CHAPTER 22

Femoroacetabular Impingement

Introduction/Etiology

• Femoroacetabular impingement (FAI) is a condition of the hip in which the femur and/or acetabulum are mildly misshapen, resulting in abnormal contact between the two, which may generate symptoms due to chondral delamination, labral avulsions or tears, or joint degeneration.

• The 3 types of impingement are cam, pincer, and combined.

• Cam impingement (femur-based disorder)

— A nonspherical femoral head impinges on the acetabulum, causing pathology in the labrum and chondrolabral junction.

— Characterized by excess bone at the head-neck junction, typically the anterolateral neck

— Shear contact stress at joint level results in consequent cartilage wear.

— More common in young males

• Pincer impingement (acetabulum-based disorder)

— Overcoverage of the acetabulum results in excessive contact between the acetabular rim and the femoral neck.

— The anterosuperior acetabular overcoverage results in relative acetabular retroversion (posterior malorientation of the acetabulum in the sagittal plane).

— Contact stress between acetabular rim and femoral neck pinches the labrum and can result in a labral tear

— Common in middle-aged women

• Combined

— Patient has both cam and pincer deformities

— Most common form of impingement

• Symptoms may be more apparent in athletes who participate in repetitive activities that require increased hip range of motion (eg, gymnastics, soccer, dance, track and field)

• A slipped capital femoral epiphysis (see Chapter 20) can also result in abnormal anatomy that predisposes to impingement.

• Most children and adolescents are treated successfully with optimized physical therapy interventions.

Signs and Symptoms

• Patients report hip pain, typically in the groin, although it may radiate laterally to the greater trochanteric region or medially near the hip adductor muscles.

• Extended periods of hip flexion, such as prolonged sitting, may result in exacerbation of symptoms.

• Patients may experience limitations in hip range of motion, typically flexion and internal rotation.

• Mechanical symptoms related to labral or chondral injury may include catching, popping, or clicking.

Differential Diagnosis

• Chondral or labral injury not related to FAI

• Osteoarthritis

• Hip dysplasia

• Internal or external snapping hip

• Lumbar radiculopathy

Diagnostic Considerations

PHYSICAL EXAMINATION

• Examination may reveal a decrease in active and passive range of motion of the hip.

— Typically, decreased flexion and internal rotation

— May exhibit greater external rotation than internal rotation

• Pain with impingement tests

— Flexion, adduction, and internal rotation (FADIR) will typically cause pain in cases of anterior impingement.

• Antalgic gait

IMAGING

• Radiographs

— Radiographs should be obtained in patients with symptoms consistent with FAI to evaluate the severity and help rule out other pathology.

— Up to 60% of young patients with hip pain will have radiographic findings consistent with FAI, although FAI may not always be the cause of the pain.

— Anteroposterior pelvis, true lateral hip with leg in 15 degrees of internal rotation, modified Dunn view, and false-profile views are typically obtained (Figure 22-1).

■May reveal abnormal contour of the femoral head or neck, acetabular retroversion or overgrowth, or both (Figure 22-2)

— Pistol grip deformity

■Result of nonspherical femoral head in cam impingement (Figure 22-3)

— Crossover sign

■Radiographic indicator of acetabular retroversion in which the anterior acetabular wall crosses lateral to the posterior wall (Figure 22-2)

Figure 22-1. Radiographic workup of a hip, including anteroposterior pelvis (A), Dunn pelvis (B), frog lateral hip (C), and false-profile hip (D) views.

Figure 22-2. Modified Dunn view radiograph demonstrates a small cam lesion of the right femoral neck (arrow). Dashed and solid lines indicate anterior and posterior walls, respectively, creating a crossover sign consistent with acetabular retroversion.

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