Shared morphology of slipped capital femoral epiphysis and femoroacetabular impingement in early-onset arthritis.

A subclinical form of slipped capital femoral epiphysis (SCFE) can lead to subtle morphologic abnormalities, such as cam-type femoroacetabular impingement (FAI). Femoroacetabular impingement is a mechanical hip abnormality that typically affects young populations and leads to hip pain and premature osteoarthritis. Imaging is critical to diagnosis, whether by radiograph, magnetic resonance imaging, or computed tomography. The authors investigated the use of imaging to detect characteristics of subclinical SCFE and cam-type FAI in patients undergoing hip resurfacing. They retrospectively assessed computed tomography scans of 81 hips from 75 patients. Measurements were taken of the proximal femur and included the alpha angle, head-neck tilt, and anterior offset taken in both the conventional oblique axial plane and the radial plane. The cohort consisted of 68 men and 13 women with an average age of 52 years. Ninety percent of hips on the oblique axial view and 95% of hips on the radial view were found to have pathologically increased alpha angles. Negative correlations were found between the alpha angle and head-neck tilt and positive correlations between head-neck tilt and anterior offset ratio. Sixty percent and 68% of hips in the oblique axial and radial planes, respectively, were abnormal for the alpha angle, head-neck tilt, and anterior offset ratio, strongly suggesting SCFE morphology. This study's results show similarity in morphology between cam-type FAI and SCFE, known precursors to osteoarthritis, in an early arthritic patient population.