Marc Darrow, MD.

In this article we will focus on how a meniscus tissue can be regenerated. In many cases, a meniscus can heal itself or can heal with a little repair. One aspect of meniscus repair borne out by research is that your meniscus is always trying to make more meniscus.

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.

  • Recent 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.

How a meniscus regenerates and heals.

A study in the Journal of orthopaedic research (1) lead by the Department of Orthopaedics and Rehabilitation, University of Iowa discusses how a meniscus regenerates and heals.

The researchers of this study suggested that the meniscus contains a population of regenerative cells that respond to the site of meniscal injury.

Let’s take a moment to discuss “White Zone,” and “Red Zone,” meniscus tears. The “Red Zone,” is part of the meniscus, the outer edges, that has a blood supply and can heal injury.  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 many patients to surgery.

This is what these researchers said: “studies revealed that migrating cells were mainly confined to the red zone in normal menisci: (The area of good blood flow). However, these cells were capable of repopulating defects and tears 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 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.

Stem cells live in all the zones of the meniscus

A study published in the journal Arthroscopy (2) 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.

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 (3) 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 [4]. 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 can guide us how helpful stem cell therapy may be.

References

1 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.
2 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.
3 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.
4 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.