Hello.According you say the result of knee MRI
was normal but in back only did they radiography
.It is necessary too make MRI of back (lumbar and sacral area) If results MRI of knee and back are normal, important pathologies are rule out because is a very sensitive test.
After rule out important pathologies, tell you that you can have pain for a long time because they are very painful areas and was intense trauma (with bruises from buttock to ankle).
It is very important to take drugs for pain.Besides the drug that you say(meperidine),I treat my patients with Diclofenac
50 mg thrice a day and Diazepam
5mg at night when severe trauma with inflammation is the diagnosis.Please consult your local doctor for a prescription.)
I wish you good health.
(In case the answer would have been useful please indicate this)