This is what collagen supplements do to your knee cartilage
Collagen supplements help ease joint pain caused by arthritis and overuse while doing sport. That collagen supplementation helps cartilage in joints to grow is not surprising, but now rheumatologists at Tufts Medical Center have recorded the effect by making MRI scans.

The Americans published in Osteoarthritis and Cartilage the results of a study in which they made use of delayed gadolinium enhanced magnetic resonance imaging of cartilage [dGEMRIC]. This is a piece of medical technology which enables doctors to examine the quality of cartilage in joints. Australian researchers used the technology to measure the deleterious effects of serious overweight on the joints. [J Rheumatol. 2009 May; 36(5): 1056-62.] The same researchers have also been able to show that weight loss leads to a restoration of cartilage in overweight people. [Ann Rheum Dis. 2012 Jan; 71(1): 26-32.]The Americans were curious to know whether they could also use the same MRI technology to measure the effect of collagen supplementation on the knee joint. They did an experiment with 30 people over the age of 49, all of whom had a mild form of arthritis. Half of the subjects took a placebo every day for 48 weeks; the other half took a daily 10 g collagen in the form of a supplement beverage, Fortigel.
The supplement had an effect. The dGEMRIC index increased in the collagen group [CH]. The higher the index, the more compact the cartilage structure. After 24 weeks the dGEMRIC index had increased significantly at two critical points in the knee joint. See the asterisk in the table below.

Below you can see the scans of the knee joint of a couple of test subjects from both the placebo and collagen groups. The cartilage is coloured. The redder it is, the worse the condition. The more yellow, the more compact it is.

Placebo Collagen

The researchers were not able to detect effects of collagen on the functioning of the joint.
"We view our results as an affirmation that the dGEMRIC technique, and the CH intervention, merit further testing in a larger study", the researchers write. "However, because of the pilot nature of this study, and its small sample size, we do not regard these results to be definitive."

Gelita, the manufacturer of Fortigel, funded the research.
Osteoarthritis Cartilage. 2011 Apr;19(4):399-405.