 ACL reconstruction surgery can help many athletes return to sport after injury. Unfortunately, it's not uncommon for surgical grafts to fail after reconstruction. One factor believed to contribute to graft failure is having a steep posterior tibial slope. That's the angle between the posterior inclination of the tibial plateau and the line perpendicular to the tibial axis. To determine whether a steep angle is associated with the need for revision surgery after ACL reconstruction, researchers examined radiographs from 728 patients undergoing ACL reconstruction. Their findings are reported in the American Journal of Sports Medicine. Over a period of up to 19 years, 10% of patients ultimately underwent revision surgery. That allowed for a comparison of posterior tibial slopes between knees that sustained re-injury and those that did not. The difference, however, was not significant. The mean posterior tibial slope in the no-revision group was 9.5 degrees, whereas the value in the revision groups was 9.3 degrees. Even when grouped by slope, having a posterior tibial slope in excess of 10, 12, 14, 16, or 18 degrees showed no association with undergoing later revision surgery. Interestingly, however, a steeper posterior tibial slope was found in injured knees versus uninjured contralateral knees. That suggests that anatomical differences within the same patient could play a role. The study also found that regardless of posterior tibial slope, those who underwent revision surgery more often tended to be younger patients, patients with a shorter time from injury to surgery, and patients with a smaller graft size. The results should be interpreted with some caution, as the study did not include a group of uninjured participants for comparison, and it did not account for all patients who experienced real graft failure, only those undergoing later revision surgery. Overall, the findings show that, in contrast to what has been reported in most studies, a steep posterior tibial slope was not associated with revision ACL surgery.