Deep Vein Thrombosis (DVT): This is the most likely diagnosis due to the increased risk of blood clot formation following a leg fracture, especially if the patient has been immobilized. The swelling is typically unilateral and can be accompanied by pain, warmth, and discoloration of the affected leg.

Cellulitis: A bacterial infection of the skin and soft tissues that can cause swelling, redness, and warmth of the affected leg. It is a common complication following trauma, including fractures.
Lymphedema: Although less common in the acute setting, lymphedema can occur if there is damage to the lymphatic vessels during the fracture or subsequent surgery, leading to chronic swelling.
Compartment Syndrome: A condition where increased pressure within a muscle compartment leads to swelling, pain, and potentially nerve and muscle damage. It is a complication that can arise after a fracture, especially if there is significant soft tissue injury.

Pulmonary Embolism (PE) Source: Although not directly causing leg swelling, a DVT can lead to a PE, which is life-threatening. Identifying and treating the DVT can prevent this complication.
Osteomyelitis: An infection of the bone that can occur after a fracture. While it might not initially present with swelling alone, it's a serious condition that requires prompt treatment to prevent long-term damage.
Arterial Injury: Damage to the arteries can lead to decreased blood flow to the leg, causing swelling, pain, and potentially gangrene. This is a medical emergency requiring immediate intervention.

Lipodermatosclerosis: A chronic condition characterized by inflammation and scarring of the subcutaneous fat, leading to swelling and skin changes. It's less common and typically associated with long-standing venous insufficiency.
Klippel-Trenaunay Syndrome: A rare congenital condition that affects blood and lymph vessels, leading to swelling, varicose veins, and other vascular anomalies. It might be considered if the swelling is part of a larger syndrome.
Fabry Disease: A genetic disorder that can lead to vascular dysfunction, including swelling in the legs due to the accumulation of a particular type of fat in the body's cells. It's very rare and would be considered in the context of other systemic symptoms.