Cam morphologies of the proximal femur may arise secondary to childhood diseases, including slipped capital epiphysis or Perthes disease, or secondary to previous trauma [4, 9, 14, 37, 50, 53]. The etiology of primary or so-called idiopathic cam morphologies remains unclear. Males have been reported to carry a fourfold increased risk for developing a cam morphology compared with females [16, 23, 32, 54]. Several studies have shown that high-impact sports during adolescence increase the prevalence of cam morphologies in young adults [1, 2, 7, 8, 26, 41, 42]. Most of these cross-sectional studies were performed in male adolescents and young men and included age-matched control groups. Typical sports activities with reported higher risks of cam morphologies include soccer, ice hockey, basketball, and, skiing [1, 28, 33, 41, 43]. The reported risk of cam morphologies ranged from 26% to 89% in athletes [1, 2, 15, 17, 19, 27, 32, 41–43]. It has been theorized that there might be a dose-response relationship between the amount of practice per week and later cam morphologies in adolescents . Practicing soccer more than three times per week in patients younger than 12 years was associated with a higher risk of developing a cam morphology later when compared with players practicing less .
Because of the cross-sectional study design of most of the abovementioned reports, an accurately defined time period for appearance of the cam morphology is lacking. A cam morphology before the age of 12 to 13 years in male adolescents has seldom been reported on [1, 52]. Agricola et al.  re-examined the hips of adolescent soccer players with plain radiographs 2.4 years after the initial examination. There was a rather large age variation of the participants at time of inclusion with a mean (range) age of the soccer players of 14.5 years (12 to 19 years). These authors found a small increase of the alpha angle during adolescence , and identify adolescence as the time of morphological changes of the proximal femur. Regarding potential prophylactic measurements or early detection of clinically important cam morphologies leading to cartilage damage, there is a need to more accurately frame the vulnerable time span for the development of primary cam morphologies. Ideally, a longitudinal prospective study should start before any cam morphology has occurred, which typically seems to be up to 13 years of age in males [1, 52]. For this reason, we designed a prospective, longitudinal MRI study to monitor morphological changes during growth. Noncontrast MRI scans with radial cuts on the proximal femur have the advantage that they can detect the morphology in a more three-dimensional (3-D) way and the lesions can be detected more easily than on plain radiographs [20, 39, 47]. In addition, MRI can differentiate open from closed physes [13, 38] and can detect alterations in the shape of the physeal scar at the area of the cam morphologies [41, 44]. An increased epiphyseal extension toward the neck has been described in association with a cam morphology in patients with idiopathic cam lesions and in adolescents playing basketball or soccer [2, 41, 44]. The association of an extended physis and cam morphology may be a hint for underlying physeal damage as cause of the cam morphology.
We therefore asked the following questions: (1) What is the frequency of cam morphologies in adolescent ice hockey players, and when do they appear? (2) Is there an association between an extension of the physeal growth plate and the development of a cam morphology? (3) How often do these players demonstrate clinical findings like pain and lack of internal rotation?
Patients and Methods
We performed a prospective cohort study on adolescent male ice hockey players who were recruited on a voluntary basis at the local ice hockey club. They were all members of the local competitive ice hockey team up to the age of 13 years. The mean (range) age at enrollment was 12 ± 0.5 years (11 to 13 years). Inclusion criteria consisted of uninterrupted participation in the club’s program of ice hockey training sessions and games since the age of 8 years. Typical athletic activities were three training sessions or games per week for 9- to 12-year-old players, four or five games or training sessions per week for 13- to 15-year-old players, and up to eight training sessions or games per week for players 16 years and older. The study protocol assigned the right hip for examination in participants with an even-numbered birthday and the left hip in participants with an odd-numbered birthday. Because the morphology of the femur and pelvis in girls is clearly distinct from the morphology in boys, and therefore the mechanism of femoroacetabular impingement differs, only male volunteers were included in the current study . Thirty-five players fulfilled the study inclusion criteria, but 10 players declined to participate (Fig. 1). Twenty-five players were included in the study and none had previous hip surgery or a history of hip disease (such as slipped capital femoral epiphysis or Perthes disease). There were 13 left hips and 12 right hips. Two participants (two hips) refused the latest follow-up; both participants had stopped playing ice hockey for reasons unassociated with hip problems (for example, groin pain). One participant (one hip) became symptomatic and developed anterior hip pain with a cam morphology at the 1.5-year follow-up interval. This participant was included in the statistical analysis of the overall prevalence of cam morphologies at 3-year follow-up. This individual underwent hip arthroscopy with bilateral femoral osteochondroplasty (Fig. 2). The remaining 22 players (22 hips) completed clinical and radiologic follow-up at 3 years.
All study participants completed a questionnaire and underwent a clinical examination and MRI at the time of enrollment and each follow-up examination. Follow-up MRI and examinations were performed 1.5 and 3 years after enrollment (Fig. 1). The questionnaire focused on the start of ice hockey training, the frequency of training per week, and the location and severity of pain in the hip, groin, greater trochanter, buttocks, or lower back within the past 6 months.
The physical examination focused on (1) a limited internal rotation with the hip and knee flexed to 90° and (2) the anterior impingement test [35, 36, 51], which is performed with combined hip flexion, adduction, and internal rotation. The anterior impingement test was considered positive when a sharp pain in the groin or anterolateral hip area was produced with more than 60° hip flexion. One of the authors (MSH) performed the clinical examination.
MR Techniques and Image Analysis
All participants underwent repeated noncontrast MRI of the hip on the same 3T scanner (Siemens Skyra, Siemens, Erlangen, Germany). The imaging protocol included axial sequences of the pelvis and distal femoral condyles. To assess the proximal femoral anatomy, radial two-dimensional (2-D) proton density-weighted turbo spin-echo images were acquired, which were aligned with the femoral neck axis and included the following sequence parameters: repetition time/echo time 1800/14 ms, 4-mm slice thickness, 150° flip angle, 16-cm field of view, 403 x 448 matrix size, and acquisition time of 04:24 minutes for 14 images.
The clockface system was applied for orientation around the femoral-neck axis . The center of the greater trochanter identified the 12 o’clock position of the femoral head-neck junction. Anterior was defined as 3 o’clock in both right and left hips (Fig. 3). The subsequent radial slices were defined in clockwise directions around the femoral head-neck axis for right hips and counterclockwise for left hips. All MRI measurements were performed with the commercially available DICOM viewer OSIRIX (Pixmeo SARL, Bernex, Switzerland).
The 3-D morphology of the femoral head, proximal femoral epiphysis, and head-neck junction was assessed using radial images of the hip and two previously published and validated radiographic parameters: alpha angle  (validated by Steppacher et al.  with an intraclass correlation coefficient [ICC] of 0.86 for intraobserver reliability and 0.81 for interobserver reliability) and epiphyseal extension  (validated by Agricola et al.  with an ICC of 0.97 for intraobserver reliability and 0.97 for interobserver reliability) (Fig. 4). All radiographic parameters were assessed circumferentially around the femoral-neck axis for all three examinations for each participant. The alpha angle was used to quantify head-neck sphericity (Fig. 4A) . Based on the midpoint of the two neck diameters and independently from the center of the femoral head, the true femoral-neck axis was determined . An alpha angle threshold of 60° according to Agricola et al.  was used to define the presence of a cam morphology. The growth pattern and the tilt of the epiphysis was evaluated by measuring the epiphyseal extension (Fig. 4B) .
The status of the capital growth plate (open versus closed) was evaluated for all three examinations for each participant. The capital growth plate was considered closed on proton-weighted sequences when it was represented only by a complete black line similar to the cortical or sclerotic bone and lack of increased signal on the T2 or Trufisp sequences . An open physis typically presents with a bright signal on T2 or Trufisp sequences, indicating a higher water content and/or cartilage [12, 13, 38].
We obtained ethical approval for this study from the local ethical committee, Kantonale Ethikommission Bern (KEK-Gesuchs-Nr.:205/12). We also acquired written consent from each participant and from one of the parents (for legal reasons).
Normal distribution was confirmed with the Kolmogorov-Smirnov test. For comparison between the three time points, we used paired t-tests. We used Bonferroni correction for multiple comparisons to compare the three time points (p = 0.05/3 = 0.017 as adjusted level of significance). Binominal data were assessed with the Fisher exact test. To correlate values of the epiphyseal extension and alpha angle at each measurement time point, we used the Spearman rank correlation test.
Frequency and Timing of Appearance of Cam Morphologies
At the baseline examination, none of the 25 players showed evidence of a cam morphology (defined as an alpha angle greater than 60° [3, 47]) at any measured location. Cam morphologies were most apparent at the 1.5-year follow-up interval (10 of 25; baseline versus 1.5-year follow-up: p = 0.007) and a few more occurred between 1.5 and 3 years (12 of 23; 1.5-year follow-up versus 3-year follow-up: p = 0.14; baseline versus 3-year follow-up: p = 0.003).
Physis Changes Associated with Cam Morphologies
During the study period, the alpha angle (Table 1) increased predominantly within the anterosuperior quadrant (most pronounced at the 2 o’clock position: baseline 45° ± 7°, 1.5-year follow-up 52° ± 7°, 3-year follow-up 59° ± 10°; baseline versus 1.5-year follow-up: p < 0.001; baseline versus 3-year follow-up: p < 0.001; 1.5-year versus 3-year follow-up: p = 0.004) (Fig. 5A). The epiphyseal extension toward the neck also increased predominantly in the anterosuperior quadrant (1 o’clock position: baseline 0.68 ± 0.07, 1.5-year follow-up 0.70 ± 0.05, 3-year follow-up 0.74 ± 0.08; baseline versus 1.5-year follow-up: p = 0.10; baseline versus 3-year follow-up: p = 0.01; 1.5-year versus 3-year follow-up: p = 0.03) (Fig. 5B). When evaluating the hips at 3-year follow-up, there was a positive correlation between increased epiphyseal extension and a high alpha angle at the anterosuperior quadrant (1 o’clock to 3 o’clock) (Spearman correlation coefficient = 0.341; p < 0.003) (Fig. 6).
Table 1. -
Mean difference between the time points per clock position of the alpha angles
|Baseline versus 1.5-year follow-up
||1 ± 2 (95% CI -2 to 5; 0.43)
||5 ± 2 (95% CI 2 to 9; 0.003)
||6 ± 1 (95% CI 4 to 9; < 0.001)
||7 ± 2 (95% CI 3 to 1 0; < 0.001)
||4 ± 2 (95% CI 1 to 7; 0.02)
||4 ± 1 (95% CI 2 to 7; 0.002)
||4 ± 1 (95% CI 2 to 7; 0.004)
||4 ± 1 (95% CI 2 to 6; < 0.001)
||0 ± 2 (95% CI -3 to 4; 0.86)
||-1 ± 1 (95% CI -3 to 1; 0.55)
||-3 ± 3 (95% CI -9 to 2; 0.56)
||0 ± 2 (95% CI -3 to 2; 0.72)
|Baseline versus 3-year follow-up
||1 ± 1 (95% CI -1 to 4; 0.34)
||9 ± 2 (95% CI 4 to 14; 0.001)
||13 ± 2 (95% CI 8 to 18; < 0.001)
||9 ± 1 (95% CI 5 to 12; < 0.001)
||4 ± 1 (95% CI 2 to 6; < 0.001)
||2 ± 1 (95% CI -1 to 5; 0.34)
||2 ± 1 (95% CI 0 to 5; 0.09)
||4 ± 1 (95% CI 2 to 7; < 0.001)
||-1 ± 2 (95% CI -4 to 3; 0.58)
||-2 ± 1 (95% CI -4 to 0; 0.26)
||-4 ± 2 (95% CI -9 to 1; 0.06)
||0 ± 1 (95% CI -2 to 3; 0.77)
|1.5-year versus 3-year follow-up
||1 ± 1 (95% CI -1 to 3; 0.48)
||3 ± 2 (95% CI -2 to 8; 0.30)
||7 ± 3 (95% CI 1 to 12; 0.004)
||1 ± 1 (95% CI -2 to 4; 0.38)
||0 ± 2 (95% CI -4 to 4; 0.90)
||-3 ± 1 (95% CI -6 to 0; 0.04)
||-2 ± 2 (95% CI -6 to 1; 0.16)
||0 ± 1 (95% CI -2 to 3; 0.95)
||-2 ± 2 (95% CI -5 to 2; 0.33)
||-2 ± 1 (95% CI -3 to 0; 0.09)
||-1 ± 2 (95% CI -5 to 3; 0.17)
||2 ± 1 (95% CI -1 to 4; 0.19)
Data are presented as the mean ± SD (95% CI; p value).
At the baseline examination, all 25 players presented with an open capital femoral physis. Complete capital femoral physis closure occurred most often in the interval between the 1.5-year follow-up (1 of 25) and the 3-year follow-up (18 of 22; p < 0.001). Four players had incomplete closure of the capital femoral physis. Two of these four individuals with a partially open physis presented with an alpha angle greater than 60°.
Clinical Findings: Pain and Restricted Internal Rotation
Internal rotation and flexion decreased during the study period. At the baseline examination, no individual demonstrated pain on any impingement test or had internal rotation of less than 20° (Table 2). The prevalence of pain on the impingement test and/or restricted internal rotation less than 20° increased most between 1.5-year (1 of 25) and the 3-year follow-up (6 of 22; p = 0.02). Five individuals with an alpha angle greater than 60° at the last follow-up examination had internal rotation less than 20°, whereas none of the players with normal alpha angles showed restricted internal rotation. Two individuals with an alpha angle greater than 60° at the last follow-up interval had a positive anterior impingement test result, compared with only negative impingement test results in the hips with a normal alpha angle. The mean internal rotation was 17° ± 9° in players with an abnormal alpha angle compared with a mean internal rotation of 28° ± 8° in hips with a normal alpha angle (p = 0.01).
Table 2. -
Demographic and clinical data
||p value (baseline versus 1.5-year follow-up)
||p value (baseline versus 3-year follow-up)
||p value (1.5-year versus 3-year follow-up)
|Age in years
||12.4 ± 0.5
||14 ± 0.5
||15.5 ± 0.6
|Height in m
||1.5 ± 0.1
||1.6 ± 0.1
||1.7 ± 0.1
|Weight in kg
||40 ± 7
||50 ± 9
||61 ± 8
|BMI in kg/m2
||18 ± 2
||19 ± 2
||21 ± 2
|Complete capital femoral physis closure, percent positive
||4 (1 of 25)
||82 (18 of 26)
|Anterior impingement test result and/or IR < 20°, percentage positive
||4 (1 of 25)
||27 (6 of 22)
||42 ± 11
||45 ± 16
||23 ± 10
| Internal rotation in 90° of flexion in °
Continuous values are expressed as the mean ± SD.
High-impact sports such as soccer, basketball, and ice hockey during adolescence are a risk factor for the development of cam morphology of the proximal femur [1, 27, 32, 41, 43]. So far, it has remained unclear at which age the cam morphology actually develops. The present study demonstrated that a cam morphology develops during the early phase of the growth spurt. At the final examination, at a mean age of 16 ± 0.6 years, a cam morphology was present in 12 of 23 hips. A local extension of the epiphyseal portion in the same area was associated with the appearance of a cam morphology at the anterosuperior head-neck junction. This finding may indicate an underlying alteration of the capital physis. At final clinical examination, six players with a cam morphology had an abnormal clinical finding in terms of a painful impingement test or a limited internal rotation of the hip of less than 20°. The daily practice now includes further MRI imaging in ice hockey players with a positive impingement test or restricted IR.
There are several limitations to this study. First, we were not able to recruit an age- and sex-matched control group. This was because of parental refusal to have their asymptomatic children undergo repeated technical imaging examinations. The reported prevalence of cam morphologies in nonathletic control groups of a similar age group is distinctly lower (8%-17%) than found in the present study [1, 20, 42]. However, the question of when cam morphologies do appear in control groups remains unanswered. Second, this study only examined ice hockey players who were boys (or young men). This is because males are more prone to develop cam morphologies than females [16, 23, 32, 54]. Thus, the study results do not apply to adolescent girls performing high-level sports. Third, because of the study design, 4 of 22 participants did not show complete closure of the physeal growth plate at latest follow-up. In theory, cam morphologies still might evolve until complete growth plate closure. Thus, the study might have underestimated the number of relevant cam morphologies. However, the high prevalence of cam morphologies at the latest examination is two to three times higher when compared with reported rates in control groups [8, 20]. Fourth, because of concerns of our ethical board about radiation exposure of these adolescent individuals, we were unable to perform conventional radiographic examinations and calculate the biological instead of the chronological bone age in this study. However, in daily practice, the knowledge about the most vulnerable phase for cam development during the chronological period between 13 to 16 years of age is the most important information. Early screening and further diagnostic tests for cam morphologies, if necessary, should focus on this life period. Fifth, most previously published studies were based on conventional radiographs and comparison of their results with MRI-based imaging may be limited [1, 2, 15, 19]. Radial MRI scan sections can depict a cam morphology circumferentially at the femoral head-neck junction, which conventional radiographs in two planes may miss and underestimate [10, 11, 20, 39, 47]. Thus, radial MRI scans seem to be the more accurate method for depicting a cam morphology. In addition, MRI may depict abnormalities in shape before ossification is complete (Fig. 7A-C) .
Another limitation is that acetabular morphology and its potential influence have not been evaluated. To the authors, noncontrast MRI scans alone without plain radiographs of the hip and pelvis are not sufficient to reliably determine dysplasia or acetabular version. The study only answered the questions about timing and frequency of morphological changes within the femur. Morphological influences from the acetabular side cannot be excluded but would need an extended study protocol. In addition, intraarticular damage like cartilage and labral lesions were not reported in the current study. A reliable evaluation of intraarticular damage should be done using contrast MRI [40, 45, 48] as a gold standard, which the local ethical committee would not have permitted in asymptomatic volunteers.
Frequency and Timing of Appearance of Cam Morphologies
Cam morphologies predominantly developed during the early phase of the final growth spurt. An abnormally high alpha angle has seldom been described in previous studies in athletes before the age of 13 years [1, 42, 43]. This finding was confirmed by the present study, where none of the young ice hockey players had an abnormally high alpha angle (> 60°) at a mean age of 12 ± 0.5 years. At the baseline examination, all femoral capital physes were open as represented by a thorough bright enhancement line on T2-weighted and a black line on proton density MRI images [13, 38]. Agricola et al.  found the highest increase in flattening of the head-neck junction (rise from 14% to 50%) in a subgroup of 12- to 13-year-old preprofessional soccer players (n = 63) with an open growth plate at the basic examination. The findings were based on a prospective cohort study with a 2.4-year follow-up radiographic examination of the hip in soccer players ranging from 12 to 19 years. Agricola et al.  reported a mean progression of the alpha angle of 2° with no further progression after complete growth plate closure. The present study and the findings from other authors [1, 2, 52] suggest an early vulnerable phase for the development of a cam morphology when the growth plate starts to close in boys around 13 years of age.
In the present study, the frequency of a cam morphology was 12 of 23 at the most recent examination. In four hips (18%), the growth plate was not completely closed, which might underestimate the ultimate rate of cam morphologies. However, the findings are consistent with a previous reported frequency of 56% cam morphologies in a different ice hockey player cohort from the same club measured with the same MRI technique . In predominantly cross-sectional studies, the prevalence of cam morphologies in high-impact sports such as soccer, football, basketball, ice hockey, and skiing range from 26% to 89% [1, 27, 32, 41, 43, 49]. The large variation in reported frequencies partially is due to the use of different thresholds for an abnormal alpha angle (50°-60°) and the use of different techniques for detecting cam morphologies (MRI versus plain radiographs) (Table 3) [1, 10, 11, 27, 32, 42, 43, 43, 49]. However, one may assume that the type of sports and training exercises also might play an important role in the appearance and frequency of cam morphologies .
Table 3. -
Selected literature on the association of sport and cam morphology
||Type of sport
||Threshold alpha angle
||Number of hips (number of patients)
|Siebenrock et al. 
||72 (37)/76 (38)
||Overall, the athletes had a 10-fold increased likelihood of having a cam morphology. After physeal closure 89% of the basketball players showed cam morphologies versus 9% in the control group.
|Nepple et al. 
||Radiographic evidence of cam FAI (abnormal alpha angle or decreased head-neck offset) was present in 72% of hips.
|Agricola et al. 
||Cam morphologies were recognizable and present from the age of 13 years and were more prevalent in soccer players than in their nonathletic peers. A cam morphology tended to be more prevalent in soccer players (26%) than in controls (17%).
|Philippon et al. 
||61 (61)/27 (27)
||Cam morphology present in the ice hockey group in 75% compared with 42% in the skier group.
|Siebenrock et al. 
||After physeal closure, a cam morphology at any measurement position was found in 56% of hips. In hips with an open physis, a cam morphology was found in 6%.
|Siebenrock et al. 
||72 (37)/76 (38)
||Correlation between a cam morphology and greater epiphyseal extension in the anterosuperior femoral head quadrant.
|Carsen et al. 
||Cam morphology was present exclusively in the closed physeal group. Daily activity level was higher for patients with cam morphology.
|Agricola et al. 
||In boys aged 12 and 13 years at baseline, the prevalence of a flattened head-neck junction increased significantly during follow-up (13.6% to 50%). The amount of growth plate extension was significantly associated with the alpha angle.
|Tak et al. 
||The prevalence of a cam morphology was 40% in players who started playing football from the age of 12 years or older, and 64% in those playing football before the age of 12 years.
|Van Klij et al. 
||Cam morphology developed from 12 to 13 years of age until growth plate closure around 18 years.
|Polat et al. 
||The prevalence of FAI was higher in players who had been playing football for 3 years or more and who had been training for 12.5 hours/week or more.
NA = not applicable; FAI = femoroacetabular impingement.
Physis Changes Associated with Cam Morphologies
The extension of the epiphysis toward the neck during the final growth spurt increased most distinctly in the anterosuperior head-neck quadrant (Fig. 5B). This head-neck quadrant represents the area where the cam morphology developed and a moderate positive correlation between cam and epiphyseal extension could be found (Fig. 6). The data confirm previous studies in young athletes showing a correlation between an increase in epiphyseal extension and cam development on MRI or plain radiographs [41, 44]. In contrast to a previous assumption that epiphyseal extension may precede the cam morphology, the present and a previously published prospective study  suggest that the two findings rather occur simultaneously during growth plate closure. The open question remains whether there is a causative link between the two observations. Theoretically, a cam morphology may be triggered by an abnormal physiological stimulus leading to a growth plate alteration or vice versa.
Clinical Findings: Pain and Restricted Internal Rotation
Pain on an anterior impingement test and/or an internal rotation of the hip of less than 20° at final examination was seen in 6 of 22 hips. In hips with a proven cam morphology, clinical findings were seen in 5 of 11 participants, one of whom underwent surgery for symptomatic cam impingement with cartilage damage. A positive anterior impingement test in hips with a relevant cam morphology (alpha angle > 60°) is suspicious for symptomatic impingement with potential cartilage damage and needs further adequate diagnostic imaging and potential surgery [5, 18, 24, 28, 35, 36, 42, 51]. Similarly, a restricted internal rotation (< 20°) with the hip flexed to 90° often has been associated with a cam morphology [30, 43]. In a large study in 244 asymptomatic young males, Reichenbach et al.  reported a prevalence of a cam morphology in 48% when internal rotation was less than 30°. We believe that the four hips without pain on an impingement test but with a restricted internal rotation (< 20°) must be considered hips at risk for developing symptomatic cam impingement.
Our data suggest that a cam morphology develops during the early phase of the final growth spurt of the femoral head in adolescent ice hockey players. Ten of 25 players already showed a relevant cam morphology at a mean age of 14 years. At the site of the cam morphology, we found a correlation with an increased extension of the physeal growth plate toward the femoral neck. Further high-resolution or biochemical MRI imaging studies might help to determine whether there is a causal link between a growth plate alteration and the appearance of a cam morphology based on vigorous sports activities. Clinical findings (pain on impingement test, restricted internal rotation < 20°) in 6 of 22 participants at the age of 16 years are a concern. These hips seem at risk for developing early cartilage damage. As a consequence, we now perform routine screening of young ice hockey players, with further diagnostic imaging in painful hips and yearly clinical controls in hips with a restricted internal rotation (< 20°).
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