4 Hip Imaging and Diagnostic Tests
I. Hip imaging modalities ( Table 4.1 ):
Computed tomography (CT).
Magnetic resonance imaging (MRI).
II. Hip pain often indicates an underlying pathology. Pain may be primary or referred from spine, sacroiliac joint, pubic symphysis, or knee ( Fig. 4.1 ).
III. Comprehensive history and physical examination will suggest possible clinical diagnosis and determine the appropriate confirmatory diagnostic tests.
IV. Disease process, patient age, general health condition, and type of tissue involved (soft tissue or bone) can determine the imaging modality to be employed ( Table 4.2 ).
I. First-line imaging to evaluate hip complaints.
II. Initial radiograph includes an anteroposterior and false profile view of the pelvis, as well as a frog-leg lateral or modified Dunn view of the symptomatic hip. 1 , 2
III. Appropriate image examination and understanding of standard radiographic techniques are necessary for diagnostic accuracy.
IV. Plain radiographic techniques:
AP hip radiographs may be taken in the supine or prone position.
Images of both hips are taken on the same film. The X-ray tube projects toward the middle of a line from the pubic symphysis to the anterosuperior iliac spine of femur.
AP view in supine position: feet in 15 degrees of internal rotation with both patellae.
Femoral anteversion and flexion contracture may distort image magnification. 3
Imaging in patients with flexion contracture is done with the legs positioned perpendicularly to in a flexed position.
AP oblique (Judet): hip should be in 45-degree oblique position. Anterior oblique (obturator oblique) positioning captures anterior column and posterior acetabular wall. Posterior oblique (iliac oblique) position captures the posterior column and anterior acetabular column. It is obtained for assessment of acetabular fracture.
The coccyx and pubic symphysis must be in a straight line and in the midline of the image.
Distance from the superior border of the pubic symphysis and the sacrococcygeal junction of 3 to 5 cm is considered normal. 4 , 5 Obturator foramen and wings of the ilium on both sides must be symmetric.
The lesser, greater trochanters and calcar femoris should be clearly visible.
Both patellae should be directed upward or limbs internally rotated by 10 degrees; this prevents the greater trochanter from overlapping with the femoral head. 3 This is important in fracture diagnosis.
Leg length, neck shaft angle, acetabular depth, acetabular inclination, acetabular coverage, acetabular version, and joint space are evaluated on the AP plain radiograph.
Lateral hip radiographs:
These are useful in the assessment of the femoral head–neck junction offset, the alpha angle (AA). Anterior femoral head–neck junction: In normal cases, the anterior and posterior concavities are symmetric. In cam deformity, it is convex anteriorly. Decreased head–neck offset is characterized by decrease in anterior concavity. Head–neck offset ratio and AA are used to determine the femoral head–neck junction.
Lateral hip radiographic views:
Frog-leg lateral view:
i. Both sides are shown on the same film. The knee is flexed to approximately 40 degrees in the supine position, with the hip externally rotated by 45 degrees. 3
ii. Image is taken with X-ray tube projecting to the middle of the line connecting the upper pubic symphysis and the anterior superior iliac spine.
iii. It evaluates joint congruency, sphericity of femoral head, and femoral head–neck junction offset.
iv. It is useful in diagnosis of femoroacetabular impingement syndrome (FAIS).
Cross-table lateral view:
i. Symptomatic limb is internally rotated by approximately 20 degrees in the supine position, while the opposing limb is flexed at the knee and hip.
ii. The greater trochanter is positioned in such a way that the femoral head–neck junction is visible.
False profile view:
i. The foot of the symptomatic limb is placed parallel to the cassette, and then the pelvis is rotated approximately 65 degrees to the wall stand.
ii. It evaluates the anterior coverage of the femoral head.
Radiographic patterns of the pathologic and developmental conditions.
I. The Young and Burgess classification system categorizes pelvic fractures into types based on mechanism of injury (high-impact injuries). 6
Anteroposterior compression (APC I–III): radiograph shows an open book fracture of the pubic ramus or symphysis.
Vertical shear (VS): radiograph shows fracture of the superior and inferior pubic rami with contralateral sacroiliac joint disruption/dislocation (bucket handle fracture or Malgaigne’s fracture).
Lateral compression (LC I–III): radiograph shows unilateral anteroposterior compression injury with or without a contralateral compression injury (i.e., wind-swept pelvis fracture).
II. Duverney’s fracture: fracture of the iliac wing is seen on plain radiograph.
III. Acetabular fractures: fractures are classified into anterior column, anterior acetabular rim, posterior column, posterior acetabular rim, transverse, posterior column and wall, transverse and posterior wall, anterior column, and posterior hemitransverse fractures based on the Judet and Letournel classification system ( Table 4.3 ).
IV. CT is more sensitive in diagnosing pelvic fractures. 7