Have you ever broken a bone? Felt something go crunch and known that there were things moving against each other inside you that shouldn’t be? Did you have the trip to the emergency room, the inspection by the doctor and radiology?
Say a person breaks their tibia and fibula, that both bones have completely, but cleanly snapped. They are sent into surgery and have some combination of plates, screws and rods inserted in your leg. You are given a walking cast, told to take it easy, and given follow up appointments. So begins the bone healing.
This is a simplified story of a significant, though straight froward, fracture. You are far better to snap your bone cleanly and completely than to have a crush injury or a significant displacement – both of which have larger risks of complications than a clean break. Though surgery was required to stabilize the fracture site the bones stayed close to alignment and there were no small fragments or jagged ends to contend with. This means that the healing will be relatively easy, with the internal stabilization they will be mobile (avoiding a lot of muscle loss) and should not have issues with alignment or leg length discrepancy.
Internally the healing process has both similarities and differences to soft tissue healing. Bone is well vascularized compared to ligaments and does heal more quickly, but the structure is quite complex and there are several stages between basic reconnection and complete restoration. With bone tissue, like skin tissue we will see regeneration more than scarring. With good healing there can be healing that is almost impossible to detect.
In the first 6-8 hours the blood that is being released by the torn capillaries in the bone forms a clot called a fracture hematoma. This clot means that the to ends of the bone are divided by dead tissue. Any cells within that clot will die and need to be carried away before repair can be carried out. Within a week the torn capillaries work their way into and through the fracture hematoma, reconnecting the to separated pieces and bone and begin delivering osteoclasts (bone destroyers), to dissolve the dead bone fragments. Phagocytes also arrive to carry away the other dead tissues. In this stage the fracture hematoma is transformed into a procallus, a proto-scar tissue made up of granulation tissue,
Over the next two weeks fibroblasts and mesenchymal stem cells invade the procallus. The fibroblasts build a latticework of fibrocartilage across the fracture site and the mesenchymal stem cells become osteoblasts (bone builders). This structure is called a soft (fibrocartilaginous) callus.
From 3 to 6 weeks the spongy bone begins to develop. This process begins close to the healthy bone tissue and works its way across the gap. As the spongy bone is deposited it begins to transform the fibrocartilage into bone too. This stage is the development of the hard (bony) callus stage. Many of you will notice that it is at this point that casts and other fixation devices (internal or external) are removed.
Over the next 3-4 months the body will be industriously remodelling this new bone. Destroying and rebuilding cells, increasing the deposition of the calcium and phosphorous to make the bone harder. In long bones the creation of Haversian canals will occurs as will the redevelopment of a central marrow canal.
This stage is when the bone becomes customized to your usage patterns and habits so that it is strong where and when you need it to be. This type of process is occurring in healthy bones all the time and until it is complete a fracture site is not completely healed.
How can this knowledge of healing help someone recovering from a fracture? By increasing their dietary intake of calcium, magnesium, phosphorus, the primary minerals needed to build bones, they can help encourage speedy and thorough rebuilding. By understanding the importance of circulation in moving cellular, nutritional and waste products to and from the area of injury they can choose massage therapy, acupuncture or physiotherapy to encourage fluid movement without increasing physical activity past safe levels.