Based on your symptoms and the CT report, there are several possible diagnoses that could explain your pain:
Osteoporosis: This is a condition in which the bones become weak and brittle, making them more prone to fractures. It is more common in older adults, but can also occur in younger individuals who have certain risk factors such as low
calcium intake or a sedentary lifestyle.
Degenerative changes: This refers to wear and tear on the joints over time, which can cause pain, stiffness, and reduced mobility. It is often associated with osteoarthritis, which is the most common type of arthritis.
Chondromalacia patella: This is a condition in which the cartilage under the kneecap softens and breaks down, causing pain and discomfort, particularly with activities that put pressure on the knee joint.
Given your symptoms, chondromalacia patella could be a possible diagnosis for the pain under your kneecap while sitting with bent legs. However, the mid spine area and lower back pain may be related to osteoporosis and degenerative changes. It would be best to consult a doctor and get a thorough examination and imaging tests such as X-rays or MRI to confirm the diagnosis and recommend appropriate treatment.