Mechanical advantage of preserving the hamstring tibial insertion for anterior cruciate ligament reconstruction - A cadaver study.

INTRODUCTION

The best fixation method for an anterior cruciate ligament (ACL) graft is debated. The tibial fixation of tendon grafts is the principal weak point for mechanical and anatomical reasons. Preserving the tibial insertion for hamstring grafts during ACL reconstruction make provide a mechanical benefit. The aim of this study was to compare the strength at the tibial tunnel of a hamstring graft with intact tibial insertion without a screw, to that of a graft with intact tibial insertion and screw fixation, and to that of a free graft with screw fixation. We hypothesized that preserving the graft's tibial insertion increases the maximum resistance of the tibial fixation relative to a free graft.

MATERIALS AND METHODS

Five pairs of knees (10 specimens) from frozen human donors were used. The tendons of the semitendinosus and gracilis were prepared as a four-strand graft while preserving their tibial insertion. The graft was passed through the tibial tunnel using standard instrumentation and the usual landmarks. Three conditions were tested: group 1 - graft with intact tibial insertion without interference screw; group 2 - graft with intact tibial insertion and interference screw; group 3 - knees from group 1 in which the tendons were detached (free graft) after the first test and fixed with an interference screw in the tibial tunnel. The screw diameter was chosen based on the graft diameter. The specimens were tested in traction using a materials testing system (Instron 8500 PLUS) in the axis of the tunnel. The main outcome measure was the maximum load at failure (N). The secondary outcome measure was the stiffness. The groups were compared using the Friedman test and the Nemenyi post-hoc test with a 5% threshold.

RESULTS

The load at failure was 33% higher in group 1 than group 3 (89.2N vs. 67.2N, p>0.05). The load at failure of group 2 was 25% higher than group 1 (111.2N vs. 89.2N, p>0.05) and 65% higher than group 3 (111.2N vs. 67.2N p=0.005). There were no differences in stiffness between groups 1 and 2 (p=1).

DISCUSSION

Our hypothesis was confirmed-preserving the tibial insertion of hamstring tendons intended for ACL reconstruction increases the maximum load to failure at the tibial tunnel. Under these experimental conditions it seems that adding a screw increases the pullout strength of the graft by +25% in absolute terms; however this difference was not statistically significant.

LEVEL OF EVIDENCE

III, controlled laboratory study.