If it's MRI proven then it's better you undergo reconstruction of both the ligaments. For both the ligaments to be torn, the knee must have been subjected to a great degree of trauma. Such a knee needs close observation and immediate surgery is not advisable. Once the acute please of injury has passed by, arthroscopic reconstruction of the ligaments is advisable.

Arthroscopic ACL/PCL reconstruction once the knee becomes quiet... Which is after 2-3 weeks of injury. Usually only ACL Recon suffices but since you are going under the knife might as well get both done. Also post surgery physiotherapy will be required for 6-12 weeks