Overuse Tendinosis, Not Tendinitis
Part 1: A New Paradigm for a Difficult Clinical Problem
Karim M. Khan, MD, PhD; Jill L. Cook, B App Sci, PT; Jack E. Taunton, MD; Fiona Bonar, MBBS, BAO
THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 5 - MAY 2021
This is the first of two articles on tendinopathies by Dr Khan and colleagues; the second, on patellar tendinopathy, will appear in a subsequent issue.
In Brief: Overuse tendinopathies are common in primary care. Numerous investigators worldwide have shown that the pathology underlying these conditions is tendinosis or collagen degeneration. This applies equally in the Achilles, patellar, medial and lateral elbow, and rotator cuff tendons. If physicians acknowledge that overuse tendinopathies are due to tendinosis, as distinct from tendinitis, they must modify patient management in at least eight areas. These include adaptation of advice given when counseling, interaction with the physical therapist and athletic trainer, interpretation of imaging, choice of conservative management, and consideration of whether surgery is an option.
Physicians in primary care, sports medicine, and orthopedics see patients with overuse tendon conditions nearly every day. Tendon conditions are not restricted to competitive athletes but affect recreational sports participants and many working people, particularly those doing manual labor (1). Unfortunately, these disorders are not only common, they can also be recalcitrant to treatment.
One factor that may interfere with optimal treatment is that common tendinopathies may be mislabeled as tendinitis. Advances in the understanding of tendon pathology indicate that conditions that have been traditionally labeled as Achilles tendinitis, patellar tendinitis, lateral epicondylitis, and rotator cuff tendinitis are in fact tendinosis. An increasing body of evidence supports the notion that these overuse tendon conditions do not involve inflammation.
If this is correct, then the traditional approach to treating tendinopathies as an inflammatory "tendinitis" is likely flawed. The recommendations presented here reflect the current scientific data and will help physicians avoid common misconceptions about tendinopathies and their management (table 1) (2-11).
Tendinosis: A Noninflammatory Disorder
Pathology. The pathology of the major tendinopathies has been well described and is based on examination of surgical specimens. In studies of the Achilles (11), patellar (12), lateral elbow (9,13), medial elbow (14), and rotator cuff tendons (15), tissue appeared remarkably consistent. Macroscopically, abnormal tissue examined at surgery shows the tendon to be dull-appearing, slightly brown, and soft. Normal tendon tissue is white, glistening, and firm.
When examined under a light microscope, abnormal tendon from patients with chronic tendinopathies differs from normal tendon in several key ways. It has a loss of collagen continuity (figure 1) and an increase in ground substance, vascularity, and cellularity (figure 2: not shown). Cellularity results from the presence of fibroblasts and myofibroblasts (figure 3: not shown), not inflammatory cells. Thus, in patients who have chronic overuse tendinopathies, inflammatory cells are absent.
Tendinosis vs tendinitis. Key features of tendinosis are described in table 2. Tendinitis is a rather rare condition but may occur occasionally in the Achilles tendon in conjunction with a primary tendinosis. Paratenonitis, one of the disorders in the differential diagnosis, is a condition of inflammation of the outer layer of the tendon (paratenon) alone, whether or not the paratenon is lined by synovium. It is commonly associated with intratendinous degeneration (16) and produces the "crepitus" that is easily felt in some cases of Achilles paratenonitis. Unfortunately, distinguishing tendinosis from the rare tendinitis is difficult clinically. But because tendinosis is far more likely, our advice is to treat patients initially as if tendinosis were the diagnosis.
Tendinosis as a concept. Although recent research has clearly demonstrated the presence of tendinosis in chronically injured tendon tissue, this is not a new discovery (17). The term tendinosis was first used by German researchers in the 1940s; the term's recent usage results from Puddu et al (18) and Nirschl and Pettrone (9). Writing about tendinopathies in 120216, Perugia et al (19) noted the "remarkable discrepancy between the terminology generally adopted for these conditions (which are obviously inflammatory since the ending 'itis' is used) and their histopathologic substratum, which is largely degenerative."
Thus, physicians must shift their perspective and acknowledge that tendinosis is the pathology being treated in most cases and that treatment needs to combat collagen breakdown rather than inflammation. Tendinosis may require a reasonable period of relative rest and attention to strengthening with the aim of first breaking the tendinosis cycle. Once this is done, the patient uses modalities that optimize collagen production and maturation so that the tendon achieves the necessary tensile strength for normal function.
Clinical Significance of the Diagnosis of Tendinosis
If we accept that a patient with overuse tendinopathy has an injury that is due to collagen degeneration, then the diagnosis has repercussions (table 3) on at least eight aspects of our practice.
1. Imaging. Tendinopathies are very well visualized with both magnetic resonance imaging (MRI) and diagnostic ultrasound (2). Histopathologic studies prove that the characteristic imaging appearances (see figure 1) are due to tendinosis (12,20,21). We use MRI to confirm our clinical diagnosis and to demonstrate to the patient that in tendinosis, tendon collagen has lost continuity.
2. Patient education. The physician should take the time to explain and illustrate the pathology of tendinosis, especially since textbooks and Web sites have yet to embrace this pathology and its clinical implications. We find that patients with chronic tendinopathy need no convincing of the veracity of tendinosis. They are generally relieved to find a scientific rationale behind their prolonged symptoms. Patients who have symptoms of short duration but are still able to "warm up" the injury and engage in sports are the ones who need the most education. They are likely to try to continue playing without undergoing appropriate treatment, and thus worsen the tendinosis.
3. Biomechanical deloading. Because tendinosis results from collagen degeneration and, generally, mechanical overload, it is vital that the physician establish why this occurred. Training errors are a common cause (22), but in some instances a more subtle mechanism underlies tendinosis. Thus, it is important to assess any equipment being used (eg, running shoes, tennis racket), examine movement biomechanics (eg, running, throwing motion, stroke pattern), and diagnose and treat any muscle imbalances (23). The details of biomechanical correction are outside the scope of this paper, but their importance cannot be overemphasized in treatment.
4. Anti-inflammatory strategies. Common strategies to reduce inflammation include cryotherapy, electrotherapeutic modalities, nonsteroidal anti-inflammatory drugs (NSAIDs), and corticosteroid injections.
Patients with tendinosis may benefit from cryotherapy because ice has a vasoconstrictive role, and abnormal neovascularization is a feature of the pathology (see figure 2A: not shown). Because a strong clinical impression exists that icing is helpful in tendinopathies, this modality should not be discarded.
Physical therapies that purport to reduce inflammation would not help treat tendinosis if that were their only role. Enwemeka and others (24,25), however, have shown that electrotherapy (eg, laser, high-voltage galvanic stimulation) can stimulate collagen synthesis in the laboratory setting. Clearly this effect would be favorable to the treatment of tendinosis.
Almekinders and Temple (26) have published a thorough review of the role of NSAIDs and corticosteroids in treating tendinopathy and found little evidence that they were helpful. It is not known whether the antiprostaglandin action of NSAIDs and cyclooxygenase-2 inhibitors helps or hinders tendon repair through mechanisms other than the pathways associated with inflammation.
The role of corticosteroid injection or iontophoresis in tendinosis remains controversial (27). In brief, because tendinosis is not an inflammatory condition, the same arguments as those for NSAIDs apply. Further, given the known deleterious effect of corticosteroid injection into tendon and inhibition of collagen repair when the drug is injected around tendon, this treatment has lost favor. Astrom (28) found that corticosteroid injection was the only predictor of partial tendon tears in a large series of cases of chronic Achilles tendinosis that eventually required surgery. This being stated, it is clear that in some cases, corticosteroid injection provides short-term but rapid symptom relief.
5. Load-decreasing devices. Because tendinosis results from excessive load on collagen, braces and supports that attenuate load through the tendon may benefit the patient. Braces have gained clinical support to unload the tendon at both the elbow and the knee. Heel lifts unload the Achilles tendon, and orthoses serve to control pronation and whip at both Achilles and patellar tendons. Further research into the efficacy of these devices is required because they have not yet undergone randomized, controlled trials. They do, however, have a solid biomechanical rationale for therapy.
6. Interaction with the physical therapist. It is important that the physical therapist and physician have a similar understanding of the pathology of tendinopathies and a parallel approach to management. When referring a patient for physical therapy, it is essential that both therapist and patient have a realistic time frame for rehabilitation. A randomized, controlled trial of strengthening treatment in Achilles tendinopathy (29) and data from other cases (1) suggest that for patients who first present with short-duration tendon symptoms, return to full sporting competition takes, on average, 2 to 3 months. A patient with chronic symptoms may require 4 to 6 months to achieve a similar outcome. Clearly, these guidelines will vary for individual patients, but they are supported strongly by the literature (1,8).
7. Appropriate strengthening. Eccentric strengthening programs have a long track record of clinical effectiveness (22,29,30), and recent research adds further scientific support (31,32). It is likely that specific eccentric training drills result in tendon strengthening by stimulating mechanoreceptors in tenocytes to produce collagen, and thus help reverse the tendinosis cycle (figure 4: not shown) (33). Collagen production is probably the key cellular phenomenon that determines recovery from tendinosis. Animal experiments have revealed that loading the tendon improves collagen alignment and stimulates collagen cross-linkage formation, both of which improve tensile strength (34). Therefore, the clinical success of tendon strengthening programs has a demonstrable biological basis that is supported by clinical (32) and laboratory evidence (35).
8. Surgery as a last resort. Surgery has been considered the treatment of last resort for tendinopathies, and this certainly applies, if not more so, for a confirmed case of tendinosis. Surgery can be used to excise tissue affected by tendinosis, but surgery has not been proven to stimulate collagen synthesis or maturation. Thus, the tendon that has had surgery requires time for repair and strengthening. Reviews suggest that surgery in tendinosis has a 75% to 85% success rate, and for some tendons this figure may well be a very-best-case estimate (7,8).
Therefore, an important implication of tendinopathy's underlying pathology being tendinosis is that conservative management must progress slowly. If the initial prognosis the patient receives is realistic, it is less likely that the patient will attempt to return to sport prematurely, suffer re-injury, and thus, "fail" conservative management. Because surgical treatment of tendinosis is not without failure, and recovery takes a minimum of 4 to 6 months, this treatment should be reserved for failure of a high-quality program of conservative management.
The New Paradigm
Tendinopathies have provided long-lasting frustration for both patients and physicians, and attributing the pathology to tendinitis rather than tendinosis may have contributed to this problem. Physicians must acknowledge that the cause is most often due to tendinosis, rather than tendinitis, and treat the problem using a fundamentally different paradigm. Advice and suggestions for patients along these lines of clinical thought can help them recover more quickly and avoid surgery.
Dr Khan is a sports physician at the Allan McGavin Sports Medicine Centre at the University of British Columbia. Ms Cook is a physical therapist at the Victorian Institute of Sport, Melbourne, Australia, and a doctoral candidate at Griffiths University in Gold Coast, Queensland, Australia; Dr Taunton is a professor in the department of family medicine and School of Human Kinetics at the University of British Columbia, Vancouver, Canada; and Dr Bonar is a pathologist at Douglass-Hanly Moir Pathology in North Ryde, Australia. Address correspondence to Karim Khan, MD, PhD, School of Human Kinetics, 210 War Memorial Gym, 6081 University Blvd, Vancouver, British Columbia V6T 1Z1; e-mail to [email protected].