Tibiale Fixation des Patellarsehnentransplantates (BPTB) zum Ersatz des vorderen Kreuzbandes in der Cross-Pin Technik mit biointegrablen CB-Pins - Eine biomechanische in-vitro-Studie an porcinen Testpräparaten-

Introduction: A variety of fixation techniques is available for the BPTB graft when performing ACL-reconstruction. The cross-Pin fixation of the BPTB graft using biointegrable CB pins derived from bovine compact bone provides to be an alternative technique besides the “gold standard” discribed fixation-technique with interference bioscrews. Materials:As test model porcine knee specimens were used. There were different biomechanical settings defined to evaluate each element of the tibial reconstruction. The CB pins provided by Tutogen after the Tutoplastverfahren® out of bovine tibia diaphysis were manufactured by 50 mm length in the diameters of 3, 4 and 5 mm. Biomechanical testings with the tibial Cross-pin fixations took place with a 10 mm broad BPTB transplant. Divided in three groups (n=15), tibiale anchorages with the BPTB transplant were accomplished in the Cross-pin technology, and tested up to the failure under rising tensile load parallel to the tunnel longitudinal axis in a universal test machine: Group of A) TC-fixation with two CB3-Pins in the distance of 8 mm to each other, which run centrically by the 25 mm long transplant bone block, group of B) FC-fixation with a CB4-Pin, which was applied directly before the bone block and through the patellartendon, group of C) FC fixation with a CB5-Pin brought in in the same way. At further five test specimens per group a cyclic submaximale load from 50 to 360 N with a number of 1000 cycles was accomplished additionally with a frequency of 1 Hz. Results: The isolated porcine BPTB transplants exhibited a middle maximum tensile strength of 1316 ± 108.1 N and a rigidity of 176 ± 68.4 N/mm. With 60 % of the tested transplants a rupture at the tibiale boneblock insertion was observed, which represented therefore the biomechanically weakest portion of the porcine BPTB transplant. The tensile strength of the patellar ligament lies on the average over the middle breaking strength of the bovinen CB pins. The CB3-Pins achieved a middle breaking strength of 392 ± 119.6 N, the CB4-Pins of 664 ± 99.6 N and the CB5-Pins of 995 ± 189,4N. The CB pins obtained a higher breaking strength and rigidity with a symmetrical distribution of 50:50, compared with a distribution from 30:70 to both sides of the transplant tunnel. Therefore the CB pins must lie, for use as fixation element in the Cross-pin technology, evenly both sides the transplant tunnel over a sufficiently long distance in the spongiosa, in order to achieve as high anchorage firmness as possible. The middle maximum failure load of the three tibial anchorages of the BPTB transplants under rising tensile load amounted to in the group of A) 745 ± 158 N, in the group of B) 736 ± 63 N and in C) 906.5 ± 136 N. All examined specimens of the three groups endured likewise the cyclic submaximun tensile load attempts. The displacement of the transplant bone blocks in the tibial transplant tunnel under the cyclic tensile load was at the 1000. load cycle in the median in the group of A) with 1.3 mm ± 0.1 mm, in group of B) with 1.2 mm ± 0.9 mm and in group of C) with 1.2 mm ± 0.8 mm. The middle maximum failure load after the dynamic testings in the three groups was not significantly smaller than in the groups of tests under the unique maximum load. Discussion: In the comparison of the own with the published biomechanical measured values it showed up that the Cross-pin fixation in the Transcross technology with two CB3-Pins and in the Front Cross technology with a CB4-Pin the same anchorage firmness for the BPTB transplant as the bioabsorbable interference screw fixation. With the FC fixation using a CB5-Pins substantially higher anchorage strength was obtained. The fixation of the BPTB transplant with CB pins in the TC- and FC-technique represents a fixation which can be accomplished joint near, which under unique maximum failure loads, as well as cyclic submaximum loads is stable in the examined porcine test model. Further studies under inclusion of groups of comparisons must clarify whether the determined stability values have their validity also with human specimens.