Tendinitis or tendonitis (from the Greek Τενοντίτις) is a painful inflammation of a tendon. Generally tendinitis is referred to by the body part involved, such as Achilles tendinitis (affecting the Achilles tendon), or patellar tendinitis (jumper's knee, affecting the patellar tendon). Chronic overuse of tendons leads to microscopic tears within the collagen matrix, which gradually weakens the tissue.
Swelling in a region of micro damage or partial tear can be detected visually or by touch. Increased water content and disorganized collagen matrix in tendon lesions may be detected by ultrasonography or magnetic resonance imaging.
Symptoms can vary from an ache or pain and stiffness to the local area of the tendon, or a burning that surrounds the whole joint around the inflamed tendon. With this condition, the pain is usually worse during and after activity, and the tendon and joint area can become stiffer the following day as swelling impinges on the movement of the tendon. Many patients report stressful situations in their life in correlation with the beginnings of pain which may contribute to the symptoms.
Due to their highly specialised ultrastructure, low level of vascularization and slow collagen turnover, tendons and ligaments are very slow to heal if injured, and rarely regain their original strength. Partial tears heal by the rapid production of disorganized type-III collagen, which is weaker than normal tendon. Recurrence of injury in the damaged region of tendon is common.
Standard treatment of tendon injuries is largely palliative. Use of non-steroidal anti-inflammatory drugs combined with rest and gradual return to exercise is a common therapy, although there is evidence to suggest that tendinitis is not an inflammatory disorder, and that anti-inflammatory drugs are not an effective treatment and that inflammation does not cause tendon dysfunction.
Both eccentric loading and extracorporeal shockwave therapy are currently being researched as possible treatments for tendinitis. One study found both modalities to be equally effective in treating tendinosis of the Achilles tendon and more effective than a 'wait and see' approach. Other treatments for which research is on-going includes vitamin E, nitric oxide and stem cell injections.
Perhaps the most promising avenue of therapy is indicated in a line of research finding dramatic rates of recovery including complete remodeling of chronically damaged tendon tissue with eccentric loading, though eccentric loading may be less effective among non-athletes. However, a 2007 meta-analysis suggested that there is insufficient research to support the use of eccentric loading for the treatment of damage to tendons.
The use of an inflatable brace (AirHeel) was shown to be as effective as eccentric loading in the treatment of chronic Achilles tendinopathy. Both modalities produced significant reduction in pain scores, but their combination was no more effective than either treatment alone.
Shock-wave therapy (SWT) may be effective in treating calcific tendinitis in both humans and rats. In rat subjects, SWT increased levels of healing hormones and proteins leading to increased cell proliferation and tissue regeneration in tendons. Another study found no evidence that SWT was useful in treating chronicpain in the Achilles tendon.
Vitamin E has been found to increase the activity of fibroblasts, leading to increased collagen fibrils and synthesis, which seems to speed up the regeneration and increase the regenerative capacity of tendons.
Nitric oxide (NO) also appears to play a role in tendon healing and inhibition of NO synthesis impairs tendon healing. Supplementing with arginine, the amino acid that the body uses to form NO, may be useful in tendon healing. The use of a NO delivery system (glyceryl trinitrate patches) applied over the area of maximal tenderness was tested in three clinical trials for the treatment of tendinopathies and was found to significantly reduce pain and increase range of motion and strength.
Common tendonitis injuries
Tendinous injuries are common in the upper and lower limbs (including the rotator cuff attachments), and are less common in the hips and torso. Individual variation in frequency and severity of tendinitis will vary depending on the type, frequency and severity of exercise or use; for example, rock climbers tend to develop tendinitis in their fingers, swimmers in their shoulders. Achilles tendinitis is a common injury, particularly in sports that involve lunging and jumping while Patellar tendinitis is a common among basketball and volleyball players owing to the amount of jumping and landing.
A veterinary equivalent to Achilles tendinitis is bowed tendon, tendinitis of the superficial digital flexor tendon of the horse.
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