Abstract. Background. Progressive muscle ischaemia results in reduced aerobic respiration and increased anaerobic respiration, as cells attempt to survive in a hypoxic environment. Acute compartment syndrome (ACS) is a progressive form of muscle ischaemia that is a surgical emergency resulting in the production of Lactic acid by cells through anaerobic respiration. Our previous research has shown that it is possible to measure H+ ions concentration (pH) as a measure of progressive muscle ischaemia (in vivo) and hypoxia (in vitro). Our aim was to correlate intramuscular pH readings and cell viability techniques with the intramuscular concentration of key metabolic biomarkers [adenosine triphosphate (ATP), Phosphocreatine (PCr), lactate and pyruvate], to assess overall cell health in a hypoxic tissue model. Methods. Nine euthanised Wistar rats were used in a non-circulatory model. A pH catheter was used to measure real-time pH levels from one of the exposed gluteus medius muscles, while muscle biopsies were taken from the contralateral gluteus medius at the start of the experiment and subsequently at every 0.1 of a pH unit decline. The metabolic biomarkers were extracted from the snap frozen muscle biopsies and analyzed with standard fluorimetric method. Another set of biopsies were stained with Hoechst 33342, Ethidium homodimer-1 and Calcein am and imaged with a Zeiss LSM880 confocal microscope. Results. Our study shows that the direct pH electrode readings decrease with time and took an average of 69 minutes to drop to a pH of 6.0. The concentrations of ATP, pyruvate and PCr declined over time, and the concentration of lactate increased over time. At pH 6.0, both ATP and PCr concentrations had decreased by 20% and pyruvate has decreased by 50%, whereas lactate had increased 6-fold. The majority of cells were still viable at a pH of 6.0, suggesting that skeletal muscle cells are remarkably robust to hypoxic insult, although this was a hypoxic model where reperfusion was not possible. Conclusions. Our research suggests that histologically, skeletal muscle cells are remarkably robust to hypoxic insult despite the reduction in the total adenine nucleotide pool, but this may not reflect the full extent of cell injury and quite possibly irreversible injury. The timely restoration of blood flow in theory should halt the hypoxic insult, but late reperfusion results in cellular dysfunction and cell death due to localised free radical formation. Further research investigating the effects of reperfusion in vivo are warranted, as this may identify an optimal time for using pharmacological agents to limit reperfusion injury, around the time of fasciotomy to treat acute compartment syndrome. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

In this work, we propose a new quantitative way of evaluating acute compartment syndrome (ACS) by dynamic mechanical assessment of soft tissue changes. First, we have developed an animal model of ACS to replicate the physiological changes during the condition. Secondly, we have developed a mechanical assessment tool for quantitative pre-clinical assessment of ACS. Our hand-held indentation device provides an accurate method for investigations into the local dynamic mechanical properties of soft tissue and for in-situ non-invasive assessment and monitoring of ACS. Our compartment syndrome model was developed on the cranial tibial and the peroneus tertius muscles of a pig's leg (postmortem). The compartment syndrome pressure values were obtained by injecting blood from the bone through the muscle. To enable ACS assessment by a hand-held indentation device we combined three main components: a load cell, a linear actuator and a 3-axis accelerometer. Dynamic tests were performed at a frequency of 0.5 Hz and by applying an amplitude of 0.5 mm. Another method used to observe the differences in the mechanical properties inside the leg was a 3D Digital Image Correlation (3D-DIC). Videos were taken from two different positions of the pig's leg at different pressure values: 0 mmHg, 15 mmHg and 40 mmHg. Two strains along the x axis (Exx) and y axis (Eyy) were measured. Between the two pressure cases (15 mmHg and 40 mmHg) a clear deformation of the model is visible. In fact, the bigger the pressure, the more visible the increase in strain is. In our animal model, local muscle pressures reached values higher than 40 mmHg, which correlate with observed human physiology in ACS. In our presentation we will share our dynamic indentation results on this model to demonstrate the sensitivity of our measurement techniques. Compartment syndrome is recognised as needing improved clinical management tools. Our approach provides both a model that reflects physiological behaviour of ACS, and a method for in-situ non-invasive assessment and monitoring

Abstract. Objectives. Acute compartment syndrome (ACS) is a progressive form of muscle ischaemia that is a surgical emergency and can have detrimental outcomes for patients if not treated optimally. The current problem is that there is no clear diagnostic threshold for ACS or guidance as to when fasciotomies should be performed. A new diagnostic method(s) is necessary to provide real-time information about the extent of muscle ischaemia in ACS. Given that lactic acid is produced by cells through anaerobic respiration, it may be possible to measure H+ ion concentration and to use this as a measure of ischaemia within muscle. Although we are familiar with the key biochemical metabolites involved in ischaemia; and the use of viability dyes in cell culture to distinguish between living or dead cells is well recognised; research has not been undertaken to correlate the biochemical and histological findings of ischaemia in skeletal muscle biopsies. Our primary aim was to investigate the potential for viability dyes to be used on live skeletal muscle biopsies (explants). Our secondary aim was to correlate the intramuscular pH readings with muscle biopsy viability. Methods. Nine euthanised Wistar rats were used. A pH catheter was inserted into one exposed gluteus medius muscles to record real-time pH levels and muscle biopsies were taken from the contralateral gluteus medius at the start of experiment and subsequently at every 0.1 of pH unit drop. Prior to muscle biopsy, the surface of the gluteus medius was painted with a layer of 50µmol/l Brilliant blue FCF solution to facilitate biopsy orientation. A 4mm punch biopsy tool was used to take biopsies. Each muscle biopsy was placed in a base mould filled with 4% ultra-low melting point agarose. The agarose embedded tissue block was sectioned to generate 400 micron thick tissue slices with a vibratome. The tissue slices were then placed in the staining solution with Hoechst 33342, Ethidium homodimer-1 and Calcein am. The tissue slices were imaged with Zeiss LSM880 confocal microscope's Z stack function. A dead muscle control was created by adding TritonX-100 to other tissue slices. For quantitative analyses, the images were analysed in Image J using the selection tool. This permitted individual cells to be identified and the mean grey value of each channel to be defined. Using the dead control, we were able to identify the threshold value for living cells using the Calcein AM channel. Results. Viability dyes, used primarily for cell cultures, can be used with skeletal muscle explants. Our study also showed that despite a significant reduction in tissue pH concentration over time, that almost 100% of muscle cells were still viable at pH 6.0, suggesting that skeletal muscle cells are robust to hypoxic insult in the absence of reperfusion. Conclusions. Viability dyes can be used on skeletal muscle biopsies. Further research investigating the likely associations between direct measured pH using a pH catheter, the concentrations of key cellular metabolic markers, and muscle tissue histology using vitality dyes in response to ischaemia, rather than hypoxia, is warranted. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction. The BOAST (British Orthopaedic Association Standards for Trauma) guidelines do advise that open pilon fractures amongst other open lower limb fractures need to be treated at a specialist centre with Orthoplastic care. The purpose of this study was to determine clinical outcomes in patients with open pilon fractures treated as per BOAST guidelines including relatively aggressive bone debridement. Methods. A retrospective analysis of a single surgeon series of open pilon fractures treated between 2014 and 2019 was conducted. Injuries were graded according to the Gustillo-Anderson classification and all patients were included for the assessment of the rate of infection and fracture healing. Functional outcome assessment was performed in all patients according to the American Orthopedic Foot and Ankle Score (AOFAS) at 6 months after definitive surgery. Initial wound with bone debridement and application of a spanning external fixator was performed within an average of 13.5 (Range: 3–24) hours. Fixation with FWF (Fine Wire Frame) was performed when the wound was healed, with the mean time from primary surgery to application of FWF being 24.5 (Range: 7–60) days. Results. There was a total of 20 patients including 16 males and 4 females. The mean age was 50.45 (Range: 16–88) years. Follow-up was for an average of 23.2 (Range: 5–51) months. There were 3 patients with Gustilo Type I injuries, 6 with Type II, 4 Type with type IIIa and 7 with Type IIIb injuries. Average time to bone union was 9.3 (Range: 2–18) months. The mean AOFAS score was 66 (Range: 15–97) points. TSF was used on 18 patients, while 2 patients had an Ilizarov frame. A corticotomy was performed on 4 patients with critical bone defect post debridement, while 2 patients had Stimulan beads with antibiotics. There was 1 case (5%) of deep infection and 9 cases (45%) of superficial infection. There were also 2 cases (10%) of non-union which required bone grafting from their femur using a RIA (Reamer Irrigation Aspirator). Other complications included 1 case of acute compartment syndrome, 1 case of pulmonary embolism, 1 case of necrotic skin and 1 case of amputation. Conclusion. Results of our study suggests that the use of staged wound debridement including relatively aggressive bone debridement in conjunction with antibiotics, external fixators and patient tailored conversion from spanning external fixator to fine wire frame achieves low rates of wound infection and complications for patients with open pilon fractures

Significance. Acute compartment syndrome (ACS) occurs after muscle injury and is characterised by increased pressure in the muscle compartment that can result in devastating complications if not diagnosed and treated appropriately. ACS is currently confirmed by repeated needle sticks to measure the compartment pressure using a hand-held compartment pressure monitor. This approach is often not reproducible and is not appropriate for continuous monitoring. To address the shortcomings of currently available technology we are developing an implantable micro-device that will measure compartment pressure directly and continuously over the 24 hours critical period following injury using a radio frequency identification (RFID) platform integrated with a MEMS capacitive pressure sensor. Methods. The prototype implantable device measuring 3mmx3mm consists of a capacitive pressure sensor, a sensor readout circuitry, an antenna and a radio frequency reader. A prototype sensor was packaged in Silicone gel (MED-6640, Nusil Technology LLC) for ex vivo and in vivo testing in three compartment models. First, it was tested ex vivo in an airtight vessel using a blood pressure monitor to pump air and increase the pressure inside the vessel. Second, it was implanted in a muscle compartment of a fresh porcine hind limb and an infusion pump with normal saline was used to raise the tissue pressure. Third, it was implanted in the posterior thigh muscle of a rat where the pressure was increased by applying a tourniquet around the thigh. The readings were compared with those from a hand-held Stryker Intra-compartmental Pressure Monitor System used in the trauma room. Results. The sensor reading from the radio frequency reader software interface in all three models showed good linearity against the pressure applied to the compartment. Conclusion. The successful completion of this project will lead to the development of an implantable miniaturised wireless pressure sensor microsystem capable of measuring tissue compartment pressures in the critical period after traumatic injury and reduce the incidence of serious complications such as severe pain, paralysis, sensory deficits, muscle necrosis and permanent disability