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

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

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

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

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

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

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

The kinematic and kinetic characteristics of the knee after TKR are known to be strongly influenced by the alignment and positioning of the implanted components. In this paper we apply a virtual multi-fiber ligament model to a rigid body model of the post-surgical knee to explore how variations in alignment and positioning affect the predicted behavior of the ligaments and contact forces. We vary the angular and translational positioning of the femoral and tibial TKR components relative to the bone. Meanwhile the proximal and distal insertion sites of the ligaments are held constant relative to the bony structures. We evaluate sensitivity of the ligament balance and peak ligament tension through the passive flexion arc in response to the variation in positioning and alignment of the TKR components. With further development, this work holds the promise of applications in surgical planning and virtual arthroplasty

The peak external knee adduction moment during walking gait has been proposed to be a clinically useful measure of dynamic knee joint load in patients with knee osteoarthritis. However, there is limited information about the reliability of this measure, or its ability to detect change. The test-retest reliability and sensitivity to change of peak knee adduction moments were evaluated in thirty patients with varus gonarthrosis. Indices of relative and absolute reliability were excellent (intra-class correlation coefficient = 0.85, standard error of measurement = 0.36 % BW*Ht), and the sensitivity to change following high tibial osteotomy was high (standardized response mean = 1.2). To estimate the test-retest reliability, measurement error and sensitivity to change of the peak knee adduction moment during gait. Thirty patients (44”11 yrs, 1.7”0.09 m, 87”20 kg, twenty males, ten females) with varus gonarthrosis underwent gait analyses on two pre-operative test occasions within one week, and on a third test occasion six months after medial opening wedge high tibial osteotomy. Three-dimensional kinematic and kinetic gait data were collected during self-paced walking and used to calculate the peak knee adduction moment. An intraclass correlation coefficient of 0.85 (95%CI: 0.71, 0.93) indicated excellent relative reliability, and a standard error of measurement of 0.36 %BW*Ht (95%CI: 0.29, 0.49) indicated low measurement error. The peak knee adduction moment after surgery (1.66”0.72 %BW*Ht) was significantly (p< 0.001) lower than before surgery (2.58”0.72 %BW*Ht). A standardized response mean of 1.2 (95%CI: 0.77, 1.6) indicated the size of this change was large. Based on 95% confidence levels, these results suggest the error in an individual’s peak knee adduction moment at one point in time is 0.70 % BW*Ht, the minimal detectable change in an individual’s peak adduction moment is 1.0 %BW*Ht, and it is sensitive to change following treatment. The peak knee adduction moment during gait has appropriate reliability for use in studies evaluating the effect of treatments intended to decrease the load on the knee. When considering measurement error, the knee adduction moment is also appropriate for clinical use in evaluating change in individual patients. Funding: CIHR, Arthrex Inc

Introduction. Scar sensitivity is a recognised complication of foot surgery. However there is very little published about it. This study looks at the incidence and natural history of scar sensitivity following hallux valgus surgery. Materials and Methods. Patients who had open hallux valgus surgery from December 2008 to December 2009, with a minimum follow up of 12 months, were contacted. Data regarding scar symptoms, their duration, severity at their worst and interventions undertaken were collected. Patients also completed a Roles and Maudsley patient satisfaction score. Results. 125 patients were contacted with response rate of 84%. 30% of patients had experienced scar symptoms following surgery. Of these, 20% had undertaken some form of nonsurgical intervention. The mean duration of symptoms was 16 weeks, and 95% of patients experienced resolution of symptoms. 99% of patients would opt to have the surgery again. Roles and Maudsley score ranged from 1 to 2. Discussion. Nearly one third of patients experienced scar symptoms, however nearly all resolved completely with or without simple treatments. Symptoms were not severe and did not affect satisfaction, function or the decision to have the surgery again. Educating patients preoperatively about scar sensitivity can relieve anxiety and improve the patient experience and they can be advised on simple and effective strategies should this common side effect occur. The results of this study provide the surgeon with valuable information in the consent and education of patients. Also, the fact that nearly all symptom settled within 16 weeks brings into question one of the purported advantages of minimally invasive surgery. Conclusion. Scar symptoms following hallux valgus surgery are common, but mild and almost all resolve in time

Introduction. The influence of the bone mineral density (BMD) on the mechanical behavior of bones can be examined using computer tomography (CT) data and finite element (FE) simulations, because the BMD correlates with the Hounsfield scale (HU) of the CT data. Therefor the material mapping strategy, which is required to assign the HU values to the FE mesh, is of crucial importance. In this study a nodal mapping strategy was analyzed concerning its sensitivity towards FE mesh parameters and an averaging of HU values from the area around the respective nodes. Method. The FE simulation is based on CT data of a human proximal femur. Once the bone shape was reconstructed, the resulting model was meshed with quadratic tetrahedral elements in ABAQUS/CAE and all nodes were assigned an HU value from the CT data by using the respective node coordinates. In this process, the mesh density, the threshold, which could be used to exclude connective tissue and fat from the material mapping process, the considered volume around the nodes and the method of averaging were varied. The material assignment was realized by an HU value dependent, linear elastic material definition. The femur model was clamped at the level of the isthmus and a displacement of 0.5 mm was applied at the femoral head. The evaluation was based on the resulting reaction forces. Results. The sensitivity analysis demonstrated, that threshold and mesh density mainly influenced the reaction force [Fig. 1]. If a threshold was applied, the reaction force increased by about 20 % in average. A threefold increase of the mesh density led to an average gain of the results of about 24 %. For a specific mesh density the curve progressions of the respective results intersected, i.e. an alteration of the considered volume or the method of averaging barely affected the reaction force [Fig. 2, Fig. 3]. Apart from this intersection, the comparison of the small and the large average volume led to a deviation of up to 11 %. On the other hand, the examination of different methods of averaging revealed only a maximum deviation of 4 % between “mean” and “median”. Discussion. The present study indicates, that the material mapping strategy is an influential part of the modeling process, which should be validated to avoid misjudgments of the load situation. Accordingly, the use of a threshold to exclude non-bone tissue could be a helpful tool. But with the exclusion of lower HU values, the load-bearing structure gains stiffness and the reaction force in the femur rises. A finer mesh leads to a higher resolution of the bone structure and, therefore, to a higher accuracy of the results. The “equilibrium” between the different models at the intersection is caused by a more homogeneous distribution of the material property which is increased by a larger considered volume and the method “mean”

The purpose of the project was to develop a questionnaire for completion by patients with elbow pathologies which is short and practical, internally consistent, valid, responsive and sensitive to changes of clinical importance. The first, pilot phase included 43 patients who each completed a 19 item questionnaire relating to elbow function. The 19 ADLs produced a total scale Cronbach Alpha of 0.96., two different groups of ADLs were identified by multivariate analysis. Group 1 consisted of ADLs requiring moderate to high isometric loading and Group 2 of ADLs requiring high flexion. From the 19 items the best 10 which represented both groups were selected. A summary score was used to create the Wrightington Elbow Disability Score (WEDS). In the second phase 89 patients completed the new WEDS form, reliability studies produced a Cronbach’s alpha value of 0.91. Internal validity of the groups of ADLs all correlated at p< 0.001 level with strength (Group1) and flexion (Group 2). A sub set of 40 patients undergoing total elbow arthroplasty were assessed for sensitivity to change in disability, the WEDS indicated a significant improvement at the p< 0.001. Convergent validity was demonstrated by the correlation with the ASES-e score at p< 0.001 level. The WEDS was significantly correlated with the ASES-e but not the DASH score. Our study confirms that the WEDS questionnaire which is short and practical, is internally consistent, valid, responsive and sensitive to changes of clinical importance

Optimal soft tissue tension maximises function following total knee arthroplasty. Excessive tension may lead to stiffness and or pain, while inadequate tension can lead to instability. Composite component thickness is a prime determinant of this soft tissue tension. The variable component thickness provided by polyethylene inserts generally allows for 2–3mm incremental change. This study analyzed the effect of 1-mm incremental changes in polyethylene thickness on soft tissue tension. Our hypothesis was that soft tissue tension would be markedly affected by increases in insert thickness. Computer assisted TKA was performed on eight cadaveric knee specimens (four pairs). The knees were passively moved through full flexion-extension range of motion, for each tibial construct thickness. Kinematics were recorded using the computer navigation software. Soft tissue tension was analyzed by measuring compartmental loads. A validated load cell instrumented tibial insert was used to measure medial and lateral compartmental loads independently. The effect of 1-mm increments in polyethylene thickness on compartmental loads was evaluated. An increase in compartmental loads was measured with increasing insert thickness. Loading in contralateral compartments showed differing behaviour, reflecting varying tension in the medial and lateral sides. Many generated loads showed a reduction after reaching a maximal level with further increase in insert thickness (seven of eight specimens), indicative of tissue failure, although there were no overt indications of failure during the procedure. With a 1-mm increase in insert thickness, six of eight specimens showed an increase in peak loads greater than 100N at some point in the testing procedure, although not always with the same shim thickness. Compartmental loads varied as a function of insert thickness. Most specimens showed signs of soft tissue “micro-failure”. The high sensitivity of compartmental loads to a 1-mm incremental increase is significant and has not been previously appreciated, especially intra-operatively. Currently available inserts with 2–3mm incremental sizes may make obtaining optimal soft tissue tension difficult. In addition to the current focus of obtaining accurate leg alignment, further computer-assisted techniques are required to address soft tissue tension

ARMD (Adverse Reaction to Metal Debris) is an increasingly recognised complication of metal on metal hip replacements. The MHRA (Medical and Healthcare Related Devices Agency) have advised a blood cobalt or chromium level above 7 mg/L is a threshold for further investigation, stating that “low levels are reassuring and strongly predict not having an adverse outcome”. Cross-sectional imaging should be performed when levels are above 7 mg/L. We have performed a study investigating the specificity and sensitivity of chromium and cobalt metal ion levels as a screening measure for ARMD. 79 ASR hip replacements were performed at our hospital and 75 (95%) of these underwent a Metal Artefact Reduction Sequence (MARS) MRI scan. All patients (64 hips) who had not undergone revision were invited to take part in this study. 57 patients with 62 hip replacements completed hip and activity scores, had blood cobalt and chromium ion level measurements and 3D-CT to measure acetabular component position. Acetabular component inclination (>50 degrees), small head size (< 51mm) and female gender were significantly correlated with raised chromium (Cr) and cobalt (Co) ion levels. An ARMD was detected using MRI in 18 (29%) of the hips in this study. The incidence of ARMD was significantly higher when chromium concentration was above 7 mg/l (p = 0.02). Chromium ion levels >7 mg/L had a sensitivity of 56% and specificity of 83% for ARMD, and cobalt ion levels >7 mg/L 56% and 76% respectively. 40 patients had cobalt levels <7 mg/L and 33 had chromium levels <7 mg/L, but 8 of these had an ARMD on MRI. All 8 patients had minimal symptoms (Oxford Hip Score ≥ 44 out of 48). The Medicines and Healthcare Products Regulatory Agency (MHRA) has recommended that cobalt and chromium levels be measured in patients with a metal-on-metal hip replacement and cross-sectional imaging performed when these levels are above 7 μg/L. This study has shown that by using this threshold, in patients with this implant combination, the sensitivity and specificity for the detection of ARMD is low and patients with soft tissue disease may be missed. Furthermore the presence of MRI detected ARMD, in the absence of significant clinical symptoms and with metal ion levels <7 μg/L is of concern. MoM implants at risk of failure are associated with raised cobalt and chromium levels. However metal ion analysis alone is not reliable as a screening tool for ARMD, which is often clinically “silent”. We recommend the routine use of MARS MRI as the safest method of ARMD diagnosis in patients with MoM implants

We have demonstrated that toxins produced by Staphylococcus aureus, a common infective agent in septic arthritis (SA), cause rapid in situ chondrocyte death. Here, we have compared the sensitivity of chondrocytes within the superficial and deep zones (SZ, DZ) of cartilage to the same toxins. Culture medium containing the toxins produced by S. aureus strain 8325-4, which include alpha-, beta-, and gamma-toxin, was prepared. Cartilage explants free of subchondral bone were taken from the metacarpophalangeal joints of 3-year-old cows, and incubated (37°C) with the toxins. Explants were stained after 6hrs with chloromethylfluorescein-di-acetate and propidium iodide, labelling living chondrocytes green and dead cells red, respectively. Full-thickness coronal sections were imaged by confocal microscopy and the percentage cell death within the SZ (100μm from articular surface) and DZ (100μm from subchondral bone interface) determined. Both zones were incubated with the same toxin culture medium for the same time period. At 0hrs, chondrocytes within all zones were >98% viable. However, after incubation with toxin-containing culture medium for 6hrs, 71.9+/−11.2% of the SZ cells were dead compared to only 47.4+/−6.7% in the DZ (p=0.03;data are means+/−SEM;N=4). These results suggest that SZ chondrocytes are considerably more sensitive to S. aureus toxins than those within deeper zones. As SZ chondrocytes are close to the synovial fluid harbouring bacterial toxins, these data emphasise the need to remove bacteria and their products aggressively as part of the treatment of SA. IDMS was supported by Orthopaedic Research UK and The Royal College of Surgeons of Edinburgh