Imaging evaluation of the painful hip in adults

INTRODUCTION — 

The hip is a stable, major weightbearing joint with significant mobility. Hip pain has different etiologies in adults and children. In adults, hip pain may be caused by intraarticular disorders such as avascular necrosis (AVN), arthritis, loose bodies, labral tears; periarticular pathology such as tendinitis and bursitis; or extraarticular conditions such as referred pain from lumbar spine, as well as sacroiliac joint and nerve entrapment syndromes.

Imaging modalities used to evaluate adults with hip pain and the appropriateness of particular examinations in different clinical scenarios will be reviewed here. The history and physical examination, which are necessary to develop a differential diagnosis prior to the selection of imaging tests; a general review of imaging tests that are used in the evaluation of bone and joint pain; and imaging modalities used to evaluate the hip in children are presented separately:

●(See "Approach to the adult with unspecified hip pain".)

●(See "Imaging techniques for evaluation of the painful joint".)

●(See "Radiologic evaluation of the hip in infants, children, and adolescents".)

TYPES OF IMAGING — 

The modalities available for evaluation of the hip include:

Plain film radiography — Plain film radiography of the hip is used in the initial evaluation of any cause of hip pain, including trauma and sports injuries, suspected avascular necrosis (AVN), arthritis, complications of hip arthroplasty, infection, dysplasia, tumor, and microinstability [1]. Plain film can also identify causes of referred hip pain, such as sacroiliitis. Plain film may not detect or accurately characterize some hip fractures and bone marrow edema associated with early stages of AVN, osteomyelitis, or sacroiliitis.

Computed tomography — Computed tomography (CT) of the hip without contrast is most useful in the setting of trauma, preoperative planning, and bone tumors, as follows:

●Trauma – In traumatic injuries, CT is used to detect intraarticular extension of a fracture, acetabular fracture, pelvic ring and sacral fractures, and intraarticular loose bodies.

●Perioperative planning – CT is also used for preoperative evaluation of hip fractures, pre- and postoperative evaluation of hip dysplasia, and hip arthroplasty.

●Bone tumor – In the setting of bone tumor, CT is useful to evaluate tumor matrix and detect cortical thinning or destruction. CT is also valuable for guiding biopsy or ablation of certain tumors, such as osteoid osteoma.

CT may not detect trabecular bone injuries, which can be present in femoral neck insufficiency fractures in osteoporotic patients, and will not demonstrate the bone marrow edema of early stages of AVN, osteomyelitis, or sacroiliitis.

Intravenous contrast is administered when septic arthritis or soft tissue abscess is suspected.

Magnetic resonance imaging — Magnetic resonance imaging (MRI) of the hip accurately evaluates the bone marrow, joint space, neurovascular structures, and soft tissues. MRI is the modality of choice for suspected femoral fracture not demonstrated radiographically, osteochondral injuries, muscle injuries, joint effusion, early diagnosis and staging of AVN, iliopsoas and greater trochanteric pain syndrome (formerly trochanteric bursitis), evaluation of infection, and tumor. More unusual disease entities (eg, tenosynovial giant cell tumor and synovial chondromatosis) can also be diagnosed with MRI.

Intravenous contrast is usually reserved for evaluation of soft tissue and bone tumors or vascular malformations. Administration of gadolinium-containing MRI contrast agents is avoided in patients with severely impaired kidney function (eg, estimated glomerular filtration rate <15 to 30 mL/min). If gadolinium-based imaging must be performed in a patient with moderately to severely impaired kidney function, there may be a role for dialysis to reduce the risk of development of nephrogenic systemic fibrosis (NFS). Approaches to prevention of NFS are discussed separately. (See "Patient evaluation before gadolinium contrast administration for magnetic resonance imaging" and "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease", section on 'Prevention'.)

Radionuclide Tc-99m bone scan — Radionuclide Tc-99m (technetium methylene diphosphonate) bone scan can be performed as a whole-body examination or as a focused examination of the hip. It is reserved for suspected fracture or AVN not demonstrated by plain film radiography when MRI is not available or is contraindicated (eg, pacemaker, aneurysm clip). Bone scan is also indicated in the evaluation of metastatic disease, as well as prosthetic device loosening or infection. Radionuclide bone scan can survey a large area when performed as a whole-body examination; however, it is often nonspecific.

Ultrasonography — Ultrasound of the hip is readily available even at the bedside, allows dynamic evaluation of the tendons and muscles, and does not involve ionizing radiation; however, diagnostic performance is highly variable and operator- and patient-dependent.

Ultrasound can readily identify hip effusions and bursal or periarticular fluid collections and is useful for guiding hip aspiration [2], injection of anesthetics and glucocorticoids into the hip joint or bursae, and soft tissue biopsies. In the appropriate clinical setting, ultrasound can be used to identify soft tissue hematoma and partial or complete muscle tears. Another indication for ultrasound is dynamic evaluation of the snapping iliopsoas syndrome [2,3]. (See "Musculoskeletal ultrasound of the hip" and 'Snapping hip syndrome' below.)

Arthrography — The hip joint may be imaged with several imaging modalities, as follows:

●MR arthrography – MR arthrography of the hip with intraarticular gadolinium administration best delineates the joint anatomy, including the acetabular labrum, articular cartilage, and ligamentum teres, and detects loose bodies. MR arthrography is used in cases of hip pain that may involve any of the above-mentioned structures. Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired kidney function (eg, estimated glomerular filtration rate less than 15 to 30 mL/min). (See "Patient evaluation before gadolinium contrast administration for magnetic resonance imaging".)

●Conventional plain film arthrography – The imaging indications for conventional plain film hip arthrography are limited due to the increased use of MR hip arthrography. However, limited conventional arthrography is useful to guide arthrocentesis (eg, when septic arthritis or crystalline arthropathy is suspected). Image-guided aspiration is also warranted when there is clinical suspicion of a hip infection.

●CT arthrography – CT arthrography of the hip with intraarticular iodinated contrast is used in cases where the use of MR arthrography is contraindicated (eg, pacemaker, aneurysm clip).

Fluoroscopic- or ultrasound-guided anesthetic and/or corticosteroid injection of the hip can be a useful tool for the diagnosis and treatment of chronic hip pain [1]. As an example, monitoring the response to local injection of anesthetic may help localize pain when imaging is inconclusive and referred pain is suspected. Persistent pain after anesthetic injection reduces the likelihood of hip pathology as the source of symptoms. This is discussed in more detail separately. (See "Approach to the adult with unspecified hip pain", section on 'Local anesthetic block'.)

IMAGING IN SPECIFIC CLINICAL SETTINGS — 

As noted in the introduction, imaging evaluation of the hip is directed by the history and physical examination findings. (See "Approach to the adult with unspecified hip pain".)

Major categories of hip pathology include rheumatic diseases (eg, osteoarthritis, inflammatory arthritis), trauma (eg, fractures, sports-related injuries), osteonecrosis (ie, avascular necrosis [AVN]), infection (eg, septic arthritis), neoplasm, complications of hip arthroplasty, and greater trochanteric pain syndrome (GTPS). Less common entities such as femoroacetabular impingement syndrome, nerve entrapment syndromes, and snapping hip syndrome are briefly addressed.

Imaging in the evaluation of pediatric hip pain is presented in the context of individual disorders. A list of some entities that affect the hip in children of various ages is presented separately. (See "Radiologic evaluation of the hip in infants, children, and adolescents".)

Rheumatic diseases

Osteoarthritis — OA is the most common arthritis seen in practice. Primary OA has a variety of risk factors, while secondary OA follows an identifiable joint injury or may result from repeated microtrauma, a prior infection, osteonecrosis, crystal disease, or metabolic disorders such as hemochromatosis and ochronosis. Plain film radiography is the initial and is often the only imaging modality needed to diagnose OA and to exclude other causes of hip pain. (See "Clinical manifestations and diagnosis of osteoarthritis", section on 'Diagnosis'.)

●Plain film radiography – Plain film radiography is the initial imaging modality of choice for evaluation of all arthritides. Hallmarks of OA of the hip seen in plain film include superolateral joint space narrowing, osteophyte formation, subchondral sclerosis, and cyst formation (image 1).

●CT – CT is valuable in the setting of premature OA to detect anatomical abnormalities such as acetabular or femoral dysplasia or femoroacetabular impingement. In advanced OA, CT is used for preoperative planning and prosthesis fitting for total hip arthroplasty. CT can also help in localization of paraarticular calcifications or ossification and detection of loose bodies.

●MRI – MRI does not have an established indication in the diagnosis and management of OA [4].

Inflammatory arthritis

●RA – The most common inflammatory arthritis of the hip is RA. (See "Articular manifestations of rheumatoid arthritis", section on 'Lower extremity'.)

•Plain film radiography – Characteristic findings of RA on plain film are bilaterally symmetric and uniform (concentric) joint space narrowing with axial migration, osteoporosis, varying degrees of erosion, and synovial cyst formation, without sclerosis and osteophytes (image 2). (See "Articular manifestations of rheumatoid arthritis", section on 'Plain film radiography'.)

•CT – CT demonstrates erosions earlier than plain film; however, CT is not routinely used for evaluation of RA.

•MRI – MRI demonstrates the hypertrophied synovium and erosions. Use of MRI has been advocated for early diagnosis of RA in the hands [5], but the usefulness of MRI of the hip in early disease is uncertain. (See "Articular manifestations of rheumatoid arthritis", section on 'Magnetic resonance imaging'.)

●AS – AS is a chronic inflammatory disease primarily affecting the axial skeleton (spine and sacroiliac joints). The most common nonaxial joint to be involved is the hip. This section covers imaging of hip disease in AS, not sacroiliitis as the source of referred hip pain. (See "Clinical manifestations of axial spondyloarthritis (ankylosing spondylitis and nonradiographic axial spondyloarthritis) in adults", section on 'Hip pain'.)

•Plain film radiography – Plain film is the single most important technique for detection, diagnosis, and follow-up of AS affecting the hip. Characteristic findings of AS are bilateral symmetrical loss of joint space with axial migration of the femoral head. Ankylosis (fusion) of the joint may ensue. (See "Diagnosis and differential diagnosis of axial spondyloarthritis (ankylosing spondylitis and nonradiographic axial spondyloarthritis) in adults", section on 'Plain radiography'.)

•CT – CT has limited use for the diagnosis of hip involvement by AS.

•MRI – MRI is useful in assessing early cartilage abnormalities and bone marrow edema; however, it is not necessary for diagnosis. (See "Diagnosis and differential diagnosis of axial spondyloarthritis (ankylosing spondylitis and nonradiographic axial spondyloarthritis) in adults", section on 'Magnetic resonance imaging'.)

Crystalline arthropathy

●Calcium pyrophosphate crystal deposition (CPPD) disease – CPPD disease is the most common crystal arthropathy in the hip, caused by deposition of calcium pyrophosphate (CPP) crystals in and around the joint that may be apparent on plain film radiographs. The diagnostic approach to CPPD disease is outlined separately, with information on specific modalities below (see "Calcium pyrophosphate crystal deposition (CPPD) disease: Clinical manifestations and diagnosis", section on 'Diagnostic imaging'):

•Plain film radiography – Plain film radiography is the gold standard in the diagnosis of CPPD. Calcification is seen in the acetabular labrum and/or the cartilage (chondrocalcinosis). Uniform loss of cartilage resulting in axial migration and prominent subchondral cyst formation are seen in later stages. (See "Calcium pyrophosphate crystal deposition (CPPD) disease: Clinical manifestations and diagnosis", section on 'Plain film radiography'.)

•CT and MRI – CT and MRI are not necessary for diagnosis. Dual-energy CT (DECT) is more sensitive and less specific than conventional radiography for CPPD diagnosis and has an overall diagnostic accuracy in the same range as conventional CT. It can be used to identify CPP deposition in cases of diagnostic uncertainty [6].

Imaging guidance may also be helpful when diagnostic arthrocentesis is required. (See "Calcium pyrophosphate crystal deposition (CPPD) disease: Clinical manifestations and diagnosis", section on 'Synovial fluid analysis'.)

●Gout – Gout is caused by deposition of monosodium urate (MSU) crystals and primarily affects peripheral joints. Deposition of MSU crystals in the hip joint is rare but can cause severe pain and significant joint effusion. Imaging modalities for diagnosing gout include plain film radiography, ultrasonography, and DECT. Plain film radiography is not useful for detecting early stages of gout, but it is helpful for diagnosis in later stages. Radiologic features include bony erosions with protruding edges and sclerotic margins as well as soft tissue masses (ie, tophi) that may be calcified. Ultrasound-guided hip aspiration is useful for obtaining joint fluid for analysis as well as for detecting specific imaging findings. DECT has a high sensitivity and specificity of over 88 percent for the diagnosis of gout [7].

Hip trauma

Hip fractures — The optimal imaging for acute hip or pelvic trauma depends on the patient's stability and the suspected type of fracture. The diagnostic approach to specific clinical scenarios involving hip trauma is outlined elsewhere:

●(See "Pelvic trauma: Initial evaluation and management".)

●(See "Minor pelvic fractures (pelvic fragility fractures) in the older adult".)

●(See "Overview of common hip fractures in adults".)

The American College of Radiology has published appropriateness criteria for evaluation of acute hip pain with suspected fracture [8]. While the initial evaluation often involves plain film radiography, they are not sensitive for all types of fractures. Specifically, fractures involving the acetabulum, pelvic ring, or sacrum are better appreciated on CT, while nondisplaced fractures, insufficiency fractures, or stress/incomplete fractures of the femoral neck are better appreciated on MRI (image 3 and image 4). More information on specific imaging modalities is as follows:

●Plain film radiography – Plain film can identify most fractures of the pelvis and hip joint, avulsion injuries, and dislocations. However, advanced imaging modalities are indicated if the clinical suspicion for fracture remains high despite negative plain film radiography.

●CT – CT is indicated in clinically suspected acetabular, pelvic ring, and sacral fractures not seen on plain radiographs. CT can also demonstrate the cortical break, intraarticular loose bodies, fracture alignment, and underlying pathological bone. In addition, CT with multiplanar reconstruction is used for preoperative planning of hip fractures and assessment of nonunion femoral fracture [9]. (See "Overview of common hip fractures in adults" and "Midshaft femur fractures in adults".)

CT is valuable in assessing the direction of the hip dislocation when plain film is not conclusive, evaluating the extent of injury, and in treatment planning. In posterior hip dislocation, CT shows the associated posterior acetabular wall fractures, intraarticular loose bodies, or other mechanical blocks, which may interfere with closed reduction or result in instability after reduction [10]. CT is also indicated after closed reduction of all hip dislocations to assess for associated fractures, residual subluxation, and osteochondral fragments [11,12].

CT may not detect trabecular bone injuries seen in insufficiency fractures of the femoral neck; these are best detected by MRI, as discussed below.

●MRI – MRI is indicated for detection of radiographically occult fractures, such as stress and insufficiency fractures of the femoral neck, intertrochanteric fractures, and subtrochanteric fractures (image 3 and image 4) [13-15]. Pelvic MRI evaluation will show any additional pelvic insufficiency fractures (image 5), avulsion fractures, bone contusions, and muscle and sciatic nerve injury [13,14,16]. MRI will demonstrate the full extent of a fracture (eg, a greater trochanteric fracture), which may appear simple on plain radiography, to determine if surgical intervention is needed [17,18]. (See "Overview of common hip fractures in adults".)

Accuracy of MRI for detecting occult hip fracture is reported to be 100 percent [16], which can be achieved using T1-weighted coronal sequence alone [15]. However, for early detection of associated edema and soft tissue injury, a fluid sensitive sequence is required.

In the follow-up of femoral neck fracture and dislocation, MRI performed at three months is useful in detecting AVN, which is a potential complication from damage to the circumflex femoral artery [13]. (See "Overview of common hip fractures in adults", section on 'Trochanteric fractures' and "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)", section on 'Imaging studies'.)

●Radionuclide Tc-99m bone scan – If there is a high clinical suspicion for fracture with negative radiographs and CT and MRI are not available, then radionuclide Tc-99m (technetium methylene diphosphonate) bone scan is an alternative. The bone scan usually becomes positive within six hours of fracture; however, in older or osteopenic patients, there may be a delay of 48 hours after injury [19]. Sacral fractures have a characteristic appearance on bone scan and can be accurately diagnosed.

●MR arthrography – MR arthrography is indicated in the setting of persistent pain and clinical suspicion of acetabular labral tear, ligamentous or capsular injury, intraarticular loose bodies, and chondral injuries. MR arthrography can detect stability of an osteochondral lesion, which can affect management.

●Ultrasound – In the appropriate clinical setting, ultrasound can identify soft tissue hematoma, as well as partial or complete muscle and tendon tear [20]. Ultrasound can also detect cortical fractures [21]. In cases of pelvic trauma, it may be helpful to identify other complications (eg, intraperitoneal bleeding). (See "Pelvic trauma: Initial evaluation and management", section on 'Ultrasound'.)

Sports injuries — The optimal imaging modality for subacute or chronic hip pain depends on the underlying etiology but generally begins with plain film radiographs. Stress fractures may require more advanced imaging techniques, such as CT, MRI, or radionuclide scanning, particularly during the first few weeks following the onset of pain. Soft tissue injuries are best evaluated on MRI. MR arthrography can be used to evaluate labrum, articular, and osteochondral injuries. The American College of Radiology has published appropriateness criteria for evaluation of soft tissue abnormalities encountered in athletic activities, such as tendonitis or tendon tears, muscle injuries, nerve injuries, and athletic pubalgia [1,8] and also for evaluation of articular cartilage and osteochondral injuries as well as labral tears [1]. The approach to imaging the hip in cases of subacute or chronic hip pain is described in detail elsewhere, with more information non specific modalities as follows (see "Running injuries of the lower extremities in adults: Patient evaluation and common conditions", section on 'Hip and groin injuries' and "Overview of bone stress injuries and stress fractures"):

●Plain film radiography – Plain film radiography detects fracture, dislocation, and avulsion injuries of the ischium, iliac spines, and iliac crest as well as of the greater and lesser trochanters. It also detects premature OA of the symphysis pubis and sacroiliac joints, which is encountered in marathon runners, skiers, and soccer players. Stress fractures of the femoral neck are often not visualized in the first two weeks on plain radiographs [22] and, when clinically suspected, should be further evaluated with MRI. (See "Overview of bone stress injuries and stress fractures", section on 'Plain radiographs'.)

●CT – CT demonstrates small avulsion injuries, which may not be visualized on plain film, and the presence of intraarticular extension of fracture. CT is used for preoperative planning of hip fractures.

●MRI – MRI detects stress fractures, subtle avulsion injuries, osteochondral injuries, periarticular soft tissue injuries such as muscle strains and contusions (image 6), tendon tears, and sciatic nerve injury. MRI is the modality of choice for early detection of stress fractures, which, in turn, prevents complications such as displacement of tensile fractures [22]. MRI of muscle injury may affect the decision for surgical repair and predict time to recovery [23-25]. (See "Overview of bone stress injuries and stress fractures", section on 'Magnetic resonance imaging'.)

●MR arthrography – MR arthrography may be helpful in evaluation of suspected injuries to the acetabular labrum, ligamentum teres, detection of intraarticular loose bodies, and chondral defects. MR arthrography has 90 percent sensitivity and 91 percent accuracy for the detection of labral tears [26].

●Radionuclide Tc-99m bone scan – Radionuclide bone scan with single photon emission CT (SPECT) is 100 percent sensitive for detecting stress fracture; however, it is not specific since it is also positive in stress reaction [27]. (See "Overview of bone stress injuries and stress fractures", section on 'Bone scan'.)

Acetabular labral tears — Labral tears are most often posttraumatic in young adults and degenerative in the older population. The American College of Radiology has published appropriateness criteria for evaluation of labral tear [1]. The approach to diagnosing acetabular labral tears is discussed in detail elsewhere, with information on specific imaging modalities below (see "Approach to hip and groin pain in the athlete and active adult", section on 'Acetabular labrum injury'):

●Plain film radiography – Radiographs cannot detect damage to the fibrocartilaginous labrum and therefore have a low diagnostic yield for labral tears, but they may reveal osteoarthritic changes resulting from a prior injury. Plain film findings that indicate sequela of labral tear are premature or rapidly progressing OA.

●MRI – Conventional MRI is less sensitive for evaluation of acetabular labral tears than MR arthrography [28,29].

●MR arthrography – MR arthrography is the modality of choice for evaluation of acetabular labral tear. MR arthrography defines the presence, morphology, and articular surface contour of the labrum. MR arthrography shows articular cartilage defects, labral tears (image 7), intraarticular loose bodies, and major abnormalities of the ligamentum teres. Sensitivity of MR arthrography for detecting labral injuries is over 90 percent, and accuracy is between 88 and 91 percent [26,30].

●CT arthrography – CT arthrography (CT arthrography) with intraarticular iodine can replace MR arthrography when there is contraindication for MRI (eg aneurysm clips, certain pacemakers) or when MRI is not available.

Avascular necrosis — The femoral head is the most common location for AVN of bone (also referred to as osteonecrosis), with trauma being the leading cause. Other risk factors include use of glucocorticoids, alcohol abuse, radiation, pancreatitis, and hemoglobinopathies. Non-traumatic cases of AVN are often bilateral. Patients on steroids may have asymptomatic AVN. The clinical and laboratory data are not specific for the diagnosis, and confirmation can be done only by imaging. Early detection and surgical intervention by core decompression can prevent progression to femoral head collapse and the need for total hip arthroplasty [31]. The American College of Radiology has published appropriateness criteria for evaluation of AVN of the hip based upon various clinical presentations [32]. The evaluation of suspected AVN is discussed in detail elsewhere, with information on various imaging modalities below (see "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)"):

●Plain film radiography – Plain film radiography is the first imaging examination done to evaluate suspected AVN. In addition to the frontal view, the frog leg view is necessary to evaluate the anterosuperior aspect of the femoral head [32]. Plain film excludes other causes of hip pain and detects advanced stages of AVN, eliminating the need for further imaging. Findings seen in later stages of AVN are subchondral sclerosis, progressing to subchondral fracture ("crescent sign") and collapse of the femoral head with secondary OA (image 8). However, the sensitivity of plain film radiography for the early stages of AVN is low. (See "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)", section on 'Plain radiography'.)

●MRI – MRI is the most sensitive and specific method for diagnosing and staging AVN (image 9) [33,34]. MRI is recommended when there is a clinical suspicion of AVN but when the plain films are negative or equivocal. When the plain films are positive for AVN in one hip, MRI is indicated for evaluation of the contralateral hip for occult AVN [32]. Limited MRI has the potential to become a screening procedure for selected groups of patients at high risk for developing AVN [35]. (See "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)", section on 'Magnetic resonance imaging'.)

The sensitivity and specificity of MRI for diagnosing early AVN range from 97 to 100 percent [33]. MRI is less sensitive in detection of subchondral fracture seen in later stage of AVN, which is better detected by CT [36,37].

The classic MRI finding is the "double line sign" at the necrotic-viable bone interface that is present in up to 80 percent of cases [34]. Associated bone marrow edema is frequently limited to the femoral head, as compared with the bone marrow edema syndrome which shows more extensive involvement. Bone marrow edema syndrome should be considered a marker for potential progression to advanced AVN, and careful follow-up is necessary [38,39] (see 'Bone marrow edema syndrome' below). The signal characteristic of the lesion determines the bone viability and, therefore, the stage of the disease [33,40]. A small percentage of AVN cases may have associated acetabular osteonecrosis [41].

In addition to being useful in diagnosis, MRI is valuable in assessing prognosis and postoperative follow-up. The extent of involvement of the weightbearing area of the femoral head by osteonecrosis and the location of the lesion correlate with progression to collapse [33-35,42]. Laterally located lesions have a higher rate of femoral head collapse than centrally or medially located lesions [33-35]. The extent of involvement of the femoral head also correlates with the likelihood of success of early surgical interventions, such as core decompression. As an example, early-stage AVN involving less than 25 percent of the weightbearing portion of the femoral head treated by core decompression did not progress to collapse, whereas 87 percent of the cases involving more than 50 percent of the femoral head proceeded to collapse [34] (see "Treatment of nontraumatic hip osteonecrosis (avascular necrosis of the femoral head) in adults"). In addition, MRI is important in postoperative follow-up of core decompression, by assessing the return of bone viability [34].

Entities that mimic AVN on MRI are subchondral insufficiency fracture and femoral head osteochondral lesion. Subchondral insufficiency fracture is a non-traumatic lesion that occurs in older osteoporotic patients and is typically seen in the superior lateral aspect of the femoral head [43]. Femoral head osteochondral lesion is a posttraumatic lesion that occurs in young athletes in the medial aspect of the femoral head. The history and location help in differentiating these lesions [44].

●Radionuclide Tc-99m bone scan – Radionuclide bone scan is sensitive for detection of early AVN when MRI is not available or is contraindicated. The changes are apparent before the plain film radiography becomes positive. The accuracy of radionuclide bone scan with SPECT for detecting AVN is approximately 78 percent, which increases to 95 percent when SPECT/CT is used for diagnosis [34,45]. (See "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)", section on 'Limited role of radionuclide bone scanning'.)

●CT – CT is not sensitive for detecting early AVN. CT may show the classic "asterisk sign" secondary to condensation of bony trabeculae and sclerosis. CT is more sensitive than MRI in detecting advanced changes of AVN manifested by subchondral fracture and articular collapse [36]. CT is useful in anatomic localization of osteonecrosis, as well as evaluation of secondary OA and the extent of bone deformity, if osteotomy or arthroplasty is planned [34]. (See "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)", section on 'Computed tomography'.)

Femoroacetabular impingement — Femoroacetabular impingement (FAI) is an important cause of hip pain, and its presence may lead to early OA, particularly in those under age 40. FAI can be caused by a nonspherical femoral head (cam type) or by excessive acetabular covering (pincer type) [46]. (See "Femoroacetabular impingement syndrome".)

Early detection can be made by plain film, CT with three-dimensional (3D) reformation, MRI, or MR arthrography [47-50]. MR arthrography also demonstrates the manifestations of untreated FAI, which include articular cartilage damage and acetabular labral tear. The American College of Radiology has published appropriateness criteria for evaluation of impingement [1]. Treatment of FAI, when indicated, is by open surgical approach or by arthroscopic repair [51]. (See "Femoroacetabular impingement syndrome", section on 'Diagnostic imaging'.)

Infection — Hip infection may present as a radiologic and orthopedic emergency. In the absence of immunosuppression, infection affecting the hip is likely due to bacterial organism (see "Septic arthritis in adults" and "Disseminated gonococcal infection"). Infection around the hip can involve the surrounding soft tissues (cellulitis, abscess, and septic bursitis), the joint (septic arthritis), and the bone (osteomyelitis), which can coexist in advanced cases. The American College of Radiology has published appropriateness criteria for evaluation of suspected osteomyelitis, septic arthritis, or soft tissue infection [52].

Soft tissue infection

●Cellulitis – Cellulitis rarely requires imaging for diagnosis. MRI can be useful to exclude associated conditions, such as myositis, abscess, sinus tract, fasciitis, or osteomyelitis. Contrast administration is valuable and highly recommended [53]. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Diagnosis'.)

●Infectious fasciitis – MRI is very sensitive for evaluation of fascial inflammation, evaluating the extent of infection and the presence of abscess or osteomyelitis, but is not specific for necrotizing fasciitis since it does not easily detect a small amount of fascial air. CT may be more useful because of high sensitivity for fascial gas [53]. (See "Necrotizing soft tissue infections", section on 'Radiographic imaging'.)

●Abscess – Abscesses can be easily detected with CT or MRI, particularly with the use of intravenous contrast. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Diagnosis'.)

●Pyomyositis – MRI is highly sensitive for detection of muscle edema and disease progression to abscess, septic arthritis, or osteomyelitis.

●Septic bursitis – The greater trochanteric bursa is most frequently involved, followed by iliopsoas bursa. MRI is most sensitive, showing focal fluid signal in the bursal location with thick rim enhancement. (See "Septic bursitis", section on 'Diagnosis'.)

Septic arthritis — Fluoroscopically or ultrasonographically guided needle aspiration of the hip is the most important examination in patients with suspected septic arthritis. Plain film radiography may not reveal any specific abnormalities in early disease but may be helpful in excluding other causes of hip pain. Patients with subacute or chronic infection may warrant MRI evaluation, which can assess for the presence of joint effusion and juxtaarticular soft tissue and bone involvement. The American College of Radiology has published appropriateness criteria for evaluation of suspected septic arthritis [52]. More information on the approach to suspected septic arthritis is provided elsewhere, with information on different imaging modalities provided below (see "Septic arthritis in adults", section on 'Radiographic imaging'):

●Plain film radiography – Radiographs are normal initially but may show joint space widening secondary to effusion and osteoporosis on both sides of the joint. In the advanced stages, joint destruction with erosive changes and joint space narrowing are seen.

●MRI – MRI is very sensitive for detecting joint effusion, destruction of the articular cartilage, and bone marrow edema. Subchondral edema is commonly due to hyperemia; however, the extension of bone marrow edema into the medullary cavity and the degree of change in bone marrow signal intensity are helpful to detect osteomyelitis [53].

●CT – CT is indicated when MRI is not available or is contraindicated for evaluation of large joint effusion and femoral head and neck erosion. CT is not sensitive for detecting cartilage destruction in the early stage of septic arthritis.

●Radionuclide Tc-99m bone scan – Radionuclide bone scan is used when MRI is not available. Bone scan demonstrates increased uptake in both sides of the joint but is nonspecific.

●Fluoroscopically or ultrasound-guided joint aspiration – Joint aspiration under fluoroscopic or ultrasound guidance is indicated for diagnostic evaluation and therapeutic drainage of septic joint effusion [20].

Osteomyelitis — Osteomyelitis, or infection of the bone, is often not appreciated on plain film radiographs in the first two weeks. Early diagnosis is enhanced by use of MRI. Radionuclide bone scanning is an alternative for those with contraindications to MRI. The approach to imaging is discussed in detail separately. (See "Imaging studies for osteomyelitis".)

Neoplasm

Tenosynovial giant cell tumor and synovial chondromatosis — Tenosynovial giant cell tumor (TGCT, historically known as pigmented villonodular synovitis [PVNS]) and synovial chondromatosis (synovial osteochondromatosis) are benign proliferative disorders of the synovial lining and are rare causes of hip pain. The American College of Radiology has published appropriateness criteria for evaluation of hip pigmented villonodular synovitis and synovial osteochondromatosis [1]. (See "Treatment for tenosynovial giant cell tumor and other benign neoplasms affecting soft tissue and bone", section on 'Tenosynovial giant cell tumor'.)

The approach to evaluation in these disorders is outlined in detail separately but generally begins with plain film radiography, followed by MRI. More information on specific imaging modalities is as follows (see "Treatment for tenosynovial giant cell tumor and other benign neoplasms affecting soft tissue and bone", section on 'Histopathology and presentation'):

●Plain film radiography – Plain film radiography is typically performed first and may demonstrate well-defined erosions with a normal joint space [54]. In synovial osteochondromatosis, multiple intraarticular loose bodies are seen [55,56].

Uncalcified cartilaginous loose bodies (synovial chondromatosis) are not visible on plain films but can be detected by CT or MRI.

●CT – CT of PVNS demonstrates hyperdense, hemosiderin-laden masses and delineates bone cysts and erosions. CT is also valuable for needle biopsy guidance, when needed, and for preoperative planning. In synovial chondromatosis, CT will show non-calcified intraarticular loose bodies.

●MRI – MRI is the modality of choice for PVNS and for synovial chondromatosis with normal plain film (image 10). MRI findings of PVNS are low-signal, nodular intraarticular masses in all sequences from hemosiderin deposition [55,57]. Bony erosions, when present, and extraarticular extension of the lesion are well-demonstrated on MRI. In synovial chondromatosis, MRI shows non-calcified loose bodies and helps in preoperative planning [55,56].

●CT arthrography or MR arthrography – Hip arthrography, utilizing either CT or MRI, can be used for better delineation of intraarticular masses.

Bone or soft tissue tumor — Plain film radiography is the first imaging modality employed in patients who present with suspected mass lesions in the region of the hip. Further evaluation of bone tumors is facilitated by CT, while MRI is the modality of choice for evaluation of soft tissue tumors. The American College of Radiology has published appropriateness criteria for evaluation of primary bone tumors and soft tissue masses, based upon clinical and radiographic findings [58,59]. The diagnostic approach to patients with suspected bone or soft tissue tumors is described in detail elsewhere, with information on imaging modalities summarized below (see "Bone tumors: Diagnosis and biopsy techniques" and "Clinical presentation, diagnostic evaluation, and staging of soft tissue sarcoma"):

●Plain film radiography – Plain film is the initial modality of choice for detection and assessment of the general features of bone tumor. Accuracy of plain film for detection of soft tissue tumors is limited. Plain film is the most valuable method to evaluate the margin characteristic of bone tumor (zone of transition), which is the important distinguishing feature between benign and malignant bone lesions. Plain film radiography also demonstrates the extent of cortical destruction, periosteal reaction, matrix calcifications, and pathological fractures. Certain radiographic patterns, combined with the age of the patient, can be very suggestive of specific tumors.

●CT – CT is the best method for detecting bony lesions not optimally seen by plain film. CT provides better assessment of cortical invasion, pathological fracture, periosteal reaction, matrix mineralization, and detection of cystic or fatty nature of tumor (image 11). CT is used for biopsy guidance and preoperative evaluation. CT is the best imaging technique for identifying and localizing the nidus of osteoid osteoma [58].

●MRI – MRI is nonspecific for differentiation of most tumors. MRI is the modality of choice for local staging, defining medullary and extracortical spread, and delineating tumor in relation to critical neurovascular structures. The zone of transition described in plain film imaging above is not valid on MRI.

Gadolinium administration is useful to differentiate solid from cystic or necrotic tumor, evaluate responses to nonsurgical therapy, and detect tumor recurrence. Additionally, it may be useful for differentiating benign from malignant soft tissue tumors [59]. As noted earlier, administration of gadolinium-containing MRI contrast agents should be avoided in patients with moderately to severely impaired kidney function (eg, estimated glomerular filtration rate <15 to 30 mL/min). (See 'Magnetic resonance imaging' above.)

●Radionuclide Tc-99m bone scan – The use of radionuclide bone scan for tumor is limited to evaluation of metastatic skeletal involvement (image 12).

Complications of hip arthroplasty — The hip is the most commonly replaced joint. Complications of total hip arthroplasty can be grouped into aseptic loosening and osteolysis, dislocation, infection, periprosthetic fracture, hardware failure, and heterotopic ossification (also known as myositis ossificans when it occurs in the muscle). (See "Complications of total hip arthroplasty".)

Plain film is the first method in the evaluation of hip arthroplasty and serial radiographs are the most important modality in assessing the hip prosthesis; most management decisions can be made based on serial plain film findings without resorting to more complex imaging [60]. However, CT, MRI, radionuclide scintigraphy, ultrasonography, aspiration, and arthrography all have different roles in the assessment of painful hip prostheses [61]. The American College of Radiology has published appropriateness criteria for imaging after total hip arthroplasty [62] (see "Complications of total hip arthroplasty"). More information on imaging findings in specific complications of hip arthroplasty is provided below:

●Aseptic loosening and osteolysis – Loosening of hip prosthesis due to mechanical factors (aseptic loosening) is the most common complication leading to revision surgery. Osteolysis is caused by particle disease resulting from wear of the polyethylene (PE) liner of the acetabulum. The PE debris incites a granulomatous reaction in the adjacent bone, resulting in erosion and cyst-like changes in the periprosthetic bone, leading to loosening. In addition, patients can develop cyst-like regions of fluid or soft tissue density material that protrude into the periacetabular region and communicate with the hip joint (pseudomembrane or pseudobursae formation). (See "Complications of total hip arthroplasty", section on 'Aseptic loosening' and "Complications of total hip arthroplasty", section on 'Osteolysis and wear'.)

•Plain film radiography – Plain film radiography is indicated in routine evaluation of the prosthetic hip and for assessing complications of hip arthroplasty. Postoperative radiographic follow-up in asymptomatic patients is routinely recommended at one, three, and five years, and every five years thereafter. In symptomatic patients in whom loosening is suspected, the initial examination should be a plain radiograph. Comparison with prior imaging is of utmost importance. Radiolucent areas greater than 2 mm adjacent to the prosthesis and progressive changes in follow-up radiographs are highly suspicious for loosening (image 13). Other signs of loosening include development of bony sclerosis adjacent to the distal tip of prosthesis (pedestal formation) and evidence of prosthesis movement. Osteolysis related to particle disease is seen as focal, well-defined radiolucencies and smooth endosteal scalloping around the acetabular or femoral component.

•CT – Multidetector CT (MDCT) with a special technique to reduce metallic artifact is more sensitive than plain film radiographs for evaluation of the prosthesis. For a cemented acetabular component, the presence of linear radiolucencies more than a few millimeters in width is suggestive of loosening. In a non-cemented acetabular component, large cysts surrounding the acetabular component may indicate particle-induced osteolysis. CT can also visualize the associated pseudomembrane formation and the amount of remaining trabecular bone at the rim of the acetabular component. For the femoral component, CT can visualize subsidence (inferior migration of the femoral stem relative to the shaft) and "bead shedding" [63]. CT can be helpful in evaluating the femoral and acetabular bone stock prior to revision surgery.

•MRI – MRI with optimization of image quality for correction of metallic hardware artifact is valuable in differentiating the soft tissue masses surrounding the prosthesis, which can be related to histiocytic osteolysis (particle disease) or infected fluid collections, by demonstrating different signal intensities [62,64,65].

•Conventional plain film arthrography – Arthrography is occasionally performed to evaluate suspected loosening of arthroplasty; however, its accuracy is limited by many false-negatives and false-positives [61]. Arthrography can detect painful pseudobursae formation and can be used for aspiration and injection of local anesthetic or steroid for symptomatic relief.

•Ultrasonography – Ultrasonography can detect pseudobursae formation.

●Adverse local tissue reactions (ALTR) and metal-on-metal (MOM) resurfacing arthroplasty – In younger patients, hip resurfacing arthroplasty has been utilized as an alternative to conventional arthroplasty. These implants consist of MOM articulations, leading to the release of small wear particles that can cause ALTR manifesting as periarticular fluid collections or masses (ie, "pseudotumors"). Although ALTR have been reported most frequently in association with MOM hip implants, they may be seen in hip arthroplasties of any type. (See "Complications of total hip arthroplasty", section on 'Sequelae from metal-on-metal wear debris'.)

Ultrasound and MRI are most commonly used to image ALTR. ALTR are contiguous with the joint capsule and are most commonly located at the posterolateral aspect of the joint, often in continuity with the greater trochanter. They are usually cystic, although anterior lesions may also be seen and are more likely to have solid components.

●Dislocation – Dislocation is the second most common reason for revision surgery. Dislocation is diagnosed on plain film radiography (image 14). CT can better assess the integrity of the acetabular component (image 15). (See "Complications of total hip arthroplasty", section on 'Dislocation'.)

●Infection – Imaging examinations for suspected infection of a prosthetic hip may be of value but are usually not diagnostic. A detailed discussion of the imaging modalities that may be used are discussed separately. (See "Prosthetic joint infection: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Radiographic imaging'.)

●Periprosthetic fracture – Periprosthetic fracture is more common in the femoral component than the acetabular component and is more common in revision hip than in primary arthroplasty. Periprosthetic fracture can occur during placement of the femoral stem or any time after hip replacement, typically at the level of the tip of the femoral stem. Diagnosis is made by plain film radiography. MRI can also identify associated soft tissue injuries such as avulsion of the abductor muscles from the greater trochanter. (See "Complications of total hip arthroplasty", section on 'Periprosthetic fracture'.)

●Hardware failure – Hardware failure can affect both the femoral and acetabular components. The stem of the femoral component can break, representing a metal fatigue stress fracture. "Bead shedding" in non-cemented hip prosthesis (dislodgement of the metal spheres sintered to the femoral metal stem) can be visualized as aggregate clumps of beads on CT, indicating hardware failure [63]. The superior aspect of the PE liner of the acetabulum can gradually wear down, resulting in asymmetric superior location of the femoral head within the acetabulum. In addition to gradual wear, the PE liner can break and separate from the metal acetabular shell, resulting in direct contact between the femoral head and acetabular metal component. Anteroposterior radiograph is diagnostic for evaluation of PE liner wear in 95 percent of cases. Arthrography can also show displaced intraarticular pieces of broken PE liner. (See "Complications of total hip arthroplasty", section on 'Implant failure or component fracture'.)

●Heterotopic calcification – Heterotopic calcification within the soft tissues surrounding the arthroplasty is a more common but less significant complication of total hip replacement, which can be easily diagnosed with plain film radiography. (See "Complications of total hip arthroplasty", section on 'Heterotopic ossification'.)

Other

Greater trochanteric pain syndrome — Greater trochanteric pain syndrome (GTPS) can be due to abductor muscle (gluteus medius and gluteus minimus) tendinopathy and tear and bursitis. The American College of Radiology has published appropriateness criteria for evaluation of soft tissue abnormalities, including bursitis [1]. The evaluation of GTPS is discussed in detail elsewhere, with information on specific imaging modalities provided below (see "Greater trochanteric pain syndrome (formerly trochanteric bursitis)", section on 'Imaging'):

●Plain film radiography – Plain film radiography is usually not helpful in the diagnosis of GTPS but may help to exclude other pathologies such as fractures. Calcifications may be seen in the bursa or adjacent soft tissues. (See "Greater trochanteric pain syndrome (formerly trochanteric bursitis)", section on 'Conventional radiography'.)

●MRI – MRI demonstrates fluid collection within the affected bursa in the case of bursitis, as well as abnormal signal or discontinuity within the abductor muscle tendons in the case of tendinitis and tear (image 16). (See "Greater trochanteric pain syndrome (formerly trochanteric bursitis)", section on 'Magnetic resonance imaging'.)

●Ultrasound – Ultrasound in trochanteric bursitis shows a distended, fluid-filled bursa. Ultrasound helps in guidance for fluid aspiration and analysis. Ultrasound can also detect tendinosis and tendon tears of the abductor muscle tendons [66]. (See "Greater trochanteric pain syndrome (formerly trochanteric bursitis)", section on 'Ultrasonography'.)

Bone marrow edema syndrome — Bone marrow edema syndrome, also referred to as the "transient bone marrow edema syndrome" or as "transient osteoporosis of the hip," was initially described in pregnant patients. This disorder of unknown etiology is most commonly seen in middle-aged males presenting with hip pain. Osteopenia may be apparent on plain radiographs, while increased T2 signal in the bone marrow of the femoral head and neck is apparent on MRI. Diffuse rather than focal involvement of the femoral head may help to distinguish this entity from osteonecrosis. (See 'Avascular necrosis' above.)

Pain and osteopenia resolve spontaneously in most cases. Diagnostic imaging is useful primarily to exclude other causes of hip pain [67]. Bone marrow edema syndrome should be considered a marker for potential progression to advanced AVN, and careful follow-up is necessary [38,39]. (See 'Avascular necrosis' above.)

●Plain film radiography – Plain film radiography is often negative or may demonstrate osteopenia within four to eight weeks after the onset of hip pain [68]. Osteopenia typically resolves within nine months of symptom onset.

●Radionuclide Tc-99m bone scan – Bone scan is more sensitive than plain film for detection of bone marrow edema syndrome. Scintigraphy reveals diffuse and homogeneously increased uptake that involves the femoral head and neck [68]. However, this modality is no longer used since the advent of MRI.

●MRI – MRI demonstrates bone marrow edema involving the entire femoral head and neck, with possible extension into the subtrochanteric region and commonly associated joint effusion. This entity can be differentiated from AVN by lack of focal changes of the femoral head on MRI [69,70]. The MRI abnormalities are reversible as early as six weeks after onset of symptoms [71].

Nerve entrapment syndromes — The piriformis syndrome usually is caused by a neuritis of the proximal sciatic nerve. Spasm or contracture of the piriformis muscle can either irritate or compress the proximal sciatic nerve and can mimic discogenic sciatica (pseudosciatica). (See "Approach to hip and groin pain in the athlete and active adult", section on 'Piriformis syndrome'.)

Hamstring syndrome is caused by tight tendinous structures of the hamstring muscle at its insertion on the ischial tuberosity and can be seen as a complication of hip arthroplasty. Patients typically experience focal pain of the affected area that radiates down the back of the thigh. (See "Hamstring muscle and tendon injuries", section on 'Hamstring syndrome'.)

Nerve entrapment syndromes are evaluated by MRI [72,73]. MRI will often show sciatic nerve inflammation in the area of piriformis muscle in the piriformis syndrome, and between the semitendinosus and biceps femoris muscles in hamstring syndrome.

Snapping hip syndrome — Snapping hip syndrome is a benign condition that results from slippage of the iliotibial band or gluteus maximus muscle over the greater trochanter (external snapping hip syndrome) or slippage of the iliopsoas tendon over the iliopectineal eminence or the femoral head (internal snapping hip syndrome). Evaluation of the snapping hip syndrome is performed with a combination of plain radiography and ultrasonography [3]. MRI should be reserved for difficult cases [3]. (See "Running injuries of the lower extremities in adults: Patient evaluation and common conditions", section on 'Snapping hip syndrome'.)

Hip microinstability — Hip microinstability is a relatively new diagnosis defined as persistent excessive hip motion. The most common symptom is hip pain. Diagnostic criteria include patient history, examination, and imaging [74]. Stability of the hip is determined by bony anatomy of the femoral head and acetabulum and by supporting soft tissues, including labrum, ligaments, capsule, and muscles. Etiologic factors include adult hip dysplasia, acetabular labral tears, capsular laxity or injury, connective tissue disorders, muscle dysfunction, iatrogenic, and idiopathic [74,75]. The condition affects younger patients 16 to 50 years old and is more common in females. Treatment is physical therapy, intraarticular corticosteroid injection, or surgical repair of underlying pathology when nonoperative treatment is ineffective [74]. Imaging modalities include plain film radiography and MR angiography (MRA). Plain film radiography can identify abnormal shape of the acetabulum and femoroacetabular impingement (cam type: nonspherical femoral head). MRA findings include labral or chondral tears, femoroacetabular cartilage or labral hypertrophy, and capsular thinning [74,75].

SUMMARY AND RECOMMENDATIONS

●Selection of modality – The imaging modality used in a given patient depends upon the differential diagnosis that has been developed based upon the history and physical examination. (See "Approach to the adult with unspecified hip pain" and "Approach to hip and groin pain in the athlete and active adult".)

●Plain radiographs – Plain film radiography of the hip is used in the initial evaluation of any cause of hip pain. Plain films can also identify causes of referred hip pain, such as sacroiliitis, but may not detect or accurately characterize some hip fractures and bone marrow edema associated with early stages of avascular necrosis (AVN), osteomyelitis, or sacroiliitis. (See 'Plain film radiography' above.)

●CT – CT of the hip without intravenous contrast is most useful in the setting of trauma, for preoperative planning, and for evaluation and guiding percutaneous biopsy of tumors. Intravenous contrast is administered for evaluating a septic joint or a soft tissue abscess.

CT can detect the intraarticular extension of fractures. CT may not detect trabecular bone injuries, which may be present in femoral neck insufficiency fractures in patients who are osteoporotic, and will not demonstrate the bone marrow edema of early osteonecrosis and early osteomyelitis. (See 'Computed tomography' above.)

●MRI – MRI of the hip accurately evaluates the bone marrow, joint space, neurovascular structures, and soft tissues. Intravenous contrast is usually not administered except for evaluation of soft tissue and bone tumors or vascular malformations. MRI is the modality of choice for suspected femoral fracture not demonstrated radiographically, osteochondral injuries, muscle injuries, joint effusion, early diagnosis and staging of AVN, iliopsoas and intertrochanteric bursitis, evaluation of infection, and tumor. (See 'Magnetic resonance imaging' above.)

●Bone scan – Radionuclide Tc-99m (technetium methylene diphosphonate) bone scan surveys a large area when performed as a whole-body examination; however, it is often nonspecific. Radionuclide bone scan is reserved for suspected fracture or AVN not demonstrated by plain film radiography when MRI is not available or is contraindicated and for the evaluation of metastatic disease and prosthetic device loosening or infection. (See 'Radionuclide Tc-99m bone scan' above.)

●Ultrasound – Ultrasound of the hip is readily available even at the bedside, allows dynamic evaluation of the tendons and muscles, and does not involve ionizing radiation; however, its diagnostic performance is highly variable and operator- and patient-dependent. Hip effusions and bursal or periarticular fluid collections are readily identified. (See 'Ultrasonography' above.)

●Arthrography – MR arthrography of the hip with intraarticular gadolinium administration best delineates the joint anatomy, including the acetabular labrum, articular cartilage, and ligamentum teres, and detects loose bodies. Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired kidney function. CT arthrography with intraarticular iodinated contrast is used in cases where the use of MR arthrography is contraindicated. Conventional plain film hip arthrography may be useful to confirm intraarticular needle placement when hip aspiration is indicated for joint fluid analysis. (See 'Arthrography' above.)