Why Does Achilles Tendon Pain Persist for Half a Year? — Reframing Achilles Tendinopathy as “Tendon Degeneration” Rather Than “Inflammation,” and the Role of Stem Cell Conditioned Media2026.07.08

“When I start running, the back of my heel pulls and hurts.” “The very first step in the morning is so stiff and painful in my Achilles tendon.” We are seeing more and more patients bring these complaints to our clinic. Many assume it is “Achilles tendon inflammation” and try rest and topical patches, but chronic Achilles tendinopathy is not actually “inflammation (-itis)” — it is “tendon degeneration (tendinosis),” which is an entirely different pathology. Miscasting the problem leads to a familiar situation: no matter how long you rest, the pain does not go away. This article organizes the mechanism of chronic Achilles pain, and explains where local injection of stem cell conditioned media fits on top of conservative treatment as a foundation, from the perspective of Dr. Moriwaki at AVAN TOKYO Ginza.

Key Points

・Chronic Achilles tendinopathy is not “inflammation” but rather “degeneration” of tendon collagen fibers, and rest or anti-inflammatory medication alone often fails to resolve it.

・The foundation of treatment is exercise therapy (eccentric loading), extracorporeal shockwave, and reviewing footwear and insoles; stem cell conditioned media is positioned as an option that combines with these.

・Stem cell conditioned media contains growth factors and extracellular vesicles (exosomes) and is thought to potentially act on the repair environment of degenerated tendon tissue.

・The insertional type and the mid-portion type of the Achilles tendon differ in blood supply and healing pattern, and the approach to injection also differs.

・Suspected rupture, severe degeneration, or active infection makes this a non-indication, so orthopedic diagnosis and imaging evaluation come first.

Achilles Tendinopathy Is Not “Inflammation” — The Real Reason It Becomes Chronic

What has long been called “Achilles tendonitis” reveals, under the microscope in the chronic phase, almost none of the classic inflammatory cells (neutrophils, macrophages). Instead, what is seen is disarray of collagen fibers, abnormal proliferation of tenocytes, abnormal neovascularization of microvessels, and mucoid degeneration — in other words, “a state in which the tendon itself has structurally degenerated and repeats micro-failure and failed repair.” This is the basis for the current understanding that Achilles tendinopathy should be called “tendinosis” rather than an extension of ordinary inflammation.

Separating -itis (Inflammation) from -osis (Degeneration)

In the acute phase (1–2 weeks), there is genuine micro-inflammation, but pain persisting beyond that for months is largely a transition to “degeneration.” Chronic-phase tendons have inherently poor blood supply, expanding a “low-metabolism zone” where oxygen, nutrients, and repair signals struggle to reach. Continuing NSAIDs in this state does little because the target — inflammation — is scant, and there are even reports suggesting that tendon repair processes may be suppressed. Shifting from an “anti-inflammatory” mindset to a “rebuild the degenerated tendon tissue environment” mindset is the key to designing treatment for this condition.

Insertional and Mid-portion Types Heal Differently

Achilles tendinopathy is broadly divided into an “insertional type” — painful at the attachment to the calcaneus — and a “mid-portion type” — painful 2–6 cm above the calcaneus in the middle of the tendon. The insertional type has a complex structure of bone, cartilage, and tendon, with inherently poor blood supply, and is known to respond less well to exercise therapy compared with the mid-portion type. Because treatment strategy differs by type, confirming findings with ultrasound (echo) or MRI is the fundamental first step.

Conservative Treatment of Achilles Tendinopathy — and Placing Stem Cell Conditioned Media “On Top of the Foundation”

For chronic Achilles pain, what should be done first is exercise therapy that reapplies “appropriate loading” to the degenerated tendon. Especially for the mid-portion type, the Alfredson protocol — eccentric loading of the triceps surae (slowly lowering the heel) — is central, and has shown efficacy in many case series. Combined with extracorporeal shockwave therapy (ESWT), footwear and insole review, and calf flexibility training, this conservative package forms the treatment foundation. For general information on joint and musculoskeletal conditions, the website of the Japanese Orthopaedic Association is a useful reference.

Actions Reasonably Postulated for Stem Cell Conditioned Media

Stem cell conditioned media contains various growth factors (TGF-β, IGF-1, VEGF, FGF, and others) secreted by mesenchymal stem cells during culture, along with extracellular vesicles (exosomes) and miRNA — signaling molecules. At the basic research level, these factors have been reported to potentially engage in collagen production by tenocytes and in improving the microenvironment of poorly vascularized degenerated tendon. However, this remains a “potential action supporting the repair environment of degenerated tendon,” and it is not a magic injection that reattaches ruptured tendons or brings pain to zero in a short time. Effects and responses vary between individuals, and there are clear limits.

Different Purpose from Steroid Injection

Steroid injection around the tendon may be considered when pain is severe, but direct injection into the tendon itself is carefully avoided because it can weaken tendon tissue and raise rupture risk. Steroids are suited for “suppressing pain quickly” via a strong anti-inflammatory effect, but do not contribute to “repair” of degenerated tendon tissue. Peri-tendinous injection of stem cell conditioned media does not aim to suppress pain; instead, it approaches the metabolic environment of the degenerated tissue to support healing over time — a fundamentally different purpose.

Precautions When Considering Conditioned Media Injection for the Achilles Tendon

Delivering “Around the Tendon,” Not “Inside the Tendon”

For conditioned media administration to the Achilles tendon, we in principle avoid large-volume injection into the tendon itself (intratendinous) and instead select a technique of delivering small aliquots into peri-tendinous tissue or around the insertion under ultrasound guidance. This is to avoid a sudden rise in intratendinous pressure and physical strain on healthy tendon fibers. Technical precision and the choice of injection site strongly influence outcomes.

Non-indications and Cases Requiring Caution

In cases such as the following, peri-tendinous injection of stem cell conditioned media is either not a first-line option or requires careful consideration:

・Suspected complete or partial rupture of the Achilles tendon (imaging evaluation is the highest priority)

・Active infectious disease

・Poorly controlled systemic disease (diabetes, collagen disease, etc.)

・Severe degeneration or advanced osteophyte formation where surgical intervention is deemed appropriate

Orthopedic diagnosis and confirmation of imaging findings come first. At our clinic, we evaluate other conservative therapies (exercise, shockwave, orthotics) in parallel and design according to each patient’s activity level and goals. For details, please see this page on stem cell conditioned media joint injection.

How to Assess Effect and Follow Up

Repair of tendon tissue takes time. After injection, some patients feel pain relief within a few weeks, while others improve gradually over months. Rather than treating a single injection as the end, we continuously monitor pain scores (VAS), morning heel stiffness, walking and stair-climbing, and symptoms after returning to running — adding further injections or revising strategy as needed. Responses vary between individuals, and we honestly convey that this is not effective for every patient.

Frequently Asked Questions

Q. Is injection for Achilles tendinopathy covered by insurance?

Local administration using stem cell conditioned media is an out-of-pocket (self-pay) treatment. It is considered as one option for chronic cases after insurance-covered conservative therapy (exercise, NSAIDs, topical patches, orthotics, and so on) has first been tried.

Q. Will a single injection cure it?

Some patients do feel symptom improvement even with a single injection, but this does not apply to everyone. Because tendon degeneration is the underlying issue, repair takes time, and it is common to follow the course with multiple injections combined with exercise therapy. Effects and limits vary between individuals.

Q. When can I return to running?

We raise the load in stages while watching pain and tendon response. Avoid all-out exercise immediately after injection; start with walking and light jogging, and confirm that pain or discomfort does not recur while gradually returning to your regular training volume over several weeks.

Q. How do you determine whether the Achilles tendon is completely torn?

We judge comprehensively through history taking (a sudden “snap” sound, inability to push off), physical findings such as the Thompson test, and imaging evaluation with ultrasound and MRI. If rupture is suspected, orthopedic evaluation and consideration of surgical indication must come before conditioned media injection.

Q. Is stem cell conditioned media approved as “regenerative medicine”?

It differs from treatments that transplant stem cells themselves — conditioned media is a fluid containing cell secretions, and its administration is performed under management at medical institutions that fall under the notification framework of Japan’s Act on the Safety of Regenerative Medicine. Because it is not the same as “a drug approved by the Ministry of Health, Labour and Welfare,” we honestly share the expected range and limits before proceeding with consultation.

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【監修】森脇 進 / Shin Moriwaki（監修医師）

日本美容外科学会(JSAS)会員 / American Academy of Aesthetic Medicine 会員

米国医師免許資格(ECFMG certificate)

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📍AVAN TOKYO Ginza Regenerative Medicine

AVAN TOKYO 銀座 再生医療

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