- Bone marrow contains rare progenitor cells with unlimited growth potential called mesenchymal stem cells. They are capable of differentiating into lineages of bone, cartilage, tendon, fat, muscle, and marrow stroma. They are capable of healing a clinically significant bone defect. (3, 4, 9, 18, 24)
Mesenchymal Stem Cell Osteo-progenitor Pre-OsteoblastTransitory OsteoblastSecretory OsteoblastOsteocytic OsteoblastOsteocyte
Figure 7- Mechanism for Osteogenic Cell Lineage
Adapted from Dr. Scott Bruder (2)
- These stem cells have been used to regenerate and repair achilles tendon and full-thickness articular cartilage defects in rabbits. They have also been used to regenerate normal muscle in a mouse with muscular dystrophy. Large segmental bone defects have been repaired in rats and dogs using these stem cells. (3)
- In one study, mesenchymal stem cells were isolated from normal human bone marrow and implanted into critical-sized segmental defects in the femurs of adult athymic rats. Radiographic and histologic evidence of new bone was shown by 8 weeks and histomorphometry showed increasing bone formation through 12 weeks. Biomechanical evidence claimed that femurs implanted with mesenchymal stem cells were substantially stronger compared to femurs not implanted with stem cells. (3)
- The same study demonstrated an increase of 215, 245, and 212% of strength, stiffness, and torsional energy absorbed, respectively, in samples with mesenchymal stem cells compared to those without. (3)
- A higher amount of bone is formed in defects that receive the stem cells in comparison to those that do not. (3) This means that mesenchymal stem cells increase the amount, rate, and success of regeneration.
- These rare mesenchymal stem cells can be isolated, cryopreserved, and culture expanded over one billion times without a decrease in their regenerative abilities (3). If these cells can be implanted during the microfracture surgery after culture expansion, perhaps older patients previously not candidates because of their low amount of stem cells could now have the procedure.
- In a rabbit study, mesenchymal stem cells were gathered from adult rabbit muscle and cultured in vitro into polyglycolic acid matrices. These matrices were implanted into 3-mm-diameter full think-ness articular cartilage defects in rabbits. The control was matrices that did not contain the stem cells. After 6 weeks post surgery, the control and experimental samples showed nonspecific fibrocartilage cells and abundant collagenous matrix. The cells were undifferentiated and nests of apparent cartilage were present. There was little difference between the control and experimental defects at the 6 week post operative evaluation. However, 12 weeks post surgery the rabbits with mesenchymal stem cells had a surface layer of cartilage about as thick as normal articular cartilage and normal appearing subchondral bone. The control did not produce bone and produced a noticeable division between the defect and surrounding tissue. In the experimental samples there was sufficient integration of the regenerated tissue of the defect with that of the surrounding tissue. The implantation of mesenchymal stem cells into cartilage defects effects the repair of both the articular cartilage and subchondral bone. (9)
Mesenchymal Stem Cell
Photo by Robert M. Hunt, provided by Wikimedia Commons
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