Differential Diagnosis for Fever with Chills and History of Knee Trauma

Single Most Likely Diagnosis

• Septic Arthritis: This condition is a strong consideration given the recent knee trauma, which could have introduced bacteria into the joint, leading to infection. The presence of fever and chills supports this diagnosis, as they are common symptoms of a systemic infection.

Other Likely Diagnoses

• Cellulitis: An infection of the skin and subcutaneous tissues, which could have been caused by the trauma to the knee. Symptoms include redness, swelling, warmth, and pain in the affected area, along with systemic symptoms like fever and chills.
• Osteomyelitis: An infection of the bone, which could be a complication of the knee trauma, especially if the bone was exposed or if there was a deep wound. Fever and chills are common, along with pain and swelling in the affected bone.
• Soft Tissue Injury Infection: Any soft tissue injury from the trauma could become infected, leading to symptoms like fever, chills, redness, swelling, and increased pain at the site of injury.

Do Not Miss Diagnoses

• Necrotizing Fasciitis: A severe infection of the fascia, the tissue that covers muscles, nerves, fat, and blood vessels in the affected area. It is a medical emergency that requires prompt treatment. Symptoms can include severe pain, fever, chills, and swelling, but the skin may not necessarily look infected in the early stages.
• Toxic Synovitis: An inflammatory condition of the synovium (the lining of the joints) that can mimic septic arthritis but is not due to an infection. It's crucial to differentiate it from septic arthritis to avoid unnecessary antibiotic treatment.
• Deep Vein Thrombosis (DVT): Although less directly related to the infection, trauma can increase the risk of DVT, which can cause fever and chills among other symptoms like leg swelling and pain.

Rare Diagnoses

• Lyme Arthritis: If the trauma occurred in an area endemic for Lyme disease and there was exposure to ticks, Lyme arthritis could be a consideration, though it typically presents with a more chronic course.
• Gonococcal Arthritis: A type of septic arthritis caused by Neisseria gonorrhoeae, which could be considered in sexually active individuals with no clear history of trauma but recent sexual activity.
• Tuberculous Arthritis: A rare form of arthritis caused by Mycobacterium tuberculosis, which could present with chronic symptoms including fever, but is less likely in the acute setting following trauma.