There are many different potential causes for joint pain and these include infection, accidents, crystals in the joint, inflammation and articular cartilage damage. The clinical history and joint examination are the strongest guides to establishing a differential diagnosis and once a provisional decision about the likely cause has been made then laboratory investigations can be useful to confirm or refute this. Without an initial guiding thought as to the possible diagnosis investigations can be more confusing than enlightening. The primary effort is in pinning down the likely pain source and then working out the disease process.
The source of joint pain can be from within the obvious joint, from structures which surround the joint or can be a referred pain from a structure elsewhere. Within the joint itself the pain can come from the surrounding capsule, the ligaments, the bone membrane, the synovial joint lining and the bone underneath the joint cartilage. The joint cartilage itself is not a source of pain as it does not possess any sensory nerve endings. It is very important to pin down the likely structure responsible for the pain as the diagnosis and so the therapy may be different depending on that evaluation.
The pathological processes which result in joint damage are several and cover infections, laying down of crystals in the joint, inflammation of the junctions between tendon and bone and ligament and bone (enthesitis), synovial inflammation and joint abnormalities. Joint changes can be structural or mechanical like injury to a meniscus. The above pathologies may occur in combination and not just one at a time. Inflammatory changes in the joint linings (synovitis) are the main pathology in many arthritic conditions including rheumatoid arthritis. The growth of the synovial membrane can cause cartilage destruction and a puffy, warm and inflamed joint.
The enthesis is the area where a tendon or a ligament inserts into the bone and this area is preferentially affected in some types of joint condition. Inflammation of these areas causes the collagenous soft tissue close to the bone to form bone which grows out from the origin either along the ligaments or the outer disc layers. If crystals are deposited in a joint this can lead to an inflamed and painful joint, with crystals forming on the cartilage itself, on the synovium or on the structures around the joint. Localised or generalised symptoms can result and a gouty joint is recognisable by the warmth, redness and extremely sharp pain on stressing or moving.
Fungi, viruses or bacteria may cause a joint infection, with infections usually resulting from the organism being carried in the blood. Typically part of a more widespread infection, the patient may also feel unwell. The synovium is where the infections occur and there is some local tissue death and increased formation of scar and healing tissues. Toxins may be released by bacteria and these can destroy joint cartilage very quickly. In joint abnormalities the most common pathological process in joints across the world is osteoarthritis and both external and internal factors affect the severity and incidence of this.
Local, more specific factors which can predispose to osteoarthritis are any previous damage to the joint, such as in sports injuries, developmental abnormalities of the joint, abnormalities of cartilage and collagen disorders such as hypermobility. Factors to do with the person include their genetic heritage, their occupation and their bodyweight, although osteoarthritis is most strongly correlated with advancing age. Articular cartilage damage in osteoarthritis is followed by an increase in density of the underlying bone and the formation of bony outgrowths at the joint margins. There may be a synovitis but inflammation is not always involved in this condition.
The first stage for the examining clinician is to determine the source of the pain more precisely. The joint may be painful or there may be pain from close anatomical structures such as ligaments, tendons or muscles or it may be pain referred from a distant source. The more central joints such as the hip and the shoulder are more difficult to diagnose. Pain referred to the hip area is often not related to the hip joint itself and hip pain could be secondary to trochanteric bursitis, hip osteoarthritis, stenotic lumbar changes or intervertebral disc disease.
Jonathan Blood Smyth is the Superintendent of
Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for
Winchester physiotherapy visit his website.
