A number of studies indicate that a small reduction in volume in an enclosed hydraulic space, as in the case of of an intact inter vertebral disc, results in a sharp reduction in intra-discal pressure. A reduction of intra-discal pressure results in the herniated disc material receding toward the disc center, thus leading to a reduction in the compression of the nerve root, and associated radicular pain. In PLDD, this mechanism is exploited by the application of laser energy to evaporate water in the nuclear pulposa of the disc. This is done by the delivery of laser energy to the nuclear pulposa by a laser fiber through a hollow needle guided into the nuclear pulposa under fluoroscopy or CT guidance. This results in a reduction in volume, and a reduction in intra-discal pressure. In addition, it also results in a temperature increase which causes a change in the protein structure of the nuclear pulposa, which limits its ability to attract water, thus causing a permanent reduction in the intra-discal pressure.

All contained disc herniations (protrusion or subannular extrusion) are good indications for treatment. Non-Contained disc herniations which are contiguous with the parent disc (transannular extrusion) are also indicated for treatment. Patients with sequestered discs or those with narrowed inter vertebral disc space or obstructive vertebral abnormalities are not consided to be well indicated for this procedure.

While a number of lasers have been tried (in many cases successfully) for the PLDD procedure, the 980 nm laser wavelength represents the laser wavelength which has the highest chance of successful treatment. It has a much higher absorption in water that either the 810 nm wavelength (5 times)  or the 1064 nm wavelength (2 times), thus resulting in a high specificity of action, which leads to a lower overall dose of laser energy energy and lesser heat diffusion, thus reducing the probability of side effects and thermal damage.

The technique of PLDD involves a fiber optic (400 microns) cable being introduced through a 20 gauge needle inserted into the nucleus pulposa of the herniated disc under local anesthesia and fluoroscopic monitoring. Laser energy is delivered into this space, which results in vaporization of nucleus material, and a consequent reduction in intradiscal pressure. This results in a migration of the herniation away from the nerve root. The gas formed by the vaporization of the nucleus material is evacuated during the procedure with the help of  a special handpiece designed by Star Lasers. Energy Levels, exposure times, and the number of pulses are decided by the operator, depending on the pathology to be treated ( protrusion or extruded disc).

The percutaneous procedure does not damage the vertebral body, by removing the inter vertebral lamina, nor does it damage the ligaments and facet joints. It has several advantages over conventional surgical procedures. These include :-