Healing of Bone Injuries
Bone is a Dynamic Living Tissue
Bone is a living tissue comprised of a number of constituents including calcium carbonate, calcium phosphate, collagen and water. The minerals and collagen provide the strength and stiffness of the bone.
The functions of bone are many including providing a framework for the body, providing attachment for muscles and ligaments, and protecting the internal organs of the body. Each type of bone has a unique purpose with its structure defining its function within the body.
Long bones (humerus, femur) are designed to allow movement. Short bones (carpals are the small bones in the wrist) are designed to transfer compressive loads from one set of long bones to another (forearm to the metacarpals in the hand). Flat bones (scapula, pelvis) are designed to protect internal organs from external forces.
Bone Growth
While long bones continue to grow in length until the epiphyseal plates (growth plates) close, the diameter of the long bones are also dynamic in nature and continue to change throughout an individual’s lifetime. New bone cells (osteoblasts) lay down on the inner layer of the periosteum (outer surface of the bone) while osteoclasts resorb bone on the inside of the bone (medullary cavity).
The relationship between osteoblasts and osteoclasts is an important one in bone health. A balance between the two will keep bone health strong. If osteoclasts are more active than osteoblasts, then the bone will become weaker. If osteoblasts out perform the osteoclasts, than the bones will become stronger.
The time that it takes for a fracture to heal will be dependent on the size of the fractured bone along with the specific type of fracture. In general, a larger bone (femur) will take longer to heal (more osteoblasts need to be laid down to bridge the bone fragments) as compared to a thinner bone (fibula).
Types of Fractures
Fractures can be classified as simple (clean fracture that stays in place) or compound (bone ends penetrate through the skin). The direction of the fracture within the bone can also define the type of fracture including:
- Transverse – across the width of the bone
- Comminuted – multiple small fractures within an area
- Oblique – diagonal across the length of the bone
- Spiral – diagonal around the length of the bone
- Avulsion – tearing away of a small piece of bone
- Impacted – bone is driven into another piece of bone
- Greenstick – partial fracture occurring in young bones
Bone Tissue Healing
The healing of bone tissue begins immediately after the fracture occurs. The first phase of healing is called the acute inflammatory phase. The goal in this phase is to stop blood loss from the wound, create a clot to occlude the end of any ruptured blood vessels, and debride the area with the assistance of increased biochemical activity.
A callus made of highly vascularized fibrous tissue is then laid down between the fractured bone ends during the second phase of the healing process. This is known as enchondral bone healing and occurs when there is a gap between the two fractured ends. If the bone is fractured and the ends are still intact, the bone will heal through direct bone healing without the need of a callus (Anderson, M.K., Parr, G.P., & Hall, S.J. 2009).
The last phase of healing is known as the maturation and remodeling phase because the callus is gradually remodeled from both osteoblast and osteoclast activity. The osteoblasts will continue to lay down new bone cells while the osteoclasts resorb bone fragments until normal shape and strength is restored.
Fracture healing can be hampered if stress is placed upon the bone before the bone has fully healed. Force exceeding the strength of the new bone growth can reinjure the fragile bone tissue. When this occurs, the healing process has to restart back in phase one extending the rehabilitation.
tibia fracture
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