How Bone Grows and Fracture Heals

How Bone Grows and Fracture Heals.

P.K.Ghatak, MD

No 49.

Bone is the main load bearing structure of the skeletal system. Two types of bones make up the skeleton. One is the long ones – arms and leg bones, the other one is the flat bones of the skull, jaw, sternum, spine, pelvis and small bones of the wrists and ankles.

The Periosteum is a double layered outer covering of bones. In long bones the periosteum covers the entire bone. In the flat bones, the periosteum is thin and incomplete in certain bones. The outer layer of the periosteum is fibrous and acts as anchoring tissue of tendons and ligaments. The inner layer is very vital for the growth and healing of fracture, and this layer is made up of cells, nerve fibers and blood vessels. This layer is compared with the cambium layer of the barks of trees that deposits wood tissues in a ring form. The scientists count the rings to determine the age of the tree, and the prevailing nutrients and sunshine were present for that time period.

How Bones Grow.

 Long Bones.

The two ends of a long bone have a layer of cartilage, which is sandwiched between bones and is called the Growth Plate. In children, and at the time of puberty this growth plate actively multiply. A layer of new cartilage cells, connective tissue and blood vessels grow. The inner cellular layer of the periosteum supplies the pro-generator cartilage cells; in the next stage the bones cells replace cartilage cells. Osteoblasts help the tissue to calcify. Another type of bone cells called Osteoclasts remodel the bone and create lattice pattern inside the long bones which provide structural suitability and space for bone marrow to reside and multiply and is also a natural harbor for fat cells.

 Flat Bones.

The Growth Plates of the flat bones are not well defined. In some flat bones the growth plate is in the middle of the bone, in some flat bones the growing site is along the edges and in others, the bone the growth takes place from both the locations. However, the mechanism of growth is the same. In the first stage connective tissues grow, then in the second stage, the connective layer is calcified by bone cells, and in the final stage remodeling takes place.

Hormones, minerals and vitamins for bone growth.

The pituitary growth hormone is vital for the growth of bones during the growth period and in the adults for remodeling and repairs. Parathormone, Calcitonin, Calcitriol, Thyroxine, Corticosteroid, Estrogen and Testosterone, Calcium, phosphorus and vitamin D have very distinct roles in these processes.

How Bone Fracture Heals in Long Bones:

The healing of fracture takes 6 weeks, and it goes through stages.

 A. Bleeding and hematoma Stage.

Bleeding starts at the moment bone breaks, and a sharp pain is felt. Hematoma provides the cellular and fibrous tissues that forms fibrin. Fibrin filaments connect bone fragments. Bone fragments must be stabilized by splints and bandages. If movements continue, the fibrin bridge breaks down and at the end, a false joint will be created.

B. Cellular stage.

Macrophages and scavenger cells remove the dead cells and derbies from the fracture site and prepare the fracture site for calcification.

C. Calcification Stage.

This soft tissue bridge is infiltrated by Osteoblasts and calcification starts. The calcified bridge gives stability and functions return.

D. Remodeling Stage.

The osteoclasts working over months and years remove extra bone growth and realigned bone fragments in the original shape and orientation.  Osteoclasts remove the dense bone materials from inner side of the bone and create the lattice pattern. and now the bone resembles before it broke. Only visible fracture lines may be visible under x-rays.

How Fractures Heal in Flat Bones.

In some flat bones the healing is just by connective tissues joining the bone fragments. This type of repair is basically unstable and fragments separate easily. In some small bones of the wrist the blood supply to some bones is so marginal that healing takes several months or not at all. Anticipating this might happen, surgeons use silverware to tie the fragments together. In spine and pelvis initial healing by connective tissue is calcified like the long bones.

Hormones and minerals required during bone growth and also required in adequate amounts for a proper healing of the fractures.

#######################################################