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.