Normal Pelvis and Hip

For visualization of osseous anatomy and pathology, bone contours, and joint alignment.

Recommended for any primary evaluation of suspected hip pathology, including fractures, dislocations, bone tumors, and infection.

Gluteal, iliopsoas, and obturator fat pads.

Readily available.

Inexpensive.

Limited soft tissue evaluation.

Patient positioning difficult if there is limited motion for any reason (pain, fracture, ankylosis). Flexion and rotation can produce a false-positive result.

Uses (minimal) ionizing radiation.

See eTable 19-1 (see Fig. 19-1 ; eFigs. 19-1 and 19-2 ).

Ileopectineal or ileopubic line: a continuous line from the medial border of the iliac wing at the junction with the sacroiliac joint along the superior border of the pubic ramus ending at the symphysis pubis. Forms the anterior column and is essential in the evaluation of pelvic trauma tumors or metabolic disease such as Paget disease.

Ileoischiatic line: a line that can be drawn from the ilium to the ischial tuberosity, forming the posterior column.

The acetabular rims form two arc-shaped lines. The anterior rim is more medial than the posterior rim that lies laterally.

Teardrop line: the summation of the shadows of the medial acetabular wall.

Acetabular fossa: normal hips have an acetabular fossa lateral to the ileoischial line.

The center-edge (CE) angle is the most important measurement on the anteroposterior view of the pelvis, and if abnormal it is diagnostic of acetabular dysplasia. This angle is used to assess the superior and lateral coverage of the femoral head by the bony acetabulum. Coverage of the femoral head is considered adequate if the angle measures at least 25 degrees (see Fig. 19-2 ); less than 25 degrees is considered acetabular dysplasia, and greater than 39 degrees is diagnostic of overcoverage.

The horizontal toit externe (HTE) angle is used to evaluate the orientation of the acetabular roof in a coronal plane and the superior lateral coverage of the femoral head ( eFig. 19-3 ).

An acetabular index of depth to width establishes the depth of the acetabulum.

Percentage of the femoral head covered by the acetabulum ( eFig. 19-4 ). Coverage of less than 75% is pathologic.

Neck-shaft angle (see Fig. 19-3 )

Although femoral neck anteversion can be determined from plain films by direct or indirect methods, each method requires specific additional radiographic views, and CT is usually performed when needed.

MDCT ( eFig. 19-5 ) defines or excludes a suspected abnormality that is ambiguous using conventional radiography, especially bone abnormalities.

Provides high-resolution true isotropic volume datasets

Postprocessing orthogonal multiplanar, oblique multiplanar, and volume-rendered reconstructions of the osseous anatomy allow visualization of complex osseous anatomy and pathology ( eFig. 19-6 ).

Evaluation of trauma: complex fractures, intraarticular fragments, and dislocations. Contrast-enhanced CT and MDCT angiography may be necessary to rule out extravasation.

Evaluation of acquired and congenital abnormalities

Evaluation of bone tumor: matrix calcification (osteoid, cartilage) in some bone tumors

Evaluation of soft tissue calcifications and infection

Posttreatment evaluation, including degree of healing, adequate reduction, joint congruity, and fixation devices

Excellent depiction of osseous structures and calcified tissues

Multiplanar and volume-rendering capabilities (compensates for metallic streak artifact)

Nonclaustrophobic

Availability

New software is being used to guide orthopedic surgeons in osteochondroplasty planning where they can dynamically visualize the relation between femoral head junction and acetabulum moving the femoral head in external rotation

Limited visualization of soft tissues, although better than conventional radiography

Uses ionizing radiation

Expensive

Invasive when used with arthrography

See eTable 19-2 .

See References and .

Femoral neck anteversion. The technique varies slightly from one author to another. It consists of two or three slices, 5 to 10 mm thick, through the femoral neck to obtain a line through its axis and two or three slices through both femoral condyles to draw the posterior bicondylar tangential line. The angle between them represents the femoral-neck anteversion angle. Normal values for adults are 12 to 15 degrees ( eFig. 19-7 ).

Acetabular coverage: axial slice through the center of both femoral heads, anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and global acetabular coverage by the horizontal acetabular sector angle (HASA). A line is drawn through the center of both femoral heads; the angle between this center and the line to the most anterior point of the acetabulum is the AASA, whereas the angle between this center and the line to the most posterior point of the acetabulum is the PASA. Normal values of AASA are 63 degrees in men and 64 degrees in women, and values for the PASA are 105 degrees in both sexes. The HASA is obtained by adding the AASA to the PASA.

A conventional arthrogram is performed first (as described under MR arthrography) using diluted iodinated contrast material (2 : 1) for a total of 13 to 15 mL.

The CT examination is performed without delay (to avoid extravasation and dilution of contrast agent and thus avoid loss of capsular expansion). Some authors recommend active movement to facilitate extensive coating of the articular surface by the contrast material.

Patient position: supine with feet in internal rotation

MDCT series on 32, 64, or higher number of rows. Our protocol for a 64 MDCT is 100-120 kVp, 200 mAs, 1 mm thick.

Kernel with bone and soft tissue reconstructions is recommended.

Visualization and assessment of soft tissue anatomy and pathology

Multiplanar

Nonionizing

Expensive

Claustrophobic in closed magnets

Long examination time

Patient motion and respiratory motion artifacts

The optimal timing for dynamic technique has not yet been determined.

Suggested parameters using a 1.5-T magnet

Pelvic or torso phased-array coil

Slice thickness: 3 to 4 mm

Matrix: 512 × 512

Field of view: 30 to 40 cm

• Axial sections from the top of the iliac crest to below the lesser trochanters ( eFig. 19-9 ).

  

• Coronal sections from the sacroiliac joint to the pubic symphysis ( eFig. 19-10 ).

  

• Sagittal sections from the anterior acetabulum to the posterior acetabulum ( eFig. 19-11 ).

  

• Oblique sagittal sections following femoral neck orientation ( eFig. 19-12 ).

  

Gadolinium injection may be necessary to assess femoral head vascularization, suspected infection, or bone or soft tissue tumors. Always compare with the unaffected side. To depict Legg-Calvé-Perthes disease, the use of dynamic technique is recommended.

T1 and T2 fat saturation images should be included. See eTable 19-3 .