Abstract. Background. Cauda equina syndrome (CES) is a rare serious condition that, if missed at initial presentation, can lead to serious disability. Early diagnosis is crucial for a favourable outcome. Few studies included urodynamic test and measurement of post-void residual urine (PVR) as an adjunct screening tool for acute CES before proceeding to MRI scan, yet there are differences in the cut-off point as a threshold volume to be considered as a red flag for doing MRI amongst these studies. Aim. Meta-analysis and systematic review of literature that included PVR as a predictive tool in CES to identify the reliability of PVR and the optimal numerical value to be considered as red flag. Material & Methods. A comprehensive literature search was undertaken in PubMed, Medline, and Embase databases using our search strategy. Meta-analysis of collated data. Results. A total of seven studies were included with a total of 938 patients. The number of cases suitable for meta-analysis was 714. CES was confirmed in 73. urodynamic testing and PVR diagnosed 86 and excluded 426. The sensitivity of PVR>100ml was 64% (CI 97.5%: 0.44–0.80), specificity 59.2% (CI 97.5%: 0.46 – 0.711), while PVR >200 showed more predictive figures, with sensitivity improved to 83.1% (CI 97.5%: 0.62–0.94) and specificity to 93.5% (CI 97.5%: 0.50–0.99). Conclusions. Urodynamics test is an essential tool in CES assessment. Authors recommend PVR > 200 ml as the numerical cut-off point to be considered as a red flag that if present with other clinical red flags, urgent MRI is recommended in suspected CES

Aims. The diagnosis of periprosthetic joint infection (PJI) can be challenging as the symptoms are similar to other conditions, and the markers used for diagnosis have limited sensitivity and specificity. Recent research has suggested using blood cell ratios, such as platelet-to-volume ratio (PVR) and platelet-to-lymphocyte ratio (PLR), to improve diagnostic accuracy. The aim of the study was to further validate the effectiveness of PVR and PLR in diagnosing PJI. Methods. A retrospective review was conducted to assess the accuracy of different marker combinations for diagnosing chronic PJI. A total of 573 patients were included in the study, of which 124 knees and 122 hips had a diagnosis of chronic PJI. Complete blood count and synovial fluid analysis were collected. Recently published blood cell ratio cut-off points were applied to receiver operating characteristic curves for all markers and combinations. The area under the curve (AUC), sensitivity, specificity, and positive and negative predictive values were calculated. Results. The results of the analysis showed that the combination of ESR, CRP, synovial white blood cell count (Syn. WBC), and polymorphonuclear neutrophil percentage (PMN%) with PVR had the highest AUC of 0.99 for knees, with sensitivity of 97.73% and specificity of 100%. Similarly, for hips, this combination had an AUC of 0.98, sensitivity of 96.15%, and specificity of 100.00%. Conclusion. This study supports the use of PVR calculated from readily available complete blood counts, combined with established markers, to improve the accuracy in diagnosing chronic PJI in both total hip and knee arthroplasties. Cite this article: Bone Jt Open 2023;4(11):881–888

Introduction. Postvoid residualurine (PVR) can be an unknown chronic disorder, but it can also occur after surgery. A pilot-study initiated in Elective Surgery Center, Silkeborg led to collaboration with a urologist to develop a flowchart regarding treatment of PVR. Depending on the severity, men with significant PVR volumes were either recommend follow up by general practitioner or referred to an urologist for further diagnose and/or treatment. Aim: to determine the prevalence of pre- and postoperative PVR in men >65 years undergoing orthopedic surgeries and associated risk factors. Method. A single-center, prospective cohort study. Male patients were consecutively included during one year from April 2022. Data was extracted from the electronic patient files: age, lower urinary tract symptoms (LUTS), co-morbidity (e.g. diabetes), type of surgery and anesthesia, opioid use, pre- and postoperative PVR. Result. 796 participants; 316 knee-, 276 hip-, 26 shoulder arthroplasties and 178 lower back spinal surgeries. 95% (755) were bladder scanned preoperatively. 12% (89) had PVR 150-300ml, and 3% (23) had PVR >300ml. There was a higher risk of preoperative PVR ≥150ml in patients reporting LUTS, OR 1.97(1.28;3.03), having known neurological disease, OR 3.09(1.41;6.74), and the risk increased with higher age, OR 1.08 per year (1.04;1.12). Diabetes and the type of surgery was not associated with higher risk of PVR. 72% (569) had a postoperative bladder scan. 15% (95%CI: 12-19%) (70) patients without PVR preoperatively had PVR ≥150ml postoperatively. Conclusion. Approximately 15% of the men had PVR ≥150ml preoperatively. Neurological disease was the most severe risk factor and secondary if reporting LUTS. As expected, the risk increased with age. Neither diabetes nor the type of surgery was associated with higher risk. 15% of men without preoperative PVR had PVR after surgery. It is not possible to conclude if it is transient or chronic but further studies are ongoing

Introduction. Pixel Value Ratio (PVR) is a radiographic measure of the relative density of the regenerate to the adjacent bone. This has been reported as an objective criterion for regenerate healing and a guide for when to allow full weight bearing (FWB) in lengthening with intramedullary telescopic nails. The threshold for which magnitude of PVR is adequate to allow bearing full weight is not yet agreed. The aim of this study was to identify from our cohort of adult limb lengthening patients the time to FWB following lengthening, the PVR at this point, and how this compared with the recommended values in the literature. Materials and Methods. A retrospective database review identified 30 adult patients treated with the PRECICE femoral nail by two senior authors. Time from completion of lengthening to instruction to fully weight bear was noted. The PVR was calculated for each cortex on plain radiographs taken at each postoperative visit following completion of lengthening. Significance was set at p <0.05. Results. The median age was 30.5 years (IQR 22.5 – 42.5), 19 male and 11 female patients were included. The underlying cause of shortening was post traumatic in 12 (40%) with the remaining due to a wide variety of causes including congenital, infective, and idiopathic leg length discrepancies. Twenty-two nails were antegrade and the mean distance lengthened was 42 mm. Median time from completion of lengthening to full weight bearing was 42 days (IQR 28 – 69). The overall mean PVR at FWB was 0.79. Each surgeon had differing protocols for weightbearing, however there was no statistical difference between time to weight bearing, nor the mean PVR at FWB. There were no implant failures, shortening, or regenerate fractures. Conclusions. We report on our cohort of adult patients treated with intramedullary lengthening nails with a mean PVR of 0.79 at time of full weightbearing. This is considerably lower than the values reported in the literature ranging from 0.90 to 0.93. We therefore suggest that weightbearing following lengthening nails can be permitted earlier than previously reported without an increased risk of complication

Background. Comminuted fractures involving the tibia are associated with a high level of complications including delayed healing and non-union, in conjunction with dramatically increased healthcare costs. Certain clinicians utilise a Pixel Value Ratio (PRV) of 1 to indicate such fracture healing. The subjectivity of this method has led to mixed outcomes including regenerate fracture. The poor prognosis of complex load bearing fractures is accentuated by the fact that no quantitative gold standard currently exists to which clinicians can reference regarding the definition of a healed fracture. The aim of the current study is to use patient specific finite element analysis of complex tibial fractures treated with Ilizarov frames to demonstrate callus maturation and to determine the optimum frame removal time. Methods. 3 patients (2 males, 1 female) were analysed following presentation with complex tibial fractures treated with Ilizarov frames. Patient specific computational analysis was performed according to radiographic data, incorporating maturing material properties to analyse the callus response to weight bearing over the healing timeframe. Computational results were compared to the PVR method to evaluate its efficacy in determining the optimum Ilizarov frame removal time. Results. All fractures were observed to clinically heal at a mean of 25.4 (±2.404) weeks. Following computational analysis however, the mean optimum Ilizarov frame removal time was seen to be 23.5 (±2.323) weeks. When compared with the PVR method, the suggested removal time presented a mean PVR of 1.025 (±0.017). Conclusion. Computational models of patient specific tibial fractures has shown promising correlations with the PVR method and has shown efficacy in predicting callus strength and subsequent optimum frame removal time. Level of Evidence. Level 4

Introduction Polymethylmethacrylate (PMMA) has been widely used in orthopaedic procedures for fixation of joint replacements or enhancing the fixation of implants. However, the use of PMMA has been associated with cardiovascular deterioration and even death. More recently, PMMA has also been used for augmenting osteoporotic vertebral bodies which have fractured or are at risk of fracture. The main complication is PMMA leakage into adjacent structures. Transient hypotension and fatal fat embolism (FE) have also been reported. The pathomechanism of cardiovascular deterioration after the injection of PMMA (i.e. FE) remains a highly controversial subject. The exact role of PMMA in the development of FE remains unclear. The aim of the present study was to elucidate the acute effects of injecting PMMA compared with bone wax into vertebral bodies on the cardiovascular system using an established animal model for vertebroplasty (VP) (Aebli, N, et al. Spine. 2002). Methods In 8 skeletally mature mixed-bred ewes (2–4 years) 6.0ml PMMA (CMW3-Depuy) or bone wax (Bone Wax, Ethicon) were injected unilaterally, through an open approach into the L1 & L2 pedicles. Blood pressure, heart rate, and cardiac output were measured. Results The major difference between the cardiovascular response of the PMMA and that of the bone wax group was the recovery in Pulmonary Artery Pressure (PAP) and Pulmonary Vascular Resistance (PVR). Three minutes post-injection, PAP had fully recovered to baseline values in the wax group. However in the PMMA group, PAP had only recovered by 52% after 3 min and fully recovered after 10 min. Discussion The augmentation of vertebral bodies resulted in transient cardiovascular changes regardless of the material used. However, the recovery of PAP and PVR values took significantly longer with the PMMA group. The peak response was a result of pulmonary vasoconstriction triggered by a reflex reaction to the embolisation of bone marrow particles or by vasoactive cytokines. The peak response was therefore mainly associated with the increase in intraosseous pressure during the augmentation causing release of bone marrow contents into the and not the cement monomer. The cement monomer however plays a role in the cardiovascular complications during FE. The delayed recovery of PAP and PVR in the PMMA group may be due to a vasoconstriction effect of the cement monomer on the pulmonary vascular system. Potentially serious cardiovascular complications may occur during VP regardless of the material used. The injection of PMMA may cause prolonged pulmonary hypertension during vertebro- and also arthroplasty. Continuous invasive cardiovascular monitoring may be required in patients with impaired cardiovascular and pulmonary function

Purpose. There are concerns with regard to the physiological effects of reamed intramedullary femoral fracture stabilisation in patients who have received a pulmonary injury. This large animal study used invasive monitoring techniques to obtain sensitive cardiopulmonary measurements and compared the responses to Early Total Care (reamed intramedullary femoral fracture fixation) to Damage Control Orthopaedics (external fixation), after the induction of acute lung injury. We hypothesised a greater cardiopulmonary response to intramedullary fracture fixation. Method. Acute lung injury (PaO2/FiO2 < 200 mmHg) was induced in 12 invasively monitored and terminally anaesthetised male sheep via the infusion of oleic acid into the right atrium. Each animal underwent surgical femoral osteotomy and fixation with either reamed intramedullary (n=6) or external fixation (n=6). Simultaneous haemodynamic and arterial blood-gas measurements were recorded at baseline and at 5, 30 and 60 minutes after fracture stabilisation. Results. The mean (S.E.) PaO2/FiO2 fell significantly (p<0.05) from 359(37) to 107 (23) and 382 (33) to 128 (18) in the externally fixated and intramedullary nailed groups respectively as a result of the acute lung injury. The further combined effect of surgical osteotomy and subsequent fracture fixation produced a mean (+/− S.E.) PaO2/FiO2 of 114 (21) and 113 (12), in the externally fixated and intramedullary nailed groups respectively, immediately after surgery. This was not significantly different either within or between groups. Similarly the pulmonary vascular resistance (PVR) measured at 4.7 (0.9) and 4.2 (0.5) in the externally fixated and intramedullary nailed groups respectively after lung injury changed to 4.9 (0.7) and 4.3 (0.6) after surgical osteotomy and subsequent fracture fixation which, again was not significantly different either within or between groups. No significant difference in either PaO2/FiO2 or PVR was detected at the monitored 5, 30 and 60 minute intervals that followed fracture stabilisation. Conclusion. Against a background of standardised acute lung injury, there appeared to be no further deterioration produced by the method of isolated femoral fracture fixation in two sensitive physiological parameters commonly used by intensive care physicians

Aims: There are concerns over the physiological effects of intramedullary femoral fracture stabilisation in patients with pulmonary injury. This large animal study used invasive monitoring to obtain sensitive cardiopulmonary measurements and compared the responses of ‘Early Total Care’ (intramedullary fracture fixation) and ‘Damage Control’ (external fixation), after the induction of lung injury. Methods: Acute lung injury (PaO2/FiO2 < 200 mmHg) was induced in 12 invasively monitored and terminally anaesthetised sheep via oleic acid infusion into the right atrium. Each animal underwent surgical femoral osteotomy and fixation with either reamed intramedullary (n=6) or external fixation (n=6). Haemodynamic and arterial blood-gas measurements were recorded at baseline, 5, 30 and 60 minutes after fracture stabilisation. Results: The mean (+/− S.E.) PaO2/FiO2 fell significantly (p< 0.05) from 401 (+/− 39) to 103 (+/− 35) and 425 (+/− 27) to 122 (+/− 21) in the externally fixated and intramedullary nailed groups respectively after acute lung injury. The further combined effect of surgical osteotomy and fracture fixation produced a mean (+/− S.E.) PaO2/FiO2 of 98 (+/− 21) and 114 (+/− 18), in the externally fixated and intramedullary nailed groups immediately after surgery. This was not significantly different within or between groups. Similarly the pulmonary vascular resistance (PVR) measured at 5.8 (+/− 0.8) and 4.8 (+/− 0.7) after lung injury in the externally fixated and intramedullary nailed groups changed to 5.7 (+/− 0.5) and 4.0 (+/− 0.7) after surgical osteotomy and fracture fixation (no significant difference within or between groups). The PaO2/FiO2 or PVR was not significantly different at the monitored 5, 30 and 60 minute intervals after fracture stabilisation. Conclusion: Against a background of standardised acute lung injury, there was no further deterioration produced by the method of isolated femoral fracture fixation in sensitive physiological parameters commonly used during intensive care monitoring