Change in Susceptibility Values in Knee Cartilage After Marathon Running Measured Using Quantitative Susceptibility Mapping

Background Quantitative susceptibility mapping (QSM) has been used to study the magnetic susceptibility properties of collagen fibers in articular cartilage; however, it is unclear whether QSM is sensitive to changes due to degradation caused by long‐distance running. It is clinically important to understand the link between long‐distance running and microstructural changes in knee cartilage. Purpose To investigate the ability of QSM to assess microstructural changes within cartilage after repetitive loading. Study Type Prospective. Population Thirteen recreational, male long‐distance runners. Field Strength/Sequence Three‐dimensional gradient recalled echo acquired at 3 T. Assessment Magnetic resonance imaging (MRI) and 3D kinematics (translations and rotations during treadmill walking and running) of the knee joint were collected before and after marathon running. The compartments for analysis included the patella, trochlea, and subregions of femoral and tibial cartilage. Changes in regional susceptibility and cartilage thickness were calculated after marathon running. A susceptibility profile was obtained by fitting susceptibility as a function of the normalized depth of cartilage from the superficial to deep layers. Statistical Tests Paired t‐test or Wilcoxon signed‐rank test, 95% confidence interval (CI) of the depth‐wise susceptibility profile, Pearson correlation or Spearman correlation. Results There was a statistically significant increase in susceptibility value in the weight‐bearing region of central medial femoral cartilage (cMF‐c) after marathon running (pre‐marathon: −0.0219 ± 0.0151 ppm, post‐marathon: −0.0070 ± 0.0213 ppm, P