Joint pain can be caused by many different processes which include degeneration of the articular cartilage, infection, inflammation, trauma and deposition of crystals. Distinguishing one type of joint diagnosis from another is mostly made by taking a history and examining the joint, as this process is able to narrow down the options well. Once a provisional diagnosis is made then investigations are typically used to confirm the diagnosis and are less useful in trying to look for a cause without a narrow range of options. Clinicians try first to establish the source of the joint symptoms and then the potential underlying pathological process.
Joint pain may be coming from within the joint itself, from the anatomical structures around the joint or it can be referred from a remote source. Joint sources of pain include the capsule which surrounds the joint, the periosteal membrane, the synovial membrane lining the capsule, the ligaments and bone under the cartilage, while the joint cartilage itself is insensitive as it possesses no pain nerve endings. Establishing the anatomical structure which is painful is very important as it feeds through to both the diagnosis and treatment of the condition.
The typical processes which can lead to joint disease include inflammation of the synovium, inflammation of the bone-ligament and bone-tendon junctions, infection, crystal deposition and abnormalities in the joint. Abnormalities can be structural or caused by joint stresses such as meniscal tears. These kinds of conditions do not just occur on their own but can present in combinations. Synovitis is inflammation of the lining of the joint and is the primary site of inflammation in rheumatoid arthritis and other diseases. The synovium proliferates and spreads, causing a warm, inflamed, puffy joint, and can eat away articular cartilage and bone.
The bony insertions of the tendons and ligaments are known as entheses, which include the annular fibres of the disc inserting into the vertebra, and these areas are especially implicated in certain conditions. Inflammation makes the entheses lay down bone in the soft tissues as bony outgrowths along the ligament, tendon or disc. The deposition of crystals can occur in the synovial lining, on the articular cartilage or on other internal joint structures so the joint can be locally or generally affected. A gouty joint can be diagnosed by its puffy, warm appearance and the severe pain involved on movement.
An infectious arthritis may be caused by bacteria, viruses or fungi and is typically carried by organisms borne in the blood. The person may be unwell as this can be part of a system wide infection. Infections occur in the synovial membranes with some death of the membrane and significant formation of healing tissue and scar. Bacteria are capable of releasing toxins which have the ability to cause rapid destruction of cartilage. In structural abnormalities of the joint osteoarthritis is the commonest joint pathology in the world, with both internal and external factors affecting its incidence and severity.
Osteoarthritis is more likely to occur in a joint which has sustained previous trauma such as a fracture or a meniscal tear, suffers from a congenital structural abnormality or suffers from an abnormality of collagen such as hypermobility. A person’s genetic inheritance, their level of obesity and their occupation may also be relevant, although one of the strongest correlating factors is age. The deterioration of the joint surfaces in osteoarthritis is accompanied by an increase in the underlying bone’s density and by the growth of bony spurs at the margins of the joints. A synovitis may occur but often osteoarthritic change does not seem to involve inflammation.
The clinician who examines the patient needs to decide the likely source of the pain. It may be that the joint truly is the pain source but other nearby areas such as tendons, ligaments and muscles may be responsible or a distant pain source may refer pain to the area. The shoulder and hip, joints closer to the centre of the body, are harder to diagnose in this way. Pain in the hip region can be due to lumbar stenotic change, degenerative disc disease, osteoarthritis or bursitis laterally.
