Background/Purpose: It has been proposed that femoroacetabular impingement (FAI) causes early osteoarthritis (OA) in non-dysplastic hips. FAI occurs predominantly in two different types, ”cam” or ”pincer”. Cam impingement is due to a cam-type deformity with a non-spherical femoral head and/or a decreased anterior head-neck offset. Pincer impingement results from increased acetabular depth with over-coverage of the femoral head, while the head-neck configuration may be normal. FAI is often seen in young male athletes referred to rheumatologists or orthopaedic surgeons because of groin pain, and internal rotation in flexion is usually diminished. The aim of this study was to determine whether diminished internal rotation can be used to detect FAI in young asymptomatic males. 

Methods: Study subjects were young males aged 18 to 21 undergoing compulsory conscription for the Swiss army. Participants completed questionnaires pertaining to pain, stiffness, and physical function, and internal rotation was measured on a validated examination chair. A random sample of the examined participants was invited for magnetic resonance imaging (MRI) of the hip. Cam-type deformities were graded from 0 to 3: 0=normal, 1=mild, 2=moderate, 3=severe. Pincer impingement was defined by increased acetabular depth, which was specified as the distance (in mm) between the center of the femoral neck and the line connecting the anterior and posterior acetabular rims. Values were positive if the center of the femoral neck was lateral to the acetabular rim, with ≤3 mm representing increased acetabular depth. Based on a fitted receiver operating characteristics (ROC) curve, we estimated sensitivity, specificity, positive and negative likelihood ratios (LR) for different internal rotation cutoffs for cam impingement, pincer impingement, and the combination of both, as compared with the reference group without deformity on MRI.

Results: 244 asymptomatic males underwent imaging, with a mean age of 19.9 years. Fifty-nine subjects showed definite cam-type deformity, eight increased acetabular depth, and eight a combination of both. Area under ROC-curves were 0.725 for detection of the first group, 0.549 for detection of the second, and 0.895 for detection of the third group as compared with the reference group. A cut-off value of 30º of internal rotation yielded a sensitivity of 0.63 and a specificity of 0.69 for the first group, 0.13 and 0.69 for the second, and 1.00 and 0.69 for the third. An internal rotation of ≥30º had sufficient power to rule out the combination of both types of impingement: the crude negative likelihood ratio (LR) was below 0.10. Conversely, an internal rotation of ≤20º had the required power to rule in the combination of both types of impingement, with a positive LR of 12.7.

Conclusion: Different cut-offs for internal rotation may be used to accurately rule in or rule out the combination of cam- and pincer-type impingement. Internal rotation is not useful for detecting pincer-type impingement.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/diagnostic-value-of-internal-rotation-measurement-in-patients-with-cam-and-pincer-type-deformities-of-the-hip/