Without a detailed understanding of how and when different kinds of tissues heal, we cannot effectively facilitate healing and may instead hinder, slow and reduce healing and the ultimate tensile strength of the injured tissue. In this blog, we discuss the three phases of healing before sharing the ways these phases of healing differ across tissues.

There are three generally accepted phases of healing: the inflammatory phase, the reparative phase, and the remodelling phase. Each of these phases is essential to the ultimate healing of a wound or injury, and the details of how and when each phase will occur, will differ slightly depending on the tissue affected.

Below, we will discuss what is involved in each phase of healing before sharing a free resource that will discuss the timeline and specific differences in healing for the tissue affected.

The Inflammatory Phase

Inflammation is the first phase of wound healing and is essential for healing to occur; if the inflammatory phase is too short or too long, healing will be impaired. The inflammatory phase kicks off with a vascular response that creates homeostasis, or a balanced state. If a wound is formed, blood vessels are disrupted, which leads to bleeding and the presence of blood between cells. Blood platelets will react with collagen to cause a coagulation cascade, resulting in the formation of a fibrin network. The fibrin network will support the blood plug, as well as the next step in the inflammatory process.

Using the fibrin network as support, cellular infiltration will be the main activity in the wound for the next two to three days. The first cells to enter the wound area are neutrophils, which make an appearance six hours after the wound is created. Their primary purpose is to clean or debride the wound and prevent contamination. The next cells to appear, within 24 to 48 hours, are macrophages, which play a role in phagocytosis, debridement, matrix synthesis regulation, cell recruitment and activation, and angiogenesis. Macrophages are essential to transition the wound to the next phase of healing – reparative.

Wounds need to transition from inflammation to the reparative phase after two to three days. This transition phase is important when choosing which modalities we use for treatment. We don’t want to suppress the inflammatory phase, but in some tissue we will benefit the body if we can speed it up, or prevent it from continuing past the first few days. Tissues like tendons and ligaments have a very limited inflammatory phase, and we’ll want to be very cautious about anything that might suppress this phase.

Reparative Phase

The reparative or proliferation phase starts off with fibroblast proliferation and migration within three days of injury, and is followed by matrix synthesis. Matrix is made up of collagen, elastin and proteoglycans. Proteoglycan synthesis starts after about two weeks. In the following weeks, matrix synthesis slowly starts to increase the tensile strength of the area. As the collagen and fibroblast scaffold forms, new capillaries grow into the area until a normal oxygen level is achieved in the tissue. This tissue is generally recognized as granulation tissue, made up of a dense network of macrophages, fibroblasts and blood vessels.

During this phase it is essential to protect the tissue from any stress that might widen the wound gap, as that would delay healing and cause scarring, which reduces tensile strength in the tissue. We need to be especially cautious with our choice in therapeutic exercise at this point, as we want to start adding enough stress to stimulate proliferation and matrix synthesis, but need to continue to protect the wound from force that may lead to gap widening or a break in the newly laid scaffold, which is still very weak. 

Remodeling Phase

In the remodelling phase, collagen fibres progressively align themselves parallel to the lines of stress and strain. As they align, crosslinks form between them to create a stable formation. This process is essential if the tissue is to regain its original tensile strength, making rehabilitation during this phase critical. If the incorrect stresses are placed on the tissue, fibrous tissue might dominate this phase and tensile strength will never be regained.

Our therapeutic exercise becomes incredibly important in the remodelling phase, as the loading and stress placed on the tissue will guide and determine the remodelling that occurs. A slow progressing in loading that is led by the patient's ability and pain levels, and has a healthy respect for the tensile strength of the compromised tissue, will allow the best change to regain the maximum tensile strength available to that specific tissue. 

Different tissues have the ability to remodel differently. Bone is incredibly effective and can regain 100% or more of the original tensile strength, depending on the load it needs to adapt to. Tendons and ligaments on the other hand are comparatively ineffective at remodelling and may only regain 80% of their original tensile strength, even after a year of healing. 

Conclusion

It is imperative that we know and understand how each of our therapeutic modalities impacts on tissue and healing, so that we can use the modalities correctly and at the appropriate phase of healing. This includes everything from the application of heat and ice, massage, therapeutic ultrasound and laser, therapeutic exercise, and all the modalities in between. All of these modalities have different effects on tissues, depending on which type of tissue we’re dealing with. If we don’t know the specifics for how our modalities impact the various tissues at different phases of healing, we may well end up delaying or impairing healing unintentionally. 

Resources

Now that we have an idea of how wound healing progresses, we can move on to the when, and the specific differences between bone, muscle, tendon, ligament and cartilage.

We have created an easy-to-follow table for each tissue type, focusing on the timelines that they will generally follow in the healing process. Feel free to print this out as a poster for your practice!

You can download the PDF from: 

1. The Onlinepethealth Free Zone

2. The Small Animal Members Portal

3. The Hydro Members Portal

4. The Equine Members Portal

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