Deformation and recovery of cartilage in the intact hip under physiological loads using 7T MRI

Accurate measurement of cartilage deformation in loaded cadaver hip joints could be a valuable tool to answer clinically relevant research questions. MRI is a promising tool, but its use requires an understanding of cartilage deformation and recovery properties in the intact hip. Our objective was to answer the following questions: (1) How long does it take for hip cartilage to reach a deformed steady-state thickness distribution under simulated physiological load, and how much does the cartilage deform? (2) How long does it take for hip cartilage to return to the original cartilage thickness distribution once the load is removed? Five human hip specimens were axially loaded to 1980N in a 7T MR scanner and scanned every 15min throughout loading. One specimen was scanned every hour throughout recovery from load. One repeatability specimen was loaded and scanned every day for 4 days. Hip cartilage was segmented as a single unit and thickness was measured radially. The hip cartilage reached a steady-state thickness distribution after 225min of load, and 16.5h of recovery. Mean strain after 225min of load was 30.9%. The repeatability specimen showed an average day-to-day change in mean cartilage thickness of 0.10mm over 4 days of data collection. The amount of deformation (0.96mm) was far greater than the image resolution (0.11mm) and error due to repeatability (0.10mm). Using an ex vivo model, this method has potential for assessing changes in hip cartilage strain due to injury or surgical intervention.