Introduction

Low back pain is one of the most frequent chief complaints in medical practices. Approximately 80% of the populations of Western countries will suffer from at least one episode of low back pain in their life. Pain is often characterized as either radicular or postural. While radicular pain is often due to an offending disc herniation, the etiology of low back pain is poorly understood. Proposed pathogenesis includes both mechanical and inflammatory mechanisms, including deformation of the annulus, stimulation of the nociceptive components of the spinal root, ischemia, venous stasis, prostaglandins, and cell-mediated immune response.¹ Various surgical procedures have been utilized to address the treatment of low back pain. These include both motion-sparing and fusion interventions. While these procedures have excellent short-term effects, they have been linked to longer-term complications including recurrent disc herniation, postoperative scarring, and adjacent motion segment disease. As a result, less invasive procedures have been developed. Two such procedures, laser spinal decompression and ozone chemodiscolysis, have shown significant promise.

Laser Decompression

Peter Choy and David Asher were the first to use laser energy to evaporate disc material in 1986. Their initial results were poor, but subsequent studies have had good to excellent outcomes in upto 80% of patients.² While various different lasers have been described, most of them use approximately 1200 joules per disc in a pulsatile manner. The principles of treatment are based on the hypothesis that the intervertebral disc functions as a closed hydraulic system. Thus, an increase in water content within the disc increases the pressure, as a result of the inelastic annulus fibrosus. The energy from the laser seeks to evaporate intradiscal material to decrease intradiscal pressure. Furthermore, the energy is hypothesized to denature and renature proteins, causing irreversible changes to the structure of the disc and its ability to rehydrate.³

As a result of the laser’s energy, the biomechanical properties of the disc are also affected. Experiments have shown that there is a negative correlation between laser energy and disc stiffness. While there is a decrease in intradiscal pressure, there is an overall increase in disc circumference and height as a result of the decrease in disc stiffness. The duration of these biomechanical changes has also been shown to be a function of laser energy. High-energy lasers have been shown to maintain disc height reductions on radiographs and MRI at 12 weeks of follow-up in animal studies.³

There is significant debate as to the type of laser most suitable for percutaneous laser decompression. Optical analysis of the properties of degenerative discs and the lasers used in clinical practice has revealed that the wavelength of the Ho:YAG laser provides the highest absorption rate (83% at 2060 nm wavelength). CO₂ lasers have also been found to be the most effective at ablating disc material in vitro.³ No matter what type of laser is chosen, a temperature of 100° C must be attained within the nucleus pulposus for the treatment to be affective. It is important that this heat be confined to the nucleus so as to avoid the potential for destruction of the vertebral endplates, possibly causing a sterile spondylodiscitis, which has been reported in animal models. Clinical complications that have been reported include discitis, vertebral osteomyelitis, worsening of low back pain, and failure of the percutaneous probe requiring surgical decompression. Overall, the complication rate is believed to be around 0.5%.²

While there is significant debate with regard to the optimum amount of energy that should be delivered to ablate the nucleus pulposus to reduce intradiscal pressure, indications for the procedure are confined to contained disc herniations. Patients with extruded disc herniations, sequestered herniations, narrowed intervertebral spaces, vertebral abnormalities, or those patients experiencing severe neurologic symptoms should be excluded from receiving treatment.⁴ Although there is a lack of randomized controlled trials regarding percutaneous laser disc decompression, observational studies have shown positive evidence in support of the technique. These studies have shown an average relief of 72% at 1 year, with sample sizes of at least 50 patients. A systematic review of the literature revealed Level II-2 evidence for short- and long-term relief with a Grade 1C strong recommendation.⁴