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^®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° of knee flexion, and the A–P laxity was measured by applying A–P drawer load of 134 N at 20° 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.