Perthes disease, also known as Legg-Calvé-Perthes disease, refers to idiopathic osteonecrosis of the femoral epiphysis seen in children. It should not be confused with Perthes lesion of the shoulder. It is a diagnosis of exclusion and other causes of osteonecrosis (including sickle cell disease, leukemia, corticosteroid administration, Gaucher disease) must be ruled out 8. Perthes disease is relatively uncommon and in Western populations has an incidence approaching 5 to 15:100,000. Boys are five times more likely to be affected than girls. Presentation is typically at a younger age than slipped upper femoral epiphysis (SUFE) with peak presentation at 5-6 years, but confidence intervals are as wide as 2-14 years 8. Perthes is considered an idiopathic condition, and there are no clear predisposing factors.
Most children present with atraumatic hip pain or limp 3,5,6. Some children have a coincidental history of trauma. This may precipitate the presentation or the realization of symptoms that in fact had been long-standing. Blood tests are typically normal in Perthes. It is important to be certain that there is no other cause of osteonecrosis (e.g. sickle cell disease) during the workup. The specific cause of osteonecrosis in Perthes disease is unclear. Osteonecrosis generally occurs secondary to the abnormal or damaged blood supply to the femoral epiphysis, leading to fragmentation, bone loss, and eventual structural collapse of the femoral head. In approximately 15% of cases, osteonecrosis occurs bilaterally. The best initial test for the diagnosis of Perthes is a pelvic radiograph. In a small number of patients with Perthes, the radiograph will be normal and persistent symptoms will trigger further imaging, e.g. MRI. The investigation of atraumatic limp will often include a hip ultrasound to look for effusion, but ultrasound is unlikely to pick up osteonecrosis. The radiographic findings are those of osteonecrosis. There are separate systems for staging of Perthes disease: The radiographic changes to the femoral epiphyses depend on the severity of osteonecrosis and the amount of time that there has been an alteration of blood supply:
As changes progress, the width of the femoral neck increases (coxa magna) in order to increase weight-bearing support.
Eventually, the femoral head begins to fragment (stage 2), with subchondral lucency (crescent sign) and redistribution of weight-bearing stresses leading to thickening of some trabeculae which become more prominent. The typical findings of advanced burnt out (stage 4) Perthes disease are:
Additionally, tongues of cartilage sometimes extend inferolaterally into the femoral neck, creating lucencies, which must be distinguished from infection or neoplastic lesions 4. The presence of metaphyseal involvement not only increases the likelihood of femoral neck deformity but also makes early physeal closure with resulting leg length disparity more likely. Traditionally arthrography performed under general anesthesia with conventional fluoroscopy is performed to assess congruence between the femoral head and the acetabulum in a variety of positions 3. MRI is increasingly replacing this, in an effort to eliminate pelvic irradiation. MRI is gaining an increasing role in a number of scenarios:
Both arthrography and dynamic MRI assess three main features 3:
Treatment in Perthes disease is largely related to symptom control, particularly in the early phase of the disease. As the disease progresses, fragmentation and destruction of the femoral head occur. In this situation, operative management is sometimes required to either ensure appropriate coverage of the femoral head by the acetabulum or to replace the femoral head in adult life. The younger the age at the time of presentation, the more benign disease course is expected, and also for the same age, the prognosis is better in boys than girls due to less maturity 5,8. Conservative treatment is favorable in children with a skeletal age of 6 years or less at time of disease onset 14. Prognosis is also influenced by the percentage of femoral head involvement and degree of primary deformity of the femoral head and the secondary osteoarthritic changes that ensue. Children with over 50% of femoral head necrosis at time of diagnosis should be considered for operative management 14. The aim of therapy is to try and maintain good femoroacetabular contact and a round femoral head. Bracing may be used in milder cases, although femoral neck and acetabular osteotomies may be required to correct more severe abnormal femoroacetabular malalignment. In later life, hip replacements may be necessary 9.
History and etymologyThe condition was first described in 1897 by Maydl, with Legg, Calvé, and Perthes popularizing it in 1910 in separate publications:
General imaging differential considerations include:
Plain radiographic findings in established osteonecrosis may be characteristic of the disease. In the epiphyseal region, an arclike, subchondral, lucent lesion may be associated with areas of patchy loss of bone opacity intermingled with sclerotic areas and bone collapse. In the diametaphyseal region, a sheetlike lucency of varying size is usually surrounded by shell-like sclerosis and/or calcification and periostitis. In flat or complex bones, patchy lucencies and sclerosis are often associated with bone collapse or fractures (see the images below). Radiographic features of bone infarction do not occur until several months after the onset of symptoms; therefore, plain radiography is not a sensitive technique in the detection of bone infarction. However, plain radiography has a role in the differential diagnosis.
Posttraumatic osteonecrosis usually follows a fracture; most cases occur in areas with vulnerable blood supply, such as the femoral head, humeral head, talus, or scaphoid bone (see the image below).
Infarcted bone appears opaque as a result of compression. The femoral head is the most common site of osteonecrosis, which is a well-known complication of femoral head fractures and dislocations. Additionally, subchondral fracture of the femoral head has been associated with osteonecrosis, transient osteoporosis of the hip, and Pastel disease (ie, rapidly progressing osteoarthritis of the hip). Radiographs obtained several months after the onset of symptoms may show a radiolucent crescent parallel to the articular surface secondary to subchondral collapse of the necrotic bone. Often, flattening of the articular surface is demonstrated, but the joint space tends to be preserved. The opacity of the infarcted femoral head is increased. Radiographic changes in traumatic osteonecrosis of the talus are delayed (by 1-3 mo) and become apparent with osteoporosis of the surrounding bones, which creates relatively increased opacity in the body of the talus. The increase in radiopacity may be associated with a collapse of the articular surface. Occasionally, a subchondral radiolucent band is demonstrated in the proximal talus; this finding is related to bone resorption. This Hawkins impingement sign usually indicates the presence of viable bone with an intact blood supply (see the image below).
Osteonecrosis of the humeral head is usually a complication of a fracture of the anatomic neck or severe fracture dislocation. Radiographic findings are delayed; they include flattening, sclerosis, and irregularity of part of the articular surface of the humeral head. In the scaphoid bone, 10-15% of the fractures are complicated by osteonecrosis in the proximal pole of the scaphoid bone. Plain radiographic findings include relatively increased opacity in the infarcted pole of the scaphoid bone. This appearance may be delayed for 4-8 weeks, a period possibly associated with delayed union or nonunion of the fracture; collapse of the infarcted part of the bone; and, eventually, changes related to secondary osteoarthrosis. Osteonecrosis of the capitate may occur after accidental or occupational trauma. The proximal part of the capitate is the site of AVN. After trauma or prolonged stress, AVN also may affect the lunate; the other carpal bones; the tarsal navicular bone; the mandibular condyle; the patella; the glenoid region of the scapula; and, occasionally, the metatarsal bones. Osteonecrosis of the vertebral body (ie, Kümmell disease) usually occurs weeks to years after acute trauma. It usually causes vertebral collapse in middle-aged or elderly men or women. Generally, the lower dorsal or upper lumbar vertebrae are involved. Gas may be apparent in the vertebral body and may extend into the psoas muscles. These changes are depicted more elegantly on CT scans than on other images. Spontaneous infarction of the femoral head is uncommon and affects men more often than women in the group aged 40-70 years. Infarction may be unilateral or bilateral. The radiographic appearance depends on the severity of the disease. A minor form of femoral head infarction is recognized; this form affects a superficial area of the femoral head in a segmental distribution. The disease is nonprogressive. Radiographs may show a lobulated or segmental subcortical lucency, which may be surrounded by a sclerotic margin. The latter is better demonstrated on CT scans. Spontaneous osteonecrosis around the adult knee (ie, Ahlbäck disease) is a distinct clinical entity that affects women more often than men. It commonly affects the medial femoral condyle and less commonly affects the medial or lateral tibial condyle. Initial radiographic findings are usually normal. Weeks or months later, subtle flattening and sclerosis of the weight-bearing femoral or tibial condyle may be seen. If untreated, further depression, sclerosis, and joint space narrowing occur. If the affected area is small, spontaneous recovery may ensue if weight-bearing is avoided. Conventional tomography may show angular or wedge-shaped areas of patchy sclerotic bones and subtle collapse of the bone surface that is undetected on plain radiographs. The diagnosis of spontaneous osteonecrosis of the knee is being questioned. Current theories suggest that this entity is actually a subchondral stress fracture that most often occurs in the medial femoral condyle. Spontaneous osteonecrosis of the tarsal navicular in adults (ie, Mueller-Weiss syndrome) may occur, especially in women. Plain radiographic features include medial or dorsal protrusion of a portion of the bone or the entire navicular bone. These findings are often associated with a comma-shaped deformity caused by collapse of the lateral part of the bone. The disease may be bilateral or asymmetric and may be associated with pathologic fractures. The disease can be progressive at times, and it is associated with severe pain and disability. This syndrome is distinct from the osteochondrosis of the tarsal navicular bone that occurs in children (ie, Köhler disease). Osteonecrosis secondary to Cushing disease occurs as a result of excess levels of endogenous steroids. Most of the steroids are present in the vertebral bodies. Characteristic features are osteoporosis, osteosclerosis, subchondral radiolucent shadows, wedging and/or collapse, and bone fragmentation associated with a relatively normal articular space. Osteonecrosis that affects the epiphysis and diaphysis is a known complication of Gaucher disease and is commonly associated with bone pain. In the long bones, bands of sclerosis and radiolucency alternate. These findings are associated with periostitis and a bone-within-bone appearance identical to that seen in sickle cell disease. [30] Osteonecrosis may complicate hemophilia and is usually found in the femoral head and talus (see the image below). Bone infarction results from intraosseous hemorrhage with the subsequent collapse of bone or intracapsular hemorrhage and an elevation in intra-articular pressure that causes vascular compromise and eventual osteonecrosis. Radiographic features are similar to those of traumatic osteonecrosis. Ossification related to bleeding in the periarticular region may be apparent.
Two types of bone lesions that occur in patients with dysbaric osteonecrosis can be identified on plain radiographs: juxta-articular lesions, which are more common and mostly affect the head of the humerus and femur, and diaphyseal and metaphyseal lesions that occur at a distance from the joint. Juxta-articular alterations are frequently encountered in the region of the head of the femur and humerus. They are depicted as radiopaque areas, spherical segmental radiopaque areas that may eventually produce a snow-capped appearance, radiolucent subcortical bands termed the crescent sign, and osseous collapse and fragmentation. Diaphyseal and metaphyseal lesions are demonstrated as ill-defined radiopaque foci; irregular intraosseous areas of shell-like calcification; and, rarely, radiolucent defects. These changes may be unilateral or bilateral. Osteonecrosis is a known complication of pancreatitis; it is usually associated with chronic or inactive forms of pancreatitis (see the image below). [31] Epiphyseal involvement is characterized by lucencies of mottled appearance or lucencies interspersed with sclerosis, subchondral radiolucent areas, and partial or complete collapse of the involved bone. Diaphyseal and metaphyseal involvement is associated with radiolucency, calcification, and periosteal new bone formation. The distal femur and the proximal tibia are the sites most commonly involved.
Osteonecrosis in pregnancy appears to be closely associated with childbirth. The femoral and humeral heads are the sites most commonly involved. The pathogenesis of osteonecrosis in patients with SLE is not clear, and the role of steroids is speculative. The overall radiographic appearances of bone infarcts are similar to those of infarcts in patients without SLE. The most commonly affected sites are the humeral head, femoral condyles, tibial plateaus, and talus. An unusual feature is the involvement of small bones of the wrist, hands, and feet; examples include the carpus, tarsus, and metatarsal and metacarpal heads. Exposure to internal or external, accidental, or diagnostic and/or therapeutic radiation may produce diverse osseous changes, including disruption of growth, bone infarction, scoliosis, and benign and malignant neoplasms. Osseous changes are usually related to dose and age. Various parts of the skeleton respond differently upon exposure to radiation. Most osseous changes result from secondary radiation exposure during radiation therapy for soft tissue cancers. Common sites of involvement include the mandible, skull, shoulder, sternum, and shoulder. The threshold for osseous radiation injury is believed to be 3000 cGy, with cell death occurring at 5000 cGy. Radiation osteitis is manifested by a mottled appearance with a mixture of osteoporosis, increased opacity, and coarse trabecular pattern demonstrated on plain radiographs. Different bones develop radiation-induced changes at varying times after the initial insult. Mandibular osteonecrosis commonly appears 1 year after radiation exposure; at other sites, the latent period is longer. Osteonecrosis is considerably more common in the mandible than in other bones because of its compact bone structure and poor blood supply. In addition, the mandible is exposed to a higher radiation dose because of its superficial location. Bone necrosis is usually mild and may be aseptic or associated with infection. Osteonecrosis appears as an ill-defined area of bone destruction without a sequestrum. An associated soft tissue mass is unusual with osteonecrosis; the presence of a soft tissue component suggests tumor recurrence. Radiation necrosis of the skull usually occurs after a minimum radiation dose of 3500 cGy. The radiographic appearance is that of a mixed lytic and sclerotic area within the calvarium. If the osteonecrosis is associated with soft tissue necrosis, infection and/or osteomyelitis may ensue. Osteonecrosis of the shoulder girdle may follow radiation therapy for breast carcinoma. Osteopenia is common after radiation therapy and is often associated with disorganized bone trabeculae that resemble findings in Paget disease. Pathologic rib fractures are common and often multiple. The edges of rib fractures show resorption, and the tips are often pointed or sclerotic. Clavicular and scapular fractures are often associated with these rib fractures. Radiation necrosis of the humerus may develop as long as 7-10 years after radiation therapy. Changes include patchy bone resorption, fractures, and necrosis of the humeral head with a slipped proximal humeral head epiphysis. Radiation necrosis of the sternum may follow treatment of breast cancer. Osseous changes may be mild and may be demonstrated as osteoporosis, abnormal trabecular patterns, localized lucencies, and sclerosis. More severe changes include abnormalities in alignment with localized pectus excavatum or complete necrosis of one or more segments of the sternum. Unilateral or bilateral femoral neck fractures are reported in 2% of patients who are exposed to pelvic irradiation. These fractures are commonly subcapital. Often, sclerotic changes occur, and trabecular opacity increases in the femoral neck, preceding a fracture. Fractures usually heal normally with abundant callous formation. Protrusio acetabuli is also reported to occur after radiation therapy of the pelvis; this condition may be associated with peritoneal calcification. Changes indistinguishable from osteitis pubis may occur in the symphysis pubis. Radionecrosis of the sacroiliac joints may cause widening and irregularity of the joint space. This condition is often associated with sclerosis, which is commonly symmetric and bilateral. Pathologic fractures of pelvic bones may occur after radiation therapy; these can involve the sacrum and may extend into one or both innominate bones. Complications from osteonecrosis usually are well depicted on plain radiographs. Cartilaginous abnormalities, such as fibrillation, erosions, and joint space narrowing, may affect joints. Changes of secondary osteoarthrosis may be apparent in cases involving significant collapse of an articular surface that occurs after an infarction. Loose bodies, either chondral or osteochondral, may be seen in a joint embedded within the depressed part of the bone or within the synovium. Cystic degeneration in areas of bone infarction may occur, particularly in the diaphysis of tubular bones. Appearances are those of a well-marginated expanding osteolytic area eroding the cortex. The well-marginated cyst and the lack of cortical disruption help in differentiating the cyst from a malignant degeneration. Malignant degeneration (eg, sarcoma) is a known complication of bone infarction irrespective of etiology. [32] Men are affected more often than women; patients are usually aged 40-70 years. Typically, the distal part of the femur or proximal tibia is involved, although other sites may be affected as well. The radiographic appearance is that of a soft tissue mass associated with bone destruction at a site of previous bone infarction. Radiographic features of bone infarction do not occur until several months after the onset of symptoms; therefore, plain radiography is not a sensitive technique in the detection of bone infarction. However, plain radiography has a role in the differential diagnosis. Early radiographic features of a bone infarct, particularly in the metaphyseal region of long bones, lack specificity. Vague areas of radiolucencies may mimic infections and neoplastic processes. Osteochondritis dissecans may mimic spontaneous osteonecrosis around the knee. Radiographic findings in dysbaric osteonecrosis are indistinguishable from those of osteonecrosis resulting from other causes. Virtually identical features may be seen with bone islands. Osteonecrosis of the vertebral body may be difficult to differentiate from an osteoporotic fracture and vertebral collapse secondary to malignancy. Cyst formation that occurs after bone infarction is occasionally difficult to differentiate from a malignant degeneration, particularly in early stages when the cysts are poorly marginated. Mimics of malignant degeneration of bone infarcts include fibrosarcoma, malignant fibrous histiocytoma, chondrosarcoma, and, rarely, osteosarcoma. Radiation-induced mandibular osteonecrosis may be difficult to differentiate from tumor recurrence. Other regions of radiation osteonecrosis may mimic osteomyelitis. Radionecrosis of the shoulder girdle may mimic Paget disease. Changes indistinguishable from osteitis pubis may occur in the symphysis pubis, with radionecrosis. Radionecrosis of the sacroiliac joints may mimic osteitis condensans ilii. |
What imaging technique is used to detect osteonecrosis of Legg CALV Perthes disease on a bone scan?
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