Good morning. In terms of introduction, posterior tibial slope, as we've heard about this morning, plays a vital role in the biomechanics of the knee. Tibial slope influences our maximum knee flexion, knee resting position, cruciate ligament tension, and chondral contact pressures. We all know that as increased posterior tibial slope, there's increasing forces on the native and reconstructed ACL, and slope influences rotational moment with axial load. And it's possible maybe we should take some advice from our veterinary colleagues who, as you can see in these radiographs, have done a slope neutralizing procedure rather than an ACL reconstruction in an ACL-deficient canine. We do know that slope-decreasing osteotomies can change our ACL reconstruction profile, and that there may be a role in either the primary ACL or in the revision setting based on our measurements. There's really no ideal or consensus on how we measure slope, and we wanted to look at radiographs versus MRIs in this study. So our purpose was to evaluate the inner observer reliability on radiographs and MRI, and then also to evaluate differences or discrepancies between radiographs and MRI. It was a retrospective study of patients between the ages of 18 and 30 with X-ray and MRI in close proximity to one another. Those that had history of fracture, infection, or surgery were excluded. We measured lateral tibial plateau, medial tibial plateau, slope, and we used the Hashimi method which you heard about earlier today. Here's just an example of how we did that on MRI as well, both for the lateral side and the medial side. In terms of our results, we had 81 patients, 90 knees, and you can see these are relatively young patients or patients who would be undergoing ACL reconstruction otherwise, and fairly equal between left and right knees in males and females. In terms of the results, you can see that the interclass correlation coefficients were excellent, and there was a significant difference between what we found on X-ray and MRI. Here this is graphically. We looked at both MRI bone and cartilage, and you can see that there's significant differences with higher posterior tibial slope on X-ray as compared to MRI. In terms of a discussion, calculations of slope on X-ray and MRI have good to excellent interrelated reliability, however, measurements of slope were significantly higher on X-ray compared to MRI, and this was consistently approximately a three to four degree difference. Where does this fit into the literature? Well, there's been a number of other great studies looking at this same topic. Roughly all have found the same thing. X-ray radiographs seem to be greater in terms of their measurement of posterior tibial slope as compared to MRI, with CT being closer to X-ray or radiographs as compared to MRI. We know that some of this is probably related to the position in which we obtain these studies. Knee flexion induces internal rotation in the tibia, and obviously the position we place the patient in for radiographs is different than the position we place the knee in for MRI, and that likely influences slope as rotation changes. In terms of limitations of our study, we did not use CT in this patient population. It's very difficult to standardize the axis of the MRI cuts. The length of the MRI, as mentioned previously, can be a difficulty in terms of using the Hashimi method, and knee flexion is not standardized on our X-ray imaging. In terms of conclusions, a measurement of slope, both on the medial and lateral sides, can be reliably reproduced between individuals measuring on the same radiographs or MRI. However, tibial slope measurements between X-ray and MRI cannot be used interchangeably, and caution should be used when interpreting or comparing between X-rays and MRI as you're preoperatively planning. Thank you.

posterior tibial slope

knee biomechanics

slope measurements

X-rays

MRIs