Tibial insertions of the anteromedial and posterolateral bundles of the anterior cruciate ligament: morphometry, arthroscopic landmarks, and orientation model for bone tunnel placement.

Purpose: For arthroscopic double-bundle (DB) anterior cruciate ligament (ACL) reconstruction, the size of the available area for tibial bone tunnel placement is crucial. Therefore, tibial insertions of the anteromedial (AM) and posterolateral (PL) bundles in the area intercondylaris anterior (AIA) of the tibia were quantified, landmarks were characterized, and an arthroscopic orientation model was developed.
Methods: The tibial insertions of the AM and PL bundles were dissected in 50 human cadaver knees. The footprints were documented on digital photographs and measured using a digital image analysis system.
Results: The average tibial ACL insertion area was 114 mm2 and varied considerably in size from 67 to 259 mm2. It was significantly smaller in female knees (P = .04) compared to male knees. The insertion area of the AM bundle was an average of 67 mm2 and that of the PL was 52 mm2. The centers of both bundles were an average of 5 mm apart near the middle of the ACL insertion. Important landmarks for arthroscopic DB bone tunnel placement were the ACL stump, respectively, its anterior and posterior borders; the rims of the articular surfaces of the medial and lateral tibial condyles, which border the AIA; and the posterior horn of the lateral meniscus. The new "tibial square model" indicates a minimum anteroposterior length of 14 to 15 mm for separate AM and PL bone tunnel placement.
Conclusions: The prospective area for tibial bone tunnels varied from spacious to very small among the specimens, and the insertions and centers of the AM and PL bundles cannot be exactly anatomically reconstructed. For DB ACL reconstruction, an intraoperative hypothetical situation of 6 mm for the AM tunnel and 5 mm for the PL tunnel may be reasonable when considering an average length of the tibial ACL insertion area of 14 mm in women and 15 mm in men. Individual anatomic variations make it difficult to have general guidelines, but tibial landmarks and the "tibial square model" may assist in individualized bone tunnel placement.
Clinical Relevance: Anatomic description of morphology of tibial AM and PL insertions, landmarks, and orientation models for reproducible arthroscopic DB bone tunnel placement.