The reliability and variation of acetabular component anteversion measurements from cross-table lateral radiographs

Measurement of the Acetabular Cup Orientation After Total Hip Arthroplasty Based on 3-Dimensional Reconstruction From a Single X-Ray Image Using Generative Adversarial Networks

BACKGROUND

The purpose of this study was to reconstruct 3-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 2 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 and the structural similarity index measure. 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 peak signal-to-noise ratio (37.40) and structural similarity index measure (0.74). The median absolute difference in radiographic anteversion was 3.45° and the median absolute difference in radiographic inclination was 3.25°, respectively. Absolute measurement errors tended to be larger in cases with cup malposition than in those with optimal cup orientation.

CONCLUSIONS

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.

Could We Expect Postoperative Cup Anteversion after Total Hip Arthroplasty Using Postoperative Plain Anteroposterior and Lateral Radiograph? A Three-Dimensional Experimental Operation Study

BACKGROUND

A postoperative radiograph in total hip arthroplasty (THA) is usually obtained to evaluate the inclination and anteversion of the acetabular components. However, there is no gold-standard method for calculating the exact inclination and anteversion of the acetabular components on post-THA radiographs. We aimed to measure the actual anteversion of the acetabular component on postoperative radiographs by obtaining correlation data between the virtual and actual acetabular component positioning using virtual three-dimensional (3D) surgery.

METHODS

A total of 64 hip scans of 32 patients who underwent lower-extremity computed tomography (CT) were retrospectively reviewed. We reconstructed 3D models of the 64 hips using customized computer software (Mimics). Furthermore, to identify the safe zone of acetabular component position in THA, we performed virtual 3D surgery simulations for five anteversion (-10°, 0°, 10°, 20°, and 30°) and five inclination (20°, 30°, 40°, 50°, and 60°) types. We analyzed the acetabular anatomy using 3D models to measure the radiographic, anatomical, and operative anteversion (RA, AA, OA) and inclination (RI, AI, OI) angles. Additionally, we used the Woo-Morrey (WM) method to calculate the anteversion angle in the reconstructed cross-table lateral (CL) radiographs and determined the correlation between these measurements.

RESULTS

The safe zone of the acetabular component was visualized on post-THA CL radiographs using the WM method of anteversion measurement based on the different anteversions and inclinations of the acetabular component. The AA, RA, OA, OI, and WM differed significantly between males and females (p value < 0.05). As the anatomical inclination or anteversion increased, the WM anteversion measurements also increased. The radiographic anteversion measurement best matched the WM method of measurement, followed by anatomical and operative methods.

CONCLUSIONS

The actual anteversion of the acetabular component after THA can be measured on CL radiographs with the WM method using a 3D virtual program, with good reproducibility.

Is Retention of the Acetabular Component at Revision Surgery a Long-Term Solution?

Background

Acetabular retention in revision total hip arthroplasty (THA) may be advantageous, yet long-term survival data is limited. Thus, we investigated long-term survivorship of retained acetabular components in revision THA with analysis of rerevision rate, instability risk, and clinical outcomes.

Methods

We reviewed 98 hips with polyethylene wear and/or osteolysis that were revised with retained acetabular components. Acetabular inclination and anteversion were measured from prerevision radiographs. A retrospective chart review was performed, collecting outcomes of interest including Harris hip score, instability events, and rerevision surgery. Kaplan-Meier analysis was used to calculate the risk of revision over time. Predictors of survival including acetabular component position were analyzed by multiple logistic regression.

Results

Average follow-up was 13 years (range, 5-24). Survivorship rates at 5, 10, 15, and 20 years were 89.7%, 81.6%, 70.8%, and 63.8%, respectively. There was improvement in average Harris hip score (61 to 76, P < .0001). There was a 9% rate of dislocation, and 6 hips (6%) were rerevised for recurrent instability. Overall, there were 23 (23%) rerevisions at an average of 6.1 years with the most common reasons being instability (6%) and aseptic loosening (6%). Use of conventional polyethylene was the only identified independent predictor of rerevision (P = .025).

Conclusions

Retention of a well-fixed acetabular component in revision THA provides acceptable long-term outcomes with a 15-year survivorship of 71%. Instability and aseptic loosening were the most common reasons for rerevision. Surgeons may consider retaining the acetabular component at revision surgery if the implant is well-fixed and well-positioned.

Reliability and Validity of Standing Lateral Radiograph Method for Measuring Acetabular Component Version: A Modified Cross-table Lateral Radiograph Method

OBJECTIVES

To investigate the effect of the X-ray incidence angle on cup version measurements and the reliability and validity of standing lateral (SL) radiography for measuring cup versions.

METHODS

Cup versions under different X-ray incidence angles were investigated by the 3D simulation analysis. Ninety-three patients, who underwent primary total hip arthroplasty (THA) with postoperative SL radiographs and CT scans between April 2020 and December 2021, were retrospectively analyzed. SL radiography was taken under naturally standing position, correcting for the measurement error of pelvic tilt in cross-table lateral (CL) radiography. Cup versions were measured on SL radiographs and CT images by two qualified orthopedic physicians. The intra- and inter-observer reliabilities were assessed by intra-class correlation coefficient. The consistency between radiographic and CT measurements was evaluated using Pearson correlation coefficient.

RESULTS

No significant differences in cup version measurements were observed between groups of different X-ray incidence angles (P = 0.663) in the 3D simulation analysis. All measurements had excellent intra- and inter-observer reliabilities, with an intraclass correlation coefficient of >0.95. Mean cup version measurements from SL radiographs correlated well with those from CT scans (r = 0.853, P < 0.001). The mean difference between radiographic and CT measurements was -0.49° (range -12.62° to 10.37°, SD 3.95°), and the majority of differences were within the 95% limits of agreement.

CONCLUSION

The cup versions measured with SL radiography were close to the CT measurements. SL radiograph method is reliable and valid for measuring acetabular component version after THA.

Assessment of Acetabular Component Anteversion after Total Hip Arthroplasty: Comparison of Anteroposterior and Cross-Table Lateral Radiographs with Computed Tomography Scans

Background

Several methods of measurement of anteversion of acetabular components after total hip arthroplasty (THA) have been described in the literature using plain radiographs or computed tomography (CT) scans. None of these have proved to be the gold standard. We aimed to study the correlation between the CT and radiographic methods of calculation of acetabulum anteversion.

Methods

CT scans of the pelvis, anteroposterior (AP) and cross-table lateral (CL) radiographs were obtained in 60 patients who underwent THA two weeks after surgery. Anteversion was measured using Widmer method and Liaw method on AP radiographs, and the ischiolateral method on CL radiographs. Anteversion measured on the CT scan was taken as the reference anteversion and the above measurements were analysed for correlation with the measurements on CT scan. Intraclass correlation coefficients (ICCs) were calculated for both intra- and interobserver reliability.

Results

Mean acetabular version on CL radiographs was 53.1 ± 10.7. Mean version on AP radiographs by Widmer method was 21.4 ± 3.6 and by Liaw method was 20.3 ± 4.8. Mean version on CT scans was 26.02 ± 6.8. There was a good correlation between the acetabular version on CT scans with the version on AP radiographs by Widmer method (r = 0.78, p < 0.001) and Liaw method (r = 0.87, p < 0.001). Good correlation was seen between the acetabular version on CL radiographs and CT scans (r = 0.91, p < 0.001). Also, a good correlation was observed between the acetabular version measurements on CL radiographs and AP radiographs by Widmer method (r = 0.81, p < 0.001) or Liaw method (r = 0.70, p < 0.001). Excellent inter- and intraobserver reliability were seen for all the measurements.

Conclusions

Calculation of acetabular component version on AP views as well as CL views of plain radiographs showed a strong correlation with the version measurements on CT scans. Good correlations were observed between different techniques of measurement on radiographs. Therefore, all these measurements can be valid methods for assessment of anteversion.

Spinopelvic mobility affects accuracy of acetabular anteversion measurements on cross-table lateral radiographs

AIMS

Cross-table lateral (CTL) radiographs are commonly used to measure acetabular component anteversion after total hip arthroplasty (THA). The CTL measurements may differ by > 10° from CT scan measurements but the reasons for this discrepancy are poorly understood. Anteversion measurements from CTL radiographs and CT scans are compared to identify spinopelvic parameters predictive of inaccuracy.

METHODS

THA patients (n = 47; 27 males, 20 females; mean age 62.9 years (SD 6.95)) with preoperative spinopelvic mobility, radiological analysis, and postoperative CT scans were retrospectively reviewed. Acetabular component anteversion was measured on postoperative CTL radiographs and CT scans using 3D reconstructions of the pelvis. Two cohorts were identified based on a CTL-CT error of ≥ 10° (n = 11) or < 10° (n = 36). Spinopelvic mobility parameters were compared using independent-samples t-tests. Correlation between error and mobility parameters were assessed with Pearson's coefficient.

RESULTS

Patients with CTL error > 10° (10° to 14°) had stiffer lumbar spines with less mean lumbar flexion (38.9°(SD 11.6°) vs 47.4° (SD 13.1°); p = 0.030), different sagittal balance measured by pelvic incidence-lumbar lordosis mismatch (5.9° (SD 18.8°) vs -1.7° (SD 9.8°); p = 0.042), more pelvic extension when seated (pelvic tilt -9.7° (SD 14.1°) vs -2.2° (SD 13.2°); p = 0.050), and greater change in pelvic tilt between supine and seated positions (12.6° (SD 12.1°) vs 4.7° (SD 12.5°); p = 0.036). The CTL measurement error showed a positive correlation with increased CTL anteversion (r = 0.5; p = 0.001), standing lordosis (r = 0.23; p = 0.050), seated lordosis (r = 0.4; p = 0.009), and pelvic tilt change between supine and step-up positions (r = 0.34; p = 0.010).

CONCLUSION

Differences in spinopelvic mobility may explain the variability of acetabular anteversion measurements made on CTL radiographs. Patients with stiff spines and increased compensatory pelvic movement have less accurate measurements on CTL radiographs. Flexion of the contralateral hip is required to obtain clear CTL radiographs. In patients with lumbar stiffness, this movement may extend the pelvis and increase anteversion of the acetabulum on CTL views. Reliable analysis of acetabular component anteversion in this patient population may require advanced imaging with a CT scan. Cite this article: Bone Joint J 2021;103-B(7 Supple B):59-65.

3D simulation of radiographic projections to test and reduce the effect of pelvic tilt on the accuracy of cross-table lateral radiography

Background

Cross-table lateral (CL) radiography is a convenient and feasible method to assess cup version angle (VA) after total hip arthroplasty; However, pelvic tilt (PT) may contribute to its measurement inaccuracy. How PT affects CL radiographic measurements have not been well studied. We sought (1) to determine the effect of the PT on cup version measurement on CL radiography and (2) to develop a method for reducing measurement errors caused by the PT.

Methods

We used 3D technique to construct standard model and capture CL radiography simulation. A linear regression model was created to analyze the relationship between PT and VA. CL radiography and computed tomography (CT) were performed for the enrolled patients after surgery. The consistency between CL and CT measurements were verified by intra-class correlation coefficient (ICC).

Results

There was a high correlation between the VA and PT. For each 1-degree increased in the PT, the VA decreased by 0.76° (R² = 0.995, p < 0.001). Based on the data, we created a corrective formula to convert the radiographic measurements into values approximating the actual VA under a natural pelvic position. The VA measurements corrected by our equation was in high agreement with the CT-measured values with reference to the corresponding PT (ICC = 0.988, p < 0.001), which was in sharp contrast to that without PT control (ICC = 0.454, p = 0.203).

Conclusions

The PT may contribute to cup version measurement inaccuracies on CL radiography. Our mathematical algorithm can serve as a reliable method to improve the accuracy of CL radiography.

Trans-lateral decubitus radiograph of the hip: A new view to measure the anteversion of the femoral stem

BACKGROUND

Malposition of the femoral stem is a risk factor for dislocation after total hip arthroplasty (THA). Currently, two radiological methods are available for the measurement of stem anteversion. However, one method is not applicable in patients with a stiff hip, and the other one cannot differentiate the anteversion and retroversion of the stem. Therefore, we developed a method to measure the stem anteversion and assessed its reliability as well as validity.

METHODS

Trans-lateral decubitus view of the proximal femur was taken with the patient in lateral decubitus position, the hip in extension and the knee in 90° flexion. Hip anteroposterior (AP) view, trans-lateral decubitus view and CT scan of the hip were taken in 36 patients, who underwent THA. Their mean age was 59.8 (27-84) years and the mean body mass index was 25.2 (18.8-30.9) kg/m². The stem neck-femoral shaft angle was measured on hip AP view and the trans-lateral decubitus view. Then, the stem anteversion was calculated using the Ogata-Goldsand formula. We assessed the intra- and inter-observer reliabilities and evaluated the validity by comparing with the measurements on CT scan.

RESULTS

The intra- and inter-observer reliabilities were 0.934 and 0.935, respectively. The calculated stem anteversion (23.72°±8.17°) correlated well with the stem anteversion on CT scan (23.91°±10.25°), especially when the radiological anteversion was <30° (correlation coefficient = 0.729, p = 0.001).

CONCLUSION

We developed a reliable and valid method to measure stem anteversion using hip AP view and trans-lateral decubitus view of the femur. This method can replace conventional radiological methods.

GeoGebra: A reliable and free software for measuring acetabular cup anteversion on digitalized plain radiographs

OBJECTIVE

Although accurate measurement of cup anteversion in hip replacement requires CT scans, however, its routine application, especially during follow-up, remains economically and ethically unreasonable. Thus, several methods have been devised for making this measurement on plain radiographs. In recent years, several ways have been adopted using software on digital radiographs. We present one such method which uses open access mathematical software GeoGebra.

METHODS

Anteversion was measured on 72 radiographs (36 cemented; 36 uncemented) by three different observers using this software. One observer repeated measurements at three weeks interval.

RESULTS

The intraclass correlation coefficient for interobserver variability and intraobserver variability was 0.982 (0.973-0.989) and 0.986 (0.978-0.991) respectively. There was a significant difference in the reliability of the method for cemented and uncemented cups with higher reliability for cemented cups (p < 0.001).

CONCLUSION

GeoGebra software can be used as a reliable alternative for measuring acetabular cup anteversion on good quality well centred digital radiographs of the pelvis.

Biplanar Low-Dose Radiography Is Accurate for Measuring Combined Anteversion After Total Hip Arthroplasty

BACKGROUND

Acetabular component position alone has not been predictive of stability after total hip arthroplasty (THA). Combined anteversion of the acetabulum and femur has the potential of being more predictive of stability. Unfortunately, femoral component position is difficult to measure on plain radiographs. Computed tomography (CT) is the gold standard for measuring implant position post-operatively, but CT exposes patients to a substantial amount of radiation.

QUESTIONS/PURPOSES

We sought to determine whether biplanar low-dose radiography can be used to accurately measure both acetabular and femoral implant position after THA.

METHODS

Twenty patients underwent standing low-dose biplanar spine-to-ankle radiographs and supine CT scans 6 weeks after THA. Measurements of acetabular inclination, acetabular anteversion, and femoral anteversion were performed by two blinded observers and compared.

RESULTS

The average absolute differences between biplanar radiographs and CT scans were 2° ± 2° for acetabular inclination, 3° ± 2° for acetabular anteversion, and 4° ± 4° for femoral anteversion between EOS measurements and CT measurements. Interobserver agreement was good for acetabular inclination, acetabular anteversion, and femoral anteversion (Cronbach's α = 0.90) using biplanar low-dose imaging.

CONCLUSION

Biplanar radiography is a reliable low-radiation alternative for measuring acetabular inclination, acetabular anteversion, femoral version, and thus combined anteversion compared to CT. Femoral anteversion had the most variability but is still clinically relevant.

Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review

Optimal acetabular cup orientation is of substantial importance to good long-term function and low complication rates after total hip arthroplasty (THA). The radiographic anteversion (RA) and inclination (RI) angles of the cup are typically studied due to the practicability, simplicity, and ease of interpretation of their measurements. A great number of methods have been developed to date, most of which have been performed on pelvic or hip anteroposterior radiographs. However, there are primarily two influencing factors for these methods: X-ray offset and pelvic rotation. In addition, there are three types of pelvic rotations about the transverse, longitudinal, and anteroposterior axes of the body. Their effects on the RA and RI angles of the cup are interactively correlated with the position and true orientation of the cup. To date, various fitted or analytical models have been established to disclose the correlations between the X-ray offset and pelvic rotation and the RA and RI angles of the cup. Most of these models do not incorporate all the potential influencing parameters. Advanced methods for performing X-ray offset and pelvic rotation corrections are mainly performed on a single pelvic AP radiograph, two synchronized radiographs, or a two-dimensional/three-dimensional (2D-3D) registration system. Some measurement systems, originally developed for evaluating implant migration or wear, could also be used for correcting the X-ray offset and pelvic rotation simultaneously, but some drawbacks still exist with these systems. Above all, the 2D-3D registration technique might be an alternative and powerful tool for accurately measuring cup orientation. In addition to the current methods used for postoperative assessment, navigation systems and augmented reality are also used for the preoperative planning and intraoperative guidance of cup placement. With the continuing development of artificial intelligence and machine learning, these techniques could be incorporated into robot-assisted orthopaedic surgery in the future.

Accuracy of planar anteversion measurements using anteroposterior radiographs

Background

Several methods using simple anteroposterior (AP) radiographs have been suggested for the measurement of anteversion of the cup component after total hip arthroplasty. Herein, we compared six widely used anteversion measurement methods using two different types of AP radiograph, the conventional pelvis AP and hip-centered AP radiographs, to identify the measurement method and the type of radiograph that would provide the highest accuracy and reliability.

Methods

We developed two custom-made bi-planar anteversion measurement models for the validation test. The models were designed for pelvis AP and hip-centered AP radiographs, respectively. The radiographs were acquired using the inclination angles of both models, changing from 10° to 70° at 10° increments. For each inclination angle, anteversion was changed from 0° to 30° at 5° increments. The measurements were obtained independently by two orthopedic surgeons blinded from each other’s measurements, using the methods of 1) Pradhan et al., 2) Lewinnek et al., 3) Widmer et al., 4) Liaw et al., 5) Hassan et al., and 6) Ackland et al. The measurements were repeated after 2 months. The accuracy, compared with that of the reference angle, and intra-observer and inter-observer reliabilities of each method were calculated.

Results

The highest accuracy was found when the method of Liaw et al. was used with hip-centered AP radiographs, which showed a difference of 1.37° ± 1.73 from the reference angle. Moreover, regardless of the type of radiograph, the methods by Pradhan et al., Lewinnek et al., and Liaw et al. showed excellent correlations with the reference anteversion. However, substantial differences were found when the methods by Widmer et al., Hassan et al., and Ackland et al. were used, regardless of the type of radiograph used. When anteversion was measured in an inclination between 30° and 50°, the method of Pradhan et al., when used with pelvis AP radiographs, showed the highest accuracy (1.23° ± 0.92°). We also found no significant difference in anteversions between the measurements made on pelvic and hip-centered AP radiographs. Both interobserver and intraobserver reliabilities were high for all the measurements tested.

Conclusions

The methods by Pradhan et al., Liaw et al., and Lewinnek et al. may provide relatively accurate anteversion measurements with high reliability, regardless of the type of radiograph.

Effect of dislocation timing following primary total hip arthroplasty on the risk of redislocation and revision

INTRODUCTION

There is little data regarding timing of index dislocation in patients who undergo primary total hip arthroplasty (THA) and subsequent risk of redislocation and revision.

METHODS

Between 1992 and 2013, 21,490 primary THAs were performed at a single institution. 189 patients (190 hips) had a first episode of dislocation within one year of index surgery (0.9 %). 32 patients (32 hips) were excluded for the following reasons: complex THA secondary to fracture malunion, Crowe III/IV developmental hip dysplasia, periprosthetic fracture, prior hip surgery, incomplete information, and hip abductor avulsion. The final cohort consisted of 157 patients (158 hips) who experienced dislocation within 1 year of primary non-complex THA. 88 patients were female (56%), mean age was 61 years (SD = 14), and mean follow-up was 76 months (range 0-229). Multivariable Cox proportional-hazards regression models with fractional polynomial models were used to estimate the association between timing of index dislocation and subsequent redislocation and revision surgery.

RESULTS

69 patients (44%) redislocated at final follow-up. Revision for any cause occurred in 26 out of 157 hips (17%). Time lapse from index THA to first dislocation was significantly associated with the risk of redislocation (p = 0.004) and with the risk of revision (p = 0.04). For every additional 7 days from surgery, risk of redislocation increased by a factor of 1.1 and risk of revision was increased by a factor of 1.13.

CONCLUSION

This study demonstrates there is a lower risk of redislocation and revision in patients who have a first episode of dislocation closer to primary THA.

Posterior Hip Precautions Do Not Impact Early Recovery in Total Hip Arthroplasty: A Multicenter, Randomized, Controlled Study

BACKGROUND

Posterior hip precautions have been routinely prescribed to decrease dislocation rates. The purpose of this study was to determine whether the absence of hip precautions improved early recovery after total hip arthroplasty via the posterolateral approach.

METHODS

Patients undergoing total hip arthroplasty via the posterolateral approach at 3 centers were enrolled. Patients meeting the selection criteria were randomized to standard hip precautions (SHP) or no hip precautions (NHP) for 6 weeks following surgery. HOOS Jr, Health State visual analog score, and rate of pain scores were recorded preoperatively and in subsequent postoperative visits; dislocation episodes were also noted. Standard statistical analysis was performed.

RESULTS

From 2016 to 2017, 159 patients were randomized to SHP and 154 patients were randomized to NHP. Controlling for the center at which the surgery was performed, the only difference in outcome scores between the 2 groups was at 2 weeks; the NHP group had a lower HOOS Jr score when compared to the SHP group (P = .03). There was no difference in outcome scores at any other time points when compared to preoperative assessments. In the SHP group, there were 2 recorded dislocations (1.3%) and 1 in the NHP group (0.7%; P = .62).

CONCLUSION

In this multicenter, randomized, controlled study, the absence of hip precautions in the postoperative period did not improve subjective outcomes which may be explained by the self-limiting behavior of NHP patients. Furthermore, with the numbers available for the study, there was no difference in the rate of dislocation between the 2 groups.

A new radiographic acetabular cup anteversion measurement method in total hip arthroplasty: a clinical study

BACKGROUND

The acetabular cup positioning is one of the most crucial steps affecting stability and wear rates in total hip arthroplasty. Different methods have been described for determining the anteversion of the acetabular cup in the literature. But there is still not a widely accepted method to assess the acetabular anteversion radiography. The aim of this study is to measure the acetabular anteversion angle on a single pelvis AP radiography with our method which was proven with an experimental study before.

MATERIALS AND METHODS

A total of 15 patients (8 males, 7 females) who underwent total hip arthroplasty and have had a pelvis computed tomography scans in our outpatient clinic were evaluated retrospectively. The anteversion angle was calculated in all of pelvis CT scans. For radiological measurement, the formula defined by the authors in an experimental model previously was used.

RESULTS

Statistically significant difference was not determined between radiographic and CT-based measurements (p = 0.207; p > 0.05). A statistically significant agreement was observed at a level of 98.8% between radiographic and CT-based measurements (ICC = 0.988; 95% CI 0.966-0.996; p < 0.01).

CONCLUSION

Assessment of the acetabular cup anteversion is very important to predict the possible complications after total hip arthroplasty. Although many methods have been defined for this purpose, each of these has advantages and disadvantages. In particular, with computed tomography method, the patient is exposed to excessive radiation, whereas we think that our method is a preferred method due to features not requiring additional equipment, low radiation exposure, being simple, cost-effectiveness, easily applicable and almost 100% accurate.

Lack of consensus on optimal acetabular cup orientation because of variation in assessment methods in total hip arthroplasty: a systematic review

INTRODUCTION:

Dislocation is 1 of the main reasons for revision of total hip arthroplasty but dislocation rates have not changed in the past decades, compromising patients' well-being. Acetabular cup orientation plays a key role in implant stability and has been widely studied. This article investigates whether there is a consensus on optimal cup orientation, which is necessary when using a navigation system.

METHODS:

A systematic search of the literature in the PubMed, Embase and Cochrane databases was performed (March 2017) to identify articles that investigated the direct relationship between cup orientation and dislocation, including a thorough evaluation of postoperative cup orientation assessment methods.

RESULTS:

28 relevant articles evaluating a direct relation between dislocation and cup orientation could not come to a consensus. The key reason is a lack of uniformity in the assessment of cup orientation. Cup orientation is assessed with different imaging modalities, different methodologies, different definitions for inclination and anteversion, several reference planes and distinct patient positions.

CONCLUSIONS:

All available studies lack uniformity in cup orientation assessment; therefore it is impossible to reach consensus on optimal cup orientation. Using navigation systems for placement of the cup is inevitably flawed when using different definitions in the preoperative planning, peroperative placement and postoperative evaluation. Further methodological development is required to assess cup orientation. Consequently, the postoperative assessment should be uniform, thus differentiating between anterior and posterior dislocation, use the same definitions for inclination and anteversion with the same reference plane and with the patient in the same position.

The best method for evaluating anteversion of the acetabular component after total hip arthroplasty on plain radiographs

Background

Several radiological methods for measuring the anteversion of the acetabular component after total hip arthroplasty (THA) exist, and no single standardized method has been established. We evaluated the reliability and accuracy of six widely utilized methods (Liaw et al., Lewinnek et al., Widmer, Hassan et al., Ackland et al., and Woo and Morrey) for measuring anteversion on plain radiographs, using a reference standard in the same definition obtained from the PolyWare programme.

Methods

We reviewed 71 patients who underwent primary unilateral THA. The anteversion of the acetabular component was measured on pelvis AP radiographs using five different methods (Liaw et al., Lewinnek et al., Widmer, Hassan et al., and Ackland et al.) and on cross-table lateral radiographs using the method of Woo and Morrey. The values obtained using the PolyWare programme, which determines the anteversion of the acetabular component by edge detection, were regarded as the reference standard.

Results

Intra- and inter-observer reliabilities were excellent for all methods using plain radiographs, including the PolyWare programme. The method of Liaw et al. obtained values similar to those obtained using the PolyWare programme and was thus considered accurate (P = 0.447). However, values obtained using the other five methods significantly differed from those obtained using the PolyWare programme and were thus considered less accurate (P < 0.001, P < 0.001, P < 0.001, P = 0.007, and P < 0.001, respectively).

Conclusion

The method of Liaw et al. is more accurate than other methods using plain radiographs for the measurement of the anteversion of the acetabular component after THA, with reference to the anteversion obtained from the PolyWare programme.

The validity and reproducibility of cross table radiographs compared with CT scans for the measurement of anteversion of the acetabular component after total hip arthroplasty

Aims

The aim of this study was to assess the reproducibility and validity of cross table radiographs for measuring the anteversion of the acetabular component after total hip arthroplasty (THA) and to compare it with measurements using CT scans.

Patients and Methods

A total of 29 patients who underwent THA between June 2010 and January 2016 were included. There were 17 men and 12 women. Their mean age was 43 years (26 to 65). Seven patients underwent a bilateral procedure. Thus, 36 THAs were included in the study. Lateral radiographs and CT scans were obtained post-operatively and radiographs repeated three weeks later. The anteversion of the acetabular component was measured using the method described by Woo and Morrey and the ischiolateral method described by Pulos et al and these were compared with the results obtained from CT scans.

Results

The mean anteversion was 18.35° (3° to 38°) using Woo and Morrey’s method, 51.45° (30° to 85°) using the ischiolateral method and 21.22° (2° to 48°) using CT scans. The Pearson correlation coefficient was 0.754 for Woo and Morrey’s method and 0.925 for the ischiolateral method. There was a linear correlation between the measurements using the ischiolateral method and those using CT scans. We derived a simple linear equation between the value of the CT scan and that of ischiolateral method to deduce the CT scan value from that of ischiolateral method and vice versa.

Conclusion

The anteversion of the acetabular component measured using both plain radiographic methods was consistently valid with good interobserver reproducibility, but the ischiolateral method which is independent of pelvic tilt was more accurate. As CT is costly, associated with a high dose of radiation and not readily available, the ischiolateral method can be used for assessing the anteversion of the acetabular component. Cite this article: Bone Joint J 2017;99-B:1006–11.

Poor Acetabular Component Orientation Increases Revision Risk in Metal-on-Metal Hip Arthroplasty

BACKGROUND

The rate of and the reasons for the failure of metal-on-metal (MoM) bearings have recently been discussed in literature. The aim of this study was to evaluate the influence of acetabular cup inclination and version angles on revision risk in patients with MoM hip arthroplasty.

METHODS

We retrospectively reviewed 825 patients (976 hips) who underwent a MoM hip arthroplasty between 2000 and 2013. There were 474 men and 351 women, with a mean age of 58 (19-86) years. Acceptable cup orientation was considered to be inside the Lewinnek's safe zone.

RESULTS

The mean acetabular inclination angle was 48.9° (standard deviation, 8.1°; range, 16°-76°) and version angle 20.6° (standard deviation, 9.9°; range, -25 to 46°). The cup was found to be outside the Lewinnek's safe zone in 571 hips (58.5%). Acetabular cup revision surgery was performed in 157 hips (16.1%). The cup angles were outside Lewinnek's safe zone in 69.2% of the revised hips. The mean interobserver reliability and intraobserver repeatability of the measurements of cup inclination and version angles were excellent (intraclass correlation coefficients >0.90). The odds ratio for revision in hips outside vs inside the Lewinnek's safe zone was 1.82 (95% confidence interval, 1.26-2.62; P = .0014).

CONCLUSION

Our findings provide compelling evidence that a cup position outside the Lewinnek's safe zone is associated with increased revision risk in patients with MoM arthroplasty.

New cross-table lateral radiography method for measuring acetabular component anteversion in total hip arthroplasty: a prospective study of 93 primary THA

INTRODUCTION

Various methods have been described for measuring acetabular component anteversion. However, accurate measurement of anteversion is difficult. We herein propose a new method using cross-table lateral (CL) radiography performed with the contralateral hip flexed to 45° (45° flexed CL radiography). The main purpose of this study was to evaluate the reliability and validity of this new method.

METHODS

The study group included 93 patients who underwent total hip arthroplasty (THA). All hips were evaluated with computed tomography (CT) and both standard and 45° flexed CL radiographs to measure acetabular component anteversion the week after THA. The intraobserver and interobserver reliability of each measurement was assessed. Plain radiography measurements were compared with reference CT measurements to evaluate their validity.

RESULTS

All measurements had excellent intraobserver and interobserver reliability, and plain radiography measurements correlated well with CT measurements. The mean measurements were 21.9° (3°-39°) with CT, 24.9° (7°-47°; p<0.001) with standard CL radiographs, and 22.5° (7°-43°; p = 0.112) with 45° flexed CL radiographs.

DISCUSSION

The anteversion values measured with our new method were closer to the CT values used as a reference standard than those with standard CL radiographs. Our new method appears to be reliable and valid for measuring acetabular component anteversion.

Acetabular Abduction and Dislocations in Direct Anterior vs Posterior Total Hip Arthroplasty: A Retrospective, Matched Cohort Study

BACKGROUND

There is purported improvement in component positioning and hip stability with the use of direct anterior approach (DAA) total hip arthroplasty (THA). We sought to determine if there is a difference in acetabular component position or dislocation frequency between DAA and posterior THA.

METHODS

One arthroplasty fellowship-trained surgeon introduced DAA THA into his practice. From the initiation of DAA in 4/2012-8/2015, this comparative series resulted in 66 DAA THAs. A matched cohort (age, gender, body mass index [BMI], and comorbidities) was then created for posterior THA, 66 hips. DAA THA used fluoroscopy with anterior capsular excision; posterior group used no image guidance and had capsular repair. Posterior group BMI was 27.8 and DAA group BMI was 27.6 (P = .36). Minimum 3-month follow-up occurred in both groups.

RESULTS

Average acetabular abduction angle in the posterior group was 41.9° (range, 32°-60°; standard deviation [sdev], 6.24) and DAA group 43.8° (range, 30°-62°; sdev 6.9), P = .12. The percentage of outliers (outside Lewinnek safe zone, 30°-50°) was 9.1% (6 of 66) in posterior group and 13.6% (9 of 66) in DAA group. There were 2 anterior dislocations in the DAA THA group and 1 anterior dislocation in the posterior THA group, resulting in P = .56. The DAA dislocation frequency in this group was overall higher at 3.0% (2 of 66) compared with the matched posterior (1.5%, 1 of 66) and unmatched posterior larger series (.8%, 3 of 360).

CONCLUSION

We demonstrated no observable difference in hip stability or acetabular abduction. This study provides realistic outcomes for surgeons implementing DAA THA into their practice.

Cross table lateral radiography for measurement of acetabular cup version

BACKGROUND

Appropriate orientation of the acetabular cup is an important factor for long-term results of total hip arthroplasty. For measurement of cup version cross-table lateral radiography is frequently used, but the reliability has been questioned. We compared cross table lateral radiography with computed tomography in patients that had undergone primary total hip arthroplasty.

METHODS

The study was prospectively done in 117 patients (117 hips). At 3 months after total hip replacement the acetabular version was measured by cross table lateral radiography and compared to measurements by computed tomography.

RESULTS

By cross table lateral radiography acetabular anteversion was on mean 13.9° with a standard deviation of 10.1° as compared to 17.8°±12.6° by computed tomography. Mean difference was -3.8 with a distribution of measurements of ±13 degrees for 95% of the cases.

CONCLUSIONS

Our study shows that cross table radiography provides acceptable information for clinical use, but has limited use for precise analysis of acetabular cup version.

Is a Stem Version on the Crosstable Lateral Radiograph Accurate in Total Hip Arthroplasty?

BACKGROUND

In contrast to the acetabular cup version (CV), stem version (SV) measurement on the crosstable lateral radiograph has not been validated. We, therefore, investigated: (1) the difference of SV on the crosstable lateral radiograph from that measured using computed tomography data and (2) the reliability of SV measurement on the crosstable lateral radiograph.

METHODS

We examined the correlations of the crosstable-CV and crosstable-SV with true-CV (operative cup anteversion) and true-SV (neck version relative to the posterior condylar line) obtained using computed tomography data from 103 patients. We also produced the digital reconstructed crosstable lateral radiograph with adjusted hip flexion and rotation and defined SV on this image as the true-crosstable SV.

RESULTS

Significant positive correlations were noted between the crosstable-CV and true-CV, with a correlation coefficient of 0.79. In contrast, the correlation between the crosstable-SV and true-SV was very low (r = 0.30), with significantly higher deviation from the true-SV values when compared with the crosstable-CV (standard deviation, 11.6° vs 6.5°, P  < .001). The true-crosstable SV was correlated with true-SV (r = 0.81); however, the average difference was 23.5° ± 8.9°.

CONCLUSION

Crosstable-SV differed from true-SV in the measurement plane and did not correlate well with the true-SV, suggesting the unreliability of its measurements. Therefore, the crosstable-SV is not recommended for clinical use.

Evaluation and management of chronic total hip instability

Given the increasing number of total hip arthroplasty procedures being performed annually, it is imperative that orthopaedic surgeons understand factors responsible for instability. In order to treat this potentially complex problem, we recommend correctly classifying the type of instability present based on component position, abductor function, impingement, and polyethylene wear. Correct classification allows the treating surgeon to choose the appropriate revision option that ultimately will allow for the best potential outcome.

Hip Resurfacing Implant Orientation Analysis: A Comparison of a Computer-Added Design Technique and Computed Tomography

BACKGROUND

Accurate acetabular component orientation in hip resurfacing is mandatory. The aim of this study is to analyze if interpretation of pelvic radiographs with computer-added design (CAD) software is comparable to computed tomography (CT) in measurement of acetabular anteversion and inclination of a Birmingham Hip Resurfacing (BHR) hip.

METHODS

A consecutive series of 49 patients (50 hips) who underwent hip resurfacing arthroplasty between 2005 and 2007 with the BHR system were retrospectively included. The surgical procedure was performed by 1 orthopedic surgeon in the beginning of his learning curve. Computer-added design software was used to measure acetabular component orientation on an anteroposterior pelvic radiograph. These measurements were compared with CT measurements. We calculated the correlation between the CAD software and CT analysis. The degree of underestimation or overestimation was determined, and a Bland-Altman plot was created to visualize the agreement between CAD software and CT results.

RESULTS

We analyzed 50 BHR hips with mean inclination of 54.6° and 55.6° and mean anteversion of 24.8° and 13.3° measured by CT and CAD, respectively. Pearson correlation coefficient for inclination was 0.69 (P < .001) and for anteversion 0.81 (P < .001). Computer-added design showed a mean underestimated anteversion of 11.6° (P < .001). There was no significant underestimation or overestimation of inclination with CAD analysis compared to CT measurements.

CONCLUSION

The CAD software is useful to assess acetabular inclination in hip resurfacing but underestimates anteversion.

The reliability and accuracy of measuring anteversion of the acetabular component on plain anteroposterior and lateral radiographs after total hip arthroplasty

There is no single standardised method of measuring the orientation of the acetabular component on plain radiographs after total hip arthroplasty. We assessed the reliability and accuracy of three methods of assessing anteversion of the acetabular component for 551 THAs using the PolyWare software and the methods of Liaw et al, and of Woo and Morrey. All measurements of the three methods had excellent intra- and inter-observer reliability. The values of the PolyWare software, which determines version of the acetabular component by edge detection were regarded as the reference standard. Although the PolyWare software and the method of Liaw et al were similarly precise, the method of Woo and Morrey was significantly less accurate (p < 0.001). The method of Liaw et al seemed to be more accurate than that of Woo and Morrey when compared with the measurements using the PolyWare software. If the qualified lateral radiograph was selected, anteversion measured using the method of Woo and Morrey was considered to be relatively reliable.

Cup version can be accurately measured on the false profile view radiograph

INTRODUCTION

Accurate measurement of cup version on plain radiographs remains difficult due to the two-dimensional projection of an ellipse and difficulty obtaining reproducible radiographs.

PURPOSE

Determine: 1) if the cup angle measured on the false profile view (FPV) could be used to determine radiographic cup version; 2) how patient positioning would affect cup angle measurement on the FPV; 3) if implant cup design affects cup angle measurement.

MATERIALS AND METHODS

Three cup version positions were assessed in a sawbone: 13° (normal); 28° (excessive anteversion) and -2° (retroversion). Cup angle was measured on the FPV at five different degrees of pelvic rotation within each cup version group. Pelvic rotation was quantified using the ratio of the inter-femoral head distance measured on the FPV versus the anteroposterior radiographs (FP/AP ratio). Eighty patients (40 metal-on-polyethylene, 40 metal-on-metal) post-total hip were also assessed. Cup version was assessed with Einzel-Bild-Roentgen-Analysis software (EBRA). R2 was calculated to assess correlation between both measurement methods.

RESULTS

For the sawbone model, an R2 of 0.95 was obtained. For patients, overall R2 was 0.56 with an FP/AP ratio of 0.3-0.49 having an R2 of 0.72. The EBRA anteversion versus cup angle scatterplot had an R2 of 0.72 (95%CI: +/-7.8°). Subgroup analysis revealed no differences between the metal-on-poly and metal-on-metal for cup angle measurements. The intra-class coefficient for intra- and inter-observer reliability for all cases (individual and combined FP/AP groups) was 0.98 to 0.99.

CONCLUSION

The FPV cup angle measurement value provides an accurate measurement of radiographic cup anteversion with well-defined patient position parameters.

Does Intraoperative Fluoroscopy Optimize Limb Length and the Precision of Acetabular Positioning in Primary THA?

Reduced limb length discrepancy and more accurate cup positioning are purported benefits of using fluoroscopy for total hip arthroplasty (THA). The authors compared limb length discrepancy and cup position in 200 patients (group I, posterior approach without fluoroscopy; group II, anterior supine approach with fluoroscopy) who underwent primary THA. Mean limb length discrepancy was 2.7 mm (SD, 5.2 mm; range, -9.8 to 20.9 mm) and 0.7 mm (SD, 3.7 mm; range, -11.8 to 10.5 mm) for groups I and II, respectively (P=.002). In group I, 7% of hips had limb length discrepancy greater than 1 cm compared with 3% in group II. Mean cup inclination measured 40.8° (SD, 5.0°; range, 26.1°-53.7°) in group I and 43.4° (SD, 5.6°; range, 31.3°-55.9°) in group II (P=.008). In group I, 96% of cups had inclination within 10° of the mean compared with 92% in group II (P=.24). Mean anteversion measured 35.3° (SD, 7.1°; range, 17.8°-60.7°) in group I and 25.9° (SD, 8.2°; range, 1.5°-44.8°) in group II (P=.0001). In group I, 87% of hips exhibited anteversion within 10° of the mean compared with 76% in group II (P=.045). Although the anterior approach with intraoperative fluoroscopy reduced mean limb length discrepancy, the clinical significance of this reduction is unclear. Fluoroscopy reduced the incidence of limb length discrepancy greater than 1 cm. However, the use of fluoroscopy did not help to improve the precision of cup positioning.

Validity, reliability and reproducibility of plain radiographic measurements after total hip arthroplasty

BACKGROUND

In total hip arthroplasty (THA), radiographic preoperative planning and postoperative evaluation of acetabular component, femoral offset (FO) and leg length discrepancy (LLD) require good validity, interobserver reliability and intraobserver reproducibility. In this study, we evaluated the validity of the Sundsvall method of FO measurement and the interobserver reliability and intraobserver reproducibility of measurement of FO, LLD, acetabular cup inclination and anteversion.

MATERIAL AND METHODS

Ninety patients with primary unilateral osteoarthritis (OA) were included in this prospective study. On postoperative radiographs FO by the Sundsvall method (femoral axis-pelvic midline), FO by a standard method (femoral axis-hip rotational centre-teardrop point), LLD (inter-teardrop line-lesser trochanter), acetabular cup inclination (on AP view the angle between the cup rim and transischial line) and anteversion (on lateral view the angle between the face of acetabulum and a line perpendicular to the horizontal plane) were measured. The interobserver reliability and intraobserver reproducibility were calculated for three independent observers. The concurrent validity and degree of prediction of the Sundsvall method are measured by comparing its results with the standard method.

RESULTS

The interobserver reliability of all measurements was excellent (ICC >0.80), except for LLD, which was substantial (ICC = 0.79). The intraobserver reproducibility of all measurements was excellent (ICC > 0.80). The concurrent validity of the Sundsvall method compared to the standard method was good with a positive correlation.

CONCLUSION

The Sundsvall method is as reliable as the standard method. The evaluated radiographic measurement methods have the required validity and reliability to be used in clinical practice.

Navigating the reaming of the acetabular cavity in total hip arthroplasty: does it improve implantation accuracy?

Computer navigation in total hip arthroplasty is used to improve accuracy of component implantation. Reaming of the acetabular cavity during total hip arthroplasty (THA) can be navigated although this is not done routinely. We hypothesised that navigating the reaming of the acetabular cavity will improve implantation accuracy. A single surgeon series of 100 navigated THAs were analysed retrospectively. In 49 the reaming of the acetabular cavity was done using navigation and in 51 this was done freehand. The verified cup position and the error from the planned position were recorded. The mean error from planned to verified inclination was 2.20 degrees (SD 1.59°) in the navigated group versus 2.33 degrees (SD 1.96°) in the freehand group. The mean anteversion error was 1.92 degrees (SD 1.51°) for the navigated group and 1.45 degrees (SD 1.38°) for the freehand group. This was not statistically significant. This rejects our hypothesis. Navigating the reaming of the acetabular cavity did not improve the accuracy of the implantation against the set inclination and anteversion target during computer navigated THA.

Revision Total Hip Arthroplasty with Retained Acetabular Component

BACKGROUND

Aseptic loosening and osteolysis commonly limit the survivorship of total hip prostheses. Retention of a well-fixed acetabular component, rather than full acetabular revision, has multiple advantages, but questions have lingered regarding the clinical success and prosthetic survivorship following this procedure. We examined the impact of acetabular component position, polyethylene type, liner insertion technique, femoral head size, and simultaneous revision of the entire femoral component (as opposed to head and liner exchange) or bone-grafting on mid-term to long-term prosthetic survival following such limited revisions.

METHODS

One hundred hips in 100 patients with osteolysis, polyethylene wear, or femoral component loosening underwent revision total hip arthroplasty with retention of the acetabular component. Acetabular component inclination and anteversion were measured on prerevision radiographs and were categorized according to predetermined positional safe zones (inclination of 35° to 55° and anteversion of 5° to 25°). Operative reports were reviewed for femoral head size, polyethylene liner type (conventional or highly cross-linked), liner insertion technique (use of the existing locking mechanism or cementation), whether the patient had revision of the entire femoral component, and use of bone graft. Outcomes of interest included the Harris hip score, University of California at Los Angeles (UCLA) activity score, episodes of instability, and need for repeat revision.

RESULTS

At an average of 6.6 years (range, two to fourteen years) postoperatively, the Harris hip and UCLA activity scores were both significantly improved compared with the preoperative scores (p < 0.0001 and p < 0.01, respectively). Overall, the failure rate was 13%. In addition, 6% of the patients had postoperative instability. Hips in which the acetabular component was outside of the safe zone for inclination had a higher rate of failure (p = 0.048). Use of conventional, rather than highly cross-linked, polyethylene at the time of revision was also associated with an increased rate of repeat revision (p = 0.025).

CONCLUSIONS

Revision total hip arthroplasty with retention of the acetabular component is associated with good outcomes in hips with an appropriately positioned, well-fixed acetabular component. Acetabular components outside the safe zone for inclination were at a higher risk for failure, as was use of conventional polyethylene.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Assessment of cup orientation in hip resurfacing: a comparison of TraumaCad and computed tomography

Purpose

The orientation of the acetabular component in metal-on-metal hip resurfacing arthroplasty affects wear rate and hence failure. This study aimed to establish if interpretation of pelvic radiographs with TraumaCad software can provide a reliable alternative to CT in measuring the acetabular inclination and version.

Methods

TraumaCad was used to measure the acetabular orientation on AP pelvis radiographs of 14 painful hip resurfacings. Four orthopaedic surgeons performed each measurement twice. These were compared with measurements taken from CT reformats. The correlation between TraumaCad and CT was calculated, as was the intra- and inter-observer reliability of TraumaCad.

Results

There is strong correlation between the two techniques for the measurement of inclination and version (p <0.001). Intra- and inter-observer reliability of TraumaCad measurements are good (p <0.001). Mean absolute error for measurement of inclination was 2.1°. TraumaCad underestimated version compared to CT in 93% of cases, by 12.6 degrees on average.

Conclusions

When assessing acetabular orientation in hip resurfacing, the orthopaedic surgeon may use TraumaCad in the knowledge that it correlates well with CT and has good intra- and inter-observer reliability but underestimates version by 12° on average.

Measuring acetabular component version after THA: CT or plain radiograph?

BACKGROUND

Although cross-table lateral radiographs are commonly used to measure acetabular component version after THA, recent studies suggest that CT-based measurement is more accurate. This has been attributed to variations in pelvic tilt, pelvic rotation, and component inclination. Furthermore, it has been suggested, based on limited data, that even with ideal positioning of the cross-table lateral radiograph, CT remains the more accurate modality.

QUESTIONS/PURPOSES

We determined whether appropriately positioned cross-table lateral radiographs could provide accurate measurements of acetabular component version, and compared accuracy and reliability of measurements from modified cross-table lateral radiographs with those from standard cross-table lateral radiographs and CT.

METHODS

We implanted 27 Sawbones pelves with an acetabular cup using computer navigation. CT, an AP view of the pelvis, and cross-table lateral and modified cross-table lateral radiographs were performed for each specimen. For the modified cross-table lateral radiograph, the beam angle varied based on the cup inclination as measured on an AP view of the pelvis. Two independent observers measured acetabular component version and inclination. We calculated intraobserver and interobserver reliabilities for each method and compared these with values obtained from navigation presuming that to be the standard for judging accuracy.

RESULTS

Interobserver and intraobserver reliabilities were greater than 0.95 (95% CI, 0.904-0.999) for all measurements. Correlation with navigated values was 0.96 or greater (95% CI, 0.925-0.998) for all methods. Although CT had the highest correlation with navigated values, the correlations for the modified cross-table lateral and cross-table lateral radiographs were similar.

CONCLUSION

CT allows for accurate measurement of acetabular component version; however, when properly positioned, cross-table lateral radiograph-derived measurements are similarly accurate.

CLINICAL RELEVANCE

Our results support the use of plain radiographs to obtain important measurements after THA.