Differentiation in Posterior Tibial Slope by Sex, Age, and Race: A Cadaveric Study Utilizing 3-Dimensional Computerized Tomography

Abstract

Background: Posterior tibial slope (PTS) has recently gained increased attention for its possible role in anterior cruciate ligament and posterior cruciate ligament injury. The possible differences among age, sex, and ethnicity in PTS have not yet been reported. Purpose: To describe demographic variances of proximal tibial anatomy and to detect differences in regard to ethnicity, sex, and age. Study Design: Cross-sectional study; Level of evidence, 3. Methods: In total, 250 cadaveric specimens with full-body computerized tomography scans from the New Mexico Descendant Imaging Database were randomly selected (inclusion/exclusion criteria: older than 18 years, complete imaging of the knee without previous surgery or arthroplasty) and reviewed by 3 independent observers measuring medial posterior tibial slope (MPTS), lateral posterior tibial slope (LPTS), and global posterior tibial slope (PTS), which was calculated as the mean of the MPTS and LPTS. Individuals were evenly divided among male and female and ethnicities/races: African American/Black, Asian American, Hispanic, Native American, and White. Intraclass correlation coefficient was calculated for interobserver reliability and analysis of variance statistical testing to determine statistical significance between groups. Fisher exact test was also used to understand PTS differences among ethnicities when looking at clinically significant values for potential ligamentous injury. Results: Measurements were obtained from 250 specimens with a mean age of 49.4 years (range, 19 to 103 years). The mean PTS was 8.92° (range, –9.4° to 14.95°). Asian Americans had a 1.7° greater mean MPTS than Whites ( P = .016), and African Americans/Blacks had a 1.6° greater mean PTS than Whites ( P = .022). No difference in mean PTS was seen between age and sex. When looking at clinically significant PTS, 61 (24.4%) individuals had tibial slopes <6° or >12°, 32 (12.8%) and 29 (11.6%), respectively. Statistically significant differences were seen among ethnicities with PTS <6° ( P = .017) but not with PTS >12° ( P = .106). No sex-based differences were seen in the percentage of specimens with a PTS of >12° or <6°. Conclusion: Among ethnicities, African Americans/Blacks and Asian Americans have increased PTS in comparison with Whites. Nearly 25% of individuals have clinically significant slopes of <6° or >12°, with no difference in tibial slope among sex or age groups.