Anatomic, radiographic, biomechanical, and kinematic evaluation of the anterior cruciate ligament and its two functional bundles.

Outcomes following single-bundle anterior cruciate ligament reconstruction are generally good. However, a critical review of the literature shows that some patients have residual instability and pain following single-bundle anterior cruciate ligament reconstruction1-4. Recent clinical investigations have demonstrated that anteroposterior knee laxity, as measured with the KT-1000 and the Lachman test, is not associated with functional outcomes after anterior cruciate ligament reconstruction5. Conversely, there is a significant association between the pivot-shift test and functional outcomes after anterior cruciate ligament reconstruction (p = 0.03), which emphasizes the importance of rotational knee stability for functional recovery5. Biomechanical and kinematic studies have suggested that a more anatomical reconstruction of the anterior cruciate ligament may provide improved long-term outcomes. In this article, we describe the anatomy, radiographic characteristics, injury patterns, biomechanics, and kinematics of the anterior cruciate ligament. We also summarize the surgical technique and augmentation procedures used in an anatomic two-bundle approach to anterior cruciate ligament reconstruction. Fig. 1 The fetal knee demonstrates the two bundles of the anterior cruciate ligament: the anteromedial (AM) and the posterolateral (PL) bundle. LFC = lateral femoral condyle. Fetal, arthroscopic, and cadaver studies have shown that the anterior cruciate ligament consists of two functional bundles, the anteromedial bundle and the posterolateral bundle6-8 (Figs. 1, 2, and 3). The nomenclature of the two bundles corresponds to their tibial insertion sites. On the femoral side, the anteromedial bundle originates more proximally and the posterolateral bundle originates more distally. On the tibial side, the anteromedial bundle inserts anteromedially while the posterolateral bundle inserts posterolaterally. The relative position of the two bundles varies with the flexion angle of the knee. In extension, the two bundles are parallel. In flexion, the femoral insertion site of the posterolateral bundle moves anteriorly, and the …