Atraumatic hip pain in older children may be due to a variety of causes. In this patient, the differential diagnoses include Legg-Calve-Perthes disease (LCPD), transient synovitis, chronic osteomyelitis, septic arthritis, slipped capital femoral epiphysis (SCFE) and juvenile idiopathic arthritis (JIA). LCPD most often occurs in children between the ages of 3 to 8 years. It is far more common in males and many patients give a history of chronic pain in the affected hip. Transient synovitis is usually encountered in young children. The hip pain usually lasts for only a few weeks, while there is often a history of a preceding viral infection. Note that children may experience multiple episodes of transient synovitis. With chronic osteomyelitis, there usually is a history of a preceding bacterial infection (i.e. skin sepsis, tonsillitis, etc). The child may also show constitutional symptoms like fever, anorexia and loss of weight. Septic arthritis is characterized by severe pain and restriction of movements. The patient is often febrile and typically keeps the leg in an externally rotated and abducted position. As with osteomyelitis, there is often a history of preceding sepsis elsewhere. The classical presentation of SCFE is an obese teenage boy who presents with a limp. Patients may have endocrinological disorders like hypothyroidism, panhypopituitarism and growth hormone deficiency. Isolated hip pain would be an unusual initial presentation of JIA. In addition, many of these patients also have extra-articular and constitutional symptoms. Septic arthritis and osteomyelitis are often associated with a neutrophil leukocytosis in the full blood count (FBC). In addition, septic arthritis, osteomyelitis and JIA are typically associated with an elevated ESR and CRP. Thus the normal FBC, ESR and CRP in this patient make these diagnoses less likely. Her x-ray shows sclerosis and flattening of the right femoral head : changes suggestive of osteonecrosis (avascular necrosis) of the femoral head, which occurs in LCPD. In JIA, transient synovitis or septic arthritis, the x-ray would most likely show no changes (except possibly for joint space widening secondary to an effusion). Osteomyelitis might show evidence of bone destruction or resorption, while a slipped epiphysis (in a lateral x-ray view) would be evident in SCFE. The MRI demonstrates the presence of the 'double line' sign (the interface between osteonecrotic bone and normal bone), thus confirming the presence of osteonecrosis. As no other etiologies for osteonecrosis (i.e. sickle cell disease, corticosteroid therapy) are apparent in this patient, LCPD is the likely diagnosis.
LCPD is a childhood hip disorder of unknown etiology which causes osteonecrosis of the growing femoral head. It is most commonly seen in children aged 3 to 8 years, with a male to female ratio of 5:1. Bilateral disease occurs in between 10 to 12% of patients. The initial osteonecrosis leads to destruction of part of the femoral head, with resultant deformity. Following this, revascularization gradually takes place, with remodeling of the femoral head occurring concurrently. The entire process takes approximately 3 to 5 years. In most patients, the head of the femur remains within the hip joint, allowing the round acetabulum to act as a mold and help maintain the spherical shape of the femoral head during remodeling. However, in patients with severe disease, subluxation of the head may occur, resulting in the femoral head becoming deformed, with resultant restriction of motion. Patients typically present with pain in the affected hip and a limp. These symptoms tend to be of insidious onset and increase over a period of months. Many of these patients give a history of trauma to the affected hip, to which they erroneously attribute the symptoms. The earliest signs are limitation of internal rotation and abduction of the hip. With progression of the disease, the other movements also become restricted. The gait is antalgic, i.e. the patient attempts to take a rapid step on the affected side (in order to minimize pain), followed by a slower step on the normal side. X-rays may appear normal in the early stages. However, as time progresses, widening of the joint space and sclerosis and fragmentation of the femoral head may be noted. Technetium bone scans have a 98% sensitivity and a 95% specificity for diagnosis of LCPD, and are of particular use in early disease. MRI scanning is believed to be of similar accuracy. LCPD is staged based on the radiographic appearance of the femoral head. While several classification schemes are available, the Catterall and Herring classifications are the two most commonly used. The Catterall classification is based on the extent of involvement of the femoral head, and ranges from involvement of only the anterior head (group I) to involvement of the entire head (group IV). The Herring classification is based on the degree of involvement of the lateral portion of the femoral head (also known as the "lateral pillar"). In stage A disease, the lateral pillar is unaffected, while in stages B and C, there is loss of < 50% and > 50% of the height of the pillar respectively. The management of LCPD is determined by the stage of the disease. Most patients have relatively mild disease (i.e. Herring stage A / Catterall group I or II) and can be managed without active intervention. However, such patients should be followed up regularly for signs of disease progression. With severe disease (Herring stage B or C / Catterall group III or IV), destruction of the lateral pillar leads to progressive subluxation of the femoral head. Thus intervention is necessary to contain the femoral head within the hip joint. Non surgical interventions include broomstick plasters and orthoses. However, these devices are cumbersome and tedious to use. Surgery focuses on realigning the acetabulum and femur in order to achieve proper containment. This may be done either via adjusting the hip bone (pelvic osteotomy), or by adjusting the proximal femur (femoral osteotomy). In certain patients a combined pelvic and femoral osteotomy may be necessary. The prognosis of Perthe's disease depends on the age of onset and severity of disease, with an older age of onset and more severe disease being associated with a poorer prognosis. In addition, failure to intervene after subluxation occurs results in a poorer prognosis. This patient falls into Herring stage B (Catterall group III) and requires intervention (for example, a femoral osteotomy). Steroids would be indicated in JIA, while IV antibiotics would be indicated in septic arthritis or osteomyelitis. Total hip replacement is not indicated in this patient.