Anatomical two-bundle versus Rosenberg's isometric bi-socket ACL reconstruction: a biomechanical comparison in laxity match pretension

It is not well known how much tension should be applied to ACL graft at the time of graft fixation. As a step to determine the optimal initial tension, it is indispensable to know the graft tension to restore normal anterior - posterior ( A - P) laxity ( laxity match pretension, LMP). The objective was to determine the LMP in ACL reconstruction for the anatomical two-bundle technique and for the Rosenberg's isometric bi-socket one, and to compare these two techniques in LMP. Twenty-four patients with unilateral chronic ACL insufficiency were divided into the following two groups. The anatomical two-bundle technique was performed on 12 patients via two femoral tunnels at 9 and 10 o'clock or 2 and 3 o'clock on the posterior margin of the notch and two tibial tunnels ( Group A), while the Rosenberg's isometric bi-socket reconstruction was performed on the remaining 12 patients through two femoral tunnels at 10 and 11 o'clock or 1 and 2 o'clock and one wider tibial tunnel ( Group B). After two doubled semitendinosus grafts were fixed with two EndoButton- CL (R) s on the femur, they were temporarily fixed to the tension-adjustable force gauge on the tibia, respectively. The total tension applied to grafts was set at 10, 20, 30, 40, or 50 N at 20 degrees of knee flexion, and the A - P laxity was measured by applying A - P drawer load of 134 N at 20 degrees of flexion. By comparing the measured laxity with that for the opposite healthy knee, the tension to restore the normal A - P laxity (LMP) was estimated. The mean LMP of 7.3 N in Group A was significantly smaller than that of 25.8 N in Group B. The anatomical two-bundle technique makes it possible to more effectively restore A - P stability with lower initial tension than the isometric Rosenberg's bi-socket reconstruction.