Prevalence of Radiographic Findings Thought to Be Associated with Femoroacetabular Impingement in a Population-based Cohort of 2081 Healthy Young Adults

Published Online:

Overall, radiographic features suggestive of femoroacetabular impingement, both cam and pincer type, are quite common in a population of healthy young adults, especially in males, with a high degree of coexistence among most findings.


To report the prevalence of qualitative radiographic findings for femoroacetabular impingement (FAI) and associations among them and to characterize the inter- and intraobserver variability of these interpretations.

Materials and Methods

This study is part of an institutional review board–approved population-based prospective follow-up of 2081 of 4006 (participation rate, 51.9%) young adults (874 [42.0%] male participants, 1207 [58.0%] female participants; mean age, 18.6 years) who took part in a randomized hip trial on developmental dysplasia of the hip. All participants gave informed consent. Two pelvic radiographs were obtained. Pistol-grip deformity, focal femoral neck prominence, and flattening of the lateral head, all suggestive of cam-type impingement, and the posterior wall sign, excessive acetabular coverage, and crossover sign, all suggestive of pincer-type impingement, were assessed subjectively by an experienced radiologist. To assess inter- and intraobserver agreement, images from 350 examinations were read independently twice by two observers.


Cam-type deformities were seen in 868 male and 1192 female participants, respectively, as follows: pistol-grip deformity, 187 (21.5%) and 39 (3.3%); focal femoral neck prominence, 89 (10.3%) and 31 (2.6%); and flattening of the lateral femoral head, 125 (14.4%) and 74 (6.2%). Pincer-type deformities were seen in the same numbers of male and female participants, respectively, as follows: posterior wall sign, 203 (23.4%) and 131 (11.0%); and excessive acetabular coverage, 127 (14.6%) and 58 (4.9%) (all P < .001, according to sex distribution). The crossover sign was seen in 446 (51.4%) and 542 (45.5%) of the male and female participants, respectively (P = .004). There was a high degree of coexistence (odds ratio [OR] > 2) among most FAI findings. Interobserver agreement was good to very good (κ = 0.74–0.84) in rating cam- and pincer-type findings. Intraobserver agreement was moderate or good (κ = 0.49–0.80) for all findings for both observers.


Overall, radiographic FAI findings are quite common in a population of healthy young adults, especially in males, with a high degree of coexistence among most findings (OR > 2).

© RSNA, 2011


  • 1 Bardakos NV, Villar RN. Predictors of progression of osteoarthritis in femoroacetabular impingement: a radiological study with a minimum of ten years follow-up. J Bone Joint Surg Br 2009;91(2):162–169. Crossref, MedlineGoogle Scholar
  • 2 Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:112–120. MedlineGoogle Scholar
  • 3 Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res 2008;466(2):264–272. Crossref, MedlineGoogle Scholar
  • 4 Leunig M, Ganz R. Femoroacetabular impingement: a common cause of hip complaints leading to arthrosis. [in German]. Unfallchirurg 2005;108(1):9–10, 12–17. Crossref, MedlineGoogle Scholar
  • 5 Ito K, Leunig M, Ganz R. Histopathologic features of the acetabular labrum in femoroacetabular impingement. Clin Orthop Relat Res 2004;(429):262–271. Crossref, MedlineGoogle Scholar
  • 6 Ganz R, Gill TJ, Gautier E, Ganz K, Krügel N, Berlemann U. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83(8):1119–1124. Crossref, MedlineGoogle Scholar
  • 7 Burnett RS, Della Rocca GJ, Prather H, Curry M, Maloney WJ, Clohisy JC. Clinical presentation of patients with tears of the acetabular labrum. J Bone Joint Surg Am 2006;88(7):1448–1457. Crossref, MedlineGoogle Scholar
  • 8 Espinosa N, Beck M, Rothenfluh DA, Ganz R, Leunig M. Treatment of femoro-acetabular impingement: preliminary results of labral refixation—surgical technique. J Bone Joint Surg Am 2007;89(suppl 2 pt 1):36–53. Crossref, MedlineGoogle Scholar
  • 9 Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis—what the radiologist should know [in Spanish]. Radiologia 2008;50(4):271–284. Crossref, MedlineGoogle Scholar
  • 10 Leunig M, Beck M, Kalhor M, Kim YJ, Werlen S, Ganz R. Fibrocystic changes at anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement. Radiology 2005;236(1):237–246. LinkGoogle Scholar
  • 11 Pitt MJ, Graham AR, Shipman JH, Birkby W. Herniation pit of the femoral neck. AJR Am J Roentgenol 1982;138(6):1115–1121. Crossref, MedlineGoogle Scholar
  • 12 Rosendahl K, Markestad T, Lie RT. Ultrasound screening for developmental dysplasia of the hip in the neonate: the effect on treatment rate and prevalence of late cases. Pediatrics 1994;94(1):47–52. MedlineGoogle Scholar
  • 13 Tönnis D. Normal values of the hip joint for the evaluation of x-rays in children and adults. Clin Orthop Relat Res 1976;(119):39–47. MedlineGoogle Scholar
  • 14 Ito K, Minka MA, Leunig M, Werlen S, Ganz R. Femoroacetabular impingement and the cam-effect: a MRI-based quantitative anatomical study of the femoral head-neck offset. J Bone Joint Surg Br 2001;83(2):171–176. Crossref, MedlineGoogle Scholar
  • 15 Nötzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002;84(4):556–560. Crossref, MedlineGoogle Scholar
  • 16 Stulberg SD, Cordell LD, Harris WH, Ramsey PL, MacEwen GD. Unrecognized childhood hip disease: a major cause of idiopathic osteoarthitis of the hip. In: The hip. Proceedings of the third meeting of the Hip Society. St Louis, Mo: Mosby, 1975; 212–218. Google Scholar
  • 17 Jamali AA, Mladenov K, Meyer DC, et al.. Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the “cross-over-sign.” J Orthop Res 2007;25(6):758–765. Crossref, MedlineGoogle Scholar
  • 18 Parvizi J, Leunig M, Ganz R. Femoroacetabular impingement. J Am Acad Orthop Surg 2007;15(9):561–570. Crossref, MedlineGoogle Scholar
  • 19 Reynolds D, Lucas J, Klaue K. Retroversion of the acetabulum: a cause of hip pain. J Bone Joint Surg Br 1999;81(2):281–288. Crossref, MedlineGoogle Scholar
  • 20 Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33(1):159–174. Crossref, MedlineGoogle Scholar
  • 21 Siebenrock KA, Kalbermatten DF, Ganz R. Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers. Clin Orthop Relat Res 2003;(407):241–248. Crossref, MedlineGoogle Scholar
  • 22 Beck M, Kalhor M, Leunig M, Ganz R. Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br 2005;87(7):1012–1018. Crossref, MedlineGoogle Scholar
  • 23 Gosvig KK, Jacobsen S, Sonne-Holm S, Palm H, Troelsen A. Prevalence of malformations of the hip joint and their relationship to sex, groin pain, and risk of osteoarthritis: a population-based survey. J Bone Joint Surg Am 2010;92(5):1162–1169. Crossref, MedlineGoogle Scholar
  • 24 Reichenbach S, Jüni P, Werlen S, et al.. Prevalence of cam-type deformity on hip magnetic resonance imaging in young males: a cross-sectional study. Arthritis Care Res (Hoboken) 2010;62(9):1319–1327. Crossref, MedlineGoogle Scholar
  • 25 Clohisy JC, Carlisle JC, Beaulé PE, et al.. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am 2008;90(Suppl 4):47–66. Crossref, MedlineGoogle Scholar
  • 26 Giori NJ, Trousdale RT. Acetabular retroversion is associated with osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:263–269. MedlineGoogle Scholar
  • 27 Tannast M, Murphy SB, Langlotz F, Anderson SE, Siebenrock KA. Estimation of pelvic tilt on anteroposterior x-rays: a comparison of six parameters. Skeletal Radiol 2006;35(3):149–155. Crossref, MedlineGoogle Scholar
  • 28 Tannast M, Zheng G, Anderegg C, et al.. Tilt and rotation correction of acetabular version on pelvic radiographs. Clin Orthop Relat Res 2005;438:182–190. Crossref, MedlineGoogle Scholar
  • 29 Kalberer F, Sierra RJ, Madan SS, Ganz R, Leunig M. Ischial spine projection into the pelvis: a new sign for acetabular retroversion. Clin Orthop Relat Res 2008;466(3):677–683. Crossref, MedlineGoogle Scholar
  • 30 Kakaty DK, Fischer AF, Hosalkar HS, Siebenrock KA, Tannast M. The ischial spine sign: does pelvic tilt and rotation matter? Clin Orthop Relat Res 2010;468(3):769–774. Crossref, MedlineGoogle Scholar
  • 31 Cobb J, Logishetty K, Davda K, Iranpour F. Cams and pincer impingement are distinct, not mixed: the acetabular pathomorphology of femoroacetabular impingement. Clin Orthop Relat Res 2010;468(8):2143–2151. Crossref, MedlineGoogle Scholar
  • 32 Kim JA, Park JS, Jin W, Ryu K. Herniation pits in the femoral neck: a radiographic indicator of femoroacetabular impingement? Skeletal Radiol 2011;40(2):167–172. Crossref, MedlineGoogle Scholar
  • 33 Kappe T, Kocak T, Neuerburg C, Lippacher S, Bieger R, Reichel H. Reliability of radiographic signs for acetabular retroversion. Int Orthop PMID 20455060. Published May 10, 2010. Accessed August 12, 2010. Google Scholar
  • 34 Clohisy JC, Carlisle JC, Trousdale R, et al.. Radiographic evaluation of the hip has limited reliability. Clin Orthop Relat Res 2009;467(3):666–675. Crossref, MedlineGoogle Scholar
  • 35 Troelsen A, Jacobsen S, Rømer L, Søballe K. Weightbearing anteroposterior pelvic radiographs are recommended in DDH assessment. Clin Orthop Relat Res 2008;466(4):813–819. Crossref, MedlineGoogle Scholar
  • 36 Meyer DC, Beck M, Ellis T, Ganz R, Leunig M. Comparison of six radiographic projections to assess femoral head/neck asphericity. Clin Orthop Relat Res 2006;445:181–185. Crossref, MedlineGoogle Scholar
  • 37 Clohisy JC, Nunley RM, Otto RJ, Schoenecker PL. The frog-leg lateral radiograph accurately visualized hip cam impingement abnormalities. Clin Orthop Relat Res 2007;462:115–121. Crossref, MedlineGoogle Scholar
  • 38 Lohan DG, Seeger LL, Motamedi K, Hame S, Sayre J. Cam-type femoral-acetabular impingement: is the alpha angle the best MR arthrography has to offer? Skeletal Radiol 2009;38(9):855–862. Crossref, MedlineGoogle Scholar
  • 39 Gosvig KK, Jacobsen S, Palm H, Sonne-Holm S, Magnusson E. A new radiological index for assessing asphericity of the femoral head in cam impingement. J Bone Joint Surg Br 2007;89(10):1309–1316. Crossref, MedlineGoogle Scholar

Article History

Received December 14, 2010; revision requested January 19, 2011; final revision received March 25; accepted April 4; final version accepted April 6.
Published online: Aug 2011
Published in print: Aug 2011