Balancing Anterior and Posterior Cruciate Ligaments in Adults

The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) represent the central pivot of the knee. The balance between these two ligaments impacts the tibiofemoral biomechanics. Each structure is the opposite of the other in terms of anteroposterior translation and rotation.

The aim of this study was to find a correlation between the cross-sectional area of the ACL and PCL in adults.

Magnetic resonance imaging (MRI) data analysis was conducted by a musculoskeletal radiologist using MRI planes tailored to the study's requirements. In all 62 studied patients, measurements were done according to the protocol.

The study observed three types of intercondylar notches: Type U was identified in 35% (22) of patients, type W in 27% (17), and type A in 37% (23). The median difference between the ACL and PCL areas was found to be statistically significant (p = 0.02). A significant difference in the area of the ACL was detected between Type A and Type U notches (p = 0.02), while no significant differences were found between Type A-W and Type W-U after post hoc corrections (p > 0.05). Additionally, no significant difference was observed in the mean area of the PCL across all three notch types (p = 0.1). In 68% of the cases, the ACL is no less than 60% of the PCL in area, and no more than 120%. The size of ACL and PCL in healthy individuals also depends on other factors like synergistic and antagonistic muscle activities, occupation, and the hip-knee-ankle axis. For example, if the PCL area is 0.79 cm² and the measured structure is round (during a reconstruction a hamstring graft is round), the diameter is 10 mm. A native ACL is, in 68% of the cases, no less than 7.7 mm, and no more than 10.9 mm.

The ACL-PCL size correlation helps in understanding the balance of the central pivot of the knee.