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Håkan Alfredson and J Cook
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Abstract
Achilles tendinopathy affects athletes, recreational exercisers and even inactive people. The pathology is not inflammatory; it is a failed healing response. The source of pain in tendinopathy could be related to the neurovascular ingrowth seen in the tendon's response to injury. The treatment of Achilles tendinopathy is primarily conservative with an array of effective treatment options now available to the primary care practitioner. If conservative treatment is not successful, then surgery relieves pain in the majority of cases. Directing a patient through the algorithm presented here will maximise positive treatment outcomes.
Pain in the Achilles tendon is relatively common in recreational exercisers and individuals active in sports.1 Achilles tendon pain has also been reported in inactive individuals.2 It is seen most commonly in the mid‐portion of the tendon, but also occurs at the bone–tendon junction.
Overuse is considered to induce the condition,3 but the aetiology and pathogenesis have not been scientifically clarified. A study on chronic Achilles tendinopathy (342 tendons) showed that physical activity was not correlated with the extent of histopathology, suggesting that physical activity could be more important in provoking the symptoms than being the root cause of pathology.4 The lack of association between activity, pain and structural abnormality has also been reported in other tendons, and pathological changes are seen on imaging in physically active asymptomatic individuals.5
Pathological change in the tendon can manifest clinically as tendon swelling or nodules. It is also clearly visible with standard soft‐tissue imaging techniques. This review focuses on treatment of Achilles mid‐tendon pain; management of rupture, insertional pathology and peritendinopathy are outside the scope of this article.
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Tendon histopathology
The four cornerstones of tendon histopathology are (1) cellular activation and increase in cell numbers, (2) increase in ground substance, (3) collagen disarray and (4) neovascularisation. It is not considered to be a primarily inflammatory condition. Histological evaluation of Achilles tendon biopsies, intratendinous microdialysis6,7 and contemporary molecular biology techniques (cDNA‐arrays, real‐time quantitative PCR) of appropriately prepared biopsy tissue8 all failed to show evidence of prostaglandin‐mediated inflammation.
There are, however, signs of neurogenic inflammation.9 The presence of neuropeptides such as substance P and calcitonin gene‐related peptide indicate that there still might be an inflammation in the tendon.10 Peripheral local noxious stimulation makes peptidergic group IV fibres release peptides from their terminals, starting various pathophysiological processes contributing to neurogenic inflammation.
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Where does the pain come from?
It is well known that the chronic painful Achilles and patellar tendons are difficult to treat, and the pain mechanisms associated with these conditions are not understood. Methods such as the above‐mentioned microdialysis, cDNA‐arrays and PCR, as well as ultrasonography combined with colour Doppler, provide novel and potentially important information about the chronic painful Achilles tendon versus normal Achilles tendon.
Glutamate, a well known neurotransmitter and very potent modulator of pain in the central nervous system, is found in high levels in painful tendons but not in normal tendons.11 In conjunction with the findings of a local neurovascular ingrowth12 and promising results of pilot studies with sclerosing injections, there is now some evidence that the neural pathways associated with tendinopathy could be associated with the neovascularisation. Biopsies taken from an area with tendinosis with neovascularisation showed nerve structures in close relationship with the vessels;12 studies have shown substance P nerves in the vascular wall and calcitonin gene‐related peptide nerves close to the vascular wall.12,13 Also, the neurokinin‐1 receptor, which is known to have a high affinity for substance P, has been found in the vascular wall.14 The findings suggest, for the first time, an explanation for the pain associated with tendinosis. As interference with this neurovascular ingrowth via sclerotherapy (see below) appears to decrease pain, further research appears well justified.
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Diagnosis
A correct clinical diagnosis can often be established solely by clinical examination, especially if the tendon exhibits focal or generalised swelling. If a clinical diagnosis is not clear, ultrasonography or MRI may reveal the pathology within the tendon.15 Although abnormalities detected by imaging are likely to be associated with pain, it is possible that these morphological abnormalities are painless and that pain may be arising from another source. Clinical acumen is important to correlate clinical and imaging examinations.
The first priority of clinical examination is to exclude acute rupture, and the calf squeeze test has excellent validity.16 After demonstrating that the tendon is intact, the examination should aim to provoke tendon pain during tendon‐loading activity. In most patients, simple single‐leg heel raises will be sufficient to cause pain. In more active individuals, however, it may be necessary to ask the patient to hop on the spot, or hop forward, to further load the tendon and reproduce pain. Repetition of the loading test may be necessary in some athletes to fully evaluate the tendon.
It is important to exclude other diagnoses such as posterior ankle impingement, os trigonum syndrome, tenosynovitis or dislocation of the peroneal or other plantar flexor tendons, an accessory soleus muscle, irritation or neuroma of the sural nerve and systemic inflammatory disease. These diagnoses cause pain in and also around the Achilles tendon; true tendon pain is nearly always confined to the tendon itself.
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Imaging
Imaging abnormalities in the tendon include hypoechoic areas seen on ultrasound and areas with increased signal intensity seen on MRI. These areas correspond with areas of altered collagen fibre structure and increased interfibrillar ground substance (proteoglycans and hydrophilic glycosaminoglycans).17,18 Signal intensity on MRI has been associated with the clinical outcome.19 However, the pathology is also found in tendons that appear normal on imaging.20
Colour and power Doppler have recently added a new dimension to standard ultrasound tendon imaging. This imaging demonstrates blood flow in tissues. In the Achilles tendon, blood flow is not detectable in normal tendons but colour Doppler often reveals blood flow in pathological tendons.21 Such blood flow has been linked to greater pain scores, poorer function and longer symptoms in the Achilles tendon,22 compared with control participants who have no visible flow. The association, however, is not absolute.23
The long‐term clinical importance of blood vessels in pathological tendons is not clear. Two longitudinal studies have shown that the addition of colour Doppler at baseline examination did not improve the diagnostic performance of ultrasound19 or indicate a poorer outcome.24
Clinically, imaging should not be the sole guide for clinical decisions; variation in symptoms such as morning stiffness and load pain should direct treatment modification. Studies in many tendons have indicated that clinical outcomes are independent of imaging and change in imaging.19,25,26
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Treatment
Many treatments are offered to patients with painful tendons, but the scientific evidence for most of the conservative and surgical treatments remains sparse. Treatments that have some evidential basis and have been investigated with randomised controlled trials include eccentric exercise, glyceryl trinitrate patches, electrotherapy (microcurrent and microwave), sclerosing injections and non‐steroidal anti‐inflammatory drugs (NSAIDs). Of these, NSAIDs showed little or no effect on outcome, and further discussion of medication has not been included in this review.27,28 There are no randomised or prospective studies that compare different conservative and surgical treatment regimens.
Conservative treatment is recommended as the initial strategy by most authors.29,30 This strategy includes identification and correction of possible aetiological factors, and a symptom‐related approach. Generally, the initial treatment consists of a multifactorial approach that may include a combination of rest (complete or modified activity), medication (NSAIDs, corticosteroids), orthotic treatment (heel lift, change of shoes, corrections of malalignments), stretching and strength training.
If conservative treatment fails, surgical treatment is instituted. It has been a general opinion that in about 25% of patients with chronic painful conditions located in the Achilles tendon, non‐surgical treatment is not successful and surgical treatment is needed.31 For the Achilles tendon, frequency of surgery has been shown to increase with patient's age, duration of symptoms and occurrence of tendinopathic changes.31,32
A treatment algorithm has been constructed to place these treatment options in a clinical reasoning order (fig 11).). This order is appropriate for most individuals with Achilles tendon pain, but may need to vary in special cases such as the elite athlete, the person with acute tendon pain unable to fully bear weight or the older individual who may be unable to complete an exercise‐based programme. The doctor must interpret individual needs and modify the algorithm for each clinical presentation.
Figure 1 Algorithm for treating Achilles tendinopathy. Timeframes are recommended and should be modified as appropriate for individual presentations. CSI, corticosteroid injectio