Interference screw fixation of soft tissue grafts in anterior cruciate ligament reconstruction: part 2: effect of preconditioning on graft tension during and after screw insertion.

Abstract

Preconditioning of tendon grafts is believed to eliminate natural viscoelasticity of the tendons and prevent knee laxity after anterior cruciate ligament (ACL) reconstruction. Preconditioned ACL grafts maintain their initially set tension. Randomized experimental study. Forty-two human anterior tibialis (AT) tendon grafts were subjected to either no preconditioning (group 1), cyclic preconditioning (group 2), or isometric preconditioning (group 3). The residual graft tension was then recorded immediately after the application of an initial graft tension of 80 N and fixation into tibia with an interference screw, as well as 10 minutes later. In another experiment, the residual graft tension was recorded 1, 10, and 60 minutes after 10 AT and quadrupled hamstring tendon (HT) grafts alone (no fixation) had been subjected to isometric preconditioning (80 N). Immediately after screw insertion, the residual (AT) graft tensions were 79 +/- 19 N, 100 +/- 17 N, and 102 +/- 15 N in groups 1 through 3, respectively. Ten minutes later, the corresponding values were 49 +/- 16 N, 60 +/- 11 N, and 64 +/- 12 N. For the AT and HT grafts alone, the residual graft tensions were 67 +/- 2 N and 67 +/- 2 N, 45 +/- 2 N and 46 +/- 4 N, and 29 +/- 3 N and 34 +/- 5 N at 1, 10, and 60 minutes, respectively. A steady decrease (-60% within 60 minutes after initial tensioning) occurs in the initially set tension of the soft tissue ACL grafts. Clinically applicable preconditioning protocols cannot eliminate the intrinsic viscoelasticity from ACL soft tissue grafts, and thus, the reasonableness of preconditioning per se is questioned in ACL reconstruction.