Marc Darrow MD, JD 

Many people today are exploring meniscus surgery alternatives. One reason is that they may be on a waiting list to get the surgery. Another is that they have been doing research and are not absolutely convinced that meniscus surgery will help them anyway.

Meniscus repair surgery, opinion as of 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 knee needs its meniscus:

  • “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.”

Surgical repair? Patients should be warned the return to sport should be delayed for up to 6 months

  • “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.

  • “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

  • “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.

  • 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.White Zone,” and “Red Zone,” meniscus tears.

The Meniscus is always trying to make more meniscus

A study in the Journal of orthopaedic research (2lead by the Department of Orthopaedics and Rehabilitation, University of Iowa discusses how a meniscus regenerates and heals.

The researchers of this 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.

“White Zone,” and “Red Zone,”

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.

The meniscus is mobilizing the stem cells already in the knee to the site of the its injury.

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.

Research from September 2020: Stem cells live in all the zones of the meniscus

A study published in the journal Arthroscopy (3) wanted to know what type of stem cell populations lived in the meniscus’s red-red (RR), red-white (RW) and white-white (WW) zones and what type of blood flow went into these areas. To find out they performed a study on human cadaver menisci. So, what did they find?

  • There were no significant differences in the clonogenicity (the ability to clone itself to start healing repair) of isolated cells between the three zones.
  • Progenitors (cells like stem cells that differentiate into different types of cells, chondrocytes for example that make cartilage) from all zones were found to be potent to differentiate to mesenchymal lineages.
  • Additionally, results demonstrate the presence of vascularization in the WW zone. The white-white is typically considered unrepairable because it is believed that no blood flow is present.

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 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.
3 Chahla J, Papalamprou A, Chan V, Arabi Y, Salehi K, Nelson TJ, Limpisvasti O, Mandelbaum BR, Tawackoli W, Metzger MF, Sheyn D. Assessing the Resident Progenitor Cell Population and the Vascularity of the Adult Human Meniscus. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2020 Sep 23.
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.