Aims. The sensitivity and specificity of electrodiagnostic parameters in diagnosing carpal tunnel syndrome (CTS) have been reported differently, and this study aims to address this gap. Methods. This case-control study was conducted on 57 cases with CTS and 58 controls without complaints, such as pain or paresthesia on the median nerve. The main assessed electrodiagnostic parameters were terminal latency index (TLI), residual latency (RL), median ulnar F-wave latency difference (FdifMU), and median sensory latency-ulnar motor latency difference (MSUMLD). Results. The mean age in cases and controls were 50.7 years (SD 9.9) and 47.9 years (SD 12.1), respectively. The CTS severity was mild in 20 patients (34.4%), moderate in 19 patients (32.8%), and severe in 19 patients (32.8%). The sensitivity and specificity of the electrodiagnostic parameters in diagnosing CTS were as follows: TLI 75.4% and 87.8%; RL 85.9% and 82.5%; FdifMU 87.9% and 82.9%; and MSUMLD 94.8% and 60.0%, respectively. Conclusion. Our findings indicated that electrodiagnostic parameters are significantly associated with the clinical manifestation of CTS, and are associated with high diagnostic accuracy in CTS diagnosis. However, further studies are required to highlight the role of electrodiagnostic parameters and their combination in CTS detection. Cite this article: Bone Jt Open 2024;5(10):898–903

Plasma levels of cobalt and chromium ions and Metal Artefact Reduction Sequence (MARS)-MRI scans were performed on patients with 209 consecutive, unilateral, symptomatic metal-on-metal (MoM) hip arthroplasties. There was wide variation in plasma cobalt and chromium levels, and MARS-MRI scans were positive for adverse reaction to metal debris (ARMD) in 84 hips (40%). There was a significant difference in the median plasma cobalt and chromium levels between those with positive and negative MARS-MRI scans (p < 0.001). Compared with MARS-MRI as the potential reference standard for the diagnosis of ARMD, the sensitivity of metal ion analysis for cobalt or chromium with a cut-off of > 7 µg/l was 57%. The specificity was 65%, positive predictive value was 52% and the negative predictive value was 69% in symptomatic patients. A lowered threshold of > 3.5 µg/l for cobalt and chromium ion levels improved the sensitivity and negative predictive value to 86% and 74% but at the expense of specificity (27%) and positive predictive value (44%). Metal ion analysis is not recommended as a sole indirect screening test in the surveillance of symptomatic patients with a MoM arthroplasty. The investigating clinicians should have a low threshold for obtaining cross-sectional imaging in these patients, even in the presence of low plasma metal ion levels

Aims. The modified Radiological Union Scale for Tibia (mRUST) fractures score was developed in order to assess progress to union and define a numerical assessment of fracture healing of metadiaphyseal fractures. This score has been shown to be valuable in predicting radiological union; however, there is no information on the sensitivity, specificity, and accuracy of this index for various cut-off scores. The aim of this study is to evaluate sensitivity, specificity, accuracy, and cut-off points of the mRUST score for the diagnosis of metadiaphyseal fractures healing. Methods. A cohort of 146 distal femur fractures were retrospectively identified at our institution. After excluding AO/OTA type B fractures, nonunions, follow-up less than 12 weeks, and patients aged less than 16 years, 104 sets of radiographs were included for analysis. Anteroposterior and lateral femur radiographs at six weeks, 12 weeks, 24 weeks, and final follow-up were separately scored by three surgeons using the mRUST score. The sensitivity and specificity of mean mRUST score were calculated using clinical and further radiological findings as a gold standard for ultimate fracture healing. A receiver operating characteristic curve was also performed to determine the cut-off points at each time point. Results. The mean mRUST score of ten at 24 weeks revealed a 91.9% sensitivity, 100% specificity, and 92.6% accuracy of predicting ultimate fracture healing. A cut-off point of 13 points revealed 41.9% sensitivity, 100% specificity, and 46.9% accuracy at the same time point. Conclusion. The mRUST score of ten points at 24 weeks can be used as a viable screening method with the highest sensitivity, specificity, and accuracy for healing of metadiaphyseal femur fractures. However, the cut-off point of 13 increases the specificity to 100%, but decreases sensitivity. Furthermore, the mRUST score should not be used at six weeks, as results show an inability to accurately predict eventual fracture healing at this time point. Cite this article: Bone Jt Open 2021;2(10):796–805

16 to 34% of the population suffer from shoulder pain, the most common cause being rotator cuff tears. NICE guidance recommends using ultrasound scan (USS) or MRI to assess these patients, but does not specify which is preferable. This study assesses the accuracy of USS and MRI in rotator cuff tears in a DGH, to establish the most appropriate imaging modality. Patients who had at least two of shoulder ultrasound, MRI or arthroscopy within a seven month period (n=55) were included in this retrospective study. Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) were calculated using arthroscopy as the true result, and kappa coefficients calculated for each pairing. 59 comparisons were made in total. Sensitivity for MRI in full supraspinatus tears was 0.83, and for USS 0.75. Specificity for MRI in these tears was 0.75, and for USS 0.83. Values were much lower in other tears, which occurred less frequently. USS and MRI completely agreed with each other 61.3% of the time. Both modalities were only completely accurate 50% of the time. Kappa coefficient between arthroscopy and MRI for supraspinatus tears was 0.658, and for USS was 0.615. There was no statistical difference between MRI and USS sensitivity or specificity (p=1), suggesting that one modality cannot be recommended over the other for full supraspinatus tears. They also do not tend to corroborate one another, suggesting that there is no benefit from doing both scans. Further research is needed to see how both modalities can be improved to increase their accuracy

Variations in component positioning of total hip replacements can lead to edge loading of the liner, and potentially affect device longevity. These effects are evaluated using ISO 14242:4 edge loading test results in a dynamic system. Mediolateral translation of one of the components during testing is caused by a compressed spring, and therefore the kinematics will depend on the spring stiffness and damping coefficient, and the mass of the translating component and fixture. This study aims to describe the sensitivity of the liner plastic strain to these variables, to better understand how tests using different simulator designs might produce different amounts of liner rim deformation. A dynamic explicit deformable finite element model with 36mm Pinnacle metal-on-polyethylene bearing geometry (DePuy Synthes, Leeds, UK) was used with material properties for conventional UHMWPE. Setup was 65° clinical inclination, 4mm mismatch, 70N swing phase load, and 100N/mm spring. Fixture mass was varied from 0.5-5kg, spring damping coefficient was varied from 0-2Ns/mm. They were changed independently, and in combination. Maximum separation values were relatively insensitive to changes in the mass, damping coefficient, or both. The sensitivity of peak plastic strain, to this range of inputs, was similar to changing the swing phase load from 70N to approximately 150N – 200N. Increasing the fixture mass and/or damping coefficient increased the peak plastic strain, with values from 0.15-0.19. Liner plastic deformation was sensitive to the spring damping and fixture mass, which may explain some of the differences in fatigue and deformation results in UHMWPE liners tested on different machines or with modified fixtures. These values should be described when reporting the results of ISO14242:4 testing. Acknowledgements. Funded by EPSRC grant EP/N02480X/1; CAD supplied by DePuy Synthes

Aims. To evaluate the histopathological examination of peri-implant tissue samples as a technique in the diagnosis of postoperative spinal implant infection (PSII). Methods. This was a retrospective analysis. Patients who underwent revision spinal surgery at our institution were recruited for this study. PSII was diagnosed by clinical signs, histopathology, and microbiological examination of intraoperatively collected samples. Histopathology was defined as the gold standard. The sensitivity for histopathology was calculated. A total of 47 patients with PSII and at least one microbiological and histopathological sample were included in the study. Results. PSII occurred in approximately 28% of the study population. Histopathology showed a sensitivity of 51.1% in the diagnosis of PSII. The most commonly found pathogens were Cutibacterium acnes and gram-positive staphylococci. Conclusion. Histopathology has low sensitivity for detecting PSII. In particular, infections caused by low-virulence microorganisms are insufficiently detected by histopathology. Cite this article: Bone Joint J 2020;102-B(7):899–903

Abstract. Background. Prosthetic joint infection (PJI) is a significant cause of morbidity and mortality following knee replacement surgery. Identifying the causative agent(s) and their antibiotic sensitivities is critical in determining the choice of treatment methods used and the likelihood of successful eradication. This study aimed to investigate:. Whether biopsy alone was superior to aspiration alone in specificity and sensitivity for diagnosing PJI following knee replacement. Whether biopsy identifies the same microbiological flora as aspiration. Methods. We identified consecutive patients passing through our knee infection Multi-Disciplinary Team meeting between December 2014 and March 2020. Data was collated data retrospectively using electronic records. Statistical analysis was performed using Stata (Timberlake, February 2020). Results. 65 of 100 patients identified had both pre-operative aspiration and biopsy. In 29% of positive patients, biopsy identified new or additional organisms not previously identified by aspiration. Aspiration had a sensitivity of 70%, specificity of 88%, positive predictive value of 90.3% and negative predictive value of 64.7%. Biopsy had a sensitivity of 97.5%, specificity of 88%, positive predictive value of 92.9% and negative predictive value of 95.7%. Conclusion. Biopsy is superior to aspiration in the diagnosis of PJI and can be performed safely and successfully. It identifies organisms when aspiration may be negative and identifies additional microorganisms in a polymicrobial setting not identified by aspiration alone (29% of positive cases). We would recommend, where possible, aspiration and biopsy as routine pre-operative sampling in order to identify all causative agents and their susceptibilities prior to embarking on revision surgery

Aims. This study aimed to answer two questions: what are the best diagnostic methods for diagnosing bacterial arthritis of a native joint?; and what are the most commonly used definitions for bacterial arthritis of a native joint?. Methods. We performed a search of PubMed, Embase, and Cochrane libraries for relevant studies published between January 1980 and April 2020. Of 3,209 identified studies, we included 27 after full screening. Sensitivity, specificity, area under the curve, and Youden index of diagnostic tests were extracted from included studies. We grouped test characteristics per diagnostic modality. We extracted the definitions used to establish a definitive diagnosis of bacterial arthritis of a native joint per study. Results. Overall, 28 unique diagnostic tests for diagnosing bacterial arthritis of a native joint were identified. The following five tests were deemed most useful: serum ESR (sensitivity: 34% to 100%, specificity: 23% to 93%), serum CRP (sensitivity: 58% to 100%, specificity: 0% to 96%), serum procalcitonin (sensitivity: 0% to 100%, specificity: 68% to 100%), the proportion of synovial polymorphonuclear cells (sensitivity: 42% to 100%, specificity: 54% to 94%), and the gram stain of synovial fluid (sensitivity: 27% to 81%, specificity: 99% to 100%). Conclusion. Diagnostic methods with relatively high sensitivities, such as serum CRP, ESR, and synovial polymorphonuclear cells, are useful for screening. Diagnostic methods with a relatively high specificity, such as serum procalcitonin and synovial fluid gram stain, are useful for establishing a diagnosis of bacterial arthritis. This review helps to interpret the value of various diagnostic tests for diagnosing bacterial arthritis of a native joint in clinical practice. Cite this article: Bone Joint J 2021;103-B(12):1745–1753

The role of metal sensitivity or allergy in causing persistent symptoms or failure and need for a revision of a total joint replacement has been the topic of debate and controversy for decades. There was renewed interest in this area with the rise of metal-on-metal hip arthroplasty and the advent of adverse local tissue reactions. This led to an increase in metal ion testing as well as metal sensitivity testing. With the decline of the use of metal-on-metal hip components, this is now mostly an issue in knee arthroplasty. It is well known that a substantial percentage of patients have persistent symptoms following knee replacement. What remains in question is whether allergy to metal or other materials such as PMMA may be a contributing factor. It is accepted that the incidence of positive skin patch tests is higher in symptomatic failed joint replacements. Nickel sensitivity is most common as a positive skin test with up to 15% of patients demonstrating this followed by chromium and cobalt. A recent review by Lachiewicz et al. concluded that there was insufficient evidence to recommend routine or widespread cutaneous or in vitro hypersensitivity testing before primary TKA, that there is no evidence-based rationale to recommend a routine metal allergy screening questionnaire, that there is only anecdotal support for Ni-free implants, and that local dermatitis should be treated with topical steroids. In another article, routine screening for metal allergy was not recommended, however, selective screening for history of sensitivity or unexplained pain or early loosening was suggested. Other experts have recommended a role for utilizing a commercially available alternative to components containing nickel or cobalt in patients thought to be hypersensitive. A recent study, however, concluded that there was no difference in complications, revisions, or reoperations among patients who tested positive with patch testing whether they were treated with standard components or nickel free components. Likewise, a consensus panel published results from the United Kingdom in which cobalt chrome implants were recommended regardless of the patients metal allergy status. Patient perception is important, however, and among patients who report multiple allergies of any kind, a higher percentage are likely to be dissatisfied with their knee replacement. Of more importance are those reporting a specific allergy to metal are substantially more likely to express some dissatisfaction with their components. Metal allergy as a cause of chronic pain and/or early failure of joint replacement is rare if it exists at all. It is always a diagnosis of exclusion. Patients who think they are allergic are probably more likely to be more symptomatic following joint replacement. Whether or not to use a nickel free or hypoallergenic component in such patients remains an area of controversy

Blood metal ions have been widely used to investigate metal-on-metal hip replacements, but their ability to discriminate between well-functioning and failed hips is not known. The Medicines and Healthcare products Regulatory Agency (MHRA) has suggested a cut-off level of 7 parts per billion (ppb). We performed a pair-matched, case-control study to investigate the sensitivity and specificity of blood metal ion levels for diagnosing failure in 176 patients with a unilateral metal-on-metal hip replacement. We recruited 88 cases with a pre-revision, unexplained failed hip and an equal number of matching controls with a well-functioning hip. We investigated the 7 ppb cut-off level for the maximum of cobalt or chromium and determined optimal mathematical cut-off levels from receiver-operating characteristic curves. The 7 ppb cut-off level for the maximum of cobalt or chromium had a specificity of 89% and sensitivity 52% for detecting a pre-operative unexplained failed metal on metal hip replacement. The optimal cut-off level for the maximum of cobalt or chromium was 4.97 ppb and had sensitivity 63% and specificity 86%. Blood metal ions had good discriminant ability to separate failed from well-functioning hip replacements. The MHRA cut-off level of 7 ppb provides a specific test but has poor sensitivity.

Magnetic resonance imaging (MRI) is a useful diagnostic tool in evaluating meniscus pathology in the knee. Data from available literature suggests sensitivity and specificity rates around 90% when compared to the gold standard findings at knee arthroscopy. We sought to evaluate the sensitivity, specificity and precision rate (positive predictive value) of MRI at diagnosing meniscus tears within our unit. A retrospective audit of a total of 79 MRI reports and arthroscopic findings spanning a one year period was carried out. There were 66 positive MRI reports and 13 negative reports. There were 6 false positives 4 false negatives when compared to arthroscopic findings. The sensitivity of MRI for detecting meniscus tears was 93.7% with 60 out of 64 tears detected. All 4 false negatives also had at least grade III osteoarthritic changes at arthroscopy. Specificity was rather low at 60% with MRI reporting 6 tears (false positives) out of 15 patients who had no tears found at arthroscopy. The positive predictive value (precision rate) of MRI detecting tears was 90.9%. This data shows that MRI in our unit has a comparable high sensitivity to that in various literature making it a useful tool at ruling out disease with a negative result in the clinical setting. A more useful parameter in the clinical setting is its high precision rate when faced with a positive result. However, its specificity is much lower than that in most published data. A total of 6 tears on MRI turned out not to be on arthroscopy meaning patients could have been subjected to an avoidable invasive procedure in the absence of any other indication. This highlights the importance of obtaining reports from experienced musculoskeletal radiologists and the need for surgeons to review MRI images and match them to clinical information prior to subjecting patients to surgery

A prospective study of allergic contact dermatitis after metal-on-plastic total hip replacement was undertaken in 69 patients, of whom 54 were available for review after operation. Before operation six patients were metal sensitive, but only one remained so afterwards; this patient had given a clear history of metal sensitivity and a titanium prosthesis had therefore been used. In all six patients the result of the operation was good and no case of loosening occurred. Sixty-three patients had negative patch tests before operation; in none of these was metal sensitivity detected after operation. Cutaneous sensitivity to various metals is well documented after the insertion of metal-on-metal prostheses and in failed prostheses. We have not found any such increased sensitivity after metal-on-plastic hip replacement. There is little evidence of a direct causal relationship between metal sensitivity and subsequent loosening. The cutaneous sensitivity may be the consequence of loosening rather than its cause. Our results suggest that, providing metal-on-plastic prostheses are used, routine patch testing before hip replacement is no longer required

FAI has been implicated in the progression of osteoarthritis (OA) and early detection may allow for treatment, which can slow or halt progression. FAI is a difficult condition to image and there is little objective evidence about imaging accuracy. We aim to measure the accuracy of five imaging modalities. Three blinded observers retrospectively reviewed five different modalities from two age and sex matched groups: A patient group referred to the outpatient clinic with a clinical diagnosis of FAI and a control group who had had CT scans of the pelvis for suspected trauma, where the Pelvic scan had been reported as showing no injuries. The imaging modalities were: Standard x-ray; Antero-Posterior, Lateral; Condition-specific x-ray projections; Dunn view, lateral internal rotation; Standard Computer Tomography (CT) multiplanar reconstruction (MPR); axial, sagittal and coronal; Condition-specific CT MPR; angled axial, angled coronal; 3D modelling; and surface rendered dynamic. We found marked variations in the sensitivity, specificity, Positive Predictive Value (PPV) and Negative Predictiive Value (NPV) for each of the following imaging modalities: Standard X-ray; Sensitivity 51.9; Specificity; 57.1; PPV; 40; NPV; 68.3 Special X-rays; Sensitivity; 66.7; Specificity; 57.1; PPV; 46.1; NPV; 75.7. Standard CT MPR; Sensitivity; 40.7; Specificity; 75.5; PPV; 47.8; NPV; 69.8 Special CT MPR; Sensitivity; 48.1; Specificity; 57.1; PPV; 46.4; NPV; 70.8 Dynamic 3D CT models; Sensitivity; 55.6; Specificity; 69.3; PPV; 42.8; and NPV; 71.8. The Dynamic 3D CT models (where the observer can manipulate the model in real time three dimension to control the perspective) proved to be the most accurate, closely followed by the special X-Ray views, which were also the most sensitive. The Standard CT MPRs were the most specific but had a low sensitivity. This is the first study to measure sensitivity, specificity and PPV and NPV for these imaging modalities in FAI. We recommend the use of condition-specific X-Ray views as well as 3D CT Models for optimal imaging accuracy in this condition. Standard X-Ray views and CTs proved less useful

Introduction. Metals used for total knee arthroplasty (TKA) are well known for their good biocompatibility, but may be a source of a release of metal ions that can be a cause of local and systemic adverse effects, aseptic loosening, and hypersensitivity reactions. One of the major difficulties in performing TKA is the selection of implants for patients who are preoperatively diagnosed as subject to metal sensitivity. Alternative solutions in cases of hypersensitivity are implants without metal constituents or metallic implants treated with a non-sensitive surface process. The aim of this study was to evaluate clinical results in patients who had been preoperatively diagnosed with metal sensitivity and who subsequently were provided with the zirconia-ceramic LFA-III TKA, and with a minimum 5-year follow-up. Methods. Five patients (8 knees) with metal sensitivity underwent TKA using cemented zirconia-ceramic LFA-III implants. The LFA-III implant (KYOCERA Medical Co., Japan) is composed of a zirconia ceramic femoral component and a titanium-alloy tibial component with a polyethylene insert. All patients were female andthe average age at the time of surgery was 76.1 years. The average follow-up time was 7.2 years. Clinical and radiographic assessments were conducted with the Knee Society scoring system. Results. No patients except one who had palmoplantar pustulosis preoperatively presented systemic or local dermatitis after surgery. The mean preoperative range of motion of 97.6 degrees improved to a mean of 110.7 degrees at the time of the most recent follow-up. The mean postoperative knee and function scores were 77.1 and 66.9, respectively. Subtle periprosthetic radiolucencies were found in 2 knees after the surgery. Discussion. The zirconia-ceramic LFA-III TKA has performed well over a 5-year period in patients with metal hypersensitivity. Although this implant has a metal tibial component made of titanium, no systemic or local adverse events related to metal hypersensitivity were recorded. Ceramic implants can be an attractive alternative solution for patients suffering from hypersensitivity reactions to metals

The success of total knee replacement surgery depends critically on proper limb alignment and implant position. Even with contemporary mechanical alignment instrumentation, errors in limb alignment and implant position do occur. To improve upon the accuracy and biomechanical efficacy of conventional surgical instrumentation while limiting the need for substantial pre-operative planning, a non-image-based computer-aided navigation system was developed for total knee replacement surgery. Clinical studies have demonstrated that use of this system, OrthoPilot® (Aesculap AG, Tuttlingen, Germany), for knee replacement surgery can lead to improved limb alignment and implant position. In this study we investigated the repeatability and sensitivity of the OrthoPilot® computer-aided navigation system for total knee replacement surgery. To assess repeatability, total knee replacement surgeries were simulated on an idealized test bench using identical input parameters and the variation in output measurements was measured. To assess sensitivity, the effect of moderate movement of position sensors on system-level accuracy was measured. The results indicate that (1) the system functions in a highly repeatable manner if it is supplied with repeatable inputs; and (2) unintentional relative movement of position sensors during surgery can substantially affect accuracy of the system outputs. Because computer-aided navigation systems are powerful tools for orthopaedic surgery, it is important to recognize that their accuracy and precision are highly dependent on pre-operative and intra-operative registration techniques. Like all instrumentation systems, their use is associated with a learning curve, even in the hands of experienced orthopaedic surgeons. The results of this study demonstrate that the OrthoPilot® in an inherently precise instrument that is sensitive to variations in surgical technique. It is critical that the users of these systems (i.e. surgeons) be aware of system sensitivities and pay careful attention to operative techniques required by the system

In spite of its incidence decreasing to 1% nowadays, prosthesis-related infections remain a research, diagnostic, therapeutic and cost-related problem. Early diagnosis, selection of an appropriate surgical strategy, accurate identification of the responsible microorganisms and construction of an appropriate antibiotic regimen are essential elements of any management strategy. Our study aim was firstly to compare the diagnostic accuracy of conventional periprosthetic tissue culture and culture of fluid derived from vortexing and bath sonication of the explanted hardware and secondly to investigate the role of possible metabolic factors affecting the sensitivity of the sonication method. We investigated 70 patients undergoing revision hip or knee arthroplasty because of loosening of the prostheses, at our institution, between October 2011 and November 2013. Patients’ medical history and demographic characteristics were recorded. We compared the culture of samples obtained by sonication of explanted hip and knee prostheses with conventional culture of periprosthetic tissue for the microbiological diagnosis of prosthetic-joint infection. Infectious Diseases Society of America (IDSA) Guidelines were used for the definition of prosthetic-joint infection. Thirty-two patients had septic loosening and 38 aseptic loosening (48 hip prostheses and 22 knee prostheses). The sensitivity of sonication fluid culture was 81.25% and the sensitivity of conventional tissue cultures was 56.25% (p-value = 0.043). The sensitivity of the sonication method was statistically higher in obese, diabetic patients, with age above 60, in uncemented arthroplasties and in arthroplasties because of primary osteoarthritis (p-values < 0.05). The sonication method represents a reliable test for the diagnosis of prosthetic – joint infections with a greater sensitivity than the conventional periprosthetic tissue cultures, especially in obese, diabetic patients, with age above 60, in uncemented arthroplasties and in arthroplasties because of primary osteoarthritis

Aims. The aims of this study were to investigate any possible relationship between a preoperative sensitivity to pain and the degree of pain at rest and on exertion with postoperative function in patients who underwent stemless total shoulder arthroplasty (TSA). Patients and Methods. In this prospective study, we included 63 patients who underwent stemless TSA and were available for evaluation one year postoperatively. There were 31 women and 32 men; their mean age was 71 years (53 to 89). The pain threshold, which was measured using a Pain Matcher (PM) unit, the degree of pain (visual analogue scale at rest and on exertion, and function using the short version of the Disabilities of the Arm, Shoulder and Hand questionnaire (QuickDASH), were recorded preoperatively, as well as three and 12 months postoperatively. Results. We found an inverse relationship between both the preoperative PM threshold and pain (VAS) at rest and the 12-month postoperative QuickDASH score (Pearson correlation coefficient (r) ≥ 0.4, p < 0.05). A linear regression analysis showed that the preoperative PM threshold on the affected side and preoperative pain (VAS) at rest were the only factors associated with the QuickDASH score at 12 months. Conclusion. These findings indicate the importance of central sensitization in the restoration of function after TSA. Further studies are required to investigate whether extra analgesia and rehabilitation could influence the outcome in at risk patients. Cite this article: Bone Joint J 2018;100-B:480–4

Aims. The risk to patients and healthcare workers of resuming elective orthopaedic surgery following the peak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been difficult to quantify. This has prompted governing bodies to adopt a cautious approach that may be impractical and financially unsustainable. The lack of evidence has made it impossible for surgeons to give patients an informed perspective of the consequences of elective surgery in the presence of SARS-CoV-2. This study aims to determine, for the UK population, the probability of a patient being admitted with an undetected SARS-CoV-2 infection and their resulting risk of death; taking into consideration the current disease prevalence, reverse transcription-polymerase chain reaction (RT-PCR) testing, and preassessment pathway. Methods. The probability of SARS-CoV-2 infection with a false negative test was calculated using a lower-end RT-PCR sensitivity of 71%, specificity of 95%, and the UK disease prevalence of 0.24% reported in May 2020. Subsequently, a case fatality rate of 20.5% was applied as a worst-case scenario. Results. The probability of SARS-CoV-2 infection with a false negative preoperative test was 0.07% (around 1 in 1,400). The risk of a patient with an undetected infection being admitted for surgery and subsequently dying from the coronavirus disease 2019 (COVID-19) is estimated at approximately 1 in 7,000. However, if an estimate of the current global infection fatality rate (1.04%) is applied, the risk of death would be around 1 in 140,000, at most. This calculation does not take into account the risk of nosocomial infection. Conversely, it does not factor in that patients will also be clinically assessed and asked to self-isolate prior to surgery. Conclusion. Our estimation suggests that the risk of patients being inadvertently admitted with an undetected SARS-CoV-2 infection for elective orthopaedic surgery is relatively low. Accordingly, the risk of death following elective orthopaedic surgery is low, even when applying the worst-case fatality rate. Cite this article: Bone Joint J 2020;102-B(9):1256–1260

1. Evidence is presented which suggests that after total joint replacement bone necrosis and consequent loosening of the prosthesis may be due to the development of sensitivity to the metals used. 2. Nine patients, from a total of fourteen with loose prostheses, were found to be metal sensitive by skin-patch testing. In twenty-four patients with intact prostheses no sensitivity was demonstrated. 3. In material from the joints of sensitive patients the metal content was raised. 4. Examination of this material showed necrosis of bone and soft tissue following obliterative changes in the vascular supply. 5. Similar reactions were found following the injection of cobalt into a sensitive patient. 6. The release of metal around a prosthesis is greatest where metal rubs against itself. 7. We conclude that prostheses in which metal articulates with polyethylene should be preferred; that any patient in whom loosening or fragmentation occurs should be patch tested; and that if sensitivity is found the implant should be removed

Computational modeling has been used to simulate the natural and prosthetic kinematic and kinetic function in an attempt to compare designs and/or predict a desired motion path from a design. The levels of soft tissue can range from basic ligaments (MCL, LCL, and ACL & PCL) to more complex models. The goal of this study was to evaluate the sensitivity of the Posterior Cruciate ligament in a virtual model and its effects on the kinematic outcome in a commercially available and validated kinematics package (KneeSim, LifeModeler San Clemente, CA). Methods:. KneeSIM is a musculoskeletal modeling environment that is built on the foundation of the ADAMS (MSC Software, Santa Ana CA), a rigid body dynamics solver to compute knee kinematics and forces during a deep knee bend. All parameters are customizable and can be altered by the user. Generic three dimensional models of cruciate retaining components of the femoral, tibial, and patellar are available with the software and were used to provide a common reference for the study. The following parameters were modified for each simulation to evaluate the sensitivity of the PCL in the model: 1) Model without PCL, 2) PCL with default properties, 3) PCL Shifted at femoral origin, 7 mm anterior, 7 mm inferior; tibial origin maintained; 4) PCL with increased stiffness properties (2x default), 5) position in the femur and tibia remained default position and 6) PCL with default properties and location, joint line shifted 4 mm superior. The standard output of tracking the flexion facet center (FFC) motion of the medial and lateral condyles was utilized (Figure 1). Results:. Figure 2 and 3 displays the output of the six conditions tested above. Comparing the curves for the medial and lateral motion show different patterns with the lateral point having more posterior translation than the medial. After approximately 95° of flexion, all cases exhibit an anterior translation in the model. This motion was consistent for all test cases. The model showed no difference with motion either with or without the PCL and with changing the stiffness. Altering the location of the PCL on the femoral insertion had the greatest effect on motion, while shifting the joint line superior was second. The shift of the ligament insertion and changing of the joint line results in the ligament being more parallel to the tibial surface which provides resistance to anterior motion or posterior translation. Discussion:. Although the model was able to discern differences, the inability to highlight variation in motion with and without the PCL suggests that the default parameters are not representative of an experimental or clinical setup. Although it is apparent that KneeSim can be used for comparative assessments between designs, simulations should be designed so as to provide similar boundary conditions. Publications (Colwell et al 2011) did successfully use KneeSim to provide a comparative assessment of CR components; however, only after the default model was altered to match the outcome of the experimental rig. Further analysis of the complexities in soft tissue modeling is warranted