Have a bone spur in left knee (very small and only one), used to hurt a little with discomfort, pain is gone with physiotherapy to strengthen quad muscles. will this lead to osteoarthritis or are bone spurs common?

This may be an early sign of degenerative changes in your knee (otherwise known as arthritis). This may also be a sign of an old injury to the knee. I would recommend you continue to do strengthening exercises and try to remain as active as possible. If it begins to become more bothersome, I recommend seeing an Orthopaedic surgeon or non-operative sports medicine physician to discuss treatment.

Bone spurs are a common early sign of arthritis. in the knee. Continue to be as active as possible.