Bone Fixator
Colorized scanning electron micrograph shows bone cells attaching to a new type of bone cement made of calcium phosphate. Credit: H.Xu/American Dental Association Foundation.

Factors Influencing Successful Fracture Healing (1/3)

Once a bone is damaged or a fracture takes place, the new cells have to be laid out so that bone segments can unite, and the fracture can be bridged and repaired. The rate of fracture healing is dependant on a wide range of factors. They can be grouped into two main groups: systematic and local. Systematic factors relate to the overall condition of the patient's body systems. Such factors might be patient age, nutrition status, tobacco use, activity level, nerve function, hormones and drugs. The oxygen supply to the fracture site is of prime importance to the healing process and therefore properly-functioning oxygen intake and delivery systems of human anatomy are advantageous.

Local factors relate to conditions at the injury site. They would reflect the severity of the injury, i.e. soft tissue damage, bone loss, infection, local damage to vascular and nerve tissue, local pathological conditions and the mechanical environment at the fracture site. Drugs can be used to promote and accelerate healing activities. One of the most important factors in the fracture healing is the controlled immobilisation and the bridging of ends of broken bone segments. This needs a correct mechanical environment at the fracture site and to some degree dictates, which healing process takes place. It is common practice to employ orthopaedic fixators for this purpose, and to align the bones correctly. The range of such fixators, their advantages, disadvantages and suitability are discussed below.

In addition to fixation of the fracture, additional mechanical or electrical stimulation can be applied in order to promote healing. To the writer's knowledge, no statistically conclusive research has been done into electrical stimulation and therefore it is not possible to draw conclusions from this method. Nevertheless, experiments on animals suggest that electrical stimulation applied correctly can increase healing rates.

On the other hand, mechanical stimulation, also know as dynamisation of the fracture anatomy, involves forced controlled relative motion between the ends of the fractured bone segments, also known as interfragmentary motion (IFM). It is specifically applicable to the external bridging callus type of healing as the IFM can stimulate callus formation. There have been many attempts to quantify the optimum magnitude of the IFM but so far no statistical conclusion can be drawn. Studies performed are very subjective and therefore it is hard to generalise the results. Motion in the axial direction of the bone is believed to help bone cell formation [1-10]. Shear between bone interfaces is believed to be a destructive influence as it leads to formation of the fibro cartilage and possibly pseudarthrosis [5, 6, 11, 12]. Torsion and bending are more complicated to analyse as they involve both axial and shear displacements. Continue reading on the next page...