Purpose: To quantify, with magnetic resonance (MR) imaging, the in vivo changes in cartilage volume and thickness after physical exercise.
Materials and methods: The patellae of eight volunteers were imaged six times at physical test by using a spoiled fat-suppressed gradient-echo sequence with an acquisition time of 4.10 minutes. The volunteers then performed 50 knee bends, and two more data sets were acquired 3-7 minutes and 8-12 minutes after exercise. The patellar cartilage volume was determined after three-dimensional reconstruction, and the thickness was assessed with a three-dimensional minimal-distance algorithm.
Results: Whereas repositioning had a small effect on the measurements (mean coefficient of variation, 1.4%), a statistically significant decrease in cartilage volume was observed 3-7 minutes (mean decrease, 6.0%; P < .05) and 8-12 minutes (mean decrease, 5.2%; P < .05) after exercise. The deformation was homogeneous throughout the joint surface. In one asymptomatic volunteer, a cartilage lesion became more pronounced after exercise.
Conclusions: MR imaging can be used to investigate the response of articular cartilage to physical exercise in vivo. Patients or volunteers should be allowed a sufficient period of physical rest if quantitative measurements of cartilage volume and thickness are to be undertaken in longitudinal studies.