Fracture of the proximal femur or hip: This is a common injury in elderly individuals after a fall, given the high incidence of osteoporosis and the significant force exerted on the hip during a fall. The pain in the right knee could be referred pain or due to the mechanism of injury.

Soft tissue injury (contusion or strain): Direct trauma to the hip or knee area can cause soft tissue injuries, which are common after falls.
Osteoarthritis flare-up: If the patient has pre-existing osteoarthritis, a fall could exacerbate the condition, leading to increased pain in the affected joints.
Ligament sprain or meniscal injury in the knee: The mechanism of the fall could also result in twisting or bending injuries to the knee, leading to ligament or meniscal damage.

Hip fracture with vascular compromise: A fracture that compromises blood flow to the femoral head or surrounding tissues is a medical emergency.
Septic arthritis: Especially if the patient has a history of joint replacement or is immunocompromised, septic arthritis is a potentially deadly condition that requires prompt diagnosis and treatment.
Nerve injury (e.g., femoral or sciatic nerve): Direct trauma or compression from a fracture or hematoma could result in nerve damage, which has significant implications for recovery and function.

Avascular necrosis of the femoral head: While not immediately apparent after a fall, avascular necrosis could be a long-term complication of a hip fracture or severe trauma, especially if there's a delay in diagnosis or treatment.
Stress fracture: If the patient has been increasing their activity level or has underlying conditions like osteoporosis, a stress fracture could be a consideration, especially if the pain is more activity-related.
Infection (osteomyelitis): Direct infection of the bone, which could occur after a penetrating injury or in the setting of compromised skin integrity over the affected area.