## 3 Remnant Preservation  
The preservation of an ACL remnants was probably the most extensively investigated method of ACL reconstruction enhancement over the last decades (Figure 1). The evidence regarding outcomes of remnant-preserving procedures is summarized in Table 1.  
The potential benefits of remnant retaining include increased stability, preservation of the proprioception, enhanced ligamentization and revascularization and prevention of the tunnel enlargement [2]. These factors laid the foundation for the rapid development of this trend in ACL reconstruction [2]. Nonetheless, certain drawbacks were also expected, including more demanding surgical techniques, range of motion (ROM) deficits or greater incidence of cyclops lesions [2]. Indeed, with growing evidence from clinical trials, these assumptions are being verified. To our knowledge, four meta-analyses have been published regarding the benefits of ACL remnant preservation in recent years [4; 5; 6; 7]. All of them have highlighted the significantly higher Lysholm score in the remnant-preserved reconstruction groups. On the contrary, the International Knee Documentation Committee (IKDC) score failed to prove any significant difference between the remnant-preserving and remnant-sacrificing group. Regarding postoperative knee stability, neither the Lachman test nor Pivot shift test has shown significant differences between these groups in all of the studies. On the other hand, the results of the side-to-side analysis performed with KT-1000/2000 were equivocal; the results of [PERSON] et al. [4], [PERSON] et al. [6] and [PERSON] et al. [7] favored the remnant-preservation group, while the results of [PERSON] et al. [5] demonstrated no significant difference between both groups. Although the loss of ROM and the incidence of cyclops lesions were speculated to be more prevalent in the remnant-preserving reconstruction, the above-mentioned analyses proved that occurrence of these complications does not differ significantly between remnant-preserving and remnant-sacrificing procedures [4; 5; 6; 7]. Although remnant-preserving procedures were designed to enhance the proprioception of the reconstructed ACL, the evidence supporting this property is still lacking. Of two studies that examined proprioception with reproduction of passive positioning (RPP) [8; 9], only one proved that the remnant-preservation group outperformed the remnant-sacrificing group. On the other hand, [PERSON] et al. [10] proved significantly better outcomes in the remnant-preserved group in RPP, threshold to detection of passive motion and single-legged hop tests. However, it is difficult to generalize these results to all remnant-preserving reconstructions as [PERSON] at al. used remnant-preserving ACL reconstruction combined with preservation of the tibial attachment of a hamstring autograft. The influence of remnant preservation on graft revascularization was assessed by magnetic resonance imaging (MRI) by means of signal/noise quotient (SNQ). [PERSON] et al. found the remnant-preserving group to have higher SNQ than the remnant-sacrificing group at 2 months of follow-up and lower SNQ at 6 months of follow-up [11]. Similarly, [PERSON] et al. found the remnant-preserving group to have higher SNQ than the remnant-sacrificing group at 2-4 months of follow-up and lower SNQ at 12-18 months of follow-up [12]. Both authors concluded that revascularization of a graft proceeds more rapidly in the remnant-preserving reconstructions. Additionally, in the study by [PERSON] et al., the SNQ in the remnant-preserving group was not significantly lower than in the remnant-sacrificing group at 6.3 months of follow-up [13]. Regarding the progress of ligamentization, the meta-analysis of [PERSON] et al. found superior results for remnant-preserving procedures [7]. On the other hand, the analysis of randomized controlled trials showed no significant difference, while analysis of cohort studies favored the remnant-preserving group.