Page 29 - ISAKOS 2020 Newsletter Volume 2

Stem Cell-Based Treatment for Rotator Cuff Repair: Are We Talking About the Same Thing?
Tendon-healing typically comprises different elements: progenitor cells (often called stem cells), growth factors, a scaffold, and the vascular supply. Because of their reduced blood supply, tendons have a poor ability to regenerate and heal. In particular, the tendons of the rotator cuff have reduced intrinsic ability to regenerate all 4 physiological zones of the tendon-bone insertion. The cuff enthesis progresses from tendon to unmineralized fibrocartilage, to mineralized fibrocartilage, and, at the end, to bone. However, this zonal structure is not reproduced after surgical repair of a torn tendon. Instead, a biomechanically weaker fibrovascular scar tissue rich in type-III collagen is produced. It is believed that this weaker construct renders repairs prone to subsequent failure. Snyder even postulated that we do not see a retear but rather a tendon that never healed. Therefore, investigators have explored different ways influence the healing process by supporting reconstructions with cells or growth factors. One of the most popular topics of research is the use of so-called stem cells. The present article will provide an overview of the basics of stem-cell therapy, with a focus on how to define stem cells, how to measure and count these cells, and how to better understand and interpret scientific articles about cuff biology.
Mesenchymal Stem Cells
Stem cells are fundamental building blocks that are necessary for tissue reparation and homeostasis. They are pluripotent, are able to control immune processes, and secrete a milieu of anabolic mediators, thereby playing a key role in tissue regeneration. It was previously thought that all mesenchymal tissues contain the same types of stem cells, which are plastic-adherent and are identifiable by a specific surface marker profile; over the years, however, this theory has been proven to be incorrect1. It is no longer believed that there are ubiquitous stem cells in the mesenchyme with identical mesenchymal differentiation and regeneration potential across tissue boundaries. According to current definitions, mesenchymal stem cells are perivascular tissue- specific progenitor cells that are differently expressed in bone marrow, adipose tissue, umbilical cord blood, or synovial membrane and that they should only be called stem cells if extensive experiments have confirmed that they are capable of self-renewal and differentiation into all tissue cell types. Bone-marrow stem cells are the most frequently investigated type of cells and are the only type that can be called “stem cells” because it has already been proven that they fulfill the criteria. For other tissues such as fat, umbilical cord blood, or synovial membrane, one should correctly speak of stromal cells because this stem-cell proof is still pending.
Introduction
Andreas Voss, MD
Associate Professor
Department of Trauma Surgery University Medical Center Regensburg, GERMANY Technical University of Munich, GERMANY
Corresponding Author
Mary Beth McCarthy, BA.
UConn Health Center, Farmington, CT, UNITED STATES
Augustus D. Mazzocca, MS, MD
UConn Health Center, Farmington, CT, UNITED STATES
Andreas B. Imhoff, MD, Prof.
Technical University of Munich, GERMANY
The development of new surgical techniques, implants, and specific postoperative aftercare protocols has led to substantial clinical improvement in patients managed with surgical rotator cuff repair. Nevertheless, this procedure is still associated with high failure rates. Older studies demonstrated retear rates ranging from 11% to 94%, and more recent studies have shown rates ranging from 11% to 57%. Given these findings, there is another factor that needs to be considered during our decision-making process: the biology. We have good data on different surgical constructs, and we are comfortable with the mechanical properties of our reconstructions. We also routinely account for the influence of additional mechanical factors, such as the critical shoulder angle or the acromial shape, on postoperative outcomes. But how do we account for the biology?
CURRENT CONCEPTS
ISAKOS NEWSLETTER 2020: VOLUME II 27