Increased medial posterior tibial slope is associated with greater postoperative anterior tibial translation over time after anterior cruciate ligament reconstruction.

PURPOSE: To investigate the longitudinal relationship between medial posterior tibial slope (PTS) and postoperative anterior tibial translation (ATT) following anterior cruciate ligament reconstruction (ACLR), and to determine whether age, cartilage lesions and the use of lateral extra-articular tenodesis (LET) modify this relationship. METHODS: We retrospectively analysed 319 patients who underwent primary ACLR with a semitendinosus autograft. Medial PTS was measured on long lateral radiographs (circle method) at 2 months and at final follow-up. ATT was assessed by Telos™ stress radiography in both knees preoperatively and at 2 months, 1 year and 2 years. Three measures were defined: the absolute ATT of the operated knee; the ATT side-to-side difference (ATT SSD; operated minus contralateral knee); and the change in this difference from the preoperative baseline (ΔATT SSD). Associations were tested with Pearson's/Kendall's correlation, group comparisons and multivariable regression; subgroups were defined by age, cartilage status and LET. RESULTS: The absolute operated-knee ATT was 5.8 ± 3.5 mm preoperatively and 2.9 ± 2.3, 4.9 ± 2.8 and 6.8 ± 4.0 mm at 2 months, 1 year and 2 years, respectively. Medial PTS correlated positively but weakly with the ATT SSD at 1 year (r = 0.2, p = 0.001) and 2 years (r = 0.3, p < 0.001); at 2 months, the correlation was negative and non-significant (r = -0.5, p = 0.3). Medial PTS at 2 months and at final follow-up were independent predictors of the ATT SSD on multivariable regression (p < 0.01). Older age (r = 0.15, p = 0.009) and medial cartilage lesions (p = 0.008) were associated with greater postoperative laxity, whereas LET was associated with a lower 2-year ATT SSD (6.1 vs. 7.3 mm; p = 0.009). Meniscal and lateral cartilage lesions showed no significant association. CONCLUSION: Steeper medial PTS is associated with a progressive, though weak, increase in the ATT SSD following ACLR. LET attenuates this effect, whereas older age and medial cartilage lesions are associated with greater early laxity. LEVEL OF EVIDENCE: Level III.