Understanding tendon injury.

Runners are fairly likely to face tendon pain, perhaps most notably in the Achilles tendon, at one point or another in their lives. Tendons form the strong but flexible linkage between the more fleshy muscles and rigid bones. Composed primarily of collagen, the tissue is woven with fibrils, and capable of bending with minimal elongation and no contraction. The overall rope-like structure is then encased in a sheath. There is a greater risk of injury in a tendon that crosses two or more joints. Tendons that pass over a convex surface--think of the rotator cuff--are also more injury-prone. And tendons exposed to the high strain of repetitive eccentric contractions, as well as tendons involved in locomotion, are also more at risk. The Achilles tendon possesses three out of four of these traits (it does not pass over a convex surface).

Not all tendon pain is tendinitis. Many tendon injuries are in fact tendinosis, and an understanding of the distinction can help you to identify one injury or the other and to adopt strategies for properly healing an injury such as Achilles tendinosis.

By and large, tendons may be injured in one of three ways: Acute trauma, which is a sudden event that causes serious damage to a previously normal tendon; chronic overuse injury, which amounts to cumulative damage from repetitive, micro-tear-causing stress that compromises the ability of a tendon to withstand tension; and sudden trauma brought on by repetitive overuse, as in an Achilles tendon rupture, which most often shows evidence of lesser injury prior to the rupture. The most relevant among these for our purposes is tendon injury caused by chronic overuse, which arrives with warning signs that do not accompany acute trauma and serves as a precursor to the third category in any case. Chronic overuse injury is often the result of insufficient rest between workouts.

When the damage to the tendon is microscopic, akin to the fraying of a rope, the injury will often heal itself. Fibroblast cells already within the tendon possess all the materials necessary to perform repairs and direct the crucial next phase of healing: remodeling. This is the cross-linking of collagen fibers to ensure that the tendon will again withstand the tension imposed on it by repetitive stress. It is this phase that provides the crucial mechanical and structural integrity so that you may later resume training.

Tendinitis

When micro-tears and the ensuing repair and remodeling occur, the result is tendinitis. The pain associated with this condition stems from microscopic damage, followed by self-healing. During this time it's important to protect the tendon not only from sudden, intense forces, but from repetitive, low-demand motions as well. And that can be difficult; it is equally important to avoid complete immobilization. As long as the demands don't overcome the tensile strength of the tendon, increased demand results in increased tendon strength. See Treatment below for more details about the rehabilitation process.

Tendinosis

By contrast, tendinosis is the result of failed healing. This condition is familiar to any runner who has experienced an Achilles tendon injury that takes unbearably long to resolve. It's not unheard of for these injuries to never heal normally. In many cases, the cause of this is an insufficient inflammatory response during the early phases of healing. While the later, remodeling phase occurs internally in the tendon without the aid of the immune system, initially it's important for outside help: Lymphocytes, neutrophils, and macrophages rush to the scene to clear out debris and prepare the damaged tissue for bridgework over torn fibers. When remodeling occurs without this preliminary step, debris remains in the scar tissue, which results in weakened structures. Under an electron microscope these chemical remnants and unconnected collagen strands reveal the lack of proper tendon structure.

This weakened tissue is obviously not desirable in and of itself, but its additional danger is that it places undue demands on the healthier areas of the tendon. The result is a kind of structural virus, with more and more of the tendon becoming compromised. Two thirds of acute ruptures of the Achilles tendon are associated with evidence of gradual pathologic changes within the tendon over time. For this reason you should not attempt to run if you find the pain severe enough to alter your form.

If after cutting back on your training you have Achilles pain that won't disappear, see a doctor. Lest you face years of frequent reinjury and lackluster running performance, it's best to err on the side of caution. There are a variety of clinical and laboratory tests that can diagnose your problem; MRIs are a common and often vital way to evaluate the severity of a tendon injury.

Treatment

Avoid cortisone shots to treat tendinitis. Cortisone, while useful for treating bursitis, disrupts the beneficial inflammatory response essential to the healing process and therefore should not be injected into tendon.

NSAIDs can help control pain in the short term but should be used judiciously so as not to completely shut down this inflammation necessary in the early healing stages. Obtain as many details as possible from your physician regarding the strength, dosage, and any long-term-use side effects of the particular NSAID or COX-2 inhibitor you may be considering taking. Additionally, ice, topical analgesics, and electrical stimulation have all been widely used to control the pain associated with tendon injuries.

The reversal of tendinosis depends greatly upon preservation of motion in the tendon and the gradual build-up of strength and endurance. Resistive exercise, stretching, and incrementally increasing aerobic activity are the key components of effective tendon rehabilitation. Since the goal of rehabilitation is to align the fibrous collagen structures along the patterns most structurally beneficial for a particular runner's form, perform activities that simulate the motions of the tendon during your running--so long as they do not exceed the tendon's capacity to resist force. Be sure your doctor provides you light weight training exercises that move the tendon appropriately. Deep water running is another way to keep up aerobic capacity and simulate the movement of training on the roads without adding impact forces to injured tissue.

Bracing and orthotics are sometimes used to help prevent reinjury. Try to correct any abnormalities in your running form that may have contributed to your injury, and closely monitor your intensity and frequency of training in a diary, always heeding painful warning signs. In extreme situations, surgery can remove damaged tissue and repair the remaining tendon structures.

(Textbook of Running Medicine, "Tendinosis and Tendon Injury," 2001, McGraw-Hill, New York, pp. 37-43)