Sympathetic dysfunction due to spinal fusion: The spinal fusion from T2 to the pelvis can disrupt the sympathetic nervous system, which controls blood flow and temperature regulation. This disruption can lead to unequal leg temperatures, with the affected leg being colder due to reduced blood flow.

Deep vein thrombosis (DVT): Immobility and recent surgery increase the risk of DVT, which can cause a decrease in blood flow to the affected leg, resulting in a temperature difference.
Infection or osteomyelitis: Post-surgical infections can cause inflammation and decreased blood flow, leading to temperature differences between the legs.
Nerve injury: Direct injury to nerves during the spinal fusion surgery can affect blood flow and temperature regulation in the legs.

Aortic or iliac artery thrombosis: Although less common, thrombosis in the major arteries supplying the legs can lead to severe ischemia and temperature differences. Missing this diagnosis could result in severe limb ischemia or loss.
Spinal epidural hematoma: A post-surgical hematoma can compress the spinal cord and disrupt blood flow, leading to temperature differences and potentially severe neurological consequences if not promptly addressed.

Complex regional pain syndrome (CRPS): This condition can cause abnormal blood flow and temperature regulation in the affected limb, although it is less common in the immediate post-surgical period.
Vasculitis: Inflammation of the blood vessels can affect blood flow and temperature, but this would be an unusual complication in the context of spinal fusion surgery.