There are three distinct phases in the healing process.
The first of the three phases of injury healing is called the inflammatory stage, which simply involves white blood cells called phagocytes, which help remove debris and damaged tissue and further help recirculation of the area. The second stage is called the proliferative phase, where red blood cells called fibroblasts form a glue-like substance, which acts as a scaffold or infrastructure of new tissue to be laid down. The last stage, known as the remodeling stage, is where more cells are added to the glue and strengthened to form a substance called type 1 collagen, which is thick, strong and resistant.
Inflammatory stage
Days 1-4: At the injury site, cells clot to seal the damaged area to stop re-aggravation and further bleeding. Similarly, the phagocytes migrate to the same area to ‘cleanse’ damaged cells that are dysfunctional. The damaged cells release a chemical that actually attracts the ‘cleansed’ cells to go to the area to begin purification. This process is called phagocytosis. After two days, more chemicals released by the damaged cells attract more white blood cells (monocytes, macrophages and lymphocytes), which also aid the reparation process of damaged cells. Additionally, once cells like the macrophages reach the wound, they release further chemicals to enhance oxygenation and nutrition that further aid healing. Once the damaged cells are clear, the space filled with the platelets (the clot that forms to stop the initial bleeding) is broken down and invaded by other cells (fibroblasts). These become more active on day seven, when more glue-like substance is laid down to form a bond. This is known as scar tissue.
Proliferative stage
Days 7-14: At this stage, the fibroblasts lay down more chemicals to begin more solidification of the scar tissue. This is known as the proliferation stage. This solidification of further cells (called collagen) to bond the already forming scar tissue is laid down in disarray, mostly haphazard with no direction of fibre orientation. This makes the tissue weak. During this stage, the original blood clot that formed to stop the initial bleeding begins to dissipate as more cells are laid down to ‘coagulate’ the torn fibers together again. Further, more specialized cells are mobilized once the glue has formed, called myofibroblasts, which begin to fuse the torn fibers that were initially damaged.
Remodeling stage
Days 14-90: The last stage is called the remodeling stage. Here the haphazard scar tissue (glue) that formed in the proliferation stage begins to orientate itself and becomes more specific to the function of the muscle/tendon. This is greatly influenced by the external stresses placed on it. More collagen is added here to reinforce the weak scar tissue and tensile strength begins to develop as more tissue is laid down.
Collagen reorientation and strength increases slowly, reaching 70% of the initial strength in six months to two years. The new scar tissue remodeled almost always differs from the original muscle/tendon it replaces by having fewer connective tissue cells, fewer blood vessels and more disorganized cells. Mostly, the new scar tissue/muscle does not restore 100% to what it used to be, therefore is vulnerable to further injury later on.
In conclusion, once a severe injury occurs to the tissue, it can take more than the ‘normal’ three to six weeks to heal, and indeed a follow-up program of rehabilitation will be required, if a full recovery is expected.
