Joint pain may have several origins relevant to this discussion: injury to the joint or other tissues around the joint, arthritis and muscular pain that feels like joint pain.
Injuries to the joint as well as arthritis can often cause bracing or constriction in the surrounding musculature. As a result the muscles may shorten, tighten and become ischemic (reduced blood flow creates oxygen and nutrient deprivation and results in a build up of metabolic waste) causing pain. This response is counter productive and exacerbates the original pain and inflammation caused by the injury or arthritis.
The trauma that injured the joint often traumatizes the surrounding muscles and triggers the pain-spasm-pain cycle (see neuromuscular therapy) that will linger long after he joint problem is corrected. Even though massage therapy cannot "fix" arthritis or joint injury it can reduce the secondary pain in the surrounding muscles, increase circulation and promote healing and rejuvenation in the area.
Sometimes "joint pain" has nothing to do with the joint at all but is the result of trigger points in near by muscles caused by overuse or any number of other factors (see What causes trigger points?). The resulting referred pain can cause the sensation of deep pain in or around the joint. Neuromuscular therapy performed by a skilled therapist will eliminate this pain.
Massage therapists do not diagnose medical conditions nor is this information intended to replace medical counsel. It is always advised to consult your physician first when you are seeking pain relief as there are many conditions with similar symptoms and some of them are life threatening and require medical attention.