Hi thanks for the query.
After the injury you might had some form of ligament injury
. This could have shown up in the MRI
. I would also suspect some of meniscal injury
inside the knee after the injury. since you are not able to bend and straighten the it could be due to localized collection of blood in knee joint or locking due to injury to the meniscus
. I advice you to contact orthopaedician who might recheck and advice you appropriatly