Original Research Prevalence of Morphological Variations Associated With Femoroacetabular Impingement According to Age and Sex A Study of 1878 Asymptomatic Hips in Nonprofessional Athletes Rodolfo Morales-Avalos,*† MD, MSc, Adriana Tapia-Náñez,*† MD, Mario Simental-Mendı́a,* PhD, Guillermo Elizondo-Riojas,‡ MD, PhD, Michelle Morcos-Sandino,§ MD, Marc Tey-Pons,k MD, PhD, Vı́ctor M. Peña-Martı́nez,* MD, PhD, Francisco J. Barrera,† MD, Santos Guzman-Lopez,† MD, PhD, Rodrigo E. Elizondo-Omaña,† MD, PhD, and Félix Vı́lchez-Cavazos,*{ MD, PhD Investigation performed at the School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León, Monterrey, México Background: Radiographic findings related to the cam and pincer variants of femoroacetabular impingement (FAI) include measurements of the alpha angle and lateral center-edge angle (LCEA). The function of these radiographic findings has been put into question because of high heterogeneity in reported studies. Purpose: The aim of this study was 3-fold: (1) to determine the prevalence of cam and pincer variants according to sex and age on anteroposterior (AP) pelvic radiographs from an asymptomatic nonathletic population, (2) to identify the most common radio- graphic signs of cam- and pincer-type variants, and (3) to determine if there are variations in the prevalence of these radiographic signs according to sex and age. Study Design: Cross-sectional study; Level of evidence, 3. Methods: There were 3 independent observers who retrospectively analyzed the 939 AP pelvic radiographs (1878 hips) of patients aged 18 to 50 years who did not have hip symptoms and who were not professional athletes. The prevalence of the cam and pincer variants according to the alpha angle and LCEA, respectively, and the presence of other radiographic signs commonly associated with these variables were determined in the overall population and by subgroup according to sex and age group (18-30, 31-40, and 41-50 years). Descriptive and inferential statistics were used to analyze the study sample. Results: The mean age of the included population was 31.0 ± 9.2 years, and 68.2% were male. The prevalence of the cam-type variant was 29.7% (558/1878), and that of the pincer-type variant was 24.3% (456/1878). The radiographic signs that were most associated with the cam and pincer variants were a pistol-grip deformity and the crossover sign, respectively. Significant differ- ences (P < .001) in the prevalence of these variants were identified between men and women in both variants. No differences were observed in the alpha angle or LCEA according to sex or age. Conclusion: Radiographic findings suggestive of FAI had significant variations with respect to sex and age in this study sample. This study provides information to determine the prevalence of these anatomic variants in the general population. Keywords: anatomic variant; cam; femoroacetabular impingement; morphology; pincer; prevalence Femoroacetabular impingement (FAI) is a clinical syn- anatomic characteristics associated with the development drome defined by pain and functional limitations of the hip of this condition include loss of the cervicocephalic offset or in young adults and middle-aged populations and may con- asphericity of the femoral head (cam-type variant), focal or tribute to the development of early hip osteoarthritis.13 The global acetabular overcoverage (pincer-type variant), and mixed characteristics (cam and pincer types),3 with the lat- The Orthopaedic Journal of Sports Medicine, 9(2), 2325967120977892 ter having the highest prevalence in patients with FAI39; DOI: 10.1177/2325967120977892 however, it has not been established whether the same ª The Author(s) 2021 prevalence occurs in the general population. 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For article reuse guidelines, please visit SAGE’s website at http://www.sagepub.com/journals-permissions. 1 2 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine multiple imaging methods (eg, plain radiography, com- general population, in a population of the same ethnic puted tomography [CT], magnetic resonance imaging group with a subgroup analysis regarding sex and age, or [MRI], computed tomography arthrography, and magnetic in asymptomatic patients who were not professional ath- resonance arthrography) have been used to determine the letes. We hypothesized that there are significant differ- prevalence and morphological characteristics of these ana- ences regarding sex and age in the prevalence of cam and tomic variants because a 2-dimensional static assessment pincer variants as well as in their main associated radio- of a 3-dimensional dynamic deformity can be imprecise.52 graphic signs in asymptomatic patients who were not pro- Even so, plain radiography of the pelvis in its different fessional athletes. Therefore, this study was intended to projections has been the most widely used imaging method encompass 3 main issues: (1) to determine the prevalence for the radiographic detection of these anatomic variations according to sex and age of cam and pincer variants in a in studies with large samples.59 large sample of anteroposterior (AP) pelvic radiographs The radiographic findings associated with FAI observed from an asymptomatic population, (2) to identify the most on plain film radiographs include the following for the cam- common radiographic findings in patients with cam- and type variant: an increased alpha angle, a pistol-grip defor- pincer-type variants, and (3) to determine if there are var- mity (PGD) of the femoral head-neck, a low femoral head– iations in the prevalence of these radiographic signs in to–femoral neck ratio (FHFNR), lateral flattening of the terms of sex and age. femoral head (LFFH; coxa recta), focal prominence of the femoral neck (FPFN), and coxa vara defined by the femoral neck-shaft angle (NSA; also called the caput-collum- METHODS diaphyseal angle). For the pincer-type variant, the findings include the following: an increased lateral center-edge This was a retrospective cross-sectional and descriptive angle (LCEA; Wiberg angle); a decreased acetabular index study that adhered to the Strengthening the Reporting of (AI; Tönnis angle); the crossover sign (COS; figure-of-8 Observational Studies in Epidemiology (STROBE) guide- sign); the posterior wall sign (PWS); excessive acetabular lines. The study received ethics committee approval and coverage (EAC) and its variant, os acetabuli; the ischial was conducted in accordance with the World Medical Asso- spine sign; coxa profunda; and protrusio acetabuli.6,23,46 ciation’s 1964 Declaration of Helsinki and its revision in The utility of these radiographic signs has been put 2013. All of the images were obtained for other (medical) into question owing to the low reliability as well as the reasons and not for conducting the present study; therefore, discrepancy between the results of radiography and those informed consent was not obtained. All sensitive informa- obtained by advanced imaging methods and intraopera- tion was concealed to protect patient confidentiality. tive findings.7,56 However, other studies support their use Eligible for the study were 1154 AP pelvic radiographs and highlight the good agreement with advanced imaging from August 2017 to January 2020 of Mexican patients methods.51,57 aged between 18 and 50 years. The medical indication for Although these morphological features may cause pain these radiographs was an evaluation of traumatic injuries. and dysfunction in some hips, many hips remain asymp- The study exclusion criteria were radiographs of subopti- tomatic despite radiographic evidence of FAI-related fea- mal technical quality (ie, excessive pelvic or femoral rota- tures.45 This has led clinicians to question the prevalence tion assessed by an obturator foramen index outside the of FAI-related morphological features in asymptomatic range of 0.6-1.8, the greater trochanter was not in profile, patients. Few studies have determined whether there are or the lesser trochanter did not project onto the inner edge differences in the prevalence of radiographic signs for FAI of the femur), poor positioning, tilting, and motion as well associated with sex and age.26,28,55 After searching the as the presence of bone abnormalities (which were ruled out available scientific literature, we did not find a study that by a musculoskeletal radiology specialist [G.E.-R.] who did determined the prevalence of these variants or the radio- not participate in the subsequent assessment or observa- graphic signs most commonly associated with them in the tion of radiographs). { Address correspondence to Félix Vilchez-Cavazos, MD, PhD, Department of Orthopedic Surgery and Traumatology, School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León, Av. Francisco I. Madero and Av. Dr. Eduardo Aguirre Pequeño, s/n, 4th Floor of the Central Building, Col. Mitras Centro, CP 64460, Monterrey, Nuevo León, México (email: rodolfot59@hotmail.com). *Department of Orthopedic Surgery and Traumatology, School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León, Monterrey, México. † Department of Human Anatomy, School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León, Mon- terrey, México. ‡ Department of Radiology, School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León, Monterrey, México. § School of Medicine, Universidad Autónoma de Nuevo León, Monterrey, México. k Department of Orthopedic Surgery, Hospitals del Mar i l’Esperança, Barcelona, Spain. Final revision submitted August 3, 2020; accepted August 10, 2020. The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto. Ethical approval for this study was obtained from the ethics and research committee of the School of Medicine, University Hospital “Dr José Eleuterio González,” Universidad Autónoma de Nuevo León (registration No. AH14-008). The Orthopaedic Journal of Sports Medicine Prevalence of FAI Variations by Age and Sex 3 Figure 1. Flow diagram of the study. Other exclusion criteria were hip, acetabular, or pelvic was 102 to 110 cm with a 35  43–cm cassette placed cross- fractures; diseases that affected the proximal femur sectionally and the tube perpendicular to the table. Advan- (tumors, infections, malformations, avascular necrosis of tage Workstation AW Volume Share 2 software (GE the hip, developmental dysplasia of the hip, malunion of a Healthcare) was used to assess the radiographs. The qual- femoral neck fracture, hip osteoarthritis of grade 3 or 4 ity of the radiographs was considered adequate when the according to the Kellgren-Lawrence scale20); presence of tips of the coccyx and pubic symphysis were in line and the an orthopaedic implant (total or partial prostheses, plates, distance between them was between 1 and 3 cm as well as screws, intramedullary nails, K-wires, etc); patients who when both teardrops, the iliac wing, and the obturator fora- underwent pelvic osteotomy or extraction of an iliac crest men were symmetric. This technique represents the autograft; a history of rheumatoid arthritis, juvenile method standardized by the emergency radiology service idiopathic arthritis, congenital hip dysplasia, Legg-Calve- of our institution for the acquisition of an AP radiograph Perthes disease, slipped capital femoral epiphysis, trochan- of the pelvis. teric bursitis, septic arthritis of the hip, lumbar discopathy, We performed 11 measurements: 6 measurements per sacroiliitis, long-term steroid use, chemotherapy or radia- observation (3 quantitative and 3 qualitative) catalogued tion, nonambulatory status, neuromuscular disorders, or as cam-type variants and another 5 measurements per hip dislocations; a history of hip, femoral, acetabular, or observation (2 quantitative and 3 qualitative) for pincer- pelvic fractures or surgery; the presence of pain or func- type variants. Patient identification details were removed tional limitations in one or both hips during an interview from all radiographs to maintain confidentiality. Mea- or physical examination (especially during flexion, adduc- surements were carried out by 3 observers independently tion, or internal rotation); and those who reported being or (R.M.-A., A.T.-N., F.V.-C.). The observers were blinded to having been high-performance athletes or who reported the the age and medical history of the patients to whom the trauma as occurring during a professional sports practice radiographs belonged as well as to the results of the other or competition. Patients who played sports recreationally observers. Before performing the measurements, each were not excluded. Last, patients with an incomplete med- observer was trained for 2 weeks on a previously estab- ical record were eliminated from the study. lished measurement protocol for each of the chosen para- Of the original 1154 radiographs, 215 (18.6%) were meters by the same musculoskeletal radiologist who excluded from the study (Figure 1), resulting in 939 radio- applied the selection criteria of the study (G.E.-R.); a set graphs (1878 hips) for our analysis. A flow diagram of the of 20 radiographs was used to teach the observers how the study is presented in Figure 1. measurements had to be performed (these patients were Orthopaedic radiology technicians with more than 15 not part of the study population), and several face-to-face years of experience were responsible for obtaining the meetings were held to review them and refine the stan- images. A Proteus XR-a radiographic system (GE Health- dardized definitions. care) was used to obtain radiographs using the following To evaluate intraobserver reliability, the raters were technique: the patient was placed in a supine position with asked to repeat the measurements and radiographic obser- the hip extended and internally rotated 15 ; the crosshairs vations 1 month after the first measurement; these were of the beam were centered on the midway point between the presented to the raters in a different order than on the first superior border of the pubic symphysis and a line drawn occasion. Finally, the 3 observers reviewed the differences connecting the anterior superior iliac spine. The following at a consensus meeting using a nominal group technique in parameters were used to acquire the images: 65-80 kV, 65- which the hierarchical position of the observers was the 80 mA, a thick focus, and a bucky. The focus-plate distance same. 4 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine Figure 2. Methodology followed for the measurement of the angles and indexes used in the present study: (A) alpha angle, (B) femoral head–to–femoral neck ratio, (C) femoral neck-shaft angle, (D) lateral center-edge angle, and (E) acetabular index. Measurements and Determination radiographs by direct observation; however, it has been rec- of Cam-Type Variants ognized that these are not present in all cases of cam-type variants.23 The reviewers considered these signs to be either The alpha angle was measured with the use of a previously positive or negative, and disagreements were resolved by a reported method by Nötzli et al.35 Although designed for consensus. Moreover, coxa vara was defined by the NSA use on CT or MRI, it is also a reliable and valid method for (Figure 2C). An NSA of <125 was considered as coxa vara, plain radiography.5 An alpha angle of <55 was considered which is recognized as a cause of FAI.10 normal, and an alpha angle of 55 was considered a cam- type variant (Figure 2A).11 A PGD included the objective measurement of a low Measurements and Determination FHFNR and the subjective pistol-grip appearance. PGD was of Pincer-Type Variants defined as a characterized loss of normal concavity morphol- ogy of the anterosuperior region of the head-neck junction, A pincer variant was defined as any hip that had an LCEA of resulting in a nonspherical head that could be seen as an 40 (Figure 2D). This angle measures the lateral coverage extended convex margin lateral to the epiphyseal scar of the acetabular roof with regard to the femoral head and (Figure 3A). Doherty et al10 determined that PGD is associ- has been shown to be a good predictor of the presence of a ated with a low FHFNR and that the ratio of the maximal deformity, with a good intraobserver correlation index; in femoral head diameter divided by the minimal parallel fem- addition, it is the radiological parameter most used in pre- oral neck diameter differentiated hips with the deformity from vious studies to determine pincer-type variants.46 An AI of those without it. A line was drawn through the femoral head <0 was considered to be consistent with acetabular over- center and a point in the middle of the femoral neck. Perpen- coverage (Figure 2E).42 The COS was positive when the dicular to this line, another line was drawn at the maximum anterior wall of the acetabulum crossed the posterior border femoral head diameter, and another line was drawn at the of the acetabulum medial to the lateral rim of the weight- minimum femoral neck diameter (Figure 2B). The ratio was bearing area (Figure 3E).23 The presence of the PWS was the head diameter divided by the neck diameter. A ratio of also determined and considered positive when the posterior 1.27 was considered abnormal.6 Other suggestive signs of wall lay medial to the center of the femoral head the cam variant are FPFN (defined as an exostosis in the (Figure 3F).23 EAC was defined as the extension of the lat- femoral neck)12 (Figure 3B) and LFFH (flattening along the eral acetabular rim in the inferior and/or lateral direction femoral head-neck junction and, in severe cases, loss of dif- (Figure 3D, right hip)23 or an unattached bone fragment ferentiation between them)23 (Figure 3C), both of which lateral to the superolateral acetabular rim (Figure 3D, left were determined by the presence of the deformity on hip).6 The reviewers considered these signs to be either The Orthopaedic Journal of Sports Medicine Prevalence of FAI Variations by Age and Sex 5 Figure 3. Radiographic signs analyzed in the present study for (A-C) cam- and (D-F) pincer-type variants: (A) pistol-grip deformity (left side), (B) focal prominence of the femoral head (both sides), (C) lateral flattening of the femoral head (both sides), (D) excessive acetabular coverage (right side) and os acetabuli (left side), (E) crossover sign (both sides), and (F) posterior wall sign (right side). In some images, mixed variants or some other radiographic signs of the same variant can be observed in the contralateral hip; however, they are not mentioned here because the purpose was only to highlight a specific deformity in each image. positive or negative. Definitions were obtained from the significant differences were found between the results of literature. the 3 observers. Quantitative variables are described as We considered the presence of a radiographic cam-type means and standard deviations. The Student t test and variant when there was an abnormal value of the alpha analysis of variance were used to compare quantitative angle and an abnormal value of the LCEA for the pincer- variables. Qualitative variables are described as frequen- type variant. If the observer identified a mixed deformity cies and percentages. The chi-square test was used to com- (alpha angle >55 and LCEA >40 ), the observer was asked pare qualitative variables; to measure their strength of to report the radiographic findings present in the cam and association, odds ratios (ORs) and 95% CIs were calculated. pincer variants as independent signs (registering the com- Intrarater and interrater reliability were calculated for bination of signs), which were classified as a mixed variant qualitative observations using the Cohen and the Fleiss (without specifying the predominance of one type over the kappa coefficients, respectively. For quantitative observa- other or the equitable contribution). tions, intrarater and interrater reliability were calculated using the intraclass correlation coefficient (ICC) between Sample Size Calculation all pairs. The interpretation of concordance values was adapted as follows: k <0.20, poor agreement; 0.21-0.40, fair To calculate the sample size, we used a formula to estimate a agreement; 0.41-0.60, moderate agreement; 0.61-0.80, good mean value (that of the alpha value) within an infinite popula- agreement; and 0.81-1.00, very good agreement. Similarly, tion. A Z value of 1.96, a sigma (SD) of 5, and a delta (magni- an ICC of 0.80 was considered good agreement. A signif- tude of error) of 0.5 were used in the calculation, which icance level of .05 was decided a priori. Statistical analyses resulted in 384 participants. However, to have sufficient power were performed using SPSS software Version 19.0 for Mac to determine the prevalence according to sex (male and female) (IBM). and age (18-30, 31-40, and 41-50 years), this division was based on the patterns of degenerative changes in the hip with age. We decided to increase the sample size to at least 1000. RESULTS Statistical Analysis Of the 939 radiographs (1878 hips) included in our analysis, 640 (1280 hips; 68.2%) of the radiographs were of men. The The average of the measurements made by the 3 observers mean age of the participants was 31.0 ± 9.2 years. The was considered the final result, as no statistically distribution of the sample based on sex and age, as well 6 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine TABLE 1 TABLE 3 Sex and Age of the Hips Prevalence of the Cam Variant (N ¼ 1878)a Men Women Total Men Women P Value (n ¼ 1280) (n ¼ 598) (N ¼ 1878) Overall 444/1280 (34.7) 114/598 (19.1) <.001 Overall age, mean ± SD, y 32.3 ± 10.4 28.6 ± 14.4 31.0 ± 9.2 Age group Age group, n 18-30 y 188/506 (37.2) 26/166 (15.7) <.001 18-30 y (25.2 ± 6.9a) 506 166 672 31-40 y 164/480 (34.2) 36/190 (18.9) <.001 31-40 y (34.6 ± 3.9a) 480 190 670 41-50 y 92/294 (31.3) 52/242 (21.5) .01 41-50 y (45.7 ± 3.1a) 294 242 536 P value .05 .03 Mean ± SD for that age group. a a Data are reported as n (%). Bolded P values indicate statisti- cally significant differences between the groups (P < .05). TABLE 2 between the different age groups for women (P ¼ .03) but Alpha Angle of the Cam Variant (n ¼ 558)a not for men (P ¼ .05). Age Group Men (n ¼ 444) Women (n ¼ 114) P Value The cam variant was found in 27.7% (260/939) and 31.7% (298/939) of the right and left femurs, respectively. None of 18-30 y 67.2 ± 9.5 62.4 ± 4.1 .16 the comparisons resulted in differences between the right 31-40 y 63.2 ± 6.1 65.2 ± 6.0 .22 and left femurs. We noted a bilateral presence of the defor- 41-50 y 59.3 ± 4.6 67.1 ± 6.2 .31 mity in 87 patients (174/558 hips), representing 31.2% of P value .07 .09 the total. Overall, the most prevalent sign was a PGD of the Data are reported as mean ± SD in degrees. a femoral head-neck (494/1878; 26.3%) when considering the objective and subjective measurements. In hips with the cam variant, PGD represented a prevalence of 88.5% as the mean age of each of these age groups, is shown in (494/558). The second most prevalent sign was LFFH, Table 1. which occurred in 11.3% (212/1878) of the general popula- No significant differences were found when the mean tion and in 38.0% (212/558) of the population with the cam values obtained from each of the observers were compared. variant. Finally, FPFN was present in 3.5% (66/1878) of the Similarly, the results of the intraobserver and interob- general population and in 11.8% (66/558) of the population server analyses resulted in good agreement (k > 0.80 and with the cam variant. Table 4 shows the distribution of ICC > 0.80) for all sets. these radiographic signs according to sex and age. There were significant differences in the prevalence of Cam-Type Variant coxa vara when comparing men versus women (with men having a higher incidence) for any age group, as well as an The mean alpha angle for the total population was 50.6 ± increasing prevalence with older age regardless of sex. The 5.2 (N ¼ 1878). Based on measurement of the alpha angle, variations in the prevalence of coxa vara according to sex the overall prevalence of the cam-type variant was 29.7% and age are shown in Table 4. (558/1878). The mean alpha angle in hips with versus with- out the cam variant was 63.8 ± 4.2 (n ¼ 558) versus 43.2 ± Pincer-Type Variant 5.0 (n ¼ 1320), respectively (P < .001). The mean alpha angle of the hips with the cam variant was not significantly The mean LCEA for the total population was 36.4 ± 3.1 (N different between men (64.1 ± 1.6 ) and women (62.7 ± ¼ 1878). In hips without the pincer variant (n ¼ 1422; 4.1 ). 75.7%), the LCEA was 29.4 ± 3.9 , and it was 49.6 ± 3.2 In the 558 hips with the cam-type variant, the mean in hips with the pincer variant (n ¼ 456; 24.3%). No signif- alpha angle according to age group and sex are shown in icant differences were found when comparing men (51.2 ± Table 2. There were no differences in the alpha angle when 2.8 ) versus women (46.7 ± 3.6 ). comparing men versus women for any age group as well as In the 456 hips with the pincer-type variant, the mean when comparing the different ages within the same sex. LCEA according to age group and sex are shown in Table 5. Notably, the cam variant was present in 114 of 598 hips There were no differences in the LCEA when comparing (19.1%) in women and 444 of 1280 hips (34.7%) in men (OR, men versus women for any age group or when comparing 2.25 [95% CI, 1.78-2.85]; P < .001). The prevalence of this the LCEA of the different age groups for the same sex. As variant in the different age groups is shown in Table 3. seen in hips with the cam variant, a greater prevalence of Differences were found when comparing the prevalence of the pincer variant was observed in men (357/1280; 27.9%) the cam-type variant between men and women; the cam than in women (99/598; 16.6%) (P < .0001). variant was strongly associated with male sex for the 18- The distribution of the pincer variant according to sex to 30-year (OR, 3.18 [95% CI, 2.01-5.02]; P < .001), 31- to and age group is shown in Table 6. The prevalence of the 40-year (OR, 2.22 [95% CI, 1.47-3.34]; P < .001), and 41- to pincer-type variant was strongly associated with male sex 50-year age groups (OR, 1.66 [95% CI, 1.12-2.46]; P ¼ .01). in the 18- to 30-year (OR, 2.36 [95% CI, 1.40-3.97]; P < The prevalence of the cam-type variant was also significant .001), 31- to 40-year (OR, 1.90 [95% CI, 1.23-2.94]; P < The Orthopaedic Journal of Sports Medicine Prevalence of FAI Variations by Age and Sex 7 TABLE 4 TABLE 6 Prevalence of Radiographic Signs Associated With Prevalence of the Pincer Variant (N ¼ 1878)a the Presence of the Cam Variant (n ¼ 558)a Men Women P Value Men (n ¼ 444) Women (n ¼ 114) P Value Overall 357/1280 (27.9) 99/598 (16.5) <.0001 PGD Age group 18-30 y 161/188 (85.6) 22/26 (84.6) .88 18-30 y 119/506 (23.5) 19/166 (11.4) <.001 31-40 y 142/164 (86.6) 30/36 (83.3) .61 31-40 y 130/480 (27.1) 31/190 (16.3) <.01 41-50 y 92/92 (100.0) 47/52 (90.4) .002 41-50 y 108/294 (36.7) 49/242 (20.2) <.001 P value .001 .58 P value .0003 <.05 FPFN a 18-30 y 23/188 (12.2) 2/26 (7.7) .50 Data are reported as n (%). Bolded P values indicate significant 31-40 y 18/164 (11.0) 4/36 (11.1) .98 differences between the groups (P < .05). 41-50 y 11/92 (12.0) 8/52 (15.4) .56 P value .93 .60 LFFH TABLE 7 18-30 y 70/188 (37.2) 7/26 (26.9) .30 Prevalence of Radiographic Signs Associated With 31-40 y 52/164 (31.7) 16/36 (44.4) .14 the Presence of the Pincer Variant (n ¼ 456)a 41-50 y 47/92 (51.1) 20/52 (38.5) .14 P value .008 .36 Men (n ¼ 357) Women (n ¼ 99) P Value Coxa vara 18-30 y 75/188 (39.9) 4/26 (15.4) .01 EAC 31-40 y 74/164 (45.1) 8/36 (22.2) .01 18-30 y 16/119 (13.4) 2/19 (10.5) .56 41-50 y 51/92 (55.4) 28/52 (53.8) .05 31-40 y 29/130 (22.3) 6/31 (19.4) .72 P value .04 .0005 41-50 y 28/108 (25.9) 10/49 (20.4) .45 P value .05 .62 a Data are reported as n (%). Bolded P values indicate significant COS differences between the groups (P < .05). FPFN, focal prominence 18-30 y 83/119 (69.7) 6/19 (31.6) .001 of the femoral neck; LFFH, lateral flattening of the femoral head; 31-40 y 95/130 (73.1) 20/31 (64.5) .34 PGD, pistol-grip deformity. 41-50 y 82/108 (75.9) 34/49 (69.4) .38 P value .57 .01 PWS TABLE 5 18-30 y 29/119 (24.4) 8/19 (42.1) .10 LCEA of the Pincer Variant (n ¼ 456)a 31-40 y 48/130 (36.9) 11/31 (35.5) .88 41-50 y 45/108 (41.7) 19/49 (38.8) .73 Age Group Men (n ¼ 357) Women (n ¼ 99) P Value P value .01 .89 AI 18-30 y 50.5 ± 2.5 43.4 ± 3.1 .06 18-30 y 81/119 (68.1) 10/19 (52.6) .05 31-40 y 52.9 ± 3.2 45.2 ± 3.3 .07 31-40 y 93/130 (71.5) 17/31 (54.8) .03 41-50 y 55.9 ± 4.1 47.7 ± 4.0 .09 41-50 y 82/108 (75.9) 23/49 (46.9) .0004 P value .12 .20 P value .42 .77 a a Data are reported as mean ± SD in degrees. LCEA, lateral Data are reported as n (%). Bolded P values indicate significant center-edge angle. differences between the groups (P < .05). AI, acetabular index; COS, crossover sign; EAC, excessive acetabular coverage; PWS, posterior wall sign. .01), and 41- to 50-year age groups (OR, 2.28 [95% CI, 1.54- 3.38]; P < .001). Similarly, differences were found when comparing the prevalence of the pincer-type variant population and 20.0% (91/456) of the pincer variant popula- between the age groups within the same sex (P ¼ .0003 for tion. Notably, the COS was strongly associated with male men; P < .05 for women). sex in the 18- to 30-year age group (OR, 4.99 [95% CI, 1.75- The pincer variant was found in the right acetabulum in 14.18]; P ¼ .001). 22.9% (215/939) of the hips and in the left acetabulum in The mean AI for the total population was 3.29 ± 5.12 (N 25.7% (241/939) of the hips. We found no differences ¼ 1878). Further, the mean value was 5.12 ± 2.67 for hips between the right and left acetabula. This variant was with a positive AI (n ¼ 1502; 83.1%) and –3.40 ± 1.96 for found bilaterally in 73 patients (146/456 hips), representing those with a negative AI (n ¼ 306; 16.9%) (P ¼ .002). The 32.0% of the total, and unilaterally in the remaining 68.0% mean AI of the hips with a negative AI was –4.98 ± 2.24 (310/456) of hips. Table 7 shows the prevalence of the radio- for men (256/1280; 20.0%) and –2.01 ± 1.03 for women (50/ graphic signs that predict the pincer variant. The most 598; 8.4%) (P ¼ .01). There were differences in the AI when prevalent sign in the total population was the COS (320/ comparing men versus women in the 31-40 and 41-50 year 1878; 17.0%), with 70.2% (320/456) in the pincer variant age groups (P < .05), but there were none when comparing population, followed by the PWS in 8.5% (160/1878) of the the AI in different age groups within the same sex. total population and 35.1% (160/456) of the pincer variant Variations in the prevalence of a negative AI according to population. EAC was found in 4.8% (91/1878) of the total sex and age are shown in Table 7. 8 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine Mixed Variant one used in the present study.33 Mineta et al29 reported a significant increase in alpha angle values and the preva- In 390 (69.9%) of the hips, we found a mixed deformity; in lence of the cam variant as age increased in a cohort of 168 hips (17.9%), there was a unique cam-type variant, and Japanese patients. Considering they used 40 years as the in 66 hips (12.2%), there was a unique pincer-type variant. cutoff age (to decide whether a patient belonged to the The most frequent combination of radiographic signs was young group or the old group), combined the values of men PGD þ COS in 217 hips (55.6%). and women, and had a sample consisting of mostly elderly patients, their results are difficult to compare with ours.29 Our study represents the largest one comparing preva- DISCUSSION lence between age groups, and although this was not a lon- gitudinal study, our findings suggest a significant increase We found significant differences regarding both cam- and in the prevalence of cam-type FAI as age increases in pincer-type variations and their main radiographic signs women. These findings confirm previous data reported by when comparing by age and sex in hips from an asymptom- our research team in contemporary osteological specimens atic and nonathletic population. Different systematic with known sex and age.32 Nonetheless, these suggestions reviews have reported a highly variable prevalence (range, should be confirmed with more comprehensive and longitu- 5%-75%) of these variants.8,11 A possible explanation for dinal studies. this high variability is the presence of heterogeneity among Another study reported a decreasing prevalence in the the baseline characteristics included in their analyses. This cam-type variant as age increased in both sexes.16 How- heterogeneity includes but may not be limited to ethnicity, ever, that study did not perform subgroup analysis by age sex, age, presence of symptoms, history of disease, physical or sex.6,16,29 Previous studies have suggested that the cam activity, imaging methods, and the operational definition of variant is an acquired phenomenon, particularly in men each included variable. To be able to provide more accurate during the second growth spurt, and that it is highly influ- estimates, studies must decrease the degree of heterogene- enced by exercise-related loads applied to the hip during ity in the included population and/or perform subgroup this phase.55 analyses, considering important covariates such as symp- The 3 radiographic signs of cam-type FAI demonstrated toms or physical activity. a constant prevalence across age and sex, resulting in no A previous systematic review reported that cam- and mixed-type variants were more prevalent among athletic, significant differences in sex. This is in contrast to the find- symptomatic, and male participants than among nonath- ings of a previous study that demonstrated a higher prev- letic, asymptomatic, and female participants.27 Similarly, alence of PGD in male versus female patients (26.13% vs several studies and reviews have reported the presence of 4.95%, respectively) without further analysis by age.6 radiographic signs suggestive of FAI in selected cohorts of We found differences across age groups for PGD, LFFH, asymptomatic patients.11 However, about half of the stud- and coxa vara in male hips. As there are no previous studies ies had small samples, without subgroup analysis by sex or with these comparisons, we cannot compare our results, age, and with highly heterogeneous selection criteria. In however clear differences in the prevalence of these 2 signs Appendix Table A1, we share a comparison of the charac- were seen in the total population, with PGD being the most teristics of the studies evaluating asymptomatic prevalent (26.3%). Our findings are comparable with those participants. from another study that found a higher prevalence of increased alpha angle than that of PGD in asymptomatic participants.59 In our study, 88.5% of participants with an Cam-Type Variant alpha angle of >55 had a PGD. Notably, this is the sign In a systematic review published in 2015, the prevalence of most strongly associated with hip pain.22 cam-type FAI in asymptomatic participants was reported Therefore, we consider PGD, along with the alpha angle, as 23.1%.11 Another systematic review evaluating asymp- as the most important radiographic sign for the screening of tomatic participants reported a prevalence of 22.4%,27 and cam-type FAI. Nonetheless, comparative studies with 2 other studies reported a prevalence between 27% and symptomatic and asymptomatic participants are needed 29%.33,45 Their results are very similar to ours (29.7%). to truly determine the screening or diagnostic value of Regarding sex and age, our study supports previous find- these variables. Another study found the prevalence of ings of a greater prevalence in male patients.18,25,41 Differ- these signs to be very similar to our findings (PGD: 21.5% ences in the prevalence of the cam-type variant within age in men and 3.3% in women; FPFN: 10.3% in men and 2.6% groups have not been widely studied. Some findings in ado- in women; and LFFH: 14.4% in men and 6.2% in women), lescent and young adult cohorts have demonstrated although they did not perform a subgroup analysis by increasing prevalence with older age until full skeletal age.11 A previous study reported that the NSA decreases development.20,37,44,48,49 However, the majority of the par- with age, causing an increase in the prevalence of coxa ticipants in these studies maintained constant physical vara; its values were also lower in female patients.6 These activity. In another study in an elderly population, the results are consistent with ours, in which a significant prevalence was reported to be 5%, however those authors increase in the prevalence of coxa vara was found with could have had a different definition of the variant than the increasing age, for both male and female hips. The Orthopaedic Journal of Sports Medicine Prevalence of FAI Variations by Age and Sex 9 Pincer-Type Variant determined the minimum number of participants required with appropriate methodology to ensure internal validity, A recent systematic review reported that approximately which was reinforced by intraobserver and interobserver two-thirds of asymptomatic patients have morphological reliability and by high external validity from our rigorous characteristics of pincer-type FAI on imaging.11 This high selection criteria. prevalence may be inaccurate to some extent because the The main limitation of our study was that the data were morphological characteristics were poorly defined among obtained from plain radiographs, and we used only 1 pro- the studies and the accuracy of the radiographic markers jection, which might not have been sensitive enough to and imaging tools were also questionable.46 These factors detect all FAI-related morphological abnormalities. could explain the majority of the variability across studies Although radiographs were taken according to a standard- that have evaluated the prevalence of this variant. Other ized protocol, there was some degree of variation as a result studies have reported a prevalence of 15.2% and 27% for of individual technique. This variability was minimized male patients and 19.4% and 21% for female patients,1,14 with the standardized technique being performed at a sin- which is similar to the results obtained in the current study gle institution. We recognize that an important limitation (27.9% for male hips, 16.6% for female hips) probably of the study was the determination of the cam-type variant because of the similar selection criteria. on AP pelvic radiographs, as it has been established by Pincer-type FAI has been reported as being more com- previous studies that the most sensitive radiographic pro- mon among middle-aged active women.38 In contrast, some jection for this deformity is the 45 Dunn view. other studies have not found differences between Our study has some further limitations. We only sexes.4,26,34 A study by Laborie et al23 reported a higher included Hispanic people; therefore, the external validity prevalence of this variant in men versus women (34% vs of our study is limited to this population, and further stud- 17%, respectively). Therefore, uncertainty remains regard- ies in other ethnic groups are required to confirm our find- ing sex-based differences. ings. Moreover, this was a noncontrolled retrospective and Our study suggests that the prevalence of this variant descriptive study. This renders impossible a true analysis increases with age in both male and female patients. This has of the diagnostic value of the variants and signs analyzed or been similarly reported by Li et al26 in a population aged a correlation of our findings with the symptoms and per- between 12 and 19 years. However, we cannot further com- sonal history of participants. pare our findings because the other 2 studies that made this Another limitation was that we classified a patient as comparison were performed in a young population.11,30 asymptomatic based on a retrospective analysis of the Regarding radiographic signs of pincer-type FAI, we found interview and physical examination performed in the past; that COS was the most prevalent (17.0% in the overall popu- although the majority of clinical evaluations were carried lation and 70.2% in hips with the pincer variant). In a 2016 out by one of the authors (R.M.-A.), this did not happen in systematic review,27 the COS was positive in 28.5% of the all cases. In all cases, the symptoms taken into account asymptomatic participants, and other studies have reported were pain and functional limitations, and an exploration a prevalence of 30%, 24.6%, 20%, and 18.5% in White Amer- of provocation maneuvers specific to FAI were not per- ican, Indian, Korean, and Brazilian populations, formed in all cases. Finally, this was a cross-sectional respectively.1,2,36,54 Additionally, 1 recent study determined study, and suggestions of time-dependent changes in the that the COS was well-correlated with findings obtained by prevalence of the studied variables need to be compared MRI and with other radiographic findings commonly associ- with further findings of longitudinal studies. ated with pincer-type FAI.57 In contrast, other studies have not found significant correlations between this radiographic sign and acetabular retroversion or chondral degeneration. CONCLUSION The PWS and EAC have not been thoroughly studied and seem to be less prevalent than the COS. In this regard, a We demonstrated by radiographic findings that the char- previous study reported similar findings to ours, as the acteristics suggestive of FAI, both the cam and pincer var- authors found a higher prevalence of os acetabuli in male iants, were common in a population of healthy young patients, although they did not perform an age subanalysis.6 adults, especially in men, with a high degree of coexistence Regarding the AI as another marker for acetabular over- between most of the findings. As the available literature on coverage, Lepage-Saucier et al24 reported a mean AI of 6 the cause of FAI suggests that it is multifactorial, we without sex-based differences, Chakraverty et al4 found a believe that these findings may reflect anatomic variations mean AI of 4.4 in young asymptomatic men and women, rather than true pathological abnormalities. This is the and Mineta et al29 reported lower AI values in men older first study to determine the true prevalence of cam and than 40 years. In our study, we identified the same pattern pincer variants as well as their more commonly associated as Mineta et al and the differences were significant. radiographic signs distributed by sex and age. The findings contribute to the increasing knowledge on the prevalence of Strengths and Limitations cam and pincer FAI according to sex and age, demonstrat- ing that they can exist in an asymptomatic population. This Our study was strengthened by the large sample size of will help clinicians correlate the radiographic findings and hips from an asymptomatic population, which was based demographic data of the patient within the context of pain on an a priori power sample calculation. Thus, we and limitations in the hip. 10 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine ACKNOWLEDGMENT 17. 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APPENDIX TABLE A1 Prevalence of Cam and Pincer Variants in Different Studies of Asymptomatic Populationsa Morphology Definitions Prevalence, % Lead Author Study Type No. of M:F (Year) (LOE) Patients/Hips Sexb Age,c y Diagnosis Cam Pincer Imagingd Cam Pincer 5 Clohisy (2007) Retrospective 24 hips 54%:46% 35 (18-49) Back and leg pain on FHS, FHNO, NA 1. Frog-leg 21 NA physical alpha angle lateral examination (cutoff point view not 2. AP pelvic specified) view 3. Cross- table lateral view Hack15 (2010) Prospective 200 patients 89:111 29.4 (24.1- Asymptomatic by Alpha angle NA MRI 53 NA (400 hips) 50.6) physical >50.5 examination of hips and impact test with patient supine (continued) 12 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine TABLE A1 (continued) Morphology Definitions Prevalence, % Lead Author Study Type No. of M:F (Year) (LOE) Patients/Hips Sexb Age,c y Diagnosis Cam Pincer Imagingd Cam Pincer 19  Kang (2010) Prospective 50 patients 23:27 15-40 Asymptomatic by Alpha angle AVA <15 , COS, CT 10 (alpha angle), 16 (4) (100 hips) clinical interview >55 , LCEA >40 12 (FHNO) and medical history FHNO <8 review mm, FHS Pollard41 Prospective 83 patients 39:44 M: 47.5; F: Asymptomatic by Alpha angle NA 1. AP pelvic 12.04 NA (2010) (166 hips) 44.4 clinical interview, >50 , view review of medical FHNO <14 2. Cross- records, and mm table physical lateral examination view Reichenbach45 Prospective 244 patients 244:0 19.9 ± 0.7 Asymptomatic by self- FHNO (grade 2 NA MRI 24 NA (2010) (only 1 hip reported and 3), per patient questionnaire and alpha angle examined) physical examination Jung18 (2011) Retrospective 380 patients 108:272 M: 62.5; F: Asymptomatic by M: alpha angle NA CT 7.89 NA (760 hips) 59.5 physical >83 ; F: examination alpha angle >57 Laborie 23 Prospective 2060 patients 868:1192 18.6 ± 0.6 Asymptomatic by PGD, FPFN, EAC, COS, PWS 1. AP pelvic M: 35.1; F: 10.2 M: 34.3; F: 16.6 (2011) (4120 hips) (17.2- physical LFFH view 20.1) examination and 2. Frog-leg review of lateral radiographs view Ranawat43 Prospective 100 patients 44:56 34.6 ± 11.3 Unilateral symptomatic FHS, FHNO, COS, PWS, ISS, 1 AP pelvic 21.5 18.5 (2011) (200 hips) FAI on alpha angle, IIL-AF, etc view questionnaire and NSA, etc 2. Cross- physical table examination lateral view Silvis50 (2011) Prospective (3) 39 patients (78 39:0 ND Asymptomatic by Alpha angle NA MRI 39 NA hips) physical >50 examination, questionnaire, and clinical interview 28 Miguel Retrospective 100 patients 42%:58% 31 Asymptomatic by FHS, alpha LCEA, AI, AVA 1. AP pelvic 3 (presence of ND (2012) review of angle (cutoff (cutoff point view bump on AP radiographs and point not not specified) 2. 45 Dunn pelvic view), 24 medical records and specified) view (presence of physical 3. Ducroquet bump on 45 examination view Dunn view) 4. Lequesne false profile view 51 Sutter (2012) Retrospective 53 patients 31:22 34.5 (20-50) Asymptomatic by Alpha angle NA MRI 53 NA (106 hips) clinical interview >55 and physical examination de Bruin6 Retrospective 262 patients 100:162 20-56 Asymptomatic by PGD, FHFNR, LCEA >39 , AI AP pelvic Total: 7.7; M: 15.6; Total: 63.2; M: (2013) (522 hips) questionnaire and NSA <125 <0 , CP, view F: 2.8 44.2; F: 74.9 physical protrusio examination acetabuli, os acetabuli, herniation pit 17 Joo (2013) Retrospective 497 patients 186:311 M: 50.02 (19- Asymptomatic by M: alpha angle NA MRI M: 0.5 (alpha angle NA (994 hips) 96); F: review of medical 83 ; F: 83 ); F: 3.1 58.19 (18- records alpha angle (alpha angle 86) 57 57 ) Leunig25 Cross- 80 patients 0:80 19.3 (18-99) Asymptomatic by FHNO (grade 2 Depth of MRI 22 (grade 1) 10 (depth of (2013) sectional questionnaire and and 3) acetabulum acetabulum), measurement of hip <3 mm, 97 (labral internal rotation labral lesions lesions) 30 Monazzam Retrospective 225 patients 103:122 10.4 (2-19) Asymptomatic by Alpha angle LCEA >40 , TA CT M: 10.2; F: 2.5 M: 12.1; F: 9.4 (2013) (244 F hips, review of medical >50 and <0 206 M hips) records >55 Nepple34 Retrospective 33 hips 32%:68% 30.5 (13.7- Asymptomatic by NA CP, LCEA >40 , AP pelvic NA 76 (2013) (3) 50.9) physical AI <0 view examination and medical history (continued) The Orthopaedic Journal of Sports Medicine Prevalence of FAI Variations by Age and Sex 13 TABLE A1 (continued) Morphology Definitions Prevalence, % Lead Author Study Type No. of M:F (Year) (LOE) Patients/Hips Sexb Age,c y Diagnosis Cam Pincer Imagingd Cam Pincer Chakraverty 4 Retrospective 50 patients 30:20 30.8 ± 6.1 Asymptomatic by Alpha angle  AVA <15 , AI CT M: 60.0; F: 26.7 M: 36.7; F: 42.5 (2013) (100 hips) (20-40) review of >55 , <0 , COS, radiographs and FHNO <8 LCEA >40 , medical records mm, PGD PWS Khanna21 Prospective 170 patients 77:93 29.5 (25.7- Asymptomatic by Alpha angle NA MRI 11.6 (alpha angle NA (2014) (318 hips) 54.5) physical >55 and >55 ), 9.4 examination without >60 (alpha angle history of hip or >60 ) groin pain Scheidt47 Prospective 82 patients 28:54 50.4 (40-60) Asymptomatic by Alpha angle LCEA >40 , AI 1. AP pelvic 25 12.65 (2014) (164 hips) clinical interview >50 , NSA <0 , COS, view and physical <125 ISS, PWS 2. 45 Dunn examination view of both hips 3. Lequesne view Diesel9 (2015) Prospective 184 patients 91:93 Total: 20-60; Asymptomatic without Alpha angle LCEA >40 , AI 1. AP pelvic 18.92 18.5 (COS), 2.4 M: 29 history of hip pain or >55 <0 , COS view (LCEA), 27.6 (26.5- orthopaedic disease 2. 45 Dunn (AI) 41.5); F: view 44 (28- 52) Kim22 (2015) Retrospective 430 patients 292:181 M: 31; F: 34 Asymptomatic by Alpha angle AVA <15 , CT M: 20.2 (alpha M: 31.2 (AVA); (473 hips) review of medical >55 , LCEA >40 angle); F: 14.4 F: 22.1 records FHNO <8 (alpha angle); (AVA); M: mm M: 11.3 28.4 (LCEA); (FHNO); F: 8.3 F: 23.8 (FHNO) (LCEA) Li26 (2017) Retrospective 558 patients 276:282 14.4 (10-18) Asymptomatic by Alpha angle LCEA >40 CT Total: 16.8; M: Total: 32.4; M: (3) (1116 hips) review of medical >55 23.9; F: 9.9 29.7; F: 35.1 records Nardo33 (2015) Retrospective 4140 patients 4140:0 77 ± 5 Asymptomatic by Impingement LCEA >40 AP pelvic 29 57 (3) (8151 hips) physical angle <40 , view examination NSA <125 Van Houcke54 Prospective 201 patients 105:96 ND Asymptomatic by Alpha angle AVA <15 , COS, CT 24 (Chinese), 40 32 (Chinese), 16 (2015) (402 hips) clinical history and >55 , ISS, TA <5 , (White) (White) physical anterior LCEA >45 examination offset ratio <0.13, NSA <125 Ahn1 (2016) Prospective 200 patients 146:254 34.7 (21-49) Asymptomatic by Alpha angle COS, LCEA 1. AP pelvic Total: 38; M: 57; F: Total: 23; M: 27; (400 hips) clinical interview, >55 >40 , PWS view 26 F: 21 physical 2. Sugioka examination, and view review of medical 3. 45 Dunn records view of both hips Mineta29 Retrospective 600 hips 352:248 58.2 (20-89) Asymptomatic by Alpha angle LCEA >40 , CT Total: 45.3; M: Total: 37.4; M: (2016) review of >55 , COS, AI <0 54.4; F: 32.3 41.7; F: 31.3 radiographs FHNO ratio <0.15 Yepez58 (2017) Prospective 56 patients 56:0 15.3 (13-18) Asymptomatic by Alpha angle LCEA >40 , AI MRI 77.7 10.7 (112 hips) physical >55 , <0 examination, FHNO <7 presence of current mm symptoms, and review of medical records Monckeberg31 Prospective 142 patients 142:0 Group 1: Asymptomatic by Alpha angle COS, LCEA AP pelvic 47.2 (immature 41.6 (immature (2017) (72 without 15.4 ± 0.8 clinical interview >55 , >40 view group), 48.5 group), 51.4 skeletal (12-16); and review of FHNO <8 (mature group) (mature maturity, group 2: medical history mm group) 70 with 24.0 ± 3.3 skeletal (19-36) maturity) (continued) 14 Morales-Avalos et al The Orthopaedic Journal of Sports Medicine TABLE A1 (continued) Morphology Definitions Prevalence, % Lead Author Study Type No. of M:F (Year) (LOE) Patients/Hips Sexb Age,c y Diagnosis Cam Pincer Imagingd Cam Pincer 53 Thier (2017) Retrospective 110 patients 60:50 56 (18–100); Asymptomatic by Alpha angle COS, LCEA 1. AP pelvic 43 13 (114 hips) ± 22.4 clinical interview >55 , >40 view and review of FHNO 2. Cross- medical history <0.18 table lateral view Pachore36 Prospective 452 patients 282:170 29.9 ± 6.06 Asymptomatic by Alpha angle LCEA >40 , AI AP pelvic 6.6 (alpha angle), 24.6 (COS), 22.4 (2018) (904 hips) physical >55 , PGD <0 , COS, view 2.9 (PGD) (ISS), 17.5 examination ISS, PWS (LCEA), 13.4 (AI) Polat40 (2018) Retrospective 1076 patients 474:602 Total: 42.1 ± Asymptomatic by Alpha angle LCEA >40 , TA 1. AP pelvic 15.9 10.6 (2152 hips) 15.6 (18- telephone >55 <0 , COS view 65); M: questionnaire 2. Frog-leg 39.1 ± lateral 15.3; F: view 44.5 ± 15.4 Current study Retrospective 939 patients 1280:598 Total: 31.0 ± Asymptomatic by Alpha angle LCEA >40 , TA AP pelvic Total: 29.7; M: Total: 24.3; M: (3) (1878 hips) 9.2 (18- review of >55 , PGD, <0 , COS, view 34.7; F: 19.1 27.9; F: 16.6 50); M: radiographs and FHFNR PWS, EAC 32.3 ± medical records <1.27, 10.4; F: FPFN, 28.6 ± LFFH, NSA 14.4 <125 a In some studies, both symptomatic and asymptomatic participants were used, and for this table, only the sample size and prevalence of the asymptomatic patients were considered. AI, acetabular index; AP, anteroposterior; AVA, acetabular version angle; COS, crossover sign; CP, coxa profunda; CT, computed tomography; EAC, excessive acetabular coverage; F, female; FAI, femoroacetabular impingement; FHFNR, femoral head–to–femoral neck ratio; FHNO, femoral head-neck offset; FHS, femoral head sphericity; FPFN, focal prominence of the femoral neck; HP, herniation pit; IIL-AF, distance from the ilioischial line to the acetabular fossa; ISS, ischial spine sign; LCEA, lateral center-edge angle; LFFH, lateral flattening of the femoral head; LOE, level of evidence; M, male; MRI, magnetic resonance imaging; NA, not applicable; ND, no data; NSA, neck-shaft angle; PA, Protusio acetabulli; PGD, pistol-grip deformity; PWS, posterior wall sign; TA, Tönnis angle. b Data are reported as n or %. c Data are reported as mean, mean (range), mean ± SD, mean ± SD (range), or range. d Radiographs are indicated by view.