BIPOLAR RADIOFREQUENCY LESION GEOMETRY: IMPLICATIONS FOR PALISADE TREATMENT OF SACROILIAC JOINT PAIN

Authors: Cosman E. Jr. and Gonzalez C.
Study type: Experimental validation. Ex vivo and In vivo data collection
Publication: Pain Practice 2011; 11(1):3-22 (Link to PubMed)
Key Words: Chronic Back Pain – Sacroiliac Joint – Bipolar RF – Lesion Geometry

Figures are reproduced with permission from Copyright Clearance Center

STUDY GOAL

To optimize the use of bipolar radiofrequency (RF) for lesioning the dorsal Sacroiliac Joint (SIJ) innervation to improve treatment and clinical outcomes in back pain management.

STRATEGY

The effect of different RF parameters on RF lesion geometry was tested by temperature mapping, both ex vivo and in vivo. These observations were translated into a new straightforward method for lesioning the dorsal SIJ innervation, to create a more continuous lesion zone than other RF methods.

METHODOLOGY

Ex vivo setup: Bipolar RF lesions were generated in bovine liver varying several configuration parameters: electrode inter-tip spacing (s), cannulae diameter (d), tips length (l), tip temperature (T), and lesion time (t). Photographic temperature mapping was used to facilitate the interpretation of post-lesions images. Quantification of RGB pixel values correlate with temperature measurements (e.g., yellow color for a “cooked” zone indicates temperatures greater than 50°C).

In vivo setup: Palisade treatment to ablate dorso-sacral innervations of the SIJ was performed in 8 patients who presented with unilateral SIJ pain. Remote temperature probes, placed at the sacral surface between two lesion cannulae, were used to confirmed sustained neurolytic temperatures.

Ex vivo setting image
Ex vivo setting. A. Bipolar RF influencing parameters (adapted from Cosman E. Jr. et al 2014. Pain Medicine 15: 2020-36). B. Pre- and post-lesion photographs of a bipolar RF configuration ex vivo. Crosshairs depict the position of the electrode’s thermocouple wires. RGB pixel values are distributed into 4 color zones. C. Temperatures measured at each color zone at the end of a 3-minute lesion (based on 154 thermocouple measures).
In vivo setting image
In vivo setting. A. Palisade treatment of SIJ pain. A row of six RF cannulae (20-gauge diameter, 10 mm tip length, 10 mm inter-spacing) were inserted to target the dorsal sacral surface between S1-S3 dorsal foramina and the SIJ line (90°C, 3- minutes lesion time). A continuous lesion is generated between adjacent cannula. B. Probes T1/2 and T5/6 include a thermocouple sensor to measure sustained neurolytic temperatures.

RESULTS

Ex vivo setup

  • Animal tissue experiments demonstrated that heating (lesioning) between bipolar tips is enhanced as tip diameter, tip length, tip temperature, and/or lesion time are increased. 
  • Lesion geometry is insensitive to variations in inter-tip angles and offsets.
  • Both ex vivo and in vivo data indicate that a parallel spacing of 10 mm is a conservative choice for generating a rounded rectangular bipolar lesion (using 10mm or 15mm tip lengths, 18- or 20-gauge cannulae, and 90°C set temperature, within a 3-minute lesion time.
Cross-sectional photograph image
Cross-sectional photograph of bipolar lesions in ex vivo bovine liver show the lesion length and width produced by different parallel tip spacings and tip diameters (90°C tip temperature and 3-minute lesion time)
Measurements of midline lesion length image
Measurements of midline lesion length (L) in ex vivo bovine liver produced by variable tip parallel spacings, diameters, and lengths (90°C tip temperature and 3-minute lesion time). Midline lesion length increases with higher cannulae diameter and tip length

In vivo setup

  • Clinical outcomes of the palisade denervation of the SIJ were positive, although assessed over a short follow-up time.
  • Bipolar RF lesions can be as large as those achieved with cooled RF
  • Temperature control is better achieved with bipolar RF compared to cooled RF, as it can be directly measured in a known position, within the electrode tip(s) or inter-tip(s) region(s). In cooled RF, the maximum tissue temperature is reached at a variable distance from the electrode tip.
Adapted figure image

In cooled RF, an increase in tip-to-tip distance can give rise to gaps between adjacent lesions in the sacral surface, whereas individual bipolar lesions can be larger than cooled RF lesions

Bipolar palisade RF produces lesions of consistent height, width, and depth, with no gaps.

Figure adapted from Cosman E. Jr. et al 2014. Pain Medicine 15: 2020-36.

AUTHOR’S CONCLUSION

  • The new bipolar palisade (a defensive fence) creates a continuous lesion area that covers the multiple sacral lateral branch nerves innervating the SIJ.
  • The size and shape of palisade bipolar RF lesions might be advantageous for pain management cases where larger lesions or lesions side-by-side (without gaps) are desired.
Top