Etiology and Pathogenesis of Trauma

Etiology of trauma

Exogenous pathogenic factors

Trauma caused by external forces

There are a total of four forces: direct force, indirect force, forced myotasis and chronic strain.

Direct force: The trauma occurs in the region directly acted on by the external forces such as fall, crush, impact, sprain and beating. The fracture caused by direct forces is often comminuted or transverse; the trauma is often open and the soft tissue is seriously damaged; the dislocation is often complicated by avulsion of the epiphysis; the tendon injury is often of contusion.

Indirect force: The trauma occurs in the region away from the part acted on 'by the external force. For example, transmitting force, rotation force, and lever force, etc. may cause fracture, dislocation and tendon injury in corresponding parts. In the case of fall from a high place, if the hip first touches the ground, it may cause compression fracture of T12 or L1 due to the force from both the impulsion of the body and the reaction of the ground. The fracture caused by indirect force is often oblique, spiral or compressive; the tendon injury is often of sprain and generally milder than that caused by direct force.

Forced myotasis: In the case of sport or work, the muscle contracts strongly because of great exertion, which may cause breaking of the tendon or bone fracture. For example, throwing a javelin may cause a fracture of humeral shaft because of strong contraction of the muscle. The fracture caused by forced myotasis is commonly avulsed or spiral.

Chronic strain: Constant walking, constant standing, overstrain or prolonged abnormal posture may result in diseases because of constant overwork of the muscle, tendon and joint. For example, constantly bending over the desk may cause strain of cervical muscles; trudging over long distance may cause fatigue or fracture of second metatarsal bone. The condition of chronic strain gradually deteriorates.
    
Invasion by six exogenous pathogenic factors and poisons

Invasion by six exogenous pathogenic factors or poisons may cause diseases of tendons, bones and joints. For example, attack by pathogenic wind, cold and dampness in the case of trauma may cause pain of the joints of the waist and the limbs, or impaired movement. Invasion by poisons in the case of trauma may give rise to infection of the local part or the whole body, often complicated by various diseases.
 
Endogenous pathogenic factors

In the occurrence of traumatic disorders, exogenous pathogenic factors are very important, but such inner factors as age, physique and local anatomic structure are also closely related to it.

Age    There are different predilection sites and incidence of trauma in persons with different ages. For example, in the case of fall with the hip first touching the ground and the same external force, fracture of neck of femur often occurs in old people, seldom in young people. Children are subject to fracture because of their delicate bones. But their fractures are often incomplete because of their thicker and flexible periosteum. The injury of epiphysis often occurs in young people who are in their growth and developmental periods and whose epiphyses are not occlusal. People in the prime of life seldom get fracture when falling, for their tendons and bones are strong.
     
Physique    The strength of physique is closely related to the occurrence of trauma. Young and vigorous people with abundance of qi and blood, rich kidney essence and strong tendons and bones seldom suffer from trauma. Old and weak people with deficiency of qi and blood, asthenia of the liver and kidney and osteoporosis are susceptible to trauma. For example, when falling on a level ground with the hip first touching the ground, they may also get fracture of neck of femur or intertrochanteric fracture even the external force is small.
     
Anatomic structures    Trauma is related to the anatomic structures to a certain extent. Transmitting force acting on a bone usually causes fracture in the junction between compact bone and spongy bone. For example, the part 2 to 3 cm away from the lower end of radius is the junction of compact bone and spongy bone, it is subject to fracture when the palm touches the ground in a fall. The clavicular fracture often occurs in the junction of the two arcuations without protection of ligaments. Take occult cleft spine of $1 as another example, because there is no spinous process, the supraspinal and interspinal ligaments are short of their attachments, thus the stability of lumbosacral joint decreases, the weak part is susceptible to trauma.
    
Occupation     The occurrence of trauma is to a certain degree related to occupation. For example, mechanical workers without necessary safety devices are subject to the trauma of hand. Workers constantly bending over or shouldering heavy load are subject to chronic lumbar strain. Athletes, acrobats and Gongfu actors are subject to various sport injuries. And middle-aged people constantly bending over the desk are subject to cervical spondylopathy.

Pathogenesis of trauma

Pathogenesis of fracture

Fracture displacement 

The extent and direction of fracture displacement are related, on the one hand, to such external factors as the strength and action direction of the force and the shift condition after trauma; and on the other hand, to such internal factors as the gravity of the distal part of limb, attachment point of the muscle and its contractility. The fracture displacement is of the following five types (see Fig. 1), and any type may be accompanied with the others.

Angulation displacement: The axial lines of the two ends of fracture cross each other, forming an angle. The angulation may be classified as forward, backward, inward or outward angulation according to the direction of its apex.

Lateral displacement. The two broken ends of bone are displaced laterally. The displacement in limb bone, according to its displacement direction of the distal end, is classified forward, backward, inward or outward displacement. In the spine, it is classified according to the displacement direction of the vertebra just above it.