It may seem to be a simple diagnosis: tendonitis. Dorland's Medical Dictionary defines tendonitis as "inflammation of tendons and of tendon-muscle attachments." Many physicians and other health care professionals seem to believe that this is a common problem. Both in occupational as well as sports-related injuries, tendonitis is one of the most common diagnoses. Estimates of the Bureau of Labor Statistics (14) indicates that chronic injuries such as tendonitis can account for 48% of reported occupational illnesses. The numbers in sports medicine as similarly impressive. It has been estimated that overuse injuries account for 30-50% of all sports injuries (76). One-fourth of all athletes treated for a knee disorder were diagnosed with tendonitis in a large European sports clinic (52). In tennis players the incidence of elbow tendonitis is as high as 40% (32).
Numerous articles in the sports medicine literature discuss the causes and treatment of tendonitis. Generally they have one central theme when addressing the causes of tendonitis. The discussion centers around microinjuries of tendon tissue as a result of repetitive mechanical load (19). If the injurious effects of the repetitive motion continues to exceed the healing capability of the tendon, a symptomatic tendon injury or tendonitis can develop (45). Often this is thought to be precipitated by other external factors such improper training techniques in athletes or incorrect use of equipment (36). The body responds with an inflammatory reaction to the injury; hence the suffix "itis" (21). Recommended initial treatment is generally focused on anti-inflammatory measures such as the use of anti-inflammatory medication and ice (19,35,66). In addition, flexibility and strengthening exercises of the involved muscle-tendon unit are often used to promote functional healing and prevent recurrence. Finally, significant emphasis has been placed on correction of external factors by improved equipment and changes in training routines for athletes (36).
In this manner, tendonitis may seem to be a benign, self-limiting injury with a rational treatment approach. However, increasing numbers of investigators as well as clinicians have questioned this approach to tendonitis (2,17,69). Both the relation to mechanical load as well as the effects of treatment with anti-inflammatory medication and physical therapy may be more complex. Degenerative rather than inflammatory features of chronic tendon injuries are now clearly recognized. This study was carried out to appraise critically our knowledge of the etiology, diagnosis, and nonsurgical treatment of tendonitis, particularly as it pertains to overuse sports injuries, through an analysis of the existing literature.
MATERIALS AND METHODS
To evaluate the literature on chronic tendon problems, a Medline search of the English literature was performed. The search strategy included several index words since the terminology on this topic can vary significantly. The words tendonitis, repetitive strain injury, tennis elbow, nonsteroidal antiinflammatory drugs (NSAIDs), corticosteroids, and physical therapy were used alone and in combination. The search included the literature from 1966 to May 1996.
Studies addressing the etiology and diagnosis were first evaluated on the basis of their scientific methods. Studies on etiologic factors were considered adequate if the etiologic variables that were being studied were objective and preferably quantifiable. For instance, age, running miles, and flexibility measurements were considered objective and quantifiable whereas undefined training errors and unspecified poor techniques were not considered objective. Reviews and case reports were excluded. Prospective studies were preferred but because of the limited number of prospective studies, studies with retrospective data collection were evaluated.
The design and data collection in the studies on the efficacy of treatment had to allow scientific conclusions. The criteria set forth by Chalmers(16) were used as guidelines. All retrospective treatment studies were excluded from the final analysis. Prospective studies were included if they were randomized, contained a control group, and had an objective outcome variable. The vast majority of studies on treatment outcome used visual analog pain scales(VAS) at the main outcome variable. Since the reliability of VAS has been documented(33,80) and few other objective measurements are possible in chronic tendon injuries, this was accepted as a objective measure of outcome. A meta-analysis of the prospective studies was not possible because of the large variability in inclusion criteria, medication use, and follow-up
The initial search yielded 2326 articles in which diagnosis, etiology, and treatment of tendonitis was addressed in some form. Based on their main focus the articles were subdivided into these categories: pathologic diagnosis, etiology, treatment by correction of extrinsic factors or intrinsic factors, and anti-inflammatory treatment.
Diagnosis. A review of the literature shows clearly that many different terms are used to describe a similar problem, namely, chronic tendon injuries. In describing occupational injuries, many authors avoid patho-anatomic diagnoses by using the descriptive terms: cumulative trauma disorder or CTD, repetitive strain injury or RSI (4), and repetitive motion injuries or overuse injuries. In the sports medicine related literature more specific diagnoses are generally used. Tendonitis, tenosynovitis, peritendinitis, paratenonitis, tendinosis, and tendinopathy are pathoanatomic terms that are used and directly point to a pathologic process in or around the tendon.
Fourteen human studies were identified that contained as their main focus an investigation of the pathology in chronic tendon injuries. These human studies largely depend on biopsied material at the time of surgery for chronic tendonitis resistant to nonoperative treatment or for tendon ruptures. The overwhelming majority of these studies show a degenerative tendon lesion without a inflammatory component (see Table 1). None of these studies presented objective evidence of inflammatory changes within the tendon itself.
Tenosynovitis, peritendinitis, and paratenonitis indicate a inflammatory disorder of tissues surrounding the tendon such as the tendon sheath. In mechanical overuse injuries to the tendon, some evidence was found to support its use as a distinct entity. In most cases this seems to result from a repetitive friction of the tendon and its sheath. Experimentally Backman (9) was able to produce this problem with repetitive motion of rabbit Achilles tendons. In clinical studies a similar problem has been described in the Achilles peritendinitis(55,56). DeQuervain's disease at the wrist (10) and iliotibial band friction syndrome at the knee (75) appear to be similar problems although pathologic studies documenting inflammatory changes are not available.
Tendonitis denotes an inflammatory problem in the tendon tissue itself. As mentioned before, no studies could be found that clearly support this as an entity in tendon injuries resulting from repetitive load. In Blackman's model (9) inflammation within the tendon was virtually absent. Zamora (88), in an overload model of the rat plantaris tendon, failed to show the presence of inflammatory cells.
Tendinosis is a diagnosis that gradually is used more often in the research literature as well as clinical practice. The suffix "osis" is indicative of a degenerative process rather than a inflammatory disorder. As mentioned before this appears to be a more appropriate pathophysiologic description for many of the chronic tendon disorders found in athletes. Involvement of the patellar tendon or jumper's knee, Achilles tendon, common wrist extensors or tennis elbow, and rotator cuff tendon are consistent with tendinosis. Since it is not clear that these disorders are purely degenerative in nature, some authors prefer the diagnosis of tendinopathy.
Extrinsic or intrinsic etiology. Classically chronic tendon injuries are classified as overuse injuries. Many articles in the literature elude to the effects of overuse as a result of excessive training intensity and duration (32,47,51,59). This is often mentioned in conjunction with training errors, inappropriate shoe wear, and anatomic predisposition resulting from inflexibility, weakness, and/or malposition(19,34,36,47). All these factors are thought to play a role in the etiology of chronic tendon injuries. An evaluation of the published studies, however, reveal that very few controlled studies on this issue are available. The majority of the investigations study patients that present with a chronic tendon injury to a physician without including a control group (19,34,36). In addition, most studies are retrospective (31,48,53,65) and difficult to interpret.
Few studies have actually focused on the role of overuse in the development of chronic tendon injuries. Jozsa et al. (41) found that 40.8% of Achilles tendon ruptures were not directly sports related. Similarly, pathologic changes in the rotator cuff tendons have been found in a significant portion of the asymptomatic or nonathletic population (18,81). On the other hand, Lysholm et al. (59) found a moderate relation between running mileage and injuries in one of the few prospective studies on this issue. Retrospectively, Gruchow (32) was able to correlate increased playing time with a higher incidence of tennis elbow. In the military, decreased physical activity before more intense military training seems a consistent risk factor for new injuries (38,77). Unfortunately the military studies tend to include not only chronic tendon injuries but also other musculoskeletal injuries such as stress fractures.
Many studies also suggest that intrinsic factors may play a significant etiologic role in these injuries. One of the most obvious factors is age. Virtually all investigations that study age as a variable reveal that chronic tendon injuries are significantly more common in aging athletes (32,43,50,54). The peak incidence appears to be between age 30 and 50, depending on the tendon involved.
The vascular supply of frequently injured tendons has been the subject of many studies. Classic articles by Codman (20) and Rathburn (73), later confirmed by others (15,28,57,60), suggested that decreased vascularity predisposed the supraspinatus tendon to injury. This concept has been questioned with studies using different techniques (6,8,12). Both in the supraspinatus, as well as Achilles tendon, increased vascularity was noted in patients who were already symptomatic using laser Doppler flowmetry. No prospective studies on the relation between vascular supply and tendon injury were found.
Anatomical variation such as differences in alignment and range of motion could theoretically predispose a tendon to injury in athletes by placing increased mechanical stress on certain tendons. Most studies on this issue are retrospective in nature (48,53,65). Cause and effect are difficult to determine in these retrospective studies.
Strength deficits or imbalances are often mentioned as an etiologic factors in chronic tendon injuries. Stanish et al. (83) have theorized that many tendon injuries occur during eccentric contractions of the involved muscle-tendon unit. This appears quite plausible and is confirmed by anecdotal observations such as the relative absence of these injuries in a sport like cycling which largely involves concentric work only. However, the conclusion that strength deficits or imbalances, eccentric or otherwise, are a causative factors has not been shown in any controlled study. Again, retrospective studies on this issue are impossible to interpret since the differences in strength could be a result of the injury and not the cause (30,46).
There are several prospective studies on flexibility and musculoskeletal injuries in general. There may to be a trend toward increased injuries with decreased or even increased flexibility although tendon injuries have not been specifically studied (38). Others have failed to find a relation between flexibility and musculoskeletal injuries (49).
Treatment by correcting extrinsic factors. Extrinsic factors such as overuse, training errors, and inappropriate equipment are often considered to be etiologic factors in chronic tendon injuries. Relative rest and change in training routines and equipment often are recommended as initial treatment. Whether relative rest is an absolute necessity is not clear. No studies were found that investigate the effects of decreased activity or change in training routines in a controlled manner.
Equipment changes are also frequently used. The most studied pieces of equipment are the shoes and orthotic inserts for the shoes. The use of appropriate athletic shoes in military recruits decreased foot and ankle injuries but did not decrease the overall incidence of overuse injuries in the military when compared with standard boots (27). Shock absorbing heel inserts also have been shown to decrease soreness and stress fractures although tendon injuries have not been studied separately (25,67). MacLellan (63) also saw improvement with heel inserts in his patients with Achilles tendonitis, but he did not include a control group. Lowdon (62) included a control group and found no effect from heel inserts. Studies on the clinical effects of custom molded orthotics are difficult to interpret. Although the authors generally report good results in the majority of their patients, they do not include an adequate control group, which does not allow a scientific evaluation of their efficacy (24,82).
Treatment by correcting intrinsic factors. Physical therapy with exercise therapy seems to be accepted as one of the mainstays of treatment for chronic tendon injuries. Exercise may influence strength and flexibility, whereas other intrinsic factors such as age and vascular supply are obviously more difficult to influence. Seventeen studies on physical therapy for chronic tendon problems are reported in the English literature. Three of the seventeen were prospective in nature and had a control group that allowed comparison of the results. Only Brox (13) and Lee (58) report improved results with physical therapy in a controlled study. Brox found improvements in supraspinatus tendonitis with physical therapy compared with a laser placebo. Lee's study reported improved range of motion with physical therapy in shoulder tendonitis, but the overall clinical results were not reported. Jensen (37) reports the strength gains with eccentric strengthening in patellar tendonitis but does not include the clinical results. A frequently quoted prospective study by Stanish (83) suggests a good result from eccentric strengthening; however, it lacks a control group.
Anti-inflammatory treatment. Since an inflammatory component in tendonitis is assumed by many physicians, anti-inflammatory drugs are still commonly used. Oral nonsteroidal anti-inflammatory drugs (NSAIDs) are usually prescribed for this purpose. Thirty-two studies in the English literature have been published regarding the use of NSAIDs in chronic tendon injuries. Nine studies were both prospective and contained a placebo group (see Table 2). Five of these nine studies showed improved pain scores at final follow-up in the patients using an NSAID. However, the maximum follow-up in these studies ranged from 7 to 28 d.
Corticosteroids are known for their potent anti-inflammatory action. Therefore, they are used mainly as an injectable medication in and around chronic tendon injuries. Twenty-three studies were found on the efficacy of a local injection of a corticosteroid preparation. Eight of the twenty-three studies were prospective and judged to have an adequate control group (see Table 3). Follow-up ranged from 2 to 12 wk. Five of these eight failed to shown a clear difference at follow-up compared with placebo or an oral NSAID. Many authors did notice an early significant improvement with steroids, but recurrences were common.
This literature review on chronic tendon injuries confirmed the high level of interest in the cause, diagnosis, and treatment of chronic tendon injuries. Numerous articles address these issues. However, once these articles are measured against scientific standards, it becomes clear that our knowledge regarding these chronic tendon problems is based largely on clinical observations that have not been verified by well-controlled studies in many cases.
There is little evidence to suggest that tendonitis in the pathoanatomic sense is a distinct entity. However, both peritendinitis and tendonosis have been seen in basic science and human biopsy studies. It could be argued that the biopsy studies represent the endstage of a nonhealing tendon injury. It is possible that the injury goes through an early inflammatory phase. This may be followed by healing or in some cases by a failure to heal with subsequent degenerative changes. Similarly, it is possible that the inflammatory processes in tendonitis do not exhibit all the classic characteristics as first described by Virchow; therefore classic inflammatory changes may not be apparent on standard histological slides. However, until some scientific evidence is found that supports the last two theories, it seems appropriate to base our conclusions on the findings that have been presented in the literature thus far. This means that there is little evidence to support the concept of tendonitis in the patho-anatomic sense as a repetitive load induced tendon injury. It is likely that repetitive load in itself can induce symptoms. However, we do not know whether this is likely to result in tendonitis, tenosynovitis, tendonosis, stress fractures, or muscle injuries. We are need better data on the pathophysiologic changes in and around the tendon, particularly in the early phase of the problem. This will allow us to say with more certainty whether tendonitis, tenosynovitis, or tendonosis are truly separate entities.
Overuse, training errors, malignment, flexibility, and strength deficits are recurrent themes in the discussion of the etiology of chronic tendon injuries. With the large number of athletes with chronic tendon injuries who present for medical evaluation, it seems likely that repetitive mechanical load plays a role in these injuries. However, it is unclear to what extent the repetitive mechanical load contributes since many of the pathologic tendon changes are also present in the nonathletic population. The studies that actually investigate the role of overuse or training errors unfortunately often lack a control group. Without data on the entire noninjured athletic population as well as the nonathletic population, it is impossible to make scientific conclusions regarding the effects of overuse, training errors, and anatomic predispositions. Similarly, strength and flexibility deficits have not been conclusively documented as predisposing factors since they are largely investigated in retrospective studies. Retrospective studies may identify a potential factor; however, they cannot conclusively determine whether the change in strength or flexibility is the cause or the effect of the injury. Intrinsic and extrinsic etiologic factors need to be studied in a prospective manner.
Mechanical overload does not seem the only factor explaining these problems and may even be merely a "permissive" factor allowing the tendon problem to become symptomatic. Age and vascular supply cannot be discounted a potential factors in the development of these injuries. Although not conclusively, they have been correlated with increased likelihood on chronic tendon injuries
The studies on the efficacy of treatment do not uniformly support the premise that currently used treatment methods significantly change the natural history of these problems. Relative rest or decreased activities are uniformly recommended in the treatment of these injuries. Regardless, whether the sports activity actually caused the injury or was merely an permissive factor, relative rest should improve the symptoms and may allow any intrinsic healing to proceed. Theoretically it is possible that athletes who are injured and fail to change their activity level can still recover from their injury at the same rate. Judging from the number of injured athletes that present for medical evaluation and treatment, however, it seems reasonable to assume that many cannot manage their injuries without a decrease in activities.
The use of exercise therapy and its effects is poorly documented. Although theoretically beneficial, the effects of a flexibility and strengthening program are uncertain. Studies on the use of oral NSAIDs indicate some pain relief from these drugs; however, actual improvement in the healing process has not been studied. With the short follow-up period in the vast majority of NSAID studies, it may be impossible to conclude that the injury is actually healed. Most studies indicate that the full recovery from chronic tendon injuries can take several months (2). Therefore, it remains to be determined whether NSAIDs actually change the natural history or whether they merely have some analgesic action in these injuries. Review of the literature on injections of steroids indicates some early pain relief. Again, the beneficial effects of steroids on the final outcome remains uncertain since recurrences seem common. Long-term prospective studies with well-defined inclusion criteria can answer these questions more conclusively.
It could also be argued that most treatment studies suggest that current treatment methods do not place the patient at any significant risk. The risk of injury with physical therapy appears small, and short courses of NSAIDs in the relatively healthy population have not been shown to result in side effects frequently. Corticosteroid injections have been associated with tendon ruptures; however, the exact relation between steroid injection and rupture remains controversial. The majority of the studies reported here did not mention any significant complications with their treatment. The main risk of the current treatment methods may the economical costs to society. The recommended rest, equipment changes, physical therapy, and medication can result in a significant financial cost. Exact data on the total cost to our society are not available. Finally, the plethora of treatment recommendations in the literature may result in a false sense of security by health care professionals who may feel that these issues have been well studied. While it may be satisfactory to continue using current methods of treatment for these problems, we must also recognize that without further scientific evidence for their efficacy we must continue looking for other answers. A analysis of the current state of knowledge indicates that there are more questions than answers in chronic tendon problems.
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