High tibial slope correlates with increased posterior tibial translation in healthy knees.

PURPOSE

Notwithstanding the importance of the tibial slope (TS) for anterior tibial translation, little information is available regarding the implications on posterior laxity, particularly in healthy subjects. It was hypothesized that increased TS is associated with decreased posterior tibial translation (PTT) in healthy knees.

METHODS

A total of 124 stress radiographs of healthy knees were enrolled in this study. Tibial slope and the posterior tibial translation were evaluated using a Telos device with a 150-N force at 90° of knee flexion. Two blinded observers reviewed independently on two different occasions.

RESULTS

One hundred and twenty-four patients [35 females and 89 males; 41 (range 18-75) years] were enrolled in this study, with a mean PTT of 2.8 mm (±1.9 mm; range 0-8 mm) and a mean TS of 8.6° (±2.6°; range 1°-14°). Pearson correlation showed a significant correlation between the PTT and TS in the overall patient cohort (P < 0.0001) with r = 0.76 and R  = 0.58. There was no statistical difference between female and male patients regarding the PTT or the TS. Subgrouping of the patient cohort (four groups with n = 31) according to their TS (groups I < 7°; II = 7°-8.5°; III = 9°-10.5°; IV ≥ 11°) revealed significant differences between each subgroup, respectively. Furthermore, there was a weak but significant correlation between age and PTT (P = 0.004, r = 0.26).

CONCLUSION

In addition to the substantial variance in tibial slope and posterior laxity among healthy knees, high tibial slope significantly correlates with increased posterior tibial translation. Increasing age is further associated with a greater magnitude of posterior tibial translation. Consequently, knowledge of the tibial slope facilitates simple estimation of posterior knee laxity, which is mandatory for PCL reconstruction and knee arthroplasty.