In recalcitrant cases, chronic osteoarthritis (OA) pain in the knee may not be effectively managed by either pharmacologic or non-drug therapies. A more successful pain-relieving alternative in such cases might be radiofrequency (RF) ablation of certain nerves serving the knee joint, according to recently reported research.
Writing in the journal Pain, researchers from Seoul, Republic of Korea, report a randomized, controlled, double-blind trial of RF neurotomy applied to articular nerve branches (genicular nerves) for treating knee joint pain due to chronic OA [Choi et al. 2011]. The genicular complex include branches of the femoral, common peroneal, saphenous, tibial, and obturator nerves feeding into the knee joint. Radiofrequency neurotomy — sometimes used to reduce back and neck pain — uses heat generated by radio waves to destroy specific nerves and interfere with their ability to transmit pain signals. Radio waves are delivered to the targeted nerves via a probe inserted through the skin and guided into position using imaging scans.
Completing the 3-month trial were 35 older patients — mean age 67 years, 83% female — who had (a) severe knee OA pain lasting more than 3 months, (b) that was unresponsive to prior conservative treatments, and (c) exhibited positive response to diagnostic genicular nerve blocks. Patients were randomly assigned to receive either percutaneous RF genicular neurotomy under fluoroscopic guidance (RF group; N = 18) or the exact same procedure but without RF and its associated heat applied (Control group; N = 17). Visual analogue scale (VAS) scores (primary outcome), Oxford knee scores, and global perceived benefit on a 7-point scale were measured at baseline and at 1, 4, and 12 weeks post-procedure.
VAS scores showed that the RF group had significantly less knee joint pain at 4 and 12 weeks compared with the control group. Ten subjects in the RF group (59%) achieved a primary outcome of at least 50% relief of knee pain at 12 weeks, compared with none in the control group.
Oxford knee scores showed similar significant findings: in the RF group, 59%, 65%, and 59% achieved at least 50% knee pain relief at 1, 4, and 12 weeks, respectively. On the global satisfaction measure, the RF group scored significantly higher than Control subjects at both 4 and 12 weeks. There were no post-procedure adverse events reported by any patients during the follow-up period.
The researchers conclude that RF neurotomy of genicular nerves leads to significant pain reduction and functional improvement in a subset of elderly patients with chronic knee OA pain. Therefore, this may be an effective and relatively safe treatment in cases that have not responded to other therapies.
COMMENTARY: This was a well-designed and carefully-conducted study, producing impressive results. However, as is usually the case, there are some important limitations and caveats to consider from an evidence-based medicine perspective before widely recommending the RF procedure…
- The researchers dutifully performed a pre-trial statistical power analysis and determined that a sample size of only 17 subjects per group would be required for detecting a large 50% effect size as being significant at the P ≤ 0.05 level. They achieved this enrollment goal and, despite these small group sizes, mean differences between groups in VAS scores were large in effect, statistically significant, and exhibited surprisingly narrow Confidence Intervals (by our own calculations; not provided by the authors) suggesting considerable precision in the estimates of effect.
- While these factors support the overall strength of the outcomes, it also must be noted that the subjects were carefully selected from a starting pool of 176 patients assessed for eligibility. Of these, only 38 (22%) qualified for randomization, and 35 completed the study — so this was a very select group.
- Two patients in the RF group (12%) achieved poor or no response to the treatment, possibly due to variations in their neuroanatomy making it difficult to adequately locate and ablate the appropriate genicular nerves. This may suggest that practitioner knowledge and skill in applying the therapy could be an important factor in its success.
- All patients had used (unsuccessfully) a variety of analgesic products (oral and topical) for a prolonged period of time, and the consumption of these specifically for knee pain was unknown. Subjects were allowed to continue their use of these, as well as any ongoing physiotherapy, following RF treatment (real or sham); hence, these might have been confounding factors distorting outcomes.
- Of interest, 4 of 14 subjects (29%) excluded during the diagnostic nerve block phase of enrollment reported complete and lasting pain relief following only that preliminary procedure. Furthermore, following the RF procedure, both the RF group (actual procedure) and the Control group (sham procedure) showed dramatic and significant decreases in VAS scores at 1 week, suggesting either a strong placebo effect or some benefit of the procedure apart from application of RF generated heat. However, beyond that time, the strong pain relief effects persisted in the RF group but pain increased back to baseline levels by weeks 4 and 12 in the Control group.
- The followup period was only 12 weeks, so the durability of beneficial effects beyond that point is completely unknown. Therfore, if and when the RF procedure would need to be repeated to sustain pain relief also is uncertain.
The researchers concede that RF neurotomy is more invasive than other, more conservative, therapies. It is best reserved for patients with chronically painful knee osteoarthritis that has been unresponsive to other treatments and that demonstrates a positive response to diagnostic nerve block. Even with those qualifications, however, it seems the external validity of outcomes from this small trial, while very promising, need confirmation in larger groups of patients followed for a much longer period of time.
REFERENCE: Choi W-J, Hwang S-J, Song J-G, et al. Radiofrequency treatment relieves chronic knee osteoarthritis pain: A double-blind randomized controlled trial. Pain. 2011(Mar);152(3):481-487 [abstract here].