Home

Musculoskeletal

Clinical Topics

Great Cases

MSK MR Technical Tips

Quick Reference

MSK Protocols

Extremity Protocols

Scan Prescription

Signa GE 1.5 T  LX 9.1 protocols

MR Information

Acronyms

Vendor Sequence Names

GE 1.5 Platforms

MSK Procedures

Discography

Referring Providers

Iodinated Contrast

Pre-IR Checklist

CAM-Type Femoro-Acetabular Impingement

Coronal scan through the right hip (left), showing the proper angle of prescription for the axial oblique (right) sequence. On the axial oblique scan, the alpha angle is calculated as the angular relationship between best fitting circle around the femoral neck as it intersects the union with the femoral neck anteriorly, and the bisecting line along the femoral neck.
Notice the anterior-superior labral tear (arrows), as well as the areas of peripheral cartilage loss (arrowheads).
AP and frog-leg lateral show a rim of osteophytes along the femoral head, as well as a prominent head-neck junction on the frog-leg view, suspicious for cam-type impingement.

Comments

Although there are many reasons to obtain an MR study of the hip, ranging from a suspected occult fracture to AVN, it is commonly the case that MR Arthrography is indicated for young patients with hip pain without a defined etiology. It is in this subset of patients, where early findings of osteoarthritis may be found on radiography, and cartilage loss confirmed on MR. In some, a history of prior trauma, SCFE, Perthes or DDH will explain the early development of degenerative changes.

However, in many such patients there is no abnormal head-neck angle to indicate past-SCFE or an abnormal head morphology to suspect prior Perthes. Further, the CE angle or the VCA angle (if faux-profile views are available) may be normal.

To explain the occurrence of OA in these patients, impingement between the acetabulum and femoral head-neck junction has been invoked. From an imaging standpoint, the triad of cartilage loss, anterior superior labral tear and an abnormal head-neck junction (alpha angle of > 50-55 degrees) has been postulated as diagnostic.

In order to measure this alpha angle, the axial views should be angled as illustrated above.

Please see following reference for additional information:
 

Triad of MR Arthrographic Findings in Patients with Cam-Type Femoroacetabular Impingement
Kassarjian et al. Radiology.2005; 236: 588-592.