Effects of knee position, graft tension, and mode of fixation in posterior cruciate ligament reconstruction: a cadaveric knee study.
OBJECTIVE
Many knees exhibit residual ligament laxity after posterior cruciate ligament (PCL) reconstruction, which is believed to be technique related. The purpose of this study was to investigate the optimal graft tension, the best angle of knee flexion, and the mode of fixation in PCL reconstruction.


METHODS
Anatomic biomechanical study.


METHODS
A testing apparatus with frictionless bearing that allows other degrees of freedom except for flexion and extension of the knee joint was designed. The normal PCL tension at different angles of knee flexion was measured with a force transducer, and the optimal tension of the PCL graft that allows full range of knee motion was studied with a tensiometer in 12 cadaver knees. The modes of fixation failure between interference screw fixation and post fixation were studied with an Instron (Canton, MA) machine in 8 cadaver knees.


RESULTS
The lowest PCL tension in normal knees was noted at 20 degrees to 30 degrees of knee flexion and the highest at 90 degrees. The optimal tension of PCL graft, which allows full range of knee motion, was 15 lb (68 N). The average load of graft failure was 417 (179-730) N with interference screw fixation and 367 (149-701) N with post fixation when the patellar bone-tendon-bone graft was tested. There was no statistical difference in the failure load between interference screw fixation and post fixation (P =.753); however, the modes of failure differ. The sites of failure for interference screw fixation were 25% caused by rupture of ligament substance and 75% bone plug pullout; those of post fixation were 25% caused by rupture of ligament substance, 37.5% caused by fracture, and 37.5% as a result of suture breakage.


CONCLUSIONS
The results of this study suggested that a 15-lb tension to the graft at 20 degrees to 30 degrees of knee flexion is optimal in PCL reconstruction. There was no statistical difference in the failure load between interference fixation and post fixation despite different modes of fixation failure.
Wang
Ching-Jen
CJ
Department of Orthopedic Surgery, Chang Gung Memorial Hospital, Yi-Su University, Kaohsiung, Taiwan. w281211@adm.cgmh.org.tw
Chen
Hsiang-Ho
HH
Chen
Han-Shiang
HS
Huang
Ting-Wen
TW
D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D006085:Graft Survival; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D016119:Posterior Cruciate Ligament / Q000293:injuries / Q000503:physiopathology / Q000637:transplantation*; D011187:Posture; D016059:Range of Motion, Articular