The position of the tibia during graft fixation affects knee kinematics and graft forces for anterior cruciate ligament reconstruction.

Ten cadaveric knees (donor ages, 36 to 66 years) were tested at full extension, 15 degrees, 30 degrees, and 90 degrees of flexion under a 134-N anterior tibial load. In each knee, the kinematics as well as in situ force in the graft were compared when the graft was fixed with the tibia in four different positions: full knee extension while the surgeon applied a posterior tibial load (Position 1), 30 degrees of flexion with the tibia at the neutral position of the intact knee (Position 2), 30 degrees of flexion with a 67-N posterior tibial load (Position 3), and 30 degrees of flexion with a 134-N posterior tibial load (Position 4). For Positions 1 and 2, the anterior tibial translation and the in situ forces were up to 60% greater and 36% smaller, respectively, than that of the intact knee. For Position 3, knee kinematics and in situ forces were closest to those observed in the intact knee. For Position 4, anterior tibial translation was significantly decreased by up to 2 mm and the in situ force increased up to 31 N. These results suggest that the position of the tibia during graft fixation is an important consideration for the biomechanical performance of an anterior cruciate ligament-reconstructed knee.