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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

Objective

To determine the prevalence of cam-type deformities on hip magnetic resonance imaging (MRI) in young males.

Methods

This was a population-based cross-sectional study in young asymptomatic male individuals who underwent clinical examination and completed a self-report questionnaire. A random sample of participants was invited for MRI of the hip. We graded the maximal offset at the femoral head–neck junction on radial sequences using grades from 0 to 3, where 0 = normal, 1 = possible, 2 = definite, and 3 = severe deformity. The prespecified main analyses were based on definite cam-type deformity grades 2 or 3. We estimated the prevalence of the cam-type deformity adjusted for the sampling process overall and according to the extent of internal rotation. Then we determined the location of the deformity on radial MRI sequences.

Results

A total of 1,080 subjects were included in the study and 244 asymptomatic males with a mean age of 19.9 years attended MRI. Sixty-seven definite cam-type deformities were detected. The adjusted overall prevalence was 24% (95% confidence interval [95% CI] 19–30%). The prevalence increased with decreasing internal rotation (P < 0.001 for trend). Among those with a clinically decreased internal rotation of <30°, the estimated prevalence was 48% (95% CI 37–59%). Sixty-one of 67 cam-type deformities were located in an anterosuperior position.

Conclusion

Cam-type deformities can be found on MRI in every fourth young asymptomatic male individual and in every second male with decreased internal rotation. The majority of deformities are located in an anterosuperior position.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

Osteoarthritis (OA) of the hip is one of the major causes of pain and disability in the developed world (1, 2). Resulting therapeutic interventions and socioeconomic expenditures pose a considerable burden on health and social services (3). The etiology of OA is multifactorial (4). Current classifications include patients with idiopathic as well as “secondary” OA in individuals with established risk factors for OA, such as hip dysplasia (5). However, it was recently proposed that most if not all cases of idiopathic OA without established risk factors may also be secondary, due to subtle developmental or acquired abnormalities (6, 7).

Based on experimental and clinical studies, including in situ inspection of adolescents and young adults undergoing surgical dislocations of the hip, femoroacetabular impingement was proposed to cause early OA in the non-dysplastic hip (7). Two different types can be distinguished: “cam” or “pincer” impingement (Figure 1). Cam impingement is caused by a nonspherical extension of the femoral head with a decreased anterior head–neck offset (8–10). The increasing radius of the femoral head entering the acetabulum results in shearing forces against the acetabular cartilage, especially during flexion and internal rotation. High velocity of the movements, frequently occurring during athletic exercises, may play a detrimental role. It leads to an outside-in abrasion of the anterosuperior acetabular cartilage and to an avulsion of the cartilage at the labrum and of the subchondral bone at the anterosuperior rim (11). Conversely, pincer impingement results from increased acetabular depth with focal or general over-coverage of the femoral head, whereas the femoral head–neck configuration may be normal (12–14). Repetitive direct impact of the femoral head–neck junction on the acetabular rim leads to damage and degeneration of the labrum and is followed by bone apposition, which results in even more pronounced over-coverage and increased restriction of the femoral head (11).

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Figure 1. Suggested mechanisms of pincer and cam impingement. In femoroacetabular impingement of the pincer type (A), increased acetabular depth with acetabular over-coverage limits the range of motion and leads to repetitive frontal impact of the acetabulum and femur and subsequent anterosuperior or anterior damage of the labrum (1). If the acetabular rim acts as an abutment for the femur, the resulting leverage of the femur against the acetabular rim can lead to shearing damage of the cartilage in the opposite posteroinferior area (contrecoupe) (2). In femoroacetabular impingement of the cam type (B), the femoral neck protuberance and the nonspherical part of the femoral head are jammed into the acetabulum, causing shear forces and damage to the peripheral cartilage (3). Adapted, with permission, from ref.11.

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Clinically, cam impingement is often seen in young active male individuals referred to an orthopedic surgeon because of groin pain (9), and internal rotation is usually found to be diminished (15). However, it remains unclear how often a cam-type deformity with a nonspherical femoral head and decreased head–neck offset can be found in the general population of young males. We therefore aimed to examine the prevalence of cam-type deformities in a population-based inception cohort study of young males.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

Participants.

We set up a population-based inception cohort of consecutive young males undergoing conscription for the Swiss army in the recruiting center in Sumiswald, Switzerland (16). In Switzerland, at least 97.5% of males of Swiss nationality are required by the army to attend a 3-day recruitment session in specialized centers, regardless of their health status. The participants completed a questionnaire including items related to pain, stiffness, and physical function. We screened all of the individuals for hip pain using a modified version of the question used in the First National Health and Nutrition Examination Survey (17): “During the past 3 months, have you had pain in or around either of your hips?” Individuals who reported hip pain of at least 3 on a Likert scale ranging from 1 (no pain) to 5 (extreme pain) were excluded from the inception cohort. Additional exclusion criteria were previous surgery in either hip joint, metabolic or inflammatory rheumatic disease or a history of hemophilia, age <18 years, and an inability to give written informed consent. Self-report questionnaires included the subscales on pain, stiffness, and function of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), version 3.1, to quantify symptoms within the previous 48 hours (18), and the European Quality of Life (EuroQol) questionnaire, which includes 5 dimensions and a visual analog scale on health-related quality of life (19). We measured internal rotation using a recently developed examination chair (20), which enabled us to accurately and consistently measure the internal rotation of the hip in a sitting position with the hips and knees flexed 90° and the lower legs hanging unsupported (20).

The study was approved by the Research Ethics Committee of the Canton of Bern. All of the participants provided written informed consent prior to data collection.

Magnetic resonance imaging (MRI) and grading of cam-type deformity.

We used a concealed central computer-generated randomization schedule, which was stratified according to the extent of internal rotation, to randomly select participants for an invitation to MRI, using oversampling in the strata with lowest (<30°) and highest (≥40°) internal rotations. Only one hip per participant was examined. In case of different ranges of motion, the hip with the smaller internal rotation was selected; in case of similar internal rotation (within 1°), the hip was randomly selected using a concealed central computer-generated randomization schedule.

All of the MRI studies were performed with a 1.5T high-field system (Magnetom Avanto; Siemens) using a flexible surface coil with high spatial resolution. Radial proton-density–weighted sequences were acquired with all of the slices oriented parallel to the femoral neck axis, which was used as the axis of rotation. Sequences were performed using a sagittal oblique localizer, which was marked on the proton-density–weighted coronal sequence, and ran parallel to the sagittal oblique course of the acetabulum. Pulse sequence parameters used were time to recovery of 2,000 msec, time to echo of 15 msec, a 260 × 260–mm field of view, a 266 × 512 matrix, a slice thickness of 4 mm, and 16 slices at 4 minutes 43 seconds. For ethical reasons, no intraarticular contrast was injected.

To determine the presence of a cam-type deformity, we graded the maximal offset at the head–neck junction on the radial sequences using a semiquantitative scoring system that ranged from grades 0–3, where 0 = normal, no evidence of a nonspherical femoral shape on any of the sequences; 1 = possible deformity with cortical irregularity and a possible mild decrease of the anterior head–neck offset; 2 = definite deformity with an established decrease of the anterior head–neck offset; and 3 = severe deformity with a large decrease of the anterior head–neck offset. The maximum extent of a grade 2 deformity was typically less than 10 mm, whereas a grade 3 deformity extended to 10 mm or more. Figures 2A–D show examples of a normal hip and grades 0–3 cam-type deformities. Grades 2 and 3 were prespecified to indicate a definite cam-type deformity. The location of any cam-type deformity was determined in a clockwise manner, with 12:00 superior, 3:00 anterior, 6:00 inferior, and 9:00 posterior on radial sequences, with their extension recorded in hours. For example, a grade 2 cam-type deformity extended from 1:00 to 3:00 and was most pronounced at 2:00. We recorded start and end locations, the location of the maximum deformity at 2:00, and the extension of the deformity, which was 2 hours (Figure 3B). In addition, we determined the alpha angle on radial sequences (see Supplementary Appendix A, available in the online version of this article at http://www3.interscience.wiley.com/journal/77005015/home), which is located in the middle of the anterosuperior quadrant at 2:00, as recently recommended by Pfirrmann et al (10, 13). All of the MRIs were read by one experienced radiologist (SW). A random sample of 30 MRIs was read by a second experienced radiologist (CWP). Both readers had access to a formal protocol, and the second reader underwent a training session of a duration of 3 hours with the first reader. Intrarater agreement for the cam-type configuration was substantial (21), with a weighted kappa value of 0.65 for the semiquantitative grading of the cam-type deformity (95% confidence interval [95% CI] 0.34–0.96) and an intraclass correlation coefficient of 0.69 for the alpha angle (95% CI 0.49–0.88). Interrater agreement was moderate (21), with a weighted kappa value of 0.52 for the semiquantitative grading of the cam-type deformity (95% CI 0.17–0.87) and an intraclass correlation coefficient of 0.50 for the alpha angle (95% CI 0.22–0.77).

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Figure 2. Semiquantitative scoring system of cam-type deformities. A, Grade 0: normal waistline of the femoral head–neck junction. B, Grade 1: cortical irregularity with a possible mild decrease of the anterior head–neck offset (arrow). For clarity, B was mirrored. C, Grade 2: definite decrease of the anterior head–neck offset (arrow) and small impingement pit (below asterisk). D, Grade 3: severe decrease of the anterior head–neck offset (arrow).

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Figure 3. Distribution of different grades of cam-type deformity across different positions (A) and graphical representation of the positions (B). The location of deformities was recorded in a clockwise manner: 12:00 superior, 3:00 anterior, 6:00 inferior, and 9:00 posterior. Only the location with the most prominent deformity was recorded for each individual. B was adapted, with permission, from ref.27.

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Statistical analysis.

We estimated the overall prevalence of the cam-type deformity with corresponding 95% CIs using poststratification weights and robust variance estimates from linear approximations, which fully accounted for the oversampling of participants in the strata with the lowest and highest internal rotation. The prespecified main analyses were based on definite cam-type deformities. Sensitivity analyses included all deformities, irrespective of their grade. Then we calculated prevalence estimates for different grades of the cam-type deformity separately for participants with reduced range of motion in the lowest stratum (<30°), normal range of motion in the middle stratum (≥30° and <40°), and increased range of motion in the highest stratum (≥40°). P values for trends in prevalence according to the extent of internal rotation were derived using logistic regression models. We then used histograms to determine the distribution of cam-type deformities across locations on radial sequences starting from 12:00 in a clockwise manner, with widths of bins of 1 hour. Anterosuperior was defined to range from 12:30 to 3:00, anteroinferior from 3:30 to 6:00, posteroinferior from 6:30 to 9:00, and posterosuperior from 9:30 to 12:00. In addition, we used different cutoffs to delineate the superior position, which was defined to range from 11:00 to 1:00. The means and SDs of alpha angles were determined separately for grades 0–3 deformities and differences in alpha angles between different grades expressed as SD units to determine the percentage overlap in distributions of angles between different grades, assuming an SD of 10°. Then we determined means and SDs of internal rotation separately for grade 0–3 deformities. The associations between prevalence estimates of cam-type deformities and alpha angles were determined using linear regression models. In sensitivity analyses, we restricted the analysis of associations between cam-type deformities and alpha angles to cam-type deformities localized between 1:00 and 3:00. WOMAC scores were standardized to range from 0–10, with higher values indicating more severe symptoms. The 5 dimensions of the EuroQol were mapped onto a single health state index based on the European value set and standardized to range from 0–10 (22), with higher values indicating better health-related quality of life. Continuous characteristics of participants were presented as means and SDs, and binary characteristics were presented as numbers and percentages. P values for the comparison of participants at baseline were derived from a one-way analysis of variance. P values are 2-sided. Analyses were performed in Stata, version 10.1 (StataCorp).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

Characteristics of the study sample.

Participants were recruited between March and July 2005. The flow of participants through the study is shown in Supplementary Appendix B (available in the online version of this article at http://www3.interscience.wiley.com/journal/77005015/home). A total of 1,098 (96%) of 1,141 consecutive individuals consented to participate. Eighteen participants were subsequently excluded, 1 because he did not complete the baseline questionnaire, 4 because they had a history of inflammatory disease, 2 because they reported to have undergone hip operations, and 11 because of relevant hip pain. Of the remaining healthy 1,080 males, 210 (19%) had an internal rotation of less than 30°, whereas 257 (24%) had an internal rotation of ≥40°. A total of 430 participants were invited for MRI examination and 244 (57%) attended. The right hip was imaged in 131 cases (54%). Reasons for nonattendance were refusal to undergo MRI (92 [50%]), time constraints (72 [39%]), and claustrophobia (6 [3%]). Miscellaneous reasons were given by 16 participants (9%). Table 1 shows a comparison of attenders, nonattenders, and noninvited participants, with little evidence for differences. The mean age of the participants attending MRI was 19.9 years (range 18.4–24.7 years), and the mean body mass index was 23.1 kg/m2 (range 17.5–39.9 kg/m2).

Table 1. Comparison of attenders of the MRI examination with nonattenders and noninvited individuals*
 Invited for MRINot invited for MRI (n = 650)P
Attenders (n = 244)Nonattenders (n = 186)
  • *

    Values are the mean ± SD. MRI = magnetic resonance imaging; BMI = body mass index; WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; EuroQol = European Quality of Life questionnaire; VAS = visual analog scale.

  • For the comparison between the 3 groups derived from a one-way analysis of variance.

  • Standardized to range from 0 to 10.

Age, years19.9 ± 0.719.9 ± 0.719.9 ± 0.80.44
Height, cm178.3 ± 7.0177.5 ± 5.9178.0 ± 6.40.46
Weight, kg73.4 ± 12.473.0 ± 13.873.3 ± 12.40.92
BMI, kg/m223.1 ± 3.723.1 ± 4.123.1 ± 3.70.98
WOMAC overall0.2 ± 0.50.1 ± 0.30.1 ± 0.40.22
 WOMAC pain0.2 ± 0.70.1 ± 0.40.1 ± 0.50.14
 WOMAC stiffness0.6 ± 1.60.5 ± 1.40.5 ± 1.30.22
 WOMAC function0.1 ± 0.40.1 ± 0.30.1 ± 0.40.51
EuroQol health state index9.3 ± 1.39.2 ± 1.39.3 ± 1.30.51
EuroQol VAS8.5 ± 1.28.2 ± 1.68.5 ± 1.30.02

Prevalence of cam-type deformities.

A total of 179 of 244 MRI attenders showed some evidence of a cam-type deformity; 112 of these were scored as grade 1, 54 were scored as grade 2, and 13 were scored as grade 3. Table 2 shows the adjusted prevalence estimates for definite cam-type deformity, defined as grades 2 and 3. The overall adjusted prevalence was 24% (95% CI 19–30%). When stratified by internal rotation, prevalence estimates for definite cam-type deformity decreased with increasing internal rotation, from 48% in participants in the lowest stratum (95% CI 37–59%) to 12% in the highest stratum (95% CI 6–22%; P < 0.001 for trend).

Table 2. Estimated prevalence of definite cam-type impingement in young asymptomatic males according to the extent of IR and overall*
 No. of MRIs examinedMRI with definite cam-type deformityPrevalence (95% CI), %P for trend
  • *

    IR = internal rotation; MRI = magnetic resonance imaging; 95% CI = 95% confidence interval.

  • Includes grades 2 and 3 deformities.

IR <30°834048 (37–59)< 0.001
30° ≤ IR < 40°811721 (13–31) 
IR ≥40°801013 (6–22) 
Overall2446724 (19–30) 

Table 3 shows the results of the sensitivity analyses of grades 1–3 deformities, stratified according to internal rotation. The adjusted prevalence of grade 1 deformities was 47%, but there was no evidence for a decrease in prevalence with increasing internal rotation. In fact, there was a trend for an increase in prevalence with increasing internal rotation (P = 0.08). Conversely, there were clear trends for a decrease in prevalence with increasing internal rotation for both grade 2 (P = 0.001 for trend) and grade 3 (P = 0.013 for trend). The mean ± SD internal rotation was 36.7° ± 8.1° for grade 0, 34.8° ± 7.2° for grade 1, 29.1° ± 8.3° for grade 2, and 22.8° ± 8.1° for grade 3 deformities (P < 0.001 for trend). The overall adjusted prevalence of definite cam-type deformities was 21% for grade 2 (95% CI 15–26%) and 4% for grade 3 (95% CI 1–6%).

Table 3. Estimated prevalence of definite cam-type impingement in young asymptomatic males according to the extent of IR and overall, stratified by different grades of deformity*
 No. of MRIs examinedCam-type deformity grade 1Cam-type deformity grade 2Cam-type deformity grade 3
No. of MRIs in the stratumPrevalence (95% CI), %P for trendNo. of MRIs in the stratumPrevalence (95% CI), %P for trendNo. of MRIs in the stratumPrevalence (95% CI), %P for trend
  • *

    IR = internal rotation; MRI = magnetic resonance imaging; 95% CI = 95% confidence interval.

IR <30°833239 (28–50)0.082935 (25–46)0.0011113 (7–22)0.013
30° ≤ IR < 40°813847 (36–58) 1620 (12–30) 11 (0–7) 
IR ≥40°804252 (41–64) 911 (5–20) 11 (0–7) 
Overall24411247 (40–54) 5421 (15–26) 134 (1–6) 

Localization of cam-type deformities.

Figure 3 shows the localization of the peaks of the 179 deformities according to their grade. The 67 definite cam-type deformities graded 2 or 3 were located predominantly in the anterosuperior position, with 1 located at 1:00, 30 located at 2:00, and 30 located at 3:00. Of the remaining 6, 3 were located anteroinferior, 2 were located posteroinferior, and 1 was located posterosuperior. The pattern was similar when the 112 possible grade 1 deformities were also included; of 179 deformities, 165 were located anterosuperior, with 16 located at 1:00, 74 located at 2:00, and 75 located at 3:00. Of the remaining 14, 5 were located anteroinferior, 4 were located posteroinferior, and 5 were located posterosuperior. Changing cutoffs to delineate the superior position between 11:00 and 1:00, we found only 16 deformities in this location, with only 1 of these graded more than 1. The adjusted prevalence of definite deformities graded 2 or 3 was 21% for the anterosuperior location and 2%, 1%, and 1% for the anteroinferior, posteroinferior, and posterosuperior locations, respectively. The adjusted prevalence of definite cam-type deformities located in the superior position was 1%. Seven individuals had the most prominent deformity in the anterosuperior position, but an additional, less prominent deformity elsewhere. Five of these were located approximately opposite, at the posterosuperior position. More prominent deformities had a wider basis: there was an association between the grade of nonspherical femoral head shape and extension (P < 0.001). The median extent of the base of the deformity was 1 hour for grade 1, 1.5 hours for grade 2, and 2 hours for grade 3.

Relationship between cam-type deformity and alpha angle.

The mean ± SD alpha angle was 44.8° ± 8.4° for grade 0, 48.4° ± 10.1° for grade 1, 57.7° ± 12.7° for grade 2, and 76.4° ± 9.7° for grade 3 deformities (P = 0.001 for trend).

This corresponded to average increments in the alpha angle of 0.36 SD units between grades 0 and 1, 0.93 SD units between grades 1 and 2, and 3.16 SD units between grades 2 and 3. The estimated overlap of alpha angles with hips without cam-type deformity was 75% for grade 1, 35% for grade 2, and 6% for grade 3 deformities. Restricting the analysis to deformities localized between 1:00 and 3:00, we found similar results: the mean ± SD alpha angle was 45.2° ± 9.2° for grade 0, 48.7° ± 10.3° for grade 1, 58.9° ± 12.4° for grade 2, and 75.9° ± 10.0° for grade 3 (P = 0.001 for trend).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

In our population-based sample of 244 asymptomatic young Swiss males, the overall prevalence of a definite cam-type deformity of 24% was surprisingly high. When stratified by internal rotation, prevalence estimates decreased with increasing internal rotation, from 48% in participants in the lowest stratum with clinically decreased internal rotation to 12% in the highest stratum with increased internal rotation. Most of the deformities were located in the anterosuperior position, irrespective of the grade. Of 67 definite cam-type deformities observed, 61 were located between 1:00 and 3:00. Deformities were graded from 1–3, with 1 indicating possible and 2 and 3 indicating definite deformities. The prespecified main analyses were based on definite cam-type deformities, whereas sensitivity analyses included all deformities, irrespective of their grade. When determining the associations of deformities with the extent of internal rotation and alpha angle, we found associations more pronounced in main analyses based on definite deformities only.

To our knowledge, this is the first population-based MRI study addressing potential biomechanical risk factors for hip OA. Our study was restricted to males only, considering that cam-type deformities are predominantly seen in males in tertiary care settings (9). Additional population-based studies are required in females to determine whether the pattern seen in hospital settings translates into lower population-based prevalence estimates of cam-type deformities in females. Out of ethical considerations, we were unable to perform an arthrography MRI. The high resolution of the MR device used in our study means, however, that the anatomic structures could be adequately evaluated even without the intraarticular contrast medium. The interrater reliability was only moderate for the grading of deformities and the measurement of the alpha angle, which makes measurement error likely. If anything, this source of random variation is likely to result in an underestimation of actual associations and will not invalidate our results. We used oversampling in the strata with the lowest and highest internal rotation, assuming that potential alterations were more frequent at the two tails of the approximate normal distribution of internal rotation. However, the approaches used for analysis fully accounted for this oversampling in both the calculations of point estimates and the corresponding variance estimates. Another limitation is the low rate of attendance for MRI: although the consent rate for clinical examination and completion of a self-report questionnaire was near 96%, only 57% of those invited attended MRI. However, an analysis of characteristics of the participants did not suggest clinically relevant differences between attenders and nonattenders, and we consider selection bias resulting from this low attendance rate to be small. Only one hip per participant was examined. In case of different ranges of motion, the hip with the smaller internal rotation was selected. A total of 144 individuals (64%) had symmetric and 100 (36%) had asymmetric internal rotation, defined as a difference in internal rotation between the left and right hips of 4° or more (20). We aimed at estimating the prevalence of the deformity at the level of the individuals rather than at the level of the hips. Our approach of using the hip with the lower internal rotation will therefore yield appropriate estimates, which tend to be conservative. A final limitation is our inability to distinguish between a developmental disorder, which may have occurred because of a genetic predisposition in the presence or absence of environmental interaction, and purely “secondary” alterations resulting from an early osteoarthritic process starting during adolescence. We do not know at which point in time cam-type deformities appear, nor do we know whether the deformities grow over time or remain stable. Additional MRI studies in children and adolescents and several followup examinations in our study are required to address these issues.

Our population-based MRI study of cam-type deformities should be interpreted in the context of a recently published population-based study by Gosvig et al, which used conventional anteroposterior radiographs of the pelvis to determine the prevalence of cam-type deformities in a random sample of individuals ages 22–93 years (23). They reported an overall prevalence of cam-type deformities of 17% in men and 4% in women. Recently, Doherty et al published prevalence data in the context of a case–control study of cases with symptomatic radiographic hip OA and asymptomatic controls without hip OA, again based on conventional anteroposterior radiographs of the pelvis (24). They found cam-type deformities in 3.6% of controls and 17.7% of cases (odds ratio 6.95, 95% CI 4.64–10.4). Both studies are subject to the same two limitations. First, they used conventional anteroposterior radiographs of the pelvis to determine whether an individual showed a cam-type deformity. This view will predominantly depict cam-type deformities at the superior position (25, 26), which corresponds to 11:00 and 1:00 in our MRI study. Our results indicate that only 16 of 179 deformities of any grade and only 1 of 67 definite deformities graded 2 or 3 were located in this region. Both studies would therefore be unable to observe the majority of deformities we found. Second, both studies included predominantly older individuals. It may be difficult, however, to distinguish between cam-type deformities observed already at a young age, such as in our study, and osseous alterations developing later in life, potentially resulting from the progression of OA. The ability of Gosvig et al and Doherty et al to distinguish between genetic predispositions and secondary alterations as discussed is even more limited than ours and some of the deformities found in their studies may be the result rather than the cause of OA. We hypothesize that even the majority of the cam-type deformities seen on anteroposterior radiographs will develop during later adulthood or result from an extension of cam-type deformities located in a more anterior position, as observed in our study. In view of the inability of anteroposterior views to detect cam-type deformities in anterior positions, a second auxiliary view may be considered, such as a lateral cross-table radiograph, but even the combination of these two views may lead to an underestimation of the frequency of cam-type deformities compared with estimates found in MRI studies (27).

The etiology of cam-type deformities is unclear. Early hypotheses suggest that the deformity results from growth disturbances of the proximal femur (28–33); growth disturbances of the head and neck, such as a delayed separation of the common physis or an eccentric closure of the capital epiphysis, will affect the anterosuperior area of the head–neck junction and result in similar alterations to those seen in our study. Several anatomic variations were described that could correspond to the radiologic finding of a cam-type deformity at the anterosuperior position of the proximal femur, including an osseous bar extending from the head to the superior tubercle of the intertrochanteric line described in 1899 (33, 34), an osseous prominence described as eminentia in 1904 (33–36), and concavities called imprints or cervical fossa in 1924 (34, 36). In 1899, Sudeck described an osseous prominence ranging from the anterosuperior area of the head to the intertrochanteric line, with a distinct extension of the cartilage from the head onto this bar (33). Cartilaginous extensions are difficult to detect on dried bones (33, 34, 36). In a study of fresh and young cadaver bones in 1931, Odgers described a gradual ossification of a thin strip of cartilage connecting the head to the greater trochanter, with the cartilage extending from the head to the medial end of the trochanter (34). This pattern was observed more frequently in femurs from males. The extension of the cartilage typically was accompanied by osseous depressions or erosions of the surface (34).

Our study is cross-sectional, and we are unable to determine whether the cam-type deformities found in asymptomatic young males are associated with future symptomatic OA of the hip with clinically relevant pain and disability. Similarly, we are unable to determine whether some of the observed deformities, particularly those of a lower grade, are secondary alterations due to anomalies of the acetabulum, including impingement of the pincer type (11). Longitudinal studies are required to determine whether cam-type deformities are associated with an increased risk of symptomatic hip OA, how established deformities will develop, and what other risk factors are associated with an increased risk of early hip OA. The high prevalence estimates for grade 1 deformities were especially surprising. We argue that grade 1 findings are clinically irrelevant, neither prognostically important nor detectable in clinical routine. In our study, internal rotation and alpha angle were nearly identical in hips with grade 1 deformity and in normal hips, and are therefore likely to be indistinguishable in routine clinical examinations and MRI assessments of the alpha angle. Conversely, grade 2 and 3 deformities, which were prespecified in our study to indicate definite alterations, could be clearly distinguished from normal hips without cam-type deformities in both clinical assessments of internal rotation and MRI assessments of the alpha angle. Taken together, this suggests that grade 1 deformities are difficult to establish in both clinical examination of internal rotation and assessment of the alpha angle in MRI. If grade 1 deformities bear any clinical relevance despite their high prevalence, they can only be established with longer-term followup examinations in our study. In the symptomatic hip, the association between the presence of the cam deformity and the cause of pain must be determined clinically, irrespective of the grade.

In conclusion, definite cam-type deformities of the hip characterized by a nonspherical extension of the femoral head with a decreased anterior head–neck offset on MRI can be found in every fourth young asymptomatic male individual and in every second male with decreased internal rotation. Longitudinal studies will be required to determine the clinical relevance of these findings.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Reichenbach had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Reichenbach, Jüni, Trelle, Odermatt, Hofstetter, Ganz, Leunig.

Acquisition of data. Reichenbach, Jüni, Werlen, Pfirrmann.

Analysis and interpretation of data. Reichenbach, Jüni, Nüesch, Ganz, Leunig.

ROLE OF THE STUDY SPONSOR

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

The Swiss National Science Foundation had no role in the study design, data collection, data analysis, data interpretation, writing of the manuscript, or decision to submit the manuscript.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information
  • 1
    MurrayCJ, LopezAD, editors. The global burden of disease: a comprehensive assessment of mortality and disability from diseases, injuries and risk factors in 1990 and projected to 2002. Geneva (Switzerland): World Health Organization; 1996.
  • 2
    Elders MJ. The increasing impact of arthritis on public health. J Rheumatol Suppl 2000; 60: 68.
  • 3
    Reginster JY. The prevalence and burden of arthritis. Rheumatology (Oxford) 2002; 41 Suppl 1: 36.
  • 4
    Harris WH. Etiology of osteoarthritis of the hip. Clin Orthop Relat Res 1986; 213: 2033.
  • 5
    Flores RH, Hochberg MC. Definition and classification of osteoarthritis. In: BrandtKD, LohmanderLS, editors. Osteoarthritis. 2nd ed. Oxford: Oxford University Press; 2003.
  • 6
    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: 26472.
  • 7
    Ganz R, Parvizi J, Beck M, Leunig M, Notzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003; 417: 11220.
  • 8
    Myers SR, Eijer H, Ganz R. Anterior femoroacetabular impingement after periacetabular osteotomy. Clin Orthop Relat Res 1999; 363: 939.
  • 9
    Ito K, Minka MA 2nd, 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: 1716.
  • 10
    Notzli 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: 55660.
  • 11
    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: 10128.
  • 12
    Beck M, Leunig M, Parvizi J, Boutier V, Wyss D, Ganz R. Anterior femoroacetabular impingement: part II. Midterm results of surgical treatment. Clin Orthop Relat Res 2004; 418: 6773.
  • 13
    Pfirrmann CW, Mengiardi B, Dora C, Kalberer F, Zanetti M, Hodler J. Cam and pincer femoroacetabular impingement: characteristic MR arthrographic findings in 50 patients. Radiology 2006; 240: 77885.
  • 14
    Reynolds D, Lucas J, Klaue K. Retroversion of the acetabulum: a cause of hip pain. J Bone Joint Surg Br 1999; 81: 2818.
  • 15
    Wyss TF, Clark JM, Weishaupt D, Notzli HP. Correlation between internal rotation and bony anatomy in the hip. Clin Orthop Relat Res 2007; 460: 1528.
  • 16
    National Research Program. Musculoskeletal health: chronic pain. Etiology of primary osteoarthritis of the hip. 2010. URL: http://www.nfp53.ch/e_module.cfm?Projects.Command=details&get=13.
  • 17
    Anderson JJ, Felson DT. Factors associated with osteoarthritis of the knee in the first national Health and Nutrition Examination Survey (HANES I): evidence for an association with overweight, race, and physical demands of work. Am J Epidemiol 1988; 128: 17989.
  • 18
    Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988; 15: 183340.
  • 19
    Hurst NP, Kind P, Ruta D, Hunter M, Stubbings A. Measuring health-related quality of life in rheumatoid arthritis: validity, responsiveness and reliability of EuroQol (EQ-5D). Br J Rheumatol 1997; 36: 5519.
  • 20
    Reichenbach S, Juni P, Nuesch E, Frey F, Ganz R, Leunig M. An examination chair to measure internal rotation of the hip in routine settings: a validation study. Osteoarthritis Cartilage 2010; 18: 36571.
  • 21
    Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977; 33: 15974.
  • 22
    Greiner W, Weijnen T, Nieuwenhuizen M, Oppe S, Badia X, Busschbach J, et al. A single European currency for EQ-5D health states: results from a six-country study. Eur J Health Econ 2003; 4: 22231.
  • 23
    Gosvig KK, Jacobsen S, Sonne-Holm S, Gebuhr P. The prevalence of cam-type deformity of the hip joint: a survey of 4151 subjects of the Copenhagen Osteoarthritis Study. Acta Radiol 2008; 49: 43641.
  • 24
    Doherty M, Courtney P, Doherty S, Jenkins W, Maciewicz RA, Muir K, et al. Nonspherical femoral head shape (pistol grip deformity), neck shaft angle, and risk of hip osteoarthritis: a case–control study. Arthritis Rheum 2008; 58: 317282.
  • 25
    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: 1815.
  • 26
    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: 11521.
  • 27
    Dudda M, Albers C, Mamisch TC, Werlen S, Beck M. Do normal radiographs exclude asphericity of the femoral head-neck junction? Clin Orthop Relat Res 2009; 467: 6519.
  • 28
    Aberle-Horstenegg W. On the anatomical basis of severe neck changes after treatment of hip luxation. Arch Orthop Unfallchir 1961; 53: 30710. In German.
  • 29
    Lindemann UC. On atypical ossifications of the metapophysis and apophysis of the coxal end of the femur: 2 observations. Arch Orthop Unfallchir 1961; 53: 44551. In German.
  • 30
    Lutken P. Bone-bridge formation between the greater trochanter and the femoral head: a normal variation of the pattern of the ossification in the upper end of the femur in adolescence. Acta Orthop Scand 1961; 31: 20915.
  • 31
    Mau H. On the etiology and pathogenesis of ossification disorders of the femur neck and head. Z Orthop Ihre Grenzgeb 1962; 96: 15663. In German.
  • 32
    Morgan JD, Somerville EW. Normal and abnormal growth at the upper end of the femur. J Bone Joint Surg Br 1960; 42B: 26472.
  • 33
    Sudeck P. On the anatomy and etiology of Coxa vara adolescentium. Arch Clin Chirurg 1899; 59: 50424.
  • 34
    Odgers PN. Two details about the neck of the femur: (1) the eminentia, (2) the Empreinte. J Anat 1931; 65: 35262.
  • 35
    Fick R. Anatomy of the joints. In: von BardelebenK, editor. Handbook of anatomy and mechanics of the joints. Jena (Germany): Gustav Fischer Verlag; 1904. p. 3129.
  • 36
    Meyer A. The “cervical fossa” of Allen. Am J Phys Anthropol 1924; 7: 25769.

Supporting Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. REFERENCES
  10. Supporting Information

Additional Supporting Information may be found in the online version of this article.

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ACR_20198_sm_appendix.doc139KSupplementary data

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