What causes pain behind the knee but pain free walk following hyperextension of the knee?
Mild soft tissue injury likely.
Thanks for posting your query.
If there is no pain on walking or climbing stairs then any serious damage is not likely.
This can be due to a mild soft tissue injury.
You can avoid any painful activities and use a knee support for a few weeks and let the area heal on its own with rest.
I hope this answers your query. In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Wishing you good health.
Dr. Praveen Tayal, Orthopaedic Surgeon