The Joint Capsule
Each one of the joints throughout our bodies is surrounded by a flexible, elastic membrane which is known as the joint capsule. The outside of the joint capsule is made of connective tissue similar in makeup to ligaments. Its function is to help provide stability to a joint while still allowing proper j
oint motion. The inside of the joint capsule is lined with tissue called synovium. Synovial cells secrete the fluid that lubricates the joint and give nutrition to the cartilage. In its normal state, the joint capsule must be tight enough to prevent slipping or abnormal movements of the bones (dislocation or subluxation). At the same time, it must also be flexible enough to allow full normal motion at each particular joint. There are no joints in our bodies that work as true hinges; rather, fluid motion is achieved by
There are no joints in our bodies that work as true hinges; rather, fluid motion is achieved by subtle rotations and gliding of one bone against its counterpart. For example, within the shoulder joint, the act of lifting the arm up to the side must be accomplished by a simultaneous downward rotation and gliding of the head of the humerus (your upper arm bone) within the socket of the joint. In other words, the arm bone must be allowed to move in the socket in order for the normal joint motion to occur. A healthy joint capsule will allow this movement to take place smoothly and without restriction.
Throughout a daily routine, each joint capsule of the body will normally be stretched in the previous manner several times per day. Normal activities, such as lifting your arm to wash your hair or getting dressed in the morning, put normal stresses on the joint capsule via movement of the joint. These normal stresses are what maintains the integrity and flexibility of each joint capsule without extraordinary efforts.
Problems may arise, however, when the activity of a joint is disrupted (i.e. following surgery or a fracture which requires immobilization of a joint; or with bursitis or tendonitis, which may restrict movement due to pain). In cases such as these, the normally flexible joint capsule may slowly tighten due to lack of normal stress. Without the normal stresses on the joint capsule, it will gradually develop adhesions, and ultimately limit the amount of motion available within the joint. To further restrict movement, the synovial fluid within the capsule will become thicker due to the decreased movement.
The capsule is a closed, contained compartment. For this reason, increased pressure within the capsule can develop as a result of restriction as described above. If there is inflammation of a structure inside the joint capsule, this will also increase the pressure within the joint capsule. Increased pressure can add pain, while further restricting available motion. A person with adhesive capsulitis (restricted joint motion, limited by tightness of the joint capsule) may notice increased pain within an affected joint with changes in the weather. As the barometric pressure changes, there may also be corresponding changes of pressure within the joint capsule.
The most commonly affected joint is the shoulder. A possible scenario is as follows: a man falls while skiing and lands on his right shoulder. The shoulder is bruised, but not seriously injured. There is pain any time the man lifts his right shoulder upwards, so he tends to carry the arm by his side, limiting the use of it. When this limited use continues for two weeks, there is a noticeable decrease in available motion (the joint capsule has now tightened because it has not been stretched to its normal limits for two weeks). Motion is now limited by pain and the inflexibility of the now inelastic capsule.In order to now re-establish full flexibility of this shoulder, a program of joint mobilization must
In order to now re-establish full flexibility of this shoulder, a program of joint mobilization must be undertaken. Unlike a muscle which will respond to gentle, gradual stretching, the joint capsule needs to be specifically addressed with a program designed to increase the mobility of the existing adhesions and restore the subtle motions which need to take place within the joint. This is supplemented with stretching to maintain the new capsular mobility and strengthening the muscles to maintain strength in the acquired ranges.
The most important thing to keep in mind is that prevention is the key word. It is far easier to prevent adhesive capsulitis than it is to deal with the problem once it has been established. If the man in the above scenario had kept his shoulder moving, he would have maintained the circulation of blood within the soft tissue structures around the joint and provided normal stresses on the joint capsule. This would have possibly avoided the end result and now the subsequent need for physical therapy.