Arthritides, Arthrography, MR, CT, Conventional radiography, Pelvis, Musculoskeletal system, Musculoskeletal joint
J. valakada1, D. N. Srivastava1, S. Sharma2, K. Vijay1, R. MALHOTRA3; 1Delhi/IN, 2NEW DELHI, DELHI/IN, 3DELHI, DELHI/IN
Imaging findings OR Procedure details
All patients with suspected FAI were subjected to plain xray AP of pelvis and hip.MRI was performed in patients having the Xray findings suggestive of FAI .
MR was performed with surface body coils for symptomatic hip from illac crest to the level of lesser trochanterusing 1.5T scanner (Siemen,
Germany) or 3 Tesla scanner (Philips).Indirect MR arthrogram was performed by injecting contrast iv and patient asked to move the affected limb lightly for 10 minutes before the scan.
In addition to the conventional sequences other sequences like MEDIC,3DSPACE were also used to evaluate the cartilage and ligaments
Three types of FAI are recognized.
The first involves an excess of bone along the upper surface of the femoral head: this is known as a Cam deformity,
the name is short for camshaft as the form of the femoral head and neck resembles a camshaft.
The second is due to an excess of growth of the upper lip of the acetabular cup and is known as the Pincer deformity.
The third is a mixture of the preceding two forms.
The result of any of these deformities is increased friction between the acetabular cup and femoral head which may result in pain and loss or reduction of hip function
Plain radiographs are the initial radiological investigation in suspected FAI.Standard conventional radiographic imaging for femoroacetabular impingement includes two radiographs : an anteroposterior pelvic view and an axial cross-table view of the proximal femur. For the anteroposterior pelvic radiograph,
the patient is in the supine position with the legs 15° internally rotated to compensate for femoral antetorsion and to provide better visualization of the contour of the lateral femoral head–neck junction
Cam FAI shows the lateral deformity of the head as the "lateral bump"(fig.1).There is also increased acetabular coverage gtermined by the femoral extrusion angle of more than 25%.Pincer FAI shows the relative small femoral head and the acetabular overcoverage seen as the figure of eight appearance of acetabular margins(fig .7)
NCCT can determine the acetabular coverage and the deformities .Alpha angle is pllotted and the angle measuring more than 55 degree signifies enlarged head in cam FAI(fig5).The acetabular coverage can be measured and focal overcoverage of actetabulum can be seen in pincer FAI(fig 6)
MRI is used to determne the labral status .MR Arthrogram can be done to look for the acetabulum,labrum and ligaments.By indirect MR arthrogram technique,
the acetabular labrum can be better evaluated for tears .Indirect arthrogram has the advantages of lesser radiation exposure,
being nontraumatic and no chance of introducing infection when compared to direct arthrogram.
The degree of cartilage loss can also be evaluated
In indirect mr arthrography the contrast is given intravenously and the patient is asked to exercise the joint for about 15 minutesafter giving the contrast intravenously .the contrast will extravagate into the joint which was active and reach the joint cavity .if there is any break in cartilage or any tearing ligaments,
the contrast will collect in the defect and can be made visible
MR arthrogram can show the labral tears .In cam fai the tears occur mainly in the anterosuperior labrun(fig3).In pincer fai the tears are common in the posterior labrum(fig 2)