## 4 Discussion  
The replacement of autografts with allografts from organ banks in ligament reconstruction is a hot topic in medicine [14; 15]. The demand for ACL allografts has increased in the last decade [1], and postoperative results are promising. This is visible in the increase in allograft use from 2% (between 1986 and 1996) to 14% (between 1996 and2001), and it further increased around 2007 as its number reached 20-30% in the US [16]. Orthopedic surgeons do not have to struggle with the problems of the donor site, size and the number of the grafts [17]. In the case of multiple ligament reconstruction or ACL revision operations, the surgeons cannot remove enough tendons from the patients to replace the injured ligaments. In our work, we have combined engineering and medical knowledge to check the feasibility of safe transplantation after freezing and irradiation treatment using different doses aimed for the disinfection of the ligaments, which are necessary for long term bank storage and transportation. Our method can provide better accuracy for strain measurement and fracture analysis of the ligaments, make the whole measurement more robust and give deeper insight into the behavior of and the differences between the tendon types, as it is based on digital image correlation. Four types of allografts for potential ligamentous reconstruction were evaluated in this study. The allografts were subjected to either freezing and a 21 kGy dose of gamma irradiation or freezing and a 42 kGy dose of gamma irradiation. The four main mechanical parameters were evaluated and compared: tensile modulus, which represents the elasticity of the materials, maximum load, which is the limiting factor for each ligaments strength, strain at maximum force, which shows the specific strain at the maximum load and fracture strain which is the ultimate limiting strain. These parameters give a good overview of material characteristics, which is useful for the selection of the right replacement by doctors and also for simulation and modelling purposes for engineers. In this study, the doubled tibialis anterior and peroneus longus tendons performed best in general. They were the stiffest, showing the highest tensile modulus (Table 1, Figure 5). Strain at maximum force (Table 1, Figure 4) and fracture strain (Table 1, Figure 6) were better than or equal to those of all other currently tested ACL grafts. Previous studies [18; 19] reported mixed effects of freezing. In the work of [PERSON] et al., no difference was shown in endurance properties [18]. In contrast, [PERSON] et al. reported decreased load-bearing capacity and stiffness as a result of freezing [19]. Comparing the native and frozen tendon samples, no significant difference was found in endurance properties (Figures 3-6). This could be the effect of the cryoprotectant solution. When comparing the reported results to the articles in the literature [1; 7; 8; 10; 20], the range of standard deviation is comparable to those reported by other research groups, which shows that considering the nature of biological samples, the results are reliable. It was previously well-known that high doses of gamma irradiation hurt the biomechanical parameters of tendon grafts [21; 22; 23; 24]. However, our measured values were significantly higher than those required for walking (303-355 N) [25] or aggressive early rehabilitation programs (450 N) [26]. The decrease in maximum load can be the result of gamma irradiation, which was visible in both irradiated groups. This means that the strength of the irradiated tendons decreased. This may be the reason behind the early failures of the grafts. The other evaluated TA's parameters did not change (Table 1). The results confirm the findings of our previous research [11]. The aggregate results of the present and prior studies [11; 12] show that there is a difference in irradiation sensitivity of the examined tendons, which has to be considered before application. The tendons types which were the most affected by the treatments were quadricep grafts.