Publications

Journal article

Garner AJ, Dandridge OW, van Arkel RJ, Cobb JPet al., 2023,

Medial bicompartmental arthroplasty patients display more normal gait and improved satisfaction, compared to matched total knee arthroplasty patients

, Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 31, Pages: 830-838, ISSN: 0942-2056

PurposeMedial bicompartmental arthroplasty, the combination of ipsilateral medial unicompartmental and patellofemoral arthroplasty, is an alternative to total knee arthroplasty for patients with medial tibiofemoral and severe patellofemoral arthritis, when the lateral tibiofemoral compartment and anterior cruciate ligament are intact. This study reports the gait and subjective outcomes following medial bicompartmental arthroplasty.MethodsFifty-five subjects were measured on the instrumented treadmill at top walking speeds, using standard metrics of gait. Modular, single-stage, medial bicompartmental arthroplasty subjects (n = 16) were compared to age, body mass index, height- and sex-matched healthy (n = 19) and total knee arthroplasty (n = 20) subjects. Total knee arthroplasty subjects with pre-operative evidence of tricompartmental osteoarthritis or anterior cruciate ligament dysfunction were excluded. The vertical component of ground reaction force and temporospatial measurements were compared using Kruskal–Wallis, then Mann–Whitney test with Bonferroni correction (α = 0.05). Oxford Knee and EuroQoL EQ-5D scores were compared.ResultsObjectively, the medial bicompartmental arthroplasty top walking speed of 6.7 ± 0.8 km/h was 0.5 km/h (7%) slower than that of healthy controls (p = 0.2), but 1.3 km/h (24%) faster than that of total knee arthroplasty subjects (5.4 ± 0.6 km/h, p < 0.001). Medial bicompartmental arthroplasty recorded more normal maximum weight acceptance (p < 0.001) and mid-stance forces (p = 0.03) than total knee arthroplasty subjects, with 11 cm (15%) longer steps (p < 0.001) and 21 cm (14%) longer strides (p = 0.006). Subjectively, medial bicompartmental arthroplasty subjects reported Oxford Knee Scores of median 41 (interquartile range 38.8&nd

Journal article

Garner AJ, Dandridge OW, van Arkel RJ, Cobb JPet al., 2023,

The compartmental approach to revision of partial knee arthroplasty results in nearer-normal gait and improved patient reported outcomes compared to total knee arthroplasty

, Knee Surgery Sports Traumatology Arthroscopy, Vol: 31, Pages: 1143-1152, ISSN: 0942-2056

PURPOSE: This study investigated the gait and patient reported outcome measures of subjects converted from a partial knee arthroplasty to combined partial knee arthroplasty, using a compartmental approach. Healthy subjects and primary total knee arthroplasty patients were used as control groups. METHODS: Twenty-three patients converted from partial to combined partial knee arthroplasty were measured on the instrumented treadmill at top walking speeds, using standard gait metrics. Data were compared to healthy controls (n = 22) and primary posterior cruciate-retaining total knee arthroplasty subjects (n = 23) where surgery were performed for one or two-compartment osteoarthritis. Groups were matched for age, sex and body mass index. At the time of gait analysis, combined partial knee arthroplasty subjects were median 17 months post-revision surgery (range 4-81 months) while the total knee arthroplasty group was median 16 months post-surgery (range 6-150 months). Oxford Knee Scores and EuroQol-5D 5L scores were recorded at the time of treadmill assessment, and results analysed by question and domain. RESULTS: Subjects revised from partial to combined partial knee arthroplasty walked 16% faster than total knee arthroplasty (mean top walking speed 6.4 ± 0.8 km/h, vs. 5.5 ± 0.7 km/h p = 0.003), demonstrating nearer-normal weight-acceptance rate (p < 0.001), maximum weight-acceptance force (p < 0.006), mid-stance force (p < 0.03), contact time (p < 0.02), double support time (p < 0.009), step length (p = 0.003) and stride length (p = 0.051) compared to primary total knee arthroplasty. Combined partial knee arthroplasty subjects had a median Oxford Knee Score of 43 (interquartile range 39-47) vs. 38 (interquartile range 32-41, p < 0.

Journal article

Ng KCG, Bankes MJK, El Daou H, Beaulé PE, Cobb JP, Jeffers JRTet al., 2022,

Capsular Mechanics After Periacetabular Osteotomy for Hip Dysplasia.

, J Bone Joint Surg Am, Vol: 104, Pages: 1015-1023

BACKGROUND: Hip dysplasia is characterized by insufficient acetabular coverage around the femoral head, which leads to instability, pain, and injury. Periacetabular osteotomy (PAO) aims to restore acetabular coverage and function, but its effects on capsular mechanics and joint stability are still unclear. The purpose of this study was to examine the effects of PAO on capsular mechanics and joint range of motion in dysplastic hips. METHODS: Twelve cadaveric dysplastic hips (denuded to bone and capsule) were mounted onto a robotic tester and tested in multiple positions: (1) full extension, (2) neutral 0°, (3) flexion of 30°, (4) flexion of 60°, and (5) flexion of 90°. In each position, the hips underwent internal and external rotation, abduction, and adduction using 5 Nm of torque. Each hip then underwent PAO to reorient the acetabular fragment, preserving the capsular ligaments, and was retested. RESULTS: The PAO reduced internal rotation in flexion of 90° (∆IR = -5°; p = 0.003), and increased external rotation in flexion of 60° (∆ER = +7°; p = 0.001) and flexion of 90° (∆ER = +11°; p = 0.001). The PAO also reduced abduction in extension (∆ABD = -10°; p = 0.002), neutral 0° (∆ABD = -7°; p = 0.001), and flexion of 30° (∆ABD = -8°; p = 0.001), but increased adduction in neutral 0° (∆ADD = +9°; p = 0.001), flexion of 30° (∆ADD = +11°; p = 0.002), and flexion of 60° (∆ADD = +11°; p = 0.003). CONCLUSIONS: PAO caused reductions in hip abduction and internal rotation but greater increases in hip adduction and external rotation. The osseous acetabular structure and capsule both play a role in the balance between joint mobility and stability after PAO.

Journal article

Kechagias S, Oosterbeek R, Munford M, Ghouse S, Jeffers Jet al., 2022,

Controlling the mechanical behaviour of stochastic lattice structures: the key role of nodal connectivity

, Additive Manufacturing, Vol: 54, ISSN: 2214-8604

Additive manufacturing has enabled the fabrication of lattice structures with controlled micro-architectures and mechanical properties. These structures are particularly attractive in the orthopaedic industry where their osseointegration capability and bone-matching mechanical properties are ideally suited for use in implants and bone scaffolds. The broad range of mechanical properties required for this application is a challenge – it typically requires a range of periodic lattice structures, each of which require separate characterisation. An alternative approach is to use a stochastic lattice structure, where a single relationship between the lattice design parameters (connectivity, strut density and strut thickness) and resulting mechanical properties should be possible. To investigate this, we manufactured stochastic lattices in pure Titanium with connectivity from 4 to 14, strut density from 3 to 7 [struts/mm3] and strut thickness of 230 and 300 µm. Specimens were compression tested in quasi-static and fatigue loading. In static loading, the low connectivity structures displayed bend-dominated deformation while the high connectivity structures displayed stretch-dominated deformation. The structures had a stiffness ranging from 0.1 to 8 GPa and different Gibson-Ashby stiffness/relative density relationships were required for high and low connectivity structures. A unified multivariable linear regression model was found to predict relative density from the connectivity, strut density and strut thickness of the structure. In fatigue loading, increasing the connectivity from 4 to 14 increased the fatigue strength by 60% for a fixed relative density. These findings provide important design information when creating structures using stochastic lattices to maximise strength for a desired relative density or stiffness. The single integrated model presented in this study can define a structure to achieve a broad range of design requirements, even as gradient

Journal article

Oosterbeek R, Jeffers J, 2022,

StrutSurf: A tool for analysis of strut morphology and surface roughness in additively manufactured lattices

, SoftwareX, Vol: 18, ISSN: 2352-7110

Additively manufactured lattice materials are of great interest in manyapplications, however the surface defects generated during manufacturingcan prove a significant barrier. The small feature size and intricate geometrymakes characterisation of lattice struts difficult, so we present StrutSurf asa new tool for analysis of lattice struts. Using micro-CT data, StrutSurfallows random sampling of struts within a lattice, and automates analysis toprovide detailed morphological information such as strut diameter, ellipticity,orientation, and surface roughness. StrutSurf will enable a range of newresearch questions to be investigated such as the effects of surface treatmentsand other manufacturing methods on strut morphology and roughness.

Journal article

Ovrebo O, Perale G, Wojciechowski J, Echalier C, Jeffers J, Stevens M, Haugen H, Rossi Fet al., 2022,

Design and clinical application of injectable hydrogels for musculoskeletal therapy

, Bioengineering and Translational Medicine, Vol: 7, Pages: 1-21, ISSN: 2380-6761

Musculoskeletal defects are an enormous healthcare burden and source of pain and disability for individuals. With an ageing population, the proportion living with these medical indications will increase. Simultaneously, there is pressure on healthcare providers to source efficient solutions, which are cheaper and less invasive than conventional technology. This has led to an increased research focus on hydrogels as highly biocompatible biomaterials that can be delivered through minimally invasive procedures. This review will discuss how hydrogels can be designed for clinical translation, particularly in the context of the new European Medical Device Regulation (MDR). We will then do a deep dive into the clinically used hydrogel solutions that have been commercially approved or have undergone clinical trials in Europe or the US. We will discuss the therapeutic mechanism and limitations of these products. Due to the vast application areas of hydrogels, this work focuses only on treatments of cartilage, bone, and the nucleus pulposus. Lastly, the main steps towards clinical translation of hydrogels as medical devices are outlined. We suggest a framework for how academics can assist small and medium MedTech enterprises conducting the initial clinical investigation and Post-Market Clinical Follow-up (PMCF) required in the MDR. It is evident that the successful translation of hydrogels is governed by acquiring high-quality pre-clinical and clinical data confirming the device mechanism of action and safety.

Journal article

Munford MJ, Xiao D, Jeffers JRT, 2022,

Lattice implants that generate homeostatic and remodeling strains in bone

, JOURNAL OF ORTHOPAEDIC RESEARCH, Vol: 40, Pages: 871-877, ISSN: 0736-0266

Journal article

Dandridge O, Garner A, Amis A, Cobb J, van Arkel RJet al., 2022,

Variation in the patellar tendon moment arm identified with an improved measurement framework

, Journal of Orthopaedic Research, Vol: 40, Pages: 799-807, ISSN: 0736-0266

The mechanical advantage of the knee extensor mechanism depends heavily on the patellar tendon moment arm (PTMA). Understanding which factors contribute to its variation may help improve functional outcomes following arthroplasty. This study optimized PTMA measurement, allowing us to quantify the contribution of different variables. The PTMA was calculated about the instantaneous helical axis of tibiofemoral rotation from optical tracked kinematics. A fabricated knee model facilitated calculation optimization, comparing four data smoothing techniques (raw, Butterworth filtering, generalized cross-validated cubic spline-interpolation and combined filtering/interpolation). The PTMA was then measured for 24 fresh-frozen cadaveric knees, under physiologically based loading and extension rates. Combined filtering/interpolation enabled sub-mm PTMA calculation accuracy throughout the range of motion (root-mean-squared error 0.2 mm, max error 0.4 mm), whereas large errors were measured for raw, filtered-only and interpolated-only techniques at terminal flexion/extension. Before scaling, the mean PTMA was 46 mm; PTMA magnitude was consistently larger in males (mean differences: 5 to 10 mm, p < .05) and was strongly related to knee size: larger knees have a larger PTMA. However, while scaling eliminated sex differences in PTMA magnitude, the peak PTMA occurred closer to terminal extension in females (female 15°, male 29°, p = .01). Knee size accounted for two-thirds of the variation in PTMA magnitude, but not the flexion angle where peak PTMA occurred. This substantial variation in angle of peak PTMA has implications for the design of musculoskeletal models and morphotype-specific arthroplasty. The developed calculation framework is applicable both in vivo and vitro for accurate PTMA measurement.

Journal article

Munford M, Liddle A, Stoddart J, Cobb J, Jeffers Jet al., 2022,

Total and partial knee replacement implants that maintain native load transfer in the Tibia

, Bone and Joint Research, Vol: 11, Pages: 1-3, ISSN: 2046-3758

Aims:Unicompartmental and total knee arthroplasty (UKA and TKA) are successful treatments for osteoarthritis, but the solid metal implants disrupt the natural distribution of stress and strain which can lead to bone loss over time. This generates problems if the implant needs to be revised. This study investigates whether titanium lattice UKA and TKA implants can maintain natural load transfer in the proximal tibia. Methods:In a cadaveric model, UKA and TKA procedures were performed on 8 fresh-frozen knee specimens, using conventional (solid) and titanium lattice tibial implants. Stress at the bone-implant interfaces were measured and compared to the native knee.Results:Titanium lattice implants were able to restore the mechanical environment of the native tibia for both UKA and TKA designs. Maximum stress at the bone-implant interface ranged from 1.2-3.3 MPa compared to 1.3-2.7 MPa for the native tibia. The conventional solid UKA and TKA implants reduced the maximum stress in the bone by a factor of 10 and caused >70% of bone surface area to be underloaded compared to the native tibia. Conclusions:Titanium lattice implants maintained the natural mechanical loading in the proximal tibia after UKA and TKA, but conventional solid implants did not. This is an exciting first step towards implants that maintain bone health, but such implants also have to meet fatigue and micromotion criteria to be clinically viable.

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, Pages: 1-11, ISSN: 1050-0472

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.

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, ISSN: 0021-9290

Journal article

Clark JN, Tavana S, Clark B, Briggs T, Jeffers JRT, 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

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, Vol: 6, Pages: 1-16, 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

van Arkel RJ, Tan N, 2021,

Topology optimisation for compliant hip implant design and reduced strain shielding

, Materials, Vol: 14, Pages: 1-16, ISSN: 1996-1944

Stiff total hip arthroplasty implants can lead to strain shielding, bone loss and complex revision surgery. The aim of this study was to develop topology optimisation techniques for more compliant hip implant design. The Solid Isotropic Material with Penalisation (SIMP) method was adapted, and two hip stems were designed and additive manufactured: (1) a stem based on a stochastic porous structure, and (2) a selectively hollowed approach. Finite element analyses and experimental measurements were conducted to measure stem stiffness and predict the reduction in stress shielding. The selectively hollowed implant increased peri-implanted femur surface strains by up to 25 percentage points compared to a solid implant without compromising predicted strength. Despite the stark differences in design, the experimentally measured stiffness results were near identical for the two optimised stems, with 39% and 40% reductions in the equivalent stiffness for the porous and selectively hollowed implants, respectively, compared to the solid implant. The selectively hollowed implant’s internal structure had a striking resemblance to the trabecular bone structures found in the femur, hinting at intrinsic congruency between nature’s design process and topology optimisation. The developed topology optimisation process enables compliant hip implant design for more natural load transfer, reduced strain shielding and improved implant survivorship.

Journal article

Garner A, Dandridge O, Amis A, Cobb J, van Arkel RJet al., 2021,

Bi-unicondylar arthroplasty: a biomechanics and clinical outcomes study

, Bone & Joint Research, Vol: 10, Pages: 723-733, ISSN: 2046-3758

Aims Bi-Unicondylar Arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL) preserving alternative to Total Knee Arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA. Methods Bi-UKA subjects (N = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age, sex and BMI-matched healthy (N = 24) and primary TKA (N = 22) subjects formed control groups. TKA subjects with pre-operative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol-5D (EQ-5D) were compared. Bi-UKA then TKA were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design. Results Bi-UKA walked 20% faster than TKA (Bi-UKA 6.70.9km/h, TKA 5.60.7km/h p<0.001), exhibiting nearer-normal vertical Ground Reaction Forces in maximum weight-acceptance and mid-stance, with longer step and stride lengths compared to TKA (p<0.05). Bi-UKAsubjects reported higher OKS (p=0.004) and EQ-5D (p<0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, whilst reduced extensor moment was measured following TKA (p<0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p<0.05). Conclusion Bi-UKA had more normal gait characteristics and improved patient reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency.

Journal article

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

Partial and combined partial knee arthroplasty: greater anterior-posterior stability than posterior-cruciate retaining total knee arthroplasty

, The Journal of Arthroplasty, Vol: 36, Pages: 3765-3772.e4, ISSN: 0883-5403

BackgroundLittle is known regarding anterior-posterior stability after anterior cruciate ligament–preserving partial (PKA) and combined partial knee arthroplasty (CPKA) compared to standard posterior cruciate–retaining total knee arthroplasty (TKA).MethodsThe anterior-posterior tibial translation of twenty-four cadaveric knees was measured, with optical tracking, while under 90N drawer with the knee flexed 0-90°. Knees were tested before and after PKA, CPKA (medial and lateral bicompartmental and bi-unicondylar), and then posterior cruciate–retaining TKA. The anterior-posterior tibial translations of the arthroplasty states, at each flexion angle, were compared to the native knee and each other with repeated measures analyses of variance and post-hoc t-tests.ResultsUnicompartmental and bicompartmental arthroplasty states had similar laxities to the native knee and to each other, with ≤1-mm differences throughout the flexion range (P ≥ .199). Bi-unicondylar arthroplasty resulted in 6- to 8-mm increase of anterior tibial translation at high flexion angles compared to the native knee (P ≤ .023 at 80-90°). Meanwhile, TKA exhibited increased laxity across all flexion angles, with increased anterior tibial translation of up to 18 ± 6 mm (P < .001) and increased posterior translation of up to 4 ± 2 mm (P < .001).ConclusionsIn a cadaveric study, anterior-posterior tibial translation did not differ from native laxity after PKA and CPKA. Posterior cruciate ligament–preserving TKA demonstrated increased laxity, particularly in anterior tibial translation.

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

Ghouse S, Oosterbeek RN, Mehmood AT, Vecchiato F, Dye D, Jeffers JRTet al., 2021,

Vacuum heat treatments of titanium porous structures

, ADDITIVE MANUFACTURING, Vol: 47, ISSN: 2214-8604

Journal article

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

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

, ADDITIVE MANUFACTURING, Vol: 46, ISSN: 2214-8604

Journal article

Karunaseelan KJ, Dandridge O, Muirhead-Allwood SK, van Arkel RJ, Jeffers JRTet al., 2021,

Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading

, BONE & JOINT RESEARCH, Vol: 10, Pages: 594-601, ISSN: 2046-3758

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