90 Septic Arthritis

Clinical Presentation

A 17-year-old presents with an acutely swollen tender ankle.

Figure 90B

Radiographic Findings

Lateral radiograph demonstrates evidence of a tibiotalar joint effusion with a large erosion showing marginal indistinct sclerosis at the talar neck (Fig. 90A). Corresponding sagittal fat-suppressed enhanced T1-weighted MRI depicts a joint effusion with diffuse increased signal intensity within talus and navicular (Fig. 90B). There is a focal area of higher signal intensity with a low-intensity margin within the talar neck with loss of adjacent anterior cortex.

Diagnosis

Septic arthritis

Differential Diagnosis

Inflammatory arthritis (usually has a more gradual onset and commonly polyarticular)
Pauciarticular form of Lyme disease (seen in endemic areas)
Trauma

Discussion

Background

Septic arthritis, defined clinically as joint inflammation, is an infection of the joint space. It is diagnosed with a positive synovial or blood culture, an antigen detection test, or a standard tube agglutination titer of 160 or greater for Brucella species. Approximately 7% of childhood arthritis is septic in origin with the vast majority of these patients being previously healthy. The incidence varies with age (ranging from 5 to 37 per 100,000), being most common in patients <2 years old (one third to one half of cases). Septic arthritis is most commonly seen in the hip and knee joints, followed by ankle and shoulder.

Etiology

Hematogenous seeding during a bacteremic episode is the most common etiology in children. Less commonly, the infectious joint is the result of direct extension from an adjacent cellulitis/myositis. Spread from an adjacent osteomyelitis is seen more often in infants <8 months or >18 months of age, particularly in the hip, where the physis is intra-articular. Traumatic penetration of the joint is a less common etiology but can be seen with plant-thorn synovitis.

Clinical Findings

Fever, motion exacerbated joint pain, erythema, and swelling are typical in older children.
Mild signs and symptoms can be present in patients <2 years of age.
Infants are more likely to present with fever, pseudoparalysis, irritability, and poor feeding.

Complications

Destruction of cartilage and underlying bone can lead to ankylosis/fibrosis/contractures.
Subluxation, dislocation, epiphyseal separation, and osteonecrosis have been reported.
Growth disturbance leading to limb-length discrepancy and ambulatory disorder
Can progress to osteomyelitis
Infrequently, heterotopic ossification develops.
Subsequent degenerative changes