Marc Darrow MD, JD 

Often I will hear remarkable statements in emails. Here is an example of one shared from someone who has knee pain, a previous meniscus surgery and the prognosis for the need of a knee replacement.

This person contacted me because they were interested in a stem cell program to help them avoid a knee replacement. He reported that he recently had an arthroscopic surgery to remove part of his meniscus.. The doctor who performed the surgery told his patient to make sure he called him when they were ready for knee replacement.The doctor said that he was already familiar with this patient’s knee anatomy and he could be counted on to do a good job when it was time for the replacement.

  • The doctor was so sure that the arthroscopic procedure he performed on this person’s knee, specifically the meniscus, would cause sufficient accelerated knee damage that knee replacement would be needed sooner rather than later. The doctor did not want to lose out on being able to perform the replacement surgery.

As the predicted knee degeneration occurred, the patient instead reached out to us and stem cell therapy. Hindsight and foresight, the person had wished they would have reached out before the surgery so we could have helped with his meniscus repair. To be fair, some people have good results with arthroscopic knee surgery. 

It you have been diagnosed with:

  • partial posterior root medial meniscus tear,
  • had a meniscus injury with ACL tear,
  • bucket handle meniscus,
  • Meniscus degeneration with osteoarthritis,

Stem cell therapy may be an option for you. Let’s examine some research.

Meniscus repair surgery, opinion as of January 2020

A 2020 study in The archives of bone and joint surgery (1) offers an updated opinion on meniscus surgery. Here are some points brought up by the surgeon researchers.

  • “The menisci (meniscus) perform many essential biomechanical functions. These functions include load transmission, shock absorption, stability, nutrition, joint lubrication, and proprioception (the sense of knee in 3D space). They also serve to decrease contact stress and increase contact area and joint congruency. The knee would be deprived of all these functions if the meniscus removed. Therefore, in the knees without the meniscus, the impact and load are three times higher.”
  • “Rehabilitation after meniscal repair is slower and different from rehabilitation after meniscectomy. The physiotherapist and surgeon should respect the slow process of biological healing of the meniscus and therefore they need to be careful with the rehabilitation program especially in active flexion. The return to sport should be delayed for up to 6 months; however, 86 to 91% of patients could back to play. It is also crucial for the patient to know there is 8 to 20% risk of failure and re-operation, however, the long term outcome of meniscal repair is better than partial meniscectomy because of chondroprotective action of meniscus.”
  • “Meniscus repair is not a small surgery without complication. It is technically challenging and has a steep learning curve. General complications of arthroscopy such as venous thromboembolism, infection and vascular injury could occur. Specific complication including nerve injuries, ligamentous injury, iatrogenic cartilage lesions, and poor suture techniques can happen during meniscal repair. The surgeon should depict and accept the eventual complications and address them as rapidly as possible. It is also important to form patients about potential complications.”
  • “Failure of meniscal repair occur in up to 25 % of patients. Failures in the first six months of surgery are usually related to technical issues during repair, while failures between 6 and 24 months are indicating poor healing process. Failure later than 2 years of repair show retear or degenerative processes in the meniscus. . . Secondary meniscectomy is a treatment for failed meniscal repair. The amount of meniscal resection is less in 35% of cases, which shows partial healing of the meniscus. Revision of meniscal repair is another option and two small series reported 25 to 33% failure rate for the procedure.”.

Can stem cell therapy regenerate meniscus tissue?

For many people, the long rehabilitation, possible need for secondary surgery, and other post-surgical factors weigh heavily in their decision making process as to how to proceed to fix their meniscus tear. For many people, regenerative medicine in the form of stem cell therapy may be something to be explored.

When seeking out stem cell therapy for meniscus tears, there needs to be a realistic expectation of what stem cell therapy can and cannot do in regard to regenerating meniscus tissue. New research into the healing world of the knee meniscus is fascinating. Despite decades of traditional medical beliefs that because of its poor or even absent network of blood vessels and blood supply, parts of the knee meniscus cannot heal. Researchers are discovering the meniscus is in fact, always trying to heal itself. HOWEVER, the expectation that stem cell therapy can regrow a meniscus from nothing or regenerate extensive amounts of meniscus tissue removed in meniscectomy must be tempered with a realistic expectation of what these treatments can and cannot do. Stem cell therapy for meniscus tears can help repair deficits in the existing meniscus. Stem cell therapy when administered as a multi-injection treatment as opposed to a single one-time shot, can also help support, rebuild, and stabilize the knee capsule and help restore a more normal knee function. A more normal knee function can remove stress from the meniscus and other supportive knee tissue such as ligaments and tendons.  What your realistic expectation of what stem cell therapy can do for your meniscus tear must be discussed with a doctor knowledgeable  and experienced in the treatment.

A strange case leads to awareness that a meniscus can regenerate meniscus tissue

In 2011, three doctors from the North Middlesex University Hospital in the United Kingdom published a strange case history in the medical journal Case Reports in Medicine.(2 What was odd about this case was that a 70 year old man who had recently undergone total knee replacement was suffering from terrible knee pain. It wasn’t the knee pain that was odd, patients frequently report knee pain after knee replacement. What was strange to the doctors was what was causing the knee pain. Here is their case:

Report: The patient’s surgery had taken place at another hospital, and he had made an initially uneventful recovery with a good clinical range of motion and satisfactory postoperative radiographs. At 9 months, however, he began to develop medial and lateral retinacular (middle and side tendon related pain) and deep knee pain, without associated knee swelling, warmth, or wound disturbance. (No infection or apparent injury)  His symptoms steadily worsened, particularly with load-bearing activity and bending his knee past 80 degrees.

“Our patient was found to have soft-tissue entrapment between the femoral component and the polyethylene tray . . . suggestive of meniscus-like tissue. Meniscal regeneration has been previously described in experimental and clinical studies following meniscectomy and has also been previously reported following TKA (total knee replacement). . . .(This may have occurred as a ) result of cellular response of mesenchymal derived cells to the application of compressive forces,” The case report concludes: “Entrapped regenerated meniscal tissue is an unusual cause of chronic knee pain following TKA and can be diagnosed and successfully treated by arthroscopic debridement. It is essential to ensure that the menisci are completely resected during the operation to prevent this phenomenon.” The small remaining meniscus was trying to make more meniscus.

White Zone,” and “Red Zone,” meniscus tears. The Meniscus is always trying to make more meniscus

A study in the Journal of orthopaedic research (3lead by the Department of Orthopaedics and Rehabilitation, University of Iowa discusses how a meniscus regenerates and heals.

The researchers of this second study hypothesized that the meniscus contains a population of regenerative cells, (cells that stimulate stem cell activity) and that these cells migrate to the site of meniscal injury. In the above study that is what the doctors speculated happened to their 70 year old patient who had the knee replacement.

If you had a meniscus tear you are familiar with “White Zone,” and “Red Zone,” meniscus tears. The “Red Zone,” part of the meniscus, the outer edges, receives a steady stream of healing cells from its well organized blood vessel network. For those of you with a meniscus injury that is being recommended to surgery, you may have had your doctor explain to you that you have a “White Zone,” tear. The “White Zone,” lies in the center of the meniscus. It does not have a well organized blood network. It is these meniscal injuries that send patients to surgery.

This is what these researchers said: “studies revealed that migrating cells were mainly confined to the red zone in normal menisci: (This is the area where the meniscus has good blood flow and healing elements are abundant). However, these cells were capable of repopulating defects made in the white zone, (the area without circulation). When the meniscus was injured, migrating cell numbers increased dramatically. Stem cells in the knee increased in number to combat the injury.These findings demonstrate that, much as in articular cartilage, injuries to the meniscus mobilize an intrinsic progenitor cell population with strong reparative potential, even into the white zone area.

The short of it? The meniscus figures out how to heal itself if it can. Even in the areas that are typically believed unhealable because of lack of blood flow to that area.

Stem cell numbers? What could be considered even more fascinating is that the meniscus signals for more stem cells from the knee capsule to come to the injured area. For those people asking about stem cell numbers that are harvested for treatment, the meniscus is mobilizing the stem cells already in the knee to the site of the its injury.

The meniscus and cartilage are always trying to heal each other

In the Journal of orthopaedic research (4doctors examined the process of meniscal regeneration and cartilage degeneration following meniscus surgical removal in mice. They found that there is a healing environment that the meniscus and cartilage create independently of each other spurred on by native stem cells, that later melds together, suggestive of a balance between meniscal regeneration and cartilage homeostasis. The meniscus and cartilage are trying to regenerate each other.

This special relationship between cartilage, meniscus and stem cells is discussed in research from the University of Iowa. The Iowa findings demonstrate that, much as in articular cartilage, injuries to the meniscus mobilize an intrinsic progenitor (stem cell) population with strong reparative potential.(5) The problem for patients is that despite the desire to heal and regenerate, as pointed out by the Iowa researchers, “Serious meniscus injuries seldom heal and increase the risk for knee osteoarthritis; thus, there is a need to develop new reparative therapies. In that regard, stimulating tissue regeneration by autologous stem/progenitor cells has emerged as a promising new strategy.”

In past articles I have written extensively about how stem cells change the environment of diseased joints to healing. Research like that above confirms that when one part of the knee is repairing, the entire knee is repairing. This change of environment is something a surgery is not expected to offer.

What are realistic expectations that stem cell therapy can help your meniscus related knee problems?

Researchers at the Osaka University Graduate School of Medicine in Japan teamed with the Mayo Clinic to release a January 2020 (6) paper outlining the current research on stem cell therapy for meniscus repair. In this study they wrote:

“Clinical studies evaluating the effects of MSC (stem cell) injections in the knee joint are limited, but early clinical data suggests encouraging results. Currently, there have not been any reported safety concerns or side-effects in the clinical use of MSC injections.

There is only one randomized double-blind controlled study to date studying the effects of MSC injections into the knee post medial meniscectomy [7]. The study contained 55 subjects in 3 groups who underwent a percutaneous injection of allogeneic MSCs with one group receiving 50 × 106 cells another 150 × 106 cells and control receiving only hyaluronic acid. At 12 months follow up, MRI scan findings reported a significant increase in meniscal volume in 24% of patients receiving 50 × 106 cells and 6% receiving 150 × 106 cells. None of the control group patients demonstrated an increase in meniscal volume. The study is limited to MRI scan being the only objective outcome measure, but the study methodology is rigorous in that it has the advantage of being blinded and randomized.”

As you have seen in this article, the meniscus has an ability to heal itself. When someone comes into our office with knee problems we start with a conversation so we can learn about the patient’s lifestyle and what are his/her goals of the treatment. Is it to get back to marathon training or is it to get up and down a staircase without his/her knee locking up? Then we will do a detailed physical examination looking for those signs that will tell us how helpful stem cell therapy may be.

Do you have questions? Ask Dr. Darrow

A leading provider of stem cell therapy, platelet rich plasma and prolotherapy

PHONE: (800) 300-9300 or 310-231-7000

Stem cell and PRP injections for musculoskeletal conditions are not FDA approved. We do not treat disease. We do not offer IV treatments. There are no guarantees that this treatment will help you. Prior to our treatment, seek advice from your medical physician. Neither Dr. Darrow, nor any associate, offer medical advice from this transmission. This information is offered for educational purposes only. The transmission of this information does not create a physician-patient relationship between you and Dr. Darrow or any associate. We do not guarantee the accuracy, completeness, usefulness or adequacy of any resource, information, product, or process available from this transmission. We cannot be responsible for the receipt of your email since spam filters and servers often block their receipt. If you have a medical issue, please call our office. If you have a medical emergency, please call 911.


1 Razi M, Mortazavi SMJ. Save the Meniscus, A good Strategy to Preserve the Knee. Arch Bone Jt Surg. 2020 Jan;8(1):1-4. doi: 10.22038/abjs.2019.45438.2242. PMID: 32090138; PMCID: PMC7007719.
2 Matar HE, Dala-Ali B, Atkinson HD. Meniscal regeneration: a cause of persisting pain following total knee arthroplasty. Case reports in medicine. 2011;2011.
3 Seol D, Zhou C, Brouillette MJ, Song I, Yu Y, Choe HH, Lehman AD, Jang KW, Fredericks DC, Laughlin BJ, Martin JA. Characteristics of meniscus progenitor cells migrated from injured meniscus. Journal of Orthopaedic Research. 2016 Nov 1.
4 Hiyama K, Muneta T, Koga H, Sekiya I, Tsuji K. Meniscal regeneration after resection of the anterior half of the medial meniscus in mice. J Orthop Res. 2016 Nov 2. doi: 10.1002/jor.23470. [Epub ahead of print]
5 Seol D et al. Characteristics of meniscus progenitor cells migrated from injured meniscus. J Orthop Res. 2016 Nov 3. doi: 10.1002/jor.23472.
6. Jacob G, Shimomura K, Krych AJ, Nakamura N. The Meniscus Tear: A Review of Stem Cell Therapies. Cells. 2019 Dec 30;9(1):92. doi: 10.3390/cells9010092. PMID: 31905968; PMCID: PMC7016630.
7 Vangsness Jr CT, Jack Farr II, Boyd J, Dellaero DT, Mills CR, LeRoux-Williams M. Adult human mesenchymal stem cells delivered via intra-articular injection to the knee following partial medial meniscectomy: a randomized, double-blind, controlled study. JBJS. 2014 Jan 15;96(2):90-8.