Perineural air injection as a means of prevention of thermal injury of the sciatic nerve during radio frequency ablation: a preliminary experimental study in rabbits

Prevention of Nerve Root Thermal Injury Caused by Bipolar Cauterization Near the Nerve Roots

STUDY DESIGN

This was a controlled, interventional animal study.

OBJECTIVE

This study aimed to investigate the thermal injury of nerve root by cauterization near the nerve root and to identify the prevention or rescue procedure of nerve root injury.

SUMMARY OF BACKGROUND DATA

In spine surgery, bipolar cauterization of epidural venous plexus near the nerve root is an essential procedure to control bleeding. Although a potential risk of neurological thermal damage exists, the underlying mechanism and prevention have not been elucidated.

METHODS

Temperature measurement and histological evaluation after bipolar cauterization near the posterior branch of the nerve root were performed using a rabbit model. Subsequently, the effect of saline irrigation or changing the direction of bipolar forceps to reduce thermal elevation during bipolar cauterization was evaluated. Finally, the effectiveness of locally injected corticosteroid after bipolar cauterization was evaluated.

RESULTS

After bipolar cauterization, temperature of the surrounding site reached 60.9 °C, and 47.8% of the nerves were histologically injured. Using saline irrigation, thermal elevation was significantly suppressed up to 42.7 °C (P < 0.01), and no nerve was histologically injured. When bipolar cauterization was performed in the perpendicular direction, temperature of the surrounding site reached only 40.4 °C (P < 0.01). Locally injected corticosteroid reduced the incidence of nerve injury to 25.0%. However, a significant increase in nerve damage remained compared with the sham group (P < 0.01).

CONCLUSION

Bipolar cauterization near the nerve roots can increase the temperature of nerve roots and cause thermal nerve root injury, despite no accidental direct nerve root injury. Using saline irrigation, or setting bipolar forceps perpendicular to nerve roots, thermal elevation could be suppressed and nerve injury could be prevented. Therefore, it is recommended that surgeons set bipolar forceps perpendicular to nerve roots or use saline irrigation for the prevention of nerve root injury.

LEVEL OF EVIDENCE

N/A.

The incidence of nerve root injury by high-speed drill can be reduced by chilled saline irrigation in a rabbit model

Aims

We aimed to evaluate the temperature around the nerve root during drilling of the lamina and to determine whether irrigation during drilling can reduce the chance of nerve root injury.

Materials and Methods

Lumbar nerve roots were exposed to frictional heat by high-speed drilling of the lamina in a live rabbit model, with saline (room temperature (RT) or chilled saline) or without saline (control) irrigation. We measured temperatures surrounding the nerve root and made histological evaluations.

Results

In the control group, the mean temperature around the nerve root was 52.0°C (38.0°C to 75.5°C) after 60 seconds of drilling, and nerve root injuries were found in one out of 13 (7.7%) immediately, three out of 14 (21.4%) at three days, and 11 out of 25 (44.0%) at seven days post-operatively. While the RT group showed a significantly lower temperature around the nerve root compared with the control group (mean 46.5°C; 34.5°C to 66.9°C, p < 0.001), RT saline failed to significantly reduce the incidence of nerve root injury (ten out of 26; 38.5%; odds ratio (OR) 0.96; 95% confidence interval (CI) 0.516 to 1.785; p = 0.563). However, chilled saline irrigation resulted in a significantly lower temperature than the control group (mean 39.0°C; 35.3°C to 52.3°C; p < 0.001) and a lower rate of nerve root injury (two out of 21; 9.5%, OR 0.13; 95% CI 0.02 to 0.703, p = 0.010).

Conclusion

Frictional heat caused by a high-speed drill can cause histological nerve root injury. Chilled saline irrigation had a more prominent effect than RT in reducing the incidence of the thermal injury during extended drilling. Cite this article: Bone Joint J 2017;99-B:554–60.

Neuroanatomic considerations in percutaneous tumor ablation

Percutaneous ablation is increasingly being used as focal therapy for tumors in the chest, abdomen, and pelvis, including tumors in proximity to neural structures. To ensure that tumor ablation is performed safely, knowledge of the regional neuroanatomy is particularly important because most relevant nerves are not visualized with the conventional imaging techniques used to guide ablation procedures. Familiarity with the expected course of nerves in commonly targeted areas is helpful in preventing inadvertent nerve injury and in accurately informing the patient of potential risks. In the chest and shoulder girdle, the brachial plexus as well as the phrenic, recurrent laryngeal, intercostal-subcostal, long thoracic, dorsal scapular, and suprascapular nerves may be encountered. Vulnerable neural structures in the abdomen and pelvis arise from the lumbar and sacral plexuses and include the femoral, obturator, sciatic, and pudendal nerves. Nerve protection and monitoring techniques should be used, when appropriate, to minimize the risk of neural injury during percutaneous tumor ablation and depend on the vulnerable nerve, the location of the targeted tumor, and the ablation device used for treatment. Nerves may be protected using displacement techniques, including instillation of air or fluid, insertion and insufflation of angioplastic or endoscopic balloons, and mechanical manipulation of the ablation device. Nerves may be monitored with cross-sectional imaging evaluation of the critical nerve or ablation zone, or with functional evaluation using electromyographic equipment or focused clinical examination. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg334125141/-/DC1.

Sonographically guided radiofrequency ablation with and without a superficial saline injection to prevent skin burns in a rabbit model

OBJECTIVES

Our aim was to determine whether sonographically guided radiofrequency ablation with superficial saline injection can minimize thermal injury of the skin without an influence on therapeutic efficacy.

METHODS

Institutional Animal Care Committee approval was obtained. Twelve percutaneous radiofrequency ablation procedures were performed in the thighs of 6 rabbits (control, n = 6, right thigh; experimental, n = 6, left thigh). The ablation with local anesthesia was performed in the most superficial area of the thigh muscle. In the experimental group, 1 mL of saline was injected before the ablation at the tissue layer between the skin and ablated muscle. The duration and energy of the ablation were the same in the control and experimental groups. Rabbits were compared for their gross skin state and histopathologic findings after the ablation.

RESULTS

The degree of thermal coagulation of the muscle was similar in both groups at pathologic examination. Grossly, skin redness was mild in the experimental group but moderate in the control group. Of the 6 rabbits, 5 tended to show more frequent histopathologic changes, including an inflammatory reaction, interruption of collagen fibers, injury of the skin adnexa, and fibrosis, in the control group when compared with the experimental group. However, there was no statistically significant difference (all P> .05). One rabbit that underwent ablation at higher energy had a partially dissected epidermis in the control group only.

CONCLUSIONS

Sonographically guided radiofrequency ablation with a saline injection superficial to a tumor might prevent skin burns and provide equivalent therapeutic efficacy for ablating superficial lesions.