The X-ray study was too small to answer the question it asked
572 knees were followed for two years with no arm slowing the joint's narrowing, but the placebo group lost only 0.166 mm, less than the trial was built around.
What the study found
A joint-space null its own authors say the trial could not have found
An X-ray substudy followed 572 knees for two years and found no arm slowing the joint's narrowing. Then it explained why that is an absent answer rather than a negative one: the placebo group lost only 0.166 mm, less than the trial was built around and small beside X-ray measurement error.
The caveat · Hydrochloride, not the sulfate salt
Milder knees showed a trend toward benefit with no significance test attached to it, so it is not a result and should not be reported as one. The trial used glucosamine hydrochloride rather than the sulfate salt, which is one of the two ways it differs from the three-year trials reporting a benefit.