Tibial Slope Strongly Influences Knee Stability After Posterior Cruciate Ligament Reconstruction: A Prospective 5- to 15-Year Follow-up

Background: The reported failure rate after posterior cruciate ligament (PCL) reconstruction remains high. Previous studies have shown that the tibial slope (TS) influences sagittal plane laxity. Consequently, alterations of TS might have an effect on postoperative knee stability after PCL reconstruction. Hypothesis: We hypothesized that flattening of TS is associated with increased posterior laxity after PCL reconstruction. Study Design: Cohort study; Level of evidence 3. Methods: This study consisted of 48 patients who underwent PCL reconstruction in a single-surgeon series. Eight patients underwent an isolated PCL reconstruction, 27 patients underwent an additional posterolateral corner reconstruction, and 13 patients underwent a combined reconstruction of the PCL, anterior cruciate ligament, and posterolateral corner. Three blinded observers measured TS and the side-to-side difference (SSD) of posterior tibial translation (PTT) before and after PCL reconstruction using standardized stress radiographs. The minimum follow-up was 5 years. Results: At a mean follow-up of 103 months (range, 65-187), the mean SSD of PTT was significantly reduced (10.9 ± 2.9 vs 4.9 ± 4.3 mm; P < .0001). The mean TS was 8.0° ± 3.7° (range, 1°-14.3°) for the operated knee and 7.9° ± 3.2° (range, 2°-15.3°) for the contralateral knee. There was a statistically significant correlation between TS and PTT ( r = −0.77 and R 2 = 0.59; P < .0001). In addition, there was a significant correlation between TS and the postoperative reduction of PTT ( r = 0.74 and R 2 = 0.55; P < .0001). Subgrouping according to the number of operated ligaments showed no significant differences regarding TS or the mean reduction of PTT. Conclusion: Flattening of TS is associated with a significantly higher remaining PTT as well as a lower reduction of PTT. Notably, these results are irrespective of sex and number of ligaments addressed. Thus, isolated soft tissue procedures in PCL deficiency may only incompletely address posterior knee instability in patients with flattening of the posterior slope.