Well, without a detailed clinical evaluation it would be difficult to determine the cause of your symptoms. With structural issues ruled out and effusion being present, possibilities that may need to be considered include inflammation, neuro-muscular causes, injuries to muscles/ ligaments etc. Though a CT is not particularly sensitive to detecting tears, this is unlikely to be a complete tear with a normal physical exam and a partial tear should not be a reason for chronic excruciating pain. I would suggest resting the knee for a few days and avoiding weight bearing. You could also use some warm compresses and tylenol/ OTC NSAIDS for pain relief. This should be followed by physiotherapy gradually to improve muscle strength. If conservative management does not seem to be helpful, you may seek a review with your treating orthopedician for alternative modes of management and if required consult with a pain management specialist may be sought.
Hope this is helpful.