There has been a great deal of "to and fro" on the effectiveness of chondroitin in treating osteoarthritis.

Oesteoarthritis (OA) describes the breakdown of the padding (cartilage) between two bones in a joint, and tends to occur later in life.  Factors that influence OA include how much stress the joints have been put under.  OA tends to occur more frequently in people who are overweight, or do a lot of sports (particularly high performance athletes) and have had injuries related to sports.

According to a studied reviewed by the Cochrane Collaboration New Zealand (an independent review body) chondroitin by itself , or in combination with glucosamine, showed meaningful improvements in  pain scores, and in the Lequesne Index (which measures both pain and function for knee and hip oestoarthritis).  People who used chondroitin also had a lower risk over control of having severe adverse reactions to treatment.

The review covered 43 studies that involved over 9,000 patients.  The review also noted some studies were funded by makers of chondroitin.

Also interesting is research that shows rub on gels are effective for OA too.
References Click Here