A full knee dislocation occurs when the tibia separates from the femur. The ACL, PCL, MCL and LCL ligaments may be all torn. This can occur when there is a high velocity twisting injury to the knee. It is a serious injury which requires immediate evaluation for vascular injuries with surgical intervention to repair or replace the damaged ligaments. post operative care including physical therapy, swelling control, range of motion exercises are the key to a great outcome.
Knees do not necessarily wear out evenly, sometimes one part of the knee is perfectly fine while another part is completely destroyed. If only part of the knee joint is worn out, why replace all of it?