Arthritis means inflammation/ pain of the joints.
Rheumatism means pain associated with joints and muscles.
The two are linked because muscles attach to the bones at or near the joints. When a muscle is tensed it exerts its pull on the joint; if the tension is excessive or prolonged this will give the sensation of pain in the joint even if the joint is healthy and normal.
Arthritis and rheumatism are most commonly seen in the older dog and this gives rise to the misconception that the problems are caused by wear and tear of the joints. In fact, much of the pain and restriction of movement is due to muscle spasm rather than to joint disease. This muscle tension is caused by
(1) the accumulation of waste metabolic products in the muscles
(2) weakness of a major internal organ system. This is a viewpoint which will be familiar to students of acupuncture but suffice to say that certain muscles relate to specific organs e.g. a weakness in stomach function affects the muscles on the front of the (hind) leg or the lumbar muscles at the level of the stomach.
These effects may be due to unrecognised adverse reaction to food ingredients. When the pet changes to a high quality food which avoids damaging ingredients, the beneficial effect on the function of the internal organs and the elimination of toxic waste from the system will often lead to the relief of rheumatism/arthritis.
Benefits are possible even when there is degenerative joint disease e.g. hip dysplasia but are less likely if there is structural damage which needs surgery e.g. ligament damage.
A programme of controlled exercise is usually helpful. It is usually best to have four or five short walks each day rather than one long walk as this will maintain mobility without overtaxing the muscles. see http://www.burns-pet-nutrition.co.uk