Assessment of technical adequacy of sacral lateral branches cooled radiofrequency neurotomy.

OBJECTIVE

There were two primary objectives of the study: 1. assessment of the association between diagnostic sacral lateral branches (SLB) blocks and the ensuing numbness in the middle cluneal nerves (MCN) distribution, irrespective of whether the patients had positive or negative responses to blocks. 2. If the consistency of this causal relationship was established, we wanted to investigate a further correlation - hypoesthesia from local anesthetic blocks vs. hypoesthesia from radiofrequency neurotomy (RFN) vs. outcomes.

DESIGN

This is a prospective observational study of sixty consecutive patients with sacroiliac (SI) joint complex pain and failure of previous intraarticular SI joint injection. The patients who had two positive diagnostic SLB blocks defined as ≥ 75% reduction in NRS scores were treated with cooled RFN of the L5 dorsal ramus and S1-S3 lateral branches. The patients were interviewed and evaluated at a one-month post-neurotomy follow-up appointment. Seven patients were also evaluated at a six-month follow-up visit after the procedure.

METHODS

The primary outcomes of the study were absence/presence of post-procedural buttock hypoesthesia after diagnostic blocks and absence/presence of post-procedural buttock hypoesthesia at one month after a cooled RFN procedure. The secondary outcome measures related to the effectiveness of this procedure and included: pre- and post-procedure NRS scores; ODI scores initially, and at post RFN follow-up; analgesic consumption initially, and at one-month RFN follow-up; patient satisfaction with the cooled RFN treatment. A procedure was considered categorically successful if the patient gained ≥50% pain relief and was satisfied with its results.

RESULTS

81/84 (96.4%; 95% CI [89.9%, 99.3%]) of the diagnostic SLB blocks lead to temporary sensory deficit to pinprick in the MCN distribution. If the block was positive, 58/58 (100.00%; 95% CI [93.8, 100.00%]) of the procedures led to hypoesthesia. For negative diagnostic blocks, 3/26 (11.5%; 95% CI [2.4%, 30.2%]) procedures lead to no hypoesthesia. The buttock hypoesthesia persisted in all patients with successful cooled RFN one month after this intervention. Among the patients with unsuccessful RFN, only 2/9 (22.2%, 95%CI [2.8%, 60.0]) still had hypoesthesia, but the rest of this group had no sensory deficit on pinprick examination. At 6-months follow-up buttock hypoesthesia had no association with the success of the procedure.The patients' average NRS scores decreased from baseline 7.1 (SD 1.7) to 4.3 (SD 3.3) at 1-month follow-up after RFN. Categorical success, based on ≥50% pain relief coupled with patients' satisfaction, was achieved in 12/21 (57.1%; 95% CI [34.0%, 78.2%]) of the subjects. Average ODI percentage score decreased from 41.7% (SD 15.1%) to 31.8% (SD 17.8%) at the primary endpoint of the study.

CONCLUSION

MCNs provide regular and clinically detectable innervation to the skin area overlaying posterior-medial aspects of the gluteus maximums muscle. Therefore, any technically accurate diagnostic block, irrespective of whether the patients have positive or negative responses, should result in the development of hypoesthesia in the area supplied by the MCNs. Immediately after the completion of the diagnostic procedure, the adequacy of the block should be tested. Absence of hypoesthesia suggests that the block may have been technically inadequate. Numbness in the buttock area innervated by the MCNs may serve as a marker of an adequately performed RFN procedure. If this procedure is unsuccessful in patients who do not develop post-neurotomy numbness in the area supplied by the MCNs, the failure of the intervention may stem from its inaccurate implementation rather than from its inherent ineffectiveness.