Biomechanics of initial tibial fixation in posterior cruciate ligament reconstruction.

PURPOSE:
Clinical success of posterior cruciate ligament (PCL) reconstruction continues to lag behind that of its anterior counterpart. The tibial site of PCL graft fixation has been a focus of recent research. This study examined the effect of combined distal and proximal tibial fixation on the ability of a transtibial PCL reconstruction to restore intact knee kinematics and in situ forces of the intact PCL.

TYPE OF STUDY:
Biomechanical study.

METHODS:
Ten human cadaveric knees were tested. A 134-N posterior tibial load was applied using a robotic/universal force moment sensor testing system at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of knee flexion. Each knee was tested under 4 conditions: intact, PCL-deficient, single-bundle transtibial reconstruction with distal tibial fixation, and single-bundle transtibial reconstruction with combined distal and proximal tibial fixation. Knee kinematics in 5 degrees of freedom for each condition were recorded and in situ forces of the intact PCL and the PCL grafts were determined.

RESULTS:
Reconstruction with combined fixation resulted in significantly less posterior tibial translation than reconstruction with distal fixation at 30 degrees, 90 degrees, and 120 degrees (P < .05), and restored intact knee kinematics at 90 degrees and 120 degrees (P > .05). Reconstruction with combined fixation more closely restored intact PCL in situ forces at 90 degrees (P < .05).

CONCLUSIONS:
Transtibial reconstruction with combined fixation more closely restores intact knee kinematics and in situ forces in the PCL at initial fixation than does reconstruction with distal tibial fixation. The improved kinematics and in situ forces seen with the combined fixation may be attributed to decreased functional graft length and increased stiffness of the PCL graft.

CLINICAL RELEVANCE:
Combined tibial fixation may provide a more stable reconstruction at initial fixation.