Differential Diagnosis for Transient Synovitis vs Septic Arthritis

Single Most Likely Diagnosis

• Transient synovitis: This is the most likely diagnosis in a child presenting with acute hip pain and limited mobility, especially if there is a recent history of upper respiratory tract infection. Transient synovitis is a common, self-limiting condition that often resolves without specific treatment.

Other Likely Diagnoses

• Septic arthritis: Although less common than transient synovitis, septic arthritis is a critical diagnosis to consider due to its potential for rapid joint destruction and long-term morbidity. It typically presents with severe pain, swelling, and decreased range of motion of the affected joint, often accompanied by systemic signs of infection such as fever.
• Osteomyelitis: Infection of the bone adjacent to the joint can cause similar symptoms to septic arthritis and transient synovitis, including pain and limited mobility. It is essential to consider osteomyelitis, especially if there are signs of systemic infection.

Do Not Miss Diagnoses

• Septic arthritis (also listed under other likely diagnoses, but included here due to its critical nature): The potential for severe and irreversible joint damage if not promptly treated makes septic arthritis a "do not miss" diagnosis. Early diagnosis and treatment are crucial.
• Osteonecrosis (e.g., Legg-Calve-Perthes disease): Although not an infection, osteonecrosis can present with hip pain and limited mobility. Missing this diagnosis could lead to long-term joint damage and disability.
• Slipped capital femoral epiphysis (SCFE): This condition, more common in obese adolescents, can present with hip pain and limited mobility. It is a surgical emergency to prevent further slippage and potential avascular necrosis.

Rare Diagnoses

• Rheumatologic conditions (e.g., juvenile idiopathic arthritis, systemic lupus erythematosus): These conditions can cause joint pain and swelling but are less common and typically have other systemic symptoms or signs.
• Hemarthrosis: Bleeding into the joint space, which can occur in patients with bleeding disorders or those on anticoagulant therapy, is a rare but important consideration.
• Neuropathic arthropathy: Although rare in the context of acute hip pain, it can occur in patients with underlying neurological conditions affecting pain perception and joint protection.