The hip joint is one of the major articulations that is often involved with numerous pathologic conditions and injuries. With recent technological advances in imaging, many new methods are available for radiologic evaluation of the hip and pelvic region. In general, conventional radiography remains the initial imaging technique in almost all cases, while computed tomography (CT) and magnetic resonance imaging (MRI) often serve as secondary or subordinate imaging evaluations. However, the accuracy, cost-effectiveness, and convenience of each technique in evaluating different conditions of the hip should be taken into account. This article reviews the most effective imaging techniques for evaluation of hip abnormalities, including trauma, infection, osteonecrosis, arthropathies, neoplasm, and developmental abnormalities.
Ms. Kwong is a medical student at the University of
California, San Diego School of Medicine, San Diego, CA.
ÝDr. Sartoris is deceased.
The hip joint is one of the major articulations that is often
involved with numerous pathologic conditions and injuries. With
recent technological advances in imaging, many new methods are
available for radiologic evaluation of the hip and pelvic region.
In general, conventional radiography remains the initial imaging
technique in almost all cases, while computed tomography (CT) and
magnetic resonance imaging (MRI) often serve as secondary or
subordinate imaging evaluations. However, the accuracy,
cost-effectiveness, and convenience of each technique in evaluating
different conditions of the hip should be taken into account. This
article reviews the most effective imaging techniques for
evaluation of hip abnormalities, including trauma, infection,
osteonecrosis, arthropathies, neoplasm, and developmental
Fractures of the hip are very common in victims of motor vehicle
accidents or postmenopausal women with severe osteoporosis.
Usually, the initial evaluation involves frontal radiography
(figure 1). Further views are recommended for additional evaluation
(i.e., oblique/Judet for the evaluation of the acetabulae, and
inlet and outlet views for information regarding the sacrum and
sacroiliac joints [figure 2]). For the evaluation of severe hip
fractures, CT is superior to simple radiography.
It provides better demonstration of the size, location, and
displacement of fractures, especially in relation to
intra-articular loose bodies, pelvic hematomas, sacral fractures,
and sacroiliac joint diastasis. Advances in spiral (helical) CT
scanning allow for rapid, high-quality, two- and three-dimensional
imaging with decreased interference from patient motion.
Three-dimensional CT imaging is best used to evaluate hip fractures
in conjunction with axial CT scans, since it does not clearly
demonstrate displaced fractures <2 mm. For minimal fractures of
the hip, pelvis, or proximal femur, radionuclide bone scintigraphy
is sensitive, but often nonspecific, and may be negative within the
first 24 hours of injury. MR imaging is superior to CT in detecting
insufficiency fractures, due to its high sensitivity to alterations
within the bone marrow and its accuracy in evaluating soft tissues
around the hip and pelvis.
Osteomyelitis, bone infection usually caused by bacteria (often
, but sometimes a Ringus), is evaluated readily with conventional
radiography (figures 3 and 4), CT, and MR imaging. According to
Bolton et al,
CT changes indicative of osteomyelitis are cortical destruction,
periosteal reaction, and increased attenuation within the marrow
space. CT is also capable of demonstrating surrounding soft-tissue
inflammation. However, MRI is superior to CT for identifying acute
osteomyelitis and areas of active and chronic osteomyelitis,
although CT is capable of detecting sequestra, an indication of
active chronic osteomyelitis.
CT and MRI are both effective in evaluating subacute osteomyelitis,
such as a Brodie's abscess, as a focal intraosseous fluid
collection with surrounding sclerosis. CT and MRI are also very
useful in identifying anatomically localized fluid collections
involved in soft-tissue infection around the hip joint or muscles.
In general, localized soft-tissue infection around the hip should
be excluded when focal fluid collections are not indicative on CT
imaging. Another important use of CT and MRI is that they can
readily distinguish nonlocalized changes of cellulitis from the
focal fluid mass of a soft-tissue abscess, which is important since
cellulitis can be treated medically, while abscess requires
Avascular necrosis and transient osteoporosis
For avascular necrosis (AVN) of the femoral head, the most
sensitive and specific radiologic evaluation is MRI (figure 5A),
specifically, coronal MR images. Occasionally, however, MRI of AVN
may show diffuse marrow edema without focal defects, which is
similar to transient osteoporosis.
The use of intravenous contrast may help to distinct between the
two. It is important to remember that there is a time lag between
the occurrence of histologic changes and the detection of AVN on
MRI. On CT, the earliest sign of AVN is a star-like condensation of
the trabeculae within the femoral head called the asterisk, which
can be central, peripheral, or sclerosis. CT is also excellent in
detecting which femoral surface is intact, which can guide the
planning and surgical treatment of this disease.
Sometimes one may be confused by AVN on MRI, which may only show
diffuse marrow edema without focal defects with transient
This problem can be solved by using intravenous gadolinium contrast
to distinguish the two.
For transient osteoporosis, which can be related to or be a variant
of AVN, radiographs (Figure 5B) and MRI are the best methods of
Radiographs generally show osteopenia, while bone scanning
demonstrates activities within the femoral head region. MRI usually
shows diffuse marrow edema with decreased signal on T1-weighted
scans and more intense signal on T2-weighted scans. Along with the
above methods, dual-energy X-ray absorptiometry is also a good
method to quantitatively assess bone density (figure 6) and
fracture risk of the proximal femur.
Pelvic and hip joints that are more commonly involved with
arthropathies include the sacroiliac joints and the symphysis
pubis. According to Hayes and Balkissoon,
in general, imaging techniques are very useful in providing
information for primary diagnosis, preoperative planning, and
follow-up treatments for suspected arthritis. Usually, conventional
radiographs are the primary imaging modality for suspected
arthritis involving the hip and the pelvis (figures 7 and 8).
Indications of joint-space narrowing, osteophytosis, sclerosis, and
subchondral cyst formation signify the existence of osteoarthritis
(figure 7). For inflammatory arthritis, joint-space narrowing and
articular erosions are involved (figure 9). According to Jelinek et
MR imaging and CT are valuable in evaluating unusual arthritides,
such as pigmented villonodular synovitis (PVNS) and synovial
chondromatosis. However, conventional radiography is not an
appropriate method for assessing sacroiliac joint disease, mainly
due to the curvature of the joint and complications caused by bowel
gas and stool. Therefore, CT, bone scintigraphy, and MR imaging are
usually used as secondary tests. Several recent studies have
suggested the use of MR imaging to assess early sacroiliac joint
Murphey et al
suggests that MR imaging is more sensitive than CT in detecting
cartilage loss, small erosion, and edema.
Primary and secondary tumors (neoplasms)
Generally, conventional radiography is the preliminary
evaluation for suspected primary bone neoplasm (figures 10 and 11).
This is a critical step in identifying the initial formation of any
potential tumors. However, additional imaging is usually needed to
prevent misinterpretation due to other overlapping structures, and
to assess the extent of the lesion for preoperative or other
treatment plans. Both CT and MR imaging are excellent in assessing
the characteristics of a lesion; however, they are not capable of
distinguishing between benign and malignant tumors.
In general, no one technique is recommended for the evaluation of
bone metastases. Bone scintigraphy suffers from low specificity and
low sensitivity. MR imaging usually presents heterogeneity in the
pelvic and proximal femoral region, especially for older or obese
patients. Hayes and Balkissoon
suggested the use of CT (figures 12 and 13) along with a
percutaneous biopsy to confirm suspected metastases on radiographs
Congenital and developmental abnormalities
Developmental dysplasia of the hip (DDH), also known as
congential hip dysplasia, is generally evaluated by radiography
(figures 14A and B, and 15), ultrasonography, and MRI.
MRI is especially useful because it does not expose patients to
radiation, and it is able to evaluate surrounding soft-tissue
structures clearly. CT arthrography, with the injection of contrast
medium to the joint, is very useful in evaluating DDH (figure 14C)
after intraoperative reduction.
For proximal femoral focal deficiency (PFFD), a cogenital
partial absence of the upper femur can be detected by MRI or CT. It
is often hard to evaluate with radiography, due to the variable
nature of the disease. In general, MRI is superior to CT for the
evaluation of PFFD due to its improved contrast resolution and
multiplanar imaging capability.
Pain of the hip and pelvic region is generally the first sign of
clinical abnormality involving this major articulation of the body.
Usually, radiography is the first step in the evaluation of
patients with hip pain; however, CT and MRI are also crucial
diagnostic tools in the accurate assessment of hip disease. The
indications or imaging findings of these different abnormalities
can provide efficient and specific evaluation of the hip.