Aims. Navigation devices are designed to improve a surgeon’s accuracy in positioning the acetabular and femoral components in total hip arthroplasty (THA). The purpose of this study was to both evaluate the accuracy of an optical computer-assisted surgery (CAS) navigation system and determine whether preoperative spinopelvic mobility (categorized as hypermobile, normal, or stiff) increased the risk of acetabular component placement error. Methods. A total of 356 patients undergoing primary THA were prospectively enrolled from November 2016 to March 2018. Clinically relevant error using the CAS system was defined as a difference of > 5° between CAS and 3D radiological reconstruction measurements for acetabular component inclination and anteversion. Univariate and multiple logistic regression analyses were conducted to determine whether hypermobile (. Δ. sacral slope(SS). stand-sit. > 30°), or stiff (. ∆. SS. stand-sit. < 10°) spinopelvic mobility contributed to increased error rates. Results. The paired absolute difference between CAS and postoperative imaging measurements was 2.3° (standard deviation (SD) 2.6°) for inclination and 3.1° (SD 4.2°) for anteversion. Using a target zone of 40° (± 10°) (inclination) and 20° (± 10°) (anteversion), postoperative standing radiographs measured 96% of acetabular components within the target zone for both inclination and anteversion. Multiple logistic regression analysis controlling for BMI and sex revealed that hypermobile spinopelvic mobility significantly increased error rates for anteversion (odds ratio (OR) 2.48, p = 0.009) and inclination (OR 2.44, p = 0.016), whereas stiff spinopelvic mobility increased error rates for anteversion (OR 1.97, p = 0.028). There were no dislocations at a minimum three-year follow-up. Conclusion. Despite high reliability in acetabular positioning for inclination in a large patient cohort using an optical CAS system, hypermobile and stiff spinopelvic mobility significantly increased the risk of clinically relevant errors. In patients with abnormal spinopelvic mobility, CAS systems should be adjusted for use to avoid acetabular component misalignment and subsequent risk for long-term dislocation. Cite this article: Bone Jt Open 2022;3(6):475–484

Aims. Adverse spinal motion or balance (spine mobility) and adverse pelvic mobility, in combination, are often referred to as adverse spinopelvic mobility (SPM). A stiff lumbar spine, large posterior standing pelvic tilt, and severe sagittal spinal deformity have been identified as risk factors for increased hip instability. Adverse SPM can create functional malposition of the acetabular components and hence is an instability risk. Adverse pelvic mobility is often, but not always, associated with abnormal spinal motion parameters. Dislocation rates for dual-mobility articulations (DMAs) have been reported to be between 0% and 1.1%. The aim of this study was to determine the early survivorship from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) of patients with adverse SPM who received a DMA. Methods. A multicentre study was performed using data from 227 patients undergoing primary total hip arthroplasty (THA), enrolled consecutively. All the patients who had one or more adverse spine or pelvic mobility parameter had a DMA inserted at the time of their surgery. The mean age was 76 years (22 to 93) and 63% were female (n = 145). At a mean of 14 months (5 to 31) postoperatively, the AOANJRR was analyzed for follow-up information. Reasons for revision and types of revision were identified. Results. The AOANJRR reported two revisions: one due to infection, and the second due to femoral component loosening. No revisions for dislocation were reported. One patient died with the prosthesis in situ. Kaplan-Meier survival rate was 99.1% (95% confidence interval 98.3 to 100) at 14 months (number at risk 104). Conclusion. In our cohort of patients undergoing primary THA with one or more factor associated with adverse SPM, DM bearings conferred stability at two years’ follow-up. Cite this article: Bone Joint J 2022;104-B(7):820–825

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. This study of patients with osteoarthritis (OA) of the hip aimed to: 1) characterize the contribution of the hip, spinopelvic complex, and lumbar spine when moving from the standing to the sitting position; 2) assess whether abnormal spinopelvic mobility is associated with worse symptoms; and 3) identify whether spinopelvic mobility can be predicted from static anatomical radiological parameters. Patients and Methods. A total of 122 patients with end-stage OA of the hip awaiting total hip arthroplasty (THA) were prospectively studied. Patient-reported outcome measures (PROMs; Oxford Hip Score, Oswestry Disability Index, and Veterans RAND 12-Item Health Survey Score) and clinical data were collected. Sagittal spinopelvic mobility was calculated as the change from the standing to sitting position using the lumbar lordosis angle (LL), sacral slope (SS), pelvic tilt (PT), pelvic-femoral angle (PFA), and acetabular anteinclination (AI) from lateral radiographs. The interaction of the different parameters was assessed. PROMs were compared between patients with normal spinopelvic mobility (10° ≤ ∆PT ≤ 30°) or abnormal spinopelvic mobility (stiff: ∆PT < ± 10°; hypermobile: ∆PT > ± 30°). Multiple regression and receiver operating characteristic (ROC) curve analyses were used to test for possible predictors of spinopelvic mobility. Results. Standing to sitting, the hip flexed by a mean of 57° (. sd. 17°), the pelvis tilted backwards by a mean of 20° (. sd. 12°), and the lumbar spine flexed by a mean of 20° (. sd. 14°); strong correlations were detected. There was no difference in PROMs between patients in the different spinopelvic mobility groups. Maximum hip flexion, standing PT, and standing AI were independent predictors of spinopelvic mobility (R. 2. = 0.42). The combined thresholds for standing was PT ≥ 13° and hip flexion ≥ 88° in the clinical examination, and had 90% sensitivity and 63% specificity of predicting spinopelvic stiffness, while SS ≥ 42° had 84% sensitivity and 67% specificity of predicting spinopelvic hypermobility. Conclusion. The hip, on average, accounts for three-quarters of the standing-to-sitting movement, but there is great variation. Abnormal spinopelvic mobility cannot be screened with PROMs. However, clinical and standing radiological features can predict spinopelvic mobility with good enough accuracy, allowing them to be used as reliable screening tools. Cite this article: Bone Joint J 2019;101-B:902–909

Aims

Precise implant positioning, tailored to individual spinopelvic biomechanics and phenotype, is paramount for stability in total hip arthroplasty (THA). Despite a few studies on instability prediction, there is a notable gap in research utilizing artificial intelligence (AI). The objective of our pilot study was to evaluate the feasibility of developing an AI algorithm tailored to individual spinopelvic mechanics and patient phenotype for predicting impingement.

Aims. Patients with abnormal spinopelvic mobility are at increased risk for instability. Measuring the change in sacral slope (ΔSS) can help determine spinopelvic mobility preoperatively. Sacral slope (SS) should decrease at least 10° to demonstrate adequate posterior pelvic tilt. There is potential for different ΔSS measurements in the same patient based on sitting posture. The purpose of this study was to determine the effect of sitting posture on the ΔSS in patients undergoing total hip arthroplasty (THA). Methods. In total, 51 patients undergoing THA were reviewed to quantify the variability in preoperative spinopelvic mobility when measuring two different sitting positions using SS for planning. Results. A total of 32 patients had standardized relaxed sitting radiographs, while 35 patients had standardized flexed sitting images. Of the 32 patients with relaxed sitting views, the mean ΔSS was 20.7° (SD 8.9°). No patients exhibited an increase in SS during relaxed sitting (i.e. anterior pelvic tilt or so-called reverse accommodation). Of the 35 patients with flexed sitting radiographs, the mean ΔSS was only 2.1° (SD 9.7°) with 16/35 (45.71%) showing anterior pelvic tilt, or so-called reverse accommodation, unexpectedly increasing the sitting SS compared to the standing SS. Overall, 18 patients had both relaxed sitting and flexed sitting radiographs. In patients with both types of sitting radiographs, the mean relaxed sit to stand ΔSS was 18.06° (SD 6.07°), while only a 3.00° (SD 10.53°) ΔSS was noted when flexed sitting. There was a mean ΔSS difference of 15.06° (SD 7.67°) noted in the same patient cohort depending on sitting posture (p < 0.001). Conclusion. A 15° mean difference was noted depending on the sitting posture of the patient. Since decisions on component position can be made on preoperative lateral sit-stand radiographs, postural standardization is crucial. If using ΔSS for preoperative planning, the relaxed sitting radiograph is preferred. Cite this article: Bone Joint J 2020;102-B(7 Supple B):41–46

Aims. Cross-table lateral (CTL) radiographs are commonly used to measure acetabular component anteversion after total hip arthroplasty (THA). The CTL measurements may differ by > 10° from CT scan measurements but the reasons for this discrepancy are poorly understood. Anteversion measurements from CTL radiographs and CT scans are compared to identify spinopelvic parameters predictive of inaccuracy. Methods. THA patients (n = 47; 27 males, 20 females; mean age 62.9 years (SD 6.95)) with preoperative spinopelvic mobility, radiological analysis, and postoperative CT scans were retrospectively reviewed. Acetabular component anteversion was measured on postoperative CTL radiographs and CT scans using 3D reconstructions of the pelvis. Two cohorts were identified based on a CTL-CT error of ≥ 10° (n = 11) or < 10° (n = 36). Spinopelvic mobility parameters were compared using independent-samples t-tests. Correlation between error and mobility parameters were assessed with Pearson’s coefficient. Results. Patients with CTL error > 10° (10° to 14°) had stiffer lumbar spines with less mean lumbar flexion (38.9°(SD 11.6°) vs 47.4° (SD 13.1°); p = 0.030), different sagittal balance measured by pelvic incidence-lumbar lordosis mismatch (5.9° (SD 18.8°) vs -1.7° (SD 9.8°); p = 0.042), more pelvic extension when seated (pelvic tilt -9.7° (SD 14.1°) vs -2.2° (SD 13.2°); p = 0.050), and greater change in pelvic tilt between supine and seated positions (12.6° (SD 12.1°) vs 4.7° (SD 12.5°); p = 0.036). The CTL measurement error showed a positive correlation with increased CTL anteversion (r = 0.5; p = 0.001), standing lordosis (r = 0.23; p = 0.050), seated lordosis (r = 0.4; p = 0.009), and pelvic tilt change between supine and step-up positions (r = 0.34; p = 0.010). Conclusion. Differences in spinopelvic mobility may explain the variability of acetabular anteversion measurements made on CTL radiographs. Patients with stiff spines and increased compensatory pelvic movement have less accurate measurements on CTL radiographs. Flexion of the contralateral hip is required to obtain clear CTL radiographs. In patients with lumbar stiffness, this movement may extend the pelvis and increase anteversion of the acetabulum on CTL views. Reliable analysis of acetabular component anteversion in this patient population may require advanced imaging with a CT scan. Cite this article: Bone Joint J 2021;103-B(7 Supple B):59–65

A total hip replacement (THR) patient's spinopelvic mobility might predispose them to an increased risk of impingement, instability and edge-loading. This risk can be minimised by considering their preoperative movement during planning of component alignment. However, the question of whether the preoperative, arthritic motion is representative of the postoperative mobility has been raised. We aimed to determine the change in functional pelvic tilt in a series of THR patients at one-year. Four-hundred and eleven patients had their pelvic tilt and lumbar lordotic angle (LLA) measured in the standing and flexed-seated (position when patients initiate rising from a seat) positions as part of routine planning for THR. All measurements were performed on lateral radiographs. At 12-months postoperatively, the same two lateral images were taken and pelvic tilt measured. Pearson correlation was used to investigate the linear relationship between pre-and post-op pelvic tilt. Furthermore, a predictive model of post-op pelvic tilt was developed using machine learning algorithms. The model incorporating four preoperative inputs – standing pelvic tilt, seated pelvic tilt, standing LLA and seated LLA. In the standing position, there was a mean 2° posterior rotation after THR, with a maximum posterior change of 13°. The Pearson correlation coefficient between pre-and post-op standing pelvic tilt was 0.84. This prediction of post-op standing tilt improved to 0.91 when the three further inputs were incorporated to the predictive model. In the flexed-seated position, there was a mean 7° anterior rotation after THR, with a maximum anterior change of 45°. The Pearson correlation coefficient between pre-and post-op seated pelvic tilt was 0.54. This prediction of post-op seated tilt improved to 0.71 when the three further inputs were incorporated to the predictive model. The best predictor of post-operative spinopelvic mobility, is the patients pre-operative spinopelvic mobility, and this should routinely be measured when planning THR. The predictive model will continue to improve in accuracy as more data and more variables (contralateral hip pathology, pelvic incidence, age and gender) are incorporated into the model

Spinopelvic mobility describes the change in lumbar lordosis and pelvic tilt from standing to sitting position. For 1° of posterior pelvic tilt, functional cup anteversion increases by 0.75° after total hip arthroplasty (THA). Thus, spinopelvic mobility is of high clinical relevance regarding the risk of implant impingement and dislocation. Our study aimed to 1) determine the proportion of OA-patients with stiff, normal or hypermobile spino-pelvic mobility and 2) to identify clinical or static standing radiographic parameters predicting spinopelvic mobility. This prospective diagnostic cohort study followed 122 consecutive patients with end-stage osteoarthritis awaiting THA. Preoperatively, the Oxford Hip Score, Oswestry Disability Index and Schober's test were assessed in a standardized clinical examination. Lateral view radiographs were taken of the lumbar spine, pelvis and proximal femur using EOS© in standing position and with femurs parallel to the floor in order to achieve a 90°-seated position. Radiographic measurements were performed for the lumbar lordosis angle (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI) and pelvic-femoral-angle (PFA). The difference in PT between standing and seated allowed for patient classification based on spino-pelvic mobility into stiff (±30°). From the standing to the sitting position, the pelvis tilted backwards by a mean of 19.6° (SD 11.6) and the hip was flexed by a mean of 57° (SD 17). Change in pelvic tilt correlated inversely with change in hip flexion. Spinopelvic mobility is highly variable in patients awaiting THA and we could not identify any clinical or static standing radiographic parameter predicting the change in pelvic tilt from standing to sitting position. In order to identify patients with stiff or hypermobile spinopelvic mobility, we recommend performing lateral view radiographs of the lumbar spine, pelvis and proximal femur in all patients awaiting THA. Thereafter, implants and combined cup inclination/anteversion can be individually chosen to minimize the risk of dislocation. No predictors could be identified. We recommend performing sitting and standing lateral view radiographs of the lumbar spine and pelvis to determine spinopelvic mobility in patients awaiting THA

Aims. Our study aimed to 1) Describe the changes in spinopelvic mobility when transitioning from standing, to ‘relaxed-seated’ and thereafter to ‘deep-seated’ position and 2) Determine the change in spinopelvic mobility types 1 year post-THA compared to preoperatively. Methods. This prospective diagnostic cohort study followed 100 consecutive patients 1 year post-THA. Preoperatively and one year postoperatively, radiographic measurements were performed for the lumbar-lordosis-angle, pelvic tilt and pelvic-femoral-angle on lateral radiographs in the standing, ‘relaxed-seated’ and ‘deep-seated’ position (torso maximally leaning forward). Patients were classified according to their spinopelvic mobility type, according to the change in PT between the standing and relaxed-seated position (stiff:ΔPT<±10°, normal:10°≤ΔPT≤30°, hypermobile:ΔPT>±30°). Results. Compared to preoperatively, when moving from a standing to a relaxed-seated position, hip flexion increased by 10°±18, leading to less posterior pelvic tilt by 6°±11 and reduced lumbar spine flexion by 6°±11 (all p<0.001). Similarly, when moving from the standing to deep-seated position, hip flexion improved by a mean of 8°±22, leading to reduced lumbar spine flexion by a mean of 5°±8, whereas the change in pelvic tilt did not change compared to preoperatively (p=0.016, p<0.001, p=0.46). The distribution of spinopelvic mobility types 1 year postoperatively was significantly different compared to preoperatively, as the percentage of patients with stiff spinopelvic mobility increased from 16% to 43% (p<0.001). Conclusion. Hip flexion improved by 10° on average 1 year after total hip arthroplasty. Thus, slightly less compensatory posterior pelvic tilt and lumbar spine flexion was needed when taking a relaxed-seated position. When taking a deep-seated position, improved hip flexion required less lumbar spine flexion. However, these changes were small when being compared to preoperative variability of these parameters. Thus, individual spinopelvic mobility remains relatively unchanged 1 year after THA compared to preoperatively

Introduction. Patients with abnormal spinopelvic mobility are at increased risk for hip instability. Measuring the change in sacral slope (ΔSS) with standing and seated lateral radiographs is commonly used to determine spinopelvic mobility pre-operatively. Sacral slope should decrease at least 10 degrees to demonstrate adequate accommodation. Accommodation of <10 deg necessitates acetabular component position change or use of a dual mobility implant. There is potential for different ΔSS measurements in the same patient based on sitting posture. Methods. 78 patients who underwent THA were reviewed to quantify the variability in pre-operative spinopelvic mobility when two different seated positions (relaxed sitting v. pre-rise sitting) were used in the same patient. Results. 34 patients had standardized pre-rise sitting x-rays, while 44 patients had standardized relaxed sitting x-rays. Of the 44 patients with relaxed sitting x-rays, the mean ΔSS (ΔrSS) was 20.4 degrees. No patients exhibited an increase in sacral slope when sitting (ie; reverse accommodation). Of the 34 patients with pre-rise sitting x-rays, the mean pre-rise sit-stand change (ΔprSS) was only 1.85 degrees with 47% (16/34) showing reverse accommodation, actually increasing the seated sacral slope compared to standing sacral slope. 18 patients had both pre-rise and relaxed sitting x-rays. In patients with both seated x-rays, the mean relaxed sit-stand change in sacral slope (ΔrSS) was 18.1 ± 6.1 degrees and only 3.0 ± 10.5 degrees for pre-rise sit-stand (ΔprSS), with a mean ΔSS difference of the 15.1 degrees (p <0.0001). Conclusion. A 15 degrees error could be made in pre-operative planning depending on the seated posture of the patient. Since decisions on component position or use of dual-mobility are made on pre-operative lateral sit-stand radiographs, postural standardization is critical. The relaxed seated radiograph is the preferred posture at the time of the seated lateral radiograph. For any tables or figures, please contact the authors directly

Introduction. Spinopelvic mobility has been associated with THA outcome. To-date spine assessments have been made quasi-statically, using radiographs, in standing and seated positions but dynamic spinopelvic mobility has not been well explored. This study aims to determine the association between dynamic (motion analysis) and quasi-static (radiographic) sagittal assessments and examine the association between axial and sagittal spinal kinematics in hip OA patients and controls. Methods. This is a prospective, IRB approved, cohort study of 12 patients with hip OA pre-THA (6F/6M, 67±10 years) and six healthy controls (3F/3M, 46±18 years). All underwent lateral spinopelvic radiographs in standing and seated bend-and-reach (SBR) positions. Pelvic tilt (PT), pelvic-femoral-angle (PFA) and lumbar lordosis (LL) angles were measured in both positions and the differences (Δ) in angles between SBR and standing were computed. All participants performed two dynamic tasks at the motion laboratory: seated maximal trunk rotation (STR) and seated bend and reach (SBR). Three-dimensional joint motion data were collected and processed by a 10-camera infrared motion analysis system (Vicon, Nexus 2.10, UK). Total axial and sagittal spine (mid-thoracic to lumbar) range of motion (ROM) were calculated for STR and SBR, respectively. Results. ΔLL for SBR and motion analysis spinal flexion for SBR moderately correlated (ρ=0.4, p=0.007). Dynamic spinal rotation and flexion significantly, strongly, correlated (ρ=0.6 p=0.007). OA patients compared to healthy participants showed significant less ΔPFA (53°±21° vs. 77°±14°; p<0.001); ΔPT (−17°±8° vs. 9°±15°; p<0.001), ΔLL (35°±15° vs. 43° ±9°; p<0.001), axial spinal rotation during STR (62° ±12°vs. 79° ±8°, p<.001) and less, but not significant, spine flexion during SBR (36° ±15° vs. 44° ±10°, P=.1). Conclusion. Dynamic sagittal and axial spinal ROM showed moderately correlated. Motion analysis can provide valid assessments for spine mobility. OA patients compared to healthy participants showed significant less ΔPFA, ΔPT, ΔLL, axial spinal rotation during STR. Surgeons should be aware that patients with less spine mobility that could affect the stability of THA and increase the risk of poor outcomes

Aims. Our study aimed to 1) determine if there was a difference for the HOOS-PS score between patients with stiff/normal/hypermobile spinopelvic mobility and 2) to investigate if functional sagittal cup orientation affected patient reported outcome 1 year post-THA. Methods. This prospective diagnostic cohort study followed 100 consecutive patients having received unilateral THA for end-stage hip osteoarthritis. Pre- and 1-year postoperatively, patients underwent a standardized clinical examination, completed the HOOS-PS score and sagittal low-dose radiographs were acquired in the standing and relaxed-seated position. Radiographic measurements were performed for the lumbar-lordosis-angle, pelvic tilt (PT), pelvic-femoral-angle and cup ante-inclination. The HOOS-PS was compared between patients with stiff (ΔPT<±10°), normal (10°≤ΔPT≤30°) and hypermobile spinopelvic mobility (ΔPT>±30°). Results. Preoperatively, 16 patients demonstrated stiff, 70 normal and 14 hypermobile spinopelvic mobility without a difference in the HOOS-PS score (66±14/67±17/65±19;p=0.905). One year postoperatively, 43 patients demonstrated stiff, 51 normal and 6 hypermobile spinopelvic mobility. All postoperative hypermobile patients had normal spinopelvic mobility preoperatively and showed significantly worse HOOS-PS scores compared to patients with stiff or normal spinopelvic mobility (21±17/21±22/35±16;p=0.043). Postoperatively, patients with hypermobile spinopelvic mobility demonstrated no significant difference for the pelvic tilt in the standing position compared to the other two groups (19±8°/16±8°/19±4°;p=0.221), but a significantly lower sagittal cup ante-inclination (36±10°/36±9°/29±8°;p=0.046). Conclusion. The present study demonstrated that patients with normal preoperative and postoperative spinopelvic hypermobility show worse HOOS-PS scores than patients with stiff or normal spinopelvic mobility. The lower postoperative cup ante-inclination seems to force the pelvis to tilt more posteriorly when moving from the standing to seated position (spinopelvic hypermobility) in order to avoid anterior impingement. Thus, functional cup orientation in the sagittal plane seems to affect postoperative patient reported outcome

Introduction. Cross table lateral (CTL) radiographs are commonly used to measure acetabular component anteversion after total hip arthroplasty (THA). CTL measurements may differ by >10 degrees from CT scan measurements, but the reasons for this discrepancy are poorly understood. We compare anteversion measurements made on CTL radiographs and CT scans to identify spinopelvic parameters predictive of inaccuracy. Methods. THA patients (n=47) with preoperative spinopelvic radiographic analysis and postoperative CT scans were retrospectively reviewed. Acetabular component anteversion was measured on post-operative CTL radiographs, and CT scans using 3D reconstructions of the pelvis. Patients were grouped by error (CTL-CT)>10° (n=11) or <10° (n=36), and spinopelvic mobility parameters were compared using t-tests. Correlation between error and mobility parameters was assessed with Pearson coefficient. Results. Patients with CTL error >10° (range 10–14) had stiffer lumbar spines with less lumbar flexion (38° vs 47°, p=0.03), greater sagittal imbalance measured by pelvic incidence-lumbar lordosis mismatch (6° vs −2°, p=0.04), more pelvic extension when seated (pelvic tilt −10° vs −2°, p=0.05), and greater change in pelvic tilt between supine and seated positions (13° vs 4°, p=0.04). The error of CTL measurements showed a positive correlation with increased CTL anteversion (r=0.5, p=0.001), standing lordosis (r=0.23, p=0.05), seated lordosis (r=0.4, p=0.01) and pelvic tilt change between supine and step-up positions (r=0.34, p=0.01). Discussion. Differences in spinopelvic mobility patterns may explain the variable accuracy of acetabular anteversion measurements on CTL radiographs. Patients with stiff spines and increased compensatory pelvic motion have less accurate measurements on CTL radiographs. Flexion of the contralateral hip is required to obtain clear CTL radiographs. In patients with a stiff lumbar spine, this movement may extend the pelvis and increase anteversion of the acetabulum on CTL views. Reliable analysis of acetabular component anteversion in this patient population may require advanced imaging with a CT scan

Adverse spinopelvic mobility (SPM) has been shown to increase risk of dislocation of primary total hip arthroplasty (THA). In patients undergoing THA, prevalence of adverse SPM has been shown to be as high as 41%. Stiff lumbar spine, large posterior standing pelvic tilt and severe sagittal spinal deformity have been identified as risk factors for increased hip instability. Dislocation rates for dual mobility articulations have been reported to be 0% to 1.1%. The aim of this study was to determine the early survivorship from the Australian National Joint Replacement Registry (AOANJRR) of patients with adverse SPM who received a dual mobility articulation. A multicentre study was performed using data from 229 patients undergoing primary THA, enrolled consecutively. All the patients who had one or more adverse spine or pelvic mobility parameters had a dual mobility articulation inserted at the time of their surgery. Average age was 76 (22 to 93) years and 63% were female. At a mean of 2.1 (1 – 3.3) years post-op, the AOANJRR was analysed for follow-up. Reasons for revision and types of revision were identified. The AOANJRR reported two revisions. One due to infection and the second due to femoral component loosening. No revisions for dislocation were reported. One patient died with the prosthesis in situ. Kaplan Meier survival was 99.3% (CI 98.3% − 100%) at 2 years. DM bearings reduce the risk of dislocation of primary THA in patients with adverse spine and pelvic mobility

Aims. The aims of the study were to determine the differences in spinopelvic mobility between a cohort of hip OA patients and a control group for the 1) standing to relaxed-seated and 2) standing to deep-seated task. Methods. A cohort of 40 patients with end-stage hip OA and a control group of 40 subjects, matched for age, gender and BMI were prospectively studied. Clinical data and lateral view radiographs in different positions were assessed. Sagittal spinopelvic mobility was calculated as the change when moving from the standing to relaxed-seated and standing to deep-seated positions for the lumbar lordosis angle, pelvic tilt and pelvic-femoral angle. Results. When moving from the standing to sitting position, hip OA patients demonstrated less hip flexion (52±18 vs. 69±11, p<0.001), an increased posterior pelvic tilt (23±13 vs. 12±9, p<0.001) and more flexion of the lumbar spine (22±15 vs. 14±11, p=0.01). Similarly, when moving from the standing to deep-seated position, hip OA patients demonstrated also less hip flexion (64±21 vs. 84±18, p<0.001), accompanied by a posterior and not an anterior pelvic tilt as in the control group (10±16 vs. −3±17, p<0.001). No difference could be found for lumbar spine flexion (40±15 vs. 43±13, p=0.28). The percentage of subjects with stiff spinopelvic mobility was significantly lower in the patient group (15% vs 48%; p=0.002) and there was a trend towards a higher percentage in spinopelvic hypermobility in patients (20% vs 2%; p=0.08). Conclusions. Decreased hip flexion due to OA leads to an increased posterior pelvic tilt when taking a relaxed-seated position. Less than 10° of posterior pelvic tilt from the standing to relaxed seated position (spinopelvic ‘stiffness’) is more frequent in controls without hip OA and results from hip mobility and not from stiffness of the lumbar spine

Aims

Posterior tilt of the pelvis with sitting provides biological acetabular opening. Our goal was to study the post-operative interaction of skeletal mobility and sagittal acetabular component position.

Aims. Spinopelvic pathology increases the risk for instability following total hip arthroplasty (THA), yet few studies have evaluated how pathology varies with age or sex. The aims of this study were: 1) to report differences in spinopelvic parameters with advancing age and between the sexes; and 2) to determine variation in the prevalence of THA instability risk factors with advancing age. Methods. A multicentre database with preoperative imaging for 15,830 THA patients was reviewed. Spinopelvic parameter measurements were made by experienced engineers, including anterior pelvic plane tilt (APPT), spinopelvic tilt (SPT), sacral slope (SS), lumbar lordosis (LL), and pelvic incidence (PI). Lumbar flexion (LF), sagittal spinal deformity, and hip user index (HUI) were calculated using parameter measurements. Results. With advancing age, patients demonstrate increased posterior APPT, decreased standing LL, decreased LF, higher pelvic incidence minus lumbar lordosis (PI-LL) mismatch, higher prevalence of abnormal spinopelvic mobility, and higher HUI percentage. With each decade, APPT progressed posteriorly 2.1°, LF declined 6.0°, PI-LL mismatch increased 2.9°, and spinopelvic mobility increased 3.8°. Significant differences were found between the sexes for APPT, SPT, SS, LL, and LF, but were not felt to be clinically relevant. Conclusion. With advancing age, spinopelvic biomechanics demonstrate decreased spinal mobility and increased pelvic/hip mobility. Surgeons should consider the higher prevalence of instability risk factors in elderly patients and anticipate changes evolving in spinopelvic biomechanics for young patients. Cite this article: Bone Joint J 2024;106-B(8):792–801

A stiff spine leads to increased demand on the hip, creating an increased risk of total hip arthroplasty (THA) dislocation. Several authors propose that a change in sacral slope of ≤10° between the standing and relaxed-seated positions (ΔSSstanding→relaxed-seated) identifies a patient with a stiff lumbar spine and have suggested use of dual-mobility bearings for such patients. However, such assessment may not adequately test the lumbar spine to draw such conclusions. The aim of this study was to assess how accurately ΔSSstanding→relaxed-seated can identify patients with a stiff spine. This is a prospective, multi-centre, consecutive cohort series. Two-hundred and twenty-four patients, pre-THA, had standing, relaxed-seated and flexed-seated lateral radiographs. Sacral slope and lumbar lordosis were measured on each functional X-ray. ΔSSstanding→relaxed-seated seated was determined by the change in sacral slope between the standing and relaxed-seated positions. Lumbar flexion (LF) was defined as the difference in lumbar lordotic angle between standing and flexed-seated. LF≤20° was considered a stiff spine. The predictive value of ΔSSstanding→relaxed-seated for characterising a stiff spine was assessed. A weak correlation between ΔSSstanding→relaxed-seated and LF was identified (r2= 0.15). Fifty-four patients (24%) had ΔSSstanding→relaxed-seated ≤10° and 16 patients (7%) had a stiff spine. Of the 54 patients with ΔSSstanding→relaxed-seated ≤10°, 9 had a stiff spine. The positive predictive value of ΔSSstanding→relaxed-seated ≤10° for identifying a stiff spine was 17%. ΔSSstanding→relaxed-seated ≤10° was not correlated with a stiff spine in this cohort. Utilising this simplified approach could lead to a six-fold overprediction of patients with a stiff lumbar spine. This, in turn, could lead to an overprediction of patients with abnormal spinopelvic mobility, unnecessary use of dual mobility bearings and incorrect targets for component alignment. Referring to patients ΔSSstanding→relaxed-seated ≤10° as being stiff can be misleading; we thus recommend use of the flexed-seated position to effectively assess pre-operative spinopelvic mobility