Biologics and Spine: Cells, Signaling, and Surfaces
For patients with spine pain, the future holds great promise. Treatment methods of the past reflect limited insight into the spine and include techniques used to treat patients with spine disorders that now seem rudimentary. Researchers are advancing our understanding of cellular biology and the ways in which cells communicate, and more efficient and effective treatments are already changing the treatment landscape. Surgeons relied on cortico-cancellous graft without instrumentation to stimulate fusion, although in retrospect, the properties and functions were not fully understood. Bone grafting failures led to the use of stainless-steel devices that provided stability but did not participate in a biological fashion to promote healing and strength. A new frontier has emerged. Autogenous and allogenic bone graft once thought to consist of dead tissue actually may contain cells and proteins that signal events that control formation of bone, cartilage, and/or soft tissue. A new era of tissue engineering is under way, with surgeons now injecting patients with proteins and other components of cancellous bone, including bone marrow, mesenchymal stem cells (MSCs), and hematopoietic cells, to promote healing of tendons, cartilage, muscle, spinal cord, and ligaments, for example. Continued studies have led to our awareness that MSCs are pericytes that live on the capillary and are activated by trauma to move off the capillary and morph into stem cells that stimulate a healing response—resulting in a change in the definition of “MSCs” by Arnold Caplan, PhD, from “mesenchymal stem cells” to “medicinal signaling cells.” How do they talk to each other? When injected into the vein, how do stem cells move from the vasculature into the tissue? Much has been learned about orthopedic treatment at organ and cellular levels, but the next advances will occur at the molecular level—cell-to-cell signaling and cell-to-cell control. Ongoing research is examining ways to manipulate biomaterial at the nano level to make the orthopedic implant biologically active and able to participate in and enhance tissue repair and tissue engineering. We have discovered inside the stem cell the entire orchestra that we need to create and repair tissue. We have modified surfaces to make them more bioreactive. Revolutionary treatments for degenerative disease and spinal deformity and injury are at hand.