Osteoarthritis (OA): This is a common condition characterized by wear and tear of the joint cartilage and underlying bone, leading to pain, stiffness, and swelling, especially in older adults. The bilateral involvement and difficulty ambulating are consistent with OA, especially if the patient has a history of similar symptoms or risk factors such as age, obesity, or previous joint injuries.

Rheumatoid Arthritis (RA): An autoimmune disorder that causes inflammation and pain in the joints. Bilateral knee swelling and difficulty walking could be symptoms of RA, especially if accompanied by morning stiffness, systemic symptoms, or a history of autoimmune diseases.
Meniscal Tears or Ligament Sprains: Acute injuries to the knee structures can cause swelling and difficulty walking. These conditions might be considered if there's a history of trauma or sudden onset of symptoms.
Bursitis: Inflammation of the fluid-filled sacs (bursae) that cushion joints and reduce friction between bone and soft tissue. Prepatellar or infrapatellar bursitis could cause swelling around the knee, especially if the patient has a history of kneeling or direct trauma to the knee.

Septic Arthritis: A serious infection within a joint that requires prompt antibiotic treatment. Although less common, it's crucial to consider, especially if the patient has a fever, significant pain, or a history of joint replacement, intravenous drug use, or immunocompromised state.
Deep Vein Thrombosis (DVT): While DVT typically presents with unilateral swelling, pain, and warmth, it's essential to consider, especially if there's a history of recent immobilization, cancer, or clotting disorders.
Osteonecrosis (Avascular Necrosis): A condition that occurs when there is loss of blood to the bone. It can cause pain and swelling, especially if the patient has a history of steroid use, excessive alcohol consumption, or previous hip or knee trauma.

Hemophilia: A genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. Patients with hemophilia can experience joint swelling and pain due to bleeding into the joints.
Pigmented Villonodular Synovitis (PVNS): A rare condition characterized by overgrowth of the joint lining (synovium), leading to swelling, pain, and potentially joint destruction.
Neuropathic Arthropathy (Charcot Joint): A condition that occurs in individuals with nerve damage (neuropathy), leading to progressive joint destruction. It's more common in patients with diabetes or other conditions causing neuropathy.