Degenerative spinal stenosis: This condition is common in the elderly population and can cause severe leg pain due to compression of the spinal nerves. The pain often worsens with walking or standing and improves with rest.

Peripheral arterial disease (PAD): PAD is a common condition in the elderly, characterized by atherosclerosis of the lower extremity arteries, leading to intermittent claudication (pain in the legs or buttocks during exercise).
Osteoarthritis: Although osteoarthritis typically affects the joints, it can cause severe leg pain, especially if the hip or knee joints are involved.
Diabetic neuropathy: Elderly patients with diabetes are at risk of developing diabetic neuropathy, which can cause severe leg pain, numbness, or tingling.

Deep vein thrombosis (DVT): DVT is a potentially life-threatening condition that requires prompt diagnosis and treatment. It can cause severe leg pain, swelling, and warmth.
Aortic aneurysm or dissection: Although less common, an aortic aneurysm or dissection can cause severe leg pain, especially if it involves the lower extremity arteries.
Spinal epidural abscess or hematoma: These conditions can cause severe leg pain, numbness, or weakness, and require prompt medical attention to prevent permanent neurological damage.
Osteonecrosis (avascular necrosis): Osteonecrosis can cause severe leg pain, especially if it affects the hip or knee joints.

Paget's disease of bone: This rare condition can cause severe leg pain, deformity, and enlargement of the affected bone.
Chronic compartment syndrome: This condition is characterized by increased pressure within a muscle compartment, leading to severe leg pain, numbness, or weakness.
Ehlers-Danlos syndrome: This rare genetic disorder can cause severe leg pain, joint hypermobility, and skin hyperextensibility.
Sickle cell disease: Although more common in younger populations, sickle cell disease can cause severe leg pain, especially during sickle cell crises.