Aims. Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre. Methods. Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre. Results. Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis. Conclusion. In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs. Cite this article: Bone Jt Open 2021;2(7):476–485

Aims. The effect of pelvic tilt (PT) and sagittal balance in hips with pincer-type femoroacetabular impingement (FAI) with acetabular retroversion (AR) is controversial. It is unclear if patients with AR have a rotational abnormality of the iliac wing. Therefore, we asked: are parameters for sagittal balance, and is rotation of the iliac wing, different in patients with AR compared to a control group?; and is there a correlation between iliac rotation and acetabular version?. Methods. A retrospective, review board-approved, controlled study was performed including 120 hips in 86 consecutive patients with symptomatic FAI or hip dysplasia. Pelvic CT scans were reviewed to calculate parameters for sagittal balance (pelvic incidence (PI), PT, and sacral slope), anterior pelvic plane angle, pelvic inclination, and external rotation of the iliac wing and were compared to a control group (48 hips). The 120 hips were allocated to the following groups: AR (41 hips), hip dysplasia (47 hips) and cam FAI with normal acetabular morphology (32 hips). Subgroups of total AR (15 hips) and high acetabular anteversion (20 hips) were analyzed. Statistical analysis was performed using analysis of variance with Bonferroni correction. Results. PI and PT were significantly decreased comparing AR (PI 42° (SD 10°), PT 4° (SD 5°)) with dysplastic hips (PI 55° (SD 12°), PT 10° (SD 6°)) and with the control group (PI 51° (SD 9°) and PT 13° (SD 7°)) (p < 0.001). External rotation of the iliac wing was significantly increased comparing AR (29° (SD 4°)) with dysplastic hips (20°(SD 5°)) and with the control group (25° (SD 5°)) (p < 0.001). Correlation between external rotation of the iliac wing and acetabular version was significant and strong (r = 0.81; p < 0.001). Correlation between PT and acetabular version was significant and moderate (r = 0.58; p < 0.001). Conclusion. These findings could contribute to a better understanding of hip pain in a sitting position and extra-articular subspine FAI of patients with AR. These patients have increased iliac external rotation, a rotational abnormality of the iliac wing. This has implications for surgical therapy with hip arthroscopy and acetabular rim trimming or anteverting periacetabular osteotomy (PAO). Cite this article: Bone Jt Open 2021;2(10):813–824

Aims

This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads.

Aims. Patient dissatisfaction is not uncommon following primary total knee arthroplasty. One proposed method to alleviate this is by improving knee kinematics. Therefore, we aimed to answer the following research question: are there significant differences in knee kinematics based on the design of the tibial insert (cruciate-retaining (CR), ultra-congruent (UC), or medial congruent (MC))?. Methods. Overall, 15 cadaveric knee joints were examined with a CR implant with three different tibial inserts (CR, UC, and MC) using an established knee joint simulator. The effects on coronal alignment, medial and lateral femoral roll back, femorotibial rotation, bony rotations (femur, tibia, and patella), and patellofemoral length ratios were determined. Results. No statistically significant differences were found regarding coronal alignment (p = 0.087 to p = 0.832). The medial congruent insert demonstrated restricted femoral roll back (mean medial 37.57 mm; lateral 36.34 mm), while the CR insert demonstrated the greatest roll back (medial 42.21 mm; lateral 37.88 mm; p < 0.001, respectively). Femorotibial rotation was greatest with the CR insert with 2.45° (SD 4.75°), then the UC insert with 1.31° (SD 4.15°; p < 0.001), and lowest with the medial congruent insert with 0.8° (SD 4.24°; p < 0.001). The most pronounced patella shift, but lowest patellar rotation, was noted with the CR insert. Conclusion. The MC insert demonstrated the highest level of constraint of these inserts. Femoral roll back, femorotibial rotation, and single bony rotations were lowest with the MC insert. The patella showed less shifting with the MC insert, but there was significantly increased rotation. While the medial congruent insert was found to have highest constraint, it remains uncertain if this implant recreates native knee kinematics or if this will result in improved patient satisfaction. Cite this article: Bone Jt Open 2024;5(7):592–600

Aims. Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. Methods. We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Results. Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. Conclusion. The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity. Cite this article: Bone Jt Open 2023;4(6):432–441

Aims. Traditionally, total hip arthroplasty (THA) templating has been performed on anteroposterior (AP) pelvis radiographs. Recently, additional AP hip radiographs have been recommended for accurate measurement of the femoral offset (FO). To verify this claim, this study aimed to establish quantitative data of the measurement error of the FO in relation to leg position and X-ray source position using a newly developed geometric model and clinical data. Methods. We analyzed the FOs measured on AP hip and pelvis radiographs in a prospective consecutive series of 55 patients undergoing unilateral primary THA for hip osteoarthritis. To determine sample size, a power analysis was performed. Patients’ position and X-ray beam setting followed a standardized protocol to achieve reproducible projections. All images were calibrated with the KingMark calibration system. In addition, a geometric model was created to evaluate both the effects of leg position (rotation and abduction/adduction) and the effects of X-ray source position on FO measurement. Results. The mean FOs measured on AP hip and pelvis radiographs were 38.0 mm (SD 6.4) and 36.6 mm (SD 6.3) (p < 0.001), respectively. Radiological view had a smaller effect on FO measurement than inaccurate leg positioning. The model showed a non-linear relationship between projected FO and femoral neck orientation; at 30° external neck rotation (with reference to the detector plane), a true FO of 40 mm was underestimated by up to 20% (7.8 mm). With a neutral to mild external neck rotation (≤ 15°), the underestimation was less than 7% (2.7 mm). The effect of abduction and adduction was negligible. Conclusion. For routine THA templating, an AP pelvis radiograph remains the gold standard. Only patients with femoral neck malrotation > 15° on the AP pelvis view, e.g. due to external rotation contracture, should receive further imaging. Options include an additional AP hip view with elevation of the entire affected hip to align the femoral neck more parallel to the detector, or a CT scan in more severe cases. Cite this article: Bone Jt Open 2022;3(10):795–803

Aims. Computer-assisted 3D preoperative planning software has the potential to improve postoperative stability in total hip arthroplasty (THA). Commonly, preoperative protocols simulate two functional positions (standing and relaxed sitting) but do not consider other common positions that may increase postoperative impingement and possible dislocation. This study investigates the feasibility of simulating commonly encountered positions, and positions with an increased risk of impingement, to lower postoperative impingement risk in a CT-based 3D model. Methods. A robotic arm-assisted arthroplasty planning platform was used to investigate 11 patient positions. Data from 43 primary THAs were used for simulation. Sacral slope was retrieved from patient preoperative imaging, while angles of hip flexion/extension, hip external/internal rotation, and hip abduction/adduction for tested positions were derived from literature or estimated with a biomechanical model. The hip was placed in the described positions, and if impingement was detected by the software, inspection of the impingement type was performed. Results. In flexion, an overall impingement rate of 2.3% was detected for flexed-seated, squatting, forward-bending, and criss-cross-sitting positions, and 4.7% for the ankle-over-knee position. In extension, most hips (60.5%) were found to impinge at or prior to 50° of external rotation (pivoting). Many of these impingement events were due to a prominent ischium. The mean maximum external rotation prior to impingement was 45.9° (15° to 80°) and 57.9° (20° to 90°) prior to prosthetic impingement. No impingement was found in standing, sitting, crossing ankles, seiza, and downward dog. Conclusion. This study demonstrated that positions of daily living tested in a CT-based 3D model show high rates of impingement. Simulating additional positions through 3D modelling is a low-cost method of potentially improving outcomes without compromising patient safety. By incorporating CT-based 3D modelling of positions of daily living into routine preoperative protocols for THA, there is the potential to lower the risk of postoperative impingement events. Cite this article: Bone Jt Open 2023;4(6):416–423

Aims. Custom triflange acetabular components (CTACs) play an important role in reconstructive orthopaedic surgery, particularly in revision total hip arthroplasty (rTHA) and pelvic tumour resection procedures. Accurate CTAC positioning is essential to successful surgical outcomes. While prior studies have explored CTAC positioning in rTHA, research focusing on tumour cases and implant flange positioning precision remains limited. Additionally, the impact of intraoperative navigation on positioning accuracy warrants further investigation. This study assesses CTAC positioning accuracy in tumour resection and rTHA cases, focusing on the differences between preoperative planning and postoperative implant positions. Methods. A multicentre observational cohort study in Australia between February 2017 and March 2021 included consecutive patients undergoing acetabular reconstruction with CTACs in rTHA (Paprosky 3A/3B defects) or tumour resection (including Enneking P2 peri-acetabular area). Of 103 eligible patients (104 hips), 34 patients (35 hips) were analyzed. Results. CTAC positioning was generally accurate, with minor deviations in cup inclination (mean 2.7°; SD 2.84°), anteversion (mean 3.6°; SD 5.04°), and rotation (mean 2.1°; SD 2.47°). Deviation of the hip centre of rotation (COR) showed a mean vector length of 5.9 mm (SD 7.24). Flange positions showed small deviations, with the ischial flange exhibiting the largest deviation (mean vector length of 7.0 mm; SD 8.65). Overall, 83% of the implants were accurately positioned, with 17% exceeding malpositioning thresholds. CTACs used in tumour resections exhibited higher positioning accuracy than rTHA cases, with significant differences in inclination (1.5° for tumour vs 3.4° for rTHA) and rotation (1.3° for tumour vs 2.4° for rTHA). The use of intraoperative navigation appeared to enhance positioning accuracy, but this did not reach statistical significance. Conclusion. This study demonstrates favourable CTAC positioning accuracy, with potential for improved accuracy through intraoperative navigation. Further research is needed to understand the implications of positioning accuracy on implant performance and long-term survival. Cite this article: Bone Jt Open 2024;5(4):260–268

Aims. Custom-made partial pelvis replacements (PPRs) are increasingly used in the reconstruction of large acetabular defects and have mainly been designed using a triflange approach, requiring extensive soft-tissue dissection. The monoflange design, where primary intramedullary fixation within the ilium combined with a monoflange for rotational stability, was anticipated to overcome this obstacle. The aim of this study was to evaluate the design with regard to functional outcome, complications, and acetabular reconstruction. Methods. Between 2014 and 2023, 79 patients with a mean follow-up of 33 months (SD 22; 9 to 103) were included. Functional outcome was measured using the Harris Hip Score and EuroQol five-dimension questionnaire (EQ-5D). PPR revisions were defined as an endpoint, and subgroups were analyzed to determine risk factors. Results. Implantation was possible in all cases with a 2D centre of rotation deviation of 10 mm (SD 5.8; 1 to 29). PPR revision was necessary in eight (10%) patients. HHS increased significantly from 33 to 72 postoperatively, with a mean increase of 39 points (p < 0.001). Postoperative EQ-5D score was 0.7 (SD 0.3; -0.3 to 1). Risk factor analysis showed significant revision rates for septic indications (p ≤ 0.001) as well as femoral defect size (p = 0.001). Conclusion. Since large acetabular defects are being treated surgically more often, custom-made PPR should be integrated as an option in treatment algorithms. Monoflange PPR, with primary iliac fixation, offers a viable treatment option for Paprosky III defects with promising functional results, while requiring less soft-tissue exposure and allowing immediate full weightbearing. Cite this article: Bone Jt Open 2024;5(8):688–696

Aims. Cam and pincer morphologies are potential precursors to hip osteoarthritis and important contributors to non-arthritic hip pain. However, only some hips with these pathomorphologies develop symptoms and joint degeneration, and it is not clear why. Anterior impingement between the femoral head-neck contour and acetabular rim in positions of hip flexion combined with rotation is a proposed pathomechanism in these hips, but this has not been studied in active postures. Our aim was to assess the anterior impingement pathomechanism in both active and passive postures with high hip flexion that are thought to provoke impingement. Methods. We recruited nine participants with cam and/or pincer morphologies and with pain, 13 participants with cam and/or pincer morphologies and without pain, and 11 controls from a population-based cohort. We scanned hips in active squatting and passive sitting flexion, adduction, and internal rotation using open MRI and quantified anterior femoroacetabular clearance using the β angle. Results. In squatting, we found significantly decreased anterior femoroacetabular clearance in painful hips with cam and/or pincer morphologies (mean -11.3° (SD 19.2°)) compared to pain-free hips with cam and/or pincer morphologies (mean 8.5° (SD 14.6°); p = 0.022) and controls (mean 18.6° (SD 8.5°); p < 0.001). In sitting flexion, adduction, and internal rotation, we found significantly decreased anterior clearance in both painful (mean -15.2° (SD 15.3°); p = 0.002) and painfree hips (mean -4.7° (SD 13°); p = 0.010) with cam and/pincer morphologies compared to the controls (mean 7.1° (SD 5.9°)). Conclusion. Our results support the anterior femoroacetabular impingement pathomechanism in hips with cam and/or pincer morphologies and highlight the effect of posture on this pathomechanism. Cite this article: Bone Jt Open 2021;2(11):988–996

Aims. Avascular femoral head necrosis in the context of gymnastics is a rare but serious complication, appearing similar to Perthes’ disease but occurring later during adolescence. Based on 3D CT animations, we propose repetitive impact between the main supplying vessels on the posterolateral femoral neck and the posterior acetabular wall in hyperextension and external rotation as a possible cause of direct vascular damage, and subsequent femoral head necrosis in three adolescent female gymnasts we are reporting on. Methods. Outcome of hip-preserving head reduction osteotomy combined with periacetabular osteotomy was good in one and moderate in the other up to three years after surgery; based on the pronounced hip destruction, the third received initially a total hip arthroplasty. Results. The described pathology is quite devastating, and extensive joint preserving surgery (which has been shown successful in Perthes’ cases) was less successful in this patient cohort. Conclusion. Supraselective angiography may be helpful to improve pathomechanical understanding and surgical decision making. Cite this article: Bone Jt Open 2022;3(9):666–673

Aims. Despite limited clinical scientific backing, an additional trochanteric stabilizing plate (TSP) has been advocated when treating unstable trochanteric fractures with a sliding hip screw (SHS). We aimed to explore whether the TSP would result in less post operative fracture motion, compared to SHS alone. Methods. Overall, 31 patients with AO/OTA 31-A2 trochanteric fractures were randomized to either a SHS alone or a SHS with an additional TSP. To compare postoperative fracture motion, radiostereometric analysis (RSA) was performed before and after weightbearing, and then at four, eight, 12, 26, and 52 weeks. With the “after weightbearing” images as baseline, we calculated translations and rotations, including shortening and medialization of the femoral shaft. Results. Similar migration profiles were observed in all directions during the course of healing. At one year, eight patients in the SHS group and 12 patients in the TSP group were available for analysis, finding a clinically non-relevant, and statistically non-significant, difference in total translation of 1 mm (95% confidence interval -4.7 to 2.9) in favour of the TSP group. In line with the migration data, no significant differences in clinical outcomes were found. Conclusion. The TSP did not influence the course of healing or postoperative fracture motion compared to SHS alone. Based on our results, routine use of the TSP in AO/OTA 31-A2 trochanteric fractures cannot be recommended. The TSP has been shown, in biomechanical studies, to increase stability in sliding hip screw constructs in both unstable and intermediate stable trochanteric fractures, but the clinical evidence is limited. This study showed no advantage of the TSP in unstable (AO 31-A2) fractures in elderly patients when fracture movement was evaluated with radiostereometric analysis. Cite this article: Bone Jt Open 2024;5(1):37–45

Aims. This systematic review aims to identify 3D predictors derived from biplanar reconstruction, and to describe current methods for improving curve prediction in patients with mild adolescent idiopathic scoliosis. Methods. A comprehensive search was conducted by three independent investigators on MEDLINE, PubMed, Web of Science, and Cochrane Library. Search terms included “adolescent idiopathic scoliosis”,“3D”, and “progression”. The inclusion and exclusion criteria were carefully defined to include clinical studies. Risk of bias was assessed with the Quality in Prognostic Studies tool (QUIPS) and Appraisal tool for Cross-Sectional Studies (AXIS), and level of evidence for each predictor was rated with the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach. In all, 915 publications were identified, with 377 articles subjected to full-text screening; overall, 31 articles were included. Results. Torsion index (TI) and apical vertebral rotation (AVR) were identified as accurate predictors of curve progression in early visits. Initial TI > 3.7° and AVR > 5.8° were predictive of curve progression. Thoracic hypokyphosis was inconsistently observed in progressive curves with weak evidence. While sagittal wedging was observed in mild curves, there is insufficient evidence for its correlation with curve progression. In curves with initial Cobb angle < 25°, Cobb angle was a poor predictor for future curve progression. Prediction accuracy was improved by incorporating serial reconstructions in stepwise layers. However, a lack of post-hoc analysis was identified in studies involving geometrical models. Conclusion. For patients with mild curves, TI and AVR were identified as predictors of curve progression, with TI > 3.7° and AVR > 5.8° found to be important thresholds. Cobb angle acts as a poor predictor in mild curves, and more investigations are required to assess thoracic kyphosis and wedging as predictors. Cumulative reconstruction of radiographs improves prediction accuracy. Comprehensive analysis between progressive and non-progressive curves is recommended to extract meaningful thresholds for clinical prognostication. Cite this article: Bone Jt Open 2024;5(3):243–251

Aims. The risk factors for abnormal spinopelvic mobility (SPM), defined as an anterior rotation of the spinopelvic tilt (∆SPT) ≥ 20° in a flexed-seated position, have been described. The implication of pelvic incidence (PI) is unclear, and the concept of lumbar lordosis (LL) based on anatomical limits may be erroneous. The distribution of LL, including a unusual shape in patients with a high lordosis, a low pelvic incidence, and an anteverted pelvis seems more relevant. Methods. The clinical data of 311 consecutive patients who underwent total hip arthroplasty was retrospectively analyzed. We analyzed the different types of lumbar shapes that can present in patients to identify their potential associations with abnormal pelvic mobility, and we analyzed the potential risk factors associated with a ∆SPT ≥ 20° in the overall population. Results. ΔSPT ≥ 20° rates were 28.3%, 11.8%, and 14.3% for patients whose spine shape was low PI/low lordosis (group 1), low PI anteverted (group 2), and high PI/high lordosis (group 3), respectively (p = 0.034). There was no association between ΔSPT ≥ 20° and PI ≤ 41° (odds ratio (OR) 2.01 (95% confidence interval (CI)0.88 to 4.62), p = 0.136). In the multivariate analysis, the following independent predictors of ΔSPT ≥ 20° were identified: SPT ≤ -10° (OR 3.49 (95% CI 1.59 to 7.66), p = 0.002), IP-LL ≥ 20 (OR 4.38 (95% CI 1.16 to 16.48), p = 0.029), and group 1 (OR 2.47 (95% CI 1.19; to 5.09), p = 0.0148). Conclusion. If the PI value alone is not indicative of SPM, patients with a low PI, low lordosis and a lumbar apex at L4-L5 or below will have higher rates of abnormal SPM than patients with a low PI anteverted and high lordosis. Cite this article: Bone Jt Open 2023;4(9):668–675

Aims. In order to release the contracture band completely without damaging normal tissues (such as the sciatic nerve) in the surgical treatment of gluteal muscle contracture (GMC), we tried to display the relationship between normal tissue and contracture bands by magnetic resonance neurography (MRN) images, and to predesign a minimally invasive surgery based on the MRN images in advance. Methods. A total of 30 patients (60 hips) were included in this study. MRN scans of the pelvis were performed before surgery. The contracture band shape and external rotation angle (ERA) of the proximal femur were also analyzed. Then, the minimally invasive GMC releasing surgery was performed based on the images and measurements, and during the operation, incision lengths, surgery duration, intraoperative bleeding, and complications were recorded; the time of the first postoperative off-bed activity was also recorded. Furthermore, the patients’ clinical functions were evaluated by means of Hip Outcome Score (HOS) and Ye et al’s objective assessments, respectively. Results. The contracture bands exhibited three typical types of shape – feather-like, striped, and mixed shapes – in MR images. Guided by MRN images, we designed minimally invasive approaches directed to each hip. These approaches resulted in a shortened incision length in each hip (0.3 cm (SD 0.1)), shorter surgery duration (25.3 minutes (SD 5.8)), less intraoperative bleeding (8.0 ml (SD 3.6)), and shorter time between the end of the operation and the patient’s first off-bed activity (17.2 hours (SD 2.0)) in each patient. Meanwhile, no serious postoperative complications occurred in all patients. The mean HOS-Sports subscale of patients increased from 71.0 (SD 5.3) to 94.83 (SD 4.24) at six months postoperatively (p < 0.001). The follow-up outcomes from all patients were “good” and “excellent”, based on objective assessments. Conclusion. Preoperative MRN analysis can be used to facilitate the determination of the relationship between contracture band and normal tissues. The minimally invasive surgical design via MRN can avoid nerve damage and improve the release effect. Cite this article: Bone Jt Open 2024;5(9):776–784

Aims. Scoliosis is a lateral curvature of the spine with associated rotation, often causing distress due to appearance. For some curves, there is good evidence to support the use of a spinal brace, worn for 20 to 24 hours a day to minimize the curve, making it as straight as possible during growth, preventing progression. Compliance can be poor due to appearance and comfort. A night-time brace, worn for eight to 12 hours, can achieve higher levels of curve correction while patients are supine, and could be preferable for patients, but evidence of efficacy is limited. This is the protocol for a randomized controlled trial of ‘full-time bracing’ versus ‘night-time bracing’ in adolescent idiopathic scoliosis (AIS). Methods. UK paediatric spine clinics will recruit 780 participants aged ten to 15 years-old with AIS, Risser stage 0, 1, or 2, and curve size (Cobb angle) 20° to 40° with apex at or below T7. Patients are randomly allocated 1:1, to either full-time or night-time bracing. A qualitative sub-study will explore communication and experiences of families in terms of bracing and research. Patient and Public Involvement & Engagement informed study design and will assist with aspects of trial delivery and dissemination. Discussion. The primary outcome is ‘treatment failure’ (Cobb angle progression to 50° or more before skeletal maturity); skeletal maturity is at Risser stage 4 in females and 5 in males, or ‘treatment success’ (Cobb angle less than 50° at skeletal maturity). The comparison is on a non-inferiority basis (non-inferiority margin 11%). Participants are followed up every six months while in brace, and at one and two years after skeletal maturity. Secondary outcomes include the Scoliosis Research Society 22 questionnaire and measures of quality of life, psychological effects of bracing, adherence, anxiety and depression, sleep, satisfaction, and educational attainment. All data will be collected through the British Spine Registry. Cite this article: Bone Jt Open 2023;4(11):873–880

Aims. The conventionally described mechanism of distal biceps tendon rupture (DBTR) is of a ‘considerable extension force suddenly applied to a resisting, actively flexed forearm’. This has been commonly paraphrased as an ‘eccentric contracture to a flexed elbow’. Both definitions have been frequently used in the literature with little objective analysis or citation. The aim of the present study was to use video footage of real time distal biceps ruptures to revisit and objectively define the mechanism of injury. Methods. An online search identified 61 videos reporting a DBTR. Videos were independently reviewed by three surgeons to assess forearm rotation, elbow flexion, shoulder position, and type of muscle contraction being exerted at the time of rupture. Prospective data on mechanism of injury and arm position was also collected concurrently for 22 consecutive patients diagnosed with an acute DBTR in order to corroborate the video analysis. Results. Four videos were excluded, leaving 57 for final analysis. Mechanisms of injury included deadlift, bicep curls, calisthenics, arm wrestling, heavy lifting, and boxing. In all, 98% of ruptures occurred with the arm in supination and 89% occurred at 0° to 10° of elbow flexion. Regarding muscle activity, 88% occurred during isometric contraction, 7% during eccentric contraction, and 5% during concentric contraction. Interobserver correlation scores were calculated as 0.66 to 0.89 using the free-marginal Fleiss Kappa tool. The prospectively collected patient data was consistent with the video analysis, with 82% of injuries occurring in supination and 95% in relative elbow extension. Conclusion. Contrary to the classically described injury mechanism, in this study the usual arm position during DBTR was forearm supination and elbow extension, and the muscle contraction was typically isometric. This was demonstrated for both video analysis and ‘real’ patients across a range of activities leading to rupture. Cite this article: Bone Jt Open 2022;3(10):826–831

Aims. After failed acetabular fractures, total hip arthroplasty (THA) is a challenging procedure and considered the gold standard treatment. The complexity of the procedure depends on the fracture pattern and the initial fracture management. This study’s primary aim was to evaluate patient-reported outcome measures (PROMs) for patients who underwent delayed uncemented acetabular THA after acetabular fractures. The secondary aims were to assess the radiological outcome and the incidence of the associated complications in those patients. Methods. A total of 40 patients underwent cementless acetabular THA following failed treatment of acetabular fractures. The postoperative clinical and radiological outcomes were evaluated for all the cohort. Results. The median (interquartile range (IQR)) Oxford Hip Score (OHS) improved significantly from 9.5 (7 to 11.5), (95% confidence interval (CI) (8 to 10.6)) to 40 (39 to 44), (95% CI (40 to 43)) postoperatively at the latest follow-up (p < 0.001). It was worth noting that the initial acetabular fracture type (simple vs complex), previous acetabular treatment (ORIF vs conservative), fracture union, and restoration of anatomical centre of rotation (COR) did not affect the final OHS. The reconstructed centre of rotation (COR) was restored in 29 (72.5%) patients. The mean abduction angle in whom acetabular fractures were managed conservatively was statistically significantly higher than the surgically treated patients 42.6° (SD 7.4) vs 38° (SD 5.6)) (p = 0.032). We did not have any case of acetabular or femoral loosening at the time of the last follow-up. We had two patients with successful two-stage revision for infection with overall eight-year survival rate was 95.2% (95% CI 86.6% to 100%) with revision for any reason at a median (IQR) duration of follow-up 50 months (16 to 87) months following THA. Conclusion. Delayed cementless acetabular THA in patients with previous failed acetabular fracture treatments produces good clinical outcomes (PROMS) with excellent survivorship, despite the technically demanding nature of the procedure. The initial fracture treatment does not influence the outcome of delayed THA. In selected cases of acetabular fractures (either nondisplaced or with secondary congruency), the initial nonoperative treatment neither resulted in large acetabular defects nor required additional acetabular reconstruction at the time of THA. Cite this article: Bone Jt Open 2021;2(12):1067–1074

Aims. Complex total hip arthroplasty (THA) with subtrochanteric shortening osteotomy is necessary in conditions other than developmental dysplasia of the hip (DDH) and septic arthritis sequelae with significant proximal femur migration. Our aim was to evaluate the hip centre restoration with THAs in these hips. Methods. In all, 27 THAs in 25 patients requiring THA with femoral shortening between 2012 and 2019 were assessed. Bilateral shortening was required in two patients. Subtrochanteric shortening was required in 14 out of 27 hips (51.9%) with aetiology other than DDH or septic arthritis. Vertical centre of rotation (VCOR), horizontal centre of rotation, offset, and functional outcome was calculated. The mean followup was 24.4 months (5 to 92 months). Results. The mean VCOR was 17.43 mm (9.5 to 27 mm) and horizontal centre of rotation (HCOR) was 24.79 mm (17.2 to 37.6 mm). Dislocation at three months following acetabulum reconstruction required femoral shortening for offset correction and hip centre restoration in one hip. Mean horizontal offset was 39.72 (32.7 to 48.2 mm) compared to 42.89 (26.7 to 50.6 mm) on the normal side. Mean Harris Hip Score (HHS) of 22.64 (14 to 35) improved to 79.43 (68 to 92). Mean pre-operative shortening was 3.95 cm (2 to 8 cm). Residual limb length discrepancy was 1.5 cm (0 to 2 cm). Sciatic neuropraxia in two patients recovered by six months, and femoral neuropraxia in one hip recovered by 12 months. Mean Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) was 13.92 (9 to 19). Mean 12-item short form survey (SF-12) physical scores of 50.6 and mental of 60.12 were obtained. Conclusion. THA with subtrochanteric shortening is valuable in complex hips with high dislocation. The restoration of the hip centre of rotation and offset is important in these hips. Level of evidence IV. Femoral shortening useful in conditions other than DDH and septic sequelae. Restoration of hip centre combined with offset to be planned and ensured

Aims. To compare the in vivo long-term fixation achieved by two acetabular components with different porous ingrowth surfaces using radiostereometric analysis (RSA). Methods. This was a minimum ten-year follow-up of a prospective randomized trial of 62 hips with two different porous ingrowth acetabular components. RSA exams had previously been acquired through two years of follow-up. Patients returned for RSA examination at a minimum of ten years. In addition, radiological appearance of these acetabular components was analyzed, and patient-reported outcome measures (PROMs) obtained. Results. In all, 15 hips were available at ten years. There was no statistically significant difference in PROMS between the two groups; PROMs were improved at ten years compared to preoperative scores. Conventional radiological assessment revealed well-fixed components. There was minimal movement for both porous surfaces in translation (X, Y, Z, 3D translation in mm (median and interquartile range (IQR)), StikTite (Smith and Nephew, Memphis, Tennessee, USA): 0.03 (1.08), 0.12 (0.7), 0.003 (2.3), 0.37 (0.30), and Roughcoat (Smith and Nephew): -0.6 (0.59),–0.1 (0.49), 0.1 (1.12), 0.48 (0.38)), and rotation (X, Y, Z rotation in degrees (median and IQR), (Stiktite: -0.4 (3), 0.28 (2), -0.2 (1), and Roughcoat: - 0.4 (1),–0.1 (1), 0.2 (2)). There was no statistically significant difference between the two cohorts (p-value for X, Y, Z, 3D translation - 0.54, 0.46, 0.87, 0.55 and for X, Y, Z rotation - 0.41, 0.23, 0.23 respectively) at ten years. There was significant correlation between two years and ten years 3D translation for all components (r = 0.81(p =< 0.001)). Conclusion. Both porous ingrowth surfaces demonstrated excellent fixation on plain radiographs and with RSA at ten years. Short-term RSA data are good predictors for long-term migration data