Posterior tibial slope in patients undergoing anterior cruciate ligament (ACL) reconstruction with patellar tendon autograft: Analysis of subsequent ACL graft tear or contralateral ACL tear

OBJECTIVES: To examine the relationship of posterior tibial slope and rate of graft tear or contralateral anterior cruciate ligament (ACL) tear among patients undergoing primary or revision ACL reconstruction with patellar tendon autograft. METHODS: From June 2001 to 2015, 2,796 patients received primary or revision ACL reconstruction with patellar tendon autograft (PTG) and were followed prospectively to determine rate of graft tear and contralateral ACL tear. Minimum follow-up for study inclusion was 4 years. Posterior tibial slope (PTS) was measured preoperatively on digital lateral view radiographs with knee flexion between 30° and 45°. Intersecting lines were drawn along the medial tibial plateau and the posterior tibia; the value of the acute angle at the lines’ intersection was then subtracted from 90° to obtain the PTS. This procedure was carried out by a clinical assistant with interrater reliability of 0.89. Chi-square analysis, Pearson correlation, and t-tests were used to determine relationships between rate of graft tear or contralateral ACL tear and PTS, age, and sex among primary and revision surgery groups. A threshold of PTS ≥10° was used for analysis. RESULTS: The mean age of patients was 24.3±10.2 years for patients undergoing primary ACL reconstruction (n=2472) and 24.3±8.8 years for revision ACL reconstruction (n=324). The mean follow-up time was 11.6 ± 4.0 years. The rate of primary graft tear was 5.1% (n=126), and primary contralateral ACL tear rate was 4.9% (n=121). The rate of revision graft tear was 5.9% (n=19), and revision contralateral tear rate was 1.9% (n=6). Among primary reconstructions, the mean surgery age of patients who experienced graft tear (19.2 ± 6.3 years) or contralateral tear (21.5 ± 9.5 years) were significantly younger (P<.001, P=.0011, respectively) than patients who did not suffer a subsequent tear (24.7 ± 10.3 years). The mean PTS among primary graft tears was 5.4 ± 3.1°, which was statistically significantly higher than the mean of 4.8 ± 2.9° for patients without tear (P=.041). The mean PTS was 4.9 ± 3.3° for patients with contralateral tears, which was not statistically significant different than other groups. Furthermore, primary reconstruction patients with PTS≥10° had a significantly higher rate of graft tear (9.6%) than patients with PTS ≤9° (4.7%) (P=0.004), but not a higher rate of contralateral tear. Among patients undergoing revision surgery, there were no statistically significant differences between graft tear, contralateral tear, and no tear groups with relation to age, PTS, or PTS ≥10°. Among all patients (primary or revision group), there was no difference in PTS between sexes (P=0.278), nor was surgery age significantly correlated to PTS (R=0.0226). CONCLUSION: Higher PTS appears to be correlated to higher rates of ACL graft tear in patients undergoing primary ACL reconstruction with PTG, particularly when PTS is greater than 10°. However, rate of graft tear remains low (5.1% overall, 9.6% with PTS≥10°). Furthermore, for patients undergoing revision surgery, there is no significant association between PTS and rate of subsequent tear. Therefore, caution should be exercised when considering more radical interventions, such as osteotomy, to prevent retear in patients with high PTS.