Joint pain, caused by inflammation of the soft tissues (synovitis), generalised joint trauma or osteoarthritis, can lead to lameness.
In some cases, obvious pain or swelling on manipulation of the joint, or lameness following flexion, suggests that the joint is painful and contributing to lameness.
In the absence of clinical signs, it is usually necessary to inject local anaesthetic into the joint. If a significant improvement is seen in the lameness or performance following the injection then the joint is likely to be the source of the problem.
Inflammation within a joint can result in the loss of important constituents of the joint cartilage. If the architecture of the joint cartilage is damaged, its role as a shock absorber will be compromised. Abnormal loads will be transmitted through to the underlying bone, which may respond by becoming stiffer.
This results in a potentially vicious circle of compromised function of a number of the structures of the joint, resulting in progressive osteoarthritis.
Joint inflammation also results in the production of an abnormal amount of joint (synovial) fluid. Although the fluid is important for joint lubrication and nutrition of the cartilage; an excessive amount may cause increased pressure within the joint and can cause pain.
Once joint pain has been confirmed, treatment, which often includes injection of a drug into the joint, can begin. There are three main types of drug used for joint medication.
Hyaluronan (hyaluronic acid or “acid”) is a normal constituent of joint fluid. It is responsible for lubricating the soft tissue and has a role in nutrition of the joint cartilage. It may also have some anti-inflammatory role.
If a joint is inflamed, the amount and quality of natural hyaluronan is reduced and this has potentially damaging consequences. By injecting hyaluronan into the joint, it is thought that this encourages it to normalise its own production of hyaluronan.
These are strong anti-inflammatory drugs. Corticosteroids can suppress the inflammation and stop the vicious cycle described above if used judiciously. They act rapidly and have a potentially valuable role. However, they have disadvantages, because in the short term they can increase the loss of important structural components (proteoglycans) from the joint cartilage. Injecting hyaluronan at the same time can reduce this effect.
Corticosteriods, because of their potent anti-inflammatory effect, also reduce the joint’s ability to respond to infection and may mask the early signs of joint infection. When infection is then recognised it may be quite advanced and potentially extremely difficult to treat effectively.
One final, fortunately uncommon, problem associated with the use of corticosteroids is the development of laminitis, which can be rapidly progressive and possibly life threatening.
Polysulphated glycosaminoglycans (marked under names such as Adequan)
These are incorporated into the articular cartilage. Although osteoarthritic cartilage has limited ability to heal, these drugs can help stabilise the cartilage and are valuable in the management of osteoarthritis.