A patient-specific finite element analysis of the anterior cruciate ligament under different flexion angles

Stress and strain changes of the anterior cruciate ligament at different knee flexion angles: A three-dimensional finite element study

OBJECTIVE

This study aimed to analyze the stress and strain changes of the anterior cruciate ligament (ACL) at different knee flexion angles using a three-dimensional finite element model.

METHODS

Computed tomography and magnetic resonance imaging scans were performed on the right knee of 30 healthy adult volunteers. The imaging data were used to construct a three-dimensional finite element model of the knee joint. The magnitude and concentration area of stress and strain of ACL at knee flexion angles 0°, 30°, 60° and 90° were assessed.

RESULTS

The magnitude of stress remained consistent at 0-30° (P > 0.999) and decreased at 30-90° (P < 0.001, P = 0.005, respectively), while the magnitude of strain increased between 0° and 30° (P = 0.004) and decreased between 30° and 90° (P < 0.001, P = 0.004, respectively). The stress concentration area remained consistent at the proximal end, midsubstance, and distal end between 0° and 60° (P > 0.05). The concentration area of strain increased at the proximal end, decreased at the midsubstance between 0° and 30°, and remained consistent between 30° and 90° (P < 0.001).

CONCLUSION

At the low knee flexion angle, ACL's magnitude of stress and strain reached the peak, and the concentration area of ACL strain gradually shifted from midsubstance to the proximal end.

A comparison of stress, contact pressure, and contact area on menisci in re-injury mechanisms after reconstruction of the anterior cruciate ligament with autograft and synthetic graft: a finite element study

PURPOSE

The anterior cruciate ligament (ACL) is crucial in maintaining knee stability. Some motion mechanisms, which are common in sports, cause excessive load to be passed on the ACL. In non-contact ACL injuries, the ACL cannot sustain the high stress and becomes injured or ruptures in the valgus-external rotation mechanism (VERM) and varus-internal rotation mechanism (VIRM). The mechanical strength of the grafts used to repair the torn ligament varies. The purpose of this study is to look at the alterations in the menisci after anterior cruciate ligament repair with autografts and synthetic grafts in cases of non-contact re-injury mechanisms.

METHODS

In the finite element analysis, VERM and VIRM motions of the injury were simulated with different ACL graft materials. During the simulations of these mechanism motions with polyethylene terephthalate (PET) and patellar tendon (PT), the contact pressures, contact areas, and von mises stress values created in the medial and lateral meniscus were compared.

RESULTS

The peak contact pressures on the menisci during the VERM are higher than the peak contact pressures during the VIRM, except for one variation. The peak contact pressure of the medial meniscus is almost the same for both graft materials and mechanisms. Furthermore, the peak contact pressures in the menisci are higher than in the VERM. For all injury mechanisms, the peak contact stresses on the lateral meniscus are higher than on the medial meniscus.

CONCLUSIONS

The findings suggest that VERM can induce further knee joint injury. It was found that the PET will lessen the pressure on the menisci even more. It is also advantageous since it does not damage the anterior extremities and transmits less pressure to the menisci. In conclusion, using a high-strength ACL is healthier for the menisci. Even though synthetic grafts are not clinically preferred, the study demonstrates that enhancing the material properties of synthetic grafts will increase the chance of their use in the future, based on the current results.