# Feasibility of Osseous Landmarks for ACL Reconstruction--A Macroscopic Anatomical Study
## 4 Discussion  
This study clearly shows the feasibility of the use of LIR and LBR as osseous landmarks for ACL reconstruction. Additionally, it points out the strong correlation of correctly identifying these landmarks with the level of experience of the investigators, verifying the primary hypothesis of this study. With a prevalence of 13.9% in the dual control group and low percentages (<10%) of correct LBR markings among the three subjects, the LBR cannot be used as a reliable landmark during knee joint arthroscopy. Meanwhile, the LIR, with a prevalence of 80.6% in the dual control group and high percentages (>70%) for the anatomist and the orthopedic surgeon, can be used as a reliable landmark for the arthroscopic reconstruction of the ACL. Additionally, with the false positive rate of 58.3% for the experienced orthopedic surgeon, this study points out the problem of an expectancy of the LBR based on its reported high frequency in the literature (see Table 2). Furthermore, based on the results of this study, the authors propose a guideline for correctly identifying the LIR and LBR if present: in a 90\({}^{\circ}\) flexed knee, with a 30\({}^{\circ}\)-arthroscopic view of the medial wall of the lateral femoral cond \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**LIR (\%)**} & \multicolumn{3}{c}{**LBR (\%)**} \\ \cline{2-7}  & **Correct** & **Unmarked** & **Incorrect** & **Correct** & **Unmarked** & **Incorrect** \\ \hline Medical student & 19.4 * & 47.2 * & 33.4 & 0 & 83.3 & 16.7 \\ Anatomist & 72.2 & 13.9 & 13.9 & 5.6 & 75 & 19.4 \\ Orthopedic surgeon & 77.8 & 2.8 & 19.4 & 8.4 & 33.3 & 58.3 * \\ \hline \hline \end{tabular} \({}^{*}p\) < 0.017.  
\end{table} 
Table 1: Interpretation of the three subjects’ results. The 36 photo-series are divided into 3 groups: the frequency of correctly and incorrectly marked pictures, as well as the frequency of unmarked pictures, concerning the LIR and the LBR. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **n** & **LIR (\%)** & **LBR (\%)** & **Material** \\ \hline [PERSON] et al. [5] & 7 & - & 85.7 & Fetus \\  & 60 & 100.0 & 81.7 & Arthroscopic \\  & 16 & 100.0 & 81.6 & Anatomical specimens \\ [PERSON] et al. [13] & 50 & 88.0 & 48.0 & Arthroscopic \\ [PERSON] et al. [16] & 26 & 100.0 & 92.3 & Anatomical specimens \\ [PERSON] et al. [24] & 166 & 97.6 & 24.7 & Bones \\  & 69 & 85.3 & 13.2 & Anatomical specimens \\ [PERSON] et al. [32] & 318 & 94.0 & - & Bones \\ [PERSON] et al. [33] & 7 & 57.0 & 29.0 & Anatomical specimens \\ [PERSON] et al. [25] & 89 & 87.5\% & - & Patients \\ This study & 36 & 80.6 & 13.8 & Anatomical specimens \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of the existence of LIR and LBR reported in the literature. horizon of the camera is approximately 45\({}^{\circ}\) (45.12 \(\pm\) 11.03\({}^{\circ}\)) and that of the LBR is 90\({}^{\circ}\) (94.0 \(\pm\) 8.49) (Figure 4). [PERSON] et al. [5] described the LBR for the first time. They demonstrated a high prevalence (>80%) of the LBR in their findings, so they suggested that it can be used as a reliable landmark during arthroscopy. The LIR was found in nearly 100% of all specimens. In a macroscopic anatomical study by [PERSON] et al. [16], the LIR was detected in all specimens. The LBR could be found in 80% of all specimens. [PERSON] et al. [24] investigated a large number of cases in their study. The overall prevalence of the LIR was 94%, whereas the prevalence of the LBR was just 21.4%. Additionally, [PERSON] et al. [34] showed in their study some different values. They were the first to use Micro-CT scanning and surface extraction to objectively evaluate the existence of the LIR and the LBR in the femoral footprint of the ACL. Although they had a very low sample size (n = 7), they showed in the quantitative analysis a frequency of 57% of the LIR and 29% of the LBR. In the qualitative analysis, the respective frequency was 86% and 14%. Additionally, [PERSON] et al. [25] reported a frequency of the LIR in their computed tomography study of 87.5%.