INTRODUCTION:Changes in mechanical properties of articular cartilage are involved in many joint diseases, particularly osteoarthrosis. Therefore, the analysis of the deformation of normal and pathologically altered joint cartilage is of high interest. However, research had to concentrate so far on explanted tissue samples, and there has been very few information about the deformational behavior of cartilage in the living.The objective of this study was to analyze the deformation of articular cartilage and load induced fluid flow in the living after physical exercise and relaxation, using MR imaging.METHODS:Seven healthy volunteers (age 23 to 32 years) were asked to rest for one hour. Then six transverse data-sets of the patella were acquired with MRI (VISION, Siemens), using a previously validated fast fat-suppressed FLASH-3D sequence (43 ms / 6 ms / 30 o ; acquisition time 4'10 min.). The joint was repositioned in between acquisitions.The volunteers then performed fifty deep knee bends and were imaged at 3-7 minutes and 8-12 minutes after the exercise. The knee bends and the imaging were repeated six times. In a second study, the same volunteers performed 100 deep knee bends, and were then imaged at ten minute intervals for 90 minutes.All data were transferred to a symmetric multiprocessing system (Onyx, SGI), and after semiautomated segmentation, the cartilage volume was determined by 3D reconstruction. The thickness was analyzed, using a previously validated minimal distance algorithm.RESULTS AND DISCUSSION:At physical rest, the reproducibility of the cartilage volume was between 0.8% and 3.7% (CV%; mean = 1.4%), and there was no systematic change with time (p = 0.45). This indicates that even small changes of cartilage volume can be determined with high precision, using the MR based technique developed.At 3-7 minutes after the knee bends, the cartilage volume had decreased by an average of 6.0% (p < 0.05) (corresponding to a fluid loss of about 10%) and the volume was still reduced at 8-12 minutes after exercise (- 5.2%; p < 0.05). Repeated knee bends (x 6) did not result in a further systematic decrease of patellar volume.After 100 knee bends (3 volunteers analyzed so far) the volume change was also 6%, and the time required for the cartilage to regain its original volume amounted to approx. 90 min.CONCLUSION:To our knowledge, this is the first study to report cartilage volume changes following physical exercise in vivo. The results show that strenuous physical exercise leads to cartilage deformation, and that during relaxation the fluid takes as much as 90 min. to flow back into the proteoglycan-collagen matrix.