Synovium and Synovitis
By Dr Kenneth Backhouse OBE
Movement of tissues in the body must be carried out with the minimum of stress from friction to avoid damage to the delicate components. At a cellular level this is one of the functions of the tissue fluid. Around larger structures such as the muscle bundles and the muscles themselves, supporting and enclosing membranes are found, the fascial layers. These, with the tissue fluid allow muscle components and particularly whole muscles with different functions to move freely with minimum stress. Each muscle is surrounded by a fascial sheath, varying in thickness with the disparity in function of the adjoining muscles: quite thin between muscles of similar function and thick where the muscles differ widely, as between flexor and extensor muscles. In other situations in the body, where friction-free mobility is vital, special serous membranes are found. These have different names, dependent on site. In the abdominal cavity the body wall and each of the enclosed viscera (stomach, intestines etc.) are separated by the peritoneum. The fibrous sheath enclosing the heart is lined by pericardium which also covers the heart allowing friction-free movement as the heart beats. The pleura acts in the same way for the chest wall and the lungs in breathing. In certain situations in the musculo-skeletal system, synovial membranes have a similar function. This is most evident in the synovial, freely movable joints, but also around certain tendons at stress points and, as bursae in other situations.
SYNOVIAL MEMBRANES OF JOINTS
Two types of material act to limit friction in synovial joints. In the load bearing areas, cartilage has this function and its role in this was discussed in a previous article. (September 2000 issue of Dance). The remaining lining of the joint space consists of a synovial membrane. This is a filmy material, little more than one cell thick and lies on the inner aspect of the capsular ligament. At its edge it is continuous with the cartilage over the bone ends. Whereas the cartilage accepts load in movement and itself assists in the joint�s freedom from friction, the synovial membrane is far too filmy and delicate for that. Any undue stress will produce an inflammatory reaction, synovitis. The synovial membrane, like the other serous membranes, has two types of cells, each with its own function. One cell type is responsible for lubrication in the joint. These cells secrete the synovial fluid, which is the effective joint lubricant. The synovial fluid itself consists of two components. The base is essentially tissue fluid but containing a very high molecular weight substance, hyaluronate proteoglycin (hyaluronic acid). This, together with the fluid squeezed from the cartilage while under load, gives an essentially friction-free state. The other type of cell is responsible for maintaining the cleanliness of the joint, ingesting any undesirable materials within the joint. Similar synovial membranes can be found as sleeves around tendons where these pass around bones or through constricting spaces, as at the ankle and the wrist, synovial sheathes. In other places synovial pockets lie between tendons or muscle and bone or between tendons, bursae.
Synovial membranes are subject to inflammatory reactions from both systemic disease as well as injury. In several general disease processes the synovial membranes appear to be a major target, as in rheumatoid arthritis. This, one of the so-called auto-immune diseases, leads to chronic synovitis, the swollen synovial membranes producing pain and joint swelling, often leading to destruction of adjoining tissues (bone, ligaments or tendons). Rheumatoid arthritis and other synovial affecting diseases are usually thought of as being in the older age groups but unfortunately juvenile forms of disease are quite common and disabling.
Acute synovitis is much more important from the view of dance. Injuries around a joint frequently lead to acute synovitis. The reaction of the synovial membrane is to secrete an excess of watery fluid of low viscosity and hence poor lubricating value. This in turn produces joint swelling which stimulates the brain to reduce activity in the muscles supporting the joint (central inhibition). The knee is a joint commonly affected and where the reaction is severe it is often described as "water on the knee". Acute swelling of the joint after injury should be taken seriously. Fortunately synovial membrane, given REST, usually repairs quickly. Total rest of the joint for little more than 48 hours is often enough, though the effect on the supporting muscle of the joint may take longer to recover if allowed to develop. Sadly the problem is often not noticed or not taken seriously and persistence of activity can result in a chronic inflammatory state, often with the formation of adhesions in the joint, take joint swelling seriously.
As the knee is a common victim, gross swelling (water on the knee) is usually pretty obvious. However minor amounts of swelling can be masked by the overlying quadriceps muscles. In the knee an extension of the synovial membrane extends upwards under the quadriceps for as much as three finger breadths above the patella. If there is doubt, a good test is the "patella tap". A hand grips the thigh immediately above the patella, pressing any fluid in the suprapatellar bursa down under the patella. Firm pressure on the patella can then produce a tap as it is pushed onto the underlying bone.
A pressure bandage around the knee is often advised but the important treatment is total rest until the swelling is absorbed. Meanwhile the quadriceps will be losing power rapidly. Maintaining a straight leg, at rest, repeatedly pull-up and hold the quads for a few seconds as firmly as possible without moving the knee; five minutes or so every hour. Continue exercising the quads even after the swelling has cleared; they will inevitably have lost power! The ankle is another common site of dance injury. Here look for swelling to the front of the ankle joint but mostly for thickening and loss of the hollowing behind the malleoli. This is also the common site for synovitis around the tendons.
Bursae are often affected. These exist around the knee in relation to the tendons but one commonly causing trouble lies beneath the tendo Achillis at the heel. Pointe work with tendency to roll or sickle under load can be a causative factor. A squeeze at the heel can give tenderness when bursitis is suspected.
For acute synovitis, whatever the cause or site, early rest is vital to prevent persistent problems, while keeping muscle as strong as possible.