Post-surgical infection: The patient's symptoms of fever, persistent foot pain, and elevated inflammatory markers (ESR 45, WBC 10.5) after recent surgery on the foot are highly suggestive of a post-surgical infection. The timing and nature of the symptoms point towards a complication related to the surgery.

Deep Vein Thrombosis (DVT): Although less directly related to the surgery itself, the recent immobilization due to the car accident and subsequent surgery increases the risk of DVT, which can cause fever and pain, though typically more localized to the affected limb.
Osteomyelitis: An infection of the bone, which could be a complication of the surgery, especially if the surgical site became infected. The persistent pain and fever are consistent with this diagnosis.
Complex Regional Pain Syndrome (CRPS): This condition can occur after trauma or surgery and is characterized by chronic pain, but it does not typically cause fever. However, it's a consideration given the patient's history of trauma and surgery.

Septic Arthritis: Although less common, if the infection has spread to the joint, it would be a medical emergency requiring prompt treatment. The symptoms could include severe pain, fever, and swelling of the affected joint.
Endocarditis: If the patient has a history of heart conditions or intravenous drug use, endocarditis (infection of the heart valves) could be a consideration, especially with persistent fever. However, it would typically be accompanied by other symptoms such as heart murmurs.
Sepsis: Any infection that is not promptly and adequately treated can lead to sepsis, a life-threatening condition. Given the patient's fever and elevated WBC, ensuring that any infection is properly managed is crucial.

Lyme Disease: If the patient was exposed to ticks during outdoor activities, Lyme disease could be a rare cause of fever and joint pain, though it would typically be accompanied by a distinctive rash and other symptoms.
Erythromelalgia: A rare disorder characterized by burning pain, heat, and redness in the hands and feet, which could be considered if other diagnoses are ruled out, though it does not typically cause fever.
Chronic Pain Syndrome: A condition that could develop after trauma or surgery, characterized by chronic pain that is not explained by other causes. However, it would not typically cause fever.