Tendinopathy: Open Controversies in the Field

Why Tendinopathy Remains One of the Most Contested Areas in Musculoskeletal Medicine

Tendinopathy is not a single, well-characterized disease. It covers a spectrum of painful tendon conditions, from reactive tendon thickening to frank degenerative change, and the absence of consensus on its very definition makes every downstream clinical decision contested. Prevalence data alone illustrate the scale of the problem: Achilles tendinopathy occurs in roughly 2.35 per 1,000 adults per year in primary care [1], patellar tendinopathy affects up to 45% of elite jumping athletes [2], and rotator cuff tendinopathy accounts for roughly 70% of all shoulder pain presentations [3].

The controversies are not trivial academic disputes. They determine whether a patient receives an injection that may accelerate rupture, a loading protocol that could worsen a reactive tendon, or surgery that has never been tested against sham in a well-powered RCT.

The Classification Problem

Most clinical guidelines still use the word "tendinopathy" as both a diagnosis and a staging label, which creates circular reasoning. The Nirschl system, the VISA scoring tools, and the Cook-Purdam continuum model each describe different constructs, and none has been prospectively validated as a treatment-selection instrument [4]. Until classification and staging are standardized, trial comparisons across centers will remain unreliable.

Epidemiology Gaps

Published incidence figures come predominantly from Western, sport-active populations. Data from sedentary and older adults are sparse. A 2019 systematic review in the British Journal of Sports Medicine found that fewer than 12% of tendinopathy RCTs reported the occupational exposure status of participants, leaving the treatment literature poorly generalizable [5].

Controversy 1: Is the Tendon Continuum Model Clinically Useful or Theoretically Elegant?

The continuum model proposed by Cook and Purdam in 2009 remains the most widely taught framework for staging tendon pathology across three phases: reactive, tendon disrepair, and degenerative [4]. The model argues that treatment should match stage, and that loading a degenerate tendon differently from a reactive one is biologically necessary. The problem is that prospective clinical evidence for this staging-to-treatment approach is almost entirely absent.

What the Model Gets Right

Cross-sectional imaging studies consistently show that degenerative tendon regions have disorganized collagen, absent tenocyte nuclei, and increased proteoglycan content compared with reactive regions [6]. These structural differences are real. The biology supports the concept that one tendon can contain both reactive and degenerative zones simultaneously.

Where the Evidence Breaks Down

No RCT has yet randomized participants by continuum stage and then compared stage-matched versus stage-unmatched loading protocols. A 2023 narrative review in the Journal of Orthopaedic and Sports Physical Therapy concluded that clinicians cannot reliably determine continuum stage from clinical examination alone, and that ultrasound findings correlate poorly with symptom severity [7]. Structural abnormality on imaging is present in up to 59% of asymptomatic Achilles tendons [8], which means imaging-based staging introduces its own validity problem.

The Practical Implication

Clinicians using the continuum model to withhold heavy loading from patients labeled "reactive" may be delaying effective treatment for weeks based on a staging system that has not been tested as a decision rule. This is not a reason to abandon the model entirely, but it is a reason to treat it as a hypothesis rather than an established clinical tool.

Controversy 2: Eccentric Loading vs. Heavy Slow Resistance. Which Protocol Is Superior?

For two decades, the Alfredson eccentric heel-drop protocol (3 sets of 15 repetitions twice daily, 12 weeks) was the standard of care for Achilles tendinopathy [9]. A 2015 RCT by Beyer et al. (N=58) published in the American Journal of Sports Medicine then found that heavy slow resistance (HSR) training produced equivalent VISA-A scores at 12 months, with superior patient satisfaction [10]. The field has not reached consensus since.

The Case for Eccentric Loading

Alfredson's original case series (N=15) showed a 100% return-to-running rate, and subsequent RCTs have replicated clinically meaningful VISA-A improvements in the range of 20-25 points at 12 weeks [9]. The protocol is simple, home-based, and requires no equipment. These features matter for adherence in a condition that requires months of consistent loading.

The Case for Heavy Slow Resistance

HSR uses concentric and eccentric contractions under progressively heavier loads, which may produce greater mechanical stimulus to tenocytes. Beyer et al. Reported a statistically significant advantage in patient satisfaction (P<0.01) at 12 weeks, though VISA-A scores converged by 52 weeks [10]. A 2020 meta-analysis in the British Journal of Sports Medicine (k=29 RCTs) found no significant difference in pain or function outcomes between eccentric and HSR protocols at any follow-up point [11].

Where the Field Now Stands

The 2023 British Journal of Sports Medicine consensus statement on Achilles tendinopathy states that "progressive tendon loading is supported by moderate-certainty evidence, but no single modality can be recommended over another" [12]. That is an honest admission of uncertainty. Clinicians should select the protocol most likely to achieve adherence for the individual patient rather than defaulting to any single regimen.

Controversy 3: Do Corticosteroid Injections Help or Harm?

Corticosteroid injections (CSI) remain among the most commonly performed procedures for tendinopathy despite a mounting body of evidence that their short-term benefits are offset by longer-term harms. This is one of the most clinically consequential open questions in the field.

Short-Term Benefit Is Real but Brief

A 2010 Cochrane review of subacromial CSI (k=26 RCTs) found a statistically significant improvement in pain at 4-6 weeks compared with placebo (SMD -0.46, 95% CI -0.62 to -0.29) [13]. A comparable pattern appears in lateral epicondylalgia, where CSI outperforms physiotherapy at 6 weeks but shows worse outcomes at 12 months, a finding confirmed in the landmark Smidt et al. RCT (N=185) in the Lancet [14].

The Rupture and Rebound Problem

A large population-based cohort study published in BMJ (N=20,298) found that patients who received three or more CSI for Achilles or rotator cuff tendinopathy had a 4.8-fold higher rate of subsequent tendon rupture compared with those who received none [15]. The mechanism is debated; collagen necrosis, cell apoptosis, and mechanical unloading during the pain-free window are all proposed contributors.

What Guidelines Currently Recommend

The American College of Rheumatology conditionally recommends against repeat CSI for Achilles tendinopathy but does not specify an absolute number. The British Orthopaedic Association limits Achilles CSI to exceptional cases with clear informed consent about rupture risk. Neither body defines an agreed maximum injection frequency across all tendons, which leaves individual clinical judgment as the operative standard.

Controversy 4: Does Platelet-Rich Plasma Work?

Platelet-rich plasma (PRP) has attracted enormous commercial interest and an equally large volume of conflicting trial data. The core controversy is whether the biological rationale (concentrated growth factors stimulating tendon repair) translates into clinically meaningful outcomes.

What the Trials Show

The 2021 Cochrane review of PRP for rotator cuff disease (k=19 RCTs, N=1,054) concluded that PRP may result in little to no difference in pain or function compared with placebo at 3-6 months (low-certainty evidence) [16]. A separate 2022 RCT published in JAMA (N=220) found no significant difference between leukocyte-rich PRP and saline injection for Achilles tendinopathy at 24 weeks, with VISA-A improvement of 21.7 points in the PRP group versus 20.5 points in the saline group (P<0.001 for within-group change, P=0.60 between groups) [17].

Why Trials Keep Disagreeing

PRP preparation varies enormously. Platelet concentration ranges from 2x to 9x baseline across commercial systems, leukocyte content differs by device, and activation protocols are inconsistently reported. A 2020 systematic review in the American Journal of Sports Medicine identified 24 distinct PRP classification variables across included studies, making meta-analytic pooling of "PRP" as a single intervention biologically unjustified [18].

The Clinical Bottom Line

Until standardized PRP preparation is required by trial registries, the evidence base will remain fragmented. Patients asking about PRP should be told that current high-quality trials do not demonstrate superiority over saline or structured loading, and that out-of-pocket cost (typically $500-$2,500 per injection in the US) is not supported by this evidence level.

Controversy 5: What Is the Role of Imaging in Diagnosis and Treatment Decisions?

Ultrasound and MRI are routinely used to diagnose tendinopathy, yet their diagnostic accuracy and prognostic value are genuinely contested. The fundamental problem is that structural abnormality on imaging does not reliably predict pain, disability, or treatment response.

Imaging Finds Pathology in Asymptomatic Tendons

A systematic review published in the British Journal of Sports Medicine (N=2,113 asymptomatic individuals) found that 59% of asymptomatic Achilles tendons and 23% of asymptomatic patellar tendons showed hypoechoic changes on ultrasound consistent with tendinopathy [8]. Using imaging alone to establish a diagnosis therefore carries a substantial false-positive rate.

Does Imaging Guide Treatment?

No RCT has yet shown that imaging-directed treatment selection produces better outcomes than clinical-examination-directed selection alone. A 2022 narrative review in the Journal of Science and Medicine in Sport concluded that ultrasound findings should be used to exclude other pathology (partial-thickness tears, bursitis, calcific deposits) rather than to confirm or stage tendinopathy per se [19].

Ultrasound Tissue Characterization

Ultrasound tissue characterization (UTC) is an emerging quantitative technique that maps tendon fiber alignment using back-scatter signal. Preliminary data suggest UTC scores correlate more strongly with symptom severity than standard greyscale ultrasound, but no prospective management trial has yet used UTC as an allocation criterion [20]. It remains a research tool in 2025.

A Proposed Diagnostic Framework for Clinical Practice

Given current evidence, a reasonable approach is to use imaging primarily to rule out structural complications (tears >50% cross-sectional area, calcific tendinitis requiring shockwave or needling, bursopathy mimicking tendinopathy) rather than to confirm tendinopathy itself. Clinical diagnosis using a validated instrument such as the Victorian Institute of Sport Assessment (VISA) score combined with the Royal London Hospital test for Achilles or the arc sign for mid-portion versus insertional differentiation provides actionable information that imaging rarely adds to.

Controversy 6: When Should Surgery Be Considered?

Surgery for tendinopathy carries a contested evidence base. Most guidelines recommend a trial of conservative management before operative referral, but they disagree on how long that trial should be, ranging from 3 months in some Australian physiotherapy guidelines to 12 months in some UK orthopaedic pathways.

What the Surgical Literature Actually Shows

A 2021 Cochrane review of surgery for lateral epicondylalgia (k=7 RCTs, N=533) found that surgery produced no statistically significant benefit over watchful waiting or physiotherapy at 12 months [21]. For Achilles tendinopathy, a 2019 systematic review in Foot and Ankle International (k=12 studies, N=412) found that open or endoscopic debridement produced meaningful symptom relief in 70-85% of patients who had failed at least 6 months of loading, but no study used a sham-surgery control arm [22].

The Sham Surgery Problem

The absence of sham-controlled surgical trials is the defining methodological weakness of the tendinopathy surgery literature. Meniscal surgery trials have repeatedly shown that sham arthroscopy produces equivalent outcomes to active surgery (NEJM, Sihvonen et al., N=146, 2013) [23]. The same design has not been applied to tendon debridement, leaving the field unable to separate placebo from procedural effect.

Practical Thresholds

A reasonable clinical threshold, consistent with the majority of level-1 evidence, is 6 months of supervised progressive loading with documented non-response before operative consultation. Patients with insertional Achilles tendinopathy and a Haglund deformity confirmed on lateral radiograph represent a subgroup where bony resection has mechanistic justification beyond soft-tissue debridement alone.

Controversy 7: Emerging Pharmacological and Systemic Factors. Are GLP-1 Agonists and Metabolic Status Relevant?

A fast-growing body of evidence suggests that systemic metabolic factors, including obesity, type 2 diabetes, and dyslipidemia, significantly alter tendon biology and treatment response. This reframes tendinopathy as a condition with both local mechanical and systemic metabolic drivers.

Metabolic Tendinopathy

A 2016 systematic review in the British Journal of Sports Medicine (k=24 studies) found that individuals with metabolic syndrome had a 2.3-fold higher prevalence of tendon pathology, particularly Achilles and rotator cuff [24]. Hyperglycemia impairs collagen cross-linking through advanced glycation end-products, reducing tendon stiffness and increasing susceptibility to failure. This mechanism is well-established in vitro [25].

GLP-1 Receptor Agonists and Tendon

Early pre-clinical data suggest that GLP-1 receptor activation may reduce tendon inflammation through suppression of NF-kB signaling in tenocytes, but human trial data are absent as of early 2025 [26]. The rapid uptake of semaglutide and tirzepatide in the metabolically obese population means that large real-world cohorts now exist from which tendon outcomes could be extracted. No prospective study has yet done so.

What Clinicians Should Do Now

For patients with tendinopathy and comorbid metabolic syndrome or type 2 diabetes, optimizing glycemic control and body weight is a reasonable adjunct to loading, supported by the mechanistic literature even in the absence of RCT evidence for this specific combination. The Endocrine Society's 2023 obesity management guideline supports GLP-1 agonist use for weight reduction in BMI >30 [27], and weight loss reduces mechanical load on lower-limb tendons by a calculable and clinically significant margin.

Controversy 8: Collagen Synthesis and the Peri-Exercise Nutrition Window

Whether a discrete peri-exercise window for collagen precursor supplementation (vitamin C, gelatin/hydrolyzed collagen) exists, and whether it improves tendon outcomes, is contested.

The Shaw et al. Data

A 2017 RCT by Shaw et al. (N=8, crossover design) published in the American Journal of Clinical Nutrition found that 15g of gelatin plus 48 mg vitamin C, consumed 1 hour before 6 minutes of skipping, doubled circulating collagen synthesis markers (P1NP) compared with placebo [28]. The trial was small and used a surrogate biomarker rather than a tendon-specific structural or clinical outcome.

What Larger Trials Show

A 2023 RCT (N=120) in the British Journal of Sports Medicine found no significant difference in VISA-A scores between hydrolyzed collagen supplementation and placebo after 24 weeks of concurrent loading in Achilles tendinopathy [29]. Circulating P1NP is not a validated surrogate for tendon structural change, and no study has used biopsy-confirmed collagen organization as a primary outcome.

Clinical Recommendation

Gelatin or hydrolyzed collagen supplementation (15g, 30-60 minutes pre-loading, with vitamin C) carries low risk and modest cost. Given the absence of harm signals and the plausible mechanism, it may be offered as an adjunct. Patients should be told the evidence is preliminary and that loading itself remains the primary driver of any benefit.