Emergent Care / Stabilization: Prompt identification and management is crucial to prevent progression and potentially irreversible damage.

Causes / typical injury mechanism: Ankle septic arthritis is a relatively rare but serious condition characterized by an infection within the ankle joint, most commonly Staphylococcus aureus. Infection can occur via hematogenous spread or direct inoculation of a pathogen within the joint. It is a potential complication following arthroscopic procedures.

Classic history and presentation: Patients will often present with acute-onset pain and limited motion in the ankle joint. The joint is also often erythematous, warm, and swollen. A history of recent illness, trauma, or surgery is common.

Prevalence: The estimated incidence of ankle septic arthritis is approximately 7.8 per 100 000 individuals. Among those who recently underwent an ankle arthroscopic procedure, the rate of infection has been reported to be between 0.13% to 1.8%.

Risk factors:

• Recent illness
• Trauma
• Surgery
• Underlying arthropathy

Pathophysiology: Infection of the ankle joint via either hematogenous spread or direct inoculation. Potentially irreversible damage within the joint can occur due to the direct action of bacterial toxins, host inflammatory response, and/or tissue ischemia.

Grade / classification system: The Gächter classification system is often used to describe the severity of septic arthritis based on arthroscopic and radiographic results.

• Stage I – Opacity of fluid, redness of the synovial membrane, and possible petechiae without radiologic changes.
• Stage II – Significant inflammation, pus, and fibrin deposition without radiologic changes.
• Stage III – Synovial membrane thickening and compartment formation without radiologic changes.
• Stage IV – Aggressive pannus with cartilage infiltration in addition to radiologic osteolysis and possible cysts and erosions.