Measurement of the Acetabular Cup Orientation after Total Hip Arthroplasty Based on Three-Dimensional Reconstruction from a Single X-ray Image Using Generative Adversarial Networks.

BACKGROUND: The purpose of this study was to reconstruct three-dimensional (3D) computed tomography (CT) images from single anteroposterior (AP) postoperative total hip arthroplasty (THA) X-ray images using a deep learning algorithm known as generative adversarial networks (GANs) and to validate the accuracy of cup angle measurement on GAN-generated CT. METHODS: We used two GAN-based models, CycleGAN and X2CT-GAN, to generate 3D CT images from X-ray images of 386 patients who underwent primary THAs using a cementless cup. The training dataset consisted of 522 CT images and 2,282 X-ray images. The image quality was validated using the peak signal-to-noise ratio (PSNR) and the structural similarity index measure (SSIM). The cup anteversion and inclination measurements on the GAN-generated CT images were compared with the actual CT measurements. Statistical analyses of absolute measurement errors were performed using Mann-Whitney U tests and nonlinear regression analyses. RESULTS: The study successfully achieved 3D reconstruction from single AP postoperative THA X-ray images using GANs, exhibiting excellent PSNR (37.40) and SSIM (0.74). The median absolute difference in radiographic anteversion (RA) was 3.45° and the median absolute difference in radiographic inclination (RI) was 3.25°, respectively. Absolute measurement errors tended to be larger in cases with cup malposition than in those with optimal cup orientation. CONCLUSION: This study demonstrates the potential of GANs for 3D reconstruction from single AP postoperative THA X-ray images to evaluate cup orientation. Further investigation and refinement of this model are required to improve its performance.

Retrospective study comparing the accuracies of handheld infrared stereo camera and augmented reality-based navigation systems for total hip arthroplasty.

BACKGROUND: The use of portable navigation systems (PNS) in total hip arthroplasty (THA) has become increasingly prevalent, with second-generation PNS (sPNS) demonstrating superior accuracy in the lateral decubitus position compared to first-generation PNS. However, few studies have compared different types of sPNS. This study retrospectively compares the accuracy and clinical outcomes of two different types of sPNS instruments in patients undergoing THA. METHODS: A total of 158 eligible patients who underwent THA at a single institution between 2019 and 2022 were enrolled in the study, including 89 who used an accelerometer-based PNS with handheld infrared stereo cameras in the Naviswiss group (group N) and 69 who used an augmented reality (AR)-based PNS in the AR-Hip group (group A). Accuracy error, navigation error, clinical outcomes, and preparation time were compared between the two groups. RESULTS: Accuracy errors for Inclination were comparable between group N (3.5° ± 3.0°) and group A (3.5° ± 3.1°) (p = 0.92). Accuracy errors for anteversion were comparable between group N (4.1° ± 3.1°) and group A (4.5° ± 4.0°) (p = 0.57). The navigation errors for inclination (group N: 2.9° ± 2.7°, group A: 3.0° ± 3.2°) and anteversion (group N: 4.3° ± 3.5°, group A: 4.3° ± 4.1°) were comparable between the groups (p = 0.86 and 0.94, respectively). The preparation time was shorter in group A than in group N (p = 0.036). There were no significant differences in operative time (p = 0.255), intraoperative blood loss (p = 0.387), or complications (p = 0.248) between the two groups. CONCLUSION: An Accelerometer-based PNS using handheld infrared stereo cameras and AR-based PNS provide similar accuracy during THA in the lateral decubitus position, with a mean error of 3°-4° for both inclination and anteversion, though the AR-based PNS required a shorter preparation time.

The accuracy of cup anteversion measurement on postoperative pelvic radiographs: A comparative retrospective cohort study between DDH and non-DDH patients.

Rationale and objectives: Postoperative pelvic radiographs remain a vital tool for assessing cup orientation after total hip arthroplasty (THA), with the accuracy influenced by various factors. The objective of this study is to investigate the accuracy of cup anteversion measurement in developmental dysplasia of the hip (DDH) patients and others based on postoperative pelvic radiographs conducted under the current heavy workload conditions. Materials and methods: Patients who underwent THA at our hospital with both postoperative X-ray and CT images from January 2020 to December 2022 were included in this retrospective cohort study. Virtual X-ray films were generated using digitally reconstructed radiographs (DRR) technology from CT images, with pelvic position perfectly controlled. Radiographic anteversion (RA) was measured on 3D-CT, virtual X-rays, and actual postoperative X-rays, abbreviated as RA_3D, RA_DRR, and RA_Xray, respectively. A repeated-measures analysis of covariance (ANCOVA) was utilized to evaluate the variations in RA within and between different groups across three methods. The Bland-Altman plot analysis showed the variations among methods in DDH and non-DDH patients, setting a clinically acceptable limits of agreement (LOA) at ±5°. Results: This study included 154 hip cases, with 63 DDH and 91 other diseases. Repeated-measures ANCOVA revealed a descending trend in RA across three methods, with differences of 2.64° (DDH) vs. 2.74° (others) from 3D to DRR, and 4.89° (DDH) vs. 1.07° (others) from DRR to X-ray. The group by methods interaction effect were significant (p = 0.002). Significant statistical differences in RA_Xray (P = 0.035) were observed between DDH and non-DDH patients, but not in RA_3D and RA_DRR. Bland-Altman plots showed 71.4 % of DDH patients exceeded the clinically acceptable LOA, compared to 36.3 % of other patients. Conclusion: Our study indicated that under the current intense workload, the reliability of assessing cup anteversion using postoperative pelvic radiographs is challenged, especially in patients with DDH.

Reliability of the transverse acetabular ligament as a landmark for functional cup anteversion in total hip arthroplasty.

BACKGROUND: The transverse acetabular ligament (TAL) can be a useful and reproducible landmark in the orientation of the acetabular cup in total hip arthroplasty (THA). Its role in guiding cup orientation when aiming to implant in a functional anteversion orientation is unclear. The aim of this study was to assess the relationship between the TAL and the planned acetabular cup anteversion when implanted in a function orientation. MATERIAL AND METHODS: In a retrospective study the anteversion of the TAL in the contralateral un-replaced hip was measured in CT scans of patients undergoing THA and compared to the functional cup anteversion using the patient-specific spinopelvic parameters. Comparative measurements of the native acetabular version were made from the superior rim to the inferior rim and at 10 mm intervals between the 2, all in reference to the anterior pelvic plane. RESULTS: 96 hips were measured. The mean TAL anteversion angle was 17.2° ± 4.5°. The mean planned acetabular cup anteversion angle was 26.3° ± 4.7°. Pearson's correlation coefficient of this measurement with the TAL was -0.03 (p = 0.769). There was a significant difference between the planned acetabular cup anteversion and the measurement of the TAL (p < 0.0001). CONCLUSIONS: If cups are implanted parallel to the TAL, almost 80% will be >5° different to targeted functional cup version. It should be aimed to implant cups with more anteversion than the TAL indicates.

Association between cup orientation and low back pain after total hip arthroplasty in patients with osteonecrosis of the femoral head.

BACKGROUND: Postoperative low back pain (LBP) following total hip arthroplasty (THA) is classified as secondary hip-spine syndrome. The purpose of this study was to explore the correlations between cup orientation of THA and postoperative LBP in patients with osteonecrosis of the femoral head (ONFH). METHODS: A retrospective cohort study included 364 ONFH patients who underwent bilateral THA between January 2011 and December 2020. Among them, 53 patients (14.6%) experienced postoperative LBP at the end of follow-up and were designated as pain group (PG). A control group (CG) consisting of 106 patients with similar age, sex, and body mass index (BMI) to those in the PG was selected. Postoperative LBP in the PG was assessed using the visual analogue scale (VAS). Demographic data, clinical information, and radiographic criteria were evaluated as potential predictors of LBP. RESULTS: Patients in PG (mean age, 47.3 years [range, 27 to 75 years]; 42 [79%] male) had a mean VAS score of 4.6 (range, 1 to 9) compared with 0 for the patients in CG (mean age, 47.6 years [range, 19 to 77 years]; 84 [79%] male). There were no significant differences in clinical data between the two groups (p > 0.05). Preoperative radiographic variables also showed no significant differences between the PG and CG (p > 0.05). However, the postoperative inclination, anteversion, and standing ante-inclination (AI) were significantly lower in the PG compared to the CG, whereas the sitting and standing sacral slope (SS) were significantly higher (p < 0.05). Moreover, the variations in standing AI, standing and sitting pelvic tilt (PT) were significantly lower in the PG compared to the CG, while the variations in standing and sitting SS and lumbar lordosis (LL) were significantly higher (p < 0.05). The variation in standing AI in the PG showed a significantly correlation with the variation of standing SS, standing PT, and LL (p < 0.05). CONCLUSION: Postoperative LBP in ONFH patients after bilateral THA is significantly associated with the intraoperative cup orientation. The variation in standing AI is correlated with the variations in standing SS, standing PT, and LL, potentially contributing to the development of postoperative LBP.

Spinopelvic challenges in primary total hip arthroplasty.

There is no universal safe zone for cup orientation. Patients with spinal arthrodesis or a degenerative lumbar spine are at increased risk of dislocation. The relative contributions of the hip (femur and acetabulum) and of the spine (lumbar spine) in body motion must be considered together. The pelvis links the two and influences both acetabular orientation (i.e. hip flexion/extension) and sagittal balance/lumbar lordosis (i.e. spine flexion/extension). Examination of the spino-pelvic motion can be done through clinical examination and standard radiographs or stereographic imaging. A single, lateral, standing spinopelvic radiograph would be able to providemost relevant information required for screening and pre-operative planning. A significant variability in static and dynamic spinopelvic characteristics exists amongst healthy volunteers without known spinal or hip pathology. The stiff, arthritic, hip leads to greater changes in pelvic tilt (changes are almost doubled), with associated obligatory change in lumbar lordosis to maintain upright posture (lumbar lordosis is reduced to counterbalance for the reduction in sacral slope). Following total hip arthroplasty and restoration of hip flexion, spinopelvic characteristics tend to change/normalize (to age-matched healthy volunteers). The static spinopelvic parameters that are directly associated with increased risk of dislocation are lumbo-pelvic mismatch (pelvic incidence - lumbar lordosis angle >10°), high pelvic tilt (>19°), and low sacral slope when standing. A high combined sagittal index (CSI) when standing (>245°) is associated with increased risk of anterior instability, whilst low CSI when standing (<205°) is associated with increased risk of posterior instability. Aiming to achieve an optimum CSI when standing within 205-245° (with narrower target for those with spinal disease) whilst ensuring the coronal targets of cup orientation targets are achieved (inclination/version of 40/20 ±10°) is our preferred method.

The accuracy and precision of acetabular implant measurements from CT imaging.

The placement of acetabular implant components determines the short- and long-term outcomes of total hip replacement (THR) and a number of tools have been developed to assist the surgeon in achieving cup orientation to match the surgical plan. However, the accuracy and precision of 3D-CT for the measurement of acetabular component position and orientation is yet to be established. To investigate this, we compared measurements of cobalt chrome acetabular components implanted into 2 different bony pelvic models between a coordinate measuring Faro arm and 3 different low dose CT images, including 3D-CT, 2D anterior pelvic plane (APP) referenced CT and 2D scanner referenced (SR) CT. Intra-observer differences were assessed using the Intraclass correlation coefficient (ICC). The effect of imaging the pelvis positioned in 3 different orientations within the CT scanner was also assessed. The measured parameters were the angles of inclination and version. 3D-CT measurements were found to closely match the "true values" of the component position measurements, compared with the 2D-CT methods. ICC analysis also showed good agreement between the coordinate measuring arm (CMA) and 3D-CT but poor agreement between the 2D SR method, in the results from two observers. When using the coordinate system of the CT scanner, the measurements consistently produced the greatest error; this method yielded values up to 34° different from the reference digitising arm. However, the difference between the true inclination and version angles and those measured from 3D APP CT was below half a degree in all cases. We concluded that low radiation dose 3D-CT is a validated reference standard for the measurement of acetabular cup orientation.

Contemporary, non-navigation, cup orientation techniques improve accuracy and eliminate differences seen between the anterior and posterior approach in THA.

BACKGROUND: This study aimed to: (1) Determine the ability to achieve the surgeons' desired cup orientation, without navigation, using contemporary measures with the anterior- (AA) and posterior- approaches (PA); and (2) assess whether surgical approach is associated with cup orientation accuracy, as previously reported, when contemporary measures are used. METHODS: A prospective, 2-centre, multi-surgeon study of 400 THAs (200 AA; 200 PA) was performed. Intraoperative radiographs were obtained with the AA. A digital inclinometer and 3-point pelvic support were used with the PA. With the PA, intraoperative cup inclination at impaction was recorded. Radiographic inclination/anteversion (RI/RA) was measured from intraoperative radiographs (AA-only) and from postoperative radiographs for all cases. Optimum inclination/anteversion was defined as 40°/20° (±10°). The difference between intra- and postoperative orientations allowed for determination of the difference in pelvic position at impaction. RESULTS: Optimum RI and RA were achieved in 91.3% (n = 365) and 92% (n = 368) of cases respectively. Optimum cup orientation was detected in 84% of cases (n = 336). There was equivalent ability to achieve cup orientation between approaches (AA: 82.5% vs. PA: 85.5%; p = 0.41). The use of an inclinometer in the PA was associated with a smaller variability of inclination at implantation (10° vs. 14°) and counteracted the greater difference in pelvic position (4.4° vs. 2.1°) seen with the PA. CONCLUSIONS: Over 80% of cases can have optimum orientation without navigation, using simple, cheap contemporary measures. Such measures eliminate differences between approaches, related to patient position. Narrower implantation angles will further reduce variability in cup orientation achieved.

Angular changes in pelvic tilt and cup orientation at a minimum of eighteen years after primary total hip arthroplasty with an uncemented cup.

BACKGROUND: Changes in pelvic tilt angle (PTA) and cup orientation have been reported in patients after total hip arthroplasty, but the current literature generally has a brief follow-up period. This study will be the first to report PTA and cup orientation changes in the supine position for a minimum 18 years after total hip arthroplasty (THA) and investigate the factors associated with pelvic tilt and cup orientation changes. METHODS: In this study, 101 patients (120 hips) who underwent THA were retrospectively analyzed. The aims of our study were to evaluate the PTA and cup orientation change over 18 years after THA to assess differential PTA, cup inclination, and anteversion. We also investigated whether factors such as gender, body mass index, and age have any influence on PTA and cup orientation after THA. RESULTS: Patients showed a significant incremental change in PTA pre-operatively, immediately post-operatively, and at final follow-up. Cup orientation increased significantly at the final follow-up compared to the immediate post-operative period. Gender subgroup analysis showed that PTA was significantly greater in females than in males at the final follow-up (p = 0.025). Age subgroup analysis showed that PTA was significantly greater in the over 60 years group than in the other groups. CONCLUSION: Our patients showed significant changes in PTA and cup orientation at a minimum 18 years after surgery, especially in females over 60 years. Female patients over 60 are a risk factor after THA.

Functional safe zone for THA considering the patient-specific pelvic tilts: An ultrasound-based approach.

The usual Lewinnek orientation for cup positioning in total hip arthroplasty is not suitable for all patients as it does not consider the patient mobility. We propose an ultrasound-based approach to compute a Functional Safe Zone (FSZ) considering daily positions. Our goal was to validate it, and to evaluate how the input parameters impact the FSZ size and barycentre. The accuracy of the FSZ was first assessed by comparing the FSZ computed by the proposed approach and the true FSZ determined by 3D modelling. Then, the input parameters' impact on the FSZ was studied using a principal component analysis. The FSZ was estimated with errors below 0.5° for mean anteversion, mean inclination, and at edges. The pelvic tilts and the neck orientation were found correlated to the FSZ mean orientation, and the target ROM and the prosthesis dimensions to the FSZ size. Integrated into the clinical workflow, this non-ionising approach can be used to easily determine an optimal patient-specific cup orientation minimising the risks of dislocation.

A method combining the use of a mobile application and a dedicated pelvic positioner for acetabular cup insertion.

BACKGROUND: We developed a mobile device application and dedicated pelvic positioner with the aim of improving the acetabular cup placement accuracy in patients undergoing total hip arthroplasty (THA). The function of the application was to display the intra-operative cup angle. The accuracy and clinical usefulness of this combined method were verified through comparison with the conventional alignment guide method. METHODS: In total, 60 patients who underwent cementless THA were included in this study. We compared the cup alignment when using this combined method with that when using the conventional alignment guide method. The absolute value error between the intra- and post-operative angles of inclination and anteversion of the cup was calculated. RESULTS: The absolute value error of inclination was 2.4° ± 2.1° in the study group and 4.0° ± 3.3° in the control group (P = 0.107). The absolute value error of anteversion was 2.8° ± 2.6° in the study group and 7.4° ± 5.3° in the control group (P < 0.001). CONCLUSION: Using the application and pelvic positioner is simple and can be introduced at a low cost. The more accurate measurement of the intra-operative cup angle using this combined method has improved the cup insertion accuracy compared with that of the conventional alignment guide method.

A Multivariate Analysis to Predict Total Hip Arthroplasty Dislocation With Preoperative Diagnosis, Surgical Approach, Spinal Pathology, Cup Orientation, and Head Size.

BACKGROUND: There are several risk factors for dislocation after total hip arthroplasty (THA), but few studies include radiographic assessment of implants, with spine pathology and patient characteristics. This study estimates the rate of dislocation by patient gender, age, race/ethnicity, body mass index, Charlson Comorbidity Index, spine pathology, prior spine fusion, levels affected, radiographic Kellgren-Lawrence score of spine osteoarthritis, THA indication, surgical approach, and femoral head size. METHODS: Seventy-six primary THA patients between January 2007 and 2020 with a dislocation were matched on age and gender to subjects without a known history of dislocation using a 2:1 allocation. Univariable and multivariable survival models that account for matched strata were used to estimate the rate of dislocation. RESULTS: Median follow-up of patients at risk for dislocation was 26.48 months (95% confidence interval [CI] 23.75-36.40). On multivariable analysis, patients with an indication other than primary osteoarthritis were 3.69 (95% CI 2.22-6.13, P < .001) times more likely to dislocate than those with osteoarthritis. Patients with a spine pathology were also nominally more likely to dislocate (hazard ratio 1.76, 95% CI 0.97-3.18, P = .06), and patients receiving a posterior surgical approach were 2.74 (95% CI 1.11-6.76, P = .03) times more likely than those receiving a non-posterior approach to dislocate. CONCLUSION: Patients with THA indication other than primary osteoarthritis and receiving a posterior surgical approach, and to a lesser degree spinal pathology, were identified as affecting the rate of dislocation. After correcting for other variables, femoral head size, cup orientation, and patient factors were not predictive. LEVEL OF EVIDENCE: Level IV, case-control study.

Well-Placed Acetabular Component Oriented Outside the Safe Zone During Weight-Bearing Daily Activities.

Background: A comprehensive and thorough understanding of functional acetabular component orientation is essential for optimizing the clinical outcome after total hip arthroplasty (THA). This study aimed to quantify the functional acetabular anteversion and inclination of unilateral THA patients during walking and static standing and to determine whether the functional acetabular orientation falls within the Lewinnek safe zone. Methods: Seventeen patients with unilateral THA received a CT scan and dual fluoroscopic imaging during level walking and static standing to evaluate in vivo hip kinematics. The pelvic functional coordinate system of the 3D CT-based computer model was defined by the line of gravity and anterior pelvic plane (APP) to measure functional acetabular anteversion and inclination in different postures. The Lewinnek safe zone was used to determine the acetabular malposition during functional activities. Results: The THA side demonstrated an average of 10.1° (± 9.6°, range -7.5° to 29.9°) larger functional anteversion and 16.0° (± 9.2°, range -7.2° to 29.9°) smaller inclination than native hips during level walking. Functional acetabular anteversion in the THA side during level walking and static standing was significantly larger than anatomical measurements (p < 0.05). Acetabular orientation of most well-placed THA components anatomically in the Lewinnek safe zone fell outside the safe zone during more than half of the gait cycle and static standing. Conclusion: The current study revealed that an anatomically well-placed acetabular cup does not guarantee a well-functional orientation during daily activities. The in vivo mechanical performance and loading conditions of the THA component during other weight-bearing activities should be investigated in further studies.

Comparison of the accuracy of the cup position and orientation in total hip arthroplasty for osteoarthritis secondary to developmental dysplasia of the hip between the Mako robotic arm-assisted system and computed tomography-based navigation.

PURPOSE: We investigated the accuracy of the acetabular cup position and orientation in robotic-assisted total hip arthroplasty (rTHA) compared to navigated THA (nTHA) using computed tomography (CT) for patients with osteoarthritis secondary to developmental dysplasia of the hip (DDH). METHODS: We studied 31 hips of 28 patients who underwent rTHA and 119 hips of 112 patients who underwent nTHA with the same target cup orientation. After propensity score matching, each group comprised 29 hips. Post-operative cup position and orientation were measured from the postoperative CT data. Errors from the target cup position and orientation were compared between the two groups. RESULTS: Post-operatively, the absolute error of the anteroposterior and superoinferior cup positions from the target position was significantly lower in the rTHA group than in the nTHA group. The change in the post-operative radiographic inclination from the target orientation was lower in the rTHA group than in the nTHA group. Screw fixation for cup implantation was required for three hips in the nTHA group but not in the rTHA group. CONCLUSION: rTHA achieved more precise cup implantation with reduced variation from the target orientation compared to nTHA in patients with osteoarthritis secondary to DDH.

The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations.

BACKGROUND: Anterior and posterior pelvic tilt appears to play a role in total hip arthroplasty (THA) stability. When changing from the standing to the sitting position, the pelvis typically rotates posteriorly while the hips flex and this affects the femoro-acetabular positions. This case-control study compares changes in 3-D acetabular cup orientation during functional pelvic tilt between posterior THA dislocations vs stable THAs. METHODS: Standing and sitting 3-D cup orientation was compared between fifteen posterior dislocations vs 233 prospectively followed stable THAs. 3-D cup orientation was calculated using previously validated trigonometric algorithms on biplanar radiographs. Those algorithms combine the angles in the three anatomical planes (coronal inclination, transverse version, and sagittal ante-inclination) in the standing position with the change in sagittal pelvic tilt from standing to sitting to calculate the 3-D orientation in the sitting position. RESULTS: The standing cup orientation of the dislocated THAs was only characterized by a lower coronal inclination (P = .039). Compared with the controls, from standing to sitting, they showed less posterior pelvic tilt (P < .001). This led to a significant lower coronal inclination (P < .001) and sagittal ante-inclination (P < .001) in the sitting position but similar transverse version (P = .366). CONCLUSIONS: Comparing posterior THA dislocations to stable THAs, there is a lower increase of all three orientation angles from standing to sitting. This leads to a decreased sitting coronal inclination and sagittal ante-inclination which may lead to an increased risk of impingement ensued by THA instability. By contrast, the transverse version was not significantly different in both positions. This confirms the importance of biplanar data on functional cup orientation. LEVEL OF EVIDENCE: Diagnostic, Level III.

Pelvic tilt between supine and standing after total hip arthroplasty an RSA up to seven years after the operation.

The pose of the prosthetic components after total hip arthroplasty (THA) is commonly evaluated on conventional radiographs. Any change of the pelvic position after the operation in supine and between supine and standing position with time will influence validity of the measurements. We evaluated the changed pelvic tilt angle (PTA) in supine and standing position up to 7 years after operation. The aims of our study were (a) to evaluate if the PTA change over time after THA, (b) to assess any difference in PTA between supine and standing positions, and (c) to investigate whether factors such as gender, the condition of the opposite hip or low-back pain have any influence on PTA after THA. Repeated radiostereophotogrammetric radiographs of 106 patients were studied. Patients had been examined in the supine position postoperatively, and in both supine and standing positions at 6 months and 7-year follow-up. Measurements of supine patients showed an increasing mean posterior pelvic tilt over time. From supine to standing, the pelvis tilted in the opposite direction. At 6 months, the mean anterior tilt was 3.6° ± 3.8° (confidence interval [CI]: 2.8° to 4.3°) which increased to 6.4° ± 3.9° (CI: 5.7° to 7.2°) at 7 years. The mean changes in pelvic rotations around the longitudinal and sagittal axis were less than 1 degree, in both positions. In individual patients, this change reached about 11.0 degrees in supine and 18.0 degrees when standing.

Does Functional Cup Orientation Change at Minimum of 10 Years After Primary Total Hip Arthroplasty?

BACKGROUND: Cup orientation has been shown to influence the postoperative risk of impingement and dislocation following total hip arthroplasty (THA) and may change over time due to changes in pelvic tilt that occur with aging. The purpose of this study is to determine if there is a significant change in acetabular cup inclination and anteversion over a 10-year period following THA. METHODS: A retrospective, multisurgeon, single-center cohort study was conducted of 46 patients that underwent THA between 1995 and 2002. A total of 46 patients were included, with a median age at surgery of 56 years, and a median time between initial postoperative radiograph and the most recent one being 13.5 years (minimum 10 years). Cup orientation was measured from postoperative and follow-up supine anterior-posterior pelvic radiographs. Using a validated software, inclination and anteversion were calculated at each interval and the change in cup anteversion and inclination angle was determined. Furthermore, the difference in the sacro-femoral-pubic angle was measured, reflecting the difference in pelvic tilt between intervals. RESULTS: No significant difference was detected between measurements taken from initial postoperative radiograph and measurements a minimum of 10 years later (P > .45), with the median (interquartile range) change in anteversion, inclination, and sacro-femoral-pubic being 0° (-1° to 3°), 1° (-3° to 2°), and 0° (-2° to 3°), respectively. CONCLUSION: Our study found no significant change in functional cup orientation a minimum of 10 years after THA. No shifts in functional cup orientation as a result of altering spinopelvic alignment seemed to be present over a 10-year period.

Portable imageless navigation system and surgeon's estimate for accurate evaluation of acetabular cup orientation during total hip arthroplasty in supine position.

BACKGROUND: This prospective study aimed to clarify whether this novel device can evaluate the cup orientation during total hip arthroplasty (THA) more closely to that measured in postoperative computed tomography (CT) compared to the surgeon's estimate using a manual goniometer. METHODS: We prospectively performed 30 cementless THAs via the anterolateral approach in supine position between October 2018 and July 2019, wherein cup orientation was evaluated by both a portable imageless navigation system (HipAlign) and a manual goniometer during surgeries. Primary outcome was the absolute estimate error [the absolute value of the difference between cup angles measured by postoperative CT and those measured by HipAlign (group H) or surgeon's estimate using the manual goniometer (group S) during surgery]. The number of outliers of the absolute estimate error (> 10°) in each group was also estimated. RESULTS: The absolute estimate error of cup inclination in groups H and S was 3.3° ± 2.7° and 3.0° ± 2.5°, respectively (p = 0.51), whereas that of cup anteversion was 3.8° ± 3.4° and 6.0° ± 3.7°, respectively (p = 0.0008). The number of outliers of the estimate error in groups H and S was one case (3.3%) and six cases (20.0%), respectively (p = 0.04). In all six outlier cases, surgeons underestimated cup anteversion during surgeries. CONCLUSIONS: This portable imageless navigation system was a useful method, especially for avoiding incorrect cup anteversion. Underestimation of cup anteversion during THA in the supine position with the conventional alignment assisting device should be given attention.

Influence of pelvic sagittal tilt on 3-dimensional bone coverage in total hip arthroplasty: a simulation analysis.

BACKGROUND: In total hip arthroplasty with computer navigation assistance, cup orientation is generally determined according to the coordinate system relative to the functional pelvic plane (FPP). However, there is a large difference in the cup anteversion between a posterior pelvic tilt relative to the computed tomography (CT) table in the sagittal plane and anterior pelvic tilt, even when the cup is set at the same orientation angle according to each FPP. The present study analysed this difference from the viewpoint of 3-dimensional (3D) coverage of the acetabular component (3D coverage) to determine how the 3D acetabular coverage is altered with changes in pelvic sagittal tilt. METHODS: We analysed 3D-simulated acetabular coverage measured in 3D pelvic models reconstructed from the preoperative CT data of 50 patients. In each patient, we created 5 pelvic models with a sagittal tilt of 10° increments between 20° anterior tilt and 20° posterior tilt relative to the CT table. RESULTS: We found that 3D coverage decreased as the pelvis tilted posteriorly. Particularly, there were significant differences between the pelvis with 20° anterior tilt and that with neutral tilt (p < 0.001). There was also a difference between the pelvis with neutral tilt and that with a 20° posterior tilt (p < 0.01). The mean decrease in 3D coverage between the pelvis with neutral tilt and that with 20° posterior tilt was 7.2 ± 1.6%. CONCLUSIONS: We found that 3D coverage differed among pelvis with different sagittal tilts when the cup orientation angle was determined according to FPP.

Effect of pelvic tilt and rotation on cup orientation in standing anteroposterior radiographs.

BACKGROUND: Individual pelvic tilt and rotation have wide variability that can affect the measurement of cup orientation in anteroposterior (AP) radiographs. The purpose of this study was to analyse the effect of pelvic tilt and rotation on radiographic measurements of cup orientation. METHODS: A total of 53 patients (63 hips) were included in this study. The patients underwent a computed tomography study with standing AP pelvis radiographs taken both preoperatively and approximately 3 months postoperatively. We used 2-dimensional/3-dimensional matching to measure the pelvic tilt and rotation, and the non-standardised and standardised cup orientation. RESULTS: There was no difference in the pelvic tilt and rotation between the preoperative and postoperative radiographs. The distribution of the differences between the non-standardised and standardised cup anteversion exhibited a change within 5° in only 34/63 (54%) hips. The pelvic tilt correlated with the difference between the non-standardised and standardised cup anteversion, but the pelvic rotation did not. When all 63 hips were separated into the right and left sides, the pelvic rotation inversely correlated with the pelvic tilt-adjusted difference between the non-standardised and standardised cup anteversion of the right side but directly correlated with that of the left side. CONCLUSIONS: The current study demonstrated that the measurement of cup anteversion in standing AP radiographs is significantly affected by both the pelvic tilt and pelvic rotation. An improved understanding of the pelvic orientation may eventually allow for desired cup positioning on a patient-specific basis to potentially reduce complications associated with the malposition of the cup.