37 results found
Wang J, Hall TAG, Musbahi O, et al., 2023, Predicting hip-knee-ankle and femorotibial angles from knee radiographs with deep learning, Knee, Vol: 42, Pages: 281-288, ISSN: 0968-0160
BACKGROUND: Knee alignment affects the development and surgical treatment of knee osteoarthritis. Automating femorotibial angle (FTA) and hip-knee-ankle angle (HKA) measurement from radiographs could improve reliability and save time. Further, if HKA could be predicted from knee-only radiographs then radiation exposure could be reduced and the need for specialist equipment and personnel avoided. The aim of this research was to assess if deep learning methods could predict FTA and HKA angle from posteroanterior (PA) knee radiographs. METHODS: Convolutional neural networks with densely connected final layers were trained to analyse PA knee radiographs from the Osteoarthritis Initiative (OAI) database. The FTA dataset with 6149 radiographs and HKA dataset with 2351 radiographs were split into training, validation, and test datasets in a 70:15:15 ratio. Separate models were developed for the prediction of FTA and HKA and their accuracy was quantified using mean squared error as loss function. Heat maps were used to identify the anatomical features within each image that most contributed to the predicted angles. RESULTS: High accuracy was achieved for both FTA (mean absolute error 0.8°) and HKA (mean absolute error 1.7°). Heat maps for both models were concentrated on the knee anatomy and could prove a valuable tool for assessing prediction reliability in clinical application. CONCLUSION: Deep learning techniques enable fast, reliable and accurate predictions of both FTA and HKA from plain knee radiographs and could lead to cost savings for healthcare providers and reduced radiation exposure for patients.
Garner AJ, Dandridge OW, van Arkel RJ, et 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
Garner AJ, Dandridge OW, van Arkel RJ, et 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.
Kohli N, Theodoridis K, Hall T, et al., 2023, Bioreactor analyses of tissue ingrowth, ongrowth and remodelling around implants: an alternative to live animal testing, Frontiers in Bioengineering and Biotechnology, Vol: 11, Pages: 1-12, ISSN: 2296-4185
Introduction: Preclinical assessment of bone remodelling onto, into or around novel implant technologies is underpinned by a large live animal testing burden. The aim of this study was to explore whether a lab-based bioreactor model could provide similar insight.Method: Twelve ex vivo trabecular bone cylinders were extracted from porcine femora and were implanted with additively manufactured stochastic porous titanium implants. Half were cultured dynamically, in a bioreactor with continuous fluid flow and daily cyclic loading, and half in static well plates. Tissue ongrowth, ingrowth and remodelling around the implants were evaluated with imaging and mechanical testing.Results: For both culture conditions, scanning electron microscopy (SEM) revealed bone ongrowth; widefield, backscatter SEM, micro computed tomography scanning, and histology revealed mineralisation inside the implant pores; and histology revealed woven bone formation and bone resorption around the implant. The imaging evidence of this tissue ongrowth, ingrowth and remodelling around the implant was greater for the dynamically cultured samples, and the mechanical testing revealed that the dynamically cultured samples had approximately three times greater push-through fixation strength (p < 0.05).Discussion: Ex vivo bone models enable the analysis of tissue remodelling onto, into and around porous implants in the lab. While static culture conditions exhibited some characteristics of bony adaptation to implantation, simulating physiological conditions with a bioreactor led to an accelerated response.
Fischer D, Cheng K-Y, Neto MQ, et al., 2022, Corrosion behavior of selective laser melting (SLM) manufactured Ti6Al4V alloy in saline and BCS solution, Journal of Bio- and Tribo-Corrosion, Vol: 8, ISSN: 2198-4220
The frequency of surgeries involving the use of metal implants in orthopedic medicine to replace degenerative or fractured joints is increasing, and it is therefore important to optimize the lifespan and quality of these implants. Advances in additive manufacturing (AM), or 3D printing, are creating new opportunities to personalize implants in ways that reduce mechanical stress at the joint implant interface and improve bone ingrowth and implant stability; however, it is not well understood if and to what degree the AM process alters the corrosion behavior of the materials it produces. In this study, six Ti6Al4V prints manufactured via a selective laser melting (SLM) method were examined regarding their corrosion behavior in both saline and bovine calf serum (BCS) solutions. Ecorr and Icorr values were comparable between the CM-Ti6Al4V control and SLM-EDM surfaces; however, SLM surfaces were found to have more narrow passivation behavior evidenced by significant decreases in Epass values relative to CM-Ti6Al4V. We believe this is a consequence of microstructural differences between CM-Ti6Al4V and SLM-Ti6Al4V. Specifically, the SLM-Ti6Al4V demonstrated a dominant α′ martensitic microstructure and decreased vanadium-rich β-phase. BCS solution had a detrimental effect on potential parameters, Ecorr and OCP, decreasing these values relative to their saline counterparts. Increased surface roughness of the SLM-printed surface seemed to amplify the effects of the BCS solution. Furthermore, modest decreases in Epass and Ipass were observed in BCS solution, suggesting that the presence of protein may also interfere with passivation behavior. These findings have implications for how SLM-Ti6Al4V implants will perform in vivo and could possibly influence implant longevity and performance.
Stoddart J, Garner A, Tuncer M, et al., 2022, The risk of tibial eminence avulsion fracture with bi-unicondylar knee arthroplasty - a finite element analysis, Bone & Joint Research, Vol: 11, ISSN: 2046-3758
Aims: To determine the risk of tibial eminence avulsion intraoperatively for bi-unicondylar knee arthroplasty (Bi-UKA) with consideration to the effect of implant positioning, overstuffing, and sex, compared to the risk for isolated medial UKA (UKA-M) and bi-cruciate retaining total knee arthroplasty (BCR-TKA).Methods: Two experimentally validated finite element models of tibia were implanted. Intraoperative loads were applied through the condyles, ACL, MCL and LCL, and the risk of fracture (ROF) was evaluated in the spine as the ratio of the 95th percentile maximum principal elastic strains over the tensile yield strain of proximal tibial bone.Results: Peak tensile strains occurred on the anterior portion of the medial sagittal cut in all simulations. Lateral translation of the medial implant in Bi-UKA had the largest increase in ROF of any of the implant positions (43%). Overstuffing the joint by 2mm had a much larger effect, resulting in a 6-fold increase in ROF. Bi-UKA had ~10% increased ROF compared to UKA-M for both the male and female models, though the smaller, less dense female model had a 1.5 times greater ROF compared to the male model. Removal of anterior bone akin to BCR-TKA doubled ROF compared to Bi-UKA.Conclusion: Tibial eminence avulsion fracture has a similar risk associated with Bi-UKA to UKA-M. The risk is higher for a smaller and less dense tibiae. To minimise risk, it is most important to avoid overstuffing the joint, followed by correctly positioning the medial implant, taking care not to narrow the bony island anteriorly.
Dandridge O, Garner A, Amis A, et 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.
Neto MQ, Yuh C, van Arkel R, et al., 2022, The Effect of Additive Manufacturing Parameters on Microstructure and Mechanical Properties of Biomedical Grade Ti-6Al-4V Alloy, Pages: 265-281, ISSN: 0066-0558
Additive manufacturing (AM) has the potential to revolutionize the biomaterials field by enabling the affordable and quick production of custom-made implants to fit specific patient needs and anatomy. There already exists literature on the relationships among process parameters, microstructure, and mechanical properties; however, the relationship of complex structures with varied shapes needs further investigation. Therefore, this study sought to determine the effects of AM laser power, exposure time, point spacing, and strut diameter on the microstructure of as-printed Ti-6Al-4V for biomedical application. Mechanical properties of as-printed Ti-6Al-4V samples were assessed by nanoindentation and compared to that of a wrought Ti-6Al-4V control. The AM samples were found to have fine needle-like shape grains, similar to martensite, where the grain size decreased with higher laser power and longer exposure time. All AM samples had low b phase content and the alloying elements were homogenously distributed. Prior b phase colonized with fine a' phase was identified by the orientation maps-electron backscattered diffraction. Manufacturing defects such as gas porosity and lack of fusion were observed, as well as the presence of cracks. The AM samples were found to have increased hardness and decreased reduced elastic modulus compared to the wrought control. The observed differences in mechanical properties are likely related to the microstructure of these samples. These findings demonstrate that AM alloy microstructure influences both bulk and local properties. This presented study provides additional context into this relationship, furthering the understanding of the complex environment of biomedical implants.
Dandridge O, Garner A, Jeffers JRT, et 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.
Wang J, Hall T, Musbahi O, et al., 2021, Predicting Hip-Knee-Ankle and Femorotibial Angles from Knee Radiographs with Deep Learning, The British Orthopaedic Research Society (BORS) Annual Meeting 2021
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.
Garner A, Dandridge O, Amis A, et 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 6.70.9km/h, TKA 5.60.7km/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.
Garner A, Dandridge O, Amis A, et 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.
Karunaseelan K, Dandridge O, Muirhead-Allwood S, et 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.
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.
Stoddart J, Dandridge O, Garner A, et 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
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.
Garner A, Dandridge O, Amis A, et 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.
Doyle R, van Arkel R, Muirhead-Allwood S, et al., 2020, Impaction technique influences implant stability in low density bone model, Bone & Joint Research, Vol: 9, ISSN: 2046-3758
Aims: Cementless acetabular cups rely on press-fit fixation for initial stability. In certain cases initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity and number of strikes) may affect cup fixation. This study seeks to answer the following research questions:(1) How does impaction technique affect a) bone strain generation and deterioration (and hence implant stability); b) seating in different density bones? (2) Can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular cup? Methods: A custom drop tower was used to simulate surgical strikes seating acetabular cups into synthetic bone. Strike velocity and drop mass were varied. Synthetic bone strain was measured using strain gauges and stability was assessed via push out tests. Polar gap was measured using optical trackers. Results: A phenomenon of strain deterioration was identified if an excessive number of strikes were used to seat a cup. This effect was most pronounced in low density bone at high strike velocities. Polar gap was reduced with increasing strike mass and velocity. Conclusions: A high mallet mass with low strike velocity resulted in satisfactory implant stability and polar gap while minimizing the risk of losing stability due to over-striking. Extreme caution not to over-strike must be exercised when using high velocity strikes in low density bone for any mallet
Doyle R, van Arkel R, Jeffers J, 2019, The effect of impaction energy on dynamic bone strains, fixation strength and seating of cementless acetabular cups, Journal of Orthopaedic Research, Vol: 37, Pages: 2367-2375, ISSN: 0736-0266
Seating a cementless acetabular cup via impaction is a balancing act; good cup fixation must be obtained to ensure adequate bone in‐growth and cup apposition, while acetabular fracture must be avoided. Good impaction technique is essential to the success of hip arthroplasty. Yet little guidance exists in the literature to inform surgeons on ‘how hard’ to hit. A drop rig and synthetic bone model were used to vary the energy of impaction strikes in low and high density synthetic bone, while key parameters such as dynamic strain (quantifying fracture risk), implant fixation and polar gap were measured. For high energy impaction (15 J) in low density synthetic bone a peak tensile strain was observed during impaction that was up to 3.4x as large as post‐strike strain, indicating a high fracture risk. Diminishing returns were observed for pushout fixation with increasing energy. 85% of the pushout fixation achieved using a 15 J impaction strike was attained by using a 7.5 J strike energy. Similarly polar gap was only minimally reduced at high impaction energies. Therefore it is suggested that higher energy strikes increase fracture risk, but do not offer large improvements to fixation or implant‐bone apposition. It may difficult be for surgeons to accurately deliver specific impaction energies, suggesting there is scope for operative tools to manage implant seating.
Garner A, van Arkel RJ, Cobb J, 2019, Classification of combined partial knee arthroplasty, Bone and Joint Journal, Vol: 101B, Pages: 922-928, ISSN: 2049-4394
AimsThere has been a recent resurgence in interest in combined partial knee arthroplasty (PKA) as an alternative to total knee arthroplasty (TKA). The varied terminology used to describe these procedures leads to confusion and ambiguity in communication between surgeons, allied health professionals, and patients. A standardized classification system is required for patient safety, accurate clinical record-keeping, clear communication, correct coding for appropriate remuneration, and joint registry data collection.Materials and MethodsAn advanced PubMed search was conducted, using medical subject headings (MeSH) to identify terms and abbreviations used to describe knee arthroplasty procedures. The search related to TKA, unicompartmental (UKA), patellofemoral (PFA), and combined PKA procedures. Surveys were conducted of orthopaedic surgeons, trainees, and biomechanical engineers, who were asked which of the descriptive terms and abbreviations identified from the literature search they found most intuitive and appropriate to describe each procedure. The results were used to determine a popular consensus.ResultsSurvey participants preferred “bi-unicondylar arthroplasty” (Bi-UKA) to describe ipsilateral medial and lateral unicompartmental arthroplasty; “medial bi-compartmental arthroplasty” (BCA-M) to describe ipsilateral medial unicompartmental arthroplasty with patellofemoral arthroplasty; “lateral bi-compartmental arthroplasty” (BCA-L) to describe ipsilateral lateral unicompartmental arthroplasty with patellofemoral arthroplasty; and tri-compartmental arthroplasty (TCA) to describe ipsilateral patellofemoral and medial and lateral unicompartmental arthroplasties. “Combined partial knee arthroplasty” (CPKA) was the favoured umbrella term.ConclusionWe recommend bi-unicondylar arthroplasty (Bi-UKA), medial bicompartmental arthroplasty (BCA-M), lateral bicompartmental arthroplasty (BCA-L), and tricompartmental arthroplasty (
Logishetty K, van Arkel RJ, Ng KC, et al., 2019, Hip capsule biomechanics after arthroplasty - the effect of implant, approach and surgical repair, Bone and Joint Journal, Vol: 101-B, Pages: 426-434, ISSN: 2049-4394
AimsThe hip’s capsular ligaments passively restrain extreme range of movement (ROM) by wrapping around the native femoral head/neck. We determined the effect of hip resurfacing arthroplasty (HRA), dual-mobility total hip arthroplasty (DM-THA), conventional THA, and surgical approach on ligament function.Materials and MethodsEight paired cadaveric hip joints were skeletonized but retained the hip capsule. Capsular ROM restraint during controlled internal rotation (IR) and external rotation (ER) was measured before and after HRA, DM-THA, and conventional THA, with a posterior (right hips) and anterior capsulotomy (left hips).ResultsHip resurfacing provided a near-native ROM with between 5° to 17° increase in IR/ER ROM compared with the native hip for the different positions tested, which was a 9% to 33% increase. DM-THA generated a 9° to 61° (18% to 121%) increase in ROM. Conventional THA generated a 52° to 100° (94% to 199%) increase in ROM. Thus, for conventional THA, the capsule function that exerts a limit on ROM is lost. It is restored to some extent by DM-THA, and almost fully restored by hip resurfacing. In positions of low flexion/extension, the posterior capsulotomy provided more normal function than the anterior, possibly because the capsule was shortened during posterior repair. However, in deep flexion positions, the anterior capsulotomy functioned better.ConclusionNative head-size and capsular repair preserves capsular function after arthroplasty. The anterior and posterior approach differentially affect postoperative biomechanical function of the capsular ligaments.
El Daou H, Ng KC, van Arkel R, et al., 2019, Robotic hip joint testing: Development and experimental protocols, Medical Engineering and Physics, Vol: 63, Pages: 57-62, ISSN: 1350-4533
The use of robotic systems combined with force sensing is emerging as the gold standard for in vitro biomechanical joint testing, due to the advantage of controlling all six degrees of freedom independently of one another. This paper describes a novel robotic platform and the experimental protocol used for hip joint testing. An experimental protocol implemented optical tracking and registration techniques in order to define the position of the hip joint centre of rotation (COR) in the coordinate system of the robot's end effector. The COR coordinates defined the origin of the task-related coordinate system used to control the robot, with a hybrid force/position law to simulate standard clinical tests. The axes of this frame were defined using the International Society of Biomechanics (ISB) anatomical coordinate system.Experiments were carried out on two cadaveric hip joint specimens using the robotic testing platform and a mechanical testing rig previously developed and described by our group. Simulated internal-external and adduction/abduction laxity tests were carried out with both systems and the resulting peak range of motion (ROM) was measured. Similarities and differences were observed in these experiments, which were used to highlight some of the limitations of conventional systems and the corresponding advantages of robotics, further emphasising their added value in vitro testing.
Correa T, Pal B, van Arkel R, et al., 2018, Reduced tibial strain-shielding with extraosseous total knee arthroplasty revision system, Medical Engineering and Physics, Vol: 62, Pages: 22-28, ISSN: 1350-4533
BackgroundRevision total knee arthroplasty (RTKA) has poorer results than primary total knee arthroplasty (TKA), and the prostheses are invasive and cause strain-shielding of the bones near the knee. This paper describes an RTKA system with extracortical fixation. It was hypothesised that this would reduce strain-shielding compared with intramedullary fixation.MethodsTwelve replica tibiae were prepared for full-field optical surface strain analysis. They were either left intact, implanted with RTKA components with cemented intramedullary fixation stems, or implanted with a novel design with a tibial tray subframe supported by two extracortical fixation plates and screw fixation. They were loaded to simulate peak walking and stair climbing loads and the surface strains were measured using digital image correlation. The measurements were validated with strain gauge rosettes.ResultsCompared to the intact bone model, extracortical fixation reduced surface strain-shielding by half versus intramedullary fixation. For all load cases and bone regions examined, the extracortical implant shielded 8–27% of bone strain, whereas the intramedullary component shielded 37–56%.ConclusionsThe new fixation design, which offers less bone destruction than conventional RTKA, also reduced strain-shielding. Clinically, this design may allow greater rebuilding of bone loss, and should increase long-term fixation.
van Arkel R, Ng KCG, Muirhead-Allwood S, et al., 2018, Capsular ligament function after total hip arthroplasty, Journal of Bone and Joint Surgery: American Volume, Vol: 100, Pages: 1-10, ISSN: 0021-9355
Background: The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading. We hypothesized that following total hip arthroplasty (THA), the reduced femoral head size impairs this protective biomechanical function.Methods: In cadavers, THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. Eight hips were examined. Capsular function was measured by rotating the hip in 5 positions. Three head sizes (28, 32, and 36 mm) with 3 neck lengths (anatomical 0, +5, and +10 mm) were compared.Results: Internal and external rotation range of motion increased following THA, indicating late engagement of the capsule and reduced biomechanical function (p < 0.05). Internal rotation was affected more than external. Increasing neck length reduced this hypermobility, while too much lengthening caused nonphysiological restriction of external rotation. Larger head sizes only slightly reduced hypermobility.Conclusions: Following THA, the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion. The posterior capsule was the most affected, indicating that native posterior capsule preservation is not advantageous, at least in the short term. Insufficient neck length could cause capsular dysfunction even if native ligament anatomy is preserved, while increased neck length could overtighten the anterior capsule.Clinical Relevance: Increased understanding of soft-tissue balancing following THA could help to prevent instability and improve early function. This study illustrates how head size and neck length influence the biomechanical function of the hip capsule in the early postoperative period.
van Arkel R, Ghouse S, Milner P, et al., 2018, Additive manufactured push-fit implant fixation with screw-strength pull out, Journal of Orthopaedic Research, Vol: 36, Pages: 1508-1518, ISSN: 0736-0266
Additive manufacturing offers exciting new possibilities for improving long-term metallic implant fixation in bone through enabling open porous structures for bony ingrowth. The aim of this research was to investigate how the technology could also improve initial fixation, a precursor to successful long-term fixation. A new barbed fixation mechanism, relying on flexible struts was proposed and manufactured as a push-fit peg. The technology was optimized using a synthetic bone model and compared with conventional press-fit peg controls tested over a range of interference fits. Optimum designs, achieving maximum pull-out force, were subsequently tested in a cadaveric femoral condyle model. The barbed fixation surface provided more than double the pull-out force for less than a third of the insertion force compared to the best performing conventional press-fit peg (p < 0.001). Indeed, it provided screw-strength pull out from a push-fit device (1,124 ± 146 N). This step change in implant fixation potential offers new capabilities for low profile, minimally invasive implant design, while providing new options to simplify surgery, allowing for one-piece push-fit components with high levels of initial stability.
Ghouse S, Babu S, van Arkel R, et al., 2017, The influence of laser parameters and scanning strategies on the mechanical properties of a stochastic porous material, Materials & Design, Vol: 131, Pages: 498-508, ISSN: 0261-3069
Additive manufacturing enables architectured porous material design, but 3D-CAD modelling of these materials is prohibitively computationally expensive. This bottleneck can be removed using a line-based representation of porous materials instead, with strut thickness controlled by the supplied laser energy.This study investigated how laser energy and scan strategy affects strut thickness and mechanical strength of porous materials. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing), 2 porous architectures and 2 materials (Titanium, Stainless Steel), with strut thickness, density, modulus, mechanical strength and build time measured.Struts could be built successfully as low as 15° with a minimum diameter of 0.13 mm. Strut thickness was linearly related to the specific enthalpy delivered by the laser to the melt-pool. For a given stiffness, Titanium specimens built at low power/slow speed had a 10% higher strength than those built at high power/fast speed. The opposite was found in Stainless Steel. As specimen stiffness increased, the Contour Strategy produced samples with the highest strength:stiffness and strength:weight ratio. The Points strategy offered the fastest build time, 20% and 100% faster than the Contour and Pulsing strategies, respectively. This work highlights the importance of optimising build parameters to maximize mechanical performance.
Ridzwan M, Sukjamsri C, Pal B, et al., 2017, 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: 1554-527X
Proximal femoral fractures can be categorized into two main types: Neck and intertrochanteric fractures accounting for 53% and 43% of all proximal femoral fractures, respectively. The possibility to predict the type of fracture a specific patient is predisposed to would allow drug and exercise therapies, hip protector design, and prophylactic surgery to be better targeted for this patient rendering fracture preventing strategies more effective. This study hypothesized that the type of fracture is closely related to the patient-specific femoral structure and predictable by finite element (FE) methods. Fourteen femora were DXA scanned, CT scanned, and mechanically tested to fracture. FE-predicted fracture patterns were compared to experimentally observed fracture patterns. Measurements of strain patterns to explain neck and intertrochanteric fracture patterns were performed using a digital volume correlation (DVC) technique and compared to FE-predicted strains and experimentally observed fracture patterns. Although loaded identically, the femora exhibited different fracture types (six neck and eight intertrochanteric fractures). CT-based FE models matched the experimental observations well (86%) demonstrating that the fracture type can be predicted. DVC-measured and FE-predicted strains showed obvious consistency. Neither DXA-based BMD nor any morphologic characteristics such as neck diameter, femoral neck length, or neck shaft angle were associated with fracture type. In conclusion, patient-specific femoral structure correlates with fracture type and FE analyses were able to predict these fracture types. Also, the demonstration of FE and DVC as metrics of the strains in bones may be of substantial clinical value, informing treatment strategies and device selection and design.
van arkel R, Jeffers J, amis A, 2017, Editorial Commentary: Anatomical vandalism of the hip? Hip capsular repair seems a sound adjunct to hip arthroscopic surgery, Arthroscopy-the Journal of Arthroscopic and Related Surgery, Vol: 33, Pages: 314-316, ISSN: 1526-3231
The study “Contribution of the Pubofemoral Ligament to Hip Stability: A Biomechanical Study” by Martin,Khoury, Schröder, Johnson, Gómez-Hoyos, Campos, and Palmer found that cutting the hip capsular ligament allowed alarge increase in femoral internal rotation, particularly in the flexed hip, causing subluxation to occur. In addition toproviding new data on the role of the pubofemoral ligament, it raises the question of whether hip joint surgeons shouldrepair the capsuledwhat are the likely consequences?dand whether any beneficial effects persist in long-term clinicalfollow-ups. For now, hip capsular repair seems a sound adjunct to hip arthroscopic surgery.
van arkel R, Jeffers J, 2016, In vitro hip testing in the International Society of Biomechanics coordinate system, Journal of Biomechanics, Vol: 49, Pages: 4154-4158, ISSN: 1873-2380
Many innovative experiments are designed to answer research questions about hip biomechanics, however many fail to define a coordinate system. This makes comparisons between studies unreliable and is an unnecessary hurdle in extrapolating experimental results to clinical reality. The aim of this studywas to present a specimen mounting protocol which aligns and registers hip specimens in the International Society of Biomechanics (ISB) coordinate system, which is defined by bony landmarks that are identified by palpation of the patient’s body. This would enable direct comparison between experimental testing and clinical gait analysis or radiographic studies. To represent the intact hip, four intact synthetic full-pelves with 8 full-length articulating femora were assembled and digitised to define the ISB coordinate system. Using our proposed protocol, pelvis specimens were bisected into left and right hemi-pelves and femora transected at the mid-shaft, and then mounted in bone pots to represent a typical experimental setup. Anatomical landmarks were re-digitised relative to mechanical features of the bone pots and the misalignment was calculated. The mean misalignment was found to be less than 1.5° flexion/extension, ab/adduction and internal/external rotation for both the pelves and femora; this equates to less than 2.5% of a normal range of hip motion. The proposed specimen mounting protocol provides a simple method to align in vitro hip specimens in the ISB coordinate system which enables improved comparison between laboratory testing and clinical studies. Engineering drawings are provided to allow others to replicate the simple fixtures used in the protocol.
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