Ablation of bone, cartilage, and facet joint capsule using Ho:YAG laser.

OBJECTIVE: The objective of this study was to determine of the efficiency of holmium:YAG laser for bone ablation, compared to cartilage and soft tissue of the intervertebral foramen of the lumbosacral spine. BACKGROUND DATA: The holmium:YAG (Ho:YAG) laser has been used for ablation of bulging or prolapsed discs and also has the potential for decompression of the nerve root when there is narrowing of the foraminae (foraminoplasty). It is proposed that laser ablation of bone and ligament of the intervertebral foramen for nerve root decompression using the Ho:YAG laser is able to produce sufficient bone ablation without inducing significant thermal necrosis in surrounding tissues due to its short absorption length, which could result in significant clinical advantages. MATERIALS AND METHODS: Experiments were performed on samples of laminar bone, facet joint capsule, and cartilage for quantitative and qualitative determination of the effect of Ho:YAG ablation on tissue mass loss using a range of pulse energies from 0.5 to 1.5 J/P at 15 pulses/sec. RESULTS: The results showed a significant linear correlation between the mass loss and pulse energy, and between the mass loss and radiant exposure. Electron microscopy and histology showed that the Ho:YAG ablation resulted in a very sharp and clear border with little charring. Applying 0.01 k.J of total energy at two different settings (1.5 J/p, high power, and 0.5 J/p, low power) at 15 pulses/sec, the cross-sectional area/mm(2) of the ablated bone was measured, using light microscopy and the Scion Image analysis program. The ablated areas were 2.28 +/- 0.87 and 1.16 +/- 0.43 mm(2) at high and low power, respectively (p = 0.008).

The effect of irrigation on peak temperatures in nerve root, dura, and intervertebral disc during laser-assisted foraminoplasty.

BACKGROUND AND OBJECTIVE: The Holmium: YAG (Ho: YAG) laser has been used for the ablation of prolapsed discs but alternative techniques are available, and this application remains controversial. It also has potential for the decompression of nerve roots within narrowed foraminae with the technique of endoscopic laser foraminoplasty. Traditional methods of decompression necessitate a major surgical procedure with potential destabilisation of the lumbar spinal segment. Nevertheless, minimally invasive techniques are attractive only if serious complications can be avoided. This study reports the peak temperatures reached in surrounding tissues with and without saline irrigation. STUDY DESIGN/MATERIALS AND METHODS: Investigation of the hypothesis was carried out in excised sheep lumbar spines. T-type thermocouples were used for the measurement of tissue temperatures during laser ablation of nerve root foraminae. The temperature was assessed in the nerve root, dura mater, and disc space. RESULTS: The Ho: YAG laser was effective in widening the foraminae by approximately 1.5 mm with a total energy of 4.60 kJ. This was statistically significant in both vertical and horizontal directions (P < 0.0003 and P < 0.00005, respectively). The mean temperature of the nerve root, dura, and disc space during the procedure was 44 +/- 3.1 degrees C, 42.8 +/- 4.7 degrees C, and 41 +/- 3.4 degrees C respectively. There were transient high peaks seen in the temperature profiles. Using saline irrigation at 27 ml/minutes these temperatures were reduced to 34.1 +/- 1.8 degrees C (P = 0.0002), 34.9 +/- 1.5 degrees C (P = 0.002), and 37.2 +/- 1.2 degrees C (P < 0.014), for nerve roots, dura, and disc space respectively. CONCLUSIONS: Laser ablation of bone and ligament for nerve root decompression using the Ho: YAG laser may offer substantial advantages, but the risk of serious complication may only be avoided if the technique is combined with saline irrigation.