Where it all began: bone marrow and the longest-studied source of repair cells

Long before anyone looked for repair cells in fat, scientists found them in bone. In the 1960s and '70s, researcher Alexander Friedenstein noticed a rare population of cells in bone marrow that could stick to a culture dish, multiply, and form bone. Two decades later, those cells were given the name that stuck: mesenchymal stem cells. Bone marrow has been the reference point for the field ever since.

What bone marrow does

Bone marrow is the soft tissue inside larger bones. Most of its work goes into making blood. Every day it produces billions of new red cells, white cells, and platelets from hematopoietic (blood-forming) stem cells.

Alongside them lives a much smaller population of mesenchymal cells, which help support the marrow's structure and signaling. They're rare. Estimates suggest they make up only a tiny fraction of a percent of the cells in marrow, and that fraction declines as we age.

How it's collected: needle aspiration

Bone marrow for orthopedic research is usually taken from the back of the hip bone (the iliac crest), which is close to the surface and holds plenty of marrow.

1. The skin and the outer surface of the bone are numbed with a local anesthetic.
2. A specialized needle is passed into the bone, and liquid marrow is drawn out with a syringe.
3. The procedure usually takes a short time; most people describe a deep pressure or a brief ache during the draw.
4. Soreness at the site for a few days is common.

What BMAC is

The collected marrow is then processed, usually in a centrifuge, to produce bone marrow aspirate concentrate (BMAC). Like PRP, the goal is concentration: separating out red cells and gathering the layer containing mesenchymal cells, other nucleated cells, platelets, and growth factors into a smaller volume.

BMAC is a mixture, not a pure population of stem cells. Researchers think its effects likely come from the combination of cells and signals rather than from mesenchymal cells alone.

Bone marrow is where the story of mesenchymal cells began, and it's still the source other tissues are measured against.

What the research says

Because it's been studied the longest, bone marrow has the deepest pool of orthopedic research: cartilage defects, knee osteoarthritis, bone healing, and tendon repair. Some studies report meaningful improvements in pain and function; others find results similar to comparison treatments such as PRP or hyaluronic acid injections. As with other sources, preparation methods vary, which makes studies hard to compare directly.

Age and the marrow

One of the most consistent findings in this field is that the number of mesenchymal cells in bone marrow, and how quickly they multiply, declines with age. A younger person's marrow generally yields more of these cells than an older person's. This connects to a broader question in regenerative science, explored in our article on cell doubling time: why does the source, and the age of the source, matter so much?

Medical Disclaimer: This article is for educational purposes only. Autologous cell therapy using bone marrow is investigational in the U.S. for many uses, and published results vary. Always consult a qualified healthcare provider before pursuing any treatment.