Radiologic evaluation of the hip in infants, children, and adolescents

INTRODUCTION — The hip is a stable, major weight-bearing joint with significant mobility. In children, common causes of hip pathology include developmental dysplasia of the hip, transient synovitis, septic arthritis, Legg-Calvé-Perthes disease, and slipped capital femoral epiphysis. Less-common hip disorders include proximal femoral focal deficiency, developmental coxa vara, neuromuscular hip dysplasia, injuries about the hip, arthritides, and tumors. The radiologic evaluation of common and less-common hip disorders is discussed below.

Accurate diagnosis and treatment of pediatric hip disorders are important because of the potential complications, which may lead to degenerative joint disease in adult life. The history and physical examination, which are necessary to develop a differential diagnosis prior to the selection of imaging tests, and a general review of the imaging tests that are used in the evaluation of bone and joint pain, including the physical principles underlying their usefulness, are presented separately. (See "Approach to hip pain in childhood" and "Evaluation of limp in children" and "Imaging techniques for evaluation of the painful joint" and "Imaging evaluation of the painful hip in adults".)

TYPES OF IMAGING STUDIES — The modalities available for evaluation of the hip include ultrasonography (US), plain film radiography, magnetic resonance imaging (MRI), computed tomography (CT), radionuclide bone scan, magnetic resonance (MR) arthrography, CT arthrography, and conventional arthrography (table 1).

●Ultrasonography – US has low cost, is readily available, allows dynamic evaluation of the tendons and muscles, and does not involve ionizing radiation; however, it is highly operator dependent. In children, US may be useful in the following conditions:

•Diagnosis and follow-up of developmental dysplasia of the hip (DDH)

•Diagnosis of hip effusions due to transient synovitis and septic arthritis

•Detection of bursal or periarticular fluid collections, which may be seen in bursitis, arthritis, and infection

•Dynamic evaluation of the snapping iliopsoas syndrome

•Guidance of hip aspiration and injection

●Plain film radiography – Plain film radiography is used in the initial evaluation of any cause of hip pain or limp. Because the appearance of a child's hips varies with age, strong consideration should be given to ordering anteroposterior (AP) and frog leg lateral views of the pelvis rather than views of a single hip [1]. This allows easy comparison with a "control" hip in children with unilateral problems. The average radiation dose from pelvic radiographs is 0.5 millisieverts [2].

●Magnetic resonance imaging – MRI accurately evaluates the bone marrow, articular and physeal cartilage, subchondral bone, periosteum, synovium, neurovascular structures, and soft tissues.

In children, MRI may be indicated in the following conditions:

•Assessment and follow-up of complicated DDH

•Diagnosis of proximal femoral focal deficiency

•Preoperative planning of developmental coxa vara

•Early diagnosis, staging, and evaluation of complications of Legg-Calvé-Perthes (LCP) disease

•Early diagnosis of slipped capital femoral epiphysis (SCFE)

•Early diagnosis of osteomyelitis and exclusion of osteomyelitis in children with septic arthritis

•Diagnosis of occult traumatic injuries, including soft tissue injuries and stress fractures

•Early diagnosis of arthritis

•Tumor staging

•Diagnosis of acetabular labral tears (requires 3 Tesla [3T] MRI)

The sensitivity of 3T MRI for detecting acetabular labral tears is comparable to 3T MR arthrography [3]. When available, 3T MRI is preferred to MR arthrography for the diagnosis of acetabular labral tears because 3T MRI is noninvasive.

Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired renal function. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

●Computed tomography – In children, CT may be indicated in the following conditions:

•Preoperative assessment and postoperative follow-up of DDH

•Pretreatment evaluation of LCP disease

•Pretreatment evaluation of SCFE

•Evaluation of tumor matrix and cortical invasion

•Guidance for biopsy or ablation of certain tumors such as osteoid osteoma

The radiation dose for pelvic CT ranges from 5 to 7 millisieverts, depending upon age and CT protocol [4]. The Image Gently campaign, launched by the Alliance for Radiation Safety in Pediatric Imaging, includes recommendations for radiation dose reduction. Consultation with a specialist (eg, pediatric radiologist or pediatric orthopedist) may be warranted before CT imaging, given the potential for radiation exposure.

The gonads are in the field of view for CT of the hips. In females, gonadal shielding is not feasible because of the deep location of the ovaries and loss of image quality. In males, gonadal shielding can be used, but artifact reduction software is necessary to mitigate beam hardening artifact from shielding.

●Radionuclide bone scan – Radionuclide bone scan surveys a large area; however, it is often nonspecific. In addition, because of the radiation exposure with radionuclide bone scan, MRI usually is preferred. In children, radionuclide bone scan may be useful in the following conditions when MRI is contraindicated:

•Early evaluation of osteomyelitis

•Early detection of LCP disease

•Detection of osteoid osteoma

•Early detection of stress fractures

Although bone scan is preferred to MRI for the detection of metastatic disease, the sensitivity of bone scan for lytic metastases is limited. Plain radiographs, MRI, and/or ¹⁸F sodium fluoride positron emission tomography-CT bone scan are indicated to evaluate lytic metastases.

The effective dose from ^99mtechnetium methylene diphosphate (^99mTc-MDP) bone scan ranges from 2.8 to 4.2 millisieverts, depending upon on the patient's age [5].

●MR arthrography – MR arthrography with intra-articular gadolinium administration best delineates the joint anatomy, including the acetabular labrum and articular cartilage. MR arthrography is used in cases of hip pain that may involve any of the above-mentioned structures. In children, MR arthrography is indicated mainly in the following conditions:

•LCP disease

•Diagnosis of acetabular labral tears if 3T MRI is not available

Administration of gadolinium-containing MRI contrast agents should be avoided in patients with impaired renal function. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

●CT arthrography – CT arthrography with intra-articular iodinated contrast is used in cases where MR arthrography is contraindicated.

●Conventional arthrography – The imaging indications for conventional hip arthrography are limited due to the increased use of MR arthrography, which visualizes joint anatomy as well as bone and surrounding soft tissues. In children, hip arthrography is occasionally used in the following conditions:

•Preoperatively and intraoperatively in the treatment of DDH

•Preoperatively in LCP disease

IMAGING STUDIES FOR SPECIFIC CLINICAL SETTINGS — The age of the child generally directs the investigation toward the most likely hip pathology, as outlined below. However, juvenile idiopathic arthritis and bone tumors may occur at any age.

Infants — Developmental dysplasia of the hip (DDH) and proximal femoral focal deficiency (PFFD) are the most common pathologic disorders affecting infants. Septic arthritis and osteomyelitis also may occur in infants but are more common in toddlers and young children. They are discussed below. (See 'Septic arthritis' below and 'Osteomyelitis' below.)

Developmental dysplasia of the hip — DDH is a relatively common condition that is more prevalent in females, following breech deliveries or oligohydramnios, in White children, and in the presence of a positive family history. DDH is defined as abnormal position of the femoral head relative to the acetabulum, which results in abnormal growth of both components of the hip. Most cases are detected in the first year of life, but DDH may present later, particularly in children with bilateral disease and no asymmetry on physical examination [6].

Static and dynamic ultrasonography is the imaging modality of choice for diagnosis in neonates and infants up to the age of four months. Plain film radiography is recommended for older infants beginning at age four months and children. CT scanning may be used for preoperative planning, conventional contrast arthrography for intraoperative evaluation, and MRI for postoperative follow-up. (See "Developmental dysplasia of the hip: Clinical features and diagnosis" and "Developmental dysplasia of the hip: Treatment and outcome".)

●Ultrasonography – Ultrasonography (US) is used in the evaluation of the femoral head, which is not ossified and not visible on plain radiographs in the first four months of life. US is the technique of choice for evaluating high-risk infants, patients with equivocal clinical findings, and for monitoring treatment. Due to normal instability of the hip in the first days of life, US should be performed in patients two weeks or older with clinical suspicion of DDH [7]. In high-risk patients with negative clinical examination, a screening US should be performed at six weeks of age, as hip laxity and mild acetabular dysplasia may resolve spontaneously by four to six weeks of life. (See "Developmental dysplasia of the hip: Clinical features and diagnosis", section on 'Normal examination and risk factors'.)

US is able to directly visualize the cartilaginous components of the hip, determine the position and coverage of the femoral head, determine the depth and morphology of the acetabulum, and evaluate dynamic instability. The main finding is superolateral displacement of the femur from the acetabulum [8]. Diagnosis of DDH on US is made by measuring the alpha angle, formed by the acetabular roof and the vertical cortex of the ilium (image 1). The degree of instability can range from mild laxity to subluxation and dislocation of the hip. When instability is present, US determines the reducibility of the femoral head, which is important for management. US also demonstrates the cause of obstruction to hip reduction, such as inverted labrum and soft tissue in the acetabulum.

US is important in follow-up of patients treated with a Pavlik harness, to demonstrate improvement in the position of the femoral head and the acetabular angle, usually seen after three weeks of treatment. (See "Developmental dysplasia of the hip: Treatment and outcome", section on 'Pavlik harness'.)

●Plain film radiography – Plain film radiography is indicated for diagnosis of DDH in patients four months or older (when the ossified femoral head can be visualized) and in follow-up of infants treated for DDH in this age group (image 2). Plain film radiography of DDH is discussed separately. (See "Developmental dysplasia of the hip: Clinical features and diagnosis", section on 'Radiographs'.)

The characteristic diagnostic features include superolateral displacement of the femur from the acetabulum, a shallow acetabulum, and delayed ossification of the femoral head [9]. Other findings are asymmetry of the femoral head ossification center and of acetabular development in unilateral cases.

●Magnetic resonance imagery – MRI is most useful in the preoperative assessment of complicated DDH and in the evaluation of postsurgical reduction and long-term sequelae of partially treated or untreated DDH. Contrast-enhanced MRI shows the position and shape of the cartilaginous femoral head and obstacles to reduction, as well as changes of the acetabulum not demonstrated by US or radiography. MRI also gives information about the acetabular labrum, which is important in the preoperative planning. MRI assesses the vascularity of the cartilaginous femoral head and can detect ischemia. Global decrease in perfusion of the femoral head is associated with significantly increased likelihood of avascular necrosis [10]. If ossification of the femoral head does not occur by one year of age, avascular necrosis is believed to be present [11]. MRI has close to 100 percent sensitivity and specificity for postoperative evaluation of hip reduction and is preferred over CT because of radiation concerns [9].

●Computed tomography – CT is valuable in the preoperative assessment of DDH. Pediatric protocols that involve reduced doses of radiation should be used. Three-dimensional CT images are particularly useful in the preoperative planning of complex cases and improve the ability to match the proper osteotomy with the specific acetabular deficiency [12].

CT is also useful in the postoperative evaluation of DDH when MRI is contraindicated or not available. Postreduction CT offers precise information regarding the position and coverage of the femoral head within the acetabulum in the cast and confirms successful reduction. Postreduction CT also has predictive value for development of avascular necrosis by measuring the abduction angle of the hip.

●Conventional arthrography – Conventional arthrography is used as a guide intraoperatively to confirm the position of the femoral head and to visualize structures which may block the reduction of the hip.

Proximal femoral focal deficiency — PFFD is an uncommon congenital condition manifested by hypoplasia of part or all of the proximal femur. PFFD encompasses a spectrum from hypoplasia of the femoral head to congenital absence of all but the distal femoral epiphysis. PFFD is unilateral in 90 percent of cases. PFFD presents in infancy with limb shortening that can mimic the Galeazzi sign of unilateral DDH.

Plain film radiography demonstrates a short femur with dysmorphic or absent head and neck. There is delayed appearance or nonappearance of the femoral capital ossification center. MRI enables early identification of an incompletely ossified femoral head and whether the intervening segment of femur is absent. MRI shows the cartilage structure of acetabulum and upper femur, therefore assisting in prognosis and treatment planning [13]. MRI is the most accurate modality for determination of the type and prognosis of PFFD, including prediction of leg length discrepancy at maturity, hip joint integrity, and stability of the deficient femoral segment [14,15].

Toddlers and children up to 10 years of age — The most common causes of hip pain in toddlers and children younger than 10 years of age include transient synovitis, septic arthritis, osteomyelitis, developmental coxa vara, and Legg-Calvé-Perthes (LCP) disease. Neuromuscular hip dysplasia may become apparent in toddlers and children younger than 10 years but is usually asymptomatic.

Acute transient synovitis — Acute transient synovitis (also sometimes called toxic synovitis) is the most common nontraumatic hip disorder in children 2 to 10 years of age [16]. It is more common in males and is characterized by pain and limitation of motion in the hip, arising without a clear precipitant, and resolving gradually with conservative therapy. (See "Approach to hip pain in childhood", section on 'Transient synovitis'.)

In cases with high clinical suspicion for acute transient synovitis, US may be the initial imaging study. US may demonstrate the effusion and be used to guide joint aspiration. Joint aspiration is the reference standard in differentiating toxic synovitis from septic arthritis. Bilateral joint effusion is more suggestive of transient synovitis than septic arthritis but does not reliably distinguish between the two [16]. Plain film radiography is used primarily to exclude other disorders involving the bone.

●Ultrasonography – US is over 95 percent sensitive for detecting a joint effusion [16]. It is not possible to distinguish the sterile effusion of transient synovitis from the purulent effusion of septic arthritis.

●Plain film radiography – Plain film radiography is indicated to exclude osseous abnormalities. Plain film radiography may be normal or may indicate a joint effusion. Sensitivity and specificity of plain film for joint effusion is 73 and 79 percent, respectively [16].

●Magnetic resonance imaging – MRI demonstrates joint effusion and synovial inflammation and enhancement with intravenous gadolinium administration. MRI findings are nonspecific and do not distinguish between toxic synovitis and septic arthritis in all cases. The presence of bone marrow edema favors septic arthritis; however this finding is not always seen. Decreased perfusion of the femoral epiphysis on contrast-enhanced MRI is seen more often in septic arthritis than in transient synovitis and is valuable in differential diagnosis [16,17]. Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired renal function. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

Septic arthritis — Septic arthritis in children usually is monoarticular; the hip is the most commonly affected joint. Septic arthritis of the hip is an emergency, as destruction of the femoral head can ensue quickly if treatment is not promptly initiated.

Unilateral joint effusion is present in nearly all cases. US may aid both in detection of an effusion and guiding needle aspiration. Joint aspiration is the reference standard in differentiating toxic synovitis from septic arthritis. Arthrocentesis is required for definitive diagnosis. It is also required for joint decompression as joint effusion is a risk factor for avascular necrosis. Plain film radiography may detect a large effusion but primarily serves to exclude bone involvement. (See "Bacterial arthritis: Clinical features and diagnosis in infants and children".)

●Ultrasonography – US is over 95 percent sensitive for detecting a joint effusion [16]. US is used to detect joint effusion and guide aspiration; absence of fluid excludes septic arthritis and eliminates the need for joint aspiration. In patients with signs of sepsis, a sterile effusion may be secondary to osteomyelitis, and a bone scan or MRI must be considered as additional modalities.

●Plain film radiography – Plain film radiography may demonstrate joint effusion (image 3) and soft tissue swelling in the early stage and cortical destruction, periosteal reaction, and subluxation in advanced cases. Sensitivity and specificity of plain film for joint effusion is 73 and 79 percent, respectively [16].

●Magnetic resonance imaging – MRI demonstrates joint effusion and synovial inflammation and enhancement with intravenous gadolinium administration (image 4). MRI findings are nonspecific and do not distinguish between toxic synovitis and septic arthritis in all cases. The presence of bone marrow edema favors septic arthritis; however, this finding is not always seen. Decreased perfusion of the femoral epiphysis on contrast-enhanced MRI is seen more often in septic arthritis than in transient synovitis and is valuable in differential diagnosis [16,17]. Bone marrow edema is limited to the periarticular subchondral bone in septic arthritis; more extensive changes raise the suspicion of osteomyelitis. MRI can also detect intramuscular abscesses near the hip [18].

Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired renal function. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

Osteomyelitis — Acute osteomyelitis can occur at any age and is usually caused by hematogenous spread of infection. Osteomyelitis of the hip is uncommon but can present with hip pain secondary to involvement of the epiphysis. In infants and children younger than 18 months, the epiphysis may be involved secondary to spread of infection from the adjacent metaphysis. In older children, epiphyseal involvement from a septic joint can occur but is uncommon. Osteomyelitis in the pelvic bones also may cause referred pain in the hip. (See "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Pelvis'.)

Evaluation of osteomyelitis is performed with plain radiographs, bone scintigraphy, and MRI. (See "Hematogenous osteomyelitis in children: Evaluation and diagnosis", section on 'Advanced imaging'.)

●Plain film radiographs – Plain film radiographs are usually normal in the early stage. In advanced cases, bone destruction and joint effusion are demonstrated.

●Magnetic resonance imaging – MRI is the modality of choice for evaluating hip or pelvic osteomyelitis [16,19]. MRI is indicated when the symptoms are localized to the pelvis and the plain radiographs are normal. MRI demonstrates bone marrow edema, joint effusion, and associated intraosseous and soft tissue abscess [16].

●Radionuclide scan – Bone scintigraphy is used in children with suspected osteomyelitis and normal radiographs when MRI is not available. Bone scintigraphy is most useful when symptoms are poorly localized (image 5).

Developmental coxa vara — Coxa vara is defined as an angle of less than 120 degrees between the femoral neck and shaft (figure 1). Normal femoral neck-shaft angle decreases from 150 degrees in infants to 120 degrees in adults [20]. Coxa vara deformity may be functional (which has a normal femoral neck-shaft angle and is secondary to prior infection, avascular necrosis, or trauma) or true coxa vara. True coxa vara may be secondary to congenital abnormalities or developmental. Developmental coxa vara usually presents at two years of age with an abnormal gait. It is bilateral in 40 percent of cases.

Plain film radiography and MRI are the modalities of choice for evaluating coxa vara deformity.

●Plain film radiography – Radiographic findings in coxa vara include decreased femoral neck-shaft angle, vertical orientation, and widening of the physis with small corner fractures along the medial aspect. In developmental coxa vara, a triangular ossification is seen in the inferomedial femoral neck; secondary changes occur in the femoral head and acetabulum.

●Magnetic resonance imaging – MRI is used in preoperative planning to demonstrate the relationship of the acetabulum, femoral head, neck, and shaft and to differentiate between cartilaginous and bony components. MRI demonstrates widening of the physis, bone marrow edema, and expansion of the cartilage [7,14].

Legg-Calvé-Perthes disease — LCP disease is a syndrome of idiopathic avascular necrosis of the femoral epiphysis, possibly due to repeated multiple vascular occlusive episodes that involve the femoral head. It typically presents as hip pain and/or limp of acute or insidious onset, most commonly in males between the ages of 3 and 12 years, with peak incidence at five to eight years of age [21,22]. LCP is bilateral in at least 10 to 20 percent of patients [23,24]. The outcome depends upon the age at onset and the extent of femoral head involvement on radiographs. Younger children (<6 years old) have a greater capacity for the acetabulum to remodel to accommodate irregularities in the shape of the femoral head. Onset in children older than eight years and nonspherical femoral head at skeletal maturity are associated with higher incidence of osteoarthritis in adulthood [20]. It is estimated that approximately 60 to 70 percent of hips affected heal spontaneously without functional impairment [25]. (See "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis'.)

LCP disease is a diagnosis of exclusion, and other causes of osteonecrosis in children such as trauma; systemic diseases such as leukemia, lymphoma, and systemic lupus erythematosus; hemoglobinopathies; coagulopathies; steroid treatment; epiphyseal dysplasia; and Gaucher disease must be ruled out [25]. These may present with similar imaging features [26].

Plain film radiography may be normal in early disease, and in such cases, a more sensitive imaging modality, typically MRI where available or radionuclide bone scanning if MRI is unavailable or contraindicated, is used to detect early osteonecrosis.

●Plain film radiography – Plain film radiography is the mainstay of diagnosis, classification, and follow-up of the disease. The degree of involvement and the shape of the femoral head on the plain film have prognostic value for outcome. LCP disease can be radiographically silent during the first three to six months [27]. Early radiographic changes in LCP include apparent joint space widening and a subchondral fracture; however, radiographs may be normal in the early stages [16]. The classic findings of later LCP are sclerosis, fragmentation, and subchondral collapse of the ossification center of the femoral head (image 6). Radiographic findings have prognostic implications [16]. (See "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis'.)

●Radionuclide bone scan – Bone scintigraphy is helpful in the early stages if the plain films are normal when MRI is not available. Scintigraphic changes precede radiographic findings by an average of three months. A focal area of decreased uptake is seen in the femoral head, the size of which correlates with the amount of involvement. Increased activity may be seen in the capsule due to synovial inflammation [20].

●Magnetic resonance imaging – MRI is useful in the diagnosis, staging, and evaluation of complications of LCP disease. MRI is more sensitive than radiography for diagnosis (due to early detection of bone marrow edema), for detection of subluxation of the femoral head, and for assessment of femoral head containment [20,28]. MRI is used to calculate percentage of femoral head involvement and to predict risk of future collapse [25]. MRI demonstrates the extent of healing of the femoral head and is recommended for follow-up in conjunction with plain radiographs [27]. MRI is able to identify children at risk for early disability due to physeal abnormalities, which may lead to growth arrest [20].

●Contrast-enhanced MRI – Contrast-enhanced MRI depicts different abnormalities associated with the two phases of LCP disease: the avascular phase and the revascularization and reparative phase. In the avascular phase, absence of bone marrow enhancement in dynamic postcontrast MRI confirms the diagnosis and evaluates the extent of involvement (image 7). Other MRI findings of the avascular phase include abnormal signal in the capital femoral epiphysis, metaphysis, and, occasionally, the physis, along with thickening of the articular cartilage and synovial proliferation. During the revascularization and reparative phase, the epiphysis may show hyperenhancement. Other findings include articular surface flattening (coxa plana), fragmentation, subluxation, and loss of containment.

●MR arthrography – MR arthrography after intra-articular administration of gadolinium may be beneficial for assessment of complications and allows detailed evaluation of articular cartilage, labrum, and femoral head-acetabular congruency [25]. MRI is comparable to arthrography for demonstrating containment and congruency of the articular surfaces of the hip [27].

Administration of gadolinium-containing MRI contrast agents should be avoided in patients with severely impaired renal function. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

●Computed tomography – CT allows early diagnosis of bone collapse, and three-dimensional reformatted images provide information about the anatomical relationship between femoral head and acetabulum and femoral head deformity. However, the use of CT is limited because of the high radiation dose [27].

●Ultrasonography – US can be used as an adjunct to other imaging modalities. Persistent hip effusion should raise the suspicion for early LCP disease. Thickening of the synovium and of the articular cartilage of the femoral head and flattening and fragmentation of the femoral head have been described [27].

●Conventional arthrography – Dynamic arthrography under direct fluoroscopic observation is used in advanced disease to assess whether femoral head containment is possible and to select the best surgical option [27].

Neuromuscular hip dysplasia — Children with abnormal muscle tone, either increased (eg, spastic cerebral palsy [CP]) or decreased (eg, dystrophinopathies, such as Duchenne or Becker muscular dystrophy), are at risk for secondary hip dysplasia, related to abnormal muscle tone and limited/no ambulation.

Children who do not walk before the age of five years due to CP or other neuromuscular disease have a 58 percent prevalence of hip dislocations, which are bilateral in 44 percent of cases [29]; plain film radiography reveals characteristic deformities of the femoral head and the acetabulum. Lack of weight bearing produces a coxa valga deformity (ie, increased angle between the femoral neck and shaft) (image 8).

●Plain film radiography – Simulated standing radiographs demonstrate the valgus deformity, abnormal shape and location of the femoral head, and dysplastic changes in the acetabulum [20].

●Computed tomography – CT is helpful preoperatively to evaluate the orientation and shape of the acetabulum and determine femoral anteversion.

Children older than 10 years and adolescents

Slipped capital femoral epiphysis — Slipped capital femoral epiphysis (SCFE) is characterized by displacement of the capital femoral epiphysis from the femoral neck along the plane of the physeal plate (image 9). It is one of the most common hip disorders of adolescence and is more frequent in African American children and children who are overweight. SCFE is caused by the repetitive stress of weight-bearing. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)".)

SCFE is bilateral at presentation in 10 to 20 percent of the cases; however, the opposite side may also become involved later, usually within 24 months of the initial occurrence. SCFE is classified as stable or unstable slip depending on the mobility of the physis; the majority of SCFE cases are stable. Complications of SCFE are discussed separately. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)", section on 'Complications'.)

●Plain film radiography – Plain film radiography is the primary method for the diagnosis of SCFE. Because of the high incidence of bilateral disease, views of both hips are frequently obtained. The lateral radiograph is more sensitive than the anteroposterior (AP) view for detection of mild displacement; therefore, a frog-leg or a cross-table lateral view should always be performed. Some authors recommend replacing the frog-leg lateral view with a cross-table lateral view in an acute SCFE, as the frog-leg lateral view may accentuate the displacement.

In undisplaced SCFE (also known as pre-slip), AP and lateral radiographs show widening and irregularity of the capital femoral physis, osteopenia, and increased density of the metaphysis due to healing response (image 10). In displaced SCFE (the majority of cases), the capital femoral epiphysis slips posteriorly and medially relative to the femoral metaphysis. Medial displacement is seen on the AP radiograph; however, this finding may be difficult to appreciate in subtle cases. Posterior displacement is appreciated on the frog-leg or cross-table lateral view, which is more sensitive than the AP radiograph for subtle cases (image 11A-B). Radiography is used for staging of the severity of slip [8].

●Computed tomography – CT is useful for treatment planning in advanced stages of SCFE by demonstrating physeal closure, precluding the need for fixation. CT may also be used postoperatively to determine if the hardware has penetrated the joint surface [30].

●Magnetic resonance imaging – MRI is more sensitive than radiography for early diagnosis of SCFE, demonstrating the physeal widening before it is apparent on radiographs. Bone marrow edema and synovitis are inconstant features. [31]. MRI is also used for early detection of avascular necrosis, a common complication of unstable SCFE. Preliminary studies show that contrast-enhanced MRI allows for accurate evaluation of the femoral head vascularization before and after surgical pinning [32].

Injuries about the hip in adolescents — Hip pain in adolescents, particularly physically active adolescents, may result from both intra-articular and extra-articular disorders. Extra-articular causes of hip pain include pelvic apophyseal injuries, iliopsoas tendinosis and bursitis, snapping hip syndrome, athletic pubalgia, and stress fractures. Intra-articular causes of hip pain include acetabular labral tears and femoroacetabular impingement [33].

Pelvic apophyseal avulsions — Pelvic apophyseal avulsions are sports injuries that occur in adolescents during forceful or repetitive traction from the attached muscles. Before ossification, the apophyseal growth cartilage is the weakest point in the musculotendinous unit, making the apophysis vulnerable to injury (image 12) [14]. The apophyses involved are the iliac crest, anterior superior iliac spine (image 13), anterior inferior iliac spine, ischial tuberosity, and the greater and lesser trochanters. The most commonly involved apophysis is the ischial tuberosity, followed by anterior inferior iliac spine and anterior superior iliac spine [34].

Evaluation is done with plain film radiography and MRI.

●Plain film radiography – Plain film radiography demonstrates displacement of the apophyseal center from its normal position, callus formation, and bony reaction.

●Magnetic resonance imaging – MRI is useful in suspected avulsion injuries with negative radiographs [35]. Bone marrow edema and soft tissue injuries such as tendon tear can be seen by MRI at the site of avulsion. Chronic microtrauma to the physis may result in physeal widening, which is difficult to see on radiographs and is diagnosed by MRI. In difficult cases, MRI is valuable in differentiating avulsion from neoplasm. MRI also detects other sites of pelvic injuries, including ilium adjacent to the sacroiliac joint and the pubic ramus, which may not be seen on radiographs.

Iliopsoas tendinosis and bursitis — Iliopsoas tendinosis may be associated with trauma, overuse injury, or arthritis. It is often seen in kicking-related sports. Due to their proximity, inflammatory processes frequently involve the iliopsoas tendon together with the bursa. MRI shows thickening and increased signal within the tendon, with increased synovial fluid or hypertrophy of the bursa, which is located anterior to the hip joint (image 14). Ultrasound can show an enlarged bursa and can guide bursal aspiration and anesthetic-corticosteroid injection [33].

Snapping hip syndrome — The snapping iliopsoas tendon is seen in young athletes who use a wide range of hip motion for activities such as ballet or karate. The "snap" results from catching of the posterior iliotibial band or anterior portion of the gluteus maximus muscle over the greater trochanter ("external snapping hip"); from intra-articular lesions such as labral tear or loose body; or from the iliopsoas tendon moving over the lesser trochanter ("internal snapping hip"). Dynamic sonography can be used to confirm the diagnosis [33,36]. (See "Running injuries of the lower extremities: Patient evaluation and common conditions", section on 'Iliopsoas tendinopathy' and "Running injuries of the lower extremities: Patient evaluation and common conditions", section on 'Labral tear'.)

Athletic pubalgia — Athletic pubalgia refers to a group of musculoskeletal processes that occur in and about the pubic symphysis. MRI is the study of choice to evaluate this condition. Numerous muscles attach to the parasymphyseal pubic bone, including anterior abdominal wall muscles and adductor muscles of the thigh. The most frequent pattern identified on MRI is injury to the insertion of the rectus abdominis muscle with or without adductor tendon injury. Another cause of pubalgia is osteitis pubis, which is thought to result from chronic repetitive trauma, as occurs in long distance runners. On radiography, there is sclerosis of the pubic symphysis with symmetric distribution. MRI shows intense edema across the pubic body. Stress fractures of the pubis can also occur [33]. (See "Sports-related groin pain or 'sports hernia'" and "Osteitis pubis".)

Stress fractures — Stress fractures of the femur are uncommon in children and adolescents, mainly occurring in athletes who engage in repetitive loading of the lower extremities, such as runners. Plain film radiographs are initially normal and detect chronic stress reaction by 2 to 14 weeks [7]. MRI and radionuclide bone scan are sensitive for early detection of stress fractures [26].

Acetabular labral tear — The acetabular labrum is a dense fibrocartilaginous ring which is attached to the margin of the acetabulum, increasing the depth and stability of the joint. The labrum is poorly vascularized, especially the anterosuperior portion, where most labral tears occur. Acetabular labral tears account for up to 20 percent of hip pain presentations in athletic adolescents. Sport activities that involve pivoting or twisting of the hip can result in injury to the labrum. Other causes of labral tears include DDH and femoroacetabular impingement. Labral tears predispose to early osteoarthritis. Direct MR arthrography with intra-articular injection of contrast is the procedure of choice for diagnosing labral tears, as well as any associated articular cartilage thinning [33]. Diagnostic accuracy of MRI for labral tears is 90 percent [36].

Femoroacetabular impingement — Femoroacetabular impingement (FAI) results from abnormal contour of the proximal femur and acetabulum, resulting in abnormal contact, which increases with motion. FAI leads to labral cartilage injury, pain, and osteoarthritis [37]. Athletes who perform motions of extreme hip flexion and rotation, such as dancers, are at increased risk for FAI. Other predisposing disorders include DDH, SCFE, and LCP disease. Plain film radiographs are the first imaging modality in the diagnosis of FAI. Two distinct forms of FAI have been described, cam-type and pincer type. Plain film radiographs of the cam-type FAI demonstrate a nonspherical femoral head or lack of femoral head-neck offset. The pincer type of FAI shows signs resulting from acetabular overcoverage. MRI helps diagnose the type of FAI and respective abnormalities of the femoral head, neck, and acetabulum, and shows associated chondral and labral injuries [33].

Idiopathic chondrolysis of the hip — Idiopathic chondrolysis of the hip is a disorder characterized by extensive loss of articular cartilage of the proximal femoral epiphysis and acetabulum, with resultant joint space narrowing and restriction of motion. It can be seen in association with SCFE, trauma, infection, arthritis, and immobilization. Females are affected more than males, and the symptoms are often unilateral. Patients present with a painful, stiff hip.

Plain film radiographic abnormalities appear several weeks to months after onset of symptoms. Findings on radiography are joint space narrowing and osteopenia, leading to protrusion acetabuli and premature physeal fusion (image 15). MRI is more sensitive for early detection of the disease and shows cartilage loss, geometric abnormal signal in the proximal femoral epiphysis (which may be associated with pin penetration into the joint following repair of SCFE), acetabular bone marrow edema, synovial hypertrophy and enhancement, and minimal joint fluid [26,38].

Children of any age

Juvenile idiopathic arthritis — Juvenile idiopathic arthritis (JIA) is the most common cause of chronic arthritis in childhood. JIA (formerly known as juvenile chronic arthritis or juvenile rheumatoid arthritis) consists of a clinically heterogeneous group of arthritides that begin before the age of 16 years and persist for more than six weeks. Clinical features and imaging of JIA are discussed separately. (See "Classification of juvenile idiopathic arthritis" and "Systemic juvenile idiopathic arthritis: Clinical manifestations and diagnosis" and "Polyarticular juvenile idiopathic arthritis: Clinical manifestations, diagnosis, and complications" and "Oligoarticular juvenile idiopathic arthritis".)

Tumors — Bone tumors and tumor-like lesions of the hip in children are rare. Signs and symptoms are nonspecific, often leading to a delay in diagnosis. In a large retrospective study of tumors and tumor-like lesions of the hip, tumor-like lesions accounted for 43 percent of cases, most commonly simple bone cyst (30 percent of cases), followed by eosinophilic granuloma and aneurysmal bone cyst [39]. In the same study, benign tumors of the hip accounted for 45 percent of cases, most commonly osteoid osteoma (30 percent of cases), followed by fibrous dysplasia and exostosis. Malignant tumors made up only 12 percent of cases, including Ewing sarcoma and osteosarcoma [39].

Benign and malignant bone tumors and tumor-like lesions in children and adolescents are discussed separately. (See "Nonmalignant bone lesions in children and adolescents" and "Clinical presentation, staging, and prognostic factors of Ewing sarcoma" and "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)

SUMMARY

●Evaluation of hip pain in children – The history, physical examination, and laboratory evaluation of hip pain and limp in children and adolescents are discussed separately. (See "Approach to hip pain in childhood" and "Evaluation of limp in children".)

●Imaging modalities – The modalities available for evaluation of the hip include ultrasonography, plain film radiography, magnetic resonance (MR) imaging, CT, radionuclide bone scan, MR arthrography, CT arthrography, and conventional arthrography (table 1). (See 'Imaging studies for specific clinical settings' above.)

●Use of imaging modalities in specific conditions – The use of the various imaging modalities in the evaluation and management of specific hip conditions is summarized in the tables for particular age groups:

•Infants (table 2)

•Toddlers and children <10 years of age (table 3)

•Children ≥10 years of age and adolescents (table 4)