Transient synovitis, septic hip, and Legg-Calvé-Perthes disease are common conditions in children. Distinguishing between these disorders can be a diagnostic challenge. Similar presentations, in an age group difficult to examine, coupled with literature that is confusing creates difficulty. It is important to make the correct diagnosis of septic hip in a timely fashion to avoid serious and potentially crippling consequences. As there is no single test for discriminating between these conditions, knowledge of the nuances of clinical presentation, physical examination, laboratory investigations, and imaging is essential. Judicious use of clinical algorithms can complement clinical acumen.
Key points
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The differentiation of septic hip from other inflammatory causes of hip pain in the child can be difficult.
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It is essential not to miss or delay the diagnosis of a septic hip.
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Using knowledge of the presentations of these diagnoses along with good clinical acumen, the physician can achieve these goals.
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It is very important to incorporate all information from the history, physical examination, laboratory tests, and imaging, with an emphasis on range of motion and the judicious use of clinical algorithms.
Epidemiology
Transient synovitis is a self-limited condition of unknown etiology. There is some evidence linking it to a viral infection, but this has not been substantiated. There is often an antecedent upper respiratory infection that may be a predisposing factor, and it is one of the most common causes of painful (irritable) hip in childhood. Synovitis can occur in toddlers and in adolescence, but most patients are between 3 and 8 years with a mean age of 6 years. The right side is slightly more commonly involved, but bilateral synovitis has been reported. There is a male predilection (approximately 2:1).
Septic arthritis is an orthopedic emergency. Purulent exudate is toxic to hyaline cartilage, and can damage or destroy a joint relatively quickly. Beginning treatment within 4 days from the initial onset of symptoms usually affords a good prognosis. Once frank purulence is established, however, the hip may be devastated in a matter of hours. Fig. 1 demonstrates the destruction that sepsis of the hip can cause when treated late. The joint can be infected through the hematogenous route, direct inoculation through trauma or surgery, and contiguous spread. In the case of the hip, the latter would be from osteomyelitis of the intra-articular portion of the femoral head and neck draining into the joint. This phenomenon is most common in the neonate and infant ( Fig. 2 ). Septic arthritis has a similar age distribution but is perhaps more common when presenting at age less than 2 years. It is more common in boys than in girls, and can present in more than 1 joint at a time, although this is rare.
Legg (United States), Calvé (France), and Perthes (Germany) described what is now known as Legg-Calvé-Perthes (LCP) disease independently in 1910. The condition is initiated by the loss of blood flow to the femoral head. The subsequent healing brings on the clinical syndrome of pain, femoral head collapse, and eventual osteoarthritis. Despite much work and many theories, the etiology continues to be unknown, making treatment highly controversial. It is more common in boys and can be bilateral in 20% to 30% of cases. Usually when bilateral the two sides present sequentially within 18 months, although bilateral LCP disease is uncommon. The age range is again similar to transient synovitis (3–10 years) but, unlike septic arthritis, it is more common in older children (6–8 years).
Epidemiology
Transient synovitis is a self-limited condition of unknown etiology. There is some evidence linking it to a viral infection, but this has not been substantiated. There is often an antecedent upper respiratory infection that may be a predisposing factor, and it is one of the most common causes of painful (irritable) hip in childhood. Synovitis can occur in toddlers and in adolescence, but most patients are between 3 and 8 years with a mean age of 6 years. The right side is slightly more commonly involved, but bilateral synovitis has been reported. There is a male predilection (approximately 2:1).
Septic arthritis is an orthopedic emergency. Purulent exudate is toxic to hyaline cartilage, and can damage or destroy a joint relatively quickly. Beginning treatment within 4 days from the initial onset of symptoms usually affords a good prognosis. Once frank purulence is established, however, the hip may be devastated in a matter of hours. Fig. 1 demonstrates the destruction that sepsis of the hip can cause when treated late. The joint can be infected through the hematogenous route, direct inoculation through trauma or surgery, and contiguous spread. In the case of the hip, the latter would be from osteomyelitis of the intra-articular portion of the femoral head and neck draining into the joint. This phenomenon is most common in the neonate and infant ( Fig. 2 ). Septic arthritis has a similar age distribution but is perhaps more common when presenting at age less than 2 years. It is more common in boys than in girls, and can present in more than 1 joint at a time, although this is rare.
Legg (United States), Calvé (France), and Perthes (Germany) described what is now known as Legg-Calvé-Perthes (LCP) disease independently in 1910. The condition is initiated by the loss of blood flow to the femoral head. The subsequent healing brings on the clinical syndrome of pain, femoral head collapse, and eventual osteoarthritis. Despite much work and many theories, the etiology continues to be unknown, making treatment highly controversial. It is more common in boys and can be bilateral in 20% to 30% of cases. Usually when bilateral the two sides present sequentially within 18 months, although bilateral LCP disease is uncommon. The age range is again similar to transient synovitis (3–10 years) but, unlike septic arthritis, it is more common in older children (6–8 years).
Clinical presentation
As noted, infants and young toddlers (<2 years) will tend to have septic arthritis. Children older than 9 years will be less likely to have septic arthritis or transient synovitis. The biggest diagnostic challenge is in the 3- to 8-year age range. It is not uncommon for any of these conditions to present during this time. Their presentations are very similar:
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Variable onset of hip pain
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Limp, refusal to bear weight
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Limitation of movement
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Fever
There are, however, some nuances that may be helpful in differentiation. Factors to consider include ( Table 1 ):
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Trauma
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Trauma is commonly noted in the history. It is a common occurrence at the beginning of symptoms in all 3 diagnoses, and should always be part of the differential. One must remember that more than 1 diagnosis may exist. Indeed, in young children the evaluation can be difficult. There are case reports of septic arthritis being mistaken for a toddler’s fracture. As a result of the way a toddler’s fracture tends to spiral, the tenderness is most commonly at the junction of the middle and distal thirds of the tibia posteromedially. It may not be as tender anterolaterally.
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Onset
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Differences in the onset can be helpful. A relatively short history of symptoms over a couple of days is common in septic arthritis and transient synovitis. One must bear in mind that concomitant osteomyelitis or antibiotic treatment may mitigate the acute nature of the presentation of septic arthritis. A longer presentation (∼10–14 days) with a more acute worsening over the previous couple of days may indicate an osteomyelitis that has seeded the joint. LCP disease tends to present over a longer period of time (weeks to months) and may even be intermittent in nature. Indeed, a recurrence of “transient synovitis” may indicate that the diagnosis is LCP disease. On occasion LCP can present with an acute irritable hip.
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Pain
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Pain is a large part of all of these diagnoses, but severity may help in differentiation. Both sepsis and transient synovitis pain can be moderate to very severe. Pain alone does not differentiate between these 2 entities. Patients with LCP disease tend not to have severe pain and indeed may not have much pain at all. Nonsteroidal anti-inflammatory medications can help relieve the discomfort of transient synovitis, but tend to be ineffective in cases of septic hip.
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Pain is usually felt in the groin region. Three nerves innervate the hip; therefore, the pain might radiate to the medial thigh (obturator nerve), the buttock (sciatic nerve), and the knee (femoral nerve). It is not uncommon for a child to undergo radiography and magnetic resonance imaging (MRI) of the knee when the problem is actually the hip. All skeletally immature individuals presenting with knee pain should, at least, have a thorough physical examination of the hip.
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Gait
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Transient synovitis and septic arthritis both can present with refusal to bear weight, which would be distinctly unusual for LCP disease. All 3 might present with an antalgic gait (decreased stance phase on the affected side). LCP disease more commonly presents with a lurch (the body leans to the affected side during stance) or a stiff hip gait (the pelvis and lower back swing the whole leg through with little hip motion, instead of the hip flexors moving the hip to swing the leg through).
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Fever
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A temperature greater than 38.5°C is not uncommon with septic arthritis, whereas a low-grade fever (<38°C) may be seen with transient synovitis. Fever is not a feature in the presentation of LCP disease.
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