Femoroacetabular Impingement

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Femoroacetabular Impingement

Femoroacetabular impingement (FAI) refers to abnormally shaped femoral head and neck junction and/or acetabulum. This creates a space conflict with hip flexion. It is a risk factor for early onset hip osteoarthritis, but is not a sufficient cause.

Classification

Pincer impingement. There is acetabular over-coverage, and the femoral neck abuts against the labrum, damaging it as well as the underlying cartilage. With continued hip flexion there is subtle joint subluxation and a contre-coup lesion forms. There is delamination of the labrum from the acetabular cartilage.

Cam impingement. The cam lesion abuts against the labrum, pushing it outwards and compressing the acetabular cartilage inwards. The labrum separates from the cartilage and the acetabular cartilage delaminates from the bone.

There are two patterns, cam and pincer, as well as a combination of both types. In cam FAI there is a thickened, aspherical femoral head-neck junction, which abuts against the anterosuperior labrum with hip flexion, and results in compression of the labrum and acetabular cartilage. This leads to separation of the labrum from the acetabular cartilage and delamination of the acetabular cartilage from the subchondral bone.

In pincer FAI, there is an overcoverage of the acetabulum with a deepened acetabular on the femoral head. The femoral neck abuts against the acetabular labrum and compresses it, damaging both the labrum and underlying cartilage. Lesions usually occur anterosuperiorly from hip flexion like with cam lesions, but also posteroinferiorly from posterior subluxation due to continued flexion causing a contre-coup lesion.

The CHECK study assessed 1002 patients aged 45–65 years with early symptoms of hip OA but without definite radiographic evidence of the same over 5 years. At baseline, 76% of the included hips had no radiographic signs of osteoarthritis and 24% doubtful osteoarthritis. Cam deformities and acetabular dysplasia were shown to be associated with an increased odds ratio for progression to early onset osteoarthritis. While pincer changes were actually associated with a reduced risk.

Clinical Features

Pain is felt in the groin or in an area. The patient often uses a C grip with their index finger and thumb proximal to the greater trochanter to indicate the painful region. There may be limited flexion or internal rotation of the hip and provocation of groin pain with FADDIR test.

Literature Review

Literature Review

Reviews from the last 7 years: review articles, free review articles, systematic reviews, meta-analyses, NCBI Bookshelf

Articles from all years: PubMed search, Google Scholar search.

TRIP Database: clinical publications about evidence-based medicine.

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