Graft Tension During Active Knee Extension Exercise in Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction

Purpose

The purpose of this study was to measure graft tension in vivo in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction during active knee extension, as well as to investigate the effect of loading a weight around the ankle on graft tension.

Methods

Seven patients with chronic ACL injury underwent anatomic double-bundle ACL reconstruction. Two grafts were temporarily fixed to the 2 tension-adjustable force gauges on the anterior tibial cortex, after they were fixed on the femur. After the creep within the femur–ACL graft–tibia construct was removed, 10 N of the initial tension was applied to each graft at 20°. First, tension to the anteromedial (AM) and posterolateral (PL) grafts was continuously measured during passive extension from 90° to 0° with the patient under general anesthesia. Then, after the patient was awoken from anesthesia, graft tension was again recorded while the knee was actively extended by the patient in the same manner. Finally, after a 2-kg weight was placed around the ankle, the tension of each graft was measured again during active knee extension by the patient himself or herself.

Results

During passive extension motion, the tension of the AM graft was 19.3 ± 4.7 N, whereas that of the PL graft was 24.5 ± 5.9 N at 0°. The tension of each graft increased when approaching full extension. During active knee extension motion, the tension of the AM graft was 24.0 ± 6.1 N, whereas that of the PL graft was 30.8 ± 7.3 N at 0°. When the 2-kg weight was placed around the ankle during active motion, the tension was significantly higher than that with no weight at all flexion angles.

Conclusions

Graft tension was greater during active motion than that during passive motion, and graft tension during active motion increased with a weight placed around the ankle. The highest graft tension was 62.8 N at 0° of flexion with a 2-kg weight placed around the ankle, when 20 N of initial tension was applied at 20° of flexion in anatomic double-bundle ACL reconstruction. Thus care must be taken during active extension exercise with weights, especially in the first few weeks after ACL reconstruction, because graft tension increases with an increase in initial tension and easily reaches a critical level.

Clinical Relevance

Our findings suggest that active knee extension exercise should be performed in moderation in the early phase after ACL reconstruction.