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

Introduction. Spatial orientation of the pelvis in the sagittal plane is a key parameter for hip function. Pelvic extension (or retroversion) and pelvic flexion(or anteversion) are currently assessed using Sacral Slope (SS) evaluation (respectively SS decrease and SS increase). Pelvic retroversion may be a risk situation for THA patients. But the magnitude of SS is dependant on the magnitude of pelvic incidence (PI) and may fail to discriminate pelvic position due to patient's anatomy and the potential adaptation mechanisms: a high PI patient has a higher SS but this situation can hide an associated pelvic extension due to compensatory mechanisms of the pelvic area. A low PI patient has a lower SS with less adaptation possibilities in case of THA especially in aging patients. The individual relative pelvic version (RPV) is defined as the difference between « measured SS » (SSm) minus the « normal SS »(SSn) described for the standard population. The aim of the study was to evaluate RPV in standing and sitting position with a special interest for high and low PI patients. Materials and Methods. 96 patients without THA (reference group) and 96 THA patients were included. Pelvic parameters (SS and PI) were measured on standing and sitting EOS images. RPV standing (SSm-SSn) was calculated using the formula SSm – (9 + 0.59 × PI) according to previous publications. SSn in sitting position was calculated according to PI using linear regression: RPV sitting was calculated using the formula RPV = SS – (3,54+ 0,38 × PI). Three subgroups were defined according to pelvic incidence (PI): low PI <45°, 45°<normal PI<65° or high PI>65°. Results. For THA patients, pelvic parameters were:. SSm standing 41° (SD 11°; 8°.73°). SSm sitting 25° (SD 12°;−3°.54°). SSm variation 16°(SD 11°; 9°.46°). RPV standing −2°(SD 9°; −27°.21°). RPV sitting 7° (SD 10; −15°.29°). For non THA patients, pelvic parameters were:. SSm standing39° (SD 10°; 13°.63°). SSm sitting 17° (SD 11°;−5°.48°). SSm variation 27°(SD 13°; −27°.46°). RPV standing −1°(SD 7°; −29°.12°). RPV sitting 0° (SD 10,5; −29.35). Standing-sitting SS variations and RPV were not correlated with PI. Low PI incidence patients had very low RPV standing and sitting. In non THA patients RPV standing and sitting were very low. In THA patients standing-sitting SS variations and RPV were higher than for non THA patients. Sitting RPV was higher than in standing position. Discussion, Conclusion. The overall analysis of SS has limitations: higher or lower SS may be linked to 2 factors: pelvic morphology (PI) and sagittal orientation of the pelvis. RPV and PI were not correlated: a higher or lower value of RPV directly represents the sagittal orientation of the pelvis. Low PI patients have a specific postural pattern with low pelvic adaptability. THA patients specificity for RPV needs further studies for understanding the impact on postoperative rebalancing and instability problems

Introduction. Optimal implant position is critical to hip stability after total hip arthroplasty (THA). Recent literature points out the importance of the evaluation of pelvic position to optimize cup implantation. The concept of Functional Combined Anteversion (FCA), the sum of acetabular/cup anteversion and femoral/stem neck anteversion in the horizontal plane, can be used to plan and control the setting of a THA in standing position. The main purpose of this preliminary study is to evaluate the difference between the combined anteversion before and after THA in weight-bearing standing position using EOS 3D reconstructions. A simultaneous analysis of the preoperative lumbo pelvic parameters has been performed to investigate their potential influence on the post-operative reciprocal femoro-acetabular adaptation. Material and Methods. 66 patients were enrolled (unilateral primary THAs). The same mini-invasive anterolateral approach was performed in a lateral decubitus for all cases. None of the patients had any postoperative complications. For each case, EOS full-body radiographs were performed in a standing position before and after unilateral THA. A software prototype was used to assess pelvic parameters (sacral slope, pelvic version, pelvic incidence), acetabular / cup anteversion, femoral /stem neck anteversion and combined anteversion in the patient horizontal functional plane (the frontal reference was defined as the vertical plane passing through centers of the acetabula or cups). Sub-analysis was made, grouping the sample by pelvic incidence (<55°, 55°–65°, >65°) and by pre-operative sacral slope in standing position (<35°, 35°–45°, >45°). Paired t-test was used to compare differences between preoperative and postoperative parameters within each subgroup. Statistical significance was set at p < 0.05. Results. In the full sample, mean FCA increased postoperatively by 9,3° (39,5° vs 30,2°; p<0.05). In groups with sacral slope < 35° and sacral slope > 45°, postoperative combined anteversion increased significantly by 11,7° and 12,9°, respectively. In the group with pelvic incidence > 65°, postoperative combined anteversion increased significantly by 14,4°. There was no significant change of combined anteversion in the remaining subgroups. Discussion. In this series the FCA increased after THA, particularly in patients with a low or high sacral slope on the pre-operative evaluation in standing position. This may be related to a greater difficulty for the surgeon in anticipating the postoperative standing orientation of the pelvis in these patients, as they were standardly oriented during surgery (lateral decubitus). Interestingly the combined anteversion was also increased in patients with a high pelvic incidence that is commonly associated with a high sacral slope. Conclusion. Post-operative increase of anatomical cumulative anteversion has been previously reported using anterior approach. The FCA concept based on EOS 3D reconstructions brings new informations about the reciprocal femoro-acetabular adaptation in standing position. Differences found in combined anteversion before and after the surgery show that a special interest should be given to patients with high pelvic incidence and low or high sacral slope, to optimize THA orientation in standing position

Introduction. Optimal implant position is the important factor in the hip stability after THA. Both the acetabular and femoral implants are placed in anteversion. While most hip dislocations occur either in standing position or when the hip is flexed, preoperative hip anatomy and postoperative implants position are commonly measured in supine position with CT scan. The isolated and combined anteversions of femoral and acetabular components have been reported in the literature. The conclusions are questionable as the reference planes are not consistent: femoral anteversion is measured according to the distal femoral condyles plane (DFCP) and acetabulum orientation in the anterior pelvic plane (APP)). The EOS imaging system allows combined measurements for standing position in the “anatomical” reference plane or anterior pelvic plane (APP) or in the patient “functional” plane (PFP) defined as the horizontal plane passing through both femoral heads. The femoral anteversion can also be measured conventionally according to the DFCP. The objective of the study was to determine the preoperative and postoperative acetabular, femoral and combined hip anteversions, sacral slope, pelvic incidence and pelvic tilt in patients who undergo primary THA. Material and Methods. The preoperative and postoperative 3D EOS images were assessed in 62 patients (66 hips). None of these patients had spine or lower extremity surgery other than THA surgery in between the 2 EOS assessments. None had dislocation within the follow up time period. Results. Pelvic values. The preoperative sacral slope was 42.4°(11° to 76°) as compared to the postoperative sacral slope (40.3°, −4° to 64°)(p=0.014). The preoperative pelvic tilt was 15.3° (−10° to 44°) as compared to the postoperative tilt (17.2°, −6° to 47°)(p=0.008). The preoperative pelvic incidence was 57.7°(34° to 93°) and globally unchanged as compared to the postoperative incidence (57.5°, 33° to 79°)(p=0.8). Acetabular values. Surgeons increased the anteversion according to the APP by an average of 12.6°(−13° to 53°)(p<0.001). Acetabular anteversion was increased by 14.3° in the PFP (−11° to 51°)(p<0.001). Femoral values. In the DFCP, preoperative neck anteversion was decreased postoperatively by an average of −3,2°(−48° to 33°)(p=0,0942). In the PFP, preoperative neck anteversion was decreased postoperatively by an average of −6,3°(−47° to 17°)(p<0,001). Combined values. According to the classical methods (acetabular orientation in the APP and femoral anteversion in the DFCP), mean preoperative combined anteversion was 36.1° (4° to 86°) and was increased postoperatively to 45.5°(−12° to 98°)(p=0.0003). According to the PFP, mean preoperative combined anteversion was 30,7°(5° to 68°) and was increased postoperatively to 38,8°(−10° to 72°)(p=0,0001). Conclusion. This study reports two methods for the measurement of acetabular and femoral anteversion, “anatomical” according to the APP and DFCP and “functional” according to the PFP. Surgeons tend to increase the anteversion of the acetabular implant and to decrease femoral anteversion during the surgery. The trend is the same for postoperative evolution of values using the “anatomical” or the “functional” methods but numerical discrepancies are explained by significant APP orientation changes. The assessment of the true combined anteversion provides new perspectives to optimize our understanding of THA stability and function

In 2021, Vigdorchik et al. published a large multicentre study validating their simple Hip-Spine Classification for determining patient-specific acetabular component positioning in total hip arthroplasty (THA). The purpose of our study was to apply this Hip-Spine Classification to a sample of Australian patients undergoing THA surgery to determine the local acetabular component positioning requirements. Additionally, we propose a modified algorithm for adjusting cup anteversion requirements. 790 patients who underwent THA surgery between January 2021 and June 2022 were assessed for anterior pelvic plane tilt (APPt) and sacral slope (SS) in standing and relaxed seated positions and categorized according to their spinal stiffness and flatback deformity. Spinal stiffness was measured using pelvic mobility (PM); the ΔSS between standing and relaxed seated. Flatback deformity was defined by APPt <-13° in standing. As in Vigdorchik et al., PM of <10° was considered a stiff spine. For our algorithm, PM of <20° indicated the need for increased cup anteversion. Using this approach, patient-specific cup anteversion is increased by 1° for every degree the patient's PM is <20°. According to the Vigdorchik simple Hip-Spine classification groups, we found: 73% Group 1A, 19% Group 1B, 5% Group 2A, and 3% Group 2B. Therefore, under this classification, 27% of Australian THA patients would have an elevated risk of dislocation due to spinal deformity and/or stiffness. Under our modified definition, 52% patients would require increased cup anteversion to address spinal stiffness. The Hip-Spine Classification is a simple algorithm that has been shown to indicate to surgeons when adjustments to acetabular cup anteversion are required to account for spinal stiffness or flatback deformity. We investigated this algorithm in an Australian population of patients undergoing THA and propose a modified approach: increasing cup anteversion by 1° for every degree the patient's PM is <20°

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

Evaluation of patient specific spinopelvic mobility requires the detection of bony landmarks in lateral functional radiographs. Current manual landmarking methods are inefficient, and subjective. This study proposes a deep learning model to automate landmark detection and derivation of spinopelvic measurements (SPM). A deep learning model was developed using an international multicenter imaging database of 26,109 landmarked preoperative, and postoperative, lateral functional radiographs (HREC: Bellberry: 2020-08-764-A-2). Three functional positions were analysed: 1) standing, 2) contralateral step-up and 3) flexed seated. Landmarks were manually captured and independently verified by qualified engineers during pre-operative planning with additional assistance of 3D computed tomography derived landmarks. Pelvic tilt (PT), sacral slope (SS), and lumbar lordotic angle (LLA) were derived from the predicted landmark coordinates. Interobserver variability was explored in a pilot study, consisting of 9 qualified engineers, annotating three functional images, while blinded to additional 3D information. The dataset was subdivided into 70:20:10 for training, validation, and testing. The model produced a mean absolute error (MAE), for PT, SS, and LLA of 1.7°±3.1°, 3.4°±3.8°, 4.9°±4.5°, respectively. PT MAE values were dependent on functional position: standing 1.2°±1.3°, step 1.7°±4.0°, and seated 2.4°±3.3°, p< 0.001. The mean model prediction time was 0.7 seconds per image. The interobserver 95% confidence interval (CI) for engineer measured PT, SS and LLA (1.9°, 1.9°, 3.1°, respectively) was comparable to the MAE values generated by the model. The model MAE reported comparable performance to the gold standard when blinded to additional 3D information. LLA prediction produced the lowest SPM accuracy potentially due to error propagation from the SS and L1 landmarks. Reduced PT accuracy in step and seated functional positions may be attributed to an increased occlusion of the pubic-symphysis landmark. Our model shows excellent performance when compared against the current gold standard manual annotation process

The sagittal orientation of the pelvis commonly called pelvic tilt has an effect on the orientation of the cup in total hip arthroplasty (THA). Pelvic tilt is different between individuals and changes during activities of daily living. In particular the pelvic tilt in standing position should be considered during the planning of THA to adapt the target angles of the cup patient-specifically to minimise wear and the risk of dislocation. Methods to measure pelvic tilt require an additional step in the planning process, may be time consuming and require additional devices or x-ray imaging. In this study the relationship between three functional parameters describing the sagittal pelvic orientation in standing position and seven morphological parameters of the pelvis was investigated. Correlations might be used to estimate the pelvic tilt in standing position by the morphology of the pelvis in order to avoid additional measuring techniques of pelvic tilt in the planning process of THA. For 18 subjects a semi-automatic process was established to match a 3D-reconstruction of the pelvis from CT scans to orthogonal EOS imaging in standing position and to calculate the morphological and functional parameters of the pelvis subsequently. The two strongest correlations of the linear correlation analysis were observed between morphological pelvic incidence and functional sacral slope (r = 0.78; p = 0.0001) and between morphological pubic symphysis-posterior superior iliac spines-ratio and functional tilt of anterior pelvic plane (r = −0.59; p = 0.0098). The results of this study suggest that patient-specific adjustments to the orientation of the cup in planning of THA without additional measurement of the sagittal pelvic orientation in standing position should be based on the correlation between morphological pelvic incidence and functional sacral slope

Introduction. Limb length discrepancy after THA can result in medicolegal litigation. It can create discomfort for the patient and potentially cause back pain or affect the longevity of the implant. Some patients tolerate the length inequality better compared to others despite difference in anatomical femoral length after surgery. Methods and materials. We analyzed the 3D EOS images of 75 consecutive patients who underwent primary unilateral THA (27 men, 48 women). We measured the 3D length of the femur and tibia (anatomical length), the 3D global anatomical length (the sum of femur and tibia anatomical lengths), the 3D functional length (center of the femoral head to center of the ankle), femoral neck-shaft angle, hip-knee-ankle angle, knee flexum/recurvatum angle, sacral slopes and pelvic incidence. We correlated these parameters with the patient perception of the leg length. Results. The values for leg length and pelvic parameters are shown in table 1. 37 patients had a perception of the LLD (49.3%). When the global anatomical length was shorter on the operated side, the perception of the discrepancy was observed in 56% of the cases. In case of anatomical length longer on the operated side, the perception of the discrepancy was described by the patients in 46% of the cases. The LLD perception was correlated with difference in functional length (p=0.0001), pelvic obliquity (p=0.003) and sacral slope (p=0.023). The anatomical femoral length was not correlated with the LLD perception (p=0,008). Discussion. The perception of LLD is a multifactorial complication. We found that the anatomical femoral length (that can be directly affected by the position of the stem) is not the only important factor. The functional length of the lower extremity which can also be affected by the knee deformities is better correlated with the LLD. The pelvic obliquity and version also affect the patient perception of the LLD

Adverse spinopelvic characteristics (ASC) have been associated with increased dislocation risk following primary total hip arthroplasty (THA). A stiff lumbar spine, a large posterior standing tilt when standing and severe sagittal spinal deformity have been identified as key risk factors for instability. It has been reported that the rate of dislocation in patients with such ASC may be increased and some authors have recommended the use of dual mobility bearings or robotics to reduce instability to within acceptable rates (<2%). The aims of the prospective study were to 1: Describe the true incidence of ASC in patients presenting for a THA 2. Assess whether such characteristics are associated with greater symptoms pre-THA due to the concomitant dual pathology of hip and spine and 3. Describe the early term dislocation rate with the use of ≤36mm bearings. This is an IRB-approved, two-center, multi-surgeon, prospective, consecutive, cohort study of 220 patients undergoing THA through anterolateral- (n=103; 46.8%), direct anterior- (n=104; 27.3%) or posterior- approaches (n=13; 5.9%). The mean age was 63.8±12.0 years (range: 27.7-89.0 years) and the mean BMI 28.0±5.0 kg/m. 2. (range: 19.4-44.4 kg/m. 2. ). There were 44 males (47.8%) and 48 females (52.2%). The mean follow-up was 1.6±0.5 years. Overall, 54% of femoral heads was 32 mm, and 46% was 36mm. All participants underwent lateral spinopelvic radiographs in the standing and deep-flexed seated positions were taken to determine lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic-femoral angle (PFA) and pelvic incidence (PI) in both positions. Spinal stiffness was defined as lumbar flexion <20° when transitioning between the standing and deep-seated position; adverse standing PT was defined as >19° and adverse sagittal lumbar balance was defined as mismatch between standing PI and LL >10°. Pre-operative patient reported outcomes was measured using the Oxford Hip Score (OHS) and EuroQol Five-Dimension questionnaire (EQ-5D). Dislocation rates were prospectively recorded. Non-parametric tests were used, significance was set at p<0.05. The prevalence of PI-LL mismatch was 22.1% (43/195) and 30.4% had increased standing PT (59/194). The prevalence of lumbar stiffness was 3.5% (5/142) and these patients had all three adverse spinopelvic characteristics (5/142; 3.5%). There was no significant difference in the pre-operative OHS between patients with (20.7±7.6) and patients without adverse spinopelvic characteristics (21.6±8.7; p=0.721), nor was there for pre-operative EQ5D (0.651±0.081 vs. 0.563±0.190; p=0.295). Two patients sustained a dislocation (0.9%): One in the lateral (no ASC) and one in the posterior approaches, who also exhibited ASC pre-operatively. Sagittal lumbar imbalance, increased standing spinal tilt and spinal stiffness are not uncommon among patients undergoing THA. The presence of such characteristics is not associated with inferior pre-operative PROMs. However, when all characteristics are present, the risk of instability is increased. Patients with ASC treated with posterior approach THA may benefit from the use of advanced technology due to a high risk of dislocation. The use of such technology with the anterior or lateral approach to improve instability is to date unjustified as the rate of instability is low even amongst patients with ASCs

Purpose. Posterior pelvis tilt (PPT) would affect lumbar lordosis and lead to hip flexion, which causes difficulties walking and standing in patients with hip disorders. Hip flexion movement associated with PPT is well known. We investigated the effect of the angle of hip flexion without the movement of PPT in the supine position. Methods. The study enrolled 24 healthy males with an average age of 20.5 ± 2.3 years. Two pelvic positions in the supine position were investigated: (1) the limited position of the PPT by 500ml PET bottle with water placed under their low back, and (2) the position without placing a PET bottle. We assessed unilateral hip flexion angle with photos taken with a digital camera. For reference, we took an X-ray of a healthy female and observed the lumbo-sacral from the sagittal plane in the supine position. Analysis. Data was processed by Image analysis software (Image J 1.42, NIH). Paired t-tests were used to assess the range of motion of individual joints in each position in the sagittal plane. MEPHAS software (Oosaka University. Japan) was used for all statistical processing, and the level of significance was set at P < 0.05. In addition, we also measured the lumbo-sacral angle (LSA), the lumbo-lordotic angle (LLA) and the sacral slope angle (SSA) with the X-ray. Results. The angle of hip flexion decreased 22.9±6.04 degrees on average in the limited position with a PET bottle compared with the position without a bottle (P<0.01). The angle of pelvis decreased 4.8±2.0 degrees on average. Discussion. The angle of hip flexion significantly decreased in the limited position with a PET bottle. Our results suggest the association movement of the PPT with hip flexion movement in the supine position. This suggests that movements of the LLA and SSA are involved greatly in hip flexion. Significance of study. Our results provide evidence that could lead to more effective way of measurement of the primary hip joint (coxal femoral joint) flexion in the supine position for the patients with hip diseases. If we can measure primary hip joint (coxal femoral joint) flexion, it may also be measured mobility of the pelvis. Measurement of the hip joint flexion should consider the movement of the lumbar vertebrae and the sacral slope

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

Introduction. Post op cup anatomical and functional orientation is a key point in THP patients regarding instability and wear. Recently literature has been focused on the consequences of the transition from standing to sitting regarding anteversion, frontal and sagittal inclination. Pelvic incidence (PI) is now considered as a key parameter for the analysis of sagittal balance and sacral slope (SS) orientation. It's influence on THP biomechanics has been suggested. Interestingly, the potential impact of this morphological angle on cup implantation during surgery and the side effects on post op functional orientation have not been studied. Our study explores this topic from a series of standing and sitting post-op EOS images. Material and methods. 310 patients (mean age 63,8, mean BMI 30,2) have been included prospectively in our current post-operative EOS protocol. All patients were operated with the same implants and technique using anterior approach in lateral decubitus. According to previous literature, 3 groups were defined: low PI less than 45° (57 cases), high PI if more than 60° (63 cases), and standard PI in 190 other cases. Results. Mean PI was 55,8° (SD 11,5). -In High PI, postop SS in standing was significantly higher than in Low and Medium PI. In Medium PI, postop SS in standing was significantly higher than in Low PI. -In High PI, postop SS in sitting was significantly higher than in Low and Medium PI. -In Low PI, postop Functional anteversion in sitting was significantly higher than in Medium PI, but not different from High PI. -In Low PI, Anatomical anteversion was significantly higher than in Medium and High PI. Discussion, Conclusion. This preliminary study points out the potential influence of pelvis morphology expressed by PI on per-operative cup orientation. As surgeons are accustomed to follow bony landmarks during cup implantation, unexpected variations for cup adjustment may be observed if PI is not standard. For any figures or tables, please contact authors directly

Background. Postural change after total hip arthroplasty (THA) is still a matter of discussion. Previous studies have mainly concentrated on the pelvic motions. We report the postoperative changes of the global sagittal posture using pelvic, spinal and lower extremities parameters. Methods. 139 patients (primary THA, without previous spinal or lower extremity surgery) were included. We measured pelvic parameters [SS: Sacral Slope, PI: Pelvic Incidence, PT: Pelvic Tilt, APP angle: Anterior Pelvic Plane angle] and the global posture parameters (SVA: Sagittal Vertical Angle, GSA: Global Sagittal Angle, TPA: T1 pelvic angle). Patients were categorized into low PI group <45°, 45°< medium PI <65° and high PI >65°. Results. Mean GSA and SVA decreased postoperatively (p=0.005 and p=0.004 respectively). The TPA change was not significant (p=0.078). In low PI group, GSA (5.4 ± 5.0 to 4.3 ± 4.0, p=0.005) and SVA (5.4 ± 4.9 to 4.2 ± 4.1, p=0.038) decreased with more posterior pelvic tilt. Postoperative TPA was significantly higher (8.4 ± 10.6 to 9.8 ± 10.7; p=0.048). In medium PI group, SVA decreased (4.2 ± 4.6 to 3.6 ± 4.5, p=0.020) with more posterior pelvic tilt. In high PI group, pelvic and global posture parameters did not evolve significantly. Conclusion. PI is the key determining factor in pelvic tilt modification after THA. Patients with low PI demonstrate significant modification in spine, pelvic and lower extremities. Pelvic tilt is the main adaptation mechanism for medium incidence patients whereas pelvic tilt does not change in high PI patients after surgery

Introduction. Limb-length discrepancy (LLD) is a common postoperative complication after total hip arthroplasty (THA). This study focuses on the correlation between patients’ perception of LLD after THA and the anatomical and functional leg length, pelvic and knee alignments and foot height. Previous publications have explored this topic in patients without significant spinal pathology or previous spine or lower extremity surgery. The objective of this work is to verify if the results are the same in case of stiff or fused spine. Methods. 170 patients with stiff spine (less than 10° L1-S1 lordosis variation between standing and sitting) were evaluated minimum 1 year after unilateral primary THA implantation using EOS® images in standing position (46/170 had previous lumbar fusion). We excluded cases with previous lower limbs surgery or frontal and sagittal spinal imbalance. 3D measures were performed to evaluate femoral and tibial length, femoral offset, pelvic obliquity, hip-knee-ankle angle (HKA), knee flexion/hyperextension angle, tibial and femoral rotation. Axial pelvic rotation was measured as the angle between the line through the centers of the hips and the EOS x-ray beam source. The distance between middle of the tibial plafond and the ground was used to investigate the height of the foot. For data with normal distribution, paired Student's t-test and independent sample t-test were used for analysis. Univariate logistic regression was used to determine the correlation between the perception of limb length discrepancy and different variables. Multiple logistic regression was used to investigate the correlation between the patient perception of LLD and variables found significant in the univariate analysis. Significance level was set at 0.05. Results. Anatomical femoral length correlated with patients’ perception of LLD but other variables were significant (the height of the foot, sagittal and frontal knee alignment, pelvic obliquity and pelvic rotation more than 10°). Interestingly some factors induced an unexpected perception of LLD despite a non-significant femoral length discrepancy less than 1cm (pelvic rotation and obliquity, height of the foot). Conclusions. LLD is a multifactorial problem. This study showed that the anatomical femoral length as the factor that can be modified with THA technique or choice of prosthesis is not the only important factor. A comprehensive clinical and radiological evaluation is necessary preoperatively to investigate spinal stiffness, pelvic obliquity and rotation, sagittal and coronal knee alignment and foot deformity in these patients. Our study has limitations as we do not have preoperative EOS measurements for all patients. We cannot assess changes in leg length as a result of THA. We also did not investigate the degree of any foot deformities as flat foot deformity may potentially affect the patients perception of the leg length. Instead, we measured the distance between the medial malleolus and ground that can reflect the foot arch height. More cases must be included to evaluate the potential influence of pelvis anatomy and functional orientation (pelvic incidence, sacral slope and pelvic tilt) but this study points out that spinal stiffness significantly decreases the LLD tolerance previously reported in patients without degenerative stiffness or fusion

The anterior pelvic plane (APP) angle is often used as a reference to decide pelvic alignment for hip surgeons. However, Rousseau criticised the validness of the APP angles because the APP angles in standing position measured on conventional standing X-ray films never showed correlation with the other pelvic alignment parameters, such as sacral slope (SS). We measured the APP angles, SS and pelvic tilt (PT) on the non-distorted anteroposterior (AP) and lateral digitally reconstructed radiography (DRR) images in supine position (with CT scans) and AP and lateral X-ray images in standing position (with EOS X-ray machine [EOS imaging, Paris, France]) by using of the same EOS software. Our data showed that the pre- and post-operative APP angles correlated with SS and PT in both supine and standing positions. Our non-distorted high quality images and the EOS software revealed these correlations. Therefore, we can still use the APP angles to decide pelvic alignment for patients who undergo total hip arthroplasty (THA). Recent papers demonstrated positional or chronological dramatic changes of the APP angles between pre- and post-operative states in patients who underwent THA. The EOS system will be a powerful tool to investigate these changes of the pelvic alignments

Introduction. Stand to sit pelvis kinematics is commonly considered as a rotation around the bicoxofemoral axis. However, abnormal kinematics could occur for patients with musculoskeletal disorders affecting the hip-spine complex. The aim of this study is to perform a quantitative analysis of the stand to sit pelvis kinematics using 3D reconstruction from bi-planar x-rays. Materials and Methods. Thirty healthy volunteers as a control group (C), 30 patients with hip pathology (Hip) and 30 patients with spine pathology (Spine) were evaluated. All subjects underwent standing and sitting full-body bi-planar x-rays. 3D reconstruction was performed in each configuration and then translated such as the middle of the line joining the center of each acetabulum corresponds to the origin. Rigid registration quantified the finite helical axis (FHA) describing the transition between standing and sitting with two specific parameters. The orientation angle (OA) is the signed 3D angle between FHA and bicoxofemoral axis and the rotation angle (RA) represents the signed angle around FHA. Pelvic incidence, sacral slope and pelvic tilt were also measured. After checking normality of distribution, parameters were compared statistically between the 3 groups (p<0.05). Results. The mean value of the orientation angle in control group was −1.8° (SD 10.8°, range −26° to 25°). The mean value of the OA was 0.3° (SD 12.3°, range to −31° to 37°) in Hip group and −4.7° (SD 21.5°, range −86° to 38°) in Spine group. There was no significant difference in mean OA among groups. However, the more subnormal and abnormal patients were in Spine group compared to C and Hip groups. The mean value of the rotation angle in C group was 18.1° (SD 9.1°, range 5° to 43°). There was significant difference in RA between Hip and Spine groups (21.1° (SD 8.0°) and 16.0° (SD 10.7°), respectively) (p=0.04). Conclusion. This study highlights new informations obtained by the quantitative analysis of pelvis rotation between standing and sitting in healthy, hip pathology patients and spine pathology patients using 3D reconstruction from bi-planar radiographs. Hip and spine pathologies affect stand to sit pelvic kinematics. Surgeons should be aware of potential abnormal stand to sit transition in such clinical situations. This improved assessment of the pelvic rotational adaptation could lead to a more personalized approach for the planning of hip prostheses

Component placement and the individual's functional posture play key roles in mechanical complications and hip dysfunction after total hip arthroplasty (THA). The challenge is how to measure these. X-rays lack accuracy and CT scans increase radiation dose. A newer imaging modality, EOSTM, acquires low-dose, simultaneous, perpendicular anteroposterior and lateral views while providing a global view of the patient in a functional standing or sitting position, leading to a 3D reconstruction for parameter calculation. The purpose of the present study was to develop an approach using the EOS system to compare patients with good versus poor results after THA and to report our preliminary experiences using this technique. A total of 35 patients were studied: 17 with good results after THA (G-THA), 18 with poor results (P-THA). The patients were operated on or referred for follow-up to a single expert surgeon, between 2001 and 2011, with a minimum follow-up of at least two years. Acetabular cup orientation differed significantly between groups. Acetabular version relative to the coronal plane was lower in P-THA (32°±12°) compared to G-THA (40°±9°) (p=0.02). There was a strong trend towards acetabular cup inclination relative to the APP being higher in P-THA (45°±9°, compared to 39°±7°; p=0.07). Proportions of P-THA vs. G-THA patients with cup orientation values higher or lower than 1 SD from the overall mean differed significantly and substantially between groups. All revision cases had a least four values outside 1 SD, including acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset and neck-shaft angle. This is the first study to our knowledge to provide acetabular, pelvic and femoral parameters for these two groups and the first to provide evidence that a collection of high/low parameters may together contribute to a poor result. The results show the importance of acetabular component placement, in both inclination and version and the importance of looking at individuals, not just groups, to identify potential causes for pain and functional issues. With the EOS system, a large cohort of individuals can be studied in the functional position relatively quickly and at low dose. This could lead to patient-specific guidelines for THA planning and execution

Introduction. Pelvic flexion and extension in different body positions can affect acetabular orientation after total hip arthroplasty, and this may predispose patients to dislocation. The purpose of this study was to evaluate functional acetabular component position in total hip replacement patients during standing and sitting. We hypothesize that patients with degenerative lumbar disease will have less pelvic extension from standing to sitting, compared to patients with a normal lumbar spine or single level spine disease. Methods. A prospective cohort of 20 patients with primary unilateral THR underwent spine-to-ankle standing and sitting lateral radiographs that included the lumbar spine and pelvis using EOS imaging. Patients were an average age of 58 ± 12 years and 6 patients were female. Patients had (1) normal lumbar spines or single level degeneration, (2) multilevel degenerative disc disease or (3) scoliosis. We measured acetabular anteversion (cup relative to the horizontal), sacral slope angle (superior endplate of S1 relative to the horizontal), and lumbar lordosis angles (superior endplates of L1 and S1). We calculated the absolute difference in acetabular anteversion and the absolute difference in lumbar lordosis during standing and sitting (Figure 1). Results. Nine patients had normal lumbar spines or scoliosis, and 11 patients had multilevel disc disease. The median change in cup anteversion for normal and scoliosis patients was 29° degrees (range 11° to 41°) compared to 21° degrees (range 1° to 34°) for multilevel disc disease patients (p=0.03). There was a positive correlation between the change in cup anteversion and the change in lumbar lordosis (p=0.01; Figure 2). From standing to sitting, cup anteversion always increased and lumbar lordosis always decreased. Conclusions. The change in cup anteversion from standing to sitting was variable in patients with normal, degenerative, and scoliosis lumbar spines. Patients with degenerative disc disease have less pelvic extension, and thus less acetabular anteversion in the sitting position compared to normal spines. This may increase their risk of posterior dislocation

Introduction. In the previous study regarding the relationship among maximum hip flexion, the pelvis, and the lumbar vertebrae on the sagittal plane, we have found in X-rays that the lumbo lordotic angle (LLA) and the sacral slope angle (SSA) have a large impact on hip flexion angle. We examined hip flexion angles to the various height of the objects (half round plastic tube) placed under the subject's lower back and compared the passive hip flexion angles in the supine position between younger and middle age groups. Participants. The participants were 14 healthy volunteers: 7 females with an average age of 17 years (Group 1: G-1), 7 females with an average age of 45 years (Group 2: G-2). The average BMI (Body Mass Index) of volunteers was less than 25, and their Tomas Tests were negative. Methods. The hip flexion angle was measured in six stages as half round plastic tube placed under the subject's lower back gradually increased in height by 5mm. StageZero is the Regular Position with nothing placed under the subject's lower back: RP (specified Japanese Orthopedics Association and Rehabilitation Medical Association). The next five stages (from Stage One) were performed in the Limited Position (LP) of the posterior pelvic tilt and lumbar movement by placing the tube under the subject's lower back. The height of tube is 2.2 cm. Stage One started at 2.2cm. Each Stage from Stage One has a difference in the height of 5mm. Stage Zero: 0cm, Stage 1: 2.2cm, Stage 2: 2.7cm, Stage 3: 3.2cm, Stage 4: 3.7cm, Stage 5: 4.2cm,. Analysis. We compared the hip flexion angle of six stages of the two groups. A two-way repeated measurement ANOVA was used to compare the differences in hip flexion angle of G1 and G2. Statistical significant was established at p < 0.05. Further, we took X-rays of a healthy female and examined the LLA, SSA, and Lumbo Sacral Angle (LSA) during hip maximum flexion. Results & Discussion. In RP (Stage Zero), the LLA and the SSA had a large impact on hip flexion angle observed in X-rays. In Stages1-6, there was a slight movement in the LLA and the SSA. The higher the tubes’ height, the smaller the hip flexion angle. When the height was low, the posterior pelvic tilt became large, resulting in a larger hip flexion angle. The fulcrum rotational point of the hip flexion would move to the lumbar side. We need to determine and tailor the height of object to each individual lumbar lordosis