Tendinopathy: Open Controversies in the Field

Tendinopathy is the general term for persistent tendon pain and dysfunction associated with loading, and it covers a spectrum that includes what older literature called "tendinitis" (implying inflammation, now known to be an incomplete description) and "tendinosis" (implying pure degeneration, also incomplete). It affects tendons such as the Achilles, patellar, rotator cuff (most often supraspinatus), and common extensor origin at the elbow. The most useful question for a patient or clinician is not "which single treatment cures tendinopathy" but "which decisions in this condition are backed by solid evidence, which rest on plausible mechanism without proof, and which are still genuinely unsettled." This article works through that question controversy by controversy.

Why this condition generates so much disagreement

Tendinopathy is not one disease with one mechanism. It is a clinical label applied to a range of tendon states, from an acutely reactive, swollen tendon to one with long-standing structural disorganization, and clinicians do not have a reliable, validated way to tell these states apart at the bedside. That uncertainty about the underlying pathology is the root of nearly every downstream disagreement: which loading protocol matches which tendon state, whether imaging should guide treatment, whether an injection helps or accelerates failure, and when surgery is warranted.

This matters practically. A patient labeled with a "reactive" tendon on the basis of ultrasound or symptom description may be told to avoid heavy loading for weeks, based on a staging framework that has not been tested as a decision rule in a randomized trial. A patient offered a corticosteroid injection may get real short-term relief while accumulating risk that is not fully quantified for their specific situation. Naming these uncertainties clearly is more useful to a reader than presenting false confidence.

Evidence hierarchy used in this article: where a professional society guideline exists, it is presented first; below that, randomized trials and systematic reviews; below that, observational or mechanistic evidence, which is labeled as such and should not be read as proof of a clinical effect.

Controversy 1: Is the tendon continuum model a useful clinical tool or a theoretical framework?

The continuum model, associated with the work of Cook and Purdam, describes tendon pathology as moving through reactive, tendon disrepair, and degenerative stages, with the idea that loading should be matched to stage. The underlying biology is not disputed: cross-sectional studies of tendon tissue consistently show that degenerative regions have disorganized collagen and altered cell content compared with more reactive regions, and a single tendon can contain both states at once.

What is not established is whether clinicians can reliably identify a patient's stage using history, examination, or standard imaging, or whether matching a loading protocol to a presumed stage improves outcomes compared with a standard progressive loading program. No randomized trial has yet allocated patients by continuum stage and then compared stage-matched against stage-unmatched loading. Structural abnormalities on ultrasound are also common in tendons that never caused symptoms, which undermines using imaging to assign a stage. The practical implication: the continuum model is a reasonable way to think about tendon biology, but using it to withhold heavier loading from a patient labeled "reactive" is applying an unproven decision rule, not a guideline-backed one.

Controversy 2: Eccentric loading versus heavy slow resistance. Does one protocol win?

For years, the Alfredson eccentric heel-drop protocol was considered the default exercise treatment for Achilles tendinopathy. A later randomized trial comparing heavy slow resistance (HSR) training, which uses both concentric and eccentric phases under progressively heavier load, found broadly similar outcomes on tendon function scores at one year, with a reported advantage in patient satisfaction favoring HSR in the shorter term. Subsequent systematic reviews and meta-analyses of loading protocols have generally not found a consistent, clinically important difference in pain or function between eccentric-only and combined concentric-eccentric approaches at comparable follow-up points.

The reasonable clinical position, consistent with how professional consensus statements have framed this question, is that progressive tendon loading works and no single loading modality has been shown to be superior. Choosing between them should be based on what the patient can adhere to for the months required, since adherence, not the specific exercise variant, appears to be the more consequential variable. (Readers should note that the specific trials referenced in earlier tendinopathy literature on this topic, including the original Beyer et al. comparison, should be checked against the primary publication before citing exact effect sizes; this article intentionally avoids restating precise numbers that could not be re-verified against the source paper.)

Controversy 3: Do corticosteroid injections help or harm tendons?

This is one of the more clinically consequential open questions because the short-term and long-term pictures point in different directions.

Short term: Corticosteroid injection produces real, statistically demonstrated pain relief in the first several weeks compared with placebo or watchful waiting, across multiple tendon sites including the rotator cuff and lateral elbow.

Longer term: Randomized comparisons of corticosteroid injection against physiotherapy for lateral epicondylitis have found injection outperforms exercise at six weeks but is outperformed by exercise-based approaches by around a year, a pattern that has shaped skepticism about injections as a primary treatment rather than a short-term bridge. Separately, observational cohort studies have associated repeated corticosteroid injections with a materially higher rate of subsequent tendon rupture compared with patients who received none or few injections. The exact magnitude of that increased risk varies by study and population, and the specific figures cited in some patient-facing summaries need to be checked against the original cohort study before being restated as precise numbers; the direction of the finding (more injections, more rupture risk) is consistent across the literature that has looked at this question.

What guidelines say: Most professional guidance does not set a single agreed maximum number of injections across all tendons. The consistent theme is caution: injections are reasonable as a short-term bridge to enable participation in a loading program, not as a repeated primary treatment, and repeated injections into weight-bearing tendons such as the Achilles warrant particular caution given the rupture signal.

A compact way to state the current picture: corticosteroid injection reliably reduces tendon pain for a period of weeks, but repeated injections are associated in observational data with a higher rate of later tendon rupture, and no guideline currently defines a universally agreed safe injection limit across tendon sites, which means the decision to repeat an injection should weigh short-term relief against a longer-term risk that is real but not precisely quantified for any individual patient.

Controversy 4: Does platelet-rich plasma (PRP) work for tendinopathy?

PRP involves injecting a concentrated preparation of the patient's own platelets into or around the affected tendon, with the rationale that growth factors released by platelets stimulate tendon healing. The controversy is whether this translates into a clinically meaningful benefit over cheaper, lower-risk alternatives such as saline injection or structured exercise.

Systematic reviews of PRP for tendon conditions, including rotator cuff disease, have generally graded the evidence as low to moderate certainty and have not found a consistent, clinically important advantage over placebo or exercise-based care. Individual randomized trials in Achilles tendinopathy have similarly reported that PRP and saline injection produce comparable improvement over time, meaning both groups improved but PRP did not clearly outperform the comparator.

A major reason the trial literature is hard to interpret is that "PRP" is not one intervention. Platelet concentration, white blood cell content, and activation method vary widely across commercial preparation systems, and many trials do not report these parameters consistently. An editorial commentary published in 2021 on platelet-rich plasma for elbow lateral epicondylitis addresses this heterogeneity directly, arguing that pooling different PRP preparations under one label makes it difficult to draw a single conclusion about whether "PRP" works, since different preparations may behave as different biological interventions. That framing is a reasonable caution for any reader evaluating PRP marketing claims for tendinopathy generally, though the commentary itself concerns lateral epicondylitis specifically and should not be read as settling the question for other tendons such as the Achilles or patellar tendon.

The practical takeaway: patients considering PRP, which typically costs several hundred to a few thousand dollars out of pocket and is not established as superior to lower-cost alternatives, should be told plainly that current evidence does not demonstrate a reliable added benefit over saline injection or structured loading for most tendons, and that preparation methods differ enough between clinics that results from one study may not generalize to another provider's product.

Controversy 5: How much should imaging drive diagnosis and treatment?

Ultrasound and MRI are commonly used in tendinopathy evaluation, but their role is genuinely contested because structural findings on imaging correlate poorly with symptoms.

What is established: Tendon structural abnormalities on ultrasound, such as hypoechoic regions or thickening, are common findings in tendons that have never caused pain, particularly the Achilles and patellar tendons. This means a positive imaging finding does not confirm that a person's pain is caused by, or will respond to treatment aimed at, that structural change.

What is not established: No randomized trial has shown that choosing treatment based on imaging findings produces better outcomes than choosing treatment based on clinical history and examination alone. Emerging quantitative techniques such as ultrasound tissue characterization remain research tools rather than validated tools for guiding individual treatment decisions as of this review.

A reasonable practical framework: use imaging primarily to rule out other explanations for tendon-area pain, such as a partial or full-thickness tear, bursitis, or calcific deposits, rather than to confirm or stage tendinopathy itself. Clinical assessment using a validated symptom and function questionnaire, combined with a focused physical examination, provides more actionable information for day-to-day treatment decisions than structural imaging typically does.

Controversy 6: When, if ever, should surgery be considered?

Guidelines disagree meaningfully on how long a patient should try conservative (non-surgical) management before being referred for surgical consultation, with published thresholds ranging from around three months to as long as twelve months depending on the tendon and the guideline body. That range itself reflects genuine uncertainty rather than a settled standard.

Randomized evidence on tendon surgery is limited and, critically, almost none of it has used a sham-surgery control arm. Trials that have compared surgery against watchful waiting or physiotherapy for conditions such as lateral epicondylitis have generally not found a clear statistically significant benefit for surgery over non-operative care by one year. In other tendons, uncontrolled surgical case series report meaningful symptom improvement in a majority of patients who had already failed a prolonged course of loading, but without a sham comparator it is not possible to separate a true procedural effect from the placebo effect of undergoing a procedure, which other orthopedic sham-surgery trials (in different joints, not tendons specifically) have shown can be substantial.

A reasonable, guideline-consistent threshold is a trial of at least several months of supervised, progressive loading, with documented lack of meaningful improvement, before considering surgical referral. Patients with a specific structural abnormality that surgery can directly address, such as a confirmed bony deformity contributing to insertional Achilles tendinopathy, represent a subgroup where the mechanistic case for surgery is clearer than for tendon debridement alone.

Controversy 7: Do metabolic health and GLP-1 medications matter for tendon outcomes?

There is a growing, largely observational and mechanistic literature connecting metabolic syndrome, type 2 diabetes, and obesity to a higher prevalence of tendon pathology. The proposed mechanism, supported by laboratory studies, is that chronic high blood sugar impairs normal collagen cross-linking through advanced glycation end-products, which can make tendon tissue stiffer and more prone to injury. This mechanistic story is plausible and reasonably well supported at the laboratory level, though it does not by itself prove that treating a patient's metabolic disease will reverse existing tendinopathy.

GLP-1 receptor agonists such as semaglutide and tirzepatide are FDA-approved for type 2 diabetes and, in some formulations, for chronic weight management; their use for tendon health specifically is not an approved indication and has not been tested in human trials as of this review. Pre-clinical laboratory data suggesting an anti-inflammatory effect on tendon cells exist, but this is early-stage evidence and should not be presented to patients as a demonstrated tendon benefit. What is more defensible is the indirect argument: for a patient with tendinopathy and comorbid obesity or poorly controlled diabetes, weight loss and improved glycemic control reduce mechanical load on weight-bearing tendons and are reasonable adjuncts to a loading program on general medical grounds, independent of any tendon-specific proof.

Controversy 8: Is there a useful post-exercise window for collagen-building nutrition?

Small studies have explored whether consuming gelatin or hydrolyzed collagen with vitamin C shortly before exercise increases markers of collagen synthesis in the blood. Some early, very small trials reported an increase in a circulating collagen synthesis marker under these conditions. However, a circulating biomarker is not the same as a proven improvement in tendon structure or symptoms, and larger trials that have looked at actual clinical outcomes, such as validated tendon function scores after months of combined loading and supplementation, have generally not found a significant benefit over loading alone.

Given the low cost and low risk of gelatin or hydrolyzed collagen supplementation, it is reasonable to offer it as an optional adjunct while being honest that the evidence for a clinical benefit specific to tendinopathy remains preliminary, and that progressive loading, not supplementation, is the intervention with the stronger evidence base.

Evidence boundary: what is established, what is plausible, what is not proven

Established: Progressive tendon loading improves symptoms across major tendon sites and is the consistent foundation of guideline-based care. Corticosteroid injections produce genuine short-term pain relief. Tendon structural abnormalities on imaging are common in people without any tendon pain, which limits imaging's value as a standalone diagnostic tool.

Plausible but not proven: That staging a tendon on the continuum model and matching loading intensity to that stage improves outcomes compared with standard progressive loading. That GLP-1 receptor activation has a direct, clinically meaningful anti-inflammatory effect on tendon tissue in humans. That a specific peri-exercise nutrition window meaningfully changes tendon structural outcomes rather than only a circulating biomarker.

Not established: That any single loading protocol (eccentric versus heavy slow resistance) is reliably superior to another. That PRP produces a clinically meaningful benefit over saline injection or exercise for most tendons. That surgery outperforms sham surgery for tendinopathy, since sham-controlled surgical trials in tendinopathy essentially do not exist. That there is one universally correct duration of conservative treatment before surgical referral.

A framework for deciding how much weight to give each controversy

Not every open question in tendinopathy carries the same practical stakes. The table below is meant to help a patient or clinician decide, for each controversy, whether it should change today's treatment decision or can be set aside as background uncertainty.

References

1. Editorial Commentary: Elbow Lateral Epicondylitis Treatment Using Platelet-Rich Plasma (2021). https://pubmed.ncbi.nlm.nih.gov/34740411/

Additional claims in this article describe well-known findings in the tendinopathy literature, including the original description of the tendon continuum model, the Alfredson eccentric-loading protocol, the Beyer heavy-slow-resistance trial, systematic reviews of corticosteroid injection and PRP, and cohort data on injection-associated tendon rupture. Specific citation identifiers for these studies were not carried into this draft because the source identifiers could not be verified against the underlying papers. Editorial and medical review should confirm and re-attach the correct primary references before publication.