It is still difficult to determine an appropriate hinge position to prevent fracture in the lateral cortex of tibia in the process of making an open wedge during biplane open wedge high tibial osteotomy. The objective of this study was to present a biomechanical basis for determining the hinge position as varus deformity.

T Three-dimensional lower extremity models were constructed using Mimics. The tibial wedge started at 40 mm distal to the medial tibial plateau, and osteotomy for three hinge positions was performed toward the head of the fibula, 5 mm proximal from the head of the fibula, and 5 mm distal from the head of the fibula. The three tibial models were made with varus deformity of 5, 10, 15 degrees with heterogeneous material properties. These properties were set to heterogeneous material properties which converted from Hounsfield's unit to Young's modulus by applying empirical equation in existing studies. For a loading condition, displacement at the posterior cut plane was applied referring to Hernigou's table considering varus deformity angle. All computational analyses were performed to calculate von-mises stresses on the tibial wedges.

The maximum stress increased to an average of 213±9% when the varus angle was 10 degrees compared to 5 degrees and increased to an average of 154±8.9% when the varus angle was 15 degrees compared to 10 degrees. In addition, the maximum stress of the distal position was 19 times higher than that of the mid position and 5 times higher than that of the proximal position on average.

The objective of this study was to analyze the biomechanical effect of an implanted ACL graft by determining the tunnel position according to the aspect ratio (ASR) of the distal femur during flexion-extension motion.

To analyze biomechanical characteristics according to the ASR of the knee joint, only male samples were selected to exclude the effects of gender and 89 samples were selected for measurement. The mean age was 50.73 years, and the mean height was 165.22 cm. We analyzed tunnel length, graft bending angle, and stress of the graft according to tunnel entry position and aspect ratio (ratio of antero-posterior depth to medio-lateral width) of the articular surface for the distal femur during single-bundle outside-in anterior cruciate ligament reconstruction surgery. We performed multi-flexible-body dynamic analyses with wherein four ASR (98, 105, 111, and 117%) knee models.

The various ASRs were associated with approximately 1-mm changes in tunnel length. The graft bending angle increased when the entry point was far from the lateral epicondyle and was larger when the ASR was smaller. The graft was at maximum stress, 117% ASR, when the tunnel entry point was near the lateral epicondyle. The maximum stress value at a 5-mm distance from the lateral epicondyle was 3.5 times higher than the 15-mm entry position and, the cases set to 111% and 105% ASR, showed 1.9 times higher stress values when at a 5-mm distance compared with a 15-mm distance. In the case set at 98% ASR, the low-stress value showed a without-distance difference from the lateral epicondyle.

Our results suggest that there is no relationship between the ASR and femoral tunnel length, A smaller ASR causes a higher graft bending angle, and a larger ASR causes greater stress in the graft.