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Femoro-Acetabular Impingement

FAI: Impingement of acetabular labrum between the femoral head-neck junction and the rim. Leads to labral tear and degenerative changes.



Causes:
- Bony overgrowth (congenital or acquired [SCFE, osteophyte]) of anterolateral head-neck junction (nonspherical femoral head) - Cam or femoral impingement during hip flexion
- Deep acetabulum with overgrowth of the anterior superior acetabulum rim - Pincer type
- Excessive acetabular retroversion (acetabulum oriented too posteriorly)
- Decreased femoral neck anteversion
- Femoral head osteophytes


Film:
- Up-sloping lateral margin of acetabular rim
- Os acetabulum (avulsion fracture)
- Crossover sign (Pincer type FAI): anterior margin of the acetabulum projecting lateral to the posterior margin
- Lateral femoral neck bump
- Herniation pit: fibrocystic change of the anterosuperior femoral neck or a Pitt pit (small well circumscribed lucency with a thin sclerotic rim)
- OA


MR:
- Labral tears
- Cartilage loss and delamination
- Subchondral cysts
- Alpha angle between the axis of the femoral neck and the head-neck junction with the apex at the center of the femoral head < 55 degrees.


XRAY dictation:

Findings: Three views of both hips demonstrate no fracture or dislocation. There is a suggestion of abnormal convexity at the [] femoral head-neck offset. The joint spaces are well maintained. Soft tissues are normal.

CONCLUSION: Findings suggest []-sided Cam FAI, better demonstrated on the accompanying CT.



CT dictation:

TECHNIQUE: 2.5 mm transverse CT images of the pelvis, with coronal and sagittal reformations, without contrast.

FINDINGS:
Multiple CT images of the pelvis and bilateral hip joints demonstrate no acute fracture or dislocation. There is no acetabular overcoverage on this exam. However, there is abnormal convexity at the femoral head-neck offset. There is moderate for age osteoarthritic change suggested at the weight bearing portion of both hips. Mild SI joint arthritis is also seen bilaterally. The arthritis of the hip and SI joints are greater on the right. There is no evidence of os acetabulum. There are no bony lesions. The reminder of osseous structures are within normal limits. Soft tissues are unremarkable.

IMPRESSION: Findings consistent with bilateral Cam FAI with osteoarthritis, greater on the right.