Radiofrequency techniques to treat chronic knee pain: a comprehensive review of anatomy, effectiveness, treatment parameters, and patient selection

Abstract

Background
The use of radiofrequency ablation (RFA) procedures to treat chronic knee pain has surged in the past decade, though many questions remain regarding anatomical targets, selection criteria, and evidence for effectiveness.

Methods
A comprehensive literature review was performed on anatomy, selection criteria, technical parameters, results of clinical studies, and complications. Databases searched included MEDLINE and Google Scholar, with all types of clinical and preclinical studies considered.

Results
We identified nine relevant clinical trials, which included 592 patients, evaluating knee RFA for osteoarthritis and persistent postsurgical pain. These included one randomized, placebo-controlled trial, one randomized controlled trial evaluating RFA as add-on therapy, four comparative-effectiveness studies, two randomized trials comparing different techniques and treatment paradigms, and one non-randomized, controlled trial. The results of these studies demonstrate significant benefit for both reduction and functional improvement lasting between 3 and 12 months, with questionable utility for prognostic blocks. There was considerable variation in the described neuroanatomy, neural targets, radiofrequency technique, and selection criteria.

Conclusion
RFA of the knee appears to be a viable and effective treatment option, providing significant benefit to well-selected patients lasting at least 3 months. More research is needed to better identify neural targets, refine selection criteria to include the use of prognostic blocks, optimize treatment parameters, and better elucidate relative effectiveness compared to other treatments.

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Journal of Pain Research 2018:11 1879–1888
Journal of Pain Research Dovepress
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REVIEW
open access to scientific and medical research
Open Access Full Text Article
http://dx.doi.org/10.2147/JPR.S144633
Radiofrequency techniques to treat chronic
knee pain: a comprehensive review of anatomy,
effectiveness, treatment parameters, and patient
selection
David E Jamison1,2
Steven P Cohen1–6
1Department of Anesthesiology,
Walter Reed National Military
Medical Center (WRNMMC),
Bethesda, MD, USA; 2Department of
Anesthesiology, Uniformed Services
University of Health Sciences
(USUHS), Bethesda, MD, USA;
3Department of Anesthesiology and
Critical Care Medicine, Johns Hopkins
School of Medicine, Baltimore, MD,
USA; 4Department of Neurology,
Johns Hopkins School of Medicine,
Baltimore, MD, USA; 5Department of
Physical Medicine and Rehabilitation,
Johns Hopkins School of Medicine,
Baltimore, MD, USA; 6Department of
Physical Medicine and Rehabilitation,
USUHS, Bethesda, MD, USA
Background: The use of radiofrequency ablation (RFA) procedures to treat chronic knee pain
has surged in the past decade, though many questions remain regarding anatomical targets,
selection criteria, and evidence for effectiveness.
Methods: A comprehensive literature review was performed on anatomy, selection criteria,
technical parameters, results of clinical studies, and complications. Databases searched included
MEDLINE and Google Scholar, with all types of clinical and preclinical studies considered.
Results: We identified nine relevant clinical trials, which included 592 patients, evaluating
knee RFA for osteoarthritis and persistent postsurgical pain. These included one randomized,
placebo-controlled trial, one randomized controlled trial evaluating RFA as add-on therapy,
four comparative-effectiveness studies, two randomized trials comparing different techniques
and treatment paradigms, and one non-randomized, controlled trial. The results of these studies
demonstrate significant benefit for both reduction and functional improvement lasting between 3
and 12 months, with questionable utility for prognostic blocks. There was considerable variation
in the described neuroanatomy, neural targets, radiofrequency technique, and selection criteria.
Conclusion: RFA of the knee appears to be a viable and effective treatment option, providing
significant benefit to well-selected patients lasting at least 3 months. More research is needed
to better identify neural targets, refine selection criteria to include the use of prognostic blocks,
optimize treatment parameters, and better elucidate relative effectiveness compared to other
treatments.
Keywords: Knee pain, osteoarthritis, radiofrequency, ablation, denervation, genicular nerve
Introduction
Knee pain has a lifetime prevalence rate of ~45%,1 and represents a source of signifi-
cant disability and reduced quality of life.2,3 Risk factors for the development of knee
pain include a history of prior injury or surgery, obesity, and advancing age.4 The most
common cause of chronic knee pain is osteoarthritis (OA), which is characterized by
the progressive loss of articular cartilage, with other etiologies including rheumatoid
arthritis, trauma, crystal arthropathies, and persistent postsurgical pain.5,6
Available treatments for knee pain vary depending on the etiology and diagno-
sis, but broadly include physical therapy, oral medications, injections, and surgery.7
Injections for knee pain consist of several types, and may be directed to the soft
tissues of the knee joint or the intra-articular joint space. Intra-articular injections
encompass a wide range of medications to include anti-inflammatory corticosteroids,
Correspondence: Steven P Cohen
Department of Anesthesiology and
Critical Care Medicine, Johns Hopkins
School of Medicine, 550 North
Broadway, Suite 301, Baltimore, MD
21029, USA
Tel +1 410 955 1818
Fax +1 410 502 6730
Email scohen40@jhmi.edu
Journal name: Journal of Pain Research
Article Designation: Review
Year: 2018
Volume: 11
Running head verso: Jamison and Cohen
Running head recto: Radiofrequency techniques to treat chronic knee pain
DOI: http://dx.doi.org/10.2147/JPR.S144633
This article was published in the following Dove Press journal:
Journal of Pain Research

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Jamison and Cohen
pro-inflammatory prolotherapy and platelet-rich plasma
(PRP) solutions, viscosupplements, and stem cell prepara-
tions.8–11 All intra-articular injections require the presence
of an intact joint, and are therefore not applicable following
total arthroplasty. Knee surgery is similarly heterogeneous
and ranges from minimally invasive arthroscopic procedures
to open partial or total arthroplasties.12,13 Pain due to severe
OA is not reliably responsive to conservative therapies, and
chronic pain may persist in over 40% of patients who undergo
joint replacement, being characterized as severe in 15% of
cases.14–16 Delivery of radiofrequency (RF) energy to the
knee’s nerve supply is a relatively new intervention that can
be safely done in the presence of an artificial joint, and may
offer an alternative to surgery or surgical revision.
Radiofrequency ablation (RFA) entails the discrete
delivery of thermal energy produced by an alternating cur-
rent to neural tissue, thereby degrading its ability to conduct
pain signals.17 First described as a treatment for pain in the
1960’s,18 RFA evolved from a therapy primarily employed to
alleviate neuropathic pain to one used today predominantly
for mechanical joint pain amidst reports of increased pain
stemming from deafferentation and neuroma formation.
Since the neurosurgeon Norman Shealy adapted its use for
the treatment of pain arising from the spinal facet joints in
the mid-1970’s,19 the accepted indications for RFA have
expanded steadily over the ensuing decades. The advent
of cooled radiofrequency ablation (CRFA)20 and the non-
ablative pulsed radiofrequency (PRF)21 therapy have further
broadened the clinical utility of RF for chronic pain states.
Accepted targets for RF treatment now include most neural
structures to include major nerves and ganglia.22–24 The use
of RF as a treatment for knee pain was first described in a
small case series involving the treatment of different types of
joint pain by Sluijter et al, who noted complete eradication
of pain with intra-articular PRF in a patient with refractory
post-traumatic knee pain.25 This area of pain medicine has
evolved in the past decade, and though knee RFA has been
the subject of numerous publications, high-quality random-
ized controlled trials (RCTs) remain sparse. The objectives
of this publication are to review the relevant neuroanatomy
of the knee and the available literature on RFA.
Search strategy
We systematically searched and screened all titles and
abstracts from MEDLINE and Google Scholar from incep-
tion to February 1, 2018 using the following key words:
“knee,” “pain,” “arthritis,” “persistent postsurgical pain,”
“chronic postsurgical pain,” “radiofrequency,” “ablation,”
“denervation,” and “pulsed radiofrequency.” This initial
search yielded 92 trials of varying design, which were then
separately reviewed by the authors. For the purposes of this
review only randomized and comparative trials were selected,
with all other study types being excluded. A total of nine ran-
domized or comparative trials were ultimately identified by
independent searches conducted by each author. The literature
search was complemented by reviewing the reference lists
of the selected publications to search for additional articles
missed by our initial electronic search.
Neuroanatomy of the knee
The innervation of the knee joint is complex given that
genicular nerves arise from branches of three major nerves:
the sciatic, femoral, and obturator, all of which are them-
selves derived from the lumbar plexus.26,27 The sciatic nerve
bifurcates into the tibial and common peroneal nerves in
the popliteal fossa. The tibial nerve remains in the posterior
compartment of the lower leg and gives off the superomedial
(SM) and inferomedial (IM) genicular nerves to the posterior
aspect of the knee joint. The common peroneal nerve passes
into the anterior compartment of the lower leg, and contrib-
utes the superior lateral (SL) genicular nerve to the anterior
portion of the knee. These genicular branches of the sciatic
nerve reliably course in approximation to the periosteum at
the medial and lateral junctions of the distal femoral shaft and
epicondyles, and at the medial junction of the proximal tibia
and epicondyle. The saphenous nerve is a cutaneous sensory
branch of the femoral nerve and gives off suprapatellar and
infrapatellar (IP) genicular nerves to the anterior portion of
the knee. The contribution of the obturator nerve is more
variable, but its posterior branch can provide an articular
branch to the posterior knee.
The complexity of the knee joint’s innervation has
resulted in a disparity in procedural technique among the
available controlled and observational studies. Studies report
on a range of procedural targets to include the SM, IM,
and SL genicular nerves in combination,28–33 the saphenous
nerve,34 the sciatic nerve,35 the IP genicular nerve,36 the IP
and SM genicular nerves in combination,37 the femoral, tibial,
saphenous nerves, and peripatellar plexus in combination,38
and the intra-articular joint space6,25,39–41 (Figures 1 and 2).
RCTs
The earliest published RCT is the 2011 study by Choi et al28
This trial was designed to compare genicular nerve RFA to
sham RFA. Nerves targeted in this trial were the SM, IM, and
SL genicular branches. Inclusion criteria were age between

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Radiofrequency techniques to treat chronic knee pain
Figure 1 Anterior-posterior radiograph of the knee depicting locations for
genicular nerve targeting.
Abbreviations: IM, inferomedial; IP, infrapatellar; MR, medial retinacular; SL,
superolateral; SM, superomedial.
Figure 2 Lateral radiograph of the knee depicting locations for genicular nerve
targeting.
Abbreviations: IM, inferomedial; IP, infrapatellar; MR, medial retinacular; SL,
superolateral; SM, superomedial.
50 and 80 years, presence of refractory knee pain of at least
3 months duration, and at least grade 2 radiographic evidence
of OA on the 5-point Kellgren–Lawrence scale.42 Thirty-eight
patients who met the criteria and had a positive response to
genicular nerve blocks were randomized to receive either
continuous, fluoroscopically guided RFA at 70°C, or sham
RFA that consisted of superficial and deep local anesthesia
with lidocaine. Primary outcomes were pain level as assessed
by visual analog scale (VAS) and the proportion of patients
reporting at least 50% pain relief at 12-week follow-up.
Overall follow-up was obtained at 1, 4, and 12 weeks post-
procedure. The results showed that RFA significantly lowered
the VAS at all time periods compared to sham, but both
groups showed similar improvement at 1 week, suggesting
a temporary improvement with local anesthetic nerve block.
Ten of the 19 RFA patients achieved at least 50% pain reduc-
tion at 12 weeks, compared to no patients in the control group.
Secondary outcomes to include Oxford knee score (OKS)
and patient satisfaction were also significantly improved in
the RFA group. The limitations of this study are primarily
its small size, the large discrepancy between the volume of
prognostic blocks and the small electrodes used, the high
proportion of positive prognostic blocks (82.5%), and lack
of long-term follow-up.
RFA was first compared to intra-articular injections in
the 2016 Sarı et al trial.29 Seventy-three patients with at least
grade 2 Kellgren–Lawrence OA were randomized to receive
either RFA of the SL, SM, and IM genicular nerves at 80°C
for 90 seconds or intra-articular injection of bupivacaine,
morphine, and betamethasone. Patients were assessed at
baseline, 1 and 3 months for pain level via VAS and function
via the Western Ontario and McMaster Universities Osteoar-
thritis (WOMAC) index. Results showed statistically superior
pain relief with RFA at 1 and 3 months, but superiority in
the total WOMAC score with RFA only at 1 month. Limita-
tions of the study include the lack of prognostic blocks, the
unrestricted and undocumented use of oral analgesics, and
the lack of a true control group.

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The SM, IM, and SL genicular nerves were also targeted
in the 2017 Qudsi-Sinclair et al trial, but in this trial the effect
of RFA was examined only in patients with a history of total
knee arthroplasty (TKA).30 Thirty patients with refractory
knee pain that persisted at least 6 months following TKA
were enrolled in the study, with 28 completing follow-up
to 12 months. Patients were randomized to receive either
continuous RFA at 80°C or sham RFA that consisted of
genicular nerve blocks with local anesthetic and corticoste-
roid. Both procedures were performed under fluoroscopic
guidance. Outcome measures were pain level assessed via a
numeric rating scale (NRS), and function assessed via both
the OKS and Knee Society Score. Outcomes with respect
to function were modest and similar between groups, with
most improvements occurring between months 1 and 6, and
declining toward baseline by 12 months. Pain also decreased
in both groups, but the reduction following RFA peaked at 3
months and persisted at 12 months, while the control group
experienced their lowest NRS on day 1 and then steadily
increased toward baseline at 12 months. This trial is limited
by a small size and the lack of prognostic blocks pre-RFA,
which may have led to the inclusion of nonresponders in the
RFA group.
The Shen et al trial compared RFA with PRP and sodium
hyaluronate (HA) to PRP and HA alone.43 Inclusion criteria
were refractory pain of at least 3 months duration due to
OA and pain level of at least 6 on a 0–10 VAS. Both groups
received intra-articular injections of PRP and HA weekly
for 5 weeks, but the treatment group also received RFA at
70°C, although the timing of the RFA was not described. The
precise nerves were also neither named, nor was it specified
whether image guidance was used. Twenty-seven patients
were randomized to each group and follow-up was obtained
at the completion of intra-articular injections and 3 months.
Outcome measures included pain intensity as measured on
a VAS, life quality as measured on the 36-item Short-Form
Health Survey, and function via the American Knee Society
Score. Both groups showed improvement in pain and func-
tion, although the gains in the RFA group were statistically
superior at all time periods. The RFA group also demonstrated
significant improvement in quality of life at 3 months, while
the control group did not.
The 2018 trial by Davis et al is the largest study and was
also the first to employ CRFA.31 Similar to the Qudsi-Sinclair
and Choi trials, the SM, SL, and IM genicular nerves were
targeted. Inclusion criteria were the presence of at least grade
2 Kellgren–Lawrence radiographic OA, refractory knee pain
of at least 6 month duration, pain of at least 6 of 10 on a NRS,
OKS score of at least 35, and at least 50% improvement with
genicular nerve blocks. One hundred and fifty-one patients
met the inclusion criteria and were randomized to receive
either CRFA or intra-articular steroid (IAS) injection. CRFA
was performed under fluoroscopic guidance with 17-gage
introducers at 60°C for 150 seconds. The primary outcome
was the percentage of patients achieving at least 50% pain
reduction at 6 month follow-up as measured by a NRS.
Secondary outcome measures included function measured
on OKS, patient’s overall perception of the treatment, and
analgesic usage. Pain relief with CRFA was superior to that
obtained with IAS at all time periods, and at 6 month follow-
up 74% of the CRFA group had at least 50% relief compared
to just 16% of the IAS group. Function and global perception
were also superior in the CRFA cohort, although there was
no statistical difference between the groups in terms of oral
opioid use. The longer duration of relief noted in this study
provides evidence for the theoretical benefit of CRFA, namely
the creation of larger lesions to reduce the technical failure
rate (ie, missed nerves).
The most recent RCT by El-Hakeim et al compared RFA
to non-interventional therapy.32 Sixty patients with at least
grade 3 Kellgren–Lawrence OA were randomized to receive
either RFA of the SM, SL, and IM branches or conventional
treatment with oral acetaminophen and diclofenac. RFA
was accomplished with three 90 seconds cycles at 90°C per
site, which is a substantially longer duration of RFA than
that employed by any other RCT. Patients were evaluated at
baseline, 2 weeks, 3 months, and 6 months. Results showed
statistically superior pain relief with RFA at all follow-up
intervals. Function as assessed by the WOMAC index was
improved in both groups at 6 months, but was superior with
RFA. Lastly, patient satisfaction as measured on a Likert
scale was significantly higher at 3 and 6 month follow-up in
the RFA group. However, the study is limited by the lack of
pre-RFA prognostic blocks and the lack of patient blinding.
Randomized, non-comparative studies
The 2017 randomized trial by McCormick et al also employed
CRFA, but the study was designed to determine the predic-
tive value of pre-RFA nerve blocks, not to compare RFA to
other modalities.33 Fifty-four patients with chronic knee pain
due to OA all received CRFA, but 29 did so after prognostic
blocks and 25 did not. Notably, only three of 32 (9.3%)
patients had a negative block, defined as <50% pain relief.
Some patients had the procedure done bilaterally; so a total
of 36 knees had CRFA following prognostic blocks and 35
knees proceeded directly to CRFA. Inclusion criteria were

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Radiofrequency techniques to treat chronic knee pain
age between 30 and 80 years, >6 months of refractory knee
pain, NRS pain score of at least four and at least grade 2
radiographic OA. Follow-up was conducted at 1, 3, and 6
months, but the primary outcome measure was attainment of
at least 50% pain relief at the 6-month mark. Results showed
significant improvements in both groups at 6 months, with
58.6% of the nerve block group and 64% of the non-nerve
block group achieving at least 50% relief at 6 months. There
were no significant differences between groups in terms of
pain and function at any of the time periods. These findings
raise questions regarding the utility of single, uncontrolled
blocks before knee RF ablation, and suggest the need for
more research to better refine selection criteria.
The intra-articular delivery of RF energy is advocated
by some as an alternative to ablating the genicular nerves,
though studies evaluating intra-articular RFA for other con-
ditions have yielded equivocal results.44,45 A 2017 trial by
Gulec et al randomized 100 patients with chronic knee pain
for at least 3 months to receive either intra-articular bipolar
or monopolar PRF, without a control group.39 Two RF can-
nulae were placed into the anterior knee joint from either
side of the patellar ligament under fluoroscopic guidance.
PRF in all cases was delivered at 42°C for 10 minutes, but
patients and the provider were blinded as to whether it con-
sisted of bipolar energy coursing between the cannulae, or a
monopolar system set up between one of the cannulae and a
dispersive (grounding) pad. The primary outcome measure
was the percent of patients with at least 50% pain reduction
at 3-month follow-up as measured by VAS while walking
on a flat ground. The results showed superior improvements
in the bipolar group, with 84% achieving a positive primary
outcome, compared to only 50% in the monopolar group.
Limitations of this trial include the lack of a control group
and no long-term follow-up.
Comparative, non-randomized trials
The 2010 Ikeuchi et al trial compared RFA to nerve blocks,
but was not randomized.37 Nineteen patients who met the
selection criteria during one time frame received RFA, while
another nineteen patients treated within a later time frame
received sham RFA; one RFA and two control patients did not
complete the study. Inclusion criteria included radiographic
evidence of moderate to severe OA, age >65 years, and knee
pain for longer than 3 months. Patients in the RFA group
received two non-image guided, continuous RFA treatments
at 70°C at a 2-week interval. Two lesion sites were targeted,
the SM and IP genicular nerves. Patients in the control
group also received two procedures 2 weeks apart, but they
consisted only of topical and deep anesthesia with lidocaine;
RFA was not performed. Other complementary treatments
were withheld for 12 weeks, and assessment was obtained at
4 weeks, 8 weeks, 12 weeks, and 6 months. Outcome mea-
sures included the WOMAC functional assessment, VAS pain
scores, and a 4-point patient global assessment. Outcomes
were overall mixed. The total WOMAC score remained lower
in the RFA group throughout the 6 month follow-up, but the
difference was not statistically significant. VAS scores were
significantly lower in the RFA group at 4-, 8-, and 12-week
follow-ups, but the effect tapered off by 6 months. Limitations
of the this study include the lack of randomization, lack of
prognostic nerve blocks, and the targeting of only two nerve
branches (Table 1).
RFA predictors of outcome
Predictors of success or failure with RFA relate to both patient
characteristics and procedural technique. This subject has been
reported extensively as it relates to other pain interventions,
notably lumbar facet and sacroiliac joint (SIJ) RFA. Patient
factors predictive of failure with SIJ RFA include age >65 years,
higher baseline pain level, and opioid use.46 Patient factors
predictive of poor success with lumbar or cervical RFA include
advanced age, certain pain referral patterns and physical exam
signs, opioid use, prior history of depression, previous back
surgery, longer duration of pain, and ongoing legal action.47–49
In individuals with chronic neck pain due to whiplash, low
levels of pain catastrophizing and functional disability were
found to be predictive of success with cervical RFA.50 In a
study evaluating prognostic factors before PRF of the occipital
nerves, treatment failure was associated with extension of pain
beyond the confines of the targeted nerve distribution, while a
lower diagnostic block volume, multiple treatment cycles, and
a traumatic precipitating event predicted success.51
Procedural factors that contribute to success with RFA
include the type of RF energy applied, the duration and tem-
perature of treatment, and the gage of the RF probe itself. An
ex vivo trial compared several types of RF and found that
CRFA created larger lesions than either continuous or PRF.52
Within RFA and PRFA groups, larger probes and longer dura-
tion of treatment were associated with larger lesions. Results
from studies on SIJ RFA have been mixed, with one reporting
superior relief with CRFA when compared to RFA,53 one
showing a trend toward superiority with CRFA,54 and another
demonstrating no difference.55 Orientation of the RF probe
parallel to the targeted nerve has also been demonstrated in
preclinical studies to create larger lesions,56 but results from
uncontrolled trials are mixed.55,57

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Table 1 Randomized and comparative studies
Trial Study
type
Trial size,
diagnosis
RF method Anatomic
targets
Prognostic
block
Follow-
up
Results Comment
Choi et al28 RCT 38, OA RFA (70°C, 90 seconds) + LA
vs sham
SM, SL, IM Yes 12 weeks RFA > sham for pain and function
at 4 and 12 weeks
High volume (2 mL) used for prognostic
blocks
Sarı et al29 RCT 73, OA RFA (80°C, 90 seconds) vs IA
steroid, LA, and morphine
SM, SL, IM No 3 months RFA superior for pain and function No prognostic blocks
Shen et al43 RCT 54, OA RFA (70°C, 120 seconds) +
PRP + HA vs PRP + HA
Not
specied
No 3 months RFA superior for pain and function Nerves targeted not described, unclear if
imaging guidance was used
Qudsi-Sinclair
et al30
RCT 28, post-
TKA
RFA (80°C, 90 seconds) vs LA
+ steroid
SM, SL, IM No 12 months RFA > nerve block for pain at 12
months; functional relief modest
and not different between groups
Signicant short-term relief with nerve
blocks. Functional improvement modest
and not statistically different between
groups
Davis et al31 RCT 151, OA Cooled RFA (60°C, 150
seconds) vs IA steroid
SM, SL, IM Yes 6 months RFA > IA injections for pain and
function
No difference in opioid usage between
groups
El-Hakeim
et al32
RCT 60, OA RFA (90°C, 270 seconds) vs PO
acetaminophen and NSAIDs
SM, SL, IM No 6 months RFA superior for pain and function Patients not blinded
McCormick
et al33
RCT 53, OA Cooled RFA (60°C, 150
seconds) either after or
without prognostic nerve block
SM, SL, IM Yes/no 6 months Both groups improved in pain and
function, no difference between
groups
29 of 32 patients in the nerve block group
received RFA
Gulec et al39 RCT 100, OA Bipolar vs monopolar IA PRF
(42°C, 10 minutes)
IA No 12 weeks Bipolar > monopolar RFA for pain
relief at 12 weeks
No control group
Ikeuchi et al37 CS-P 35, OA RFA (70°C, 90 seconds) + LA
vs LA
SM, IP No 6 months RFA > LA for pain at 12 weeks Not image guided, non-randomized
Abbreviations: CS-P, case series, prospective; HA, hyaluronic acid; IA, intra-articular; IM, inferomedial; IP, infrapatellar; LA, local anesthetic; NSAID, nonsteroidal anti-inammatory drug; OA, osteoarthritis; PO, per os; PRF, pulsed
radiofrequency; PRP, platelet-rich plasma; RCT, randomized controlled trial; RF, radiofrequency; RFA, radiofrequency ablation; SL, superolateral; SM, superomedial; TKA, total knee arthroplasty.

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The predictive value of prognostic genicular nerve blocks
prior to RFA is similarly questionable. Among the eight RCTs
discussed, only three employed positive response to nerve
block as a criterion for the performance of RFA. The Choi
et al trial, which is the only RCT to compare RFA to sham,
required a positive response to prognostic nerve blocks for
patients to proceed to the RF portion of the study.28 However,
2 mL lidocaine per site was used to perform the nerve blocks,
and a positive response was defined as at least 50% pain
relief lasting for 24 hours. Higher volume local anesthetic
nerve blocks have been shown to decrease the specificity of
prognostic blocks as local anesthetics may spread farther than
a subsequent RF lesion,51 and pain relief lasting 24 hours is
inconsistent with the pharmacodynamics of lidocaine.
The McCormick et al trial specifically addressed the prog-
nostic value of nerve blocks by comparing RFA outcomes per-
formed after positive genicular nerve blocks to results obtained
without the use of prior injections.33 Blocks were performed with
1 mL of lidocaine, with a positive response defined as ≥50%
pain reduction persisting for at least 1 hour following injection.
Given the lack of statistical difference between the groups, the
authors concluded that their method of genicular nerve block
has little prognostic value. Methods postulated by the authors to
increase the prognostic utility of genicular nerve blocks include
the use of a higher threshold for defining a positive response to
nerve blocks (90% relief), or using double comparative nerve
blocks. However, studies evaluating the effect of using higher
cutoffs to select patients for SIJ and lumbar and cervical RFA
have mostly found no improvement in outcomes.46,58,59 The use
of comparative medial branch blocks with local anesthetics of
differing durations of action is also of unclear benefit, having
been shown to have marginal sensitivity60 and little impact on
lumbar facet RFA outcomes61,62 (Table 2).
Complications
No major adverse events were reported in any randomized or
observational trial. All patients in the RF limb of the Ikeuchi
trial noted 2–6 weeks of hypoesthesia in the IP region, but
these symptoms self-resolved.37 A review in 2016 discussed
the potential adverse effects of knee RFA given the proximity
of genicular arteries to the genicular nerves.63 Multiple
genicular arteries arise from the popliteal artery, and they
course along the epicondyles of the distal femur and proximal
tibia in the region where the SL, SM, and IM genicular nerves
are normally targeted64 (Figure 3). Injuries to the genicular
arterial system are described in the surgical literature, from
both open and arthroscopic procedures, and sequelae include
pseudoaneurysm formation, hemarthrosis, arteriovenous
fistula formation, and patellar osteonecrosis.65–68 The authors
are also aware of several unpublished reports of skin burns,
which may arise because of the close proximity of the target
nerves to the skin. Other potential complications include
those generic to other interventional procedures, namely
infection, bleeding, or bruising. Intra-articular approaches
also confer the risk of joint sepsis or chondrolysis, but these
have not been described following RFA.
Discussion
Chronic knee pain is a recent addition to the growing list
of indications for RF, having first been described only a
Table 2 Factors associated with radiofrequency ablation treatment outcomes for knee pain and other conditions
Predictors of success Predictors of failure
Medial compartment osteoarthritis and concordant pain Greater disease burden (eg, longer duration of symptoms, greater disability)
Large and/or multiple lesions Previous surgery
Controlled prognostic blocks Opioid use
Psychopathology
Diffuse pain symptomatology (bromyalgianess)
Figure 3 Anterior-posterior radiograph of the knee with overlay of the genicular
arteries.
Abbreviations: LI, lateral inferior; LS, lateral superior; MI, medial inferior; MS,
medial superior.

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decade ago. Among the eight RCTs found in the literature,
six compared knee RFA to sham28,30 or other accepted
treatments,29,31,32,43 but all demonstrated superior pain relief
and function with RFA.28–33,37,39,43 Fundamental differences
between studies make the aggregate body of literature dif-
ficult to interpret, as the type of RFA and the anatomic targets
vary considerably. However, the preponderance of evidence
suggests that RF denervation can be a safe and effective
treatment for chronic knee pain, with the duration of benefit
similar to that targeting other joints, ranging between 3 and
12 months.
The use of PRF for knee pain is not well supported, and
was featured in only one RCT that compared two types of
PRF, without a control group.39 PRF is generally acknowl-
edged as an effective treatment for neuropathic pain based on
dozens of preclinical studies and numerous clinical trials.69–72
Considering that knee arthritis is a non-neuropathic pain
condition, the conceptual basis for the use of PRF in this
condition (ie, neuromodulation without significant injury to
the neural architecture) is lacking. RCTs comparing PRF to
RFA for lumbar facet joint pain have shown greater and more
sustained pain relief with continuous RFA, raising further
questions regarding its utility for knee pain.73,74 Although
pain was improved compared to baseline in the PRF groups
of both studies, these differences were small and may be
attributable to a placebo response. In any case, these results
are not easily extrapolated to PRF of the knee given that the
targets were neural structures (ie, the medial branch nerves),
and not the intra-articular space.
The utility of prognostic blocks prior to RFA is also
unclear. Employment of a higher pain relief threshold and the
use of comparative local anesthetic blocks may increase the
specificity of prognostic blocks, but at the inevitable cost of
decreased sensitivity (ie, increased false-negative results).60,62
The primary downside for a prognostic procedure associated
with a high false-negative rate is the denial to patients of a
safe and effective RFA procedure.
It should be acknowledged that comparisons to and from
the spine pain literature regarding RFA are based primarily on
the similarity of the intervention, not on similarities in pathol-
ogy or anatomy. Therefore, in addition to neuroanatomical
studies and large multicenter studies that further elucidate
the benefit of knee RFA in comparison to sham ablation
(ie, placebo-controlled studies), different types of ablation
(eg, cooled vs conventional, techniques targeting different
genicular nerves and anatomical locations), and alternative
treatments (ie, comparative-effectiveness studies), other areas
ripe for future research include modification of facet and SIJ
RFA trials that have shed light on patient selection criteria,
and the effects of prognostic nerve blocks on RFA outcomes.
Acknowledgment
The assistance offered by the Center for Rehabilitation
Sciences Research, Bethesda, MD, USA is gratefully
acknowledged.
Disclosure
SPC has served as a consultant to Halyard, Boston Scientific,
and Abbott within the past 3 years. The opinions or assertions
contained herein are the private views of the authors and are
not to be construed as official or as reflecting the views of the
Department of the Army or the US Department of Defense.
The authors report no other conflicts of interest in this work.
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