Exercise: medicine for knee cartilage?

Many of the 10–60% of the working-age population with knee pain will develop osteoarthritis (OA), a progressive joint disease with cartilage deterioration and increased disability. In knee OA, exercise decreases joint pain and improves function. Lack of human in vivo monitoring methods has made studies of influence of exercise on cartilage composition impossible. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) can estimate joint cartilage glycosaminoglycan (GAG) content. It is based on the principle that the negatively charged Gd-DTPA^2- ions distribute in the cartilage in an inverse relationship to the GAG content. A high GAG content results in a low contrast medium distribution and a long T₁ relaxation time that can be measured by magnetic resonance imaging. We used dGEMRIC in a cross-sectional study in healthy subjects with different exercising levels, and in a longitudinal exercise study in patients at risk for OA.

Methods

Study 1 included healthy, nonexercising individuals (n = 12), moderately exercising individuals (n = 16), and elite male track and field athletes (n = 9). Study 2 included medially meniscectomized patients that were randomized to exercise three times weekly for 4 months (n = 22) or to a control group (n = 23).

T₁ measurements were made in sagittal slices in a 1.5T magnetic resonance imaging system, using sets of turbo inversion recovery images with different inversion times in a region of interest in weight-bearing cartilage 2 hours after intravenous Gd-DTPA^2- injection at 0.3 mmol/kgbody weight. T₁ (s) was calculated using the mean signal intensity fromeach region of interest as input to a three-parameter fit. In study 2, subjects were examined before and after the exercise period.

Results

In study 1, there was a significant relationship between T₁ relaxation time and the level of physical exercise, with longer T₁ values in physically active subjects. In study 2, the exercise group showed asignificant higher mean change in T₁ than the control group.

Conclusions

In vivo cartilage monitoring by dGEMRIC indicates, for the first time, that human articular cartilage in mature individuals seems to adapt to physical activity levels by increasing its matrix GAG content. This may improve the resistance to mechanical compression, and thus protect the collagen network and prevent knee OA development.