Summary

A flat or decreased posterior tibial slope is an independent risk factor for PCL injury.

Abstract

Background

Recent biomechanical studies have identified sagittal plane posterior tibial slope as a potential risk factor for posterior cruciate ligament (PCL) injury because of its effects on the kinematics of the native and surgically treated knee. However, the literature lacks clinical correlation between primary PCL injuries and decreased posterior tibial slope.

Purpose/Hypothesis: The purpose of this study was to retrospectively compare the amount of posterior tibial slope between PCL injured patients and an age/gender matched PCL intact controls. It was hypothesized that patients with PCL injuries would have a significantly decreased amount of posterior tibial slope compared to patients without PCL injuries.

Study Design: Case-control study; Level of evidence, 3.

Methods

Patients who underwent a primary PCL reconstruction without ACL injury between 2010 and 2017 by a single surgeon were retrospectively analyzed. Measurements of posterior tibial slope were performed using the lateral radiographs of both PCL injured patients and matched controls without clinical or MRI evidence of ligamentous injury. Mean values of posterior tibial slope were compared between the two groups. Inter-rater and intra-rater agreement was assessed for the tibial slope measurement technique using a two-way random-effects model to calculate the intraclass correlation coefficient (ICC).

Results

One hundred four patients with PCL tears met the inclusion criteria and 104 control patients were matched to the PCL injured group according to age and gender. There were no significant differences in patient age (P=.166), gender (P=.345), or BMI (P=.424) between the PCL injured and control groups. Of the PCL tear cohort, 91 patients (87.5%) sustained a contact mechanism of injury, while 13 patients (12.5%) reported a non-contact mechanism of injury. The mean posterior tibial slope was 5.7 ± 2.1 degrees (95% confidence interval [CI]: 5.3°, 6.1°) and 8.6 ± 2.2 degrees (95% CI: 8.1°, 9.0°) for the PCL injured and matched control groups, respectively (P<.0001). Subgroup analysis of the PCL injured patients according to mechanism of injury demonstrated significant differences in posterior tibial slope between non-contact (4.6 ± 1.8°) and contact (6.2 ± 2.2°) injuries for all PCL tear patients (P=.013) and among patients with isolated PCL tears (P=.003). The tibial slope measurement technique was highly reliable, with an ICC of 0.852 for inter-rater and an ICC of 0.872 for intra-rater reliability.

Conclusion

A decreased posterior tibial slope was associated with PCL tear patients compared to age and gender-matched control patients with intact PCLs. Decreased tibial slope appears to be a risk factor for primary PCL injury. However, further clinical research is needed to assess if decreased posterior tibial slope affects posterior knee stability and outcomes following PCL reconstructions.