2015 ISAKOS Biennial Congress ePoster #1216

The Influence of Initial Graft Tension During Insertion of the Tibial Screw on Graft Tension in ACL Reconstruction

Sebastian Kopf, MD, PhD, Brandenburg An Der Havel, Brandenburg GERMANY
Robert Collette, Berlin GERMANY
Jan Erik Ode, graduate engineer, Berlin GERMANY
Tobias M. Jung, MD, Berlin GERMANY
Clemens Gwinner, MD, Berlin GERMANY
Klaus-Dieter Schaser, Prof., Berlin GERMANY
Norbert Haas, Berlin GERMANY

Charite University Medicine Berlin, Berlin, GERMANY

FDA Status Cleared

Summary: Inserting the tibial screw can increase intra-articular graft tension forces. Maximum manual forces showed equal intra-articular graft forces compared to 80N. As there was a huge decrease in intra-articular graft tension force after releasing the extra-articularly applied graft tension forces, backup-fixations should be applied as quickly as possible.

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Abstract:

Objective

The reconstruction of the anterior cruciate ligament (ACL) is an often performed procedure in orthopedic surgery. As previously shown, the outcome depends on factors like the force which is applied on the graft during fixation [1, 2, 3]. But it is unknown in which way the intra-articular graft tension is influenced by different screw diameters and different extra-articular graft forces applied during graft fixation.
The aim of the present study was to evaluate the influence of different extra-articular forces applied on the graft during screw insertion, and of different screw sizes onto the intra-articular graft portion from the beginning of screw insertion up to the first 100 minutes.

Methods

Procine lower legs were used for this biomechanical cadaveric study. Tendons of the lateral digital extensor muscle were harvested, fourfold to receive a graft with a diameter of 7 mm. A 7mm tibial tunnel was drilled using a tibial drill guide from the anteromedial cortex into the native ACL footprint. The graft was pulled through the tunnel and fixed on a hook positioned at the approximate location of the native femoral human ACL insertion. The specific angles of the intra-articular course of human ACL were imitated. The hook was connected to a load cell. Three different screw diameters (6, 7 and 8mm) and three different extra-articularly applied forces (20N, 80N, maximal manual force [maxN]) during screw insertion were tested.
There were nine groups in total, and each group consisted of ten specimen. All used screws were bioabsorbable interference screws (MegaFix®, Karl Storz, Germany). The intra-articular tension forces were measured during screw insertion and up to 100min after releasing the extra-articularly applied tension forces. The graft force was recorded with 1Hz. Non-parametric statistical tests were used after disproving normal distribution.

Results

Inserting the tibial screw significantly increased the intra-articularly tension force of the graft for all three screw diameters at 20N, for the 6 and 8mm screws at 80N, and for the 6mm screw at maximum manual forces.
After 100min, the 20N group showed significantly the lowest intra-articular graft tension forces compared to the 80N and maxN groups. No statistical difference was calculated between the 80N and maxN group.
It was remarkable that during the first five seconds after releasing the extra-articularly applied graft tension force there was a huge decrease in intra-articular graft tension force (up to -59%).

Conclusion

Inserting the tibial screw can increase intra-articular graft tension forces. Compared to maximum manual forces, 80N of extra-articular graft tension force during inserting the tibial screw showed equal intra-articular graft forces over the first 100min. As there was a huge decrease in intra-articular graft tension force after releasing the extra-articularly applied graft tension forces over the first minutes, backup-fixations should be applied as quickly as possible.
REFERENCES
[1] Burks, R. T. et al. Arthroscopy 1988
[2] Nicholas, S. J. et al. AJSM 2004
[3] Yasuda, K. et al. AJSM 1997