Is Medial Tibial Slope Associated With Non-contact ACL Tears? An Analysis Of Primary And Revision Acl Reconstruction Patients

Abstract

Objectives:

Increased tibial slope (TS) may be associated with non-contact ACL injuries although potential confounding effects from various patient characteristics and radiographic quantification methods have not been rigorously studied. The association of TS with recurrent non-contact ACL injury after primary reconstruction is less defined. The purpose of this study was: 1) to assess the reliability and variability of TS values among different examiners, and 2) to compare TS between patients undergoing primary ACL reconstruction, re-injured patients undergoing revision ACL reconstruction, and an ACL-intact cohort.

Methods:

A total of 206 patients were prospectively enrolled in this single center, IRB-approved study that consisted of 3 groups: 1) ACL intact controls (CTRL, n=83), 2) first-time ACL injured patients from a non-contact mechanism (PRIM, n=77), and 3) patients with repeated non-contact ACL injury after primary ACL reconstruction (REV, n=46). Patients with prior knee surgery, radiographic signs of arthritis, chondral lesions ≥ grade 2, or insufficient radiographs were excluded. Repeated measurements of anterior and posterior TS were performed by 3 fellowship-trained sports medicine surgeons based on the previously described Utzschneider method that has a strong correlation to CT and MRI measurements. The anterior tibial slope (ATS) and posterior tibial slope (PTS) were measured to calculate an approximate mean medial tibial slope (MTS) based on the anatomic tibial axis. (Fig. 1). The intra- and inter-observer reliability were assessed by intra-class correlation coefficients (ICC). The MTS, ATS, PTS, age, BMI and sex distribution were compared among the three groups using one-way ANOVA with Tukey’s post hoc test and Chi-square test, respectively. The independent association of TS with ACL-intact controls (CTRL) vs. positive ACL injury (PRIM + REV) was assessed by multivariable logistic regression for MTS, ATS, and PTS, respectively. An a priori power analysis determined that 45 patients per group were needed to achieve a statistical power > 80% to detect a 1° difference (SD=3°) with α=0.05.

Results:

The ICC for intra- and inter-observer reliability in the calculation of TS ranged from 0.73-0.89 indicating substantial agreement. There was no significant difference in values for MTS, ATS, and PTS between the CTRL, PRIM and REV groups (p=0.42, 0.12, and 0.42, respectively). Patient age was highest in the CTRL group, followed by the REV, then PRIM groups (p<0.001) (Table 1). None of the TS values were independently associated with ACL injury based on multivariable logistic regression adjusted for age and sex. The mean ATS for all 206 subjects was 5° and 10° greater than that of the MTS and PTS, respectively (p < 0.001). ATS correlated only moderately to PTS (R²=0.49, p < 0.001).

Conclusion:

There is substantial intra- and inter-observer reliability in the radiographic assessment of medial tibial slope. Medial tibial slope was not associated with first time non-contact ACL tears or recurrent ACL graft tears undergoing reconstruction.

Table 1.

Patient characteristics and tibial slope quantified for three study groups.

	CTRL (n=83)	PRIM (n=77	REV (n-46)	p value
Age (y.o)	37.1 +/-12.3	18.9 +/- 4.6	25.0 +/- 8.2
Sex (female, %)	56.6%	53.3%	39.1%	0.15
BMI (kg/m2)	26.6 +/- 5.9	24.7 +/- 4.5	26.5 +/- 4.4	0.83
ATS (degrees)	14.7 +/- 3.4	13.8 +/- 2.8	13.8 +/- 3.0	0.12
MTS (degrees)	10.2 +/- 3.1	9.6 +/- 2.7	10.0 +/- 2.7	0.42
PTS (degrees)	5.6 +/- 3.3	5.4 +/- 3.0	6.1 +/- 2.9	0.12