In vivo length change in the posterior cruciate ligament in full and small ranges of motion

Abstract Background In vivo studies have shown that the posterior cruciate ligament (PCL) has different mechanical functions at high- and low-flexion angles. For example, native PCL fibers are under higher tension during high flexion than during low flexion. However, most studies have not focused on dividing the entire range of motion (ROM) into high- and low-flexion parts and assessed them separately. Materials and Methods Thirty-two healthy participants (10 females and 22 males) were recruited from the local community. Magnetic resonance imaging (MRI) and computed tomography (CT) were performed to obtain the change in PCL length with the knee flexion angle (0°–130° at 10° intervals). Results As the knees were flexed across the full 0°–130° ROM, the end-to-end distance of the native PCL continuously increased, with no shortening. Length changes of the most isometric points (MIPs) of 0°–60° and 70°–130° were significantly smaller than those of the anatomical centers of the posteromedial bundle (PMB)/anterolateral bundle (ALB). Conclusions The a-MIP-70-130/-0-60 avoids the pitfalls of both techniques: graft laxity (traditional isometry) and excessive strain (anatomical reconstruction). This dual benefit addresses a key limitation in PCL surgery: the graft's limited elastic modulus. Level of evidence III. Clinical relevance Understanding the biomechanical role of native PCL can help replicate its function, thereby improving surgical outcomes (particularly for double-bundle reconstruction).