Achilles tendinosis is a condition marked by degeneration of the tissue in the Achilles tendon at the cellular level. The Achilles tendon, the thickest and strongest in the human body, is located in the back of the lower leg and serves to attach three muscles in the lower leg (the plantaris, soleus, and gastrocnemius muscles) to the calcaneus, or heel bone. The Achilles tendon is also known as the calcaneal tendon. It is about six inches long in adult humans, measuring from its beginning near the middle of the calf to its point of insertion in the calcaneus. Because of the tendon's importance in the motions of walking and running, injury to the tendon or degeneration of its tissue can lead to pain, stiffness, and gait impairments.
The term “tendinopathy” is frequently used to refer to several different categories of Achilles tendon injuries. The first is paratenonitis, a condition marked by inflammation of the paratenon, a sheet of fatty tissue that lies between the tendon and its outer sheath. The second is tendinosis itself, and the third is paratenonitis with tendinosis, in which inflammation of the paratenon exists together with degeneration of the tendon.
Achilles tendinosis is a thickening of the tendon resulting from tissue degeneration and is categorized according to the area of the tendon that is affected. Tendinosis that affects the upper portion of the tendon is referred to as midsubstance tendinosis; tendinosis that occurs where the tendon meets the calcaneus is called insertional tendinosis. Tendinosis by itself is usually painless, although when it occurs together with paratenonitis, the patient will usually experience pain while walking, running, or jumping.
Tendinosis is characterized on the cellular level by damage to collagen, the basic structural protein of connective tissue. Examination of the tissue of a tendon affected by tendinosis will reveal the presence of collagen fibrils that are not in the correct parallel formation or are not uniform in length or diameter. Abnormally shaped tenocytes (fibroblasts in the tendon that produce collagen) will be present, along with neovascularization (an increased number of new blood vessels) and an increased amount of ground substance (a gel-like watery material surrounding the cells). There will, however, be no increase in the number of inflammatory cells. Externally, the only sign of tendinosis is usually a nodule or lump that can be felt in the tendon and that moves with the tendon as the patient's ankle is moved through its range of motion. There may be some tenderness in the area over the nodule, but no redness or other signs of inflammation.
Risk factors for Achilles tendinosis include:
Achilles tendinosis is one of the most common reasons for visits to a primary care physician as well as a sports medicine specialist; in fact, 30% of all consultations with a sports physician are related to disorders of the Achilles tendon. People who are inactive can develop Achilles tendinosis, although the disorder is more common in athletes. According to the American Physical Therapy Association (APTA), 24% of athletes will develop Achilles tendinosis, and 50% of runners will experience pain in the tendon at some point in their running careers. Other sources state that 9% of dancers, 5% of gymnasts, and 2% of tennis players are diagnosed with Achilles tendinosis. It is thought that the incidence of Achilles tendinosis is rising in the general American population because more adults are participating in recreational running or in sports that require jumping or pivoting motions for longer periods of time than was the case in previous generations.
Adult males are more susceptible to Achilles tendinosis than females; as of 2016, 89% of cases occur in males. In terms of age, most cases of Achilles tendinosis are diagnosed in adults between 30 and 50 years of age. As far as is known, the disorder is equally common in all racial and ethnic groups.
The causes of Achilles tendinosis are complex and overlap with the causes of paratenonitis. They may include a combination of factors:
In terms of symptoms, patients with Achilles tendinosis by itself may have no pain at all, although there may be some tenderness when the skin over the affected area of the tendon is pressed. The patient may also experience a sense of fullness in the back of the leg or feel a nodule in the tendon when the ankle is moved. If the patient has paratenonitis as well as tendinosis, he or she will usually experience a localized burning sensation during or after exercising. As the paratenonitis progresses, the patient will feel pain at an earlier point during exercise or even at rest.
The diagnosis of Achilles tendinosis may be made by a primary care physician, although many patients are referred to a specialist in sports medicine or a podiatrist (a specialist in disorders of the foot and ankle) for diagnosis.
The office examination begins with taking the patient's history of discomfort in the Achilles tendon, including an account of his or her activities, recent changes in activity level, and whether specific movements of the foot or ankle bring on the discomfort. The doctor will also note the patient's age and weight. He or she may also ask the patient to walk back and forth to evaluate the biomechanics of the patient's gait.
The patient will then be asked to lie prone (flat on the examination table with the chest downward and the back upward) while the doctor palpates the back of the leg for soreness, warmth, loss of muscle tissue, swelling of the sheath over the tendon, the presence of nodules, and any other defects in the Achilles tendon. The examiner will also test the foot and ankle joints for strength and range of motion, and observe the resting position of the forefoot and ankle to check for signs of Blount's disease and other structural abnormalities.
Laboratory tests of blood or urine are not useful in diagnosing Achilles tendinosis, although they may be helpful in diagnosing or monitoring systemic disorders that may have predisposed the patient to tendinosis.
Imaging tests are routinely used to diagnose tendinosis. Plain x-rays are not helpful in diagnosing tendinosis, although they may help to exclude osteoarthritis as the cause of the patient's discomfort. Ultrasound studies can be used to identify some signs of tendinosis. Magnetic resonance imaging (MRI), however, is the preferred diagnostic imaging technique, as it can distinguish between tendinosis and paratenonitis as well as identify tendinosis. When tendinosis is present, degenerative changes will be seen on the MRI, and sometimes small tears in the tendon as well. Paratenonitis will appear on the MRI as increased fluid in and around the tendon; the tendon may also appear to be thickened and fibrotic.
Treatment of Achilles tendinosis (or tendinosis combined with paratenonitis) is aimed at lowering the risk of a ruptured Achilles tendon as well as allowing the tendon itself to heal, as untreated disorders of the Achilles tendon may lead to complete rupture.
The initial treatment of Achilles tendinosis is conservative and noninvasive. It usually includes one or more of the following measures:
Patients with paratenonitis as well as tendinosis may benefit from taking NSAIDs (nonsteroidal antiinflammatory drugs) or other anti-inflammatory medications to treat the inflammation as well as relieve discomfort. Tendinosis by itself, however, does not respond well to NSAIDs. Cortisone injections are no longer recommended for paratenonitis because they increase the risk of tendon rupture.
Acupuncture has been reported to be a useful adjunctive therapy for patients with Achilles tendinosis.
The prognosis for recovery from Achilles tendinosis and paratenonitis is very good, with most patients able to resume their previous level of activity after appropriate therapy; 80% of patients will recover within 12 months. The Achilles tendon is slow to heal, however, and full recovery takes a long time. At one time, doctors thought that tenocytes could not repair the tissues in the Achilles tendon; however, as of 2016, researchers know that the tenocytes actually direct the healing process. Following injury to the tendon, the tenocytes rapidly multiply and begin to secrete collagen to form new tissue at the site of the injury. This cell proliferation and collagen formation can be speeded up by controlled movement of the Achilles tendon under the guidance of a physical therapist. After about six weeks of collagen formation, the tenocytes begin to remodel the new tissue. Tissue remodeling in a healing tendon consists of a phase in which the tissue becomes increasingly fibrous, followed by a phase in which the new collagen fibrils become cross-linked, which stiffens the tendon.
Initial recovery from tendinosis takes between three and six months following conservative therapy. If surgery is required, recovery will take an additional four to six months. In general, patients who exercised regularly or were otherwise active prior to therapy heal more rapidly than those who were sedentary.
The APTA recommends the following measures to prevent chronic injury to or deterioration of the Achilles tendon:
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American College of Sports Medicine (ACSM), 401 West Michigan Street, Indianapolis, IN, United States, 46202-3233, (317) 6379200, Fax: (317) 634-7817, http://acsm.org/ .
American Orthopaedic Foot and Ankle Society (AOFAS), 9400 W. Higgins Road, Suite 220, Rosemont, IL, United States, 60018, (847) 698-4654, (800) 235-4855, .
American Physical Therapy Association (APTA), 1111 North Fairfax Street, Alexandria, VA, United States, 22314-1488, (703) 684-APTA (2782), Fax: (703) 684-7343, (800) 999-2782, http://www.apta.org/ .
Rebecca J. Frey, PhD