I'm a current MD PhD student at the University of California, Irvine. Today I'm going to be sharing some of our work on the reliability of PTS measurements on MRI versus CT. Here are our disclosures, and we will go ahead and get started. So the posterior tibial slope, the PTS, reflects the relative tilt of the tibial plateau. Greater PTS measurements are associated with increased rates of ACL injury and graft failure. More recently, there have been investigations that delineate distinct roles of the medial and lateral tibial plateaus of the MTP and LTP on geometries in anterior-posterior and also rotary knee stability. It's hypothesized that increased LTP slope and slope differential relative to MTP slope may result in more internal tibial rotation. And thus, it's predicted that individual measurements of MTP and LTP slope may help to guide treatments of ACL injury. As many of you are well aware, the diagnostic workup of patients with ACL injury typically includes MRI but not CT, although CT is a gold standard for evaluating osseous geometry. And it's currently unknown whether or not traditional MRI can be used to accurately measure PTS at the medial and lateral plateaus and how MRI measurements might correlate to those on CT. So the purpose of this study was to compare PTS measurements medially and laterally on MRI and CT. To do this, we retrospectively queried a PACS imaging database at our institution for patients with concurrent MRI and CT imaging, which is defined as MRI and CT at the same knee within a one-year interval. Excluded knees with significant deformity, osteoarthritis, proximal tibial fracture, or artifact obscured visualization of the proximal tibial landmarks, which will make sense in a minute. And in total, we had 46 knees in 45 patients included in the study. Average patient age 37, 75% male, and a third of our patients had ACL injury on MRI. To actually measure the posterior tibial slope, which was, again, the angle between the perpendicular to the long axis of the tibia and the tangent to the tibial slope, we used the method validated by Hudak in 2009. So we drew two circles in the proximal portion of the tibia, connected the midpoints of those circles, and considered that the long axis, dropped it perpendicular to that, and measured our angle against that line. Measurements were made by two independent radars on paired MRI and CT scans. And the medial and lateral plateaus were found using a concurrent kernel imaging. Interrater and interrater reliability were assessed using interclass correlation coefficient, ICC. And intermethod agreement was assessed, again, using ICC and also Bland-Altman analysis. So we found that our measurements were very consistent with each other. Interrater reliability was moderate to high, and interrater reliability was very high. Whereas measurements were different. Between MRI and CT, we found at the medial plateau, intermethod agreement was poor. And at the lateral plateau, intermethod agreement was moderate. We also have our Bland-Altman plots here, which you can see demonstrate high variability. So the points are located throughout the plots. And we also have minimal bias, so we don't have all of our points clustered above or below the zero line. So this study demonstrated poor to moderate agreement and high variability in posterior tibial slope measurement between MRI and CT at both medial and lateral plateaus. These results are consistent with other studies that have shown variable agreement between MRI and CT measurements of bony landmarks surrounding the knee. And however accurate and consistent measurements of the slope are going to be needed for it to be a useful clinical tool. It's been shown the differences, even as small as less than a degree, may be associated with clinically significant effects on ACL grafts. A couple limitations of the study were that only a third of our patients in the study actually had ACL pathology. Our patient population, again, was those who received both MRI and CT within a one-year interval at our medical center. And many of these patients did end up being trauma patients. Additionally, standard MRI protocols were used here. And thin slice MRI may more accurately measure the slope. So in conclusion, CT may be required clinically to accurately quantify the individual slopes at the medial and lateral plateaus. And further studies may include comparing posterior tibial slope measurements on MRI versus CT in a clinically relevant patient cohort. For example, those with ACL pathology and elevated slopes are also using thin slice MRI. Thank you.

posterior tibial slope

MRI

CT scans

ACL injury

graft failure