Femoral Antetorsion: Comparing Asymptomatic Volunteers and Patients with Femoroacetabular Impingement
To assess the range of femoral antetorsion with magnetic resonance (MR) imaging in asymptomatic volunteers and patients with different subtypes of femoroacetabular impingement (FAI) because abnormal femoral antetorsion might be a contributing factor in the development of FAI.
Materials and Methods
This study was institutional review board approved; all individuals provided signed informed consent. Sixty-three asymptomatic volunteers and 63 patients with symptomatic FAI between age 20 and 50 years were matched for age and sex. They underwent standard MR imaging with two additional rapid transverse sequences over the proximal and distal femur for antetorsion measurement. Twenty volunteers underwent a second MR imaging examination in the same leg. Two readers independently measured femoral antetorsion. The time for the additional sequences was tabulated. Interobserver agreement was calculated; differences in antetorsion were assessed by using analysis of variance and the unpaired t test.
Femoral antetorsion can be assessed with MR imaging in about 80 seconds, with high interobserver agreement (intraclass correlation coefficient [ICC] = 0.967) and high agreement between different MR examinations (ICC = 0.966). Women had a significantly larger antetorsion than men (P < .001 for both readers), and antetorsion of the left femur was significantly larger than that of the right femur (P = .01 for reader 1, P = .02 for reader 2). Overall, antetorsion was similar in volunteers and in patients for reader 1 (12.7° ± 10.0 [standard deviation] vs 12.6° ± 9.8, respectively; P = .9) and reader 2 (12.8° ± 10.1 vs 13.5° ± 9.8, respectively; P = .7). Femoral antetorsion was significantly higher in patients with pincer-type FAI than in those with cam-type FAI for reader 1 (18.3° ± 9.8 vs 10.0° ± 9.1, P = .02) and reader 2 (18.7° ± 10.5 vs 11.6° ± 8.8, P = .04).
Femoral antetorsion can be measured rapidly and with good reproducibility with MR imaging. Patients with pincer-type FAI had a significantly larger femoral antetorsion than patients with cam-type FAI.
© RSNA, 2012
Femoroacetabular impingement (FAI) is thought to be a major cause for the development of early-onset osteoarthritis of the hip (1,2). FAI is divided into cam-type hips with abnormal morphology of the femoral head-neck junction, pincer-type hips with focal or general overcoverage of the acetabulum, and mixed-type FAI with both cam- and pincer-type features (3,4). Cam-type deformities can be depicted on radiographs and magnetic resonance (MR) images, and the osseous changes associated with pincer-type FAI are usually depicted on radiographs (3,5,6). FAI typically becomes symptomatic in early adult age, with most patients being between 20 and 50 years old (2).
Cam-type FAI reduces internal rotation of the hip and results in increased mechanical impact during internal rotation (2). Reduced femoral antetorsion also impairs the internal rotation of the hip (Fig 1) and thus may lead to increased mechanical impact during hip internal rotation (7,8). There are some adolescent patients with typical clinical signs of FAI and reduced femoral antetorsion but without radiologic findings of FAI; these patients are treated with subtrochanteric rotational osteotomy, on the basis of mechanical considerations (7,9). To date, the role of abnormal antetorsion in the development of FAI remains unclear.
Measurement of femoral antetorsion has been validated for MR imaging and is a reliable alternative compared with computed tomography (CT) as a reference standard (10,11). Because the performance of CT is generally much faster than that of MR imaging, evaluation by using CT is often preferred, even though this means exposing young patients to radiation (9).
In short, abnormal femoral antetorsion might be a contributing factor in the development of FAI. The purpose of our study was to assess the range of femoral antetorsion with MR imaging in asymptomatic volunteers and in patients with different subtypes of FAI.
Materials and Methods
Volunteers and Patients
This study was approved by the institutional review board. All individuals who participated in the study provided signed informed consent.
Sixty-three asymptomatic volunteers were prospectively included in our study. Volunteers were included if they were asymptomatic (no symptoms, unremarkable medical history regarding the hip joint, negative result for impingement test, and an internal hip rotation >25° at clinical examination by R.S. [6 years of experience]) and were between 20 and 50 years old. Volunteers were excluded from the study if they were pregnant or reported prior trauma to the hip, hip problems in infancy or childhood, or symptoms or pain of the hip or groin. Recruiting was structured according to sex to attain a volunteer group consisting of almost an equal number of male and female individuals. All volunteers underwent unenhanced MR imaging of the hip on the same day they were clinically examined. In addition, 20 volunteers (32%) underwent a second unenhanced MR examination in the same leg on a different day to assess the influence of patient positioning on the measurements of femoral antetorsion.
All patients were clinically examined by one of three staff hip surgeons (P.O.Z.) from our hospital. The inclusion criteria for the patient group were met if (a) typical symptoms (persistent groin pain for more than 3 months) and clinical signs (positive result for impingement test and internal hip rotation < 20°) of FAI were present and (b) the patient was between 20 and 50 years old. Patients were excluded if they did not give informed consent. Of 153 consecutive patients who were referred for MR arthrography of the hip within a period of 6 months by the orthopedic surgery department of our hospital, 46 patients had to be excluded because they were younger than 20 years or older than 50 years. Thirty-six patients were excluded because they did not have clinical signs and symptoms of FAI. Three patients did not provide signed informed consent. During the last phase of patient selection, five male patients were excluded to attain a patient group consisting of almost an equal number of male and female individuals. Thus, from the patients aged 20–50 years, a total of 44 patients were excluded, resulting in a patient group of 63 patients.
Patients were further classified into three subgroups: For this purpose, cam-type deformities were assessed on MR images, and pincer-type findings (acetabular retroversion or coxa profunda) were assessed on supine anteroposterior radiographs of the pelvis by one reader (R.S.) in a separate readout session at least 2 months apart from the main readout to avoid recollection bias (3,12). Cam-type deformities at the femoral head-neck junction were defined as an α angle greater than 55° at any location around the femoral neck (3). Acetabular retroversion was defined as either a positive crossover sign (6,13), a positive posterior wall sign (13), or a positive ischial spine sign (14). Coxa profunda was diagnosed if the floor of the acetabular fossa touched or overlapped the ilioischial line medially (15,16). If patients showed either a cam-type or a pincer-type deformity, they were included in the corresponding subgroup. If both cam- and pincer-type findings were present in patients, they were included in the mixed-type FAI subgroup.
At our institution, all clinical patients suspected of having FAI undergo MR arthrography. A radiologist injected intraarticular contrast material in a standardized fashion in all patients. One milliliter of a local anesthetic (lidocaine hydrochloride 2%, Rapidocain; Sintetica, Mendrisio, Switzerland), 1 mL of an iodinated contrast agent (iopamidol 200 mg/mL, Iopamiro 200; Bracco, Milan, Italy), and 8–10 mL of a diluted MR contrast agent (gadopentetate dimeglumine, Magnevist; Bayer Healthcare, Berlin, Germany) at a concentration of 2 mmol/L were injected with fluoroscopic guidance. The interval between the contrast material injection and MR imaging was less than 15 minutes. Volunteers underwent unenhanced MR imaging of the hip by using the same MR protocol.
MR imaging was performed with a 1.5-T system (Magnetom Avanto; Siemens Medical Solutions, Erlangen, Germany); Syngo MR B17 software was used (Siemens Medical Solutions). A body matrix phased-array surface coil (which was placed over the hip of the patient) and a spine matrix coil (which was integrated in the patient table) were used for imaging of the hip, and the spine matrix coil was also used for imaging of the distal femur for the assessment of femoral antetorsion. Patients were placed in the supine position on the MR examination table; special attention was given to symmetric positioning of the pelvis and lower extremities. No knee flexion was allowed. As part of the routine MR protocol, a three-dimensional data set was obtained with a transverse oblique (parallel to the femoral neck axis) water-excitation true fast imaging with steady-state precession gradient-echo sequence (repetition time msec/echo time msec, 12.3/5.45; section thickness, 1.25 mm; no intersection gap; flip angle, 28°; field of view, 17 cm; matrix, 384 × 384; one signal acquired). The three-dimensional data set was used to reconstruct radial reformations by using the long axis of the femoral neck as a rotation axis. Our routine MR protocol further includes a coronal T1-weighted spin-echo sequence, a coronal intermediate-balanced fast spin-echo sequence with fat saturation, and a sagittal water-excitation three-dimensional double-echo steady-state sequence.
To assess femoral antetorsion, two additional short sequences were performed at the level of the proximal and distal femur: First, a transverse T2-weighted fast spin-echo sequence was performed over the femoral head and neck (700/42; 12 sections; section thickness, 5 mm; intersection gap, 0.5 mm; flip angle, 40°; field of view, 22 cm; matrix, 384 × 192; two signals acquired; echo train length, 14; duration, 19 seconds) (Figs 2, 3). Immediately afterward, a second transverse T2-weighted sequence was performed over the femoral condyles just above the knee joint (700/42; nine sections; section thickness, 5 mm; intersection gap, 0.5 mm; flip angle, 40°; field of view, 22 cm; matrix, 384 × 192; two signals acquired; echo train length, 14; duration, 15 seconds). Between these two short sequences, the examination table was moved, so the region to be examined was positioned in the center of the imager. All individuals were instructed not to move their legs during acquisition, and the feet were immobilized by using MR cushions and fastened with tape to minimize unintentional patient movement. The additional time used for the planning and performance of the two antetorsion sequences at the end of the regular MR examination was measured by the radiologic technologist by using a stop watch.
Two radiologists (R.S., T.J.D.) who were blinded to the clinical data independently analyzed all MR images, after having completed a training session: In this training session, results from 10 patients who were not included in the study were analyzed in consensus. To calculate the antetorsion of the femur, the line of reference in the proximal femur was defined as the line connecting the femoral head center and the center of the femoral neck at its narrowest point (Figs 2, 3). The line of reference in the distal femur was defined as the line connecting the dorsal border of the two femoral condyles. The femoral antetorsion angle was then calculated between the proximal and distal reference line (Fig 2) according to the method described by Tomczak et al (11). Positive values are called femoral antetorsion, and negative values are called femoral retrotorsion.
The analysis was performed on a picture archiving and communication system workstation (ProVision Release 5.0; Cerner, Kansas City, Mo) that allowed measuring and modifying an angle on different images of one series simultaneously; therefore, the readers were able to verify and correct the position of the reference lines on several adjacent sections of the transversal acquisitions.
Radially reformatted images were used to assess the morphology of the head-neck junction circumferentially around the femoral head and neck in the following positions: anteroinferior, anterior, anterosuperior, superior, posterosuperior. These images were used to calculate the α angle. The α angle was measured between the axis of the femoral neck and the line from the center of the femoral head to the point where the distance from the center of the femoral head to the peripheral contour of the femoral head exceeded the radius of the femoral head (17). At every readout session, each reader independently defined on the radial reconstructions the axis of the femoral neck as a line that passed through the center of the femoral head and the center of the femoral neck at its narrowest point. When evaluating the radial images, each reader was allowed to see results from other MR sequences from the same examination for orientation purposes.
Differences in age between volunteers and patients and between subtypes of FAI were assessed by using the two-tailed Mann-Whitney U test, with P less than .05 indicating significant difference. Differences of the number of female and male individuals within each group were assessed by using the χ2 test. Descriptive statistics were used to characterize femoral antetorsion for study subgroups, and means and standard deviations were calculated. Differences in antetorsion between the study subgroups were assessed by using one-way analysis of variance and the unpaired t test. Interobserver agreement was quantified by using the intraclass correlation coefficient (ICC). In the subgroup of volunteers who underwent a second MR examination in the same leg, agreement between the two measurements was quantified with ICC. Correlation between antetorsion and age was analyzed by using a Pearson correlation. All analyses were performed with statistical software (SPSS for Windows, release 17.0; SPSS, Chicago, Ill).
The study population consisted of 63 asymptomatic volunteers (mean age, 34.4 years) and 63 patients with FAI (mean age, 35.3 years). The group of volunteers consisted of 32 men (mean age, 34.3 years; age range, 24–50 years) and 31 women (mean age, 35.2 years; age range, 23–50 years). The group of patients consisted of 34 men (mean age, 35.0 years; age range, 20–50 years) and 29 women (mean age, 36.4 years; age range, 22–50 years). Age was not significantly different between the volunteer group and the patient group (P = .6). The number of male and female individuals within the volunteer group and the patient group was not significantly different (P = .7).
Of 63 patients, 33 (52%) had cam-type FAI, 10 (16%) had pincer-type FAI, and 20 (32%) had mixed-type FAI. Mean age was 36.1 years for cam-type FAI, 33.4 years for pincer-type FAI, and 34.9 years for mixed-type FAI. There were no statistically significant differences in age between subtypes of FAI (P = .5).
The additional time used to plan and perform the two antetorsion MR sequences at the level of the proximal and distal femur was 81.3 seconds ± 11.7 (range, 63–106 seconds). There was high agreement between both readers for measurements of femoral antetorsion (Fig 4), with ICC of 0.970 for volunteers (95% confidence interval [CI]: 0.952, 0.982) and 0.964 for patients (95% CI: 0.936, 0.979). ICC for the whole population was 0.967 (95% CI: 0.953, 0.977). There was also high agreement between the measurements of femoral antetorsion for the subgroup of 20 volunteers who underwent two MR examinations in the same leg, with an ICC of 0.966 (95% CI: 0.917, 0.986).
When all FAI subtypes were taken together, femoral antetorsion was similar in asymptomatic volunteers and in patients for both reader 1 (12.7° ± 10.0 vs 12.6° ± 9.8, respectively; P = .9) and reader 2 (12.8° ± 10.1 vs 13.5° ± 9.8, respectively; P = .7). Women had a significantly larger antetorsion than men, both in volunteers and patients (Table 1), and the antetorsion of the left femur was significantly larger than the antetorsion of the right femur, both in volunteers and patients (Table 2).
With increasing age, antetorsion was moderately reduced in asymptomatic volunteers, with a Pearson correlation coefficient of −0.187 for reader 1 and −0.204 for reader 2, but this was not statistically significant (P = .1 for both readers). In the patient group, this effect was not present, with a Pearson correlation coefficient of −0.039 for reader 1 (P = .8) and −0.016 for reader 2 (P = .9).
Mean femoral antetorsion was significantly higher in patients with pincer-type FAI than in those with cam-type FAI for both reader 1 (18.3° ± 9.8 vs 10.0° ± 9.1, P = .02) and reader 2 (18.7° ± 10.5 vs 11.6° ± 8.8, P = .04) (Tables 3, 4; Fig 5). Mean antetorsion was also higher in patients with pincer-type FAI than in the combined subgroup of patients with cam- or mixed-type FAI for both readers; however, this was only statistically significant for reader 1 (P = .045) but not for reader 2 (P = .07). The femoral antetorsion of the three subgroups of patients taken together was statistically significantly different for reader 1 (P = .04) but not for reader 2 (P = .132).
Femoral antetorsion was slightly smaller in individuals with α angles greater than 55° than in the rest of the population, both for volunteers (10.8° ± 9.1 vs 14.0° ± 10.5 for reader 1, 11.7° ± 10.5 vs 14.6° ± 9.5 for reader 2), as well as for patients (12.3° ± 9.4 vs 13.6° ± 11.6 for reader 1, 13.0° ± 9.5 vs 15.8° ± 11.3 for reader 2), but this was not a statistically significant difference for volunteers (P = .2 and P = .3 for reader 1 and 2, respectively) or patients (P = .7 and P = .4).
FAI is characterized by a mechanical impaction between the femoral head and the acetabular rim (2). For the past decade, it has been known that early-onset osteoarthritis of the nondysplastic hip is often caused by FAI (18,19). However, there is still much debate about the cause of FAI and contributing factors leading to FAI: Cam- and pincer-type deformities are identified as causes, but reduced femoral antetorsion impairs internal rotation as well (7,20–22). Because rotational osteotomy is performed in some adolescent patients with typical signs of FAI and reduced femoral antetorsion but none of the radiologic findings of FAI (7,9,23–25), it is possible that abnormal femoral antetorsion plays a role in the development of FAI.
Femoral antetorsion is defined as the angle between the femoral neck and the femoral condyles (11,26). For the antetorsion measurement, the proximal reference line can be drawn on either transverse sections or oblique sections along the femoral neck axis (11,26). The transverse measurement technique was initially used on only a single section at the level of the proximal femur, which is disadvantageous compared with the oblique measurement technique (10,11). However, with the method of measuring and modifying angles on several images of one series simultaneously in modern picture archiving and communication systems, measurements on transverse sections are feasible and correspond to the anatomically correct definition of antetorsion (26).
Some authors use differing techniques for measuring femoral antetorsion: On biplanar radiographs, femoral antetorsion was calculated trigonometrically from the neck-shaft angles measured on anteroposterior and lateral radiographs (27,28). Several antetorsion measurement techniques at CT and MR vary slightly, so one needs to assess which method was utilized when comparing values obtained by different studies (10,11,28,29). Most important, the femoral antetorsion should not be estimated on the basis of imaging of the proximal femur alone but rather on the basis of measurements over the proximal and the distal femur, because it is not possible to determine the exact orientation of the femoral condyles during patient positioning, which will result in incorrect antetorsion angles (28).
It only took around 80 seconds to acquire the MR images needed to measure femoral antetorsion in our study. There was a high level of observer agreement, as well as reproducibility with repeat imaging for the measurement of femoral antetorsion. With such fast acquisition times and highly reliable measurements, the evaluation of femoral antetorsion might be included in the routine MR evaluation of the hip. This allows the evaluation of the morphology of the proximal femur and acetabulum, the detection of labrum and cartilage lesions, and the measurement of femoral antetorsion at one single examination, without the need of using radiation for measuring femoral antetorsion in these mostly young patients.
The normal antetorsion of the femur was first described by Wolff in 1868 (30). Femoral antetorsion is age dependent, with a large antetorsion right after birth that decreases during childhood and adolescence. Fabry et al (31) examined a large pediatric population (age 1–16 years) with radiographs and found a femoral antetorsion of 31.1° ± 8.9 at age 1 year and an antetorsion of 15.4° ± 7.6 at age 16 years, with a mean antetorsion of 24.1° in the whole population.
The average antetorsion of the femur in our asymptomatic volunteers was 12.7° ± 10.0 for reader 1 and 12.8° ± 10.1 for reader 2, which is comparable to an anatomic study from the 1990s with 171 dried femora, where a mean femoral antetorsion of 12.3° ± 7.3 was found in persons aged 25–55 years (32). In a recent anatomic study with 375 dried femora, mean antetorsion in their population (range, 18–89 years) versus 34 years in our population and the known reduction of femoral antetorsion with increasing age (33). It is interesting that there is a wide range of normal femoral antetorsion reported both in those anatomic studies (32,33) and in our data. Therefore, a femoral antetorsion that differs from the mean value might not be a pathologic abnormality by itself, but it could contribute to FAI pathomechanics together with other described factors.
The femoral antetorsion was around 4° larger on the left side than on the right side in our study population. Our study design was not suited for explaining this side difference, but the results are in accordance with a study performed in 13 young volunteers (3.2° side difference) and with an older study performed in 140 fetuses (side difference up to 4°, depending on developmental stage) (34,35).
A decade ago, Ito et al (36) reported in a study with 24 patients a significant reduction of femoral antetorsion with FAI, with a mean antetorsion of 9.7° ± 4.7 at MR imaging (compared with 15.7° ± 4.4 in the control group). In our study population, antetorsion was also smaller in patients with cam-type FAI than in the volunteers, but this was not statistically significant. It is not possible to directly compare our results on femoral antetorsion to those reported by Ito et al, because they did not acquire MR images of the distal femur, did not describe how the femoral antetorsion was measured, and did not analyze different subgroups of patients with FAI (36). However, both studies suggest that reduced femoral antetorsion might be a contributing factor in the development of FAI because of increased mechanical impact during internal rotation. In addition, a possible connection between psoas impingement and an increased femoral antetorsion has been recently discussed (37).
Our results could offer new insight into the development of cartilage lesions with pincer-type FAI. The current theory of how pronounced cartilage defects occur at the posteroinferior position in pincer-type FAI is that these was 9.7° 6 9.3 (33). The lower mean antetorsion in their data can partly be explained by an average age of 44 years defects are countercoup lesions that form during internal rotation of the hip and during the associated mechanical conflict between the anterosuperior portion of the proximal femur and the acetabulum (2,3). Our data show a significantly larger femoral antetorsion in pincer-type FAI than in cam-type FAI, which may be associated with an increased direct mechanical impact in the posterior and posteroinferior aspect of the hip joint during external rotation, thereby offering an alternative explanation of how some of these posteroinferior cartilage defects arise.
Our study had limitations: In addition to the MR sequences used for measuring the femoral antetorsion and the α angles, the two readers were allowed to see results from the other MR sequences from the same examination for the purpose of orientation when evaluating the radial images, which is a potential source of bias. Compared with the size of the patient group, the subgroup of 10 patients with pincer-type FAI is small, because cam- and mixed-type FAI are encountered much more often in our hospital. Furthermore, we only acquired data on femoral antetorsion in one leg, so we cannot assess whether an abnormal antetorsion might correlate with the side of symptoms in a patient. While femoral antetorsion could play a role in FAI pathomechanics, our study design does not allow the quantification of the role of abnormal femoral antetorsion as a contributing factor of FAI. Mechanical simulations might be more suitable to solve this question.
Orthopedic surgeons might be interested to know the femoral antetorsion angle of a patient with FAI before performing osteochondroplasty of the proximal femur and acetabular rim resection, because abnormal antetorsion angles could influence their treatment plan. However, on the basis of the wide range of femoral antetorsion angles we found in the population of volunteers, there is no single cutoff value that separates a normal versus an abnormal femoral antetorsion.
In conclusion, femoral antetorsion can be measured rapidly and with good reproducibility at MR imaging and might be assessed in FAI treatment planning. Patients with pincer-type FAI had a significantly larger femoral antetorsion than patients with cam-type FAI, although there was a wide range of values in both volunteers and patients with FAI.
• Measuring femoral antetorsion with MR imaging requires only a short additional imaging time and demonstrates good reproducibility.
• Femoral antetorsion is significantly larger in patients with pincer-type femoroacetabular impingement (FAI) than in those with cam-type FAI, but antetorsion angles are dispersed across a wide range in both volunteers and patients with FAI.
• Because of the short acquisition times of about 80 seconds, the measurement of femoral antetorsion might be included in the routine MR evaluation of the hip.
Disclosures of Potential Conflicts of Interest: R.S. No potential conflicts of interest to disclose. T.J.D. No potential conflicts of interest to disclose. P.O.Z. No potential conflicts of interest to disclose. C.W.A.P. No potential conflicts of interest to disclose.
Author contributions: Guarantors of integrity of entire study, R.S., C.W.A.P.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, all authors; clinical studies, all authors; statistical analysis, R.S.; and manuscript editing, all authors
- 1 . Early osteoarthritic changes of human femoral head cartilage subsequent to femoro-acetabular impingement. Osteoarthritis Cartilage 2003;11(7):508–518. Crossref, Medline, Google Scholar
- 2 . Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003;(417):112–120. Medline, Google Scholar
- 3 . Cam and pincer femoroacetabular impingement: characteristic MR arthrographic findings in 50 patients. Radiology 2006;240(3):778–785. Link, Google Scholar
- 4 . Prevalence of associated deformities and hip pain in patients with cam-type femoroacetabular impingement. J Bone Joint Surg Br 2009;91(5):589–594. Crossref, Medline, Google Scholar
- 5 . Radiographic markers of acetabular retroversion: correlation of the cross-over sign, ischial spine sign and posterior wall sign. Acta Orthop Belg 2010;76(2):166–173. Medline, Google Scholar
- 6 . Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the “cross-over-sign”. J Orthop Res 2007;25(6):758–765. Crossref, Medline, Google Scholar
- 7 . Diminished femoral antetorsion syndrome: a cause of pain and osteoarthritis. J Pediatr Orthop 1991;11(4):419–431. Crossref, Medline, Google Scholar
- 8 . Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am 1999;81(12):1747–1770. Crossref, Medline, Google Scholar
- 9 . Treatment of reduced femoral antetorsion by subtrochanteric rotational osteotomy. Acta Orthop Belg 2009;75(4):490–496. Medline, Google Scholar
- 10 . Measurement of femoral antetorsion and tibial torsion by magnetic resonance imaging. Br J Radiol 1997;70(834):575–579. Crossref, Medline, Google Scholar
- 11 . MR imaging measurement of the femoral antetorsional angle as a new technique: comparison with CT in children and adults. AJR Am J Roentgenol 1997;168(3):791–794. Crossref, Medline, Google Scholar
- 12 . Femoroacetabular cam-type impingement: diagnostic sensitivity and specificity of radiographic views compared to radial MRI. Eur J Radiol 2011;80(3):805–810. Crossref, Medline, Google Scholar
- 13 . Retroversion of the acetabulum: a cause of hip pain. J Bone Joint Surg Br 1999;81(2):281–288. Crossref, Medline, Google Scholar
- 14 . Ischial spine projection into the pelvis: a new sign for acetabular retroversion. Clin Orthop Relat Res 2008;466(3):677–683. Crossref, Medline, Google Scholar
- 15 . The protrusive malformation and its arthrosic complication. I. Radiological and clinical symptoms: etiopathogenesis [in French]. Rev Rhum Mal Osteoartic 1962;29:476–489. Medline, Google Scholar
- 16 . Pathomorphologic alterations predict presence or absence of hip osteoarthrosis. Clin Orthop Relat Res 2007;465:46–52. Crossref, Medline, Google Scholar
- 17 . 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, Medline, Google Scholar
- 18 . Debridement of the adult hip for femoroacetabular impingement: indications and preliminary clinical results. Clin Orthop Relat Res 2004;(429):178–181. Crossref, Medline, Google Scholar
- 19 . Osseous abnormalities and early osteoarthritis: the role of hip impingement. Clin Orthop Relat Res 2004;(429):170–177. Crossref, Medline, Google Scholar
- 20 . Femoroacetabular impingement: caution is warranted in making imaging-based assumptions and diagnoses. Radiology 2010;257(1):4–7. Link, Google Scholar
- 21 . Femoroacetabular impingement: evidence of an established hip abnormality. Radiology 2010;257(1):8–13. Link, Google Scholar
- 22 . Cams and pincer impingement are distinct, not mixed: the acetabular pathomorphology of femoroacetabular impingement. Clin Orthop Relat Res 2010;468(8):2143–2151. Crossref, Medline, Google Scholar
- 23 . The role of acetabular and femoral osteotomies in reconstructive surgery of the hip: 2005 and beyond. Clin Orthop Relat Res 2005;441:188–199. Crossref, Medline, Google Scholar
- 24 . Intertrochanteric osteotomy combined with acetabular shelfplasty in young patients with severe deformity of the femoral head and secondary osteoarthritis: a long-term follow-up study. J Bone Joint Surg Br 2005;87(1):25–31. Crossref, Medline, Google Scholar
- 25 . Rationale of osteotomy and related procedures for hip preservation: a review. Clin Orthop Relat Res 2002;(405):108–121. Crossref, Medline, Google Scholar
- 26 . The effect of varus and valgus osteotomies on femoral version. J Pediatr Orthop 2009;29(7):666–675. Crossref, Medline, Google Scholar
- 27 . A simple biplanar method of measuring femoral anteversion and neck-shaft angle. J Bone Joint Surg Am 1979;61(6A):846–851. Crossref, Medline, Google Scholar
- 28 . Measurement of femoral anteversion by biplane radiography and computed tomography imaging: comparison with an anatomic reference. Invest Radiol 2003;38(4):221–229. Crossref, Medline, Google Scholar
- 29 . Femoral anteversion. J Bone Joint Surg Am 1987;69(8):1169–1176. Crossref, Medline, Google Scholar
- 30 . A new method for determination of torsion of the femur. J Bone Joint Surg Am 1953;35-A(2):289–311. Crossref, Medline, Google Scholar
- 31 . Torsion of the femur: a follow-up study in normal and abnormal conditions. J Bone Joint Surg Am 1973;55(8):1726–1738. Crossref, Medline, Google Scholar
- 32 . Angle of torsion of the femur and its correlates. Clin Anat 1996;9(2):109–117. Crossref, Medline, Google Scholar
- 33 . Proximal femoral anatomy in the normal human population. Clin Orthop Relat Res 2009;467(4):876–885. Crossref, Medline, Google Scholar
- 34 . NMR tomographic measurement of femoral ante-torsion and tibial torsion [in German]. Rofo 1995;162(3):229–231. Crossref, Medline, Google Scholar
- 35 . Morphometric study of the fetal development of the human hip joint: significance for congenital hip disease. Yale J Biol Med 1981;54(6):411–437. Medline, Google Scholar
- 36 . 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, Medline, Google Scholar
- 37 . Does femoral anteversion play a role in the pathomechanics and subsequent surgical treatment of femoroacetabular impingement? Arthroscopy 2011;27(5 suppl):e53. Crossref, Google Scholar
Article HistoryReceived September 5, 2011; revision requested October 27; revision received November 7; accepted November 22; final version accepted December 8.
Published online: May 2012
Published in print: May 2012