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==
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.
Pincer impingement.jpg|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.jpg|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.
==Clinical Features==
The pain is often insidious with mild groin pain that occurs over many years and then suddenly worsens. The patient often uses a C grip with their index finger and thumb proximal to the greater trochanter to indicate the painful region. The pain is most noticeable when sitting with the hips flexed to 90 degrees for long periods and reduces with standing. There may be additional pain in the back or thigh. The patient may describe mechanical symptoms such as catching, stiffness, or restricted motion. In the presence of an associated labral tear there may be sharp pain with catching sensations.
There may be limited flexion or internal rotation of the hip and provocation of groin pain with FADDIR test. The flexion internal rotation test may also be positive. However both of these tests are sensitive but not specific.
== Differential Diagnosis ==
== Imaging ==
Obtain AP and lateral plain films. See Hip Radiograph for measurements. MRI is the definitive scan.
==Prognosis==
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.
There is also risk for development of labral tears.
==Resources==
==References==
Category:Pelvis, Hip and Thigh Conditions
Category:Developmental Disorders