Aims

Prompt and sufficient broad-spectrum empirical antibiotic treatment is key to preventing infection following open tibial fractures. Succeeding co-administration, we dynamically assessed the time for which vancomycin and meropenem concentrations were above relevant epidemiological cut-off (ECOFF) minimal inhibitory concentrations (T > MIC) in tibial compartments for the bacteria most frequently encountered in open fractures. Low and high MIC targets were applied: 1 and 4 µg/ml for vancomycin, and 0.125 and 2 µg/ml for meropenem.

Summary Statement. A porcine model using Yucatan minipigs was found to be very promising for the investigation of healing around transcutaneous osseointegrated implants. Pigs demonstrated surprising agility and adaptability including the ability to ambulate on three legs during the immediate postoperative period. Introduction. Previous non weight-bearing and weight-bearing caprine, canine and ovine models have evaluated design, material, and biological coating variations in an attempt to improve the wound healing and skin-implant seal around transcutaneous osseointegrated implants. Although these models have primarily been used as a window into the application of transcutaneous osseointegrated implants in humans, some important model characteristics affecting wound healing and infection have been missing including: 1) replication of the physiological tissue response, and 2) availability of a transcutaneous site with sufficient soft tissue coverage. Pig skin, like human, is relatively hairless, tightly attached to the subcutaneous tissue, vascularised by a cutaneous blood supply, and healed by means of epithelialization. Swine have been extensively utilised for superficial and deep wound healing studies and can offer ample soft tissue coverage following a lower limb amputation. Development of a porcine model is important for continued understanding and improvement of weight-bearing transcutaneous osseointegration. Methods. Two male Yucatan mini-pigs (9 months, 36kg) were fit with transcutaneous osseointegrated prostheses using a single-stage transtibial amputation and prosthesis implantation procedure. The endo-prosthesis consisted of a cylindrical intraosseous threaded section and a smooth transcutaneous section. The transcutaneous sections were smooth to promote epithelialization and deter direct skin-implant adhesion. The implants were custom manufactured from medical grade Ti-6Al-4V alloy. The exo-prosthesis, consisting of an adjustable length leg and foot, was attached by clamp to the supercutaneous portion of the implant following either one or two days of sling constraint to limit initial weight-bearing. Various exo-prosthesis designs and configurations were trialed. The animals’ behavior and gait were closely observed. Weight-bearing was monitored using a force plate. At 5 and 8 weeks, clinical, microbiological, and histological data were examined to assess wound healing and infection at the skin-bone-implant interface. Results. The pigs demonstrated surprising agility and adaptability. They were able to successfully ambulate on three legs during the post-op period before weight-bearing was permitted. They adapted quickly to changes in exo-prosthesis design, position, and length. Although bacterial colonization was verified, neither of the animals exhibited clinical signs of infection over the respective eight and five week studies. Histological results indicated that there was no skin to implant adhesion but that epithelial growth was progressing towards the implant in one animal. Healing of the transcutaneous wound site showed substantial progress but a definitive skin seal was non-existent at the eight week time point. Discussion/Conclusion. This is likely the first animal model developed, having soft tissue characteristics similar to those found in humans, in which an axially-loaded, weight-bearing implant was successfully used. Results indicated that this porcine model offers many advantages over previous models for the development, evaluation, and comparison of the various techniques being advocated to achieve successful transcutaneous osseointegration in humans. The Yucatan miniature pig's ability to ambulate on three legs during the immediate post-operative period and quickly adjust to changes in the exo-prosthesis design, coupled with their physiological similarity to humans, makes them a valuable model for future studies

Aims. CERAMENT|G is an absorbable gentamicin-loaded biocomposite used as an on-site vehicle of antimicrobials for the treatment of chronic osteomyelitis. The purpose of the present study was to investigate the sole effect of CERAMENT|G, i.e. without additional systemic antimicrobial therapy, in relation to a limited or extensive debridement of osteomyelitis lesions in a porcine model. Methods. Osteomyelitis was induced in nine pigs by inoculation of 10. 4. colony-forming units (CFUs) of Staphylococcus aureus into a drill hole in the right tibia. After one week, the pigs were allocated into three groups. Group A (n = 3) received no treatment during the study period (19 days). Groups B (n = 3) and C (n = 3) received limited or extensive debridement seven days postinoculation, respectively, followed by injection of CERAMENT|G into the bone voids. The pigs were euthanized ten (Group C) and 12 (Group B) days after the intervention. Results. All animals presented confirmatory signs of bone infection post-mortem. The estimated amount of inflammation was substantially greater in Groups A and B compared to Group C. In both Groups B and C, peptide nucleic acid fluorescence in situ hybridization (PNA FISH) of CERAMENT|G and surrounding bone tissue revealed bacteria embedded in an opaque matrix, i.e. within biofilm. In addition, in Group C, the maximal measured post-mortem gentamicin concentrations in CERAMENT|G and surrounding bone tissue samples were 16.6 μg/ml and 6.2 μg/ml, respectively. Conclusion. The present study demonstrates that CERAMENT|G cannot be used as a standalone alternative to extensive debridement or be used without the addition of systemic antimicrobials. Cite this article: Bone Joint Res 2020;9(7):394–401

Aim. To develop a new system for antibacterial coating of joint prosthesis and osteosynthesis material. The new coating system was designed to release gentamicin immediately after insertion to eradicate surgical contamination. Method. Steel implants (2×15mm) were coated with a solid nanocomposite xerogel made from silica and the dendritic polymer, hyperbranched polyethyleneimine. The xerogel was anchored inside a porous surface made by pre-coating with titanium microspheres. Finally, gentamicin was encapsulated in the xerogel, i.e. no chemical binding. A total of 50 µg gentamicin was captured into each implant. The efficacy of the new coating was evaluated in a porcine model of implant associated osteomyelitis. In total, 30 female pigs were randomized into 3 study groups (n=10). Group A; plain implants + saline, Group B; plain implants + 10. 4. CFU of Staphylococcus aureus, and Group C; coated implants + 10. 4. CFU of S. aureus. Implant + inoculum was placed into a pre-drilled implant cavity of the right tibia and the pig was euthanized 5 days afterwards. Postmortem microbiology and pathology were performed. Two additional pigs were used in a pharmacokinetic study where microdialysis (MD) catheters were placed alongside coated implants. Extracellular fluid was sampled regularly for 24 hours from the MD catheters and analyzed for gentamicin content. Results. Within Groups A and C, all implants were found sterile by sonication and bacteria could not be identified within the surrounding bone tissue. In contrast, all Group B animals had S. aureus positive implant and tissue microbiology. Macroscopic and microscopic pathological examinations confirmed that Group A and C animals were complete identic, i.e. no pus around implants and only minor peri-implant inflammation related to insertion of implants per se. All Group B animals had pus around their implants and a massive peri-implant inflammatory response dominated by neutrophil granulocytes. Maximum gentamicin release (35 µg /mL) was measured in the first obtained MD sample, i.e. after 30 min, and the concentration stayed above the MIC level for the used S. aureus strain for 8 hours. Conclusions. The new xerogel coating prevented development of osteomyelitis. Prevention was due to a fast gentamicin release immediately following insertion and antimicrobial active concentrations were detectable several hours after implantation. This means that the critical time point of most relevant surgical procedures potentially could be protected by the novel coating. The new coating will be investigated on larger scale implants and full-size prosthesis in the future

Background. Systemically administered vancomycin may provide insufficient target-site concentrations. Intraosseous vancomycin administration has the potential to overcome this concern by providing high target-site concentrations. Aim. To evaluate the local bone and tissue concentrations following tibial intraosseous vancomycin administration in a porcine model. Method. Eight female pigs were assigned to receive 500 mg diluted vancomycin (50 mg/mL) through an intraosseous cannula into the proximal tibial cancellous bone. Microdialysis was applied for sampling of vancomycin concentrations in tibial cancellous bone adjacent to the intraosseous cannula, in cortical bone, in the intramedullary canal of the diaphysis, in the synovial fluid of the knee joint, and in the subcutaneous tissue. Plasma samples were obtained. Samples were collected for 12 hours. Results. High vancomycin concentrations were found in the tibial cancellous bone with a mean peak drug concentration of 1,236 (range 28–5,295) µg/mL, which remained high throughout the sampling period with a mean end concentration of 278 (range 2.7–1,362.7) µg/mL after 690 min. The mean (standard derivation (SD)) peak drug concentration in plasma was 19 (2) µg/mL, which was obtained immediately after administration. For the intramedullary canal, in the synovial fluid of the knee joint, and subcutaneous tissue, comparable mean peak drug concentration and mean time to peak drug concentration were found in the range of 7.5–8.2 µg/mL and 45–70 min, respectively. Conclusions. Tibial intraosseous administration of vancomycin provided high mean concentrations in tibial cancellous bone throughout a 12-hour period, but with an immediate and high systemic absorption. The concentrations in cancellous bone had an unpredictable and wide range of peak concentration. Low mean concentrations were found in all the remaining compartments. Our findings suggest that intraosseous vancomycin administration in proximal tibial cancellous bone only is relevant as treatment in cases requiring high local concentrations nearby the intraosseous cannula

Aim. This study investigated if co-administration of rifampicin with moxifloxacin led to a decrease in moxifloxacin concentrations in relevant tissues in a porcine model of implant-associated osteomyelitis caused S. aureus. Pharmacokinetics were measured using microdialysis and treatment effect was measured by quantifying bacterial load from implant and periprosthetic bone following a 1-stage revision and antibiotics. Method. 15 female pigs received a stainless-steel implant in the right proximal tibia and were randomized into two groups. Infection was introduced by inoculating the implant with Staphylococcus aureus as previously described. 1. On day 7 post surgery, all pigs were revised with implant removal, debridement of implant cavity and insertion of a sterile implant. 7 days of treatment was then initiated with either moxifloxacin 400 mg iv q.d. (M) or moxifloxacin and rifampicin 450 mg iv b.i.d. (RM). At day 14, animals were sedated and microdialysis was applied for continuous sampling of moxifloxacin concentrations during 8 h in five compartments: the implant cavity, cancellous bone in both the infected and non-infected proximal tibia, and adjacent subcutaneous tissue on both the infected and non-infected side using a previously described setup. 2. Venous blood samples were collected. Implant and adjacent bone were removed for analysis. Results. Comparable cure rates (sterilization of both implant and bone) were observed with 5/8 pigs in the RM group compared to 3/7 in the M group, p= 0.62 (Fisher's exact test). Due to the small number of samples with growth, median log CFU/ml was 0 for implant and bones in both groups. AUC. 0-last. was significantly smaller in plasma for the RM group, 407; 315 – 499 min µg/mL vs 625; 536 – 724 min µg/mL (mean;95% CI), p= 0.002 (Student's t-test). For the implant cavity, there was a trend toward a lower AUC. 0-last. 425; 327 – 524 min µg/ml vs 297; 205 – 389 min µg/ml in the RM group compared to M, yet this difference was not statistically different, p = 0.06. For the other compartments for other parameters (C. max. and T. max. ) across all compartments, there was no difference. Conclusions. While the AUC. 0-last. was lower in plasma for animals treated with RM, both the concentrations at the site of infection and treatment outcomes were comparable between groups

Aim. Local treatment with gentamicin may be an important tool in the prevention and treatment of surgical site infections in high-risk procedures and patients. The aim of this study was to evaluate the pharmacokinetic profile of gentamicin in bone and surrounding tissue, released from a controlled application of a GentaColl sponge in a porcine model. Method. In 8 female pigs, a GentaColl sponge of 10×10 cm (1.3 mg gentamicin/cm. 2. ) was placed in a cancellous bone cavity in the proximal tibia. Microdialysis was used for sampling of gentamicin concentrations over 48 hours from the cavity with the implanted GentaColl sponge, cancellous bone parallel to the cavity over and under the epiphyseal plate, cortical bone, the intramedullary canal, subcutaneous tissue, and the joint cavity of the knee. Venous blood samples were obtained as reference. Results. The main finding was a mean peak drug concentration (95-CI) of gentamicin in the cancellous bone cavity containing the implanted GentaColl sponge of 11,315 (9,049–13,581) μg/ml, persisting above 1000 μg/ml until approximately 40 hours after application. Moreover, the concentrations were low (< 1 μg/ml) in the surrounding tissues as well as in plasma. Conclusions. The mean peak gentamicin concentration from the cancellous bone cavity after a controlled application of a GentaColl sponge was high and may be adequate for the prevention of biofilm formation. However, high MIC strains and uncontrolled application of the GentaColl sponge may jeopardize this conclusion

Aims: To investigate the optimal dimension interference screw for fixation of a tendon graft in a bone tunnel. Methods: A porcine model was developed to represent ACL reconstruction in the distal femur. A standard 8mm size pig flexor tendon graft was inserted into a standard 8mm bone tunnel. The screw dimensions were varied. The tendon was loaded with a constant force using a Universal Testing Machine. The construct was tested to failure at a rate of 50mm/minute. Load, deformation data and mechanism of construct failure were recorded. The screw diameters of 7, 8 and 9mm and lengths of 20, 25 and 30mm were tested in 80 individual reconstructions. Results: The mean pull out force was similar between the 7mm (191N) and 8mm screws (188N), but significantly different for the 9mm screw (109N) (p< 0.05) The 30mm screw (231N) was marginally better than the 20mm screw (215N) (p> 0.05). The mechanism of failure however, was significantly different between the groups. All grafts fixed with a 9mm screw failed at the tunnel opening (100%), whereas those fixed with a 7mm screw failed by slippage of the graft along the length of the tunnel (83%). The screw length did not affect the mechanism of graft failure. Conclusion: Our results suggest that a screw size equal to or 1mm less than the diameter of the tunnel gives the optimum initial interference screw fixation of tendon in a bone tunnel

To evaluate the effectiveness of Pulsed-Lavage and of Versajet-hydrosurgery in removing two Staphylococcus aureus strains from porcine tissue and graphite powder from simulated fractures. Overnight broth cultures (NCTC-6571) and S.aureus strains were diluted to yield inocula containing 1x103c. f.u. ml-1. Initially 8 porcine legs were used; porcine tissues were inoculated with 10ml of either of the two S.aureus strains. Control tissues were inoculated with PBS. All inoculated samples were irrigated with 300ml of saline using the pulsed-lavage system or using the Versajet. 10ml of each of the following were plated out in triplicate:. inoculum pre-incubation. inoculum post-incubation,. each left over inoculum following removal of tissue and dilutions of 10-1 and 10-2 and. Wash from all samples. Eight additional porcine legs were used where 2 incisions were made down to bone in a cross-hatch pattern. 1g of graphite powder was infiltrated into each fracture site to simulate a contaminated open fracture. Each fracture site was irrigated with 500ml saline through pulsed-lavage or Versajet. The average microbiological reduction using Pulsed-Lavage or Versajet was 2% and 15% respectively. The clinical S.aureus strain was more adherent than the laboratory strain. The Versajet maintained a 12–16% reduction of S.aureus, whereas pulsed-lavage did not reduce contamination. The number of graphite particles was significantly reduced with the use of the Versajet system compared with the pulsed-lavage. Versajet system was more effective in removal of foreign particles and more effectively reduced the micro-biological load of both examined S.aureus strains in a porcine model. Further studies are indicated to evaluate the efficacy of this system in clinical practice

Articular cartilage repair is assumed to improve by covering the cartilage lesion with a biomaterial scaffold tailored to the specific requirements of the weight-bearing joint surface. We have tested the feasibility of a novel composite collagen-polylactide scaffold rhCo-PLA in cartilage repair. To confirm these results and further challenge the scaffold, we tested it in a large porcine cartilage defect. A critical-sized full-thickness chondral defect was made in the medial femoral condyle of 18 domestic pigs. This technically widest possible defect size of 11×17 mm was determined in a pilot test. Five weeks later, the defect was either treated with the novel rhCo-PLA scaffold or left untreated to heal spontaneously. After four months, the medial condyles were evaluated macroscopically using Goebel's score, in which the worst possible result receives a total of 20 points and imaged with µCT to evaluate subchondral bone. Macroscopic score and subchondral bone microstructure were similar in both study groups. The total Goebel score was higher in spontaneous group (9.75±3.9 for spontaneous and 9.1±3.7 for rhCo-PLA, respectively) but differences between individual animals were large. Subchondral bone volume fraction was 48.2±3.6% for rhCo-PLA and 44.2±3.4% for spontaneous. Trabecular thickness was greater in operated joints (207.9±18.8 µm for spontaneous and 242.9±32.9 µm for rhCo-PLA) than in contralateral non-operated joints (193.3±15.1 µm and 213.4±33.2 µm, respectively). These preliminary data demonstrate that individual differences in the macroscopic appearance were large but there were no significant differences between the two study groups in the score or subchondral bone structure.

Back pain is a significant socio-economic problem affecting around 80% of the population at some point during their lives. Chronic back pain leads to millions of days of work absence per year, posing a burden to health services around the world. In order to assess surgical interventions, such as disc replacements and spinal instrumentations, to treat chronic back pain it is important to understand the biomechanics of the spine and the intervertebral disc (IVD). A wide range of testing protocols, machines and parameters are employed to characterise the IVD, making it difficult to compare data across laboratories.

The aim of this study was to compare the two most commonly used testing protocols in the literature: the stiffness and the flexibility protocols, and determine if they produce the same data when testing porcine specimens in six degrees of freedom under the same testing conditions. In theory, the stiffness and the flexibility protocols should produce equivalent data, however, no detailed comparison study is available in the literature for the IVD, which is a very complex composite structure.

Tests were performed using the unique six axis simulator at the University of Bath on twelve porcine lumbar functional spinal unit (FSU) specimens at 0.1 Hz under 400 N preload. The specimens were divided in two groups of six and each group was tested using one of the two testing protocols. To ensure the same conditions were used, tests were firstly carried out using the stiffness protocol, and the equivalent loading amplitudes were then applied using the flexibility protocol.

The results from the two protocols were analysed to produce load-displacement graphs and stiffness matrices. The load-displacement graphs of the translational axes show that the stiffness protocol produces less spread between specimens than the flexibility protocol. However, for the rotational axes there is a large variability between specimens in both protocols. Additionally, a comparison was made between the six main diagonal terms of the stiffness matrices using the Mann-Whitney test, since the data was not normally distributed. No statistically significant difference was found between the stiffness terms produced by each protocol. However, overall the stiffness protocol generally produced larger stiffnesses and less variation between specimens.

This study has shown that when testing porcine FSU specimens at 0.1 Hz and 400 N preload, there is no statistically significant difference between the main diagonal stiffness terms produced by the stiffness and the flexibility protocols. This is an important result, because it means that at this specific testing condition, using the same testing parameters and environment, both the stiffness and flexibility methods can be used to characterise the behaviour of the spine, and the results can be compared across the two protocols. Future work should investigate if the same findings occur at other testing conditions.

Linear spinal cord distraction, in animal models, leads to elevated intra-compartmental spinal cord pressure. We developed an in vitro model of distraction, with increasing tensile force, to demonstrate the relationship between the degree of spinal curvature and the proportional elevation of intra-compartmental pressure.

Six Porcine spinal sections, two cervical, two thoracic, and two lumbar were harvested from 30kg pigs. These cord sections were individually stretched in a saline solution with increasing tensile force applied. Cord interstitial pressure (CIP) was monitored with an arterial line pressure monitor. The sections were each tested six times fresh, and then thawed and tested an additional six times. An additional ten freshly thawed cords were tested in linear distraction and over forty-five degree and ninety degree curved surfaces with CIP monitoring.

Increased tension, by adding increasing weights of distraction, lead to a proportionally elevated CIP in the linear model (R=0.986). We achieved a 99% confidence interval via paired T testing to demonstrate that there was no significant difference between fresh specimens and recently thawed cords. As the degree of spinal curvature increased from a linear model, to a forty-five and ninety degree (cobb) curve, there were significant increases in CIP at the same distraction force. The more significant the curve, the greater the CIP for each increment in distraction force; ninety degree curves produced a 2.3x higher pressure than linear distraction.

High cord interstitial pressure (CIP) can be achieved through spinal cord distraction (> 140mm Hg). This CIP is no only directly proportional to tension, but also proportionally magnified by the degree of spinal curvature. It is not affected by freezing/thawing. This may suggest that spinal cord compartment syndrome is a potential mechanism for spinal cord distraction injury, and these distraction pressures are potentially magnified in the setting of scoliosis.

Introduction: The aetiology of scoliosis is not known. Many different mechanisms have been suggested as playing a part in the development. Dysfunction of the segmental paravertebral muscles have been suggested to have some impact on the condition. It is known that the injection of botulinum toxin type B will paralyse muscles by blocking of the motor endplate. The effect has been shown to last up to three months. The experiment was designed to study if segmental muscles in the thoracic region of the spine in pigs play a role in the development of the spine.

Materials and Methods: Six seven days old piglets were used in the experiment. In the lower thoracic region in three levels on the left side the paraspinal muscles were infiltrated with botulinum toxin type B. It was used 10 units of Botox® on each level, a total of 30 units were used on each animal. It was taken care to infiltrate the different small muscles as the toxin does not spread readily to adjacent muscles. The pigs were then left for normal care and development. They all were assessed at four weeks intervals until they were sacrificed three months after initial injection. x-ray were then taken of the spine.

Results: During the follow-up there were no visible changes in the alignment of the spine. The piglets developed normally. On x-ray there were no signs of developmental disturbances and we did not see any signs of scoliotic development. If anything, there was the development of a long curvature in the thoracic spine. On examination there was clear atrophy of the segmental muscles in the injected regions.

Discussion: This experiment suggests that the development of the spine is not guided by either the presence or absence of muscle activation. The dose of Botox® applied to these small muscles should be more than adequate to stop nearly all muscle activity. The pig has a rapid growth period from seven days to three months. Any changes caused by muscle activation should have been detected in this period. It could be that the effect on fast growing animals is shorter than three months. Nevertheless we still saw muscle atrophy at time of sacrifice.

Aim

Prompt and sufficient broad spectrum empirical antibiotic treatment is key to prevent infection following open tibial fractures. Succeeding co-administration, we dynamically assessed the time for which vancomycin and meropenem concentrations were above relevant epidemiological cut-off minimal inhibitory concentrations (T>MIC) in tibial compartments for the bacteria most frequently encountered in open fractures. Low and high MIC-targets were applied: 1 and 4 µg/mL for vancomycin and 0.125 and 2 µg/mL for meropenem.

Introduction: Flexor tendon repair in zone 2 has a high re-rupture rate. Various pulleyplasties were described to reduce gliding resistance. In an experimental study on pig trotters, we performed pulleyplasty by meshing alike split skin graft and determined its effect on breaking strength and gliding resistance of repaired tendon.

Method: Phase 1: Two pairs of middle pulley of the same pig were pulled apart from bone on Universal testing machine. One of each pair were meshed (10 rows of 1mm slits 2 mms apart longitudinally).

Phase 2: The two ends of two repaired flexor tendons were attached to a tension load cell each. The proximal end load cell was connected to Universal testing machine. Gliding resistance was measured under saline before and after meshing.

Phase 3: The test was repeated on 4 specimens using a digital load scale. Ten observations of peak resistance were obtained each with normal pulley, meshed pulley, after edge tying of the pulley.

Results: Breaking strengths were 162 and 59 N in one pair and 89 and 50 N in another. The pulleys became 1.5 – 4 times stretchable.

Meshing increased the gliding resistance by approximately 20% and 30% in phase 2 and 3 respectively. Edge tying decreased the gliding resistance by 27% below that of normal pulley

Discussion and Conclusion: Meshing weakens significantly but breaking strength stayed above 50 N, which is more than average breaking strength of a tendon repair (30N, Norris et al). Meshed pulley were dragged farther and preventing it by edge tying decreased the gliding resistance.

No animal was killed for the study.

Percutaneous Radiofrequency Ablation (RFA) has become the method of choice in the treatment of a wide spectrum of disorders. It was introduced for the treatment of Trigeminal Neuralgia and has since been used both extensively and successfully in the treatment of this disorder. Over the past two decades it has been advocated in the treatment of hepatic metastases, lung tumours and cerebral tumours. In 1992 Rosenthal et al reported using this procedure for the treatment of Osteoid Osteomas with good outcome. Further case series have supported this modality of treatment. However, the biomechanical effects of RFA on cortical bone have not been reported to date.

The study comprised of 16 large white land-raised male pigs. All were between 70–80kg in weight at the time of treatment. RFA was performed on the femur, tibia and humerus of each animal 24 hours, 1 week and 4 weeks before euthanisation. RFA was carried out via a percutaneous technique under fluoroscopic guidance. The fibula was not treated in each case and used as an intrinsic control to account for inter-group variability. The Modulus of Rigidity, Maximum Torsional Strength of all bones were determined and compared.

There were three pathological fractures, all occurring in the hemerii and all occurring at 4 weeks post treatment. The Modulus of Rigidity and Maximum Torsional strength were significantly reduced at 24 hours and 1 week when compared with the control. However in the 4 weeks group the biomechanical strength of cortical bone was not significantly different and had almost returned to normal which is contradictory to the clinical setting. There was no significant difference at 24 hours and 1 week.

RFA has become well established as the method of choice for the treatment of Osteoid Osteomas, however the biomechanical consequences of this procedure have not been reported to date. The torsional strength of RF ablated cortical bone is severely attenuated after 1 week, 40% reduction in torsional strength when compared with the control group. This study demonstrated that RFA of cortical bone is an effective treatment for cortical lesions however the biomechanical weakness promotes the need for weight-bearing restrictions when managing these patients postoperatively.

A pre-clinical experimental simulation model has been previously successfully developed, and was shown to have the potential for investigation of the biomechanical and tribological performance of early stage knee therapies. In order to investigate interventions that may necessitate sacrifice of the natural ligaments, it is necessary to replicate their function. This study investigated the most effective spring constraint conditions for the porcine knee model with the aim of replicating the natural ligament function. The replication of natural ligament function was achieved through the use of physical springs in the anterior-posterior (AP) axis. Spring-9 (9 N/mm) and spring-20 (20 N/mm) were set at different free lengths in a natural knee simulator. The A/P displacement and shear force outputs from porcine knee samples (N=6) were measured and the most appropriate spring setting was determined by comparing the outputs at different spring settings with intact knee. The A/P displacement of both spring-9 and spring-20 showed similar shapes to the all ligament control. Spring-9 with a free length of 4 mm and spring-20 with a free length of 5 mm showed minimal differences in A/P displacement output compared to the all ligament controls. There was no statistical difference between the two minimal differences either in A/P displacement or in shear force (paired t-test, p>0.05), which indicated that both conditions were appropriate spring constraint settings for the natural porcine knee model. A porcine knee simulation model with refined spring constraint conditions was successfully developed in this study. Human knee model is currently under investigation using the methodology developed in porcine knee model, which will be more appropriate to investigate the effect of early stage knee therapies on the tribological function of the natural knee

Aims. This study aimed to establish the optimal fixation methods for calcaneal tuberosity avulsion fractures with different fragment thicknesses in a porcine model. Methods. A total of 36 porcine calcanea were sawed to create simple avulsion fractures with three different fragment thicknesses (5, 10, and 15 mm). They were randomly fixed with either two suture anchors or one headless screw. Load-to-failure and cyclic loading tension tests were performed for the biomechanical analysis. Results. This biomechanical study predicts that headless screw fixation is a better option if fragment thickness is over 15 mm in terms of the comparable peak failure load to suture anchor fixation (headless screw: 432.55 N (SD 62.25); suture anchor: 446.58 N (SD 84.97)), and less fracture fragment displacement after cyclic loading (headless screw: 3.94 N (SD 1.76); suture anchor: 8.68 N (SD 1.84)). Given that the fragment thickness is less than 10 mm, suture anchor fixation is a safer option. Conclusion. Fracture fragment thickness helps in making the decision of either using headless screw or suture anchor fixation in treating calcaneal tuberosity avulsion fracture, based on the regression models of our study. Cite this article: Bone Joint Res 2023;12(8):504–511

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of a technique of anterior cruciate ligament (ACL) reconstruction using the Soffix polyester fixation device. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent bio-mechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts.

Method: Ten stifle joints were obtained from 5 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon-Soffix graft was used to reconstruct the ACL of the porcine knee using over the top femoral placement with bicortical screw fixation. Mechanical testing of 10 specimens was performed.

Results: The mode of failure included 4 midsubstance tendon failures, 3 Soffix failures and 3 failures at the suture-Soffix interface. The mean ultimate tensile load for the ACL reconstruction was 1360 N (standard deviation (SD) =354), elongation to failure of 41 mm (SD=7.5) and a structural stiffness of 35 N/mm (SD=8.1).

Conclusion: This in vitro study has shown that the technique of ACL reconstruction using the Soffix soft tissue fixation device with a tendon graft placed in the over the top position is biomechanically strong, providing a sufficiently high UTL immediately following reconstruction, therefore allowing early weight bearing and rehabilitation.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of a technique of anterior cruciate ligament (ACL) reconstruction using the Soffix polyester fixation device. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent bio-mechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts.

Method: Ten stifle joints were obtained from 5 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon-Soffix graft was used to reconstruct the ACL of the porcine knee using over the top femoral placement with bicortical screw fixation. Mechanical testing of 10 specimens was performed.

Results: The mode of failure included 4 midsubstance tendon failures, 3 Soffix failures and 3 failures at the suture-Soffix interface. The mean ultimate tensile load for the ACL reconstruction was 1360 N (standard deviation (SD) =354), elongation to failure of 41 mm (SD=7.5) and a structural stiffness of 35 N/mm (SD=8.1).

Conclusion: This in vitro study has shown that the technique of ACL reconstruction using the Soffix soft tissue fixation device with a tendon graft placed in the over the top position is biomechanically strong, providing a sufficiently high UTL immediately following reconstruction, therefore allowing early weight bearing and rehabilitation.