Range of Hip Joint Motion Is Correlated With MRI-Verified Cam Deformity in Adolescent Elite Skiers

Abstract

Background:

Radiologically verified cam-type femoroacetabular impingement (FAI) has been shown to correlate with reduced internal rotation, reduced passive hip flexion, and a positive anterior impingement test.

Purpose:

To validate how a clinical examination of the hip joint correlates with magnetic resonance imaging (MRI)–verified cam deformity in adolescents.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

The sample group consisted of 102 adolescents with the mean age 17.7 ± 1.4 years. The hip joints were examined using MRI for measurements of the presence of cam (α-angle ≥55°) and clinically for range of motion (ROM) in both supine and sitting positions. The participants were divided into a cam and a noncam group based on the results of the MRI examination. Passive hip flexion, internal rotation, anterior impingement, and the FABER (flexion, abduction, and external rotation) test were used to test both hips in the supine position. With the participant sitting, the internal/external rotation of the hip joint was measured in 3 different positions of the pelvis (neutral, maximum anteversion, and retroversion) and lumbar spine (neutral, maximum extension, and flexion).

Results:

Differences were found between the cam and noncam groups in terms of the anterior impingement test (right, P = .010; left, P = .006), passive supine hip flexion (right: mean, 5°; cam, 117°; noncam, 122° [P = .05]; and left: mean, 8.5°; cam, 116°; noncam, 124.5° [P = .001]), supine internal rotation (right: mean, 4.9°; cam, 24°; noncam, 29° [P = .022]; and left: mean, 4.8°; cam, 26°; noncam, 31° [P = .028]), sitting internal rotation with the pelvis and lumbar spine in neutral (right: mean, 7.95°; cam, 29°; noncam, 37° [P = .001]; and left: mean, 6.5°; cam, 31.5°; noncam, 38° [P = .006]), maximum anteversion of the pelvis and extension of the lumbar spine (right: mean, 5.2°; cam, 20°; noncam, 25° [P = .004]; and left: mean, 5.85°; cam, 20.5; noncam, 26.4° [P = .004]), and maximum retroversion of the pelvis and flexion of the spine (right: mean, 8.4°; cam, 32.5°; noncam, 41° [P = .001]; and left: mean, 6.2°; cam, 36°; noncam, 42.3° [P = .012]). The cam group had reduced ROM compared with the noncam group in all clinical ROM measures.

Conclusion:

The presence of cam deformity on MRI correlates with reduced internal rotation in the supine and sitting positions, passive supine hip flexion, and the impingement test in adolescents.

Femoroacetabular impingement (FAI) is caused by an abnormal morphology of the hips and can be divided into 2 categories: cam (femoral based) and pincer (acetabular based).^5,13,16,24 These 2 pathologies may occur alone or together.⁵

The mechanism of cam-type impingement is a collision between the abnormally formed femoral neck/head (cam) and the acetabular margin during flexion and internal rotation of the hip joint.¹⁶ This type of collision may lead to cartilage damage, primarily to the anterosuperior area of the acetabulum, and less frequently to labral damage.^5,9,13,16,21 Cam impingement is regarded by some researchers as a cause of early hip joint osteoarthritis (OA), while pincer impingement is not believed to cause hip OA but rather labral damage.^{1–3,18,29,33}

FAI can be diagnosed by a history of hip symptoms and by a combination of clinical examinations and confirmatory radiology, on plain radiographs or magnetic resonance imaging (MRI).^20,35 Symptoms that have been associated with FAI syndrome are motion-related or position-related pain in the hip, groin, back, buttocks, or thigh. Clicking, catching, locking, stiffness, restricted range of motion (ROM), or giving way are other frequently reported symptoms.¹⁴

There are several studies that have evaluated the clinical examination findings in the hip in patients with FAI.^10,13,32 Radiologically verified cam impingement has previously been shown to be associated with reduced internal rotation of the hip in 90° of flexion, reduced passive hip flexion, and a positive anterior impingement test/FADIR (flexion, adduction, and internal rotation) test.^10,13,32 Reiman et al²⁶ concluded that only an anterior impingement test and supine flexion–internal rotation are valuable screening tests for FAI, and they suggested that more high-quality studies are needed to evaluate the validity of clinical tests. It may therefore be of importance to investigate and evaluate clinical tests that may help diagnose cam-type FAI and thereby minimize the need for radiological examinations.

To our knowledge, this is the first study to evaluate the relationship between an MRI-verified cam deformity and clinical ROM in a healthy population with no prior diagnosis of cam-type FAI. Furthermore, there are no prior studies that we are aware of that have examined internal and external rotation of the hip when the patient is sitting with the pelvis and spine in 3 different positions. The purpose of this study was to investigate and validate how ROM in a clinical examination correlates to MRI-verified cam deformity in young patients.

Methods

Study Population

The sample group consisted of young athletic elite skiers from the Åre Ski Academy high school (n = 75) and a nonathletic population (n = 27) from 3 high schools in Östersund and Järpen. All students attending the Åre Ski Academy (76 grade 1-4, professional, skiers aged between 16 and 20 years) were invited to participate in this prospective study. Seventy-five of the skiers, 35 females and 40 males, volunteered to participate.

The inclusion criterion for the nonathletic group was first-year high school students who had previously not participated and at present did not participate in any organized sports or physical activity for more than 2 hours per week. The exclusion criteria for both groups were individuals with previously diagnosed hip, spine, or pelvic disease or growth disturbance and previous surgery on the hips, spine, or pelvis.

The MRI examinations were performed at the Radiographic Department, Östersund Hospital, Östersund, and the clinical examination was carried out at the Åre Ski Academy and at the Orthopaedic Department, Östersund.

All the participants were informed about the study both orally and in writing. Participation was totally voluntary. Written consent was given by all individuals and, for participants younger than 18 years, written consent was obtained from their parents. The present study was approved by the Regional Ethical Review Board, Gothenburg.

A total of 53 females and 49 males volunteered to participate in the study. One skier had to withdraw due to diagnosed cam-type FAI that was treated with arthroscopic surgery before the examinations had been carried out. Two of the nonathletes were excluded because of previous high-level training in skiing and ice hockey. In addition, failure to attend investigations meant that only MRI data from 89 participants and physical examination data from 87 participants were available for the final analysis. The cam group consisted of 10 females and 26 males, whereas the noncam group consisted of 36 females and 17 males. Table 1 summarizes the demographic characteristics of the study population (N = 102).

TABLE 1.

Baseline Characteristics for All Participants Stratified by Group^a

	All Participants (N =102)b	Cam (n = 36)	Noncam (n = 53)	P Value
Age, y	17.7 (1.4)	18.0 (1.2)	17.4 (1.3)	.021
Female sex, n [%]	53 [52]	10 [28]	36 [68]	<.001
Height, cm	173 (8.3)	177 (7.6)	171 (7.5)	<.001
Weight, kg	69 (12.2)	71 (9.9)	68 (13.8)	.143
Body mass index, kg/m2	22.9 (3.3)	22.7 (2.5)	23.1 (3.9)	.556

^aValues are presented as mean (SD) unless indicated otherwise.

^bMagnetic resonance imaging data from 13 participants and physical examination data from 15 participants were unavailable.

MRI Examination

All participants underwent MRI of both hips without contrast. The MRI that was used was a GE Optima 450 Wide 1.5 T, at Hospital Östersund. Coronal T2 fat-saturated and axial 3D Cube sequences were obtained angled on the femoral neck using a coil surface of HD 8-channel Cardiac Array by GE. The α-angle was measured on the superior half of the femoral head. Seven measurements, from the 9 o’clock to 3 o’clock positions (180°), were performed to determine the morphological features of the femoral head-neck junction.¹⁶ Measurement of the α-angle was performed according to Nötzli et al.²¹ The α-angle was measured between the femoral neck axis and a line from the center of the femoral head to a point where the contour of the femoral head-neck junction exceeds the radius of the femoral head (Figure 1). The α-angle is used to define the presence of a cam deformity, and in previous studies a threshold of 55° has been considered pathological.^4,25,30,31 In the present study, an α-angle ≥55° was considered pathological. In the 89 study participants, 178 hips were analyzed. A total of 54 hips had cam changes, 26 hips on the right side and 28 on the left.

Figure 1.

Measurement of the α-angle, between the femoral neck axis and a line from the center of the femoral head to a point where the contour of the femoral head-neck junction exceeds the radius of the femoral head.

The MRI images were evaluated and measured by an experienced radiologist, together with a resident radiologist. All participants had been deidentified and given a random number, and the MRI examinations were mixed and evaluated randomly in a blinded manner. The images were evaluated according to a standardized protocol, including assessment of the α-angle. To test the interobserver reliability, MRI images were selected randomly from 10 participants and were re-examined by another experienced radiologist. The result of the interobserver test, intraclass correlation coefficient (ICC) analysis for the α-angle, epiphyseal extension, and diameter of the femoral head, indicated a good to excellent level of agreement (α-angle ICC, 0.75; epiphyseal extension ICC, 0.92; diameter of caput femur ICC, 0.97).

Clinical Examination

In the present study, the sitting position was selected, as it best replicates the sports specificity of skiing, but more importantly because it enabled us to investigate the relationship between the position of the pelvis and lumbar spine with the hip ROM.

A specially constructed chair was used to allow participants to sit with their legs hanging freely over the edge. With the use of 4 wooden bolsters, the chair fortified the isolation of movement in the hip by preventing any adduction or abduction of the femurs (Figure 2).

Figure 2.

Sitting in a neutral position, both hips and knees at a 90° angle and the thighs held in position by 4 wooden bolsters to prevent hip abduction/adduction translation.

All examinations were performed by the coauthors (C.A. and A.S.A.) in a specific order to optimize the accuracy of the measurements. While one examiner examined a participant, the other examiner stabilized, read, and recorded the results. Both C.A. and A.S.A. performed the intraobserver tests. Four months passed between the first and second examination. Interobserver tests were performed comparing C.A. and A.S.A. The interobserver test was performed on the same day, and the examiners were blinded to each other’s measurements. Both the intra- and interobserver tests included 10 of the skiers. The result of the intraobserver test (ICC analysis) for all physical examinations indicated good to very good agreement (passive hip flexion ICC, 0.77; supine internal rotation ICC, 0.78). The interobserver test (ICC) indicated a good to excellent level of agreement (passive hip flexion ICC, 0.83; supine internal rotation ICC, 0.94).

Digital Goniometer Measurements

The goniometer has been used in previous studies of cam-type deformity in athletes.^12,15,31 In the present study, a digital goniometer was used (HALO Medical Devices), combined with a universal goniometer with prolonged arms to measure ROM.^8,11,12,15 A few times, when held horizontally, the digital goniometer was shown to measure angles higher than the universal goniometer. The measurements of hip internal rotation in the supine position were therefore made using both the digital goniometer and a universal goniometer. When the angles differed, the angles measured by the universal goniometer were used because the universal goniometer is more widely used and acknowledged.

Functional Tests

In this study, we defined the standing leg as the leg that felt most natural for the participant to stand on when performing a 1-leg activity. To identify the standing leg, the participant was asked to kick a football the way that felt the most natural (Figure 3). The participant was then asked to do a pirouette the way that felt the most natural and comfortable (Figure 4). If a participant used different legs in the 2 tests (n = 28 of 89), we were not able to register the standing leg.

Figure 3.

Kicking a football the way that feels most natural.

Figure 4.

Performing a pirouette the way that feels most natural and comfortable.

Supine Examination

To standardize the supine examination, verbal instructions were given to the participant in the following order: bend your knees, place your feet flat on the bed, raise your pelvis from the bed, lower your hips onto the bed, and then straighten your legs. This helped place the participant in a neutral, aligned position prior to the measurements.

Passive Hip Joint Flexion

A reference line was drawn from the middle of the lateral femoral condyle and the greater trochanter by one examiner (Figure 5). The digital goniometer was initially calibrated and zeroed. It was then held in place by the same examiner, with its laser beams set along the previously marked line of reference. The other examiner flexed the hip and knee joints. The leg was raised in a sagittal plane, avoiding abduction or adduction of the hip. This examiner also maintained pressure on the contralateral thigh to limit pelvic rotation. Passive hip flexion was recorded in degrees. This process was then repeated for the opposite hip.

Figure 5.

Passive hip joint flexion.

Passive Internal Rotation of the Hip

Passive flexion in the sagittal plane was introduced to the hip and knee joint to 90° by one examiner. The other examiner marked a line of reference from the apex of the patella to midway between the lateral and medial malleolus (Figure 6). With the knee and hip held at 90° of flexion, the goniometer was calibrated, zeroed, and handheld with its laser beams set on the previously marked reference line. The hand of one examiner was placed around the participant’s iliac crest to prevent any accessory lumbopelvic translation, while the other hand held the thigh manually in a vertical position. The other examiner held the leg in a horizontal position and internally rotated the hip until the point of initial resistance. The examiner who stabilized the pelvis also noted the first movement of the pelvis, which matched the endpoint of internal rotation felt by the other examiner. In this way, the accuracy of the measured internal rotation was double-checked by both examiners.

Figure 6.

Passive internal rotation of the hip.

Hip Anterior Impingement Test

With the hip and knee flexed at 90° and maximally internally rotated (Figure 7), the examiner adducted the hip until resistance, according to Klaue et al.¹⁷ The examiner held this position for a few seconds. This examination was graded with 3 possible options: no pain, discomfort, or pain.

Figure 7.

Hip anterior impingement test.

Patrick’s or FABER (Flexion, Abduction, and External Rotation) Test

This examination was performed as previously described by Ross et al²⁸ and Byrd,⁷ but it included the use of a digital goniometer for quantitative measurements.¹⁹ The digital goniometer was calibrated and zeroed and held in place by one examiner, with the laser beams set on the reference line previously marked along the tibia. One examiner stabilized the pelvis to prevent any accessory lumbopelvic rotation and to keep the pelvis in a neutral stabilized position. The other examiner raised one of the participant’s legs and placed the participant’s ankle superior and lateral to the contralateral knee (Figure 8). This motion created the hip joint flexion, abduction, and external rotation. The participant was instructed to relax and lower the tested leg, either to the point of pain or to the endpoint of motion. The angle was recorded in degrees. This process was then repeated for the opposite hip.

Figure 8.

Patrick’s or FABER (flexion, abduction, and external rotation) test.

Seated Examination

For these examinations, the participant was seated with both hips and knees placed at a 90° angle and the thighs held in position. Because of the anatomic differences in the thigh circumference distally, a 1-cm thick pad was placed under the distal femurs to ascertain that the femurs were in a horizontal position. To standardize the sitting position, participants were instructed to focus on a point straight ahead on the wall and have their arms folded across their chest, hands on opposite shoulders.

Hip Joint Internal and External Rotation Range of Motion Testing

Measurements of the internal and external rotations of the hip joints were performed using a digital goniometer, calibrated, zeroed, and handheld along the previously marked reference line along the tibia. The reference line made it possible to set the goniometer laser beams during the measurement, to optimize the accuracy.

Internal and external rotations were measured in 3 different pelvic and lumbar spine positions as follows.

Neutral Lumbar Position

To measure the lumbar position when sitting in a neutral position, the participant was instructed to sit in a straight position, thus creating a vertical line from the participant’s shoulder to the hip (Figure 9). Measurements of the 3 pelvic positions (neutral, maximum anteversion, and maximum retroversion) using the PALM palpation meter (Performance Attainment Associates) and the lumbar spinal sagittal positions (neutral, maximum extension, and maximum flexion) using the Debrunner Kyphometer (Protek AG).^22,23 were recorded, as described by Todd et al.³⁴ The angle of pelvic incline was measured on both sides and recorded. When measuring the internal and external rotation of the hips, the lumbar spine position was re-evaluated with the Kyphometer before changing sides, to ensure the same lumbar position when measuring both hips. One examiner stabilized the thigh and pelvis on the examined side, and passive internal rotation was then performed, to the point of initial resistance, by the other examiner. The examiner stabilizing the thigh and pelvis also observed the initial movement of the pelvis, which matched the endpoint of internal rotation palpated by the other examiner. In this way, the accuracy of the internal rotation was double-checked. The rotation was recorded in degrees. This process was repeated for the opposite hip, and the same procedure was then repeated for passive external rotation.

Figure 9.

Neutral lumbar position in sitting.

Lumbar Spine in Maximum Extension

The participants were instructed to arch their lumbar spine and tilt their pelvis forward, thereby increasing the anteversion of the pelvis and lumbar lordosis (Figure 10). The lumbar spine position and the angle of pelvic anteversion were measured as previously described. In this position, passive internal and external rotations were measured in degrees; the participant was instructed to adopt the neutral position between each test for a short rest, and the lumbar spine position was remeasured before measuring the other hip.

Figure 10.

Lumbar spine in maximum extension.

Lumbar Spine in Maximum Flexion (SLUMP Position)

The participant was instructed to flex his or her lumbar spine and tilt his or her pelvis backward to the endpoint, essentially increasing the retroversion of the pelvis and lumbar kyphosis (Figure 11). The lumbar spine position and the angle of pelvic retroversion were measured as previously described. In this position, passive internal and external rotations were measured in degrees; the participant was instructed to adopt the neutral position between each test for a short rest, and the SLUMP position was remeasured before measuring the other hip.

Figure 11.

Lumbar spine in maximum flexion (SLUMP position).

Statistical Analysis

The data were analyzed using IBM SPSS Statistics for Windows, version 22.0 (IBM Corp). The description of data was expressed in terms of the mean and standard deviation. An independent t test and Pearson chi-square test were performed to compare variables (cam vs noncam). A chi-square test for association was conducted between pain/discomfort of the anterior impingement test and cam/noncam. All tests were 2-sided and significance was set at P < .05 for each test. An ICC analysis was made for the intra- and interobserver tests.

Results

Participants in the cam and noncam groups were similar in terms of body mass index (cam, 22.7 [SD, 2.5] and noncam 23.1 [SD, 3.9]), but a significant age difference was found between groups. The mean age for the enrolled population was 17.7 (SD, 1.4) years: cam group 18.0 years (SD, 1.2) and the noncam group 17.4 years (SD, 1.3) (P = .02) (Table 1).

The values for and distribution of clinical and radiological measurements are presented in Tables 2 and 3. The mean values for comparison of the clinical examination between the cam and noncam groups are presented for the right leg in Table 2 and for the left leg in Table 3.

TABLE 2.

Range of Motion Versus MRI Cam Findings: Right Hip^a

Test	Cam (n = 26)	Noncam (n = 63)	Difference	95% CI		P Valueb
				Lower	Upper
Supine hip flexion	116.89 (10.45)	121.92 (11.33)	5.03	−0.008	10.08	.050
Supine, internal rotation	24.15 (7.91)	29.03 (9.36)	4.88	0.71	9.05	.022
Supine, FABER test	66.77 (6.68)	68.18 (9.27)	1.41	−2.59	5.41	.485
Sitting neutral, internal rotation	29.00 (9.56)	36.95 (9.71)	7.95	3.45	12.45	.001
Sitting neutral, external rotation	36.04 (8.17)	37.93 (8.48)	1.90	−2.01	5.80	.337
Sitting extension, internal rotation	20.27 (7.43)	25.45 (7.38)	5.18	1.73	8.63	.004
Sitting extension, external rotation	29.31 (7.38)	32.13 (8.24)	2.83	−0.91	6.56	.136
Sitting flexion, internal rotation	32.46 (11.05)	40.90 (9.82)	8.44	3.69	13.19	.001
Sitting flexion, external rotation	34.73 (7.54)	37.61 (7.91)	2.88	−0.76	6.51	.119

^aValues are presented in degrees as mean (SD). FABER, flexion, abduction, and external rotation; MRI, magnetic resonance imaging.

^b P values in boldface indicate statistical significance.

TABLE 3.

Range of Motion Versus MRI CAM Findings: Left Hip^a

Test	Cam (n = 28)	Noncam (n = 61)	Difference	95% CI		P Valueb
				Lower	Upper
Supine hip flexion	116.00 (9.19)	124.47 (9.19)	8.47	4.24	12.69	.001
Supine, internal rotation	25.78 (8.50)	30.60 (9.62)	4.82	0.54	9.10	.028
Supine, FABER test	62.30 (6.48)	65.3 (11.07)	2.97	−1.59	7.53	.199
Sitting neutral, internal rotation	31.56 (8.64)	38.02 (10.34)	6.46	1.92	11.00	.006
Sitting neutral, external rotation	35.93 (6.89)	36.02 (6.93)	0.09	−3.10	3.28	.955
Sitting extension, internal rotation	20.56 (6.44)	26.41 (9.16)	5.85	1.96	9.74	.004
Sitting extension, external rotation	29.56 (7.93)	29.56 (7.20)	0.004	−3.43	3.44	.998
Sitting flexion, internal rotation	36.07 (10.31)	42.32 (10.53)	6.24	1.42	11.06	.012
Sitting flexion, external rotation	35.30 (6.06)	36.17 (6.69)	0.87	−2.13	3.87	.565

^aValues are presented in degrees as mean (SD). FABER, flexion, abduction, and external rotation; MRI, magnetic resonance imaging.

^b P values in boldface indicate statistical significance.

For both the right and the left legs, there was a significantly reduced ROM in the cam group compared with the noncam group for the anterior impingement test, passive supine hip flexion, supine internal rotation, and sitting internal rotation with the pelvis and lumbar spine in all 3 different positions.

Magnetic Resonance Imaging

The cam group consisted of those with an α-angle of ≥55° (Figure 12), while the noncam group’s α-angle was <55° (Figure 13). Eighteen percent had bilateral cam. There were 26 hips (29%) with cam on the right side and 28 hips (31%) with cam on the left side, leading to a total of 54 hips (30%) with cam-type morphology. At an individual level, 40% of the 89 participants who underwent MRI had cam (22% of the females, 61% of the males).

Figure 12.

Magnetic resonance image of the right hip of a 20-year-old female alpine skier with a cam lesion (arrow).

Figure 13.

Magnetic resonance image of the right hip of a 19-year-old female control without any cam lesion.

Clinical Examination

The correlation between an MRI-verified cam and a specific clinical examination is presented below.

Supine Examinations

Standing Leg

No significant association was found between the standing leg and MRI-verified cam.

Passive Hip Joint Flexion

There was a significant difference between the MRI-verified cam and noncam groups for supine hip flexion, with a mean difference of 5° (P = .05) for the right hip and 8.5° (P = .001) for the left hip.

Passive Internal Rotation of the Hip

Supine internal rotation was also significant, with a mean difference of 4.9° (P = .02) on the right leg and 4.8° (P = .03) on the left leg.

Anterior Impingement Test

There was a significant association between pain/discomfort in the anterior impingement test and cam: χ²(1) = 6.628 (P = .01) for the right hip and χ²(1) = 7.675 (P = .006) for the left hip.

FABER Test

No significant differences were found for FABER test.

Seated Examination

Internal Rotation

There was a significant association between all 3 examinations of internal rotation and cam. When the participant was sitting with the pelvis and lumbar spine in a neutral position, there was a mean difference between the cam and noncam groups of 8° (P = .001) for the right hip and 6.5° (P = .006) for the left hip, respectively. Internal rotation when sitting with the pelvis maximally anteverted and the lumbar spine maximally extended showed a mean between-group difference of 5.2° (P = .004) for the right hip and 5.8° (P = .004) the left hip, and internal rotation with the pelvis maximally retroverted and the lumbar spine in a SLUMP position (maximally flexed) showed a between-group mean difference of 8.4° (P = .001) for the right hip and 6.2° (P = .012) for the left hip.

External Rotation

No significant differences were found between the cam and noncam groups in terms of external rotation when sitting.

Discussion

The main findings in the present study show that reduced hip joint internal rotation in the supine and sitting positions, with the pelvis and lumbar spine in all 3 positions, is associated with MRI-verified cam deformity. No significant differences were shown between the validity of the 3 different lumbar and pelvic positions and for the diagnosis of hip joint cam-type FAI.

Moreover, passive supine hip flexion and the anterior impingement test were shown to be associated with MRI-verified cam. This correlates well with what previous studies have shown: that reduced internal rotation in 90° of hip flexion, reduced passive flexion of the hip, and a positive anterior impingement test are associated with radiologically verified FAI.^10,13,32 Clohisy et al¹⁰ found a mean 97° of hip flexion and 9° of internal rotation among participants with symptomatic FAI and 101° of hip flexion and 12° of internal rotation among those with asymptomatic FAI. The tendency in the present study appears similar to that of Clohisy et al,¹⁰ but the mean values for both flexion and internal rotation are higher. However, the groups in these studies are not entirely comparable, as the participants in the present study were from a healthy population sample without diagnosed FAI. Sink et al³² found that 100% of the participants with FAI had a positive impingement test, and Clohisy et al¹⁰ found that 88% of the symptomatic FAI hips had a positive impingement test. This correlates well with the present study, where 82% of the participants with cam on the left hip had a positive impingement test and 85% on the right. Moreover, the findings in the current study also suggest that the degree of internal hip rotation is associated with the position of the pelvis (neutral, anteversion, or retroversion) and the lumbar spine (neutral, extension, or flexion). By testing the internal and external rotation in sitting, it was possible to control and minimize any increased movement in the lumber spine, pelvis, and hip joints, making the results more reliable. In the position with maximum pelvic anteversion and lumbar spine extension, the rotation of the hip joint was shown to be decreased. With pelvic retroversion and lumbar spine flexion, hip joint rotation was shown to be increased. This correlates with a study by Ross et al²⁷ that was able to show, with 3-dimensional models, that dynamic changes in pelvic tilt significantly influence hip joint ROM. The clinical findings in the present study support the findings of Ross et al.²⁷

Although the present study was able to show a statistically significant difference between the 2 groups analyzed, these results must be interpreted with caution, as the mean differences between the cam group and noncam group appear to be small. Moreover, these results emphasize that for the diagnosis of FAI impingement, a combination of symptoms, positive clinical tests, and imaging findings should all be used.¹⁴ The cohort that was examined in the present study were all healthy adolescents, and this may therefore differ from a study involving a symptomatic population with hip/groin problems or patients waiting for FAI surgery. One reason for the modest difference in ROM between the cam and noncam groups could be the relatively late fusion of the separate centers of ossification that form the bones of the pelvis. Partial fusion of the iliac crest can occur from 15 to 22 years of age, with complete union in all individuals by the age of 23 years.⁶ The ischial epiphysis appears between 13 and 16 years of age, begins to fuse at the superior rim of the epiphyseal surface, and continues to develop into the ramal epiphysis, which will continue to fuse toward the pubic body with complete union by 20 and 21 years of age.⁶ It is therefore tempting to speculate that the acetabulum permits slight movement before fusion, making it harder clinically to diagnose a cam-type lesion of the hip. It would be interesting to examine the same cohort after their pelvic physes have fused and study whether the difference in the clinical examination between the cam and noncam groups is greater compared with the findings in the present study.

Limitations

There are some limitations to the present study. A larger sample group might have revealed a greater difference between the cam and noncam groups. The inclusion criteria in the present study selected only a healthy population, but this may have limited the ability to identify greater differences in ROM in the presence of cam compared with a symptomatic group. Other limitations include the accuracy and interpretation of the radiological measurements. Physical examination is always dependent on the examiner, and we attempted to limit the variation in results by limiting the examiners to only 2. Finally, it was difficult to recruit young nonathletes, especially males. An equally large number of nonathletes, with equal sex distribution, would have been desirable.

Clinical Relevance

The clinical relevance of this study is based on the results of an evaluation of a range of clinical tests for diagnosing hip joint cam impingement, facilitating the diagnosis of the condition, and passing the right patients through to radiology. The statistically significant findings highlight that the reduction in internal hip joint rotation is associated with the position of the pelvis (neutral, anteversion, or retroversion) and that the position of the lumbar spine (neutral, extension, or flexion) is relevant when examining a patient with hip symptoms. A greater awareness of the lumbar spine and pelvic positions while examining hip joint ROM clinically may prevent the clinician from misinterpreting results.

Conclusion

The presence of a cam deformity on MRI correlates with reduced internal rotation of the hip in both the supine and sitting positions, passive supine hip flexion, and the anterior impingement test.