Introduction:. The lateral radiographs are useful in evaluation of the acetabular cup anteversion. However, this method was affected by variations in pelvic position and radiographic technique. In this study, we employed the ischial axis (IA) as an anatomical landmark on the lateral radiographs, and we investigated a relationship between IA and the anterior pelvic plane (APP) using three-dimensional computed tomography (3D-CT). Using these findings, we report a new method for accurate measurement of the acetabular cup anteversion on plain lateral radiographs using IA as an anatomical reference. Materials and Methods:. At first, preoperative3D-CT images were obtained in 109 patients who underwent total hip arthroplasty. The diagnosis was osteoarthritis in all patients. The angle between the IA (defined by a line connecting the anterior edge of the greater sciatic notch and the lesser sciatic notch) and APP (defined by the bilateral anterosuperior iliac spine and the symphysis) was measured on 3D-CT (Fig. 1). Secondly, postoperative lateral radiographs were obtained at 2 weeks, 4 weeks, 12 weeks, 24 weeks, and 52 weeks after surgery in 15 patients. The angle between a line tangential to the opening of the cup and a line perpendicular to APP was measured (Fig. 2). Three methods of acetebular cup position assessment were compared: 1) the present method, 2) Woo and Morrey method, and 3) software (2D template, Kyocera) method. Results:. The mean angle between IA and APP was 18.0 ± 3.5°. The mean acetabular cup anteversion measured using present method was 21.3°, Woo and Morrey method was 26.6°, and software method was 21.2°. The mean SDs of present method was 0.64°, Woo and Morrey method was 1.17°, and software method was 0.46°. Conclusions:. APP, considered as vertical in weight bearing, has a relatively consistent relationship between IA. The findings of this study provide a more consistent measurement of acetabular cup by reducing variation due to pelvic position

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°

Introduction. Lumbar spine fusion in patients undergoing THA (total hip arthroplasty) is a known risk factor for hip dislocation with some studies showing a 400% increased incidence compared to the overall THA population. Reduced spine flexibility can effectively narrow the cup anteversion safe zone while alterations in pelvic tilt can alter the center of the anteversion safe zone. The use of precision cup alignment technology combined with patient-specific cup alignment goals based on preoperative assessment has been suggested as a method of addressing this problem. The current study assess the dislocation rate of THA patients with stiff or fused lumbar spines treated using surgical navigation with patient-specific cup orientation goals. Methods. Seventy-five THA were performed in 54 patients with a diagnosis of lumbar fusion, lumbar disc replacement, and scoliosis with Cobb angles greater than 40 degrees were treated by the senior author (SM) as part of a prospective, non-randomized study of surgical navigation in total hip arthroplasty. All patients were treated using a smart mechanical navigation tool for cup alignment (HipXpert System, Surgical Planning Associates, Inc., Boston, MA). Cup orientation goals were set on a patient-specific basis using supine pelvic tilt as measured using CT. Patients with increased pelvic tilt had a goal for increased cup anteversion and patients with decreased pelvic tilt had a goal for decreased cup anteversion (relative to the anterior pelvic plane coordinate system). Each patient's more recent outpatient records were assessed for history of dislocation, instability, mechanical symptoms, decreased range of motion or progressive pain. Additionally, last clinic radiographs were reviewed to confirm lumbar pathology in the form of spinal surgical hardware. Results. Seventy-five total hip arthroplasties with stiff lumbar spine were reviewed with and average follow up of 6.04 years. The average number of levels of lumbar fusion was 2.3 levels. Since the most recent follow up on all patients in this cohort no hip dislocations had occurred. Discussion and Conclusion. Fusion or stiffness of the lumbar spine is a known risk factor for instability following elective THA. The current study demonstrates that patient-specific planning of cup placement taking abnormal pelvic tilt into consideration combined with the use of accurate intra-operative cup alignment technology can be used to address this problem

Introduction. Many authors have described component position and leg length discrepancy (LLD) after total hip arthroplasty (THA) as the most important factors for good postoperative outcomes. However, regarding the relationships between component position and different approaches for THA, the optimal approach for component position and LLD remains unknown. The aims of this study were to compare these factors among the direct anterior, posterolateral, and direct lateral approaches on postoperative radiographs retrospectively, and determine which approach leads to good orientation in THA. Methods. We retrospectively evaluated 150 patients who underwent unilateral primary THA in our department between January 2009 and December 2014, with the direct anterior, posterolateral, or direct lateral approach used in 50 patients each. Patients with significant hip dysplasia (Crowe 3 or 4), advanced erosive arthritis, prevented osteotomy of the contralateral hip, and body mass index (BMI) of more than 30 were excluded. The mean age, sex, and preoperative diagnosis of the affected hip were equally distributed in patients who underwent THA with the different approaches. The mean BMI did not differ significantly among the groups. The radiographic measurements included cup inclination angle, dispersion of cup inclination from 40°, and LLD on an anteroposterior pelvic radiograph, and cup anteversion angle and dispersion of cup anteversion from 20° on a cross-table lateral radiograph postoperatively. We also measured the ratios of patients with both cup inclination of 30–50° and cup anteversion of 10–30° (target zone in our department), femoral stem varus/valgus, and LLD of 10 mm or less. Statistical analyses used an unpaired t-test and Fisher's exact test, with significance set at p<0.05. Results. The mean cup inclination was 36.9±5.1° for direct anterior approach, 40.8±7.5° for posterolateral approach, and 38.5±7.5° for direct lateral approach. Dispersion of cup inclination from 40° was almost identical in the three groups, with no significant differences. The mean cup anteversion was 23.4±5.5° for direct anterior approach, 25.9±9.2° for posterolateral approach, and 24.3±8.6° for direct lateral approach. Dispersion of cup anteversion from 20° differed between direct anterior approach and posterolateral or direct lateral approach (P<0.05 for each). The mean LLD was 1.3±6.6mm for direct anterior approach, 3.0±8.6mm for posterolateral approach, and 2.6±7.4mm for direct lateral approach. The mean LLD did not differ significantly among the three groups. The ratio of patients with both cup inclination of 30–50° and cup anteversion of 10–30° was significantly better for direct anterior approach than for posterolateral or direct lateral approach (78% vs. 52% and 52%, respectively; p<0.05). The ratios of femoral stem varus/valgus and LLD of 10 mm or less did not differ among the groups. Conclusions. The direct anterior approach in THA appeared to have small dispersion of cup anteversion angle and high ratio of cup component position in our target zone compared with the posterolateral and direct lateral approaches. However, the LLD and femoral stem varus/valgus after THA did not differ significantly among the three approaches postoperatively

Introduction. To control implant alignments (anteversion and abduction angle of the acetabular cup and antetorsion of the femoral stem) within an appropriate angle range is essentially important in total hip arthroplasty to avoid implant impingement. A navigation system is necessary for accurate intraoperative evaluation of implant alignments but is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative evaluation of the alignments is desired in the clinical field. I presented an idea of marking ruler-like scales on a trial femoral head in the last ISTA Congress. The purpose of this study is to introduce an idea further improved in evaluating the combined implant alignment intraoperatively. Materials and Methods. We can evaluate the combined anteversion (sum of cup anteversion and stem antetorsion) and cup abduction angle by reading the scales at the most proximal point of inner edge of the liner when horizontal and vertical scales are marked on the femoral head appropriately and the hip joint is kept at the neutral position after implant settings and trial reduction. Whether the impingement occurred within the target ROM (Flx 130, IR40@Flx90, Ext 40, ER 40) was judged under specific conditions of the oscillation angle (139), neck-shaft angle of the stem (130), stem adduction angle (7), stem antetorsion (20 or 30), and cup anteversion and abduction angles. Cup anteversion and abduction angles were changed from 0 to 40 and 30 to 50 degrees in 1-degree increments, respectively. Impingement judgment was performed mathematically for each combination of implant alignment based on matrix transformations and trigonometric formulas. Results. Impingement-free combinations of implant alignments were identified using spreadsheet software. Points which indicated impingement-free when they matched with the most proximal point of the inner edge of the liner when the hip joint was kept neutral were plotted on the surface of the head on a 3-dimensional computer graphic software. Thus, the safe zone could be indicated visually on the trial head by a collection of these points. Discussion. We can easily judge whether the implant impingement occurs or not by using this trial head intraoperatively. However, there are several factors which make the judgment inaccurate. First, the safe zone varies according to the stem antetorsion. Second, the position at which the hip is kept intraoperatively is not necessarily neutral. Third, stem adduction angle varies according to the length of the femur. Conclusion. Safe zone mapping on the trial femoral head is low cost and easy method to be introduced in the clinical practice for the purpose of a rough judgment of implant impingement

The purpose of this preliminary study was to evaluate the feasibility and accuracy of HipAlign (OrthAlign, Inc., USA) system for cup orientation in total hip arthroplasty (THA). The subjects of this study were 5 hips that underwent primary cementless THA via a posterior approach in the lateral decubitus position. Evaluation 1; after reaming acetabular bone, a trial cup was placed in the reamed acetabulum in an aimed alignment using HipAlign. Then, the trial cup alignment was measured using HipAlign and CT-based navigation system in the radiographic definition. Evaluation 2; a cementless cup was placed in the reamed acetabular in an aimed alignment using CT-based navigation and cup alignment was measured using both methods. After operation, we measured the cup alignment using postoperative CT in each patient. In the results, the average cup inclination measured with HipAlign was around 5 degrees of true cup inclination angles. The average cup anteversion with HipAlign tended to be larger than that with CT-based navigation or postoperative CT in both evaluations. That is because there is a difference in the pelvic sagittal tilt between the lateral position and supine position. In conclusion, this study suggests that guiding cup alignment with the use of HipAlign is feasible through a posterior approach and the mean cup inclination measured with HipAlign showed an acceptable level of accuracy, but the mean cup anteversion is not reliable. We need a further modification for pelvic registration to improve the accuracy of cup anteversion

Iliopsoas impingement occurs in between 5–30% of patients after hip arthroplasty and has been thought to only be caused by an oversized cup, cup malpositioning, or the depth of the psoas valley. However, no study has associated the relationship between preoperative measurements with the risk of impingement. This study sought to assess impingement between the iliopsoas and acetabular cup using a novel validated model to determine the risk factors for iliopsoas impingement. 413 patients received lower limb CT scans and lateral x-rays that were segmented, landmarked, and measured using a validated preoperative planning protocol. Implants were positioned according to the preference of ten experienced surgeons. The segmented bones were transformed to the standing reference frame and simulated with a novel computational model that detects impingement between the iliopsoas and acetabular cup. Definitions of patients at-risk and not at-risk of impingement were defined from a previous validation study of the simulation. At-risk patients were propensity score matched to not at-risk patients. 21% of patients were assessed as being at-risk of iliopsoas impingement. Significant differences between at-risk patients and not at-risk patients were observed in standing pelvic tilt (p << 0.01), standing femoral internal rotation (p << 0.01), medio-lateral centre-of-rotation (COR) change (p << 0.01), supine cup anteversion (p << 0.01), pre- to postoperative cup offset change (p << 0.001), postoperative gross offset (p = 0.009), and supero-inferior COR change (p = 0.02). Impingement between the iliopsoas and acetabular cup is under-studied and may be more common than is published in the literature. Previously it has been thought to only be related to cup size or positioning. However, we have observed significant differences between at-risk and not at-risk patients in additional measurements. This indicates that its occurrence is more complex than simply being related to cup position

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. The direct anterior approach (DAA) for total hip arthroplasty continues to gain popularity. Consequently, more procedures are being performed with the patient supine. The approach often utilizes a special leg positioner to assist with femoral exposure. Although the supine position may seem to allow for a more reproducible pelvic position at the time of cup implantation, there is limited evidence as to the effects on pelvic tilt with such leg positioners. Furthermore, the DAA has led to increased popularity of specific softwares, ie. Radlink or JointPoint, that facilitate the intra-op analysis of component position from fluoroscopy images. The aim of this study was to assess the difference in cup orientation measurements between intra-op fluoroscopy and post-op CT. Methods. A consecutive series of 48 DAA THAs were performed by a single surgeon in June/July 2018. All patients received OPS. TM. pre-operative planning (Corin, UK), and the cases were performed with the patient supine on the operating table with the PURIST leg positioning system (IOT, Texas, USA). To account for variation in pelvic tilt on the table, a fluoroscopy image of the hemi-pelvis was taken prior to cup impaction, and the c-arm rotated to match the shape of the obturator foramen on the supine AP Xray. The final cup was then imaged using fluoroscopy, and the radiographic cup orientation measured manually using Radlink GPS software (Radlink, California, USA). Post-operatively, each patient received a low dose CT scan to measure the radiographic cup orientation in reference to the supine coronal plane. Results. Mean cup orientation from intra-op fluoro was 38° inclination (32° to 43°) and 24° anteversion (20° to 28°). Mean cup orientation from post-op CT was 40° inclination (29° to 47°) and 30° anteversion (22° to 38°). Cups were, on average, 6° more anteverted and 2° more inclined on post-op CT than intra-op. These differences were statistically significant, p<0.001. All 48 cups were more anteverted on CT than intra-op. There was no statistical difference between pre- and post-op supine pelvic tilt (4.1° and 5.1° respectively, p = 0.41). Discussion. We found significant differences in cup orientation measurements performed from intra-op fluoro to those from post-op CT. This is an important finding given the attempts to adjust for pelvic tilt during the procedure. We theorise two sources of error contributing to the measurement differences. Firstly, the under-compensation for the anterior pelvic tilt on the table. Although the c-arm was rotated to match the obturator foramen from the pre-op imaging, we believe the manual matching technique utilised in the Radlink software carries large potential errors. This would have consistently led to an under-appreciation of the adjustment angle required. Secondly, the manual nature of defining the cup ellipse on the fluoro image has previously been shown to underestimate the degree of cup anteversion. These combined errors would have consistently led to the under-measurement of cup anteversion seen intra-operatively. In conclusion, we highlight the risk of over-anteversion of the acetabular cup when using 2D measurements, given the manual inputs required to determine a result

Introduction. To obtain a better range of motion and to reduce the risk of dislocation, neck and cup anteversion are considered very important. Especially for the reduction of the risk of dislocation, the mutual alignment between neck and cup anteversion (combined anteversion) is often discussed. A surgeon would compare the neck direction to the calf direction with the knee in 90 degrees flexion. When an excessive anteversion was observed, the neck anteversion would be reduced using modular neck system or setting the stem a little twisted inside the canal with the tradeoff of the stem stability. Another choice would be the adjustment of cup alignment. Combined anteversion is defined the summation of cup anteversion in axial plane and stem anteversion in axial plane. But in realty the impingement occurs with 3 dimensional relationships between neck and cup with very complicated geometries. In that meaning, the definition of the angles could be said ambiguous too. The bowing of the femur also makes the relationships more complicated. Upon those backgrounds, we have been performing 3D preoperative planning for total hip arthroplasty on every case. In the present study, in vivo position of the stem in each case was determined then the anteversion observed on surgical view and anteversion around femoral mechanical axis are compared using 3D CAD software. Materials and Methods. Ten recent cases from our hip arthroplasty with 3D preoperative planning were reviewed for this purpose. The bone geometries were obtained from CAT scans with very low X-ray dose using Mimics® (Materialize, Belgium). Preoperative planning for Revelation stem® (DJO, USA) was performed using Mimics® (Materialize, Belgium). Femoral mechanical axis was defined as a line between center of femoral head and the middle point of medial and lateral epicondyle of the femur. Then mechanical anteversion is assessed from posterior condylar line. On the other hand, the calf was rotated 90 degrees around epiconlylar axis of each femur, and in vivo stem position was estimated then, stem axis was aligned perpendicular to the view. The anteversion in the surgical view was assessed from that view as the angle toward the calf. (Fig. 1) Using in vivo stem alignment, the impingement angle was also assessed. Results. Anteversion was in average 10 degree overestimated in the surgical view. Only one case was considered to have impingement risk and reduction of the anteversion was performed using custom stem. Discussion. In real surgical view, the anteversions are often observed to be more. In the present study instability of the knee was not considered. If the surgeon has performed inappropriate modification of the stem and cup anteversion, it can increase the risk of the dislocation and worse mechanical conditions. The in vivo prosthesis alignment should not be discussed with the angles from surgical view, but should be well planed 3 dimensionally preoperatively

Introduction. Although pelvic tilt does not significantly change after primary total hip arthroplasty (THA) at a short term, can vary over time due to aging and the possible appearence of sagittal spine disorders. Cup positioning relative to the stem can be influenced due to these changes. Purpose. We assessed the evolution of pelvic tilt and cup position after THA for a minimum follow-up of five years and the possible appearence of complications. Materials and methods. 47 patients underwent same single THA between 2008 and 2012. All were diagnosed with primary osteoarthritis and their mean age was 70.2 years (range, 63 to 75). There were 28 male patients, 19 had a contralateral THA, 17 were studied for lumbar pathology and three were operated for lumbo-sacral fusion. Radiological analysis included sacro- femoral-pubic and acetabular abduction angles on the anteroposterior pelvic view; and cup anteversion angle on the lateral cross-table hip view according to Woo and Morrey. All assessments were done pre-operatively and at 6 weeks, one, two and five years post-operatively. Three measurements were recorded and mean was obtained at all intervals All radiographs were evaluated by the same author, who was not involved in surgery. Results. There were four dislocations: one early and two contralateral dislocations which were solved wiith closed reduction, and one late recurrent dislocation five years after surgery which required cup revision. No other revision surgeries were performed. Mean sacro-femoral pubic angle decreased at all intervals from 60.6º preoperatively, to 60.0º at one year and 58.8 º at five years. This decrease was more significant in female, 63.3º preoperatively to 59.3º, than in male patients, 58.7º to 58.3º at five years. Mean acetabular abduction angle increased from 47.3º at 6 weeks to 48.2º at five years. Mean cup anteversion increased from 24.3º at 6 weeks to 26.4º at one year and 34.3º at five years. Conclusions. Posterior pelvic tilt increased with aging over time, particularly in women. These changes increased cup inclination and anteversion which may result in more dislocations after primary THA

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. The safe zone of the acetabular cup for THA was discussed based on the AP X-ray films of hip joints. A supine position is still used to determine the cup position for CAOS such as navigation systems. There were few data about the implant positions after THA in standing positions. The EOS X-Ray Imaging Acquisition System (EOS system) (EOS imaging Inc, Paris, France) allows image acquisition with the patients in a standing or sitting position. We can obtain AP and lateral X-ray images with high-quality resolution and low dose radiation exposure. Recently, we have obtained the EOS system for the first time in Japan. We investigated 3D accuracy of the EOS system for implant measurements after THA. Patients and Methods. We measured the implant angles of the 68 patients (59 females and 9 males, average age: 61y.o.) who underwent THA using the EOS system. The cup inclination and anteversion were measured in the anterior pelvic plane (APP) coordinate. The femoral stem antetorsion was defined as angles between the stem neck axis and the posterior condylar axis. These data were compared with the implant angles of the same patients measured by the post-operative CT scan images and the 3D image analysis using the ZedHip software (LEXI, Japan). Results. The cup inclinations (average ±SE) measured by the EOS system and the CT scan were 40.6 ± 0.64° and 42.9 ± 0.53°, respectively. The cup anteversions were 22.9 ± 1.3° and 22.8 ± 1.0°, respectively. The stem antetorsions were 28.9 ± 1.3° and 29.8 ± 1.6°, respectively. The differences (average ± SE) between the EOS system and the CT scan in the cup inclination, the cup anteversion, and the stem antetorsion were −2.3 ± 0.38°, −0.09 ± 0.82°, and −0.90 ± 0.91°, respectively. There were strong correlations in measurement values between the EOS system and the CT scan (the Spearman's correlation coefficients of the cup inclination, the cup anteversion, and the stem antetorsion were 0.6521 [p<0.001], 0.7154 [p<0.001], and 0.8645 [p<0.001], respectively). Discussion. The EOS system provides acceptable clinical accuracies in measuring acetabular cup and femoral stem angles after THA. The accuracy of the cup angles was accorded with that of the basic experimental data using a dry pelvis. Our data also demonstrated clinically acceptable accuracy in the measurement of stem antetorsion. This system can provide accurate snap shots of variable postures with high resolution. Using the EOS system, we may establish real optimum positions of THA implants by measuring the patients after THA in several postures including standing, squatting or sitting positions which required for Japanese ADL

Introduction. Computer navigation is a highly sophisticated tool in orthopedic surgery for component placement in total hip arthroplasty (THA). In order to apply it adequately it is of upmost importance that the targets the surgeon is trying to hit are well-defined. This concept considers all four component orientations: cup inclination (cIncl) and anteversion (cAV), stem antetorsion and neck-to-shaft angle. The optimising goal in this concept is maximising the size of the cSafe-Zone. Methods. A computerised 3D- model of a total hip prosthesis was used to systematically analyse all combinations of component orientations in automatised batch runs. Component orientations were varied for cup inclination, cup anteversion, neck antetorsion and neck inclination. Results. The combined Safe-Zone outlines spaces in a 3D-diagram that show the relationship between cup inclination, cup anteversion and neck anteversion, while the neck inclination is used as a curves parameter. These spaces include all component orientation that allow the predefined iROM without prosthetic impingement. In order to compare these results to Lewinnek's recommendation cross-sections were taken at distinct neck antetorsions in 5° intervals. Conclusion. The new combined Safe-Zone (cSafe-Zone) includes all orientation parameters of both total hip components and such gives well-defined recommendations for combined positioning of both components. Ideally it can be introduced into a smart computer navigation system in order to compute in real-time the best combined orientation of both components

INTRODUCTION. Golf is considered low-impact sport, but concerns exist about whether golf swing can be performed in safe manner after THA. The purpose of this study was to clarify dynamic hip kinematics during golf swing after THA using image-matching techniques. METHODS. This study group consisted of eight right-handed recreational golfers with 10 primary THAs. Each operation was performed using a posterolateral approach with combined anteversion technique. Nine of ten polyethylene liners used had elevated portion of 15°. Continuous radiographic images of five trail and five lead hips during golf swing were recorded using a flat panel X-ray detector (Fig. 1) and analyzed using image-matching techniques (Fig. 2). The relative distance between the center of cup and femoral head and the minimum liner-to-stem distance were measured using a CAD software program. The cup inclination, cup anteversion, and stem anteversion were measured in postoperative CT data. Hip kinematics, orientation of components, and cup-head distance were compared between patients with and without liner-to-stem contact by Mann-Whitney U test. RESULTS. At the top of backswing, lead hips showed 26 ± 11° ER, and trail hips showed 24 ± 19° IR. At the end of follow-through, lead hips showed 24 ± 19° IR, and trail hips showed 24 ± 12° ER. The mean cup inclination and anteversion, stem anteversion, and combined anteversion were 40 ± 5°, 18 ± 11°, 33 ± 14°, and 50 ± 8°, respectively. The minimum liner-to-stem distance showed the smallest value of 3 ± 4 mm at the maximum ER. Bone-to-bone and bone-to-implant impingements were not observed in all hips at all phases. The liner-to-stem contact was observed in four hips with elevated liners (two trail and two lead hips; Fig 3). Patients with elevated liner-to-stem contact demonstrated significantly (p < .05) larger maximum ER and larger cup anteversion than patients without contact. The mean cup-head distance was 0.9 ± 0.5 mm of translation. No significant difference was found in the flexion/extension and adduction/abduction at the maximum ER, cup inclination, combined anteversion, and cup-head distance between patients with and without contact. DISCUSSION. Golf swing produced approximately 50° of axial rotations in both lead and trail hips after THA. The mean cup-head distances showed less than 1.0 mm, and there was no significant difference between patients with and without neck-liner contact. Therefore, we consider that dynamic stability without excessive hip rotations or subluxation was demonstrated during golf swing. Despite no evidence of component malpositioning, elevated liner-to-stem contact was observed in 40% of hips with significantly larger ER and cup anteversion. Because the liner-to-stem contact may be a concern with regard to the long-term prognosis following THA, further attention must be given to the anteversion of the components and the use of elevated liner at the time of surgery. To view tables/figures, please contact authors directly

Introduction. Most of studies on Total Hip Arthroplasty (THA) are focused on acetabular cup orientation. Even though the literature suggests that femoral anteversion and combined anteversion have a clinical impact on THA stability, there are not many reports on these parameters. Combined anteversion can be considered morphologically as the addition of anatomical acetabular and femoral anteversions (Anatomical Combined Anatomical Anteversion ACA). It is also possible to evaluate the Combined Functional Anteversion (CFA) generated by the relative functional position of femoral and acetabular implants while standing. This preliminary study is focused on the comparison of the anatomical and functional data in asymptomatic THA patients. Material and methods. 50 asymptomatic unilateral THA patients (21 short stems and 29 standard stems) have been enrolled. All patients underwent an EOS low dose evaluation in standing position. SterEOS software was used for the 3D measurements of cup and femur orientation. Cup anatomical anteversion (CAA) was computed as the cup anteversion in axial plane perpendicular to the Anterior Pelvic Plane. Femoral anatomical anteversion (FAA) was computed as the angle between the femoral neck axis and the posterior femoral condyles in a plane perpendicular to femoral mechanical axis. Functional anteversions for the cup (CFA) and femur (FFA) were measured in the horizontal axial patient plane in standing position. Both anatomical and functional cumulative anteversions were calculated as a sum. All 3D measures were evaluated and compared for the repeatability and reproducibility. Statistical analysis used Mann-Whitney U-test considering the non-normal distribution of data and the short number of patients (<30 for each group). Results. Functional cumulative anteversion was significantly higher than anatomical cumulative anteversion for all groups (p<0.05). No significant difference could be noted between the cases according to the use of short or standard stems. Conclusion. This study shows the difference of functional implant orientation as compared to the anatomical measurements. This preliminary study has limitations. First the limited sample of patients. Then this series only includes asymptomatic subjects. Nevertheless, this work focused on the feasibility of the measurements shows the potential interest of a functional analysis of cumulated anteversion. Standing position influences the relative position of THA implants according to the frontal and sagittal orientation of the pelvis. The relevance of these functional measurements in instability cases must be demonstrated, especially in patients with anterior subluxation in standing position which is potentially associated with pelvic adaptative extension. Further studies are needed for the feasibility of measurements on EOS images in sitting position and their analysis in case of instability. For any figures or tables, please contact authors directly

Introduction. The combination of spinal fusion and THP is not exceptional. Disorders of the pelvic tilt and stiffness of the lumbosacral junction modify the adaptation options while standing or sitting. Adjusting the cup can be difficult and THP instability is a potential risk. This study reports an experience with EOS® simultaneous measurements on AP and lateral views of spine and hips in THP patients. Material and methods. 29 men and 45 women were included in this prospective study. 21cases had bilateral THP. Patients were separated into two groups: long fusions including the thoraco-lumbar junction (group 1) and shorter fusions below L1 (group 2). We analyzed the impact of the arthrodesis on the position of the pelvis by measuring variations of the sacral slope (SS) and APP angle. Cup position was defined by coronal inclination and functional anteversion in the horizontal plane standing and sitting. We compared the data to a previous series of 150 THP patients with asymptomatic and non fused spine. Results. Table1 reports the results of the fusion series. The overall analysis of all patients demonstrates that the values for the cup functional anteversion and coronal inclination are statistically different when comparing standing to sitting (respectively p <0.01and p <0.001). The same results are obtained for SS and APP. This difference is not significant for group 1 patients. The mean range of variation for cup anteversion and inclination is 5° and 7° in the fused cases. Table 2 reports the results of the non fusion series. SS, APP and cup orientation values are statistically significant between standing and sitting. All of the values are statistically different when compared to the fused patients. The mean range of variation for cup anteversion and inclination is 11,6° and 10°. Discussion. The population of THP patients is characterized by pelvic retroversion and a significant reduction of sagittal pelvic mobility when compared to young asymptomatic individuals. Patients combining THP and spine fusion showed significant reduction of adaptation possibilities due to low variations for SS and cup orientation angles. Conclusion. This preliminary study shows the importance of planning THP taking into account not only the orientation of the spine but also its mobility for adaptation in standing and sitting positions. This is a key issue because of the growing number of elderly THP patients whose spine is degenerative or fused. A particular attention must be drawn to the cases with long fusions. The interest of a global vision of the hip-spine relationship is evident in the prevention or in management of dislocations and subluxations, and especially for the indications of dual-mobility prostheses. To view tables/figures, please contact authors directly

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. Dislocation is a major cause of Total Hip Arthroplasty (THA) early failure and is highly influenced by surgical approach and component positioning. Robotic assisted arthroplasty has been developed to improve component positioning and therefore reduce post-operative complications. The purpose of this study was to assess dislocation rate in robotic total hip arthroplasty performed with three different surgical approaches. Methods. All patients undergoing Robotic Arm-Assisted THA at three centers between 2014 and 2019 were included for assessment. After exclusion, 1059 patients were considered; an anterior approach was performed in 323 patients (Center 2), lateral approach in 394 patients (Center 1 and Center 2) and posterior approach in 394 patients (Center 1 and Center 3). Episodes of THA dislocation at 6 months of follow up were recorded. Stem anteversion, Cup anteversion, Cup inclination and Combined Anteversion were collected with the use of the integrated navigation system. Cumulative incidence (CI), incidence rate (IR) and risk ratio (RR) were calculated with a confidence interval of 95%. Results. Three cases of dislocation (2 posterior approach, 1 anterior approach) were recorded, with a dislocation rate of 0.28% and an IR of 0.14%. Placement of cup in Lewinnek safe zone rate was 82.2% for posterior approach, 82.0% for lateral approach and 95.4% for anterior approach. Placement in the Combined Version safe zone rate was 98.0% for posterior approach, 73.0% for lateral approach and 47.1% for anterior approach. Despite the difference, dislocation IR was 0.30% for anterior approach, 0.34% for posterior approach and 0% for lateral approach. Conclusion. Robotic assisted technique is associated with low dislocation risk, especially in posterior approach. The Combined version technique appears to be a reliable way to reduce dislocation risk in the posterior lateral approach, but does not appear to be essential for lateral and anterior approaches

Background. Between 1999 and August 2005, we performed Direct Lateral Approach (DLA) in lateral decubitus position as the main approach for primary total hip arthroplasty (THA). After August 2005, we introduced Direct Anterior Approach(DAA) in supine position. Intraoperative target orientation in primary THA was planned in 40–45°cup abduction, 10–20°cup anteversion, and 10–20° stem anteversion. Precice implant positioning has been considered to be very important for postoperative function and stability. The purpose of this study was to compare the DLA and DAA for implant positioning accuracy. Methods. From 1999 to July 2009, we performed 566 primary THAs(78 male, 488 female). The subjects were divided into two groups of 224 DLA and 342 DAA (72 in early stage and 270 in late stage) The difference of the mean age at surgery and preoperative diagnosis among the groups were not significant. We planned to set the cup anteversion at 20°in DAA early stage and 12.5°in late stage DAA due to the development of postoperative dislocation in several cases with early stage DAA. We measured the cup and stem alignment postoperatively using radiography and computed tomography, and measured the combined anteversion angle by Widmer. Statistical analysis was done using the Bartlett Statistical Test and F-test. The results were expressed as median and interquartile range, with an alpha level set at less than 0.05. Results. Cup abduction angle with DLA was 42.7±6.25 °(average±standard deviation), 42.1±4.1°with early stage DAA and 41.9±5.3°with late stage DAA. There was no significant difference between the approaches with average and standard deviation (SD) of cup abduction. The mean cup anteversion with DLA (17.3±10.0°) was significantly smaller than that with early stage DAA(26.6±8.1°) and late stage DAA(21.0±8.0°). SD of cup anteversion with DLA was significantly larger than that with both DAA groups. The mean stem anteversion was significantly smaller with DLA (18.9±14.3) and late stage DAA (16.7±11.1°) than that with early stage DAA (23.5±11.9°). SD of stem anteversion with DLA was significantly larger than that with both DAA groups. There were 9 hips of dislocation: 5 hips in DLA, 3 in early DAA and one in late DAA. SD of combined anteversion Value with DLA(30.5±13.7) was significantly larger than that with early DAA (40.3±12.2) and late DAA (32.7±11.1.∗∗∗∗∗. Conclusion. Significantly less SD for anteversion of stem and cup was demonstrated with DAA compared with DLA. Stable operative positioning with DAA could yield a more accurate and reliable implantation compared with DLA in lateral position. DAA in supine position was a superior approach for primary THA