The posterior cruciate ligament stops the knee from gliding backward and often is not considered to be as serious as injury to its anterior counterpart (the ACL). Indeed, there is a line of thought that injury to the ACL increases the risk of knee OA, but this is being debated, but generally this is not the case for the PCL.
For the PCL, in general, you don't need surgery. Usually rehab is sufficient at restoring a good level of function and stability around the knee. If you take part in contact sports, have sustained a further injury to the knee or you are having lots of symptoms despite good rehab, then it maybe necessary to consider a surgical option.
Hope this helps.
BW
Dr Dinesh