Normal Pelvis and Hip


Technical Aspects

Techniques and Relevant Aspects

Conventional Radiography

Rationale and Indications

  • 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.

Advantages

  • Readily available.

  • Inexpensive.

Limitations

  • 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 ).

eTABLE 19–1
Conventional Radiography of the Hip-Pelvis
Projections Main Visualized Anatomy and Pathology
Pelvis anteroposterior : Patient is placed supine with feet placed in approximately 15 degrees of internal rotation. The criteria for an acceptable pelvic radiograph include a symmetric appearance of obturator foramina and iliac crest and a true view of both femoral necks (see Fig. 19-1 ) Sacrum, innominate bones (ilium, ischium and pubis, rami), and proximal femur
Anterior column, iliopubic line
Posterior column, ischiopubic line
Anterior and posterior acetabular rims
The medial acetabular wall normally projects lateral to the ilioischial line; if the acetabular wall projects medial to the ilioischial line, the patient has protrusio acetabuli.
Normal trabecular pattern
Osteoporosis
Fat pads
Standing hip anteroposterior (see eFig. 19-1 ) Acetabular dysplasia
Oblique—45 degree anterior oblique * Anterior acetabular rim
Oblique—45 degree posterior oblique Posterior acetabular rim
Axial view—hip abducted * Femoral neck
False profile (Le Quesne method) * Articular joint
View of the acetabulum in profile
Frog-leg view * Used when a hip abnormality is suspected in newborn, toddler, or child
Femoral physis
Lateral projection of both hips and femoral neck

* Standard hip series (see eFig. 19-2 ).

eFIGURE 19–1, Normal standing hip anteroposterior radiograph.

eFIGURE 19–2, Standard hip series. A , Anterior oblique view. B , Axial view, hip abducted. C , False profile, Le Quesne projection. Patient standing with the unaffected hip moved forward so that the pelvis is rotated 65 degrees to the film and central ray centers on the affected hip. D , Frog-leg view, with patient supine with the knees flexed and thighs abducted to approximately 40 degrees so the soles of the feet are in contact.

Measurements from an Anteroposterior View

Normal Pelvic Lines

  • 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.

Acetabular Measurements

  • 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 ).

    eFIGURE 19–3, Horizontal toit externe (HTE angle). This is measured between the horizontal and a line extending from the most medial point of the weight-bearing acetabulum ( T point) to E point. Its normal value should be 10 degrees or less.

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

Femoral Head

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

eFIGURE 19–4, Femoral head coverage. Percentage of the femoral head covered by acetabulum: (A/B) × 100. Coverage of less than 75% is pathologic.

Proximal Head

  • 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.

Multidetector Computed Tomography

Rationale and Indications

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

    eFIGURE 19–5, Hip multidetector CT (MDCT). A , Axial plane. B , Postprocessing orthogonal multiplanar reformatted (MPR) coronal images. C , Postprocessing orthogonal multiplanar sagittal images. D , Coronal 1-mm thick MPR.

  • 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 ).

    eFIGURE 19–6, Volume-rendering 3D reconstructions. A , Anteroposterior view. B and C , Oblique views. D , Posterior view.

  • 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

Advantages

  • 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

Limitations

  • Limited visualization of soft tissues, although better than conventional radiography

  • Uses ionizing radiation

  • Expensive

  • Invasive when used with arthrography

Technical Aspects

eTABLE 19–2
Imaging Protocol Used for a 16-Slice MDCT
Slice thickness 3 mm × 3 mm
Collimation 0.75 mm × 16 slices
Table speed 3-6
Kilovolt peak 120-140
Milliampere seconds 240-280
Intravenous contrast material (polytrauma patient) 120-150 mL 3-4 mL/s
Kernel Soft tissue, bone
Pitch 1-2
Reconstruction Multiplanar, surface rendering
Note: Optimal scanning depends on the clinical question to be answered. Imaging parameters must be adjusted depending on the number of detectors and distribution of the detectors.

Measurements

  • 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 ).

    eFIGURE 19–7, Femoral neck anteversion. Anteversion is an angular measurement that relates the femoral neck's position or posture to the frontal plane. Normal values for adults are 12 to 15 degrees.

  • 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.

Computed Tomographic Arthrography

  • See Reference .

  • Intraarticular injection of iodine contrast material allows visualization of the internal capsular anatomy and pathology. The dilution of saline, gadolinium, iodine contrast, and local anesthetic has been proved safe, and therefore CT and MR arthrography can be performed after a single injection. If iodine contrast exceeds 25%, a decrease of signal intensity on T1Wi has been reported. However, in our experience up to 40% is safe and gives good image quality.

  • Indicated when MRI is contraindicated, in patients with claustrophobia, or in suspected associated injuries

  • Main indication: assessment of bone involvement, acetabular and femoral cartilage surface, and suspected labral tears. The sensibility of CT arthrography is superior to that of MRI for detecting cartilage lesions because of the higher spatial resolution and better delineation between cartilage and high density of the iodine solution ( eFig. 19-8 ).

eFIGURE 19–8, CT arthrography. A , Coronal multiplanar reformatted (MPR) image. B , Coronal thick MPR image; the iodine contrast nicely outlines labrum and cartilage.

Technical Aspects

  • 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.

Magnetic Resonance Imaging: Conventional Pelvis Imaging

Rationale and Indication

  • Visualization and assessment of soft tissue anatomy and pathology

Advantages

  • Multiplanar

  • Nonionizing

Limitations

  • 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.

Technical Aspects

  • 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 ).

      eFIGURE 19–9, Pelvis MRI, axial planing. Axial sections go from the top of the iliac crest to below the lesser trochanters.

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

      eFIGURE 19–10, Pelvis MRI, coronal planing. Coronal sections go from the sacroiliac joint to the pubic symphysis.

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

      eFIGURE 19–11, Pelvis-hip sagittal planing. Sagittal sections go from the anterior acetabulum to the posterior acetabulum.

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

      eFIGURE 19–12, Pelvis-hip oblique sagittal planing. Oblique sagittal sections follow femoral neck orientation.

  • 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 .

eTABLE 19–3
Features of Conventional Pelvis Magnetic Resonance Imaging of the Hip-Pelvis
Imaging Planes Pulse Sequences
Axial T1-weighted, fast spin-echo, proton density–weighted; T2-weighted fat saturated; STIR
Coronal T1-weighted, fast spin-echo, proton density–weighted; T2-weighted fat saturated
Sagittal T1-weighted; fast spin-echo T2-weighted
Additional Optional
Oblique sagittal T1-weighted, STIR
Axial Gradient-recalled echo
STIR, Short tau inversion recovery.

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