Definition

Theoretically, sciatica pain is defined as pain in the lower back which radiates own the leg and that is possibly caused by abnormal stimulation such as pressure, on the sciatic nerve 

Accompanying signs & symptoms

Pain in the lower back and/or buttock, and follow down a line at the back or side of the leg. 

Possible Causes

Swelling or inflammation of the vertebral disk
Vertebral disk injury or displacement
Herniated disk
Accumulated physical exhaustion
Poor posture
Deep muscle spasm
Severe muscle fatigue

Physiological Mechanisms

Although sciatica pain has been correlated with pressure on the sciatic nerve, many clinical cases have shown that "sciatica back pain" or "sciatica pain" seldomly related to or very indirectly related to sciatic nerve. Many cases presented with sciatica have no structural abnormalities. In other cases, structural abnormalities may be CO-EXIST with the symptoms, but cannot be linked as the direct cause of the symptom. Many clinic seen sciatica conditions are related to extreme and cumulative physical exhaustion in the past, with severe signs and symptoms of muscle fatigue, poor blood circulation, muscle tenderness, heat sensation around the front and lateral side of the leg.

From Chinese medicine point of view, cumulative physical exhaustion and without proper rest, local muscles produced muscle waste which is failed to be removed by the body in time. This results in muscle tenderness and soreness. Physical stress results in the production of cortisol which can suppress immune responses and prevent the body from healing mild muscular injuries and results in on going pain and ache.

Treatment Modalities

Acupuncture

Mechanism of action of the herbs used

Acupuncture and Chinese medicine treats the condition by doing the following:
Releasing muscle tensions
Relieving deep muscle spasm
Reducing local inflammation and swelling
Reducing harmful hormones accumulated in the affected areas. 
Improving local blood circulation 
Facilitating the self repairing processes
Promoting deep relaxation of the muscle
Calming the mind and body
Reducing pain, soreness and local stiffness.

Health Advice

Reducing the intake of caffeine and cigarette smoking
Eat a balance diet
Establishing a regular eating habit
Encouraging moderate, regular and outdoor exercises

References

Longman concise medical dictionary, 1994

Chinese-English Manual of Common-Used in Traditional Chinese Medicine, Ou Ming, 1995