Comparison of 3-dimensional Obliquity and Anisometric Characteristics of Anterior Cruciate Ligament Graft Positions Using Surgical Navigation

Background: Surgical navigation allows continuous intraoperative monitoring of ACL graft anisometry and 3-dimensional obliquity. However, normative anisometry and obliquity measurements for different single-bundle anterior cruciate ligament graft positions are not well described.

Hypothesis: ACL Grafts placed in anteromedial and posterolateral bundle positions will have distinct anisometric profiles and 3-dimensional obliquities. A graft placed centrally in anterior cruciate ligament insertion sites will have different obliquity and anisometry than a conventional (single-bundle) graft extending from the tibia's posterolateral aspect to the femur's anteromedial aspect.

Study Design: Controlled laboratory study.

Methods: Five cadaveric knees were tested. A surgical navigation system was used to create 4 virtual graft positions in the anterior cruciate ligament footprint: (1) anteromedial, (2) posterolateral, (3) central, and (4) posterolateral tibia to anteromedial femur (conventional). Obliquity at various flexion angles and anisometry of each virtual graft's central fiber were determined.

Results: Anteromedial and posterolateral fibers are relatively parallel up to 30 degrees of flexion. At higher degrees of flexion, the anteromedial position is more oblique in the sagittal plane, while the posterolateral position is more oblique in the axial plane. The conventional single-bundle position is significantly more vertical than the central position in multiple planes throughout the range of motion. The anteromedial fiber is most isometric, while the posterolateral fiber is the least isometric at all flexion angles. There is no significant difference in the anisometry between the central or conventional positions at any flexion angle. The posterolateral, central, and conventional fibers were longest at full extension and slackened with progressive flexion.

Conclusion: Anteromedial and posterolateral graft positions can be distinguished by sagittal and axial plane obliquity at flexion angles >30 degrees and by anisometry measurements. Conventional positioning produces a relatively vertical graft placement compared with the central position but has similar anisometry characteristics. Our data suggest that posterolateral, central, and conventional grafts should be fixed at or near full extension to avoid excessive tightening during motion.

Clinical Relevance: This study provides anisometry and 3-dimensional obliquity data for various graft positions using surgical navigation. The failure of single-bundle anterior cruciate ligament reconstruction to restore intact knee kinematics may be partly due to the relative vertical placement of conventional grafts compared with the central anterior cruciate ligament footprint position.