Rheumatoid Arthritis Foot Involvement: Given the patient's history of rheumatoid arthritis, it is likely that the foot pain is related to the progression or flare-up of the disease, which commonly affects the feet and can cause significant pain and disability.

Osteoporotic Fractures: The patient's osteopenia increases the risk of fractures, and foot pain could be indicative of a stress fracture or other osteoporotic fracture in the feet.
Peripheral Neuropathy: Rheumatoid arthritis and other chronic conditions can lead to peripheral neuropathy, which may cause pain, numbness, and tingling in the feet.
Gout: Although not directly related to rheumatoid arthritis or osteopenia, gout is a common cause of foot pain, especially in the big toe, and can coexist with other conditions.

Infection (e.g., Cellulitis, Osteomyelitis): Infections in the foot can be serious, especially in patients with compromised immune systems due to chronic conditions like rheumatoid arthritis. Early diagnosis and treatment are crucial.
Deep Vein Thrombosis (DVT): While less common, DVT can cause foot and leg pain and is a potentially life-threatening condition if not promptly diagnosed and treated.
Charcot Foot: A complication of peripheral neuropathy, Charcot foot can lead to significant deformity and disability if not recognized and managed properly.

Complex Regional Pain Syndrome (CRPS): A rare condition characterized by intense burning or aching pain in the hands or feet after an injury or trauma, which could potentially be related to the patient's osteopenia or rheumatoid arthritis.
Erythromelalgia: A disorder that causes burning pain, heat, and redness in the hands and feet, which could be considered in the differential diagnosis due to its association with various systemic diseases.