Femoroacetabular impingement

Figures

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  Fig. 1. Illustration of the anatomical and functional features of the cervico-cephalic junction of the hip. (A) Femoral neck offset in relation to the free border of the femoral head (d). (B) Normal movements of the head in the acetabulum occur when the joint is concentric, i.e., there is a coincidence between the geometrical centers of the femoral head and acetabulum. This allows for a harmonic bearing of the femoral head within the acetabulum. The cervico-cephalic offset (d) allows for the extension in the last degrees of movement. (Drawing adapted from Emary28).

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  Fig. 2. Illustration of the types of movement blocking in cases of femoroacetabular impact. (A) In the absence of cervico-cephalic offset, or its inversion, the femoral head strikes the lateral edge of the acetabulum in the last degrees of flexion movement, associated with internal rotation and/or adduction (cam impingement). (B) When the acetabulum is deep or retroverted, the femoral neck strikes the acetabular rim and causes injury to the labrum (pincer impingement). In sequence, by counter-movement, the femoral head is forced against the posterior edge of the acetabulum, which leads to an additional labral tear. (Drawing adapted from Emary28).

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  Fig. 3. Clinical tests for impingement. (A) For the anterior impingement, the hip is flexed at 90°, adducted, and internally rotated. (B) For posterior impingement, the lower limb to be evaluated is placed outside of the examination table, extended, abducted, and externally rotated. Both maneuvers should trigger the patient's usual pain.

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  Fig. 4. Alterations on hip X-rays in cases of femoroacetabular impact. (A) In the proximal region of the left femur, there is a typical pistol grip deformity, with rectification of the sphericity of the anterior portion of the femoral head (black arrow). In this radiograph there is a greater prominence of the ischial spine, which suggests an associated acetabular retroversion (white arrowhead). (B) The same patient on the Lauenstein view; this radiograph shows the decrease in the head-neck offset on both sides, with alterations that predispose to impingement (black arrows).

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  Fig. 5. The same patient from the previous figure. Profile radiography of the femoral neck, with a measurement of the alpha angle. The center of the femoral head is determined. From this point, a line is drawn until the limit of the spherical portion of the femoral head and another line is drawn along the center of the neck. The angle between the two straight lines is the alpha angle (normal 50°).

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  Fig. 6. Radiography of a hip model with metal repairs to the acetabular rim. On the right side, a Salter osteotomy was simulated, with a 20° edge. Osteotomy causes retroversion of the acetabulum, which can be observed by the crossing of the anterior and posterior edges of the acetabulum (crossover sign; arrow), prominence of the ischial spine (arrowhead), and asymmetry of the obturator foramen.

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  Fig. 7. X-rays in cases of coxa profunda (A) and protrusio acetabula (B). In the latter case, the cephalic entrapment is more severe and there is a bulging in the iliopubic line.