Femoroacetabular impingement in athletes, part 1: cause and assessment

Abstract

Context: Femoroacetabular impingement (FAI) is a common cause of intra-articular hip pathology and secondary osteoarthritis. It affects athletes at a young age as they push their bodies beyond the diminished physiologic limits imposed by the altered joint morphology. Understanding the cause of this condition and its assessment in athletes is important.

Evidence acquisition: The scientific literature was reviewed to reflect the current understanding of hip joint pathology among athletic individuals. Focus is given to the literature since 2003, when FAI was first reported as a cause of joint damage in the native hip.

Results: There are 3 types of FAI: pincer, cam, and combined. The pathomechanics and pattern of secondary intra-articular pathology are different among the types. History and examination usually reflect findings of joint damage among athletes, and radiographs can reveal the presence of underlying FAI. Other imaging studies may variably aid in detecting the pathology.

Conclusions: FAI is a common cause of hip problems in athletes. Early recognition is an important first step in order to avoid the severe secondary damage that can occur.

Keywords: assessment; athletes; cause; femoroacetabular impingement; hip arthroscopy.

Figure 1.

Pincer impingement occurs from a bony prominence of the anterior acetabulum crushing the labrum against the neck of the femur (A → B). Secondary articular failure occurs over time.

Figure 2.

Cam impingement occurs with hip flexion as the bony prominence of the nonspherical portion of the femoral head (cam lesion) glides under the labrum, engaging the edge of the articular cartilage and resulting in progressive delamination (A → B). Initially, the labrum is relatively preserved, but secondary failure occurs over time.

Figure 3.

The iliopsoas tendon flipping back and forth across the anterior hip and pectineal eminence: A, with flexion of the hip, the iliopsoas tendon lies lateral to the center of the femoral head; B, with extension of the hip, the iliopsoas shifts medial to the center of the femoral head.

Figure 4.

As the iliotibial band snaps back and forth across the greater trochanter, the tendinous portion may flip across the trochanter with flexion and extension, or the trochanter may move back and forth underneath the stationary tendon with internal and external rotation.

Figure 5.

A, the hip joint receives innervation from branches of L2 to S1 of the lumbosacral plexus but predominantly from the L3 nerve root. B, the L3 dermatome crosses the anterior thigh and extends distally along the medial thigh to the level of the knee.

Figure 6.

The C sign: A, the shape of the hand when a patient describes deep interior hip pain; B, the hand is cupped above the greater trochanter, with the thumb posterior and the fingers gripping deep into the anterior groin.

Figure 7.

Log roll test—the most specific test for hip pathology. With the patient supine, gently roll the thigh internally (A) and externally (B) to move the articular surface of the femoral head in relation to the acetabulum without stressing any of the surrounding extra-articular structures.

Figure 8.

The impingement test is performed by provoking pain with flexion, adduction, and internal rotation of the symptomatic hip.

Figure 9.

Carefully palpating the anterior hip, groin, lower abdominal, and adductor region aids in assessing for the presence of soft tissue pelvic pathology.

Figure 10.

Examination maneuver for snapping of the iliopsoas tendon: A, the hip is initially placed in abduction, flexion, and external rotation; B, the hip is then brought into extension with internal rotation, producing the snap of the iliopsoas tendon.

Figure 11.

A properly centered anteroposterior radiograph must be controlled for rotation and tilt. Proper rotation is confirmed by alignment of the coccyx over the symphysis pubis (vertical line). Proper tilt is controlled by maintaining the distance between the tip of the coccyx and the superior border of the symphysis pubis (1- to 2-cm).

Figure 12.

Anteroposterior view of the right hip. The anterior and posterior rims of the acetabulum are marked (white dots and black dots, respectively). The superior portion of the anterior rim lies lateral to the posterior rim (white arrow) indicating overcoverage of the acetabulum. Anteriorly, it assumes a more normal medial position, creating the crossover sign (black arrow) as a positive indicator of pincer impingement.

Figure 13.

Anteroposterior view of the right hip. Acetabular retroversion as a cause of pincer impingement is indicated by a shallow posterior wall in which the posterior rim of the acetabulum (black dots) lies medial to the center of rotation of the femoral head (white dot).

Figure 14.

Anteroposterior radiograph of a right hip. An os acetabulum (arrows) is present, and although the cause is variable, it is often associated with femoroacetabular impingement.

Figure 15.

A frog lateral view of the right hip: A, the cam lesion (arrow) is evident as the convex abnormality at the head–neck junction, where there should normally be a concave slope of the femoral neck; B, the alpha angle is used to quantitate the severity of the cam lesion. A circle is placed over the femoral head. The alpha angle is formed by a line along the axis of the femoral neck and a line from the center of the femoral head to the point where the head diverges outside of the circle (arrow).

Figure 16.

Anteroposterior radiograph of a right hip. A herniation pit is present (arrow), often associated with cam impingement.

Figure 17.

Anteroposterior radiograph of a right hip. A large cystic lesion is present (arrows), which can be confused with a neoplasm but simply represents a large herniation pit.

Figure 18.

A sagittal T2-weighted MRI of a right hip. Subchondral edema of the acetabulum (arrows) is present as an indicator of subjacent articular failure seen in association with cam impingement.

Figure 19.

A, a coronal T2 MRI of a right hip illustrates a paralabral cyst (arrows) pathognomonic of associated labral pathology; B, a sagittal T2-weighted MRI of a right hip demonstrates a subchondral cyst (arrows) indicative of associated articular damage.

Figure 20.

A, coronal MRA image of a right hip demonstrates contrast separating the lateral acetabulum from the labrum (arrow). Although a labral detachment cannot be ruled out, the smooth margins suggest a normal labral cleft. B, a coronal MRA image of a right hip demonstrates contrast interdigitating within the substance of the lateral labrum (arrow) indicative of true labral pathology.

Figure 21.

T2-weighted MRI in the coronal (A) and sagittal (B) planes demonstrates significant subchondral edema (arrows). On postcontrast MRA images in the coronal (C) and sagittal (D) planes, the subchondral changes are only subtly evident.

Figure 22.

Computed tomography 3-dimensional reconstructed images of a right hip illustrate a characteristic cam lesion (asterisks).