[Causes and mechanisms of sciatic pains].

Pain along the sciatic nerve can be due to many causes. Sciatica of radicular origin caused by compression of L5 or S1 root is usually separated from truncular or peripheral sciatica. Radicular sciatica is divided into mechanical sciatica and the so-called inflammatory sciatica. In the majority of cases radicular pain is of mechanical origin and due to discal herniation in L4-L5 or L5-S1. The herniation can be visualized by lumbar computerized tomography or by radiculography. However, discal herniation alone does not fully account for the pain suffered, and inflammatory processes around the disc and the nerve root play an important role. Posterior intervertebral osteoarthritis and lumbar canal stenosis also are frequent causes of sciatic pain. Truncular sciatica is much less frequent and should incite clinicians to investigate for pelvic tumoral infiltration. Peripheral sciatica is usually caused by suffering of the external popliteal nerve around the neck of the fibula, but it may also be caused by compression of a ramus from the internal popliteal nerve, resulting in tarsal tunnel syndrome or in Morton's syndrome.