# Feasibility of Osseous Landmarks for ACL Reconstruction--A Macroscopic Anatomical Study
## 4 Discussion
The results of 80.6% for the LIR and especially 13.9% for the LBR in this study are therefore more in line with the data of [PERSON] et al. [24] and [PERSON] et al. [34] than with the other previous studies (see Table 2). This study is also the first one to put the quantitative data of the ridges' frequency in the context of different experience levels in applied knee anatomy. As the LIR is present in over 80% of the cases, this ridge is the perfect tool to point out a possible difference between the three experience levels investigated in this study. The results show that there was a significant difference in correct identifications of the LIR between the medical student and the anatomist and the orthopedic surgeon (\(p<0.01\)). The medical student, despite having sufficient anatomical knowledge, has a lack of experience concerning the detailed anatomy of the intercondylar notch and knee joint arthroscopy. This made it more difficult for them to find the LIR on the pictures. The anatomist and orthopedic surgeon both had an equal number of correct markings, suggesting that the identification of the LIR and therefore its feasibility as a landmark in arthroscopic reconstruction of the ACL requires profound anatomical knowledge of the intercondylar notch, but does not depend on experience in arthroscopic knee surgery. This is especially important, as the LIR is used to identify the anterior border of the femoral ossees insertion of the ACL. In reconstruction, the femoral tunnel has to be positioned posterior to this landmark to result in adequate postoperative joint biomechanics [35; 36; 37; 38; 39; 40; 41; 42; 43; 44]. If it were positioned anterior of the LIR, and thus in a non-anatomical location, the result would be a biomechanically unstable knee [45]. As this incorrect positioning of the femoral tunnel most frequently happens in unexpected surgeons, it was also called the \"resident's ridge\" by [PERSON]. [5; 6; 7; 46]. This terminology also exactly reflects the results presented in this study: profound anatomical knowledge of the intercondylar notch is important for correct tunnel placement. The results of the markings of the LBR presented another interesting finding. Here, the overall frequency reported in newer studies [24] is lower than the LIR (less than 25%). Additionally, the low number of correct markings of the LBR made a statistical comparison between the three investigators impossible. However, the prevalence of incorrect LBR markings differed significantly between the orthopedic surgeon and the medical student and the anatomist. The orthopedic surgeon incorrectly marked the LBR in 58.3% of all cases. The subject with the greatest expertise had the highest prevalence of incorrect LBR markings. This result shows that a high experience level in combination with the knowledge of the high detectability of the LBR in previous studies could cause a subject to detect the LBR more often. This could perhaps also be the reason for the high number of LBR findings in previous studies [5; 13; 16; 26]. The kappa-coefficients of the intra-rater reliability tests among the three subjects indicate a good repeatability of finding the LIR and LBR. Here, the experience level had an important influence on the intra-rater reliability. The most experienced subject, the orthopedic surgeon, was the one with the highest kappa-coefficient (\(\kappa=0.917\)). Here, the high number of arthroscopic procedures performed by the orthopedic surgeon clearly had an impact on the high repeatability. Improving the surgical performance of residents and increasing their skills through options like training in a laboratory setting with anatomical specimens have to be considered [47]  
This study is one of the very few evaluating the identification of the osseous ridges in different subjects and focuses on different experience levels, which therefore defines the main strength of the study. [PERSON] et al.