clark J, Tavana S, Heyraud A, Tallia F, Jones J, Hansen U, Jeffers Jet al., 2020,

    Quantifying 3D strain in scaffold implants for regenerative medicine

    , Materials, Vol: 13, ISSN: 1996-1944

    Regenerative medicine solutions require thoughtful design to elicit the intended biological response. This includes the biomechanical stimulus to generate an appropriate strain in the scaffold and surrounding tissue to drive cell lineage to the desired tissue. To provide appropriate strain on a local level, new generations of scaffolds often involve anisotropic spatially graded mechanical properties that cannot be characterised with traditional materials testing equipment. Volumetric examination is possible with three-dimensional (3D) imaging, in situ loading and digital volume correlation (DVC). Micro-CT and DVC were utilised in this study on two sizes of 3D-printed inorganic/organic hybrid scaffolds (n = 2 and n = 4) with a repeating homogenous structure intended for cartilage regeneration. Deformation was observed with a spatial resolution of under 200 µm whilst maintaining displacement random errors of 0.97 µm, strain systematic errors of 0.17% and strain random errors of 0.031%. Digital image correlation (DIC) provided an analysis of the external surfaces whilst DVC enabled localised strain concentrations to be examined throughout the full 3D volume. Strain values derived using DVC correlated well against manually calculated ground-truth measurements (R2 = 0.98, n = 8). The technique ensures the full 3D micro-mechanical environment experienced by cells is intimately considered, enabling future studies to further examine scaffold designs for regenerative medicine.

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