Posterior tibial slope increases over time in patients undergoing revision ACL reconstruction: A long-term radiographic follow-up study

Purpose: Increased medial posterior tibial slope (PTS) is recognized as a significant risk factor for anterior cruciate ligament reconstruction (ACL-R) failure. This study investigated radiographic changes in medial PTS over time among skeletally mature individuals undergoing revision ACL-R and identified associated factors contributing to PTS changes. Methods: A 10-year chart review of patients who underwent revision ACL-R was performed. Inclusion criteria included having index knee radiographs spanning at least 5 years, with the first radiograph taken before primary ACL-R, and age >14 years. Exclusion criteria included inadequate radiographs, multi-ligament injuries and concomitant meniscus transplantation. Radiographic analysis involved determining the reliability of measuring PTS by two blinded raters across three time points using 25 selected radiographs, employing the standard error of measurement to ascertain the minimum detectable change (MDC), which was 1.0° (95% confidence interval). Changes in PTS were categorized into two groups based on the threshold of >2° (Group 1) and ≤2° (Group 2), to eliminate measurement errors. Two blinded researchers collected demographic data, clinical and operative histories and return-to-sports status. Results: Seventy-six patients were included, with a mean age of 25.3 ± 10.3 years at the time of primary ACL-R and an average radiographic follow-up of 8.9 ± 3.6 years after the initial preoperative radiograph. Interobserver and intraobserver reliabilities indicated high consistency (Intraclass correlation [ICC] = 0.92 and 0.97–0.99, respectively). There was a statistically significant increase in PTS from initially measured to most recent radiographs, averaging an increase of 1.1 ± 1.5° (p < 0.001), surpassing the MDC. A PTS increase >2° was associated with previous posterior medial meniscal resection (p = 0.003). A significant association was observed between having a PTS ≥ 12° on the latest radiograph and a greater change in PTS over time (p < 0.001). Conclusions: Radiographic evaluations demonstrated a consistent increase in PTS over an average of 9 years among patients undergoing revision ACL-R. Notably, a posterior medial meniscus resection was significantly linked to these increases. This continual increase in PTS may both contribute to and result from failed ACL-R. PTS ≥ 12° may be considered a deformity that may continue to progress over time unless corrected. Level of Evidence: Level III.