The Effects of ACL Deficiency on the Meniscus and Articular Cartilage

OBJECTIVES: Through altered tibiofemoral kinematics, isolated tears of the anterior cruciate ligament (ACL) likely affect the meniscus and its ability to distribute joint forces. Changes in meniscal movement and deformation may result in altered cartilage contact location and volume, possibly leading to osteoarthritis. Little is known regarding the effects of acute ACL injury on meniscal translation and deformation as well as cartilage contact location and deformation. Using a newly developed, minimally invasive methodology, we investigated meniscal behavior and cartilage contact during dynamic knee flexion in ACL-intact and ACL-deficient states. We hypothesized that after ACL-transection, both the menisci and cartilage will show greater deformation and the menisci will translate more posteriorly. METHODS: Five human cadaveric knees were tested with six 1.0 mm steel beads injected in both the medial and lateral meniscus and three into the femur and tibia. 3D bone models were created using CT scans and articular cartilage was mapped on MRIs to create rigid cartilage models. Dynamic stereo x-ray (DSX) images were obtained during dynamic knee flexion from 10-40 degrees with a 50 lb load before and after ACL transection (Figure 1). Meniscal deformation and movement were measured by change in arc length along the implanted bead locations and translation of the center of the created ellipse (Figure 1). Cartilage models were co-registered with DSX data to evaluate cartilage deformation, measured by depth of penetration and location of contact. ACL intact and ACL transected states were compared. RESULTS: After ACL transection, the total arc length of the lateral meniscus decreased 2.7 mm in the mid portion and posterior horn while the change in arc length of the medial meniscus was minimal. The medial and lateral meniscus translated 0.9 mm (sd= 1.0 mm) and 1.6 mm (sd= 0.7 mm) more posteriorly. The cartilage penetration change was minimal in the medial and increased by 0.3 mm in the lateral compartment. Cartilage contact location moved posteriorly 1.7 mm and 2.7 mm in the medial and lateral meniscus, respectively (Figure 1). CONCLUSION: Following ACL-transection, both menisci and cartilage contact location translate more posteriorly, lateral compartment more than medial. Cartilage deformation increased in the lateral compartment as well. Circumferential meniscal deformation decreased in the lateral compartment along the mid portion and posterior horn. The authors hypothesize this may be due to meniscal complexity that is not completely understood. The posterior horn may be subjected to compressive forces or altered knee kinematics that have yet to be correlated. This model illustrates that dynamic evaluation of changes in the meniscus and cartilage is feasible and that ACL injury may lead to altered wear patterns. Further testing with higher knee flexion angles, higher loads, and other injury patterns will be performed. The authors thank and acknowledge the AOSSM for the Young Investigator Grant for the financial support of this study.