Biomechanical Effects of Chronic Ankle Instability on the Talar Cartilage Matrix: The Value of T1ρ Relaxation Mapping Without and With Mechanical Loading

Background: T1 rho mapping has been proposed for the detection of early cartilage degeneration associated with chronic ankle instability (CAI). However, there are limited data surrounding the influence of ankle loading on T1 rho relaxation. Purpose: To evaluate T1 rho relaxation times of talar cartilage, as an indicator of early degenerative changes, associated with CAI and to investigate the influence of acute axial in situ loading on T1 rho values in CAI patients and healthy controls. Study Type: Prospective. Subjects: A total of 9 patients (age = 21.8 +/- 2.5 years, male/female = 2/7) with chronic ankle instability and 18 healthy control subjects (age = 22.8 +/- 3.6 years, male/female = 5/13). Field Strength: 3 T. Sequence: 3D gradient echo fast low-angle shot (FLASH) sequence augmented with a variable spin-lock preparation period. Assessment: Ankle T1 rho mapping was performed without and with axial loading of 500 N. The talar cartilage was segmented in five coronal slices covering the central talocrural joint. Median talar T1 rho values were separately calculated for the medial and lateral facets. Statistical Tests: Mann-Whitney U and Wilcoxon signed-rank tests, significance level: P < 0.05. Results: For the combined cohorts, the statistical analysis yielded significantly lower T1 rho values with loading compared to the no-load measurement for both the lateral (no load: [51.0 +/- 4.0] msec, load: [49.5 +/- 5.4] msec) as well as the medial compartment (no load: [50.0 +/- 5.4] msec, load: [47.8 +/- 6.8] msec). In the unloaded scans, the CAI patients showed significantly increased talar T1 rho values ([53.0 +/- 7.4] mse ) compared to the healthy control subjects ([48.8 +/- 4.1] msec) in the medial compartment. Data Conclusion: Increased talar T1 rho relaxation times in CAI patients compared to healthy controls suggest that T1 rho relaxation is a sensitive biomarker for CAI-induced early-stage cartilage degeneration. However, the load-induced T1 rho change did not prove to be a viable marker for the altered biomechanical properties of the hyaline talar cartilage.