Can the Posterior Cruciate Ligament (Pcl) Predict Anterior Cruciate Ligament (Acl) Size For Planning During Acl Reconstruction?

BACKGROUND: Pediatric Anterior Cruciate Ligament reconstruction (ACLR) has increased over the past several years. Estimating the native ACL size on pre-op imaging would ideally inform graft size during surgery and make it possible to individualize ACL graft size to each patient. HYPOTHESIS/PURPOSE: To establish a correlation between the ACL and PCL size in normal pediatric knees, with the goal of informing appropriate graft size for ACL reconstruction. METHODS: MRIs of 540 patients ages 8-18 years were assessed. Measurements included: ACL and PCL length, thickness and width (Figure 1). ACL footprint thickness and width at the tibial insertion was also measured. Inter-rater reliability was assessed with a random set of 25 patients. Pearson correlation coefficients were used to assess the correlation between ACL and PCL measurements. Linear regression models were used to test whether the relationship between ACL and PCL measurement differed by sex or age. RESULTS: Demographic data for 540 patients are shown in Table 1. Inter-rater reliability was high for all measurements except PCL thickness at midsubstance. ACL length was most strongly correlated with PCL length (r=0.57, p<0.0001). ACL origin thickness was most strongly correlated with PCL mid-thickness (r=0.26, p<0.0001). ACL origin width was most strongly correlated with PCL insertion width (r=0.49, p<0.0001). ACL insertion thickness was most strongly correlated with PCL insertion thickness (r=0.27, p<0.0001). ACL insertion width was most strongly correlated with PCL mid-width (r=0.39, p<0.0001). Sample equations for estimating ACL size from each sex and age category are as follows: ACL Origin Thickness = 3.21 + 0.26PCL Origin Thickness (R(2)=0.07; 8-12yo males), ACL Origin Width = 1.35 + 0.15PCL Insert Width (R(2)=0.23; 8-12yo females), ACL Insert Thickness = 7.02 + 0.22PCL Mid Thickness – 0.17PCL Insert Width, (R(2)=0.10; 13-18yo males), ACL Insert Width = 2.31 – 0.09PCL Length + 0.39PCL Mid Thickness + 0.27PCL Mid Width + 0.25PCL Insert Width (R(2)=0.31; 13-18yo females). CONCLUSIONS: Correlations exist between ACL and PCL measurements with some moderated by sex and/or age. This study is the first step in potentially informing normal ACL size in pediatric patients based on an intact PCL on MRI.