Stem Cells vs PRP for Knee Osteoarthritis in Japan
Stem cell injections have not been shown to be consistently better than PRP for knee osteoarthritis. A direct comparison of bone marrow concentrate and PRP found no significant difference after two years. That result applies to the preparations studied. It does not establish that every cell treatment and every PRP preparation work equally well.[1]
PRP may reduce pain for some patients, although trials have produced different results. Cell injections may also improve pain and function, but the evidence remains uncertain. Neither finding means that an injection will rebuild damaged cartilage or remove the need for future treatment.[2][3][4]
If you are comparing treatment in Japan, start by finding out exactly what each clinic offers. The preparation, evidence, number of visits and total cost can differ even when both providers use the same treatment name.
How the Treatments Differ
PRP, or platelet-rich plasma, is prepared from your blood. The clinic separates and concentrates platelets before administering the preparation. It is not a stem cell treatment.[2]
The term “stem cell injection” can refer to several different preparations. Bone marrow concentrate, cells separated from fat, and cells grown in a laboratory should not be treated as the same product. The MILES trial, for example, studied several cellular preparations separately.[5]
| Preparation | What It Contains |
|---|---|
| PRP | A platelet-rich preparation made from the patient’s blood |
| Bone marrow concentrate (BMC or BMAC) | A mixture collected and concentrated from bone marrow, rather than a purified dose of laboratory-grown stem cells |
| Adipose stromal vascular fraction (SVF) | A mixture of cells separated from fat tissue |
| Culture-expanded mesenchymal stromal cells (MSCs) | Cells grown in a laboratory, which may come from the patient or a donor |
These differences matter when reading a study or comparing a quotation. A result for bone marrow concentrate does not establish how an unrelated cultured-cell preparation will perform.[5] The autologous versus allogeneic stem cell guide explains the difference between using your own cells and donor-derived cells.
What Does PRP Help With?
A 2025 review combined 18 randomized placebo-controlled trials involving 1,995 patients. Its search ended on September 26, 2023. Overall, PRP performed better than placebo on pain and total WOMAC scores, which measure pain, stiffness and physical function.[2]
The amount of additional pain relief varied by follow-up time. The figures below use a 0–10 pain scale. They describe the average difference between PRP and placebo, not the total improvement after a PRP injection.[2]
| Follow-up | Difference Favoring PRP | 95% Confidence Interval |
|---|---|---|
| 1 month | 0.62 points | 0.11–1.13 |
| 3 months | 1.43 points | 0.71–2.16 |
| 6 months | 1.65 points | 0.97–2.33 |
| 12 months | 1.12 points | 0.25–1.99 |
The review used 1.37 points as its threshold for a clinically important difference. The average benefits at three and six months exceeded that threshold. However, their confidence intervals also included smaller benefits below it. All four comparisons were statistically significant, but that does not mean every difference was large enough to be important to patients.[2]
The confidence intervals show uncertainty around the estimated average difference. They are not a range of results that an individual patient can expect. The review also had limitations: seven studies were rated at low risk of bias, nine had some concerns, and two were at high risk.[2]
One of the included trials, RESTORE, had a less encouraging result. Published in JAMA in 2021, it involved 288 adults aged 50 or older with radiographic grades 2 or 3 knee osteoarthritis. Participants received three weekly injections of leukocyte-poor PRP or saline. After twelve months, pain had improved by 2.1 points with PRP and 1.8 points with saline. The trial reported a between-group difference of −0.4 points, with a 95% confidence interval of −0.9 to 0.2. This was not statistically significant.[3]
RESTORE used a clinically important difference of 1.8 points, rather than the review’s 1.37-point threshold. RESTORE is already included in the review’s total of 1,995 patients, so its 288 participants should not be added to that total.[3][2]
RESTORE also measured cartilage volume in the medial tibia. It fell by 1.4% in the PRP group and 1.2% in the saline group, without a significant difference. This trial did not show that PRP prevented cartilage loss.[3] A lower pain score should therefore not be presented as proof that cartilage has regrown.
What Do Cell Studies Show?
Cochrane’s 2025 review included 25 trials with 1,341 participants. Eight trials, involving 459 participants, compared cell injections with placebo. The review’s search ended on September 15, 2023.[4]
At up to six months, the placebo comparisons suggested:
- Pain: an average benefit of 1.2 points on a 0–10 scale. The uncertainty interval ranged from no benefit to 2.5 points better. This analysis included seven studies and 445 participants.[4]
- Function: an average benefit of 14.2 points on a 0–100 scale, where lower scores were better. The interval ranged from 3.1 to 25.3 points better. This analysis included seven studies and 432 participants.[4]
Cochrane rated this evidence as low certainty. The studies used different cell sources, preparations and doses, and missing results from larger studies raised concern about publication bias. None of the included studies assessed radiographic progression, so this review could not answer whether injections slowed structural changes seen on imaging.[4]
The MILES trial was published in November 2023, after Cochrane’s search cutoff.[5][4] It randomized 480 people with grades 2–4 knee osteoarthritis to bone marrow concentrate, adipose SVF, donor umbilical-cord-derived stromal cells or a corticosteroid injection. The main analysis included 440 patients. At one year, none of the cellular treatments was superior to corticosteroid on the two primary pain outcomes. No group had a significant change in its MRI osteoarthritis score.[5]
MILES did not compare cells with PRP, and it did not test every cultured-cell preparation offered in Japan. It also had no saline or untreated group. Improvement at the one-year visit does not establish that corticosteroids provided a year of continuous relief.[5]
Including people with grade 4 disease does not make the overall trial result a prediction for every person with advanced osteoarthritis. The clinic still needs to consider your diagnosis and the preparation it plans to use.
Have They Been Compared Directly?
A trial involving 90 people with radiographic grades 1–3 knee osteoarthritis compared a single bone marrow concentrate injection with a single leukocyte-rich PRP injection. At two years, bone marrow concentrate was not superior on WOMAC or IKDC scores. Twenty-five participants were lost to follow-up at 24 months.[1]
Both groups received an active treatment; there was no placebo group. Improvement within either group therefore cannot, by itself, establish how much benefit the injection caused. The lack of a significant difference also does not prove formal equivalence.[1]
If PRP has not helped, this study does not establish that a more expensive cell injection should be the next treatment. An orthopedic review can help determine whether another injection, further nonsurgical care or a surgical assessment is more appropriate.
What to Check Before Treatment
The doctor needs to understand which knee is affected, what limits your daily activity, and what treatment you have already tried. Bring your current medicine list, previous surgery details, and information about earlier injections and their effects.
An MRI is not automatically needed. NICE describes a typical clinical diagnosis in someone aged 45 or older who has activity-related joint pain and either no morning stiffness or stiffness lasting no more than 30 minutes. It advises against routine diagnostic imaging unless another or additional diagnosis is suspected. It also advises against routine imaging for follow-up or to guide nonsurgical care.[6]
If a clinic requests a new scan, ask what it needs to assess. If you already have imaging, find out whether it wants the report, original image files or both. The MRI preparation guide covers these questions.
Exercise remains part of osteoarthritis treatment. NICE recommends therapeutic exercise suited to the person’s needs, with supervised sessions where appropriate. For people living with overweight or obesity, weight loss can also help; 10% is likely to provide more benefit than 5%.[6] For someone weighing 80 kg, these amounts would be 8 kg and 4 kg. This is an example, not a requirement for injection treatment or advice to lose weight when your weight is already appropriate.
NICE recommends a topical NSAID for knee osteoarthritis. An oral NSAID may be considered when topical treatment is ineffective or unsuitable, after reviewing gastrointestinal, kidney, liver and cardiovascular risks. Corticosteroid injections can sometimes support exercise or be considered when other medicines are unsuitable or ineffective; expected relief is short term, about 2–10 weeks.[6]
Joint-replacement referral is another option when symptoms substantially affect quality of life and nonsurgical treatment is ineffective or unsuitable.[6] Discuss these alternatives before paying for another injection course. Do not change prescribed medicines without advice from your treating clinician.
What to Ask About the Preparation
For PRP, ask for the preparation name, platelet concentration, injection volume, white-cell content and number of injections. A label such as “five times concentrated” only compares the preparation with the starting blood sample.
For example, 5 mL containing 1,000,000 platelets per microlitre contains 5 billion platelets in total. This is a calculation, not a recommended dose. The PRP review used a concentration cutoff described as 1,000,000 ±20% platelets per microlitre. Some higher-concentration study groups had longer-lasting benefits, but comparisons between studies do not prove that increasing the dose will improve an individual patient’s result.[2]
Leukocyte-poor and leukocyte-rich describe white-cell content, not platelet dose. Laboratory concerns about white cells have not consistently translated into different clinical outcomes.[2]
Also check whether the proposed treatment is fresh PRP, APS or PRP-FD. Kitasato describes APS as further processing of PRP to concentrate selected proteins. PRP-FD involves extracting components, removing cells and freeze-drying the preparation.[7] Results for fresh PRP should not automatically be applied to these other preparations.
For a cell treatment, request:
- the cell type and tissue source;
- whether the cells come from you or a donor;
- whether they are cultured;
- the planned dose and what the cell count measures;
- where processing takes place; and
- which quality results must be available before injection.
A total nucleated cell count is not the same as a stem cell count. Viability describes the proportion of cells alive, while microbiological tests address contamination. Ask whether any results will still be pending when treatment is given and who will contact you if a later result is abnormal.
In MILES, researchers checked total nucleated cell count, viability and endotoxin before injection. One BMC participant and four SVF participants did not receive injections because their preparations failed release criteria. The researchers also performed 14-day sterility testing after administration.[5] These figures describe that trial, not a failure rate for Japanese clinics.
How Much Does Treatment Cost?
Published prices can help you understand the likely scale of the expense, but they are not a personal quotation. The following university-provider fees were checked on September 8, 2026.
| Provider and Treatment | Published Fee, Including Tax | What to Check |
|---|---|---|
| Fujita Health University Haneda Clinic: knee PRP, described as 20-fold concentration | ¥440,000–¥880,000[8] | Overseas residents pay different fees and need to contact the clinic. |
| Fujita Health University Haneda Clinic: autologous adipose-derived MSC culture and injection | ¥1,650,000–¥3,300,000[8] | The published range is not an international-patient quotation. |
| Kitasato University Kitasato Institute Hospital: APS | ¥330,000[7] | APS is a separately processed blood preparation, not a standard PRP price. |
Kitasato says its APS fee includes the treatment-day consultation, blood collection, injection, preparation kit and other materials.[7] Fujita’s published ranges do not explain every difference in course size or patient circumstances.[8] Neither provider’s price list establishes a Japanese average or proves that its treatment is more effective.
Ask whether your quote covers one knee or both, how many injections are included, and whether assessment and follow-up visits cost extra. Keep travel and accommodation separate. The knee treatment cost guide explains the other expenses to consider.
For cultured cells, check cancellation terms before collection, during processing and before injection. Also ask what you would owe if the clinic cannot prepare a usable batch. Do not assume that a listed fee will be covered by your insurer.
What Does “Approved” Mean?
A regenerative medicine provision plan is different from product approval. Under the process described by Japan’s Ministry of Health, Labour and Welfare, a provider prepares a plan, obtains a committee’s opinion and submits it to the regional health bureau before providing treatment covered by that framework.[9]
PMDA separately reviews the quality, efficacy and safety of products, including cellular and tissue-based products.[10] A plan number or a processing-facility record does not establish that a particular product has marketing approval or works better than PRP.[9][10]
If a clinic describes its treatment as approved, ask for the exact Japanese treatment name, provider name, applicable plan number and patient information document. For a claimed product approval, ask for the product and approved indication. The Japan registration and compliance guide explains these separate records.
How Many Visits Are Needed?
Preparation time does not tell you the full appointment schedule. Kitasato says fresh PRP or APS separation and extraction takes about 30 minutes after blood collection. However, it first holds a consultation and schedules treatment for another day. It mainly lists fresh leukocyte-rich PRP for conditions outside the joint and APS for conditions inside it, including osteoarthritis.[7]
Kitasato lists blood draws of 26–56 mL for PRP and 55–56 mL for APS. Its PRP-FD preparation uses 51 mL and takes about three weeks before administration.[7] These are that hospital’s arrangements, not a standard knee-treatment itinerary for Japan.
Fresh PRP can also involve several visits. RESTORE, for example, used weekly injections rather than a single appointment.[3] Cultured cells require time for collection, processing and release checks. Confirm the proposed dates, repeat visits and policy for delays before booking non-refundable travel.
Risks and Follow-up
Kitasato warns that pain, swelling or redness may last several days to two weeks after its injections.[7] Sudden severe joint pain, swelling, skin-colour changes, or feeling unwell with fever or shivering need urgent assessment. These can be symptoms of septic arthritis and should not be dismissed as normal recovery.[11]
In Cochrane’s review, serious adverse events occurred in 4 of 242 cell-treated participants and 5 of 219 placebo-treated participants across seven trials. The evidence was very low certainty. These small numbers do not establish that cells are safer or provide a reliable personal complication rate.[4] If treatment includes marrow or fat collection, consent should also cover collection-site and anaesthetic risks.
Before treatment, record pain during an activity you want to improve, walking tolerance and pain medicine use. If the clinic uses a questionnaire, keep the same version and scale at follow-up; WOMAC and KOOS are not interchangeable. Note medicine changes so they can be considered when reviewing your progress.
Before leaving Japan, request a treatment summary with:
- the affected knee and procedure date;
- the preparation and administered volume or dose;
- the batch identifier and clinic release record for processed cells;
- medicines given and any immediate complications;
- exercise or weight-bearing instructions;
- warning signs and an urgent-care plan; and
- follow-up dates and clinical contact details.
Your doctor at home may need these records if symptoms change. Agree on a review date, and have a poor response reassessed before paying for further injections.