[Femoral tunnel positioning in posterior cruciate ligament double-bundle reconstruction by computer aided design]

To study mechanical affect of knee joint of reasonable positioning of femoral tunnel during knee posterior cruciate ligament (PCL) double-bundle reconstruction and graft fixation after reconstruction by virtual reality interactive technology and evaluate the biomechanical response of knee after reconstruction by finite element analysis.

Knee specimens from five fresh frozen cadavers were used. Computer simulations and biomechanical experiments were used in this study. Experiments on flexion and extension movements of the knee joint were performed on specimens of fresh human knee joint. Laser three dimensional scanning was used to record and calculate the indexes of movements. Three-dimensional models of knee joint bone structure were then reconstructed on computer with the experimental data. Simulations of flexion and extension movements were carried out on the models to show the spatial positions of femur and tibia and label the attachment sites of PCL. Ten test points in the anterior,posterior, proximal, distal at the femoral attachment area of anterior and lateral bundle (ALB) and postoperior medial bundle (PMB) were selected and the central points of tibial en attachment areat anchored. The distance btween each two points of two article surface was calculated and contacted by software of Geomagic. Model was import software Ansys, adopting the tetrahedron unit a finite element model of complex tibial and femoral was set up to simulat human walking in one leg,on this condition the the joint surface force of model under weight impact load were analyzed.

The three-dimensional models could demonstrate the spatial positions of the bone structure of the knee in different flexions and extensions. The models could be used to measure the spatial distance between 2 points on the femoral and tibial planes by software Geomagic. There was significantly difference among the length changes of anterolateral bundle and posteromedial bundle at every fixed point with different flexion angles (P<0.05), so the fixed angle with different points. The length changes of anterior lateral bundle's A2, A1 and posterior medial bundle's B3, B1 points were (1.35±0.19) mm, (5.41±1.22) mm, (1.95±0.04) mm and (5.23±2.21) mm, respectively. The A2 and B3 points' length changes were the less, and that of the Al and B1 points were the more. It had no significant difference between the length changes of anterior lanteral bundle's A2 and A3 point (P=0.913>0.05). All of the maximal length changes of anterior lateral bundle's A2, A3 and postterior medial bundle's B3 points were less than 2 mm.

The models of knee joint were builded through computer technology and it can be measure the lenth of cruciate ligament with software Geomagic exactly. The femoral tunnel for the PCL double-bundle reconstruction should be located as follows: ALB at the middle point of upper edge of femoral attachment site (proximal point),while PMB at the middle point of femoral attachment site (proximal point). This model provides a satisfactory method for the evaluation of the biomechanical response of knee after cruciate ligament reconstruction.