Synovial joints (those with the most movement in the body) consist of two articulating ('contacting') bones whose contact surfaces are covered with articular cartilage. The bones are held together by ligaments, and the entire joint is housed within a protective articlar capsule. Inside this protective capsule is a synovial membrane consisting in part of cells that produce synovial fluid, providing lubrication within the joint. Joint injury can include damage to bone, ligaments, the articular cartilage, other cartilagenous support structures in the joint (the menisci in the knee, the labrum in the shoulder), and can result in an inflammatory response that increases the synovial volume, pressurizing the joint so that the joint incurs stiffness and pain. Knowing which of these factors are included in any particular joint injury requires significant medical investigation (including thorough exam, X-ray, MRI, etc). Nutritionally, the most important things to do are to stay hydrated (the joint received nutrients primarily through diffusion because blood flow is low to regions where compressive stresses would destroy blood vessels), a balanced diet (tha provides for all the things cells need to be healthy, which includes the fibroblasts making the structures in the connective tissue), polyunsaturated fats (to inhibit the production of inflammatory compounds) and supplement with glucosamine sulfate at 1 to 1.5 g / day (you will know if this benefits you within roughly one month; if it does not there is little reason to continue using it). The research is not sufficient as of yet to make recommendations for or against any other compounds in the various joint formulas on the market.