A tendon heals through a complex process, primarily via extrinsic healing when the tendon sheath is involved, characterized by three overlapping phases: inflammation, repair, and remodeling.
The Three Phases of Tendon Healing
Here's a breakdown of the healing process:
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Inflammation: This initial phase begins immediately after the injury.
- Blood vessels in the damaged area become leaky, causing swelling and attracting inflammatory cells.
- These cells help clear debris and initiate the healing response.
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Repair: This phase involves the proliferation of cells to repair the damaged tendon. According to the reference provided, extrinsic healing occurs through the chemotaxis of the specialised fibroblasts into the defect from the ends of the tendon sheath. This means that specialized cells called fibroblasts migrate from the tendon sheath into the injured area to begin building new tissue.
- Fibroblasts synthesize collagen, the main protein component of tendons.
- New blood vessels also form (angiogenesis) to support the repair process.
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Remodeling (or Organisation): In this final phase, the newly formed tissue is reorganized and strengthened.
- Collagen fibers align along the lines of stress.
- The tendon gradually regains its strength and function.
- This phase can take many months to complete.
Key Players in Tendon Healing: Fibroblasts
Fibroblasts are crucial for tendon healing. They are responsible for:
- Synthesizing collagen
- Organizing the collagen matrix
- Responding to mechanical stimuli
Extrinsic vs. Intrinsic Healing
The provided reference focuses on extrinsic healing. It's important to note that tendons can also heal intrinsically, which means healing originates from within the tendon itself, without significant involvement of the surrounding sheath. This primarily occurs in tendons without a synovial sheath.
