Aims. This study aimed to investigate the optimal sagittal positioning of the uncemented femoral component in total knee arthroplasty to minimize the risk of aseptic loosening and periprosthetic fracture. Methods. Ten different sagittal placements of the femoral component, ranging from -5 mm (causing anterior notch) to +4 mm (causing anterior gap), were analyzed using finite element analysis. Both gait and squat loading conditions were simulated, and Von Mises stress and interface micromotion were evaluated to assess fracture and loosening risk. Results. During gait, varied sagittal positioning did not lead to excessive Von Mises stress or micromotion. However, under squat conditions, posterior positioning (-4 and -5 mm) resulted in stress exceeding 150 MPa at the femoral notch, indicating potential fracture risk. Conversely, +1 mm and 0 mm sagittal positions demonstrated minimal interface micromotion. Conclusion. Slightly anterior sagittal positioning (+1 mm) or neutral positioning (0 mm) effectively reduced stress concentration at the femoral notch and minimized interface micromotion. Thus, these positions are deemed suitable to decrease the risk of aseptic loosening and periprosthetic femoral fracture

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. The aim of this study was to identify the optimal lip position for total hip arthroplasties (THAs) using a lipped liner. There is a lack of consensus on the optimal position, with substantial variability in surgeon practice. Methods. A model of a THA was developed using a 20° lipped liner. Kinematic analyses included a physiological range of motion (ROM) analysis and a provocative dislocation manoeuvre analysis. ROM prior to impingement was calculated and, in impingement scenarios, the travel distance prior to dislocation was assessed. The combinations analyzed included nine cup positions (inclination 30-40-50°, anteversion 5-15-25°), three stem positions (anteversion 0-15-30°), and five lip orientations (right hip 7 to 11 o’clock). Results. The position of the lip changes the ROM prior to impingement, with certain combinations leading to impingement within the physiological ROM. Inferior lip positions (7 to 8 o’clock) performed best with cup inclinations of 30° and 40°. Superior lip positions performed best with cup inclination of 50°. When impingement occurs in the plane of the lip, the lip increases the travel distance prior to dislocation. Inferior lip positions led to the largest increase in jump distance in a posterior dislocation provocation manoeuvre. Conclusion. The lip orientation that provides optimal physiological ROM depends on the orientation of the cup and stem. For a THA with stem anteversion 15°, cup inclination 40°, and cup anteversion 15°, the optimal lip position was posterior-inferior (8 o’clock). Maximizing jump distance prior to dislocation while preventing impingement in the opposite direction is possible with appropriate lip positioning. Cite this article: Bone Joint Res 2023;12(9):571–579

Aims: For planning of Total Hip Arthroplasties (THA) plain X-rays of the pelvis in anterior posterior orientation are used. New methods such as CT scans and intraoperative digitization with navigation devices introduce the third dimension into orthopaedic planning. In order to compare measurements derived from three-dimensional data-acquisition with standard pelvic measurements it is important to estimate the underlying variances of those standards. Methods: 120 patients were investigated and subdivided in 4 groups depending of their age or the condition of their hip joints. The patients were positioned in a supine position on a table and in a standing position. Three landmarks at the patientñs pelvis (left and right anterior superior iliac spine (ASIS) and the pubic tubercle (PT)) were percutaneously digitized with a digitizing arm (Micro-Scribe-3DX, Vizion, Glendale, CA). The pelvic positions in space were calculated in relation to the horizontal and the vertical plane. Results: Despite the anatomical deþnition (0¡), we found an inclination of 4-6¡. There is no signiþcant difference between supine and standing position and no signiþcant difference between the groups and no diffenrence between genders. All patients lyed ßat in supine position without special positioning effort Conclusions: The pelvis orientation ist very stable in standing as well in supine position no matter if the patient is old or young, has coxarthrosis ore none or a THA. Therefore it can be concluded that our knowledge derived from measurements of planar a.-p.x-rays is not inßuenced by a massive variance in pelvic positions

The aim of this study was to investigate the effect of different loading scenarios and foot positions on the configuration of the distal tibiofibular joint (DTFJ). Fourteen paired human cadaveric lower legs were mounted in a loading frame. Computed tomography scans were obtained in unloaded state (75 N) and single-leg loaded stand (700 N) of each specimen in five foot positions: neutral, 15° external rotation, 15° internal rotation, 20° dorsiflexion, and 20° plantarflexion. An automated three-dimensional measurement protocol was used to assess clear space (diastasis), translational angle (rotation), and vertical offset (fibular shortening) in each foot position and loading condition. Foot positions had a significant effect on the configuration of DTFJ. Largest effects were related to clear space increase by 0.46 mm (SD 0.21 mm) in loaded dorsal flexion and translation angle of 2.36° (SD 1.03°) in loaded external rotation, both versus loaded neutral position. Loading had no effect on clear space and vertical offset in any position. Translation angle was significantly influenced under loading by −0.81° (SD 0.69°) in internal rotation only. Foot positioning noticeably influences the measurement when evaluating the configuration of DTFJ. The influence of the weightbearing seems to have no relevant effect on native ankles in neutral position

Pressure ulcers are a common occurrence in individuals with spinal cord injuries, and are attributed to prolonged sitting and limited mobility. This therefore creates the need to better understand soft tissue composition, in the attempt to prevent and treat pressure ulcers. In this study, novel approaches to imaging the soft tissue of the buttocks were investigated in the loaded and unloaded position using ultrasound (US) and magnetic resonance imaging (MRI). Twenty-six able-bodied participants (n=26, 13 males and 13 females) were recruited for this study and 1 male with a spinal cord injury. Two visits using US were required, as well as one MRI visit to evaluate soft tissue thickness and composition. US Imaging for the loaded conditions was performed using an innovative chair which allowed image acquisition in the seated upright position and MRI was done in the lateral decubitus position and loading was applied to the buttocks using a newly developed MRI compatible loader. The unloaded condition was a lateral decubitus position. Soft tissue was measured between the peak of the ischial tuberosity (IT) and the proximal femur and skin. Tissue thickness reliability for US was excellent, ICC=0.934–0.981 with no significant differences between the scan days. US and MRI measures of tissue thickness were significantly correlated (r=0.68–0.91). US underestimated unloaded tissue thicknesses with a mean bias of 0.39 – 0.56 for total tissue and muscle + tendon thickness. When the buttocks were loaded, total tissue thickness was reduced by 64.2±9.1%. US assessment of soft tissue thicknesses was reliable in both positions. The unloaded measurements using US were validated with MRI with acceptable limits of agreement, albeit tended to underestimate tissue thickness. Tissue thickness, but not fatty infiltration of muscle played a role in how the soft tissue of the buttocks responded to loading

Introduction: Hip dislocation remains a relevant complication of total hip arthroplasty.The implants position plays a major role, especially cup anteversion.It has been demonstrated that anteversion measured on CTscan depends on the pelvic position in a lying patient. This prospective study evaluates the influence of pelvic tilt according to standing and sitting positions. Material and Methods: The radiological records of 328 consecutive asymptomatic patients with THP were analyzed. These were routine radiological controls of non cemented THP with metal back acetabular implants. All patients had AP and lateral radiographs in standing and sitting position and a “low-dose” CT scan of the pelvis in lying position.Patients were checked for the absence lower limb length discrepancy and lumbosacral junction abnormality. All the measurements were done by two independent observers and averaged. From the standard radiographs, the sacral slope (SS), the acetabular frontal inclination (AFI), and the acetabular sagittal inclination (ASI) were measured in standing, sitting, and lying positions. From the CT scan sections, the anatomical ante-version (AA) was measured in lying position on axial images according to Murray. The results were compared to a previously described protocol replicating standing and sitting positions: CTscan sections were oriented according to sacral slope. Results: We confirmed that the anatomical anteversion (AA), the frontal inclination (FI), and the sagittal inclination (SI) were functional parameter which significantly varied between standing, sitting, and lying positions according to sacral slope variations.The acetabular parameters in lying position highly correlated to the one in standing position, while poorly correlated with sitting position. The difference between the lying and the sitting positions was about 10°, 25°, and 15° for the AA, the AFI, and the ASI respectively.Mean lying anteversion angle was 24.2° (SD6,9°).Posterior pelvic tilt in sitting position, (sacral slope decrease) was linked to anteversion increase (mean value 38,8° - SD 5,4°). Anterior pelvic tilt in standing position (sacral slope increase) was linked to lower anteversion (mean value 31,7° - SD5,6°). Discussion and Conclusions: Our study confirms the interest CTscan sections oriented according to sacral slope.The strong correlation between lying and standing measurements suggests that classical CTscan protocol is relevant for standing anteversion. According to the poor correlation between lying and sitting positions, it is less contributive for the investigation of dislocations in sitting position

Introduction. Assessment of the humeral head translation with respect to the glenoid joint, termed humeral head migration (HHM), is crucial in total shoulder arthroplasty pre-operative planning. Its assessment informs current classification systems for shoulder osteoarthritis as well as the evaluation of surgical correction. In current clinical practice, HHM assessment relies on computed-tomography (CT) imaging. However, the associated supine position might undermine its functional relevance as it does not reflect the weight-bearing condition with active muscle engagement associated with the upright standing position of most daily activities. Therefore, we assessed to what extent HHM in a supine position is associated with HHM in a range of functional arm positions. Method. 26 shoulder osteoarthritis patients and 12 healthy volunteers were recruited. 3D shapes of the humerus and scapula were reconstructed from their respective CT scans using an image processing software. 3. , and their CT-scan-based HHMs were measured. Furthermore, all subjects underwent low-dose biplanar radiography . 4. in four quasi-static functional arm positions while standing: relaxed standing, followed by 45 degrees of shoulder extension, flexion, and abduction. Using a previously validated method implemented in the programming platforms. 5. , 3D shapes were registered to the pairs of biplanar images for each arm position and the corresponding functional HHM was measured. Bivariate correlations were assessed between the CT-based HHM and each functional arm position. Result. HHM in 45 degrees of flexion and extension both showed significant and strong correlations (r>0.66 and P<0.01) with HHM assessed in the supine position. However, such a high correlation was not found for relaxed standing and 45 abduction. Conclusion. Although HHM in a supine position correlates with HHM in 45-degree extension and flexion, it is poorly associated with the HHM in abduction and relaxed standing. These results may suggest the inclusion of more functionally-relevant patient positioning toward better-informed shoulder arthroplasty planning. Acknowledgement. Funding from PRosPERos-II Project

Total hip arthroplasty (THA) using minimally invasive surgeries (MIS) now become popular operative procedures. It is not easy to understand geometric information of pelvis and femur in the restricted operative fields during MIS-THA. Recently, THA in supine position comes into the limelight again to place acetabular cups in an optimum position because we can minimise the intra-operative pelvic motion during THA in supine position. To verify the usefulness of supine position, we measured the angels of acetabular trial cups intra-operatively using the CT-based navigation system. The trial cup positions were placed according to a conventional acetabular cup alignment guide. We compared the angles of acetabular trial cups between supine and lateral positions through the same MIS antero-lateral (AL) surgical approach. Thirty eight hips underwent THA in lateral position (the AL group; average age: 63.9 years old, female: 29 cases, 33 hips, male: 5 cases, 5 hips) and 40 hips underwent THA in supine position (the AL Supine group; average age: 62.2 years old, female 40 cases, 40 hips) were subjected in this study. The single surgeon (the first author) performed all surgeries. We used the Roettinger's modified Watson-Jones approach in both groups. The pelvic registration for navigation was carried out using the CT-fluoro matching procedure with VectorVision Hip (BrainLAB, Germany). After acetabular reaming, the acetabular trial cups were placed into the reamed acetabulum to be at 45 degrees of operative inclination (OI) and at 20 degrees of operative anteversion (OA) using a conventional acetabular cup alignment guide. These angles of the trial cups were measured intra-operatively using the CT-based navigation system, VectorVision Hip. After removing the acetabular trial cup, the acetabular cups were placed using the navigation system. Trilogy cups (Zimmer, USA) and AMS HA shells (JMM, Japan) were used in this study. The average angles of OI were 45.7 degrees (SD 5.5 degrees) in the AL group and 46.3 degrees (SD 4.6 degrees) in the AL Supine group. The average angles of OA were 30.0 degrees (SD 13.5 degrees) in the AL group and 23.5 degrees (SD 8.2 degrees) in the AL Supine group. The hip numbers whose errors were less than 10 degrees were 13 hips in the AL group and 26 hips in the AL Supine group, respectively. There was significant difference in hip numbers whose errors of angles were less than 10 degrees between the AL and Supine groups. The hip numbers whose errors were less than 5 degrees were 7 hips in the AL group and only 6 hips in the AL Supine group, respectively. There was no significant difference in hip numbers whose errors of angles were less than 5 degrees between the AL and Supine groups. The error values of OI were less than 10 degrees except one hip in both groups. However, the error values of 25 hips in the AL group were more than 10 degrees. In lateral position, the pelvis easily rotated when the affected lower extremity was extended, externally rotated, and adducted during the femoral preparation in the AL group, which resulted in malalignment of acetabular OA. In contrast, most hips could be set with the error values less than 10 degrees in the AL Supine position because the pelvis could be stabilised on the operative table. In addition, landmarks, such as bilateral antero-superior iliac spines and the symphysis pubis, were palpable in supine position. However, the hips with error values less than 5 degrees were only 6 out of 40 hips even though in supine position. Using MIS techniques, we can provide more stable hip joint just after surgery since the muscles surrounding hip joints can be preserved. We have to place acetabular cups in an optimum position to achieve wide range of hip motion to prevent dislocation and to provide limitation-free daily activities for patients. These data suggests that we should use more accurate guide systems for acetabular cup replacement such as navigation systems, patient specific templates, and patient specific mechanical instruments to place acetabular cups in an optimum position

Introduction. The position and orientation of the lower extremities are fundamental for planning and follow-up imaging after arthroplasty and lower extremity osteotomy. But no studies have reported the reproducibility of measurements over time in the same patient, and experience shows variability of the results depending on the protocols for patient positioning. This study explores the reproducibility of measurements in the lower extremity with the patients in “comfortable standing position” by the EOS® imaging system. Materials and Methods. Two whole-body acquisitions were performed in each of 40 patients who were evaluated for a spine pathology. The average interval between acquisitions was 15 months (4–35 months). Patients did not have severe spine pathology and did not undergo any surgery between acquisitions. The “comfortable standing position” is achieved without imposing on the patient any specific position of the lower limbs and pelvis. All the measurements were performed and compared in both 2- and 3-dimensional images. Distances between the centers of the femoral heads and between the centers of the knees and ankles were measured from the front. The profile is shown by the flexion angle between the axis of the femur (center of the femoral head and the top of the line Blumensaat) and the axis of the tibia. Results. The average radiation dose was 0.80 mGy (0.5–1.11). For the first acquisition, the mean distance between the femoral heads was 17.9 cm (15.8–20.2), the mean distance between the middle of the knee joints was 16.7 cm (11.2–23.1) and the mean distance between the medial malleoli was 13.1 cm (0 to 18). For the second acquisition, the mean distance between the femoral heads was 17.9 cm (14.9–21.5), the mean distance between the middle of the knee joints was 16.9 cm (11.4–23.1) and the mean distance between the medial malleoli was 13.6 cm (0–19.4). For all comparisons no significant difference was demonstrated in related samples by Wilcoxon rank test and paired Student t test. Discussion. Two- and 3-dimensional data are not affected by repeated acquisitions several to many months apart in “comfortable standing position.” This work shows the reproducibility of measurements of the lower extremity in the “comfortable standing position” by the EOS® imaging system. Additional research should be considered for combined measures in the face-profile position of each patient

Aims. This study aimed to evaluate the accuracy of implant placement with robotic-arm assisted total hip arthroplasty (THA) in patients with developmental dysplasia of the hip (DDH). Methods. The study analyzed a consecutive series of 69 patients who underwent robotic-arm assisted THA between September 2018 and December 2019. Of these, 30 patients had DDH and were classified according to the Crowe type. Acetabular component alignment and 3D positions were measured using pre- and postoperative CT data. The absolute differences of cup alignment and 3D position were compared between DDH and non-DDH patients. Moreover, these differences were analyzed in relation to the severity of DDH. The discrepancy of leg length and combined offset compared with contralateral hip were measured. Results. The mean values of absolute differences (postoperative CT-preoperative plan) were 1.7° (standard deviation (SD) 2.0) (inclination) and 2.5° (SD 2.1°) (anteversion) in DDH patients, and no significant differences were found between non-DDH and DDH patients. The mean absolute differences for 3D cup position were 1.1 mm (SD 1.0) (coronal plane) and 1.2 mm (SD 2.1) (axial plane) in DDH patients, and no significant differences were found between two groups. No significant difference was found either in cup alignment between postoperative CT and navigation record after cup screws or in the severity of DDH. Excellent restoration of leg length and combined offset were achieved in both groups. Conclusion. We demonstrated that robotic-assisted THA may achieve precise cup positioning in DDH patients, and may be useful in those with severe DDH. Cite this article: Bone Joint Res 2021;10(10):629–638

We have previously reported on the improved all-cause revision and improved revision for instability risk in lipped liner THAs using the NJR dataset. These findings corroborate studies from the Australian (AOANJRR) and New Zealand (NZOA) joint registries. The optimal orientation of the lip in THAs utilising a lipped liner remains unclear to many surgeons. The aim of this study was to identify impingement-free optimal liner orientations whilst considering femoral stem version, cup inclination and cup version. A cementless THA kinematic model was developed using a 20 degree XLPE liner. Physiological ROM and provocative dislocation manoeuvre analyses were performed. A total of 9 cup positions were analysed (inclination 30–40–50 degrees, anteversion 5-15-25 degrees) and combined with 3 stem positions (anteversion 0-15-30 degrees) and 5 lip orientations (right hip 11 to 7 o'clock). Some lip orientation/component position combinations lead to impingement within the physiological ROM range. Using a lipped liner increases the femoral head travel distance prior to dislocation when impingement occurs in the plane of the lip. In THAs with a cup inclination of 30 and 40 degrees, inferior lip orientations (7–8 o'clock for a right hip) performed best. Superior lip orientation performed best with a cup inclination of 50 degrees. Femoral stem version has a significant effect on the range of movement prior to impingement and hence the preferred lip orientation. The optimal orientation of the lip in lipped liner THA is dependent on the position of both the acetabular and femoral components. In the common component orientation combination of stem anteversion 15, cup inclination 40 and cup anteversion 15, the optimal lip orientation was postero-inferiorly (8 o'clock for a right hip). Preventing impingement during physiological ROM is possible with appropriate lip liner orientation

The jackaling position within rugby has not been previously described as a mechanism for proximal hamstring injuries. This prospective single surgeon study included 54 professional rugby players (mean age 26 ± 4.8 years) undergoing acute primary surgical repair of complete, proximal hamstring avulsion injuries confirmed on preoperative magnetic resonance imaging. All study patients underwent a standardised postoperative rehabilitation programme. Predefined outcomes were recorded at regular intervals. Mean follow-up time was 17 months (range, 12 months to 24 months) from date of surgery. 51 patients (94.4%) returned to their pre-injury level of sporting activity. Mean time from surgical repair to full sporting activity was 7 months (range, 4 months to 12 months). Zero patients had recurrence of the primary injury. At 1 year after surgery compared to 3 months after surgery, patients had increased mean isometric hamstring muscle strength at 0° (98.4 ± 2.8% vs 88.1% ± 5.4%, p<0.001), 15° (95.9 ± 2.9 vs 88.2 ± 8.1%, p<0.001) and 45° (92.9% ± 4.1% vs 76.8% ± 9.7%, p<0.001), higher mean lower extremity functional scores (77.0 ± 2.3 vs 64.5 ± 4.5, p<0.001), and improved Marx activity rating scores (14.3 ± 1.5 vs 10.7 ± 2.6, p<0.001). Acute surgical repair of proximal hamstring avulsion injuries caused by the contact jackaling position produces high patient satisfaction, high return to preinjury level of sporting activity, with low risk of recurrence at short-term follow-up

Acetabular component positioning is commonly referenced with the pelvis in the supine position in direct anterior approach THA. Changes in pelvic tilt (PT) from the pre-operative supine to the post-operative standing positions have not been well investigated and may have relevance to optimal acetabular component targeting for reduced risk of impingement and instability. The aims of this study were therefore to determine the change in PT that occurs from pre-operative supine to post-operative standing, and whether any factors are associated with significant changes in tilt ≥13° in posterior direction. 13° in a posterior direction was chosen as that amount of posterior rotation creates an increase in functional anteversion of the acetabular component of 10°. 1097 THA patients with pre-operative supine CT and standing lateral radiographic imaging and 1 year post-operative standing lateral radiographs (interquartile range 12–13 months) were reviewed. Pre-operative supine PT was measured from CT as the angle between the anterior pelvic plane (APP) and the horizontal plane of the CT device. Standing PT was measured on standing lateral x-rays as the angle between the APP and the vertical line. Patients with ≥13° change from supine pre-op to standing post-op (corresponding to a 10° change in cup anteversion) were grouped and compared to those with a <13° change using unpaired student's t-tests. Mean pre-operative supine PT (3.8±6.0°) was significantly different from mean post-operative standing PT (−3.5±7.1°, p<0.001), ie mean change of −7.3±4.6°. 10.4% (114/1097) of patients had posterior PT changes ≥13° supine pre-op to standing post-op. A significant number of patients, ie 1 in 10, undergo a clinically significant change in PT and functional anteversion from supine pre-op to standing post-op. Surgeons should be aware of these changes when planning component placement in THA

Periprosthetic femoral fractures are increasingly seen in recent years, adding considerable burden to the National Health Service. These require complex revision or fixation and prolonged post-operative care, with significant morbidity with associated costs. The purpose of this study was to assess whether the size of femoral cement mantle is associated with periprosthetic femoral fractures (PPF). This retrospective study was carried out on a cohort of 49 patients (Fracture Group - FG) who previously had a revision procedure following a proximal PPF between 2010 and 2021. Inclusion criteria – all primary cemented total hip replacements (THR). Exclusion criteria – complex primary THR, any implant malposition that required early revision surgery or any pre-fracture stem loosening. The antero-posterior (AP) radiographs from this cohort of patients were assessed and compared to an age, sex, time since THR-matched control group of 49 patients without PPF (Control Group - CG). Distal cement mantle area (DCMA) was calculated on an AP radiograph of hip; the position of the femoral stem tip prior to fracture was also recorded: valgus, varus or central. Limitations: AP radiographs only. Statistical analyses were performed using Microsoft® Excel. Chi-square test demonstrated statistically significant difference in DCMA between FG and CG. DCMA of 700 to 900 mm² appeared to be protective when compared to DCMA of 0 to 300 mm². Also, a valgus position observed in 23% in FG Vs 4 % in CG increased the risk, with a smaller area of DCMA. This study demonstrates and recommends that a size of 700 – 900 mm² of the DCMA is protective against periprosthetic fractures, which are further influenced by the positioning of the distal stem tip. This could be due to the gradual decrease in the stiffness gradient from proximal to distal around the stem tip than steep changes, thereby decreasing possibility of a stress riser just distal to the cement mantle or restrictor. Further biomechanical research specific to this finding may be helpful to validate the observation, progressing to suggest a safe standardised surgical technique

Pelvic tilt can vary over time due to aging and the possible appearance of sagittal spine disorders. Cup position in total hip arthroplasty (THA) can be influenced due to these changes. We assessed the evolution of pelvic tilt and cup position after THA and the possible appearance of complications for a minimum follow-up of ten years. 343 patients received a THA between 2006 and 2009. All were diagnosed with primary osteoarthritis and their mean age was 63.3 years (range, 56 to 80). 168 were women and 175 men. 250 had no significant lumbar pathology, 76 had significant lumbar pathology and 16 had lumbar fusion. Radiological analysis included sacro-femoral-pubic (SFP), acetabular abduction (AA) and anteversion cup (AV) angles. Measurements were done pre-operatively and at 6 weeks, and at five and ten years post-operatively. Three measurements were recorded and the mean obtained at all intervals. All radiographs were evaluated by the same author, who was not involved in the surgery. There were nine dislocations: six were solved with closed reduction, and three required cup revision. All the mean angles changed over time; the SFP angle from 59.2º to 60º (p=0.249), the AA angle from 44.5º to 46.8º (p=0.218), and the AV angle from 14.7º to 16.2º (p=0.002). The SFP angle was lower in older patients at all intervals (p<0.001). The SFP angle changed from 63.8 to 60.4º in women and from 59.4º to 59.3º in men, from 58.6º to 59.6º (p=0.012). The SFP angle changed from 62.7º to 60.9º in patients without lumbar pathology, from 58.6º to 57.4º in patients with lumbar pathology, and from 57.0º to 56.4º in patients with a lumbar fusion (p=0.919). The SFP cup angle was higher in patients without lumbar pathology than in the other groups (p<0.001), however, it changed more than in patients with lumbar pathology or fusion at ten years after THA (p=0.04). Posterior pelvic tilt changed with aging, influencing the cup position in patients after a THA. Changes due to lumbar pathology could influence the appearance of complications long-term

Aims. The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position. Methods. A total of 16 fresh-frozen knees in eight human cadavers, without macroscopic anatomical defects, were selected. The knees from each cadaver were randomized to have the OUKA implanted in the HL or SL position. Results. Tibial base plate rotation was significantly more variable in the SL group with 75% of tibiae mal-rotated. Multivariate analysis of navigation data found no difference based on all kinematic parameters across the range of motion (ROM). However, area under the curve analysis showed that knees placed in the HL position had much smaller differences between the pre- and post-surgery conditions for kinematics mean values across the entire ROM. Conclusion. The sagittal tibia cut, not dependent on standard instrumentation, determines the tibial component rotation. The HL position improves accuracy of this step compared to the SL position, probably due to better visuospatial orientation of the hip and knee to the surgeon. The HL position is better for replicating native kinematics of the knee as shown by the area under the curve analysis. In the supine knee position, care must be taken during the sagittal tibia cut, while checking flexion balance and when sizing the tibial component

Aims. The aim of this study was to determine the association between knee alignment and the vertical orientation of the femoral neck in relation to the floor. This could be clinically important because changes of femoral neck orientation might alter chondral joint contact zones and joint reaction forces, potentially inducing problems like pain in pre-existing chondral degeneration. Further, the femoral neck orientation influences the ischiofemoral space and a small ischiofemoral distance can lead to impingement. We hypothesized that a valgus knee alignment is associated with a more vertical orientation of the femoral neck in standing position, compared to a varus knee. We further hypothesized that realignment surgery around the knee alters the vertical orientation of the femoral neck. Methods. Long-leg standing radiographs of patients undergoing realignment surgery around the knee were used. The hip-knee-ankle angle (HKA) and the vertical orientation of the femoral neck in relation to the floor were measured, prior to surgery and after osteotomy-site-union. Linear regression was performed to determine the influence of knee alignment on the vertical orientation of the femoral neck. Results. The cohort included 147 patients who underwent knee realignment-surgery. The mean age was 51.5 years (SD 11). Overall, 106 patients underwent a valgisation-osteotomy, while 41 underwent varisation osteotomy. There was a significant association between the orientation of the knee and the coronal neck-orientation. In the varus group, the median orientation of the femoral neck was 46.5° (interquartile range (IQR) 49.7° to 50.0°), while in the valgus group, the orientation was 52.0° (IQR 46.5° to 56.7°; p < 0.001). Linear regression analysis revealed that HKA demonstrated a direct influence on the coronal neck-orientation (β = 0.5 (95% confidence interval (CI) 0.2 to 0.7); p = 0.002). Linear regression also showed that realignment surgery was associated with a significant influence on the change in the coronal femoral neck orientation (β = 5.6 (95% CI 1.5 to 9.8); p = 0.008). Conclusion. Varus or valgus knee alignment is associated with either a more horizontal or a more vertical femoral neck orientation in standing position, respectively. Subsequently, osteotomies around the knee alter the vertical orientation of the femoral neck. These aspects are of importance when planning osteotomies around the knee in order to appreciate the effects on the adjacent hip joint. The concept may be of even more relevance in dysplastic hips. Cite this article: Bone Jt Open 2021;2(12):1057–1061

Nearly one quarter of ankle fractures have a recognized syndesmosis injury. An intact syndesmosis ligament complex stabilizes the distal tibio-fibular joint while allowing small, physiologic amounts of relative motion. When injured, malreduction of the syndesmosis has been found to be the most important independent factor that contributes to inferior functional outcomes. Despite this, significant variability in surgical treatment remains. This may be due to a poor understanding of normal dynamic syndesmosis motion and the resultant impact of static and dynamic fixation on post-injury syndesmosis kinematics. As the syndesmosis is a dynamic structure, conventional CT static images do not provide a complete picture of syndesmosis position, giving potentially misleading results. Dynamic CT technology has the ability to image joints in real time, as they are moved through a range-of-motion (ROM). The aim of this study was to determine if syndesmosis position changes significantly throughout ankle range of motion, thus warranting further investigation with dynamic CT. This is an a priori planned subgroup analysis of a larger multicentre randomized clinical trial, in which patients with AO-OTA 44-C injuries were randomized to either Tightrope or screw fixation. Bilateral ankle CT scans were performed at 1 year post-injury, while patients moved from maximal dorsiflexion (DF) to maximal plantar flexion (PF). In the uninjured ankles, three measurements were taken at one cm proximal to the ankle joint line in maximal DF and maximal PF: Anterior (ASD), middle (MSD), and posterior (PSD) syndesmosis distance, in order to determine normal syndesmosis position. Paired samples t-tests compared measurements taken at maximal DF and maximal PF. Twelve patients (eight male, six female) were included, with a mean age of 44 years (±13years). The mean maximal DF achieved was 1-degree (± 7-degrees), whereas the mean maximal PF was 47-degrees (± 8-degrees). The ASD in DF was 3.0mm (± 1.1mm) versus 1.9mm (± 0.8mm) in PF (p<0.01). The MSD in DF was 3.3mm (±1.1mm) versus 2.3mm (±0.9mm) in PF (p<0.01). The PSD in DF was 5.3mm (±1.5mm) versus 4.6mm (±1.9mm) in PF (p<0.01). These values are consistent with the range of normal parameters previously reported in the literature, however this is the first study to report the ankle position at which these measurements are acquired and that there is a significant change in syndesmosis measurements based on ankle position. Normal syndesmosis position changes in uninjured ankles significantly throughout range of motion. This motion may contribute to the variation in normal anatomy previously reported and controversies surrounding quantifying anatomic reduction after injury, as the ankle position is not routinely standardized, but rather static measurements are taken at patient-selected ankle positions. Dynamic CT is a promising modality to quantify normal ankle kinematics, in order to better understand normal syndesmosis motion. This information will help optimize assessment of reduction methods and potentially improve patient outcomes. Future directions include side-to-side comparison using dynamic CT analysis in healthy volunteers

Accurate cup placement in total hip arthroplasty (THA) for the patients with developmental dysplasia of the hip (DDH) is one of the challenges due to distinctive bone deformity. Robotic-arm assisted system have been developed to improve the accuracy of implant placement. This study aimed to compare the accuracy of robotic-arm assisted (Robo-THA), CT-based navigated (Navi-THA), and manual (M-THA) cup position and orientation in THA for DDH. A total of 285 patients (335 hips) including 202 M-THAs, 45 Navi-THAs, and 88 Robo-THA were analyzed. The choice of procedure followed the patient's preferences. Horizontal and vertical center of rotation (HCOR and VCOR) were measured for cup position, and radiographic inclination (RI) and anteversion (RA) were measured for cup orientation. The propensity score-matching was performed among three groups to compare the absolute error from the preoperative target position and angle. Navi-THA showed significantly smaller absolute errors than M-THA in RI (3.6° and 5.4°) and RA (3.8° and 6.0°), however, there were no significant differences between them in HCOR (2.5 mm and 3.0 mm) or VCOR (2.2 mm and 2.6 mm). In contrast, Robo-THA showed significantly smaller absolute errors of cup position than both M-THA and Navi-THA (HCOR: 1.7 mm and 2.9 mm, vs. M-THA, 1.6 mm and 2.5 mm vs. Navi-THA, VCOR:1.7 mm and 2.4 mm, vs. M-THA, 1.4 mm and 2.2 mm vs. Navi-THA). Robo-THA also showed significantly smaller absolute errors of cup orientation than both M-THA and Navi-THA (RI: 1.4° and 5.7°, vs. M-THA, 1.5° and 3.6°, vs. Navi-THA, RA: 1.9° and 5.8° vs. M-THA, 2.1° and 3.8° vs. Navi-THA). Robotic-arm assisted system showed more accurate cup position and orientation compared to manual and CT-based navigation in THA for DDH. CT-based navigation increased the accuracy of cup orientation compared to manual procedures, but not cup position