Fact-sheet: Femoroacetabular impingement
Updated on 10/03/2018 at 9:15 AM
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Definition
Abnormal contact between the femur and the acetabulum causing pain and significant functional impairment, resulting either from a non-spherical femoral head or from a non-covering anterior acetabular wall.
--> localized excess mechanical stress during extreme hip movements.
Risk of early osteoarthritis.
Cam-type impingement: deformity at the head-neck junction (bony bump) that conflicts with the labrum and, over time, the cartilage
Pincer-type impingement: excessive coverage of the femoral head by the acetabulum
Clinical features
Young patients 30-40 years old, athletes.
Mechanical groin pain with flexion, internal rotation, and adduction (impingement sign on clinical examination).
Radiography
AP and lateral hip radiographs and Dunn view (hip flexed at 90° and abducted at 20°: detection of head-neck junction deformity).
Cam effect:
- Pistol-grip deformity in advanced forms due to filling-in and flattening of the head-neck junction.
- Decreased head-neck offset = distance between the line passing through the most anterior point of the femoral head and its parallel passing through the anterior border of the femoral neck, which should be greater than 9 mm.
Possible calcifications in cases of degenerative labral lesions.
Pincer effect:
- Signs of coxa profonda or acetabular retroversion (=crossover sign: posterior rim of the upper acetabulum projecting lateral to the anterior rim of the acetabulum, and the center of the femoral head projecting lateral to the posterior rim).
CT
Allows better measurement of morphologic abnormalities through reconstructions in both planes: femoral anteversion, alpha angle (cf. MRI), presence of a bump, femoral offset.
MRI
MRI performed with intra-articular contrast injection.
The previously described morphologic abnormalities are found + measurement of the Nötzli alpha angle.
Nötzli alpha angle = reflects filling-in of the head-neck junction --> angle between the line joining the center of the femoral head and the neck, and the line passing through the center of the femoral head and the point at the head-neck junction.
Best measured on MRI rather than other imaging modalities.
Evaluation of the acetabular labrum: labral tear, detachment, paralabral cysts, labral calcifications.
Evaluation of the acetabular cartilage: chondrolysis, sclerotic and geodic changes of the subchondral bone.
Management
Functional medical treatment: rest.
Surgical treatment.
