Ankle Sprain: This is the most common injury to the ankle, often resulting from a sudden twisting motion. The lack of a fracture (fx) on imaging supports this diagnosis, as sprains involve ligamentous injury rather than bone fracture.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth of the skin. It's a common condition that could easily affect the ankle area.
Gout or Pseudogout: These are forms of arthritis characterized by sudden, severe attacks of pain, swelling, redness, and tenderness. The ankle is a common site for these conditions, although they are more typically associated with the big toe.
Septic Arthritis: An infection within a joint, which can cause pain, swelling, and redness. While less common than other conditions, it's a significant concern due to potential long-term damage if not promptly treated.

Deep Vein Thrombosis (DVT): A blood clot in a deep vein, which can cause swelling, redness, and warmth. Although less common in the ankle, DVT is a potentially life-threatening condition if the clot dislodges and travels to the lungs (pulmonary embolism).
Osteomyelitis: A bone infection that can cause pain, swelling, and redness. It might not be immediately suspected without a fracture, but it's crucial to consider, especially in patients with certain risk factors (e.g., diabetes, recent trauma).
Compartment Syndrome: A condition resulting from increased pressure within a muscle compartment, which can lead to muscle and nerve damage. It's a medical emergency that requires prompt recognition and treatment.

Erythema Nodosum: A condition characterized by the sudden formation of painful, red lumps on the skin, often on the shins. It can be associated with various underlying conditions, including infections and autoimmune diseases.
Complex Regional Pain Syndrome (CRPS): A chronic pain condition that most often affects one of the arms, legs, hands, or feet after an injury or trauma. It's rare and can be challenging to diagnose but should be considered in cases of unexplained, severe pain and swelling.
Lymphangitis: An infection of the lymphatic channels, which can cause red streaks from the infected area towards the nearest lymph node. It's relatively rare but can be a sign of a more serious underlying infection.