Abstract

There has been significant debate over the role of white blood cells (WBCs) in autologous therapies, with several groups suggesting that WBCs are purely inflammatory. Misconceptions in the practice of biologic orthopedics result in the simplified principle that platelets deliver growth factors, WBCs cause inflammation, and the singular value of bone marrow is the stem cells. The aim of this review is to address these common misconceptions which will enable better development of future orthopedic medical devices. WBC behavior is adaptive in nature and, depending on their environment, WBCs can hinder or induce healing. Successful tissue repair occurs when platelets arrive at a wound site, degranulate, and release growth factors and cytokines which, in turn, recruit WBCs to the damaged tissue. Therefore, a key role of even pure platelet-rich plasma is to recruit WBCs to a wound. Bone marrow contains a complex mixture of vascular cells, white blood cells present at much greater concentrations than in blood, and a small number of progenitor cells and stem cells. The negative results observed for WBC-containing autologous therapies in vitro have not translated to human clinical studies. With an enhanced understanding of the complex WBC biology, the next generation of biologics will be more specific, likely resulting in improved effectiveness.

Highlights

  • There has been recent significant debate on the role of white blood cells (WBCs) in autologous therapies in the orthobiologics literature [1,2,3,4,5,6]

  • After more than 15 years of clinical use of autologous therapies, there are few randomized and controlled clinical trials (RCTs) and even fewer RCTs which characterize the cellular content of the autologous therapy for any orthopedic disease or injury

  • Key misconceptions arising from these preclinical studies are that platelets only contain growth factors, WBCs are purely inflammatory, and bone marrow contains only stem cells

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Summary

Introduction

There has been recent significant debate on the role of white blood cells (WBCs) in autologous therapies in the orthobiologics literature [1,2,3,4,5,6]. Key misconceptions arising from these preclinical studies are that platelets only contain growth factors, WBCs are purely inflammatory, and bone marrow contains only stem cells. In the field of autologous therapies, platelet-rich plasma (PRP) is a catch-all term that refers to a fraction of blood containing a higher concentration of platelets than whole blood. Devices that isolate the buffy coat in a small volume of plasma generally produce PRP containing high concentrations of platelets and WBCs, known as leukocyterich PRP (L-PRP). Platelets are known in orthopedic literature for containing tissue healing growth factors like transforming growth factor-beta (TGF-β), platelet derived growth

The Behavior of WBCs Is Adaptive
Bone Marrow Concentrate Contains a Complex Mixture of Cell Types
Findings
Future Direction
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