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. Pelvic tilt is believed to affect the symptomology of osteoarthritis (OA) of the hip by alterations in joint movement, dysplasia of the hip by modification of acetabular cover, and femoroacetabular impingement by influencing the impingement-free range of motion. While the apparent role of pelvic tilt in hip pathology has been reported, the exact effects of many forms of treatment on pelvic tilt are unknown. The primary aim of this study was to investigate the effects of surgery on pelvic tilt in these three groups of patients. Methods. The demographic, radiological, and outcome data for all patients operated on by the senior author between October 2016 and January 2020 were identified from a prospective registry, and all those who underwent surgery with a primary diagnosis of OA, dysplasia, or femoroacetabular impingement were considered for inclusion. Pelvic tilt was assessed on anteroposterior (AP) standing radiographs using the pre- and postoperative pubic symphysis to sacroiliac joint (PS-SI) distance, and the outcomes were assessed with the Hip Outcome Score (HOS), International Hip Outcome Tool (iHOT-12), and Harris Hip Score (HHS). Results. The linear regression model revealed a significant negative predictive association between the standing pre- and postoperative PS-SI distances for all three groups of patients (all p < 0.001). There was a significant improvement in all three outcome measures between the pre- and postoperative values (p < 0.05). Conclusion. There is a statistically significant decrease in pelvic tilt after surgery in patients with OA of the hip, dysplasia, and femoroacetabular impingement. These results confirm that surgery significantly alters the pelvic orientation. Pelvic tilt significantly decreased after total hip arthroplasty, periacetabular osteotomy, and arthroscopy/surgical hip dislocation. The impact of surgery on pelvic tilt should be considered within the therapeutic plan in order to optimize pelvic orientation in these patients. Cite this article: Bone Joint J 2022;104-B(9):1025–1031

Aims. The aim of this study was to evaluate the reliability and validity of a patient-specific algorithm which we developed for predicting changes in sagittal pelvic tilt after total hip arthroplasty (THA). Methods. This retrospective study included 143 patients who underwent 171 THAs between April 2019 and October 2020 and had full-body lateral radiographs preoperatively and at one year postoperatively. We measured the pelvic incidence (PI), the sagittal vertical axis (SVA), pelvic tilt, sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis to classify patients into types A, B1, B2, B3, and C. The change of pelvic tilt was predicted according to the normal range of SVA (0 mm to 50 mm) for types A, B1, B2, and B3, and based on the absolute value of one-third of the PI-LL mismatch for type C patients. The reliability of the classification of the patients and the prediction of the change of pelvic tilt were assessed using kappa values and intraclass correlation coefficients (ICCs), respectively. Validity was assessed using the overall mean error and mean absolute error (MAE) for the prediction of the change of pelvic tilt. Results. The kappa values were 0.927 (95% confidence interval (CI) 0.861 to 0.992) and 0.945 (95% CI 0.903 to 0.988) for the inter- and intraobserver reliabilities, respectively, and the ICCs ranged from 0.919 to 0.997. The overall mean error and MAE for the prediction of the change of pelvic tilt were -0.3° (SD 3.6°) and 2.8° (SD 2.4°), respectively. The overall absolute change of pelvic tilt was 5.0° (SD 4.1°). Pre- and postoperative values and changes in pelvic tilt, SVA, SS, and LL varied significantly among the five types of patient. Conclusion. We found that the proposed algorithm was reliable and valid for predicting the standing pelvic tilt after THA. Cite this article: Bone Joint J 2024;106-B(1):19–27

The pelvic girdle and spine vertebral column work as a long chain influenced by pelvic tilt. Spinal deformities or other musculoskeletal conditions may cause patients to compensate with excessive pelvic tilt, producing alterations in the degree of lumbar lordosis and subsequently causing pain. The objective of this study is to assess the effect of open and closed chain anterior or posterior pelvic tilt on lumbar spine kinematics using an in vitro cadaveric spine model. Three human cadaveric spines with intact pelvis were suspended with the skull fixed in a metal frame. Optotrak 3D motion system tracked real-time coordinates of pin markers on the lumbar spine. A force-torque digital gage applied consistent force to standardize the acetabular or sacral axis’ anterior and posterior pelvic tilt during simulated open and closed chain movements, respectively. In closed chain PPT, significant differences in relative intervertebral compression existed between L1/L2 [-2.54 mm] and L5/S1 [-11.84 mm], and between L3/L4 [-2.78 mm] and L5/S1 [-11.84 mm] [p <.05]. In closed chain APT, significant differences in relative intervertebral decompression existed between spinal levels L1/L2 [2.87mm] and L5/S1[24.48 mm] and between L3/L4 [2.94 mm] and L5/S1 [24.48 mm] [p <.05]. In open chain APT, significant differences in relative intervertebral decompression existed between spinal levels L4/L5 [1.53mm] and L5/S1 [25.14 mm] and between L2/L3 [1.68 mm] and L5/S1 [25.14 mm] [p<.05 for both]. Displacement during closed chain PPT was significantly greater than during open chain PPT, whereas APT showed no significant differences. In PPT, open chain pelvic tilts did not produce as much lumbar intervertebral displacement compared to closed chain. In contrast, APT saw no significant differences between open and closed chain. Additionally, results illustrate the increase in lumbar lordosis during APT and the loss of lordosis during PPT

Acetabular retroversion is a recognised cause of hip impingement. Pelvic tilt influences acetabular orientation and is known to change in different functional positions. While previously reported in patients with developmental dysplasia of the hip, positional changes in pelvic tilt have not been studied in patients with acetabular retroversion. We retrospectively analysed supine and standing AP pelvic radiographs in 22 patients with preoperative radiographs and 47 with post-operative radiographs treated for symptomatic acetabular retroversion. Measurements were made for acetabular index (AI), lateral centre-edge angle (LCEA), crossover index, ischial spine sign, and posterior wall sign. The change in pelvic tilt angle was measured both by the Sacro-Femoral-Pubic (SFP) angle and the Pubic Symphysis to Sacro-iliac (PS-SI) Index. In the supine position, the mean calculated pelvic tilt angle (by SFP) was 1.05° which changed on standing to a pelvic tilt of 8.64°. A significant increase in posterior pelvic tilt angle from supine to standing of 7.59° (SFP angle) and 5.89° (PS –SI index) was calculated (p<0.001;paired t-test). There was a good correlation in pelvic tilt change between measurements using SFP angle and PS-SI index (rho .901 in pre-op group, rho .815 in post-op group). Signs of retroversion were significantly reduced in standing x-rays compared to supine: Crossover index (0.16 vs 0.38; p<0.001) crossover sign (19/28 vs 28/28 hips; p<0.001), ischial spine sign (10/28 hips vs 26/28 hips; p<0.001) and posterior wall sign (12/28 vs 24/28 hips; p<0.001). Posterior pelvic tilt increased from supine to standing in patients with symptomatic acetabular retroversion, in keeping with previous studies of pelvic tilt change in patients with hip dysplasia. The features of acetabular retroversion were much less evident on standing radiographs. The low pelvic tilt angle in the supine position is implicated in the appearance of acetabular retroversion in the supine position. Patients presenting with symptoms of hip impingement should be assessed by supine and standing pelvic radiographs so as not to miss signs of retroversion and to assist with optimising acetabular correction at the time of surgery

Acetabular retroversion is a recognised cause of hip impingement. Pelvic tilt influences acetabular orientation and is known to change in different functional positions. While previously reported in patients with developmental dysplasia of the hip, positional changes in pelvic tilt have not been studied in patients with acetabular retroversion. We retrospectively analysed supine and standing AP pelvic radiographs in 22 patients with preoperative radiographs and 47 with post-operative radiographs treated for symptomatic acetabular retroversion. Measurements were made for acetabular index (AI), lateral centre-edge angle (LCEA), crossover index, ischial spine sign, and posterior wall sign. The change in pelvic tilt angle was measured both by the Sacro-Femoral-Pubic (SFP) angle and the Pubic Symphysis to Sacro-iliac (PS-SI) Index. In the supine position, the mean calculated pelvic tilt angle (by SFP) was 1.05° which changed on standing to a pelvic tilt of 8.64°. A significant increase in posterior pelvic tilt angle from supine to standing of 7.59° (SFP angle) and 5.89° (PS –SI index) was calculated (p<0.001;paired t-test). The mean pelvic tilt change of 6.51° measured on post-operative Xrays was not significantly different (p=.650). There was a good correlation in pelvic tilt change between measurements using SFP angle and PS-SI index (rho .901 in pre-op group, rho .815 in post-op group). Signs of retroversion were significantly reduced in standing x-rays compared to supine: Crossover index (0.16 vs 0.38; p<0.001) crossover sign (19/28 vs 28/28 hips; p<0.001), ischial spine sign (10/28 hips vs 26/28 hips; p<0.001) and posterior wall sign (12/28 vs 24/28 hips; p<0.001). Posterior pelvic tilt increased from supine to standing in patients with symptomatic acetabular retroversion, in keeping with previous studies of pelvic tilt change in patients with hip dysplasia. The features of acetabular retroversion were much less evident on standing radiographs. The low pelvic tilt angle in the supine position is implicated in the appearance of acetabular retroversion in the supine position. Patients presenting with symptoms of hip impingement should be assessed by supine and standing pelvic radiographs so as not to miss signs of retroversion and to assist with optimising acetabular correction at the time of surgery

Purpose. Patients with acetabular dysplasia demonstrate altered biomechanics during gate and other activities. We hypothesized that these patients exhibit a compensatory increase in the anterior pelvic tilt during gait. Materials & Methods. Twelve patients were included in this prospective radiographic and gait analysis study prior to the PAO. All were women. The mean age was 27 years (+/− 8 yrs). Tonnis grade was zero in nine, and one in three hips. All patients performed multiple one-minute walking trials on the level, the incline, and the decline treadmill surfaces in an optical motion capture lab. Anterior pelvic tilt is reported in (+), while the posterior pelvic tilt is reported in (–) values. Results. Radiographic Data. : The mean alpha angle measured from the Dunn and the frog lateral images was 63.0º±17.4, and 54.7º±16.4, respectively. The mean LCEA was 14.9°±6.1, and the mean anterior center edge angle was 18.3°±8.9. the mean acetabular version at 1, 2, and 3 o'clock were 12.1°±11.6, 29.2°±9.9, and 23.3°±7.4, respectively. Intra-class correlation coefficient (ICC) for these measurements were 0.934, 0.895, and 0.971, respectively. The mean femoral anteversion, as measured on the 3D CT scan was 21.3°±16.1. The mean hip flexion range was 107.1°± 7.2. The mean pelvic tilt was 88.7 mm ± 14.4 using the PS-SI distance with an ICC of 0.998. Gait Data. : Baseline measurements were done in the standing position. On the leveled surface, 5 patients had anterior (+) while 7 had posterior (−) pelvic tilt. The mean posterior pelvic tilt was 1.0° with the range of −2.8° to +0.67°. On the inclined surface, all patients had posterior (−) pelvic tilt. The mean pelvic tilt was −4.9° with the range of −6.4° to −3.1°. On the declined surface, 8 patients had anterior (+) while 4 patients had posterior (−) pelvic tilt. The mean pelvic tilt was −0.39° with the range of −1.9° to +1.0°. The pelvic tilt was negatively correlated with the PS-SI distance on all three surfaces with the Spearman coefficients of −0.27, −0.04, and −0.18 on the 3 different surfaces, respectively. Conclusion. Our results demonstrated that the patients with hip dysplasia exhibit variable degrees of the pelvic tilt while walking on different surface inclinations. Weak negative correlation with the standing pelvic tilt measurements from the radiographs suggests that those patients with more anterior standing pelvic tilt tend to have greater compensatory posterior tilt during gait

Aims. The pelvis rotates in the sagittal plane during daily activities. These rotations have a direct effect on the functional orientation of the acetabulum. The aim of this study was to quantify changes in pelvic tilt between different functional positions. Patients and Methods. Pre-operatively, pelvic tilt was measured in 1517 patients undergoing total hip arthroplasty (THA) in three functional positions – supine, standing and flexed seated (the moment when patients initiate rising from a seated position). Supine pelvic tilt was measured from CT scans, standing and flexed seated pelvic tilts were measured from standardised lateral radiographs. Anterior pelvic tilt was assigned a positive value. Results. The mean pelvic tilt was 4.2° (-20.5° to 24.5°), -1.3° (-30.2° to 27.9°) and 0.6° (-42.0° to 41.3°) in the three positions, respectively. The mean sagittal pelvic rotation from supine to standing was -5.5° (-21.8° to 8.4°), from supine to flexed seated was -3.7° (-48.3° to 38.6°) and from standing to flexed seated was 1.8° (-51.8° to 39.5°). In 259 patients (17%), the extent of sagittal pelvic rotation could lead to functional malorientation of the acetabular component. Factoring in an intra-operative delivery error of ± 5° extends this risk to 51% of patients. Conclusion. Planning and measurement of the intended position of the acetabular component in the supine position may fail to predict clinically significant changes in its orientation during functional activities, as a consequence of individual pelvic kinematics. Optimal orientation is patient-specific and requires an evaluation of functional pelvic tilt pre-operatively. Cite this article: Bone Joint J 2017;99-B:184–91

Anteroposterior (AP) radiographs remain the standard of care for pre- and post-operative imaging during total hip arthroplasty (THA), despite known limitation of plain films, including the inability to adequately account for distortion caused by variations in pelvic orientation. Of specific interest to THA surgeons are distortions associated with pelvic tilt, as unaccounted for tilt can significantly alter radiographic measurements of cup position. Several authors have proposed methods for correcting for pelvic tilt on radiographs but none have proven reliable in a THA population. The purpose of our study was to develop a method for correcting pelvic tilt on AP radiographs in patients undergoing primary or revision THA. CT scans from 20 patients/cadaver specimens (10 male, 10 female) were used to create 3D renderings, from which synthetic radiographs of each pelvis were generated (Figure 1). For each pelvis, 13 synthetic radiographs were generated, showing the pelvis at between −30° and 30° of pelvic tilt, in 5° increments. On each image, 8 unique parameters/distances were measured to determine the most appropriate parameters for calculation of pelvic tilt (Figure 2). The most reliable and accurate of these parameters was determined via regression analysis and used to create gender-specific nomograms from which pelvic tilt measurements could be calculated (Figure 3). The accuracy and reliability of the nomograms and correction method were subsequently validated using both synthetic radiographs (n=50) and stereoradiographic images (n=58). Of 8 parameters measured, the vertical distance between the superior margin of the pubic symphysis and the transischial line (PSTI) was determined to be the most reliable (r=−0.96, ICC=0.94). Mean tilt calculated from synthetic radiographs (0.6°±18.6°) correlated very strongly (r=0.96) with mean known tilt (0.5°±17.9°, p=0.98). Mean pelvic tilt calculated from AP EOS images (3.2°±9.9°) correlated strongly (r=0.77) with mean tilt measured from lateral EOS images (3.8°±8.2°, p=0.74). No gender differences were noted in mean tilt measurements in synthetic images (p=0.98) or EOS images (p=0.45). Our method of measuring PSTI and POD on AP images and applying these measurements to nomograms provides a validated and reliable method for estimating the degree of pelvic tilt on AP radiographs during THA. For any figures or tables, please contact authors directly

Aims. Excessive posterior pelvic tilt (PT) may increase the risk of anterior instability after total hip arthroplasty (THA). The aim of this study was to investigate the changes in PT occurring from the preoperative supine to postoperative standing position following THA, and identify factors associated with significant changes in PT. Methods. Supine PT was measured on preoperative CT scans and standing PT was measured on preoperative and one-year postoperative standing lateral radiographs in 933 patients who underwent primary THA. Negative values indicate posterior PT. Patients with > 13° of posterior PT from preoperative supine to postoperative standing (ΔPT ≤ -13°) radiographs, which corresponds to approximately a 10° increase in functional anteversion of the acetabular component, were compared with patients with less change (ΔPT > -13°). Logistic regression analysis was used to assess preoperative demographic and spinopelvic parameters predictive of PT changes of ≤ -13°. The area under receiver operating characteristic curve (AUC) determined the diagnostic accuracy of the predictive factors. Results. PT changed from a mean of 3.8° (SD 6.0°)) preoperatively to -3.5° (SD 6.9°) postoperatively, a mean change of -7.4 (SD 4.5°; p < 0.001). A total of 95 patients (10.2%) had ≤ -13° change in PT from preoperative supine to postoperative standing. The strongest predictive preoperative factors of large changes in PT (≤ -13°) from preoperative supine to postoperative standing were a large posterior change in PT from supine to standing, increased supine PT, and decreased standing PT (p < 0.001). Flexed-seated PT (p = 0.006) and female sex (p = 0.045) were weaker significant predictive factors. When including all predictive factors, the accuracy of the AUC prediction was 84.9%, with 83.5% sensitivity and 71.2% specificity. Conclusion. A total of 10% of patients had > 13° of posterior PT postoperatively compared with their supine pelvic position, resulting in an increased functional anteversion of > 10°. The strongest predictive factors of changes in postoperative PT were the preoperative supine-to-standing differences, the anterior supine PT, and the posterior standing PT. Surgeons who introduce the acetabular component with the patient supine using an anterior approach should be aware of the potentially large increase in functional anteversion occurring in these patients. Cite this article: Bone Joint J 2024;106-B(3 Supple A):74–80

Introduction. A comprehensive understanding of pelvic orientation prior to total hip arthroplasty is necessary to allow proper cup positioning and mitigate the risks of complications associated with component malpositioning. Measurements using anteroposterior (AP) radiographs have been described as effective means of accurately predicting pelvic orientation. The purpose of our study was to describe the inter- and intra-observer reliability and predictive accuracy of predicting pelvic tilt using AP radiographs. Methods. Five fellowship-trained orthopaedic surgeons independently analyzed pelvic tilt, within 10 degrees, for 50 different AP pelvis radiographs. All surgeons were blinded to patient information, diagnosis, and correct measurements prior to analysis. Responses were then compared to correct measurements using sitting-standing AP and lateral stereoradiographs. Results. The average correct predictive value of pelvic tilt between all surgeons was 54%. The intra-observer accuracy of predicting pelvic tilt ranged from 48% to 64%. Discussion. Pelvic tilt cannot be accurately predicted using anteroposterior radiographs. Pre-operative evaluation of pelvic parameters requires multiple views for detailed assessment. Therefore, lateral radiographs are required for accurate prediction of pelvic tilt

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. Acetabular retroversion is a recognized cause of hip impingement and can be influenced by pelvic tilt (PT), which changes in different functional positions. Positional changes in PT have not previously been studied in patients with acetabular retroversion. Methods. Supine and standing anteroposterior (AP) pelvic radiographs were retrospectively analyzed in 69 patients treated for symptomatic acetabular retroversion. Measurements were made for acetabular index (AI), lateral centre-edge angle (LCEA), crossover index, ischial spine sign, and posterior wall sign. The change in the angle of PT was measured both by the sacro-femoral-pubic (SFP) angle and the pubic symphysis to sacroiliac (PS-SI) index. Results. In the supine position, the mean PT (by SFP) was 1.05° (SD 3.77°), which changed on standing to a PT of 8.64° (SD 5.34°). A significant increase in posterior PT from supine to standing of 7.59° (SD 4.5°; SFP angle) and 5.89° (SD 3.33°; PS-SI index) was calculated (p < 0.001). There was a good correlation in PT change between measurements using SFP angle and PS-SI index (0.901 in the preoperative group and 0.815 in the postoperative group). Signs of retroversion were significantly reduced in standing radiographs compared to supine: crossover index (0.16 (SD 0.16) vs 0.38 (SD 0.15); p < 0.001), crossover sign (19/28 hips vs 28/28 hips; p < 0.001), ischial spine sign (10/28 hips vs 26/28 hips; p < 0.001), and posterior wall sign (12/28 hips vs 24/28 hips; p < 0.001). Conclusion. Posterior PT increased from supine to standing in patients with symptomatic acetabular retroversion. The features of acetabular retroversion were less evident on standing radiographs. The low PT angle in the supine position is a factor in the increased appearance of acetabular retroversion. Patients presenting with symptoms of hip impingement should be assessed by supine and standing pelvic radiographs to highlight signs of acetabular retroversion, and to assist with optimizing acetabular correction at the time of surgery. Cite this article: Bone Joint J 2022;104-B(7):786–791

Introduction. The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures. Methodology. Pre-operatively, 90 total hip replacement patients had their pelvic tilt measured in 3 functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair), Fig 1. Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography, Fig 2. Results. The mean standing pelvic tilt was −2.1° ± 7.4°, with a range of −15.2° – 15.3°. Mean supine pelvic tilt was 4.1° ± 5.5°, with a range of −9.7° – 17.9°. Mean pelvic tilt in the flexed seated position was −1.8° ± 14.1°, with a range of −31.8° – 29.1°, Fig 3. The mean absolute change from supine to stand, and stand to flexed seated was 6.9° ± 4.1° and 11.9° ± 7.9° respectively. 86.6% of patients had a more anteriorly tilted pelvis when supine than standing. 52.2% of patients had a more anteriorly tilted pelvis when seated than standing. Conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Planning and measurement of cup placement in the supine position can lead to large discrepancies in orientation during more functionally relevant postures. As a result of the functional changes in pelvic position, cup orientations during dislocation and edge-loading events are likely to be significantly different to that measured from standard CT and radiographs. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles

Unstable pelvic injuries in young children with an immature pelvis have different modes of failure from those in adolescents and adults. We describe the pathoanatomy of unstable pelvic injuries in these children, and the incidence of associated avulsion of the iliac apophysis and fracture of the ipsilateral fifth lumbar transverse process (L5-TP). We retrospectively reviewed the medical records of 33 children with Tile types B and C pelvic injuries admitted between 2007 and 2014; their mean age was 12.6 years (2 to 18) and 12 had an immature pelvis. Those with an immature pelvis commonly sustained symphyseal injuries anteriorly with diastasis, rather than the fractures of the pubic rami seen in adolescents. Posteriorly, transsacral fractures were more commonly encountered in mature children, whereas sacroiliac dislocations and fracture-dislocations were seen in both age groups. Avulsion of the iliac apophysis was identified in eight children, all of whom had an immature pelvis with an intact ipsilateral L5-TP. Young children with an immature pelvis are more susceptible to pubic symphysis and sacroiliac diastasis, whereas bony failures are more common in adolescents. Unstable pelvic injuries in young children are commonly associated with avulsion of the iliac apophysis, particularly with displaced SI joint dislocation and an intact ipsilateral L5-TP. Cite this article: Bone Joint J 2015; 97-B:696–704

Background. Over 10% of total hip arthroplasty (THA) surgeries performed in England and Wales are revision procedures. 1. Malorientation of the acetabular component in THA may contribute to premature failure due to mechanisms such as edge loading and prosthetic impingement. It is known that the pelvis flexes and extends during activities of daily living (ADLs), and excessive pelvic motion can contribute to functional acetabular malorientation. Preoperative radiographs can be performed to measure changes in pelvic tilt during ADLs to identify high risk individuals and inform surgical decision making. However, radiographs require time-consuming radiation exposure, and are unable to provide truly dynamic 3-dimensional analysis. The purpose of this study was to develop and evaluate a motion capture method using inertial measurement units (IMUs). This would provide a rapid, non-invasive analysis of pelvic tilt which could be used to support surgical planning. Methods. Patients awaiting THA were fitted with a bespoke device consisting of a 3D-printed clamp which housed the IMU and positioned over the sacrum. A wide elastic belt was fitted around the patient's waist to keep the device in place. Movement data was transmitted wirelessly to a tablet computer. Pelvic tilt was measured in standing, flexed seated and step-up positions while undergoing X-rays with the IMU capturing the data in parallel. Statistical analysis included measures of correlation between the X-ray and IMU measurements. Results. Measurements from 30 patients indicated a moderate-strong correlation (R. 2. = .87; Figure 1) between IMU and radiological measures of AP pelvic tilt. Conclusions. A novel device has been developed that can suitably track pelvic movements. This could potentially be used to identify patients with large changes in pelvic tilt, and thereby inform surgical planning. For any figures or tables, please contact the authors directly

Pelvic tilt (PT) is always described as the pelvic orientation along the transverse axis, yet four PT definitions were established based on different radiographic landmarks: anterior pelvic plane (PT. a. ), the centres of femoral heads and sacral plate (PT. m. ), pelvic outlet (PT. h. ), and sacral slope (SS). These landmarks quantify a similar concept, yet understanding of their relationships is lacking. Some studies referred to the words “pelvic tilt” for horizontal comparisons, but their PT definitions might differ. There is a demand for understanding their correlations and differences for education and research purposes. This study recruited 105 sagittal pelvic radiographs (68 males and 37 females) from a single clinic awaiting their hip surgeries. Hip hardware and spine pathologies were examined for sub-group analysis. Two observers annotated four PTs in a gender-dependent manner and repeated it after six months. The linear regression model and intraclass correlation coefficient (ICC) were applied with a 95% significance interval. The SS showed significant gender differences and the lowest correlations to the other parameters in the male group (-0.3< r <0.2). The correlations of SS in scoliosis (n = 7) and hip implant (female, n = 18) groups were statistically different, yet the sample sizes were too small. PT. m. demonstrated very strong correlation to PT. h. (r > 0.9) under the linear model PT. m. = 0.951 × PT. h. - 68.284. The PT. m. and PT. h. are interchangeable under a simple linear regression model, which enables study comparisons between them. In the male group, SS is more of a personalised spinal landmark independent of the pelvic anatomy. Female patients with hip implant may have more static spinopelvic relationships following a certain pattern, yet a deeper study using a larger dataset is required. The understanding of different PTs improves anatomical education

Introduction. The optimal goal for cup positioning in hip arthroplasty in individual patients is affected by many factors including surgical exposure, femoral anteversion, and pelvic tilt. Some navigation systems ignore pelvic tilt and are based strictly on the anterior pelvic plane while others incorporate pelvic tilt, as measured in the supine position on the operating table. Neither approach incorporates knowledge of preoperative spino-pelvic flexibility or predictions of the change in spino-pelvic attitude or flexibility following surgery. While prior studies have shown little change in pelvic tilt postoperatively, one recent study based on gait analysis, suggested that changes in pelvic tilt are not predictable. The current study aims to assess changes in pelvic tilt following surgery. Methods. 24 patients, 12 male and 12 female, underwent THA using CT-based navigation. Each patient had supine and standing AP pelvis radiographs both pre-operatively and at a minimum of 1 year post-operatively. Pelvic tilt on each radiograph was measured using a noncommercial two-dimensional/three-dimensional matching application. (HipMatch; Institut for Surgical Technology and Biomechanics, Bern, Switzerland). This software application uses a fully auto- mated registration procedure that can match the three- dimensional model of the preoperative CT with the projected pelvis on a postoperative radiograph. This method has been validated and for measurement of cup position for example showed a mean accuracy of 1.7° +/− 1.7° (rang-4.6° to 5.5°) in the coronal plane and 0.9° +/− 2.8° (rang-5.2° to 5.7°) in the sagittal plane compared with postoperative CT measurements. The software showed a good consistency with an intraclass correlation coefficient (ICC) for inclination of 0.96 (95% confidence interval [CI]: 0.93 to 0.98) and for anteversion of 0.95 (95% CI: 0.91 to 0.98). A good reproducibility and reliability for both inclination and anteversion was found with an ICC ranging from 0.95 to 0.99. No systematic errors in accuracy were detected with the Bland- Altman analysis. Using the HipMatch 2D/3D application, changes in pelvic tilt before and after surgery were assess in both the supine and standing positions. Results. Preoperatively, the mean standing pelvic tilt was .9 degrees (range 10.9 to −9.2) and the mean supine pelvic tilt was 3.7 degrees (range 11.8 to −7.7). Postoperatively, the mean standing pelvic tilt was 1.1 degrees (range 13.8 to −12.3) and the mean supine pelvic tilt was 5.9 degrees (−4.0 to 16.5). The maximum change following surgery in individual patients was −4.9 degrees standing and −8.5 degrees supine. Pre-operative supine pelvic tilt predicts post-operative supine pelvic tilt with an r. 2. of .67. Pre-operative standing pelvic tilt predicts post-operative standing pelvic tilt with an r. 2. of 0.91. Discussion. Overall, in both the standing and supine positions, pelvic tilt changed very little as a result of total hip arthroplasty in this sample of patients and pre-operative pelvic tilt is clearly predictive of post-operative pelvic tilt. Preoperative assessment of pelvic tilt, as measured either in the supine or standing position, may be useful information when determining optimal cup positioning goals for total hip arthroplasty. We recommend that both preoperative assessment of pelvic tilt and preoperative or intraoperative assessment of femoral anteversion should be considered when determining optimal acetabular component positioning

Human error is usually evaluated using statistical descriptions during radiographic annotation. The technological advances popularized the “non-human” landmarking techniques, such as deep learning, in which the error is presented in a confidence format that is not comparable to that of the human method. The region-based landmark definition makes an arbitrary “ground truth” point impossible. The differences in patients’ anatomies, radiograph qualities, and scales make the horizontal comparison difficult. There is a demand to quantify the manual landmarking error in a probability format. Taking the measurement of pelvic tilt (PT) as an example, this study recruited 115 sagittal pelvic radiographs for the measurement of two PTs. We proposed a method to unify the scale of images that allows horizontal comparisons of landmarks and calculated the maximum possible error using a density vector. Traditional descriptive statistics were also applied. All measurements showed excellent reliabilities (intraclass correlation coefficients > 0.9). Eighty-four measurements (6.09%) were qualified as wrong landmarks that failed to label the correct locations. Directional bias (systematic error) was identified due to cognitive differences between observers. By removing wrong labels and rotated pelves, the analysis quantified the error density as a “good doctor” performance and found 6.77°-11.76° maximum PT disagreement with 95% data points. The landmarks with excellent reliability still have a chance (at least 6.09% in our case) of making wrong landmark decisions. Identifying skeletal contours is at least 24.64% more accurate than estimating landmark locations. The landmark at a clear skeletal contour is more likely to generate systematic errors. Due to landmark ambiguity, a very careful surgeon measuring PT could make a maximum 11.76° random difference in 95% of cases, serving as a “good doctor benchmark” to qualify good landmarking techniques

Introduction. The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures. Methodology. Pre-operatively, 1,517 total hip replacement patients had their pelvic tilt measured in 3 functional positions – standing, supine and flexed seated (point when patients initiate rising from a seated position). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Results. The mean supine pelvic tilt was 4.2°, with a range of −20.5° to 24.5°. The mean standing pelvic tilt was −1.3°, with a range of −30.2° to 27.9°. Mean pelvic tilt in the flexed seated position was 0.6°, with a range of −42.0° to 41.3°. The mean absolute change from supine to stand, and supine to flexed seated was 6.0° (SD = 3.8°) and 10.7° (SD = 8.1°) respectively. 6% of patients rotated posteriorly by more than 13° from supine to stand, consequently putting them at risk of excessive functional anteversion in extension. 11% of patients rotated anteriorly by more than 13° from supine to seated, consequently retroverting their cup and putting them at risk in flexion. Therefore, 17% of patients had sagittal pelvic rotations that could lead to functional cup malorientation even with a supposedly ideal orientation of 40°/20°. Factoring in an intraoperative delivery error of ± 5° extends this risk to 51% of patients. Conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. 17% of patients had sagittal pelvic rotations that could lead to functional cup malorientation in functional flexion or extension, even with an apparently perfectly-orientated component. This number extended to 51% when an intra-operative delivery error of ± 5° was considered. Planning and measurement of cup placement in the supine position can lead to large discrepancies in orientation during more functionally relevant postures. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles