Patellar tendinopathy (jumper's knee) is a knee injury associated with overuse that is characterized by pain with jumping and landing. This injury affects athletes participating in jumping sports (20). It is an insertional tendinopathy and most commonly affects the proximal patellar tendon. Patellar tendinopathy is not self-limiting; rest from sport may reduce symptoms, but return to training and competition is often accompanied by worsening symptoms (19). Indeed, more than 50% of athletes with this injury were forced to retire from their sport but continue to have pain on climbing stairs when surveyed 15 years later (16), and more than a third of patients presenting to a sports medicine clinic with this injury were unable to return to their sport within 6 months (7). Therefore, it is important to identify treatments that can reduce pain and allow return to sport.
There are relatively few studies on the treatment of patellar tendinopathy. It is rare for people not competing in high-intensity jumping sports, such as volleyball and basketball, to experience this injury; thus, the number of research participants is limited.
We aimed to report the risks and benefits of various treatment approaches for patellar tendinopathy. The review is grounded in evidence-based practice, and the authors draw attention to informative and high-quality studies; however, some recent treatment innovations do not have adequate evidence yet and are described as experimental at best.
A literature search combining the terms patellar, tendinopathy, tendinosis, tendinitis, and jumper's knee, along with spelling variations, was performed in February 2011 using five electronic databases of medical literature (Embase, MEDLINE, Scopus, SPORTDiscus, Web of Science) and was supplemented by the authors' personal libraries. Articles published between 2001 and 2011 were considered because of the small number of studies in this area. Titles and abstracts were reviewed for relevance by one author (J.E.G.) who excluded review articles, case reports, retrospective studies, studies in non-peer-reviewed journals, and articles not published in English. The resulting 32 relevant articles formed the basis of this review.
Published research on each treatment approach was grouped according to study design (case series, case-control, randomized controlled trial (RCT), placebo-controlled RCT) to give an overall view of the literature (Table 1). Study details are summarized, and strengths and weaknesses of the study design are highlighted in Table 2.
This review focuses on changes in pain symptoms after treatment. Only pain scores obtained at the latest follow-up are included. Changes in tendon imaging are beyond the scope of the current review. Where possible, the number of patients in each study rather than the number of tendons studied is reported. If the mean and standard deviation (SD) of outcomes of interest were not reported in the text, they were calculated from graphs or raw data. Typically, the mean and the 95% confidence interval (95% CI) were extracted (GraphClick; Arizona Software) and then converted to mean and SD using the t-distribution. When the median and the 95% CI were given, the mean was assumed to lie in the center of the 95% CI. All scores in the visual analog scale (VAS) are reported as 100 mm. Outcomes are reported as mean ± SD unless otherwise stated.
Where recent high-quality studies exist (i.e., RCTs), earlier lower-quality studies are mentioned only briefly. If no high-quality studies exist on the subject, the best available studies are reviewed. Recent innovations in treatment are given special consideration; if there is little supporting evidence, this is clearly stated.
RCTs that include a placebo group often break allocation concealment after a defined period, either by design or by instruction from the local ethics committee. It is typical for the placebo group to be offered the active treatment and for both groups to be followed up for a further period. In this review, only the results collected before breaking allocation concealment are included.
The included studies cover a range of treatments; detailed information extracted from each publication (Table 2) is synthesized under three main sections: conservative management, injection therapies, and surgery.
Eccentric exercise has been a cornerstone of tendinopathy rehabilitation for more than a decade, and a substantial body of evidence supports its effectiveness. The first RCT investigating eccentric exercise for patellar tendinopathy was by Cannell et al. (4); eccentric drop squats were compared with a knee extension and hamstring curl exercise program and found to be equally effective. The field was revolutionized only a few years later by Purdam et al. (26), who introduced the 25°-decline eccentric squat (Fig.). In a nonrandomized trial, the eccentric decline squat was shown to be superior to the standard eccentric squat (26).
Understanding how best to apply eccentric load when treating patellar tendinopathy is improving. For example, we know that the 25° decline is more likely to produce a clinically relevant improvement in the Victorian Institute of Sport Assessment for patellar tendinopathy (VISA-P) scores (≥20 points) during 12 months compared with traditional drop squats (94% vs 41%) in elite athletes who continue to play (38). We also know that concentric-only decline exercises are not effective (15).
In contrast to its effectiveness during rehabilitation, Visnes et al. (31) showed that the decline squat protocol was not effective during the competitive season in elite athletes with very high levels of tendon loading. This study progressed load by adding weights if the pain was less than 5 of 10 during the exercise. Fewer than half of the athletes were able to add weight, and those who did add weight added an average of only 4 kg. This limited increase in load may explain why the intervention was not effective during the competitive season. The study by Visnes et al. is the only one to report how much weight was added when performing the exercise; we encourage researchers to report this outcome in future studies to improve our understanding of this treatment. The effectiveness of the decline squat was investigated further in a high-quality RCT, which showed that 12 wk of 25°-decline eccentric squats achieved results at 12 months equivalent to the results after open surgery combined with a well-designed rehabilitation program (3).
Although the decline squat is clearly the first-line treatment of choice, outcomes are still less than ideal; Bahr et al. (3) found that only 55% of elite athletes achieved either excellent (return to previous level of sport with no pain) or good (return to previous level of sport with mild or moderate pain) outcomes at 12 months.
Heavy, slow resistance training (double-leg exercises).
An alternative exercise treatment for patellar tendinopathy recently was proposed in which patients performed heavy, slow resistance (HSR) training (squat and leg press) using gym equipment (18). This high-quality RCT randomized 39 patients to 25°-decline squat, corticosteroid injection, or HSR training. At 6 months, patients in both exercise groups achieved outcomes superior to those of the steroid injection group. Because both exercise groups improved an equivalent amount, it is worthwhile exploring the pros and cons of each approach. Patient motivation and exercise compliance are an important consideration. The decline squat is performed twice a day, 7 d·wk−1 for 12 wk, but takes 10 to 15 min each time. In contrast, the resistance training is less demanding, performed once per day, 3 d·wk−1 for 12 wk, but takes 45 min each time (Kongsgaard, M., personal communication, March 2011). Cost and equipment access are another consideration. A decline board is inexpensive and easily transportable for continued treatment during holidays or when on tour with a sporting team. In contrast, HSR requires access to professional gym equipment and professional supervision. The consideration of access to equipment also applies to the study by Frohm et al. (12), which used a barbell supported by steel cables to provide controlled and heavy eccentric loads.
Extracorporeal shock wave therapy.
Extracorporeal shock wave therapy (ESWT) delivers a pressure wave into the affected tissue and is an established treatment for kidney stones (lithotripsy). During recent years, ESWT has been explored as a treatment for a variety of musculoskeletal conditions.
Until recently, ESWT research was dominated by studies of low methodological quality, which universally supported ESWT for treating patellar tendinopathy. This conclusion is challenged by a recent RCT of outstanding quality, which showed no benefit of ESWT compared with placebo ESWT in the treatment of athletes during the competitive season (40). It is virtually impossible to suggest a way in which this study could have been improved - this was a placebo-controlled RCT; it was registered on a trial registry; the project protocol was published; the primary outcome was the VISA-P score; and the analysis was conducted using the intention-to-treat (ITT) approach. Specifically, this study showed no added benefit of ESWT over placebo for the primary outcome (VISA-P score) and most of the secondary outcomes. No differences were detected for pain during activities of daily living, pain during sports, pain during one decline squat, pain during 10 decline squats, pain during 3 single-leg jumps, or pain during triple jump at 1, 12, or 22 wk of follow-up. The only secondary analysis that showed a benefit of ESWT was the 1-wk subjective rating of whether the patients felt their "symptoms had improved and evaluated the treatment as beneficial" (65% vs 32%, P = 0.01) and whether they would "recommend their treatment for this injury to family and friends" (84% vs 52%, P = 0.01). These findings may point to the benefit of ESWT as a temporary pain-relieving modality that may have a place in cases where patients are unable to perform eccentric-based exercises because of severe pain.
These results from the RCT by Zwerver et al. (40) contrast with the results from the RCT by Wang et al. (34), in which 27 patients received 1 or 2 ESWT treatments and 23 patients were provided with usual care. At follow-up of 2 to 3 years, the VISA-P score of the ESWT group (92 ± 10) was significantly greater than that of the control group (41 ± 11) (P < 0.001). A major limitation of this study was that the usual treatment group did not receive treatments consistent with the current understanding of tendinopathy. The patients were managed with nonsteroidal anti-inflammatory drugs (NSAIDs), hot and cold packs, phonophoresis, friction massage, an exercise program (primarily "eccentric stretching" of the patellar tendon and strengthening exercise of the quadriceps and hamstrings), a knee strap, and modification of activity levels. Primary treatment was NSAID and one other modality; when this failed, the patients were given multiple modalities simultaneously. The finding that not 1 of the 24 patients in the usual-care group achieved an excellent outcome rating (average VISA-P score was unchanged from 39 ± 11 to 41 ± 11) suggests that the control treatment was suboptimal, which unfairly biases the study toward showing a benefit of ESWT. Also notable was that the ESWT group rested from sport after treatment (4 to 6 wk for most patients and 8 to 12 wk for those receiving two rounds of ESWT treatments) and then gradually returned to training. The rest and gradual return to sport in the ESWT treatment group might partially explain their better results.
The other studies investigating ESWT for the treatment of patellar tendinopathy were of much lower quality; some lacked a control group (33,39), whereas another was a prospective case series of ESWT in which results were compared with a retrospective review of surgical cases (25). On the whole, these lower-quality studies show benefit from ESWT, but we should remember lessons learned from other areas of tendinopathy research; studies with lower method scores often report higher success rates (r = 0.57, P < 0.01) (5).
Therefore, we can conclude that ESWT treatment delivered during the competitive season is not an effective treatment for patellar tendinopathy, and any short-term gains in pain relief are lost quickly (40). However, some might argue that this study should not sound the death knell for ESWT in the management of patellar tendinopathy because other treatments have been shown to be effective when applied during off-season but not when applied during the competitive season (31).
Low-intensity pulsed ultrasound.
There is good evidence that low-intensity pulsed ultrasound (LIPUS) is not an effective treatment for patellar tendinopathy. As a stand-alone therapy, LIPUS was shown to be inferior to eccentric exercise: 0 of 10 patients rated LIPUS as successful, whereas 10 of 10 patients rated eccentric exercise as successful at 3 months of follow-up (30). When combined with 25°-decline eccentric squats, LIPUS had no benefit over placebo (35).
Deep tissue massage to the quadriceps was recently investigated as a treatment approach for patellar tendinopathy (24). After a single treatment session, substantial reductions in pain experienced during a 30-cm step-down and a squat jump were reported when reassessed immediately after the treatment and 4 wk later; however, the study is limited by the lack of a control group.
A variety of injection therapies have been proposed in the treatment of patellar tendinopathy. These include platelet-rich plasma (PRP), autologous blood, corticosteroids, sclerosing substances (i.e., polidocanol), and hyperosmolar dextrose. Sclerosing injections aim to destroy abnormal blood vessels that are seen with patellar tendinopathy, whereas the other injections aim to stimulate a healing response with the tendon.
PRP delivers a cocktail of growth factors and cytokines to the injured area of the tendon, and this is purported to lead to improved tissue repair and regeneration. The underlying rationale to this treatment has been questioned (8), and the International Olympic Committee consensus statement highlighted the lack of well-designed studies in this area (9). The findings of this review support that conclusion.
The literature search identified two small case series (17,32) and one fundamentally flawed case-control study (10) that investigated PRP injection for the treatment of patellar tendinopathy.
Volpi et al. (32) followed 8 athletes with therapy-resistant patellar tendinopathy for 120 d after a single PRP injection. Return to sport was allowed after 12 wk of structured rehabilitation. Data from only seven of the original eight participants were reported because one underwent surgery before the end of the study. Although VISA-P scores improved from 39 ± 14 to 75 ± 11, P < 0.001, the lack of a control group means we are unable to distinguish improvements due to the PRP injection, the natural history of the condition, the rehabilitation protocol, and the placebo effect. This was the only study of PRP to use the VISA-P score as an outcome measure.
Kon et al. (17) followed 20 male athletes for 6 months with therapy-resistant patellar tendinopathy treated with three PRP injections (separated by 15 d). Athletes were allowed to return to sport 4 wk after the final injection; a rehabilitation program was followed before returning to sport. Although pain outcomes improved as the study progressed, the lack of a control group means that we cannot separate effects due to the injections, the rehabilitation protocol, the natural history of the condition, and the placebo effect. An insightful observation was that patients not compliant with the postinjection rehabilitation protocol had the worst results (Tegner score = 3.2 ± 0.5 vs 7.7 ± 1.6, P < 0.0005; EuroQol-VAS = 59 ± 17 vs 85 ± 12 mm, P = 0.005). This finding highlights that rehabilitation is at least as important as, if not more important than, the substance that is injected into the tendon.
The case-control study of male athletes by Filardo et al. (10), unfortunately, was flawed fundamentally in its design and analysis. One group received three PRP injections plus physiotherapy; the control group received identical treatment but without the injection. Results were reported at 6 months of follow-up. The first serious flaw was that the inclusion criteria differed for the two groups: the PRP group had failed prior treatments, whereas the control group had not failed prior treatments. This is a very serious limitation for a case-control study.
The second issue follows the first and relates to baseline differences between the groups owing to the different inclusion criteria. The Tegner activity score (0 to 10) measures sporting participation (scores 5 to 10) or physical exertion at work (scores 0 to 4) that is possible in the context of an injured knee. At baseline, the Tegner score was 3.7 ± 1.8 in the PRP group and 5.3 ± 2.0 in the control group. An independent t-test calculation shows that the groups are significantly different (P = 0.027). However, the authors report that "the groups were matched for sex, age, and sport activity level." It is possible that they were referring to sport activity level before developing patellar tendinopathy, which was 7.5 ± 1.6 in the PRP group and 7.8 ± 1.3 in the control group (P = 0.570).
The issue of baseline differences is compounded when outcomes are reported as percentage improvement from baseline. Working from a lower baseline, percentage improvement is a misleading and inappropriate way to report the outcomes for the PRP group. In fact, after treatment, the control group actually had slightly higher Tegner scores (6.8 ± 1.6) than the PRP group (6.6 ± 2.4)! Despite this, the authors iterate their finding of greater percentage improvement several times.
The fourth and arguably the most misleading issue is the abstract. The abstract fails to clearly state the main outcomes of the study - that there were no differences between the PRP and control groups for pain, health-related quality of life, or patient satisfaction. Instead, it is reported that "the clinical results are encouraging" and that "PRP injections have the potential to promote the achievement of a satisfactory clinical outcome." These statements do not reflect the results of the study.
It should also be mentioned that PRP has been associated with mild adverse outcomes. Kon et al. (17) reported one case of marked pain after injection lasting for 3 wk. The other subjects in the study reported an average pain score of 6 of 10 after injection, which lasted for a few days. In conclusion, there is no high-quality evidence that PRP injection is helpful in patellar tendinopathy, and the treatment is best described as unproven and experimental at this stage.
Sclerosing injections are directed under Doppler ultrasound guidance and delivered in small volumes to blood vessels just before their entry into the tendon. The theory is that destroying the blood vessels with sclerosing injections will also destroy accompanying nerves and, in doing so, cure the pain associated with patellar tendinopathy.
Alfredson and Ohberg (2) piloted this treatment where 15 athletes had decreased pain at 6 months (VAS score decreased from 80 ± 14 mm at baseline to 19 ± 25 mm, P < 0.001). Next, Hoksrud et al. (13) conducted a well-designed 4-month RCT of sclerosing injections versus placebo injections in 33 elite jumping athletes. There were no differences between groups (P = 0.052) at 4 months of follow-up. However, a significant increase in VISA-P scores was seen in the sclerosing group (54 ± 15 vs 65 ± ? mm, P = 0.01) but not in the placebo group (53 ± 12 vs 54 ± ? mm, P = 0.86). (Question mark indicates we were unable to calculate this based on the data provided in the published article).
Very recently, Willberg et al. (36) compared sclerosing injections to a new treatment of ultrasound-guided arthroscopic shaving (37) of the paratendinous tissue containing abnormal blood vessels in a randomized trial. They demonstrated better outcomes from arthroscopic shaving (P = 0.001); VAS score for pain improved from 69 ± 17 to 41 ± 29 mm after sclerosing injections compared with improvement from 77 ± 14 to 13 ± 19 mm after arthroscopic shaving.
The available evidence on the effectiveness of sclerosing injections is mixed. Whereas the primary analysis of VISA-P scores in the study by Hoksrud et al. (13) showed no effect (P = 0.052) at 4 months, secondary analyses supported the effectiveness of this treatment. Furthermore, although the study by Willberg et al. (36) showed that arthroscopic shaving was more effective than sclerosing injections, this treatment (sclerosing injections) has yet to be compared with other approaches such as open surgery or other injection therapies. Note that it may not be appropriate to compare this treatment to conservative therapies because patients receiving this treatment have usually already failed to respond to conservative therapy.
Two studies in this review used steroid injections. Steroid injection was compared with placebo injection in an RCT of 24 athletes who had failed to respond to conservative treatments (11). Injections were delivered to either side of the affected tendon under ultrasound guidance. The athletes were advised to rest for 4 d after each injection and then gradually resume training. All athletes had a second injection on day 7, and some also had a third injection on day 21. Although this placebo-controlled RCT continued for 26 wk, we can report only results before allocation concealment was broken and the placebo group crossed over to steroid injections on day 21. Therefore, 7-d results are presented. Pain on walking, an insensitive outcome measure for patellar tendinopathy, assessed with a 0-to-10 numerical rating scale (NRS) decreased from 2.9 to 1.7 after 7 d. No ruptures were reported, although steroid-induced atrophy (of the subcutaneous tissues) was noted in 9 of the 24 athletes.
Kongsgaard et al. (18) used steroid injection as one of the three treatments studied in their RCT of 39 male athletes. Similar to the previous study, the injections were guided by ultrasound; however, in this case, they were delivered into the paratendinous tissue posterior to the affected patellar tendon. A total of 2 injections were given: the first on day 0 and the second on day 28. At 6 months of follow-up, outcomes in the injection group were inferior to outcomes in the other 2 groups (P < 0.05). The VISA-P score was unchanged from 64 ± 14 to 64 ± 22 in the steroid injection group; was increased from 53 ± 13 to 76 ± 16 in the 25°-decline eccentric squat group; and was increased from 56 ± 13 to 86 ± 12 in the HSR training group.
In conclusion, there is evidence that steroid injections delivered adjacent to the patellar tendon under ultrasound guidance reduce walking pain after 1 wk but are significantly inferior to exercise-based interventions at 6 months of follow-up. On the basis of this evidence, they cannot be recommended for the treatment of patellar tendinopathy.
Autologous blood and dry needling.
James et al. (14) presented a case series of 44 patients who received 2 sessions of ultrasound-guided dry needling and autologous blood injection separated by 4 wk. A rehabilitation program was prescribed (3 to 6 months of eccentric decline squats combined with quadriceps, hamstring, and calf stretches), and sporting activity was ceased after the first treatment. Patients were advised to expect a 3-month break before returning to sport. The VISA-P score increased from 40 ± 16 to 74 ± 18, P < 0.001. Despite the encouraging results, it is not possible to say how much of the improvement was due to the injection, the rest from sport, the structured eccentric exercise program, or the placebo effect.
A recent case series by Ryan et al. (28) investigated the effect of hyperosmolar dextrose injections delivered inside the tendon under ultrasound guidance in 45 patients who had not responded to previous treatments. Injections were repeated every 6 wk until symptoms resolved or ceased to respond to the injection; the median number of injections was 4 (range = 2 to 8). Patients were advised to avoid heavy loading for 1 wk after injections, and outcomes were measured 45 wk after the first injection. VAS score for pain during sport decreased from 78 ± 16 to 39 ± 26 mm, P < 0.01; however, because there was no control, the benefits attributable to injections, natural recovery, and placebo cannot be distinguished.
Open surgical techniques include removal of the tip of the patella (23), tenotomy to remove abnormal tissue with (29) or without multiple longitudinal incisions (3), removal of abnormal tissue, and fat pad detachment from the posterior surface of the patellar tendon (1). Articles in this group were generally of low quality (case series), which usually reported good outcomes; the exception to this study design was the study by Bahr et al. (3).
Bahr et al. (3) conducted an extremely well designed RCT comparing open surgery to 25°-decline eccentric squats among 35 athletes with severe patellar tendinopathy (VISA-P score ∼ 30) who were willing to undergo surgical intervention. Eccentric squats on a 25°-decline board were performed for 12 wk, adding extra weight to achieve pain levels of 4 to 5 of 10. Athletes rested from sport for 8 wk but were allowed to begin to cycle, jog, and exercise in water after 4 wk if the activity could be performed without pain. Surgery was a full-thickness wedge excision, with the base of the wedge at the patella. No intervention was directed to the patella itself. Patients then followed an extremely well designed rehabilitation program, which included 25°-decline eccentric squats from week 6 onward. In the surgery group, extra weight was not added unless squats could be performed without pain. The 12-month ITT analysis showed no difference between the groups (P = 0.87); the VISA-P score of the eccentric group increased from 29 ± 16 to 66 ± 29, and the VISA-P score of the surgical group increased from 31 ± 15 to 73 ± 20.
Arthroscopic surgical techniques include arthroscopic shaving (36,37), release of posterior paratenon and bone denervation (22), and resection of the lower pole of the patella (21). All studies bar one were case series.
Willberg et al. (36) randomized 45 patients into two groups, to receive sclerosing injections or to undergo a new arthroscopic shaving technique (37) that removes the area with abnormal blood vessels. Patients in both groups were allowed to bear weight fully immediately after treatment. There was no specific rehabilitation protocol, and patients were advised that, after 2 wk, they could progress gradually to full tendon loading. At 12 months of follow-up, the shaving group had better outcomes (P < 0.001). VAS score for pain improved from 69 ± 17 to 41 ± 29 mm in the injections group and from 77 ± 14 to 13 ± 19 mm in the shaving group.
The quality of studies on the treatment of patellar tendinopathy varies greatly. The most informative study design is the RCT; this can be used to compare several competing treatment approaches or to compare one treatment to an appropriate placebo treatment. In the context of patellar tendinopathy, injection therapies, ESWT, and LIPUS are suitable to be studied using a placebo control. The key here is that it is possible to conceal from the clinician, the patient, and the outcome assessor the therapy that the patient has received. This contrasts with exercise interventions and surgical interventions, in which it is not as easy to conceal from the patient or the treating clinician (physician, physical therapist, or surgeon) the therapy that the patient has received. For these treatment approaches, the ideal study design is an RCT in which the outcome assessor is independent of the treating clinician and is unaware of group allocation.
A wealth of evidence supports the use of 25°-decline eccentric squats in managing patellar tendinopathy (3,12,15,26,31,38). Several new approaches of applying eccentric load (12,27) or HSR training (18) seem promising.
Sclerosing injections seem to be beneficial (2,13), but the newly developed arthroscopic shaving approach technique produced even better results (37). Open surgery combined with excellent rehabilitation produces results equivalent to the decline squat protocol, although neither approach produces outstanding results (3).
Treatments that do not lead to long-term improvement, and therefore cannot be recommended, include ESWT (40), LIPUS (35), and steroid injections (18,30). Other treatments lack high-quality evidence to support their effectiveness (hyperosmolar dextrose injection (28), autologous blood injection (14), and deep tissue massage (24)). At present, the evidence in support of PRP injections is characterized by serious methodological flaws (e.g., Filardo et al. (10)), and this intervention cannot be recommended on the basis of this evidence.
This review focused on the treatment methods for patellar tendinopathy. However, it is unknown whether these treatments are more effective in the hands of experienced clinicians than in the hands of less-experienced clinicians. By its nature, research aims to simplify and answer specific questions; the clinical environment is not always so simple. Both correct differential diagnosis and treatment of patellar tendinopathy require knowledge, training, and experience. Consider a patient with patellar tendinopathy who also presents with significant quadriceps atrophy and dysfunctional lower limb kinematics; do these issues need to be addressed before introducing an eccentric training program? The literature does not guide the clinician in making these decisions, and clinical decision making and experience must be the foundation in these scenarios. Readers seeking a clinical perspective on the management of patellar tendinopathy are directed to a recent publication by Kountouris and Cook (19). Patient parameters also must form part of the decision making tree. If the patient expresses resistance to performing eccentric decline squats, should the clinician push the issue or instead offer treatments that require less patient compliance (e.g., injection therapy)? Questions such as this one remain unanswered in the published literature and should be addressed in consultation with the patient.
It has been said that treatment effectiveness is inversely proportional to the number of available treatment choices (6). Applying this truism demonstrates that there is currently no definitive treatment for patellar tendinopathy. Research into the basic science of tendinopathy may reveal promising new treatments in the coming years. When these advances come, we look forward to RCTs comparing these new treatments to existing treatments or, where possible, to an appropriate placebo intervention.
This review was supported by the Australian Centre for Research into Sports Injury and Its Prevention, which is one of the International Research Centres for Prevention of Injury and Protection of Athlete Health supported by the International Olympic Committee.
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