the curious case of fracture healing

The human body is an amazing thing. Back in early October, I fell and shattered my left ankle in more than a dozen places. The lateral and medial malleolus were a splintered HM–hot mess. If I didn’t have access to quality surgery (not to mention 12 screws and a really long orthopedic plate holding everything together), my left ankle would certainly be disfigured. I’d also be crippled.

Just two months after surgery, I was back on both feet. Walking. Perhaps not extremely capably, but still walking. Four months later I have excellent range of motion, and my step is pretty sprightly. I am amazed to be where I am. And the process of fracture healing is an incredible journey. Follow me on this.

When you break a bone or bones, the human body springs into action. As Richard Marsell and Thomas Einhorn put it in their scholarly article, The Biology of Fracture Healing:

The biology of fracture healing is a complex biological process that follows specific regenerative patterns and involves changes in the expression of several thousand genes.

Several thousand genes? That’s right. The process of fracture healing can be described as four overlapping stages, roughly:

  1. Inflammation. Within a few hours after the break, the body rushes blood to the break site. A protective blood clot (hematoma) is formed. Think lots of swelling, bruising. Granulation tissue forms at the ends of the fracture, and specialized cells called phagocytes eat away at any dead tissue and unwanted bacteria.
  2. Creation of a primary (soft) callus. More specialized cells–this time chondroblasts–are recruited to develop a callus made of two types of collagen at the break site. Revascularization also kicks into action, ensuring a healthy blood supply.
  3. Creation of a bony (hard) callus. The soft callus is replaced by a bony callus, which helps stabilize the healing bone. At this stage, you can thank cells called osteoblasts for mineralizing the collagen to create the bony callus.
  4. Bone remodeling. This stage is pretty cool and time intensive, taking months to years. Yes, years. (As many as nine years.) The bony callus is remodeled as lamellar bone with its own medullary cavity–the area within the bone where marrow is stored. In the remodeling stage, the bone regenerates itself. It’s nerdy cool and amazing to learn up on.

Want to get schooled on the specific biological processes in fracture healing in the medical literature? Visit here.


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