Measurement of the Posterior Tibial Slope Depends on Ethnicity, Sex, and Lower Limb Alignment: A Computed Tomography Analysis of 378 Healthy Participants.

Background: There is no general consensus on the normal and pathological values for the posterior tibial slope (PTS).
Purpose/hypothesis: The primary aim of this study was to determine standard values for the PTS in healthy participants using 3-dimensional (3D) computed tomography (CT). A secondary aim was to determine the effect of demographic factors and coronal-plane lower limb alignment on the PTS measurement. The hypothesis was that the PTS would be significantly influenced by demographic factors and coronal-plane lower limb alignment.
Study Design: Cross-sectional study; Level of evidence, 3.
Methods: A CT-based modeling and analytics system was used to examine and measure lower limb alignment and the PTS in 378 patients (193 male and 185 female; mean age, 58.3 ± 16.4 years [range, 18-92 years]; mean body mass index, 25.0 ± 4.4 kg/m ² ). The lateral, medial, and global PTS were measured for each patient. All measurements were constructed using algorithm-calculated landmarks, resulting in reproducible and consistent constructs for each specimen. The results were then evaluated based on ethnicity, sex, and hip-knee-ankle (HKA) angle.
Results: The study population comprised 219 white and 159 Asian participants. The mean global, medial, and lateral PTS were 6.3° (range, -5.5° to 14.7°; 1% with ≥12°), 6.2° (range, -4.1° to 17.2°; 3% with ≥12°), and 5.3° (range, -4.7° to 16.2°; 2% with ≥12°), respectively. The lateral (Δ = -1.0° [95% CI, 0.6°-1.6°]; P < .0001) and global (Δ = -0.5° [95% CI, 0.0°-0.8°]; P = .0332) PTS were smaller in the female subpopulation. The global PTS was greater (Δ = 1.9° [95% CI, 1.5°-2.3°]; P < .0001) in the Asian subpopulation. The mean HKA angle was 179.6° (range, 170°-190°). The HKA angle was significantly correlated with the medial and global PTS. Specimens with a genu varum knee exhibited a significantly greater global (Δ = 1.2° [95% CI, 0.8°-1.7°]; P < .0001) and medial (Δ = 1.9° [95% CI, 1.3°-2.5°]; P < .0001) PTS.
Conclusion: The present study gives a benchmark for the physiological values of the PTS in a healthy population and highlights several factors influencing the PTS, such as ethnicity, sex, and alignment. Anatomic variants with a PTS ≥12° were very uncommon (≤3%) in our Asian and white groups and thus could be considered as pathological. The PTS is a crucial anatomic factor for anterior cruciate ligament injuries and reconstruction. A general consensus is lacking regarding the cutoff for abnormal values, thus guiding standard of care. This study investigated the dispersion of global, medial, and lateral posterior plateau tibial angles in a large population representing a range of demographic diversity.
Competing Interests: One or more of the authors declared the following potential conflict of interest or source of funding: S.L., P.W., and A.F. are employees of Stryker. M.O. has received consulting fees from Arthrex, Newclip Technics, and Stryker. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
(© The Author(s) 2020.)