Radiographic evaluation of the painful adolescent and young adult hip

Abstract

Radiographic evaluation of hip pain in adolescents and young adults is an important component of the assessment to aid in the identification of the cause of pain, distinguish between etiologies of early hip degeneration such as acetabular dysplasia (instability) and femoroacetabular impingement, and guide further workup and management. Recent advances in radiographic assessment include the importance of obtaining a standing anterior-posterior radiograph to illustrate the functional position of the pelvis, the use of anterior and posterior wall indices to illustrate anterior and posterior wall coverage and the importance of interpreting radiographic measures in the context of a patient's sagittal balance. Advances in magnetic resonance imaging, computed tomography, and ultrasound have also occurred and can provide further diagnostic clarity. The purpose of this work is to review the literature to provide a systematic approach to the radiographic evaluation of hip pain in skeletally mature adolescents and young adults.

Key concepts: (1)The standing AP pelvis, 45° Dunn, and false-profile views provide a preliminary comprehensive radiographic assessment of the symptomatic hip in the skeletally mature adolescent and young adult and help to distinguish between instability and impingement.(2)The Lateral Center Edge Angle (LCEA) should be augmented by the anterior center edge angle (ACEA), anterior wall index (AWI), and posterior wall index (PWI) to obtain a more complete understanding of 3-dimensional femoral head coverage from plain radiographs.(3)While the crossover and posterior wall signs on radiographs can be helpful in screening for acetabular retroversion and anteversion, CT should be used to confirm if considering reorientation or resection.(4)Cam morphology should be quantitatively assessed using the alpha angle and head-neck offset on the 45° Dunn view.(5)Dynamic ultrasound may be useful in illustrating the motion associated with impingement and instability in real-time but may be limited by the technician-dependent nature of this modality.

Keywords: Borderline dysplasia; CT; Femoroacetabular impingement; Hip dysplasia; Instability; MRI; Radiograph; Ultrasound.

Figure 1

Radiographic Views of the pelvis: Anterior-Posterior (left), 45° Dunn (middle), False Profile (right).

Figure 2

A: Positioning for standing AP view, with limbs in 15° internal rotation and tube-to-film distance of 120 cm. Fig. 2B: Positioning for 45° Dunn view, with affected hip flexed to 45° and abducted to 20°. Fig. 2C: Positioning for false profile view, with pelvis rotated 65° from cassette and foot of affected side parallel to cassette.

Figure 3

Landmarks on AP radiograph that help to define the acetabulum: anterior wall, posterior wall, iliopectineal line, ilioischial line, teardrop, and sourcil.

Figure 4

Lateral Center Edge Angle (LCEA) using the Wiberg method utilizing the lateral acetabular rim, resulting in a “normal” LCEA value (left). Ogata method utilizing lateral margin of sourcil, on the same image, resulting in an LCEA value associated with borderline dysplasia (right).

Figure 5

Anterior center edge angle, measured as the angle between the vertical and a line connecting the center of the femoral head to the anterior sourcil.

Figure 6

Measurements for calculating anterior wall index (AWI) and posterior wall index (PWI). a = distance along neck axis from edge of femoral head to anterior wall. p = distance along neck axis from the edge of femoral head to posterior wall. r = radius of femoral head. AWI = a/r. PWI = p/r.

Figure 7

Tönnis angle for measuring acetabular inclination. Angle formed between horizontal line parallel to pelvis and line connecting medial and lateral edges of sourcil.

Figure 8

Ischial spine sign shown by prominent extension of ischial spine into pelvis (left), compared to normal AP pelvis (right). The presence of ischial spine sign indicates acetabular retroversion.

Figure 9

Positive crossover sign (left). Positive posterior wall sign (right), with the center of femoral head (X) lying lateral to posterior wall. The presence of crossover sign and posterior wall sign together indicate true acetabular retroversion.

Figure 10

Femoroacetabular Roof (FEAR) Index, measured as the angle between a line through the central third femoral physeal scar and a line connecting the medial and lateral sourcil.

Figure 11

Shenton’s line, formed as an arc from the superior border of the obturator foramen to the inferomedial aspect of the femoral neck.

Figure 12

Prominent low-lying anterior inferior iliac spine (AIIS). Mistaking the AIIS for the anterior rim can lead to a false positive crossover sign (left). Using the appropriate landmarks for the anterior wall in this radiograph illustrates that the crossover sign is absent (right).

Figure 13

An adolescent male with cam deformity. Alpha angle is measured as the angle between the femoral neck axis and a line connecting the center of the femoral head to where the femoral head-neck junction exits a best fit circle around the femoral head (left). Head-neck offset is determined by drawing a line along the femoral neck axis (dashed line). The head-neck offset is then measured as the distance between a parallel line at the concavity of the femoral neck and a parallel line at the convexity of the femoral head (right). Alpha angle >50 to 55° and head-neck offset ratio <0.18 are indicative of cam impingement.

Figure 14

Sagittal parameters of pelvic incidence, pelvic tilt, and sacral slope. Pelvic incidence = pelvic tilt + sacral slope.

Figure 15

T2 MRI sagittal (left) and axial (right) views of hip demonstrating labral hypertrophy in adolescent with dysplasia. The labrum (white arrow) is hypertrophied as indicated by the dashed line showing increased labral length.

Figure 16

T2 MRI radial (left) and coronal (right) views of hip demonstrating labral tear in adolescent with cam deformity and dysplasia. The labrum (arrow) should be triangular with low signal intensity, but in this case demonstrates irregularity with increased signal intensity, indicating a tear. Image obtained with 3T magnet rather than arthrogram.

Figure 17

Acetabular version measurement on axial CT, measured as an angle between the line connecting anterior and posterior acetabulum, and a line tangent to the horizontal axis of posterior acetabulum. Normal acetabular version = 15 to 20°. Anteversion >25°. Retroversion <15°.

Figure 18

Femoral torsion, measured using the Jarrett technique on oblique axial CT view, as the sum of the femoral neck angle (left) and the femoral condylar angle (right). Femoral anteversion is 15 degrees in this example.

Figure 19

Dynamic ultrasound of left hip demonstrating anterior translation of femoral head relative to the anterior acetabular rim of ∼4 mm from rest position in neutral (top) to stressed position in extension, abduction, and external rotation (bottom).

Figure 20

Systematic approach to the painful adolescent and young adult hip.