Biomechanische Studie an porcinen Testpräparaten zur tibialenFrontcross Fixation des Patellarsehentransplantates (BTB) zumvorderen Kreuzbandersatz in transtendinöser und extratendinöserTechnik mit bovinen Kompaktapins (CB-Pins)

Rasche Mobilisation und frühes Muskeltraining in der Kreuzbandchirurgie führen sowohl zu einzelnen Spitzenbelastungen als auch zu zyklischen Belastungen auf das fixierte Transplantat. Die in dieser Arbeit untersuchte Crosspin-Fixation in der transtendinösen und extratendinösen Frontcross-Technik mit...

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Bibliographic Details
Main Author: Tuschen, Stefan
Contributors: Schnabel, Michael (Professor Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2011
Online Access:PDF Full Text
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Rapid mobilization and early muscle training in cruciate ligament surgery result in both individual peak loads and cyclical load on the fixed transplant. The cross-pin fixation method analyzed here, using trans-tendon and extra-tendon front-cross techniques with a cortical bone pin with 4mm (CB4) or 5 mm (CB5) diameter, is a biological fixation for BTB transplants. In a front-cross load model, it was shown in a combined shear and bend trial that after single loads and previous cyclical loads, the maximum CB pin breaking strength was 600.7 N or 735 N in the groups with a CB4 pin, and 1393.9 N or 1452.5 N in the groups with a CB5 pin above maximum load during rehabilitation. In a second preliminary trial, the influence of the dorsal drilling channel distance or the implantation depth of the pin in cancellous bone was tested for breaking strength using a porcine tibia. In both cases—the three CB4 pin groups with an average maximum breaking strength of 535.2 N to 558.7 N and the three CB5 pin groups with an average maximum breaking strength of 1222.7 N to 1332.7 N—there was no significant difference between implantation depths of 3.5 cm, 4.5 cm, and 5.5 cm in the porcine tibia heads. To determine the extent of ligament damage, in a further preliminary trial the maximum tensile strength of isolated BTB porcine transplants was compared with that of a control group after the implantation of CB4 or CB5 pins in front of the bone plug. Following the implantation of both CB4 and CB5 pins, there was no significant reduction in maximum tensile strength until failure compared to the control group. However, with an average maximum tensile strength of 978.8 N in the control group, 953.4 N in the CB4 pin group, and 880 N in the CB5 pin group, maximum tensile strength decreased with increasing pin diameter to a degree that may be critical. In the main trial, maximum retention strength or maximum load until failure and the rigidity of the entire system were determined for five variants of front-cross fixation after both single loads and cyclical load. In the trans-tendon technique of front-cross fixation, a CB pin was inserted directly in front of the bone plug and through the middle of the patellar tendon. In two extra-tendon variants, the bone plug was turned by 90 degrees in the drilling channel and one CB pin was placed parallel to the underside of the patellar tendon. In a fifth variant, the length of the bone plug was reduced to 10 mm and a CB5 pin inserted with the trans-tendon technique. In this way, a total of 10 groups were compared for the maximum load until failure and rigidity of the individual variants in at least 10 stress trials. Measurements showed average maximum loads until failure from 619 N to 962 N in all variants—significantly higher than forces in a rehabilitation phase. Previous cyclical loads, such as occur during physical therapy, did not result in a significant difference compared to maximum failure loads in single loads groups (p = 0.587). However, the groups with the 10 mm bone plug and CB5 pin had significantly lower maximum failure loads than the groups with the 20 mm bone plug and CB5 pin (p < 0.001 and p < 0.009) due to the weakening of the tendon insertion and the bone plug slipping past the CB pin. As another biomechanical parameter, the rigidity of the fixation system was studied. In contrast to groups with single loads averaging 56.1 to 71.6 N/m, rigidity improved significantly (p < 0.001) after initial cyclical load, to an average of 137.7 to 173.8 N/m. This can be attributed to a very limited slipping and settling of the system during the first cycles. It showed the importance of preconditioning the entire system during surgical care. The values are still lower than those for the rigidity of a native cruciate ligament, but fixation systems that have similarly good rigidity as shown in this study are few. The technique described here ensures stabile fixation of the BTB transplant even with low bone quality, along with the possibility of comprehensive healing and in-growth of the transplant plugs. In this trial series, front-cross fixation exhibited promising biomechanical parameters and could contribute to the optimization of transplant fixation in a number of important ways. However, transferring the results of an animal trial model to human knee joints would require critical evaluation. Therefore, further measurements are needed on donor knee joints from young individuals in comparison to fixation systems that have been proven in practice.