We recorded inter- and intra-observer variations in the classification of ankle fractures by the Lauge Hansen and Weber systems. Radiographs of 94 patients were classified independently by four observers. The observer variation was calculated by kappa statistics, which corrects the obtained values for the agreement expected by chance. There was an acceptable level of agreement for the overall classification into both systems. For the staging of supination-adduction and supination-eversion fractures in the Lauge Hansen system the agreement was poor. The results indicate that future classification systems should be subject to reliability analysis before they are accepted

A study was undertaken to assess the degree of inter-observer error when a panel of observers classified the radiographs of patients with early Perthes' disease, using Catterall grouping and "at risk" signs. The anteroposterior and lateral radiographs, taken within three months of diagnosis of Perthes' disease, were available for 69 hips and were shown in turn to 10 observers. The radiological end-results were assessed at least four years from diagnosis. The results showed a poor ability of the observers to delineate Groups 1, 2 and 3, with a more satisfactory performance in Group 4 and when Groups 2 and 3 were combined. Interpretation of "at risk" signs was unsatisfactory except when there was an increase in medial joint space greater than two millimetres. The end-results correlated well with early Catterall grouping and "at risk" signs when these were correctly interpreted

We studied 19 videotaped knee arthroscopies in 19 patients with mild to moderate osteoarthritis (OA) of the knee in order to compare the intraobserver and interobserver reliability and the patterns of disagreement between four orthopaedic surgeons. The classifications of OA of Collins, Outerbridge and the French Society of Arthroscopy were used. Intraobserver and interobserver agreements using kappa measures were 0.42 to 0.66 and 0.43 to 0.49, respectively. Only 6% to 8% of paired intraobserver classifications differed by more than one category. Observer-specific disagreement was evident both within and between observers. A small, but significant, occasional variation was also seen. Although reliability may improve by an analysis of disagreement, it appears that the arthroscopic grading of early osteoarthritic lesions is inexact

Aims. This aim of this study was to assess the reliability and validity of the Unified Classification System (UCS) for postoperative periprosthetic femoral fractures (PFFs) around cemented polished taper-slip (PTS) stems. Methods. Radiographs of 71 patients with a PFF admitted consecutively at two centres between 25 February 2012 and 19 May 2020 were collated by an independent investigator. Six observers (three hip consultants and three trainees) were familiarized with the UCS. Each PFF was classified on two separate occasions, with a mean time between assessments of 22.7 days (16 to 29). Interobserver reliability for more than two observers was assessed using percentage agreement and Fleiss’ kappa statistic. Intraobserver reliability between two observers was calculated with Cohen kappa statistic. Validity was tested on surgically managed UCS type B PFFs where stem stability was documented in operation notes (n = 50). Validity was assessed using percentage agreement and Cohen kappa statistic between radiological assessment and intraoperative findings. Kappa statistics were interpreted using Landis and Koch criteria. All six observers were blinded to operation notes and postoperative radiographs. Results. Interobserver reliability percentage agreement was 58.5% and the overall kappa value was 0.442 (moderate agreement). Lowest kappa values were seen for type B fractures (0.095 to 0.360). The mean intraobserver reliability kappa value was 0.672 (0.447 to 0.867), indicating substantial agreement. Validity percentage agreement was 65.7% and the mean kappa value was 0.300 (0.160 to 0.4400) indicating only fair agreement. Conclusion. This study demonstrates that the UCS is unsatisfactory for the classification of PFFs around PTS stems, and that it has considerably lower reliability and validity than previously described for other stem types. Radiological PTS stem loosening in the presence of PFF is poorly defined and formal intraoperative testing of stem stability is recommended. Cite this article: Bone Joint J 2021;103-B(8):1339–1344

Aims. Besides conventional radiographs, the use of MRI, CT, and bone scintigraphy is frequent in the diagnosis of a fracture of the scaphoid. However, which techniques give the best results remain unknown. The investigation of a new imaging technique initially requires an analysis of its precision. The primary aim of this study was to investigate the interobserver agreement of high-resolution peripheral quantitative CT (HR-pQCT) in the diagnosis of a scaphoid fracture. A secondary aim was to investigate the interobserver agreement for the presence of other fractures and for the classification of scaphoid fracture. Methods. Two radiologists and two orthopaedic trauma surgeons evaluated HR-pQCT scans of 31 patients with a clinically-suspected scaphoid fracture. The observers were asked to determine the presence of a scaphoid or other fracture and to classify the scaphoid fracture based on the Herbert classification system. Fleiss kappa statistics were used to calculate the interobserver agreement for the diagnosis of a fracture. Intraclass correlation coefficients (ICCs) were used to assess the agreement for the classification of scaphoid fracture. Results. A total of nine (29%) scaphoid fractures and 12 (39%) other fractures were diagnosed in 20 patients (65%) using HR-pQCT across the four observers. The interobserver agreement was 91% for the identification of a scaphoid fracture (95% confidence interval (CI) 0.76 to 1.00) and 80% for other fractures (95% CI 0.72 to 0.87). The mean ICC for the classification of a scaphoid fracture in the seven patients diagnosed with scaphoid fracture by all four observers was 73% (95% CI 0.42 to 0.94). Conclusion. We conclude that the diagnosis of scaphoid and other fractures is reliable when using HR-pQCT in patients with a clinically-suspected fracture. Cite this article: Bone Joint J 2020;102-B(4):478–484

Aims. Various radiological parameters are used to evaluate a flatfoot deformity and their measurements may differ. The aims of this study were to answer the following questions: 1) Which of the 11 parameters have the best inter- and intraobserver reliability in a standardized radiological setting? 2) Are pre- and postoperative assessments equally reliable? 3) What are the identifiable sources of variation?. Patients and Methods. Measurements of the 11 parameters were recorded on anteroposterior and lateral weight-bearing radiographs of 38 feet before and after surgery for flatfoot, by three observers with different experience in foot surgery (A, ten years; B, three years; C, third-year orthopaedic resident). The inter- and intraobserver reliability was calculated. Results. Preoperative interobserver reliability was high for four, moderate for five, and low for two parameters. Postoperative interobserver reliability was high for four, moderate for five, and low for two parameters. Intraobserver reliability was excellent for all parameters preoperatively as recorded by observer A (PB) and B (MP), and for eight parameters as recorded by observer C (SR). Intraobserver reliability was excellent for ten parameters postoperatively as recorded by observer A and B, and for eight parameters as recorded by observer C. Conclusion. The following parameters can be recommended. For preoperative and postoperative evaluation of flatfoot: anteroposterior, talonavicular coverage angle; lateral, talometatarsal I angle, calcaneal pitch angle, and cuneiform-medial height (high interobserver reliability); and anteroposterior, talometatarsal II angle; lateral, talocalcaneal angle,tibiocalcaneal angle (moderate interobserver reliability). For more experienced observers, we also recommend the anteroposterior talometatarsal I angle (moderate reliability). The inter- and intraobserver reliability for most parameters were similar pre- and postoperatively. The experience of the observer and the definition and ability to measure the parameters themselves were sources of variation. Cite this article: Bone Joint J 2018;100-B:596–602

Aims. Accurate measurement of the glenoid version is important in performing total shoulder arthroplasty (TSA). Our aim was to evaluate the Ellipse method, which involves formally defining the vertical mid-point of the glenoid prior to measuring the glenoid version and comparing it with the ‘classic’ Friedman method. Methods. This was a retrospective study which evaluated 100 CT scans for patients who underwent a primary TSA. The glenoid version was measured using the Friedman and Ellipse methods by two senior observers. Statistical analyses were performed using the paired t-test for significance and the Bland-Altman plot for agreement. Results. The mean glenoid version was -3.11° (-23.8° to 17.9°) using the Friedman method and -1.95° (-29.8° to 24.6°) using the Ellipse method (p = 0.002). In 16 patients the difference between methods was greater than 5°, which we considered to be clinically significant. There was poor agreement between methods with relatively large 95% limits of agreement. There was excellent inter-rater agreement between the observers for the Ellipse method and similarly, the intrarater agreement was excellent with a repeatability coefficient of 0.94. Conclusion. We recommend the use of the Ellipse modification to define the mid glenoid point prior to measuring the glenoid version in patients undergoing TSA. Cite this article: Bone Joint J 2020;102-B(2):232–238

Aims. Obtaining solid implant fixation is crucial in revision total knee arthroplasty (rTKA) to avoid aseptic loosening, a major reason for re-revision. This study aims to validate a novel grading system that quantifies implant fixation across three anatomical zones (epiphysis, metaphysis, diaphysis). Methods. Based on pre-, intra-, and postoperative assessments, the novel grading system allocates a quantitative score (0, 0.5, or 1 point) for the quality of fixation achieved in each anatomical zone. The criteria used by the algorithm to assign the score include the bone quality, the size of the bone defect, and the type of fixation used. A consecutive cohort of 245 patients undergoing rTKA from 2012 to 2018 were evaluated using the current novel scoring system and followed prospectively. In addition, 100 first-time revision cases were assessed radiologically from the original cohort and graded by three observers to evaluate the intra- and inter-rater reliability of the novel radiological grading system. Results. At a mean follow-up of 90 months (64 to 130), only two out of 245 cases failed due to aseptic loosening. Intraoperative grading yielded mean scores of 1.87 (95% confidence interval (CI) 1.82 to 1.92) for the femur and 1.96 (95% CI 1.92 to 2.0) for the tibia. Only 3.7% of femoral and 1.7% of tibial reconstructions fell below the 1.5-point threshold, which included the two cases of aseptic loosening. Interobserver reliability for postoperative radiological grading was 0.97 for the femur and 0.85 for the tibia. Conclusion. A minimum score of 1.5 points for each skeletal segment appears to be a reasonable cut-off to define sufficient fixation in rTKA. There were no revisions for aseptic loosening at mid-term follow-up when this fixation threshold was achieved or exceeded. When assessing first-time revisions, this novel grading system has shown excellent intra- and interobserver reliability. Cite this article: Bone Joint J 2024;106-B(5):468–474

Aims. The primary aim of this study was to develop a reliable, effective radiological score to assess the healing of humeral shaft fractures, the Radiographic Union Score for HUmeral fractures (RUSHU). The secondary aim was to assess whether the six-week RUSHU was predictive of nonunion at six months after the injury. Patients and Methods. Initially, 20 patients with radiographs six weeks following a humeral shaft fracture were selected at random from a trauma database and scored by three observers, based on the Radiographic Union Scale for Tibial fractures system. After refinement of the RUSHU criteria, a second group of 60 patients with radiographs six weeks after injury, 40 with fractures that united and 20 with fractures that developed nonunion, were scored by two blinded observers. Results. After refinement, the interobserver intraclass correlation coefficient (ICC) was 0.79 (95% confidence interval (CI) 0.67 to 0.87), indicating substantial agreement. At six weeks after injury, patients whose fractures united had a significantly higher median score than those who developed nonunion (10 vs 7; p < 0.001). A receiver operating characteristic curve determined that a RUSHU cut-off of < 8 was predictive of nonunion (area under the curve = 0.84, 95% CI 0.74 to 0.94). The sensitivity was 75% and specificity 80% with a positive predictive value (PPV) of 65% and a negative predictive value of 86%. Patients with a RUSHU < 8 (n = 23) were more likely to develop nonunion than those with a RUSHU ≥ 8 (n = 37, odds ratio 12.0, 95% CI 3.4 to 42.9). Based on a PPV of 65%, if all patients with a RUSHU < 8 underwent fixation, the number of procedures needed to avoid one nonunion would be 1.5. Conclusion. The RUSHU is reliable and effective in identifying patients at risk of nonunion of a humeral shaft fracture at six weeks after injury. This tool requires external validation but could potentially reduce the morbidity associated with delayed treatment of an established nonunion. Cite this article: Bone Joint J 2019;101-B:1300–1306

Aims. The purpose of this study was to report bone adaptive changes after anatomical total shoulder arthroplasty (TSA) using a standard-length hydroxyapatite (HA)-coated humeral component, and to report on a computer-based analysis of radiographs to determine changes in peri-implant bone density objectively. Methods. A total of 44 TSAs, performed between 2011 and 2014 using a cementless standard-length humeral component proximally coated with HA, were included. There were 23 males and 21 females with a mean age of 65 years (17 to 65). All shoulders had good quality radiographs at six weeks and five years postoperatively. Three observers graded bone adaptive changes. All radiographs were uploaded into a commercially available photographic software program. The grey value density of humeral radiological areas was corrected to the grey value density of the humeral component and compared over time. Results. Stress shielding was graded as mild in 14 shoulders and moderate in three; the greater tuberosity was the predominant site for stress shielding. The mean metaphyseal and diaphyseal fill-fit ratios were 0.56 (SD 0.1) and 0.5 (SD 0.07), respectively. For shoulders with no radiologically visible stress shielding, the mean decrease in grey value in zones 1 and 7 was 20%, compared with 38% in shoulders with radiologically visible stress shielding. Conclusion. The rate of moderate stress shielding was 7%, five years after implantation of a cementless standard-length HA-coated humeral component. Clinical observation of stress shielding identified on radiographs seems to represent a decrease in grey value of 25% or more. Cite this article: Bone Joint J 2021;103-B(5):958–963

Assessment of skeletal age is important in children’s orthopaedics. We compared two simplified methods used in the assessment of skeletal age. Both methods have been described previously with one based on the appearance of the epiphysis at the olecranon and the other on the digital epiphyses. We also investigated the influence of assessor experience on applying these two methods. Our investigation was based on the anteroposterior left hand and lateral elbow radiographs of 44 boys (mean: 14.4; 12.4 to 16.1 ) and 78 girls (mean: 13.0; 11.1 to14.9) obtained during the pubertal growth spurt. A total of nine observers examined the radiographs with the observers assigned to three groups based on their experience (experienced, intermediate and novice). These raters were required to determined skeletal ages twice at six-week intervals. The correlation between the two methods was determined per assessment and per observer groups. Interclass correlation coefficients (ICC) evaluated the reproducibility of the two methods. The overall correlation between the two methods was r = 0.83 for boys and r = 0.84 for girls. The correlation was equal between first and second assessment, and between the observer groups (r ≥ 0.82). There was an equally strong ICC for the assessment effect (ICC ≤ 0.4%) and observer effect (ICC ≤ 3%) for each method. There was no significant (p < 0.05) difference between the levels of experience. The two methods are equally reliable in assessing skeletal maturity. The olecranon method offers detailed information during the pubertal growth spurt, while the digital method is as accurate but less detailed, making it more useful after the pubertal growth spurt once the olecranon has ossified. Cite this article: Bone Joint J 2014;3:1556–60

Aims. Some patients presenting with hip pain and instability and underlying acetabular dysplasia (AD) do not experience resolution of symptoms after surgical management. Hip-spine syndrome is a possible underlying cause. We hypothesized that there is a higher frequency of radiological spine anomalies in patients with AD. We also assessed the relationship between radiological severity of AD and frequency of spine anomalies. Methods. In a retrospective analysis of registry data, 122 hips in 122 patients who presented with hip pain and and a final diagnosis of AD were studied. Two observers analyzed hip and spine variables using standard radiographs to assess AD. The frequency of lumbosacral transitional vertebra (LSTV), along with associated Castellvi grade, pars interarticularis defect, and spinal morphological measurements were recorded and correlated with radiological severity of AD. Results. Out of 122 patients, 110 (90.2%) were female and 12 (9.8%) were male. We analyzed the radiographs of 122 hips (59 (48.4%) symptomatic left hips, and 63 (51.6%) symptomatic right hips). Average age at time of presentation was 34.2 years (SD 11.2). Frequency of LSTV was high (39% to 43%), compared to historic records from the general population, with Castellvi type 3b being the most common (60% to 63%). Patients with AD have increased L4 and L5 interpedicular distance compared to published values. Frequency of pars interarticularis defect was 4%. Intraclass correlation coefficient for hip and spine variables assessed ranged from good (0.60 to 0.75) to excellent (0.75 to 1.00). Severity of AD did not demonstrate significant correlation with frequency of radiological spine anomalies. Conclusion. Patients with AD have increased frequency of spinal anomalies seen on standard hip radiographs. However, there exists no correlation between radiological severity of AD and frequency of spine anomalies. In managing AD patients, clinicians should also assess spinal anomalies that are easily found on standard hip radiographs. Cite this article: Bone Joint J 2021;103-B(8):1351–1357

Aims. Malreduction of the syndesmosis has been reported in up to 52% of patients after fixation of ankle fractures. Multiple radiological parameters are used to define malreduction; there has been limited investigation of the accuracy of these measurements in differentiating malreduction from inherent anatomical asymmetry. The purpose of this study was to identify the prevalence of positive malreduction standards within the syndesmosis of native, uninjured ankles. Methods. Three observers reviewed 213 bilateral lower limb CT scans of uninjured ankles. Multiple measurements were recorded on the axial CT 1 cm above the plafond: anterior syndesmotic distance; posterior syndesmotic distance; central syndesmotic distance; fibular rotation; and sagittal fibular translation. Previously studied malreduction standards were evaluated on bilateral CT, including differences in: anterior, central and posterior syndesmotic distance; mean syndesmotic distance; fibular rotation; sagittal translational distance; and syndesmotic area. Unilateral CT was used to compare the anterior to posterior syndesmotic distances. Results. A difference of anterior to posterior syndesmotic distance > 2 mm was observed in 89% of ankles (n = 190) on unilateral CT assessment. Using bilateral CT, we found that 35% (n = 75) of normal ankles would be considered malreduced by current malreduction parameters. In 50 patients (23%), only one parameter was anomalous, 18 patients (8%) had two positive parameters and seven patients (3%) had three. Difference in fibular rotation had the lowest false positive rate of all parameters at 6%, whereas posterior syndesmotic distance difference had the highest at 15%. Conclusion. In this study, 35% of native, uninjured syndesmoses (n = 75) would be classified as malreduced by current diagnostic standards on bilateral CT and 89% had an asymmetric incisura on unilateral CT (n = 190). Current radiological parameters are insufficient to differentiate mild inherent anatomical asymmetry from malreduction of the syndesmosis. Cite this article: Bone Joint J 2021;103-B(1):178–183

Aims. The primary aim of this study was to compare the postoperative systemic inflammatory response in conventional jig-based total knee arthroplasty (conventional TKA) versus robotic-arm assisted total knee arthroplasty (robotic TKA). Secondary aims were to compare the macroscopic soft tissue injury, femoral and tibial bone trauma, localized thermal response, and the accuracy of component positioning between the two treatment groups. Methods. This prospective randomized controlled trial included 30 patients with osteoarthritis of the knee undergoing conventional TKA versus robotic TKA. Predefined serum markers of inflammation and localized knee temperature were collected preoperatively and postoperatively at six hours, day 1, day 2, day 7, and day 28 following TKA. Blinded observers used the Macroscopic Soft Tissue Injury (MASTI) classification system to grade intraoperative periarticular soft tissue injury and bone trauma. Plain radiographs were used to assess the accuracy of achieving the planned postioning of the components in both groups. Results. Patients undergoing conventional TKA and robotic TKA had comparable changes in the postoperative systemic inflammatory and localized thermal response at six hours, day 1, day 2, and day 28 after surgery. Robotic TKA had significantly reduced levels of interleukin-6 (p < 0.001), tumour necrosis factor-α (p = 0.021), ESR (p = 0.001), CRP (p = 0.004), lactate dehydrogenase (p = 0.007), and creatine kinase (p = 0.004) at day 7 after surgery compared with conventional TKA. Robotic TKA was associated with significantly improved preservation of the periarticular soft tissue envelope (p < 0.001), and reduced femoral (p = 0.012) and tibial (p = 0.023) bone trauma compared with conventional TKA. Robotic TKA significantly improved the accuracy of achieving the planned limb alignment (p < 0.001), femoral component positioning (p < 0.001), and tibial component positioning (p < 0.001) compared with conventional TKA. Conclusion. Robotic TKA was associated with a transient reduction in the early (day 7) postoperative inflammatory response but there was no difference in the immediate (< 48 hours) or late (day 28) postoperative systemic inflammatory response compared with conventional TKA. Robotic TKA was associated with decreased iatrogenic periarticular soft tissue injury, reduced femoral and tibial bone trauma, and improved accuracy of component positioning compared with conventional TKA. Cite this article: Bone Joint J 2021;103-B(1):113–122

Aims. The Wrightington classification system of fracture-dislocations of the elbow divides these injuries into six subtypes depending on the involvement of the coronoid and the radial head. The aim of this study was to assess the reliability and reproducibility of this classification system. Methods. This was a blinded study using radiographs and CT scans of 48 consecutive patients managed according to the Wrightington classification system between 2010 and 2018. Four trauma and orthopaedic consultants, two post CCT fellows, and one speciality registrar based in the UK classified the injuries. The seven observers reviewed preoperative radiographs and CT scans twice, with a minimum four-week interval. Radiographs and CT scans were reviewed separately. Inter- and intraobserver reliability were calculated using Fleiss and Cohen kappa coefficients. The Landis and Koch criteria were used to interpret the strength of the kappa values. Validity was assessed by calculating the percentage agreement against intraoperative findings. Results. Of the 48 patients, three (6%) had type A injury, 11 (23%) type B, 16 (33%) type B+, 16 (33%) Type C, two (4%) type D+, and none had a type D injury. All 48 patients had anteroposterior (AP) and lateral radiographs, 44 had 2D CT scans, and 39 had 3D reconstructions. The interobserver reliability kappa value was 0.52 for radiographs, 0.71 for 2D CT scans, and 0.73 for a combination of 2D and 3D reconstruction CT scans. The median intraobserver reliability was 0.75 (interquartile range (IQR) 0.62 to 0.79) for radiographs, 0.77 (IQR 0.73 to 0.94) for 2D CT scans, and 0.89 (IQR 0.77 to 0.93) for the combination of 2D and 3D reconstruction. Validity analysis showed that accuracy significantly improved when using CT scans (p = 0.018 and p = 0.028 respectively). Conclusion. The Wrightington classification system is a reliable and valid method of classifying fracture-dislocations of the elbow. CT scans are significantly more accurate than radiographs when identifying the pattern of injury, with good intra- and interobserver reproducibility. Cite this article: Bone Joint J 2020;102-B(8):1041–1047

Our study evaluated the reliability of the Crowe and Hartofilakidis classification systems for developmental dysplasia of the hip in adults. The anteroposterior radiographs of the pelvis of 145 patients with 209 osteoarthritic hips were examined twice by three experienced hip surgeons from three European countries and the abnormal hips were rated using both classifications. The inter- and intra-observer agreement was calculated. Interobserver reliability was evaluated using weighted and unweighted kappa coefficients and for the Crowe classification, among the three pairs there was a minimum kappa coefficient with linear weighting of 0.90 for observers A and C and a maximum kappa coefficient of 0.92 for observers B and C. For the Hartofilakidis classification, the minimum kappa value was 0.85 for observers A and B, and the maximum value was 0.93 for observers B and C. With regard to intra-observer reliability, the kappa coefficients with linear weighting between the two evaluations of the same observer ranged between 0.86 and 0.95 for the Crowe classification and between 0.80 and 0.93 for the Hartofilakidis classification. The reliability of both systems was substantial to almost perfect both for serial measurements by individual readers and between different readers, although the information offered was dissimilar

Aims. The aim of this study was to identify the origin and development of the threshold for surgical intervention, highlight the consequences of residual displacement, and justify the importance of accurate measurement. Methods. A systematic review of three databases was performed to establish the origin and adaptations of the threshold, with papers screened and relevant citations reviewed. This search identified papers investigating functional outcome, including presence of arthritis, following injury. Orthopaedic textbooks were reviewed to ensure no earlier mention of the threshold was present. Results. Knirk and Jupiter (1986) were the first to quantify a threshold, with all their patients developing arthritis with > 2 mm displacement. Some papers have discussed using 1 mm, although 2 mm is most widely reported. Current guidance from the British Society for Surgery of the Hand and a Delphi panel support 2 mm as an appropriate value. Although this paper is still widely cited, the authors published a re-examination of the data showing methodological flaws which is not as widely reported. They claim their conclusions are still relevant today; however, radiological arthritis does not correlate with the clinical presentation. Function following injury has been shown to be equivalent to an uninjured population, with arthritis progressing slowly or not at all. Joint space narrowing has also been shown to often be benign. Conclusion. Knirk and Jupiter originated the threshold value of 2 mm. The lack of correlation between the radiological and clinical presentations warrants further modern investigation. Measurement often varies between observers, calling a threshold concept into question and showing the need for further development in this area. The principle of treatment remains restoration of normal anatomical position. Cite this article: Bone Joint J 2021;103-B(9):1457–1461

Aims. This combined clinical and in vitro study aimed to determine the incidence of liner malseating in modular dual mobility (MDM) constructs in primary total hip arthroplasties (THAs) from a large volume arthroplasty centre, and determine whether malseating increases the potential for fretting and corrosion at the modular metal interface in malseated MDM constructs using a simulated corrosion chamber. Methods. For the clinical arm of the study, observers independently reviewed postoperative radiographs of 551 primary THAs using MDM constructs from a single manufacturer over a three-year period, to identify the incidence of MDM liner-shell malseating. Multivariable logistic regression analysis was performed to identify risk factors including age, sex, body mass index (BMI), cup design, cup size, and the MDM case volume of the surgeon. For the in vitro arm, six pristine MDM implants with cobalt-chrome liners were tested in a simulated corrosion chamber. Three were well-seated and three were malseated with 6° of canting. The liner-shell couples underwent cyclic loading of increasing magnitudes. Fretting current was measured throughout testing and the onset of fretting load was determined by analyzing the increase in average current. Results. The radiological review identified that 32 of 551 MDM liners (5.8%) were malseated. Malseating was noted in all of the three different cup designs. The incidence of malseating was significantly higher in low-volume MDM surgeons than high-volume MDM surgeons (p < 0.001). Pristine well-seated liners showed significantly lower fretting current values at all peak loads greater than 800 N (p < 0.044). Malseated liner-shell couples had lower fretting onset loads at 2,400 N. Conclusion. MDM malseating remains an issue that can occur in at least one in 20 patients at a high-volume arthroplasty centre. The onset of fretting and increased fretting current throughout loading cycles suggests susceptibility to corrosion when this occurs. These results support the hypothesis that malseated liners may be at risk for fretting corrosion. Clinicians should be aware of this phenomenon. Cite this article: Bone Joint J 2020;102-B(7 Supple B):20–26

Aims. Trochlear dysplasia is a significant risk factor for patellofemoral instability. The Dejour classification is currently considered the standard for classifying trochlear dysplasia, but numerous studies have reported poor reliability on both plain radiography and MRI. The severity of trochlear dysplasia is important to establish in order to guide surgical management. We have developed an MRI-specific classification system to assess the severity of trochlear dysplasia, the Oswestry-Bristol Classification (OBC). This is a four-part classification system comprising normal, mild, moderate, and severe to represent a normal, shallow, flat, and convex trochlear, respectively. The purpose of this study was to assess the inter- and intraobserver reliability of the OBC and compare it with that of the Dejour classification. Methods. Four observers (two senior and two junior orthopaedic surgeons) independently assessed 32 CT and axial MRI scans for trochlear dysplasia and classified each according to the OBC and the Dejour classification systems. Assessments were repeated following a four-week interval. The inter- and intraobserver agreement was determined by using Fleiss’ generalization of Cohen’s kappa statistic and S-statistic nominal and linear weights. Results. The OBC showed fair-to-good interobserver agreement and good-to-excellent intraobserver agreement (mean kappa 0.68). The Dejour classification showed poor interobserver agreement and fair-to-good intraobserver agreement (mean kappa 0.52). Conclusion. The OBC can be used to assess the severity of trochlear dysplasia. It can be applied in clinical practice to simplify and standardize surgical decision-making in patients with recurrent patella instability. Cite this article: Bone Joint J 2020;102-B(1):102–107