I would suggest getting a doctor's note to help but TSA has a special procedure for people with disabilities or medical conditions:
Disabilities and Medical Conditions
To ensure your security, all travelers are required to undergo screening at the checkpoint. You or your traveling companion may consult the TSA officer about the best way to relieve any concerns during the screening process. You may provide the officer with the TSA notification card or other medical documentation to describe your condition. If you have other questions or concerns about traveling with a disability please contact passenger support.
If you are approved to use TSA Pre✓® lane at a participating airport, you do not need to remove shoes, laptops, 3-1-1 liquids, belts, or light jackets during the screening process and TSA officers may swab your hands, mobility aids, equipment and other external medical devices to test for explosives using explosives trace detection technology.
You are not required to remove your shoes if you have disabilities and medical conditions. However, your shoes must undergo additional screening including visual/physical inspection as well as explosives trace detection testing of the footwear. You can request to be seated during this portion of the screening.
Please choose a situation to see more information.
Prosthetics, Casts, Braces, Support Appliances
Inform the TSA Officer
Inform the TSA officer if you have a prosthetic, cast, brace or support appliance and require assistance with the screening process. You may provide the officer with the TSA notification card or other medical documentation to describe your condition.
Passengers with prostheses can be screened using imaging technology, metal detector, or a pat-down.
A prosthetic, cast, brace or support appliance may be subject to additional screening. You may be asked to lift or raise your clothing to screen the prosthetic. Sensitive areas should not be exposed during the screening process.
You may voluntarily remove your prosthetic, cast, brace or support appliance and have it screened by the X-ray.
So you may have to remove it just request that you're seated and your leg in a comfortable position before you do this.