Post-Traumatic Arthritis: This is a common complication following a fracture, especially if the joint surface was involved. The trauma can lead to early onset of osteoarthritis, causing swelling, pain, and stiffness in the ankle.

Residual Hardware Irritation: If hardware (e.g., screws, plates) was used to stabilize the fracture, it can sometimes cause irritation or allergic reactions, leading to swelling.
Chronic Ligament Instability: After a fracture, especially if it involved significant displacement or if the ligaments were also injured, there can be chronic instability leading to repeated sprains and swelling.
Deep Vein Thrombosis (DVT): Although less common, DVT can occur after immobilization for a fracture, leading to swelling in the affected limb.

Osteomyelitis: An infection of the bone that can occur after a fracture, especially if the fracture was open or if there was a complication with the hardware. It's crucial to diagnose and treat promptly to avoid serious consequences.
Compartment Syndrome: A condition where pressure within the muscles builds to dangerous levels, which can occur after a fracture. It's a medical emergency that requires immediate attention.

Complex Regional Pain Syndrome (CRPS): A rare condition characterized by intense burning or aching pain in the affected limb, often accompanied by swelling, skin changes, and extreme sensitivity. It can occur after a fracture but is relatively rare.
Tumor or Cyst: In rare cases, a swollen ankle could be due to a benign or malignant tumor, or a cystic lesion that has developed in the ankle region. Although rare, it's an important consideration in the differential diagnosis, especially if other causes have been ruled out.