The bone above the knee joint is the femur. The bone just below the knee or stifle joint is the tibia.   The top of the tibia is the tibial plateau. The large quad (thigh) muscle end with the patellar tendon and attaches the knee cap (patella) to the tibial tuberosity.

During weight bearing, the femur pushes down the tibial plateau slope. The ACL stops this downward slide down the slope, therefore, is under constant tension during weight bearing. This is a biomechanical problem when the ACL is ruptured.  The grinding motion during weight bearing with a torn ACL is directly related to the angle between the tibial plateau slope and the patellar tendon. A more perpendicular angle results in a more stable joint.

The TTA involves an osteotomy (cut) in the non-weight bearing thin crest portion of the tibia, just in front of the main bone shaft. The tibial tuberosity is advanced to achieve a perpendicular relationship between the tibial plateau slope and patellar tendon. This relationship results in a stable joint.