Empiric antibiotic therapy in patients with septic arthritis should take into account the prevalence of MRSA in the community. Clindamycin is a popular choice due to its high oral bioavailability, which facilitates transition to a home regimen. Vancomycin is another option and can be reserved for more severely ill children. Empiric coverage for suspected septic arthritis in children younger than 3 years of age should also include an anti-gram negative agent, such as a cephalosporin, to treat Kingella.7
Osteomyelitis
Acute osteomyelitis is a common cause of limp among children and is usually caused by the hematogenous spread of bacteria. Staphylococcus aureus, including MRSA, is responsible for up to 90% of cases of osteomyelitis, though recent studies have identified Kingella as an etiologic agent among children younger age 3 years.7 The highly vascular metaphysis of the tibia and femur in children can become infected during times of otherwise asymptomatic bacteremia in healthy patients.8 Among younger children with less well-developed anatomic separation between the bone and joint space, it is possible for infection to spread into the joint space. Younger children with osteomyelitis may present with poorly localized pain with or without systemic symptoms; older children and those with more advanced disease may describe point tenderness on the bone. In many cases it may be difficult clinically to distinguish osteomyelitis from septic arthritis; excessive pain with passive range of motion of the joint is more indicative of septic arthritis.
Ideally, antibiotic therapy should be deferred until cultures from the site of infection are obtained operatively or via aspiration. The local staphylococcus aureus resistance pattern should guide empiric antibiotic therapy. With the rise of MRSA, clindamycin has become first-line therapy with vancomycin as an alternative for severely-ill or clindamycin-allergic patients. For children younger than 3 years of age with a more subacute presentation, the possibility of Kingella infection should be considered and treated with a cephalosporin. Some children with osteomyelitis will require operative debridement, though
many can be treated with antibiotics alone. The standard duration of antibiotic treatment is 4 to 6 weeks, with transition to an oral regimen once the patient is afebrile with downtrending inflammatory markers.7,8,11
Perthes Disease
Perthes disease (also called Legg-Calve-Perthes disease) is an idiopathic process that involves avascular necrosis and revascularization of the blood supply of the femoral head. The condition is most common in children ages 3 to 12 years and has a 4:1 male to female predominance. The remodeling takes place over the course of 2 to 4 years. During this process, the epiphysis of the femoral head is weakened and undergoes irreversible deformation that, if uncorrected, will persist throughout life. Severe degenerative arthritis may result and ultimately require hip replacement.12
Perthes disease typically presents as a subacute limp, sometimes with referred pain to the groin, thigh, or knee of the affected side. Range of motion of the hip may be limited, particularly in abduction and internal rotation. Plain films demonstrate necrotic avascular areas of the distal femoral head during active disease; after the remodeling process is complete, the femoral head often shows residual deformities. Magnetic resonance imaging is useful in cases in which plain film findings are subtle, particularly early in the course of the disease.12,13
Management of Perthes disease depends on the age of the child and clinical factors such as radiographic progression and range of motion of the hip. The goal of therapy is to limit damage to the femoral head during the revascularization process. In children younger than 5 years of age, nonsurgical management with an abduction splint to keep the femoral head contained and protected within the acetabulum may be used. Surgical osteotomies are used in older and more severely affected children to artificially contain the femoral head during the healing process.13
Slipped Capital Femoral Epiphysis
A common cause of limp among older children, the average age of presentation for SCFE is 13.5 years for boys and 12 years for girls. This condition occurs when the proximal femoral epiphysis slides posteriorly and inferiorly relative to the metaphysis. Epidemiological studies have established a connection between SCFE and obesity. Although the precise pathogenesis remains unknown, it is hypothesized that increased mechanical forces during a time of rapid pubertal growth lead to weakness at the physis. Among children who develop SCFE outside of the usual age distribution, endocrinopathies such as hypothyroidism, hypogonadism, and panhypopituitarism are often discovered.14