Measurement Of Acetabular Version Research Articles

Acetabular morphology variations in a Hispanic population.

Rotational abnormalities of the hip have been implicated in the etiology of diseases, such as hip dysplasia, osteoarthritis, and femoroacetabular impingement. Despite the extensive literature on hip morphology, there is a gap in knowledge regarding variations in the Hispanic population. To describe the bony anatomy variations of the acetabulum in a Hispanic population. This is a cross-sectional study. We studied 182 computed tomography (CT) images in patients aged older than 21 years, who had undergone pelvic CT for any condition, except hip fracture. Measurements of acetabular version, anterior and posterior acetabular sector angles (AASA/PASA) and horizontal acetabular sector angles (HASA) were made. Acetabular variations were then compared to weight and sex data. The mean acetabular anteversion was greater in women (P < 0.001). Women exhibited a greater PASA (P < 0.05); however, men had a greater AASA (P < 0.05). Underweight individuals had a smaller PASA (P < 0.01) and HASA (P < 0.05) than individuals with a normal weight. The Hispanic hip is morphologically similar to other populations previously reported in the literature; however, Hispanic men have less coverage of the femoral head by the posterior acetabular wall when compared to women of the same ethnicity. These abnormalities have a direct impact on management and surgical approach in patients treated for femoroacetabular impingement and hip dysplasia.

Is Quantitative Radiographic Measurement of Acetabular Version Reliable in Anteverted and Retroverted Hips?

The acetabular version is crucial for hip function, and its accurate assessment is necessary for treating patients with hip disorders. Current studies reveal discrepancies in the precision of quantitative radiographic measurements versus CT measurements, but there is a lack of focused analysis on anteverted versus retroverted hips. This study aims to fill this gap by directly comparing the reliability of these two methods in assessing varied hip configurations. (1) How reliable are quantitative radiographic and CT methods in measuring the acetabular version angle? (2) Is there any difference in the reliability of acetabular version angle measurements using radiography compared with CT in anteverted and retroverted hips? (3) What is the extent of variation in acetabular version measurements when quantitative radiographic and CT methods are compared in anteverted and retroverted hips? We searched our image archives for patients who had received both radiographs and CT scans between January 2020 and June 2022 and found 84 patients who met the criteria. From these patients, we selected those who presented with hip pain of different causes and who had no previous elective and/or hip trauma surgery, no hip dysplasia, and results from adequate radiographic examinations. Accordingly, 73% (61 of 84) of the patients were included in this study, and angle measurements were performed on both hips of these patients (122 hips). Standardized positioning was meticulously verified for all plain radiographs and CT scans utilized in the measurement process. We measured quantitative angles and assessed qualitative signs of retroversion, including crossover, posterior wall, and ischial spine findings. We considered a hip with at least one of these findings a retroverted hip, and the hips without these findings were included in the anteverted hip group. Three clinicians took measurements independently. Measurement reliability and agreement were examined using intraobserver and interobserver intraclass correlation coefficients (ICCs), with statistical analyses including paired and independent t-tests. To investigate the reliability of quantitative radiographic and CT methods, we assessed both intraobserver and interobserver agreements. To explore the reliability disparities in measuring the acetabular version via radiography and CT in anteverted and retroverted hips, we analyzed the agreement between measurements from both modalities in the hip groups. Furthermore, to evaluate the degree of variation in acetabular version measurements when comparing quantitative radiographic and CT methods in anteverted and retroverted hips, we utilized paired and independent t-tests to examine the measurement differences within these hip categories. The difference between radiographic and CT measurements was also evaluated by Bland-Altman analysis. Quantitative radiographic measurements showed intraobserver and interobserver reliabilities with ICCs of 0.87 (95% CI 0.84 to 0.91) and 0.78 (95% CI 0.75 to 0.82), respectively, and CT measurements demonstrated higher reliabilities with ICCs of 0.92 (95% CI 0.90 to 0.93) and 0.91 (95% CI 0.89 to 0.92), respectively. The reliability of measuring the acetabular version in anteverted hips was moderate, with an ICC of 0.59 (95% CI 0.49 to 0.68). In contrast, retroverted hips showed an ICC of -0.41 (95% CI -1.17 to 0.08), indicating a lack of consistency between quantitative radiographic and CT measurements. Variation in measurement on plain radiographs in anteverted hips was less than that of retroverted hips (mean ± SD absolute difference between anteverted hips and retroverted hips 3° ± 3° versus 6° ± 4°; p = 0.0001), indicating greater variability in the radiographic measurement of retroverted hips. According to Bland-Altman analysis, we observed that the difference between radiographic and CT measurements was well outside the CI, especially in retroverted hips. Although quantitative radiographic measurement demonstrates acceptable intraobserver and interobserver reliabilities, its precision is lower than that of CT-based measurements. Specifically, quantitative radiographic methods are prone to a larger margin of error in retroverted hips. For more precise assessments of acetabular version, especially in retroverted hips, we recommend using CT measurement instead of the radiographic method. Level III, diagnostic study.

MRI-based assessment of acetabular version and coverage after previous Pemberton osteotomy in skeletally mature patients.

PurposeIn hip dysplasia the Pemberton osteotomy can modify the shape of the acetabulum and is indicated for children aged between two and 12 when the triradiate cartilage is still open. However, there have been concerns about acetabular retroversion following this type of osteotomy. The studies, however, have been based on plain radiographs. The aim of our investigation was to assess the 3D acetabular orientation in patients with previous Pemberton osteotomy after skeletal maturation.MethodsTen patients with 12 operated hips were included who received Pemberton osteotomy for hip dysplasia between January 3, 2005 and March 25, 2011. Mean age at surgery and at follow-up were 7.2 years (sd 3.7) and 19.2 years (sd 3.7), respectively. MRIs were conducted with 1.5 T. Besides the measurement of acetabular version, the analysis included alpha angles, acetabular sector angles (ASAs) as well as modified ASAs (cartilage covered area angles). Furthermore, the presence of osteoarthritis (OA) as well as acetabular retroversion was determined on plain radiographs. Patient-related outcome measures included the international Hip Outcome Tool (iHOT) and EuroQol-5-Dimensions (EQ5D) scores.ResultsIn comparison with the contralateral native and healthy hips the operated hips showed similar version (19.5° (sd 4.6°) versus 18.6° (sd 7.0°); p = 0.974). Also, there were no differences in terms of femoral head sphericity (alpha angles) and acetabular coverage (ASA angles). Five of 12 Pemberton hips showed signs of beginning OA (Kellgren-Lawrence classification I or II) while none of the non-operated hips did. Patients who received surgery before the age of six years had similar functional and radiological results when compared with patients who were older than six years at surgery. Among all patients, iHOT was 91.9 (sd 10.0) and EQ5D was 90.3 (sd 7.3)).ConclusionThe Pemberton osteotomy provides good long-term radiographic and functional results without compromising acetabular version or coverage.Level of EvidenceLevel III: retrospective comparative study

The Salter innominate osteotomy does not lead to acetabular retroversion

In children with developmental dysplasia of the hip (DDH), Salter's innominate osteotomy aims to surgically manipulate the acetabulum to increase anterior coverage and aid joint support. Consequently, this procedure may retrovert the acetabulum, predisposing patients to pain, osteoarthritis, impingement, or further surgical intervention. In this study, we aim to address whether the innominate osteotomy leads to acetabular retroversion postoperatively or at follow-up. Ninety-two patients were identified from our institutions DDH database between 2009 and 2016, who underwent a unilateral innominate osteotomy for DDH, performed by expert surgeons in a leading paediatric hospital. A novel technique was utilized to measure acetabular version on postoperative computed tomography (CT) scans, where acetabular version was compared between the pathological and contralateral control hips. Measurement of acetabular version in postoperative and control hips demonstrated no incidence of acetabular retroversion. A significant difference was observed when comparing the acetabular version of control versus post-operative hips (P < 0.001), where hips postinnominate osteotomy had a larger degree of acetabular anteversion compared to the control hip. Furthermore, on follow-up radiographic imaging, there was no evidence of acetabular retroversion when using previously defined markers. This study confirms that the Salter innominate osteotomy does not lead to acetabular retroversion both immediately post-operatively and throughout follow-up. In fact, it demonstrates that the acetabula are more anteverted than the contralateral control hip, which has not been previously documented. Additionally, this study demonstrates a novel method of measuring acetabular retroversion using CT technology that adjusts for pelvic tilt, which is repeatable among individuals.

THE RELATIONSHIP OF ACETABULAR AND FEMORAL VERSION IN PATIENTS UNDERGOING PERIACETABULAR OSTEOTOMY

Background: Hip dysplasia is a complex, three dimensional diagnosis. Little is known about version (acetabular, femoral and the relationship between the two) in dysplastic patients. We sought to 1) compare femoral and acetabular version between hips that underwent a primary periacetabular osteotomy (PAO) versus nondysplastic hips (CEA &gt;25degrees); 2) estimate the correlation between femoral and acetabular version in dysplastic hips; 3) estimate the correlation of femoral and acetabular version with preoperative range of motion in dysplastic hips; 4) estimate the association of femoral and acetabular version with patient-reported outcome measures 11-23 months postoperatively in patients that underwent PAO. We hypothesized an association between acetabular and femoral version, and an association between version and patient reported outcomes. Methods: We retrospectively reviewed our institution’s hip registry to identify all PAO patients from March 2010 and June 2016. We included patients who had pre-operative computed tomography (CT) imaging and a minimum of 1 year follow-up. We created a comparison group of non-dysplastic patients (CEA &gt; 25degrees). We calculated the association between acetabular version, femoral version and hip range of motion (ROM), as well as between femoral version, acetabular version, age, sex, and preoperative and 1 year postoperative modified Harris Hip Score (mHHS), Hip Outcome Score (HOS), and International Hip Outcome Tool 33 (iHOT33) score. Results: 75 PAO patients met inclusion criteria (93% female, mean age 24) and 1332 non-dysplastic patients (45% female, mean age 25). Pre-operative CT measurements (95% CI) demonstrated mean CEA for our PAO patients was 24, and for the non-dysplastic group 37. We found a very weak correlation between acetabular version and femoral version. Dysplastic patients had significantly greater acetabular and femoral version than nondysplastic patients (8 vs 1 at 1 o’clock; 15 vs 10 at 2 o’clock; 21 vs 16 at 3 o’clock, FV 21 vs 14, all p&lt;0.001). We found only a weak correlation of hip ROM to acetabular version, but there was a moderate correlation of hip ROM and femoral version. We found no evidence of an association between mHHS, HOS-activities of daily living (ADL), HOS-sport specific (SS), or iHOT-33 scores and pre-operative femoral version, acetabular version, age, or sex. Conclusions/Significance: Our current investigation confirmed a statistically higher acetabular and femoral version in dysplastic hips than nondysplastic hips. However, while acetabular version measurements correlated strongly, there was only a very weak correlation between acetabular version and femoral version. Pre-operative ROM was correlated only moderately with femoral version, but not correlated with acetabular version. Additionally there was no association with acetabular or femoral version and patient reported outcomes after PAO, suggesting that femoral version does not need to be addressed at the time of PAO surgery.

Validation of a new radiographic measurement of acetabular version: the transverse axis distance (TAD).

This study has three aims: (1) validate a new radiographic measure of acetabular version, the transverse axis distance (TAD) by showing equivalent TAD accuracy in predicting CT equatorial acetabular version when compared to a previously validated, but more cumbersome, radiographic measure, the p/a ratio; (2) establish predictive equations of CT acetabular version from TAD; (3) calculate a sensitive and specific cut point for predicting excessive CT acetabular anteversion using TAD. A 14-month retrospective review was performed of patients who had undergone a dedicated MSK CT pelvis study and who also had a technically adequate AP pelvis radiograph. Two trained observers measured the radiographic p/a ratio, TAD, and CT acetabular equatorial version for 110 hips on a PACS workstation. Mixed model analysis was used to find prediction equations, and ROC analysis was used to evaluate the diagnostic accuracy of p/a ratio and TAD. CT equatorial acetabular version can accurately be predicted from either p/a ratio (p < 0.001) or TAD (p < 0.001). The diagnostic accuracies of p/a ratio and TAD are comparable (p =0.46). Patients whose TAD is higher than 17 mm may have excessive acetabular anteversion. For that cutpoint, the sensitivity of TAD is 0.73, with specificity of 0.82. TAD is an accurate radiographic predictor of CT acetabular anteversion and provides an easy-to-use and intuitive point-of-care assessment of acetabular version in patients with hip pain.

Acetabular Version Measurement in Total Hip Arthroplasty: the Impact of Inclination and the Value of Multi-Planar CT Reformation.

The orientation of the acetabular cup component of a total hip arthroplasty can be evaluated in a number of ways, utilizing a myriad of imaging techniques and measurement parameters, including intraoperative surgical estimates, postoperative radiographs, and cross-sectional imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). How do traditional versus corrected measurements of acetabular version vary from one another based on the inclination of the cup? What is the reliability of the corrected acetabular version measurements based on interobserver and intraobserver consistency? Two fellowship-trained musculoskeletal radiologists reviewed CT scans on 60 total hip arthroplasties. Acetabular inclination, traditional CT acetabular version, and CT acetabular version corrected for inclination (by utilizing multi-planar reformations to measure in the plane of the cup face) were each measured. The difference was then calculated between the "traditional" axial CT and "corrected" acetabular version measurements, and the association between this difference and the acetabular inclination was assessed. The "traditional" axial CT and "corrected" acetabular version measurements differed from one another in every case, with the traditional method yielding a version measurement that was on average 9.5° higher than the corrected technique. However, as the acetabular cup inclination angle decreased, the "traditional" measurement became more variable and increasingly discordant with the "corrected" version measurement. There is inherent variability between the many methods utilized for defining and measuring acetabular version, with axial CT measurements often used as an accepted proxy for true cup anteversion. However, the variability between different measurement techniques is correlated with acetabular inclination, and this variability is most pronounced when acetabular inclination is low, ultimately leading to potential confusion in measurement terminology. The increasingly widespread availability of multi-planar CT reformations provides an opportunity to standardize methodology, eliminate the impact of inclination on acetabular version measurements, and potentially provide a more reliable comparison of the impact of cup orientation on surgical outcomes.

Functional acetabular orientation varies between supine and standing radiographs: implications for treatment of femoroacetabular impingement.

Often, anteroposterior (AP) pelvic radiographs are performed with the patient positioned supine. However, this may not represent the functional position of the pelvis and the acetabulum, and so when assessing patients for conditions like femoroacetabular impingement (FAI), it is possible that standing radiographs better incorporate the dynamic influences of periarticular musculature and sagittal balance. However, this thesis remains largely untested. The purpose of this study was to determine the effect of supine and standing pelvic orientation on (1) measurements of acetabular version and common radiographic signs of FAI as assessed on two- and three-dimensional (3-D) imaging; and (2) on terminal hip range of motion (ROM). Preoperative pelvic CT scans of 50 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI between July 2013 and October 2014 were analyzed. The mean age of the study population was 29 ± 10 years (range, 15-50 years) and 70% were male. All patients had a standing AP pelvis radiograph, a reconstructed supine radiograph from the CT data, and a 3-D model created to allow manipulation of pelvic tilt and simulate ROM to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign were recorded on simulated plain radiographs. Measurements of ROM to bony impingement were made during (1) simulated hip flexion; (2) simulated internal rotation in 90° of flexion (IRF); and (3) simulated internal rotation in 90° of flexion and 15° adduction (FADIR), and the location of bony contact between the proximal femur and acetabular rim was defined. These measurements were calculated for supine and standing pelvic orientations. A paired Student's t-test was used for comparison of continuous variables, whereas chi square testing was used for categorical variables. A p value of < 0.05 was considered significant. When changing from supine to the standing radiographs, both mean cranial and central version increased by 2° ± 4° (95% confidence interval [CI], 1°-3°) and 2° ± 3° (95% CI, 1°-3°), respectively (both p < 0.001). However, with the numbers available, there were no changes in the proportion of positive crossover, posterior wall, and prominent ischial spine signs. Standing pelvic position tilt resulted in an increased hip flexion of 3° (95% CI, 2°-4°) as well as an increase in IRF of 2° (95% CI, 1°-3°) and FADIR of 3° (95% CI, 2°-4°) (all p < 0.001). The functional orientation of the acetabulum varies between supine and standing radiographs and must be considered when diagnosing and treating patients with symptomatic FAI. Standing pelvic orientation results in posterior pelvic tilt and later occurrence of FAI in the arc of motion. Although we cannot recommend standing radiographs on the current study alone, we do recommend larger studies to determine whether any significant differences truly exist.

Effect of Changes in Pelvic Tilt on Range of Motion to Impingement and Radiographic Parameters of Acetabular Morphologic Characteristics

Background: The current understanding of the effect of dynamic changes in pelvic tilt on the functional acetabular orientation and occurrence of femoroacetabular impingement (FAI) is limited. Purpose: To determine the effect of changes in pelvic tilt on (1) terminal hip range of motion and (2) measurements of acetabular version as assessed on 2- and 3-dimensional imaging. Study Design: Controlled laboratory study. Methods: Preoperative pelvic computed tomographic scans of 48 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI were analyzed. The mean age of the study population was 25.7 years (range, 14-56 years), and 56% were male. Three-dimensional models of the hips were created, allowing manipulation of the pelvic tilt and simulation of hip range of motion to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign was recorded on simulated plain radiographs. Measurements of range of motion to bony impingement during (1) hip flexion, (2) internal rotation in 90° of flexion, and (3) internal rotation in 90° of flexion and 15° adduction were performed, and the location of bony contact between the proximal femur and acetabular rim was defined. These measurements were calculated for −10° (posterior), 0° (native), and +10° (anterior) pelvic orientations. Results: In native tilt, mean cranial acetabular version was 3.3°, while central version averaged 16.2°. Anterior pelvic tilt (10° change) resulted in significant retroversion, with mean decreases in cranial and central version of 5.9° and 5.8°, respectively (P < .0001 for both). Additionally, this resulted in a significantly increased proportion of positive crossover, posterior wall, and prominent ischial spine signs (P < .001 for all). Anterior pelvic tilt (10° change) resulted in a decrease in internal rotation in 90° of flexion of 5.9° (P < .0001) and internal rotation in 90° of flexion and 15° adduction of 8.5° (P < .0001), with a shift in the location of osseous impingement more anteriorly. Posterior pelvic tilt (10° change) resulted in an increase in internal rotation in 90° of flexion of 5.1° (P < .0001) and internal rotation in 90° of flexion and 15° adduction of 7.4° (P < .0001), with a superolateral shift in the location of osseous impingement. Conclusion/Clinical Relevance: Dynamic changes in pelvic tilt significantly influence the functional orientation of the acetabulum and must be considered. Dynamic anterior pelvic tilt is predicted to result in earlier occurrence of FAI in the arc of motion, whereas dynamic posterior pelvic tilt results in later occurrence of FAI, which may have implications regarding nonsurgical treatments for FAI.

Native Acetabular Version: 3D CT Analysis of the Psoas Valley

Insufficient version has been demonstrated to be a significant factor in increasing metal-on-metal cup wear. Another implication is the impingement of the psoas tendon at the anatomical depression on the anterior acetabular rim, called the psoas valley. It is not known whether the psoas valley has any anatomical significance when measuring native version. The effect of this landmark on the measurement of acetabular version has not been assessed using 3D CT. Sixty five high resolution CT scans of non-diseased hips (performed for colonography) were used to measure the anatomical version angles of the bony acetabular rim. Our new method, using the psoas valley, was compared to the reference method, which used the full 320° of the acetabular rim. The measurement of acetabular version was highly reproducible between the methods. Both methods measured the angle of version over a wide range: 5° to 35° for males and 10° to 40° for females. There were no statistically significant differences between genders (p = 0.3670). The Bland-Altman 1.96 SD lower and upper limits of agreement between the two methods were +4.6° and -4.3°, respectively. Intra-observer and inter-observer reliability were high for the new method. This adds to our understanding of native bony anatomy, and specifically provides a landmark that 3D CT has demonstrated to be potentially useful in assessing native version.

Acetabular Version on Magnetic Resonance Imaging: Analysis of Two Different Measuring Techniques

Both increased anteversion and retroversion of the acetabulum can lead to clinical problems. Although computed tomography (CT) is the gold standard in acetabular version imaging, magnetic resonance imaging (MRI) is becoming increasingly popular. We conducted this retrospective study to answer the following questions: 1) can the bony landmarks necessary to outline and measure acetabular version on MRI be consistently and reproducibly identified; 2) are soft-tissue (labral) landmarks comparable to bony landmarks for the measurement of acetabular version? Twenty-nine MRI torsional profile examinations were studied. A total of 232 readings (116 each for right and left sided acetabulae) were involved. Acetabular anteversion angle (AAA) was measured using two different methods (i.e. bony acetabulum landmarks and labrum), by two investigators, at two separate times. Mean age was 13 years, 8 months with a range of 14 years. There were 12 male patients and 17 female. It was possible to consistently identify bony and labral landmarks in all MR images. AAA measurements using both methods were consistent and reproducible. When comparing the two methods to each other we found them to be in excellent agreement with an ICC of 0.943 (95% confidence interval, 0.927 to 0.956), 37% of all readings were in perfect agreement and 97% were within 5 degrees. The mean difference in measurement between methods was 1.34 degrees. Measurement of acetabular version using MRI remains consistent independent of the method used (bone versus labrum). MRI can provide adequate information for calculating acetabular version.

Analysis of acetabular version in the native hip: comparison between 2D axial CT and 3D CT measurements

To compare two-dimensional (2D) axial with three-dimensional (3D) computerized tomography (CT) measurements of acetabular version in native hips. CT scans of 34 hips in 17 consecutive patients being investigated for femoroacetabular impingement were analyzed. Acetabular version was measured using 2D CT at two different axial levels, one cranial (slice 2) and the other at the equator (slice 3). The measurements were repeated after correction for pelvic tilt. The results were compared to the measurements of anatomical version obtained using a 3D CT method that automatically corrects for pelvic tilt. The mean acetabular version using the 3D CT method was 15.7° (SD 6.9°). The mean version using slice 2 was 9.3° (SD 6.5°) before correction for pelvic tilt and 15.7° (SD 8.0°) after the correction. The mean version using slice 3 was 16.4° (SD 4.2°) before tilt correction and 19.0° (SD 5.0°) after the correction. In relation to the 3D method, the intraclass correlation coefficient (ICC) was 0.58 for the uncorrected and 0.93 for the corrected slice 2 method. For the uncorrected and corrected slice 3 methods, the ICC was 0.64 and 0.89, respectively. The 2D axial methods produced variable results. The results that correlated best with the 3D method were those of the cranial slice (slice 2) after correction for pelvic tilt. Interpretation of 2D axial CT measurements of acetabular version should be done with caution. The level at which the measurement is done and the presence of pelvic tilt appear to be significant factors.

Multilevel Measurement of Acetabular Version Using 3-D CT-generated Models: Implications for Hip Preservation Surgery

BackgroundNumerous structural deformities of the acetabulum are associated with hip osteoarthritis (OA). Acetabular retroversion has been implicated in the development of femoroacetabular impingement. However, it is unknown if retroversion occurs from isolated excessive bone in the superior acetabulum or a torsional phenomenon of the entire pelvic segment.Questions/purposesA method was developed to measure acetabular version (AV) using 3-D models thus eliminating positional factors. This method was used to determine if acetabular retroversion is an isolated entity or an effect involving the entire pelvic segment containing the acetabulum.MethodFifty pelvic CT scans were selected from a large database. Measurements were performed for abduction, ischial spine position, and AV at multiple levels. The relationships between anteversion at multiple levels and between midacetabular anteversion and ischial spine position were analyzed.ResultsThe mean upper and midlevel acetabular anteversion values were 14.4° ± 10.5° and 21.3° ± 5.8°, respectively. The mean abduction was 39.7° ± 4.3°. The prevalence of acetabular retroversion was 7%. Females had greater anteversion than males at all levels. Correlations were found between Levels 1 and 4 version (r = 0.74) and the ischial spine index and Level 4 version (r = 0.67).ConclusionsThese data suggest retroversion involves the acetabulum at all levels and includes the entire pelvic segment containing the acetabulum and the ischial spine.Clinical RelevanceThese data are relevant for surgeons in providing targets for normal positioning of the acetabulum during periacetabular osteotomies and acetabular recontouring procedures.

Measurement of Acetabular Version on the Axiolateral Radiograph

There are 3 definitions of acetabular version: true (anatomic) version, planar (radiographic) version, and operative version. Although planar version can be measured on standard radiographs, the measurement may be inaccurate when applied to metal-backed acetabular components. However, another version angle is depicted clearly on an angled, cross-table lateral radiograph of the hip--the axiolateral view, and this angle readily distinguishes anteversion from retroversion. If the angle of the xray beam is known or is standardized, version measured on the axiolateral view can be converted to the other version angles. Nomograms for these conversions are presented. In most cases, acetabular version measured on the axiolateral radiograph closely approximates planar version.