25–40% of unicompartmental knee replacement (UKR) revisions are performed for unexplained pain possibly secondary to elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on cancellous bone strain in a finite element model (FEM) of a cemented fixed bearing medial UKR, validated using previously published acoustic emission data (AE). FEMs of composite tibiae implanted with an all-polyethylene tibial component (AP) and a metal backed one (MB) were created. Polyethylene of thickness 6–10mm in 2mm increments was loaded to a medial load of 2500N. The volume of cancellous bone exposed to <−3000 (pathological overloading) and <−7000 (failure limit) minimum principal (compressive) microstrain (µ∊) and >3000 and >7000 maximum principal (tensile) microstrain was measured. Linear regression analysis showed good correlation between measured AE hits and volume of cancellous bone elements with compressive strain <−3000µ∊: correlation coefficients (R= 0.947, R2 = 0.847), standard error of the estimate (12.6 AE hits) and percentage error (12.5%) (p<0.001). AP implants displayed greater cancellous bone strains than MB implants for all strain variables at all loads. Patterns of strain differed between implants: MB concentrations at the lateral edge; AP concentrations at the keel, peg and at the region of load application. AP implants had 2.2 (10mm) to 3.2 (6mm) times the volume of cancellous bone compressively strained <−7000µ∊ than the MB implants. Altering MB polyethylene insert thickness had no effect. We advocate using caution with all-polyethylene UKR implants especially in large or active patients where loads are higher

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage. Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events. DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads

This article presents a unified clinical theory that links established facts about the physiology of bone and homeostasis, with those involved in the healing of fractures and the development of nonunion. The key to this theory is the concept that the tissue that forms in and around a fracture should be considered a specific functional entity. This ‘bone-healing unit’ produces a physiological response to its biological and mechanical environment, which leads to the normal healing of bone. This tissue responds to mechanical forces and functions according to Wolff’s law, Perren’s strain theory and Frost’s concept of the “mechanostat”. In response to the local mechanical environment, the bone-healing unit normally changes with time, producing different tissues that can tolerate various levels of strain. The normal result is the formation of bone that bridges the fracture – healing by callus. Nonunion occurs when the bone-healing unit fails either due to mechanical or biological problems or a combination of both. In clinical practice, the majority of nonunions are due to mechanical problems with instability, resulting in too much strain at the fracture site. In most nonunions, there is an intact bone-healing unit. We suggest that this maintains its biological potential to heal, but fails to function due to the mechanical conditions. The theory predicts the healing pattern of multifragmentary fractures and the observed morphological characteristics of different nonunions. It suggests that the majority of nonunions will heal if the correct mechanical environment is produced by surgery, without the need for biological adjuncts such as autologous bone graft. Cite this article: Bone Joint J 2016;98-B:884–91

Aim. To investigate the biomechanical behaviours of the TL-Hex & Taylor Spatial Frame (TSF) Hexapod external fixators, with comparison to traditional ring-fixator constructs. Methods. Standardised four-ring TL-Hex and TSF constructs, as well as matched ilizarov threaded-rod constructs for each set of components, were tested alone and mounted with an acrylic bone model with simulated fracture gap using fine-wires. Load-deformation properties for each construct and mode of loading were calculated and analysed statistically using ANOVA. Results and Conclusions. Under axial loading the Ilizarov construct utilising TL-Hex components demonstrated greatest rigidity followed by the TL-Hex Ilizarov using TSF components (p<0.01). Under torsional loading both hexapod frames were seen to be significantly more rigid than the Ilizarov (p<0.01), with the TSF demonstrating greater rigidity than the TL-Hex. Under cantilever bending loads the difference in rigidity seen across all constructs was less marked. When loaded with the bone model both hexapods demonstrated reduced axial rigidity as compared to Ilizarov constructs, but without any appreciable difference in translational shear strain. Under cantilever bending the Ilizarov construct using TL-Hex components p<0.01) demonstrated less translational shear strain than the TSF and TSF using Ilizarov components. In conclusion, both hexapod designs were less rigid axially, but more so under bending and torsional loads, than their Ilizarov construct counterparts, producing greater overall planar shear strain, largely due to the observed “toe-in” laxity. Overall, the TL-Hex was seen to be more rigid that the TSF under bending loads although the difference in shear strain at the fracture site was not significantly different

This international multicentre retrospective cohort study aimed to assess: 1) prevalence of COVID-19 in hip fracture patients, 2) effect on mortality, and 3) clinical factors associated mortality among COVID-19-positive patients. A collaboration among 112 centres in 14 nations collected data on all patients with a hip fracture between 1st March-31st May 2020. Patient, injury and surgical factors were recorded, and outcome measures included admission duration, COVID-19 and 30-day mortality status. There were 7090 patients and 651 (9.2%) were COVID-19-positive. COVID-19 was independently associated with male sex (p=0.001), residential care (p<0.001), inpatient fall (p=0.003), cancer (p=0.009), ASA grade 4–5 (p=0.008; p<0.001), and longer admission (p<0.001). Patients with COVID-19 had a significantly lower chance of 30-day survival versus those without (72.7% versus 92.6%, p<0.001), and COVID-19 was independently associated with increased 30-day mortality risk (p<0.001). Increasing age (p=0.028), male sex (p<0.001), renal (p=0.017) and pulmonary disease (p=0·039) were independently associated with higher 30-day mortality risk in patients with COVID-19 when adjusting for confounders. The prevalence of COVID-19 in hip fracture patients was 9% and was independently associated with a three-fold increased 30-day mortality risk. Clinical factors associated with mortality among COVID-19-positive hip fracture patients were identified for the first time. This is the largest study, and the only global cohort, reporting on the effect of COVID-19 in hip fracture patients. The findings provide a benchmark against which to determine vaccine efficacy in this vulnerable population and are especially important in the context of incomplete vaccination programmes and the emergence of vaccine-resistant strains

Staphylococcus aureus is responsible for 60–70% infections of surgical implants and prostheses in Orthopaedic surgery, costing the NHS £120–200 million per annum. Its ability to develop resistance or tolerance to a diverse range of antimicrobial compounds, threatens to halt routine elective implant surgery. One strategy to overcome this problem is to look beyond traditional antimicrobial drug therapies and investigate other treatment modalities. Biophysical modalities, such as ultrasound, are poorly explored, but preliminary work has shown potential benefit, especially when combined with existing antibiotics. Using a methicillin-sensitive S. aureus reference strain and the dissolvable bead assay, biofilms were challenged by a low-intensity ultrasound (1.5MHz, 30mW/cm2, pulse duration 200µs/1KHz) for 20 minutes and gentamicin. The outcome measures were colony-forming units/mL (CFU/mL) and the minimum biofilm eradication concentration (MBEC) of gentamicin. The mean number of S. aureus within control biofilms was 1.04 × 109 CFU/mL. There was no clinically or statistically significant (p=0.531) reduction in viable S. aureus following ultrasound therapy alone. The MBEC of gentamicin for this S. aureus strain was 256 mg/L. The MBEC of gentamicin with the addition of ultrasound was 64mg/L. Further studies confirmed that the mechanism of action was due to incomplete disruption of the extracellular matrix with subsequent metabolic stimulation of the dormant biofilm-associated bacteria due to increased nutrient availability and oxygen tension. Low intensity pulsed ultrasound was associated with a 4-fold reduction in the effective biofilm eradication concentration of gentamicin; bringing the MBEC of gentamicin to within clinically achievable concentrations

Introduction. Our unit has extensive experience with the use of Ilizarov circular frames for acute fracture and nonunion surgery. We have observed and analysed fracture healing patterns which question the role of relative stability in fracture healing and we offer limb mechanical axis restoration as a more important determinant. Aim. To assess for the presence of external callus, when only relative stability has been achieved but with anatomical restoration of the mechanical axis (ARMA). Methods. We retrospectively reviewed diametaphyseal proximal and distal tibial fractures treated with Ilizarov frame fixation in our unit between 2009 and 2017. We also reviewed cases where the Ilizarov frame technique had been used for complex femoral and humeral non-unions. Radiographs in 4 views were reviewed to assess bone healing, the presence of external callus and correction of lower limb mechanical axis. Results. 45 tibial plateau fractures, 42 distal tibial fractures and 20 humeral and 3 femoral non-unions were reviewed. Where ARMA was achieved, bone healing was observed to occur without external callus. ARMA proved more challenging in the distal tibia and where ARMA was not achieved external callus was visible during fracture healing. Conclusion. ARMA bone healing is reliable and occurs without formation of external callus, despite relative stability. This would suggest that external callus is produced not in response to just the magnitude of strain but also the direction of strain. Restoration of the mechanical axis is an important step in achieving union and needs to be considered when fixing fractures or treating non-unions

Aims

The aim of the present study was to assess the outcomes of the induced membrane technique (IMT) for the management of infected segmental bone defects, and to analyze predictive factors associated with unfavourable outcomes.

Enterococcus faecalis is a rare but recognized cause of prosthetic joint infection. It is notorious for formation of biofilm on prosthetic surfaces. We hypothesized that a ‘serum factor’ was responsible for transformation of E. faecalis from its planktonic form to a biofilm existence upon making contact with prostheses. Using a novel ‘proteomic approach’, we studied the protein expression profiles of this bacterium when grown on an artificial surface in a serum environment against a control. E.faecalis 628 transconjugant formed by conjugation clinical strain (E55) and laboratory strain (JH2-2) was used to inoculate each of rabbit serum (RS) and Brain Heart Infusion (BHI) agar as a control and grown for 24 hours. Proteins were harvested for analysis in fractions including cell surface, membrane and cytosolic proteins. Recovered proteins were separated using 2-dimentional polyacrylamide gel electrophoresis (2D PAGE). Gels were stained and spots of interest harvested. These were analyzed using MALDI mass spectrometry followed by peptide mass fingerprinting using online database searches. Two surface exclusion proteins Sea1 and PrgA were only expressed from the serum culture. These proteins are both encoded by genes very close to the gene for enterococcal aggregation substance PrgB, which plays an integral role in biofilm formation. PrgA and PrgB are both encoded by the prgQ operon and hence expressed simultaneously upon activation of the operon. This tendency for serum only protein expression suggests the possibility of a pheromone-like activator in serum that could be a potential therapeutic target for management of biofilm associated E. faecalis prosthetic infections

Aims

The aim of this study was to describe the current pathways of care for patients with a fracture of the hip in five low- and middle-income countries (LMIC) in South Asia (Nepal and Sri Lanka) and Southeast Asia (Malaysia, Thailand, and the Philippines).

Aims

Due to the recent rapid expansion of scooter sharing companies, there has been a dramatic increase in the number of electric scooter (e-scooter) injuries. Our purpose was to conduct a systematic review to characterize the demographic characteristics, most common injuries, and management of patients injured from electric scooters.

Aims

This is a multicentre, prospective assessment of a proportion of the overall orthopaedic trauma caseload of the UK. It investigates theatre capacity, cancellations, and time to surgery in a group of hospitals that is representative of the wider population. It identifies barriers to effective practice and will inform system improvements.

Osteoinductive bone substitutes are in their developmental infancy and a paucity of effective grafts options persists despite clinical demand. Bone mineral substitutes such as hydroxyapatite cause minimal biological activity when compared to osteoinductive systems present biological growth factors in order to drive bone regeneration. We have previously demonstrated the in-vitro efficacy of a bioengineered system at presenting growth factors at ultra low-doses. This study aimed to translate this growth factor delivery system towards a clinically applicable implant. Osteoinductive surfaces were engineered using plasma polymerisation of poly(ethyl acrylate) onto base materials followed by adsorption of fibronectin protein and subsequently growth factor (BMP-2). Biological activity following ethylene oxide (EO) sterilisation was evaluated using ELISAs targeted against BMP-2, cell differentiation studies and atomic force microscopy. Scaffolds were 3D printed using polycaprolactone/hydroxyapatite composites and mechanically tested using a linear compression models to calculate stress/strain. In-vivo analysis was performed using a critical defect model in 23 mice over an 8 week period. Bone formation was assessed using microCT and histological analysis. Finally, a computer modelling process was developed to convert patient CT images into surface models, then formatted into 3D-printable scaffolds to fill critical defects. Following EO sterilisation, there was no change in scaffold surface and persistent availability of growth factors. Scaffolds showed adequate porosity for cell migration with mechanical stiffness similar to cancellous bone. Finally, the in vivo murine model demonstrated rapid bone formation with evidence of trabecular remodelling in samples presenting growth factors compared to controls

Aims

Hip fracture commonly affects the frailest patients, of whom many are care-dependent, with a disproportionate risk of contracting COVID-19. We examined the impact of COVID-19 infection on hip fracture mortality in England.

Aims

The purpose of this study was to determine the weightbearing practice of operatively managed fragility fractures in the setting of publically funded health services in the UK and Ireland.

Introduction. ACL reconstruction using hamstring tendons has gained general acceptance. However, it has been recommended to seek a tight fit of the tendon in the bone canal in order to provide circumferential contact and healing of the graft, and to prevent secondary tunnel widening. Recent findings show, that the graft dynamically adapts to pressure in the canal resulting in a potentially loose graft-bone contact. It was the goal of this study to understand the viscoelastic behaviour of hamstring grafts under pressure and to develop a new method for tendon pre-conditioning to reduce the graft volume before implantation, in order to reduce the necessary bone canal diameter to accommodate the same graft. Material and Methods. Flexor digitorum tendons of calf and extensor digitorum tendons of adult sheep were identified to be suitable as ACL grafts substitutes for human hamstring tendons in vitro. The effect of different compression forces on dimensions and weight of the grafts were determined. Further, different strain rates (1mm/min vs 10mm/min), compression methods (steady compression vs. creep) and different compression durations(1, 5, 10min) were tested to identify the most effective combination to reduce graft size by preserving its macroscopic structure. Results. The effect of compression on volume reduction (25% of initial volume) reached a plateau at 6000N. Both, steady compression and creeping were able to reduce dimensions of the graft, however, creeping was more effective. There was no difference in effect with different durations for compression (p>0.05) in both methods. With a strain rate of 1mm/min no macroscopic destruction was documented, however with 10mm/min some parts were ruptured. During all pressure tests, considerable amounts of liquid were pressed out from the tendons, and if the graft was submersed in saline solution overnight, the volume reduction was mostly reversible. Conclusion. Compression reduces the dimensions of the ACL graft reversibly, to the greatest part by squeezing out of interstitial water. It is reasonable to assume that this effect also occurs if tendons are under constant pressure in the body, such as at the bend where entering a bone tunnel or under the pressure of interference screws. This in vitro experiment suggests that preconditioning of a 8mm hamstring graft is achieved best by creeping compression with 6kN at a strain rate of 1mm/min. By using this technique, indeed a canal of approximately 10–15% less diameter (i.e. 7 instead of 8mm) may be drilled for the same tendon, resulting in a tight fit of the graft in the bone

Background. Humerus fracture non-union is a challenge for which a wide range of treatments exist. We present our experience of managing these by hybrid Ilizarov frame fixation, without bone graft or debridement of the non-union site. Methods. Case notes review of a consecutive series of 20 patients treated for aseptic humeral non-union between 2004 and 2016. Eighteen patients had previous plate or intramedullary nail fixations, and 2 had no prior surgery. During Ilizarov application, any existing metalwork preventing dynamisation of the fracture site was removed through minimal incisions before compression of the fracture site was then achieved. Only 3 patients had open debridement or osteotomy of the non-union site, otherwise all other patients had no debridement of their non-union. Results. Bony union was achieved in 17 patients (85%), with a further 2 achieving a functional fibrous union. The remaining patient subsequently had successful open surgery. Union rates were 66% (2/3) and 88% (15/17) for the debridement/osteotomy and non-debridement groups respectively. Mean frame duration was 193 days. One patient was treated for pin-site infection. The Chertsey Outcome Score for Trauma was used to assess patient reported outcomes. Conclusions. Simple changes to the physical properties acting upon a humeral non-union, such as adequate control of its strain environment and restoration of the mechanical axis, are enough on their own to initiate healing. In our practice, this eliminates any morbidity associated with extensive fracture debridements or donor harvest sites

Staphylococcus aureus is a highly virulent pathogen and is implicated in approximately 50% of cases of septic arthritis. Studies investigating other S. aureus-related infections have suggested that alpha (Hla), beta (Hlb) and gamma (Hlg) toxins are key virulence factors. In particular, the ‘pore-forming’ alpha toxin is believed to be most potent. In this study, we have assessed the influence of alpha toxin on in situ chondrocyte viability. Osteochondral explants were harvested from the metacarpophalangeal joints of 3-year-old cows and placed into flasks containing Dulbecco's Modified Eagle's Medium. The flasks were then inoculated with the following isogenic ‘knockout’ strains of S. aureus: DU5946 (Hla+Hlb-Hlg-) or DU1090 (Hla-Hlb+Hlg+). The explants were incubated (37°C) and stained after 18, 24 and 40hrs with chloromethylfluorescein di-acetate and propidium iodide, labelling living chondrocytes green and dead cells red, respectively. Axial sections were imaged by confocal microscopy and the percentage cell death obtained using Volocity 4 software. The alpha toxin-producing S. aureus caused rapid cell death, with 24.8+/−3.7% at 18hrs and 44.6+/−7.2% at 24hrs. At 40hrs, there was significantly more chondrocyte death (87.4+/−3.6%; p<0.001) compared to the alpha toxin knockout strain (4.1+/−1.7%; means +/− SEM; n=4). In situ chondrocyte viability was significantly compromised by alpha toxin, with beta and gamma toxins having minimal effect. Further work will clarify the exact mechanism through which this important toxin induces chondrocyte death. Thereafter, it is hoped that targeted treatments can be developed to reduce the extent of cartilage destruction during, and after, an episode of septic arthritis

Introduction. Due to the commercial launch of newly developed ceramic-on-metal (COM) bearings, we compared the deformation and stresses in the liner with ceramic-on-ceramic (COC), metal-on-metal (MOM) as well as ceramic-on-polyethylene (COP) bearings using a finite-element (FE)-model, analyzing a variety of head size and implant position. Liner deformation in terms of change in inner diameter as well as peak stresses were evaluated. Methods. The FE-model consisting of a commercial THR, the proximal femur and a section of the hemipelvis was created based on our previously published approach. Static load and muscle forces were applied according to the maximum load during gait. Polyethylene was modelled using a nonlinear definition with isotropic hardening, cobalt-chromium was modelled elastic-plastic and ceramic was modelled linear-elastic. Validity of the model was checked using an experimental setup with artificial bone and strain gauges located at the rim of the liner. Implant material (COM vs. COC vs. MOM vs. COP), head size (28 mm vs. 36 mm) and cup position (45° inclination/15° anteversion vs. 60° incl./0° antev.) were varied. Results. The experimental validation showed high correlation between strain measurements and FE-results. Liner deformation was evaluated by change in diameter at different levels. Change in head size had a high influence on cup deformation in COM, COC and MOM bearings, most possibly due to decreased liner thickness using bigger heads. Differences in MOM, COC and COM liner deformation were only in sub-micrometer range and not further evaluated. Evaluation of von Mises stress and minimum principal stress showed high differences between the bearing couples, implant positions and head sizes. COM liner stress was less sensitive to the steep cup position, but principal stress amounts were about ten times higher than in polyethylene liners. Thereby, MOM liners developed about 13 % less peak stress than COM. COC liners showed 11 % to 16 % higher stresses than COM. In accordance with published results, bigger head size correlated with lower principal stresses in the liner. Also, bigger heads were less sensitive to steep cup positions. Discussion. Deformation of the liner in total hip replacement has an important influence on lubrication, wear and clinical long-term success. The deformation occurring during intraoperative impaction and press-fit of the metal shell was not included in this study, hence the results are only valid considering the late postoperative phase when the implant is fully integrated in the bone. The FE-analysis showed no significant difference in liner deformation between COM, COC and MOM bearings. However, principal stresses were slightly higher in COM under the same conditions, but lower than COC

Background:. Little is known about the forces carried by the Taylor Spatial Frame (TSF) hexapod fixator. Our aim was to measure the TSF resultant force and how this changed during the consolidation phase. Method:. Five patients undergoing correction of tibial deformities were recruited. Measurements were taken at 2, 4, 8 and 12 weeks post-correction during various activities. Instrumented struts incorporating strain gauges measuring axial force were temporarily used each time. Strut forces and lengths were used to determine frame kinetics. The resultant axial fixator forces and moments were calculated relative to sitting. Ground reaction forces (GRF) were measured using the treadmill force plates. Results & Discussion:. Due to the subjects' varying confidence in weight bearing the forces varied both inter- and intra-activity and over post-corrective time. Variation in individual strut forces produced a resultant force and bending moment across the fixation. As the healing bone assumed more load over time there was a reduction in the force and bending excursions across the frame as a percentage of GRF, achieving a minimum by 8 weeks. Conclusion:. Instrumented TSFs are a useful means of assessing the forces acting during healing. Monitoring of these forces can determine optimal removal