Understanding knee joint biomechanics is crucial, but studying Anterior cruciate ligament (ACL) biomechanics in human adolescents is challenging due to limited availability cadaveric specimens. This study aims to validate the adolescent porcine stifle joint as a model for ACL studies by examining the ACL's behavior under axial and torsion loads and assessing its deformation rate, stiffness, and load-to-failure. Human knee load during high-intensity sports can reach 5-6 times body weight. Based on these benchmarks, the study applied a force equivalent to 5-times body weight of juvenile porcine samples (90 pounds), estimating a force of 520N. Experiments involved 30 fresh porcine stifle joints (Yorkshire breed, Avg 90 lbs, 2-4 months old) stored at -22°C, then thawed and prepared. Joints were divided into three groups: control (load-to-failure test), axially loaded, and 30-degree torsion loaded. Using a servo-hydraulic material testing machine, the tibia's longitudinal axis was aligned with the load sensor, and specimens underwent unidirectional tensile loading at 1 mm/sec until rupture. Data on load and displacement were captured at 100 Hz.Introduction
Methods
Postoperative knee stability is critical in determining the success after reconstruction; however, only posterior and anterior stability is assessed. Therefore, this study investigates medial and lateral rotational knee laxity changes after partial and complete PCL tear and after PCL allograft reconstruction. The extending Lachman test assessed knee instability in six fresh-frozen human cadaveric knees. Tibia rotation was measured for the native knee, after partial PCLT (pPCLT), after full PCLT (fPCLT), and then after PCLR tensioned at 30° and 90°. In addition, tests were performed for the medial and lateral sides. The tibia was pulled with 130N using a digital force gauge. A compression load of 50N was applied to the joint on the universal testing machine (MTS Systems) to induce contact. Three-dimensional tibial rotation was measured using a motion capture system (Optotrak). On average, the tibia rotation increased by 33%-42% after partial PCL tear, and by 62%-75% after full PCL tear when compared to the intact case. After PCL reconstruction, the medial tibia rotation decreased by 33% and 37% compared to the fPCL tear in the case that the allograft was tensioned at 30° and 90° of flexion, respectively. Similarly, lateral tibial rotation decreased by 15% and 2% for allograft tensioned at 30° and 90° of flexion respectively, compared to the full tear. Rotational decreases were statistically significant (p<0.005) at the lateral pulling after tensioning the allograft at 90°. PCLR with the graft tensioned at 30° and 90° both reduced medial knee laxity after PCLT. These results suggest that while both tensioning angles restored medial knee stability, tensioning the Achilles graft at 30° of knee flexion was more effective in restoring lateral knee stability throughout the range of motion from full extension to 90° flexion, offering a closer biomechanical resemblance to native knee function.
