INTRODUCTION
Osteoarthritis (OA) of the knee is the most frequent progressive degenerative joint disease with a 20% prevalence in India.[ 1 , 2 ] OA not only affects the cartilage and the subchondral bone but also Hoffa’s fat pad, synovia, ligaments, and muscles, leading to the concept of observing it as a whole joint disease.[ 3 ] It is the most common cause of physical disability and pain in the elderly age group.[ 3 ] Nonsteroidal anti-inflammatory drugs (NSAIDs) have been suggested not to have long-term benefits[ 4 , 5 ] and only limited use for a maximum of 4 weeks is recommended due to serious gastrointestinal, cardiovascular, and renal side effects.[ 5 ] An intra-articular corticosteroid injection can only provide short-term symptomatic relief for at least one to 8 weeks, and the usual practice is limited to four injections annually.[ 6 ] There are conflicting results for viscosupplementation despite being approved by the Food and Drug Administration in 1997 for the use in knee OA.[ 7 , 8 ] Acupuncture and prolotherapy have provided at least some benefits, but high-quality evidence is lacking.[ 8 , 9 ] Intra-articular platelet-rich plasma is a promising regenerative therapy for use in a younger patient with early OA knee and may be superior to the current clinical therapy. However, it lacks robust clinical evidence to support this.[ 9 , 10 ] Chronic OA patients often opt for total knee arthroplasty (TKA) to regain adequate ability for daily activity with limited pain. However, the surgery itself is associated with a variety of perioperative and postoperative risks, including chronic pain in nearly 20% of patients following TKA.[ 11 , 12 ] Many patients with knee OA elect to avoid surgery, and others are poor surgical candidates due to medical comorbidities.[ 13 ]
Radiofrequency ablation (RFA) of the genicular nerve was introduced in 2010 for severe knee OA pain lasting more than 3 months, with no response to conservative treatments. This initial treatment response was a significant pain reduction and functional improvement without any postprocedure adverse events.[ 14 ]
RFA creates a high-frequency current in an electrode tip that causes high-frequency ionic vibrations, resulting in frictional heat at the cellular level surrounding the electrode tip. The area of protein denaturation and coagulation necrosis depends on electrode size, temperature, the duration of RFA, and proximity or alignment of the electrode tip to the tissue of interest.[ 15 ]
Sensory innervation of the knee involves the articular branches of the femoral, common peroneal, saphenous, tibial, and obturator nerves. The culmination of these articular branches is referred to as the genicular nerves.[ 16 ] The targeted branches consist of the superior lateral, superior medial, and inferior medial nerves because of their relatively reliable anatomic positions at periosteal areas connecting the femur or tibia shafts to their respective epicondyle. The inferior lateral was not targeted due to its proximity to the common peroneal nerve.[ 17 ]
Standard radiofrequency (RF) technology is limited in size and elliptical shape of the lesion, making it difficult to reach the affected areas; in contrast, the cooled RF system has continuously circulated water that moderates the temperature near the tip of the probe allowing more energy to be applied without charring of the tissue near the probe tip. As a result, larger spherical-shaped lesions are produced that accomplish effective denervation and a longer duration of effects.[ 18 , 19 ]
The purpose of this study was to determine 3-, 6-, and 12-month clinical outcomes of genicular nerve cooled RFA (CRFA) for the treatment of chronic pain due to primary knee OA, as measured by the change in pain and global subjective improvement of the knee function.
METHODS
The present study, a single-armed prospective observational study, was conducted in a tertiary care hospital between March 2020 and March 2021 and followed up completed on March 2022, after the institutional ethics committee approval (G/39/DNB/EC/1520).
A total of 70 patients with chronic knee OA pain were enrolled in the study. Out of this, two patients were Excluded (n = 2) because of not meeting inclusion criteria (n = 1) and declined to participate (n = 1). 68 patients were allocated for the intervention. Six patients were lost to follow-up (n = 6). Rest 62 patients were analyzed for the study [Figure 1 ].
Figure 1: CONSORT flow diagram. CONSORT: Consolidated Standards of Reporting Trials. CRFA: Cooled radiofrequency ablation
Patients aged between 50 and 80 years with moderate to severe knee pain for longer than 6 months that interfere with functional activities (for example, ambulation, prolonged standing, radiologic confirmation (X-ray) of OA grade of 2 (mild), 3 (moderate) or 4 (severe) (Kellgren and Lawrence system), and refractory to conservative treatments, including activity modification, home exercise, protective weight-bearing, and/or analgesics (for example, acetaminophen or NSAIDs) and viscosupplements, and >50% pain relief from a single block of the genicular nerves (no more than 1 ml 2% lidocaine per block) were included into the study.
Patients with acute knee pain >3 months), chronic rheumatologic disorder, inflammatory arthritis (for example, rheumatoid arthritis), other systemic inflammatory conditions (for example, gout, fibromyalgia), previous or pending lower limb amputation, neurological or psychiatric disorders, uncontrolled immunosuppression (e.g. AIDS, cancer, diabetes, etc.), patients with pacemaker, stimulator, or defibrillator were excluded from the study.
Patients had provided their written informed consent to participate in the study and follow-up interviews. Follow-up in-person interviews were conducted at 3, 6, and 12 months by two trained interviewers retrieved from the case records.
During the preprocedure scheduled visit, the enrolled patients were explained about the Numeric Rating Scale (NRS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)[ 20 ] score. Interviews consisted of questions relating to the patient’s experience undergoing RFA of the genicular nerves and the perceived results. Patients were asked to describe their NRS pain score (0 – no pain and 10 – maximum pain) and WOMAC scores pre- and post-RFA from https://www.orthopaedicscore.com/. They were asked about their symptom duration, what other treatment modalities they had tried before RFA, and what pain medications they were taking before and also after the procedures. Patients described their experience with the procedure itself by quantifying their satisfaction with procedure length, preprocedure anxiety, and complications incurred.
All the patients were inserted intravenous cannula and monitored using standard monitors (Drager, Germany) including noninvasive blood pressure, electrocardiography, and pulse oximetry. All the patients received premedication injection fentanyl 2 mcg/kg. After that, procedural sedation (if not contraindicated) in the form of injection dexmedetomidine 1 mcg/kg for 10 min and then 0.5 mcg/kg/h was given during the procedure. Minimal sedation and supplemental nasal cannula oxygen were administered allowing the patient to communicate during the procedure.
Patients were placed in the supine position on the operating table with a towel beneath the popliteal fossa of the index knee to minimize discomfort during the procedure and 30°–40° flexion of the knee. This position was secured by applying wide tape over the foot and ankle with the table. The operative area was draped by sterile technique. Three genicular nerves were targeted, i.e. superior lateral, superior medial, and inferior medial genicular nerves. Diagnostic blocks consisted of injections of 1 mL 1% lidocaine at each genicular nerve. In the same sitting, genicular nerve RFA was performed on patients with knee OA if diagnostic blocks provided the patient with 50% or better pain relief as per the OA Research Society International criteria.[ 21 ]
Fluoroscopy-guided CRF genicular nerve ablation was performed using anatomic landmarks for proper probe placement. Initial CRF needle (17-gauge 75 mm) (Coolief, Avanos Medical, Alpharetta, GA, USA) placement was done with true anteroposterior (AP) fluoroscopic view, i.e. open knee joint space with equal-width interspaces on both sides and patella in the midline. Three target points are superomedial and superolateral areas connecting the femoral shaft to the femoral epicondyle and the inferomedial area connecting the tibial shaft to the tibial epicondyle for the genicular nerves. Local anesthetic (1 mL of 1% lidocaine) was administered at each point using a 25-gauge needle into the skin and soft tissues. Using the tunnel vision under fluoroscopic guidance, the CRF needle was advanced percutaneously toward areas connecting the shaft to the epicondyle until the needle tip made contact with the bone. Final needle positions were confirmed by true lateral view, i.e. condyles of the femur superimposed over one another. In this lateral view, the needle tip was at the junction of the 50% shaft depth of the femur and tibia, respectively [Figure 2 ].
Figure 2: Fluoroscopy-guided CRFA final needle position for genicular nerve ablation and CRFA machine. CRFA: Cooled radiofrequency ablation
After confirming the needle position, 18-gauge internally cooled and 4-mm active tip RFA electrode (Make-Coolief, Avanos Medical, Alpharetta, GA, USA) was inserted into the CRF needle. Motor stimulation (2 Hz) up to 2.0 V established the absence of muscular contractions in its corresponding area of the lower limb, and sensory stimulation (50 Hz) at < 0.5 V in all the three locations reproduced concordant knee pain. The volume of 2 mL of 1% lidocaine was injected through the CRF needles to anesthetize the region before thermal ablation. Each target was sequentially lesioned for 2 min and 30 s at a set temperature of 60°C. The average procedure duration was 40 min for the index knee.
Injection triamcinolone 20 mg mixed with 0.2% ropivacaine 6 ml volume was injected 2 ml at each site before removing the CRF needle. All the patients were shifted to the postoperative ward for vitals monitoring after the application of the dressing. The patient was discharged on the same day and instructed to rest for 24 h with the application of ice and use of oral paracetamol (maximally 1 g/6 h) if required as analgesics. All patients were followed up in person after 3, 6, and 12 months. Patients answered the WOMAC questionnaire (96 points) and NRS pain score (0 – no pain and 10 – maximum pain) before the procedure and during each follow-up after treatment. They also answered about other treatment modalities they had tried before RFA and pain medications they were taking before.
Patients were allowed to use analgesics oral nonsteroidal anti-inflammatory aceclofenac 100 mg 2 times a day and tramadol 37.5 mg plus paracetamol 325 mg 2 times a day for a short period (5–7 days) during the study. Dosing for membrane stabilizers and antidepressants for chronic pain remained constant throughout the study. Additional treatments for the index knee were prohibited during the study periods.
The main primary objective was the global subjective improvement of the knee function in WOMAC score. It is a 24-item questionnaire focusing on pain, stiffness, and functional limitation and the maximum score is 96. A higher score indicates worse pain, stiffness, and functional limitation. The number of subjects whose global subjective improvement of the knee function in WOMAC score was by ≥50% from the baseline was good response, 25%–49% fairly good response, and 0%–24% same as before response.
The second primary objective was to change the pain level measured by the NRS. The NRS is an 11-point scale (0–10 points), where 0 point equals “no pain” and 10 points equal the “worst pain.” The number of subjects whose knee pain is reduced by ≥50% based on the NRS was good response, 25%–49% fairly good response, 0%–24% same as before response.
The secondary objectives were (1) changes in analgesic medication use and (2) any complications related to the procedures (e.g. weakness, numbness, paresthesia, neuralgia pseudoaneurysm, and others) immediate (0 days) and late (after 1 month).
The sample size was calculated using the formula:
n (sample size) = n = z2 * p * (1 − p)/e2
n was the sample size, z was the z-score associated with a level of confidence, p was the sample proportion, expressed as a decimal, e was the margin of error, expressed as a decimal, z = 1.96 for a confidence level (α) of 95%, p (prevalence of OA in India) =20%, and e = 10%.
Using these values in the above formula, n was coming as 62. Hence, a minimum of 62 cases were included in the study.
Categorical variables were expressed as the number of patients and percentage of patients and compared, if required, using Pearson’s Chi-square test for independence of attributes/Fisher’s exact test as appropriate.
Continuous variables were expressed as mean ± standard deviation and compared using unpaired t -test/one-way ANOVA if the data follow normal distribution or median and interquartile range and compared using Mann–Whitney U -test/Kruskal–Wallis test if the data do not follow a normal distribution.
The association between continuous variables was captured by Pearson’s correlation coefficient if the data follow normal distribution or Spearman’s rank correlation coefficient if the data do not follow a normal distribution.
The statistical software SPSS version 20 was used for the analysis (IBM SPSS Inc.Chicago.USA. version 20.0).
An alpha level of 5% had been taken, i.e. if any P < 0.05, it was considered statistically significant.
RESULTS
In the study, the average age of the total 62 patients with OA was 63 years (51–68; median: 63.00, mean: 62.25 ± 3.79), body mass index was 30.40 (28.20–33.70; median: 30.40), and there were 45 females and 17 males [Table 1 ]. Patients with bilateral knee pain were not excluded from the study, but only one knee intervention was performed at a time as index knee. In our study, ten patients presented with bilateral knee pain and the rest 52 patients with unilateral knee pain. The CRFA procedure was performed on the right side in 32 patients and on the left side in 30 patients and mostly (51.61%) inGrade 3 cases (Grade 2:3:4 – 24 [38.70%]:32 [51.61%]:6 [09.68%]). Almost all patients were on oral analgesics, acetaminophen, NSAIDs, opioids (tramadol, etc.), and other co-analgesics (anticonvulsant and serotonin–norepinephrine reuptake inhibitor) before enrollment into the study. Only a few patients (8, 12.91%) had a history of (>3 months ago) intra-articular steroid (IAS), whereas most of the patients (48, 77.41%) had a history of intra-articular hyaluronidase before enrollment into the study. Only 4 (4.17%) patients with post-total knee replacement (TKR) knee pain were enrolled in the study.
Table 1: Demographic characteristics and baseline parameters
The average mean baseline pain score was 9.00 (8.41 ± 0.66) and the mean WOMAC score was 80.00 (80.02 ± 6.92) [Figures 3 and 4 ].
Figure 3: Changes in the pain score (NRS) at different time intervals. NRS: Numeric Rating Scale
Figure 4: Changes in the WOMAC score at different time intervals. WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index
Pain scores (NRS) at 3-, 6-, and 12-month intervals after postprocedure follow-up were reduced significantly from the baseline level (P < 0.001) (Wilcoxon signed-rank test). The average median pain score was reduced to 3 (2.63 ± 0.58), 3 (3.32 ± 0.95), and 4 (4.03 ± 1.04) during a subsequent follow-up visit at 3, 6, and 12 months, respectively [Table 2 and Figure 3 ].
Table 2: Pain score at different time intervals and changes from the baseline
A total of 91.93% (57/62) of the patients successfully responded (≥50% improvement from the baseline was a good response) to the treatment according to the NRS pain score during 3-month follow-up visit. Then, it was 91.93% (57/62) and 77.41% (48/62) of the patients during 6- and 12-month follow-up visits, respectively [Table 4 ].
Similarly, WOMAC scores at 3-, 6-, and 12-month intervals during postprocedure follow-up were reduced significantly from the baseline level (P < 0.001) (Wilcoxon signed-rank test). The average median WOMAC score was reduced to 25.00 (28.80 ± 10.82), 25.00 (29.35 ± 11.12), and 34.00 (34.96 ± 11.28) during a subsequent follow-up visit at 3, 6, and 12 months [Table 3 and Figure 4 ].
Table 3: Western Ontario and McMaster Universities Osteoarthritis Index score at different time intervals and changes from the baseline
In another way, a total of 88.70% (55/62) patients successfully responded (≥50% improvement from the baseline was a good response) to the treatment according to the WOMAC score during 3-month follow-up visit. Then, it was reduced to 85.48% (53/62) of the patients during both 6- and 12-month follow-up visits [Table 4 ].
Table 4: Improvement of the NRS & WOMAC score from baseline during the study (Pearson’s Chi Square test for Independence of Attributes)
During the 3-month follow-up period, only 8.06% (5/62) of the patients received short-term analgesics (oral paracetamol, aceclofenac, and tramadol use for 5–7 days if not contraindicated) as supplementary analgesics. The use of analgesics was increased slightly with the long-term follow-up period. Use of analgesics was initially 14.52% (9/62) during 6- month follow up and then it was increased to 22.59% (14/62) during 12-month follow-up.
During the 12-month follow-up, two patients of Grade 2 OA received opioid-based analgesics (tablet tramadol 37.5 mg plus paracetamol 325 mg 2 times a day) for a total of 30 days and nonopioid analgesics (tablet aceclofenac 100 mg BD) for total 15-day period. On the other hand, six patients from each Grade 3 and 4 OA category received opioid-based analgesics (tablet tramadol 37.5 mg plus paracetamol 325 mg 2 times a day) for a total of 60 days and nonopioid analgesics (tablet aceclofenac 100 mg BD) for total 20 days during the 12-month follow-up.
There were a few 11 (17.74%) minor complications, e.g. mild swelling and pain were reported in the immediate postprocedure period. Moreover, only 4 (6.45%) patients had late complication as hypoesthesia over shin bone in our study.
DISCUSSION
The present study describes the treatment effectiveness of the CRFA in treating chronic knee OA patients. In our study, we found that NRS pain score and WOMAC functional score significantly improved (≥50% from baseline) (77.41% and 85.48%, respectively) after the CRFA intervention up to 12-month duration. Our observational study outcome, related to the duration of pain relief and functional status improvement following CRFA application, is comparable to the previously published randomized controlled trial (RCT) studies.
Choi et al . 2011 first reported that RFA of the genicular nerve had provided a significant improvement in pain and functional status for 12 weeks without any significant adverse events by a double-blind RCT.[ 14 ]
Kocayiğit and Beyaz while comparing cooled and conventional RF applications for the treatment of osteoarthritic knee pain found that both treatments were equally effective in improving physical function and reducing pain over a 12-week duration.[ 19 ]
Bellini and Barbieri retrospectively analyzed in their 1st case series of nine patients during 2015 that CRFA of the genicular nerve relieved chronic knee OA pain at 1-, 3-, 6-, and 12-month follow-up.[ 18 ]
McCormick et al ., in their cross-sectional survey, reported that CRFA of the genicular nerves provides a marked improvement in the quality of life and pain assessment scales for 6-month follow-up.[ 22 ]
Davis et al ., in their prospective, multicenter, randomized, crossover clinical trial while comparing CRFA with IAS injection, concluded that CRFA with the fluoroscopy-guided method can provide pain relief and improved knee function for 6-month duration and no procedure-related serious adverse events.[ 23 ]
Davis et al . further followed up the CRFA patients at 12 months, with 65% of the patients having pain reduction ≥50% following a single treatment.[ 24 ]
Cooled RF now established treatment for knee OA for providing long-term pain relief.
In the study by Hunter et al ., they followed up the patients for as long as 18-month and even 24-month duration. In their study, 12 out of 25 patients reported ≥50% pain relief compared to baseline at 18-month duration, while 11 out of 25 patients reported ≥50% pain relief at 24 months. They concluded that CRFA provides sustained pain relief and improved knee function even for 24-month duration.[ 25 ]
Overall most of the studies mentioned in the above discussion, demonstrated that cooled RFA provides effective pain relief for 12-month duration.
Our findings were also similar to the previous study that RF intervention can significantly decrease knee pain, stiffness, and difficulties as per WOMAC score during follow-up compared with baseline.[ 17 ]
As per our prospective observational study, CRFA treatment provides a significant improvement in the pain and functional status for 12-month duration.
In our study, we had not modified any long-term co-analgesic medications during the study period. However, the short-term analgesic requirement was significantly reduced during the subsequent follow-up. During 12-month follow-up, only 22.59% of the patients provided a history of short-term intermittent analgesic (NSAIDs) use to control their knee pain. During the 12-month follow-up, only 2 (8.34%) patients of Grade 2 OA required rescue analgesics and only 6 (18.75%) patients of Grade 3 OA required rescue analgesics. Whereas, all six patients of Grade 4 OA required rescue analgesics during the 12-month follow-up.
Grade 2 OA patients in the study (24/62) (38.70%) responded well to the CRFA procedure with only two patients requiring rescue analgesia throughout the study period. Further study is required to assess the relationship of the CRFA procedure outcome with the radiological grade of the OA.
One retrospective electronic chart review study demonstrated the effectiveness and safety of the CRFA procedure even for post-TKR knee pain.[ 26 ] Here, in our study, we had got only four patients with post-TKR knee pain for whom the CRFA intervention proved effective in reducing pain and suffering. Further large-scale randomized control trial is required to compare the effectiveness of the procedure in post-TKR knee pain versus chronic OA pain.
There is a recent meta-analysis of the RCT study that showed the efficacy of the CRFA procedure for at least 6-month duration in improving both knee pain and function in patients with OA.[ 27 ] Even if few RCT studies demonstrated that CRFA is effective even for 18 and 24 months, further randomized control trial is required before any definitive conclusion.
There are a few limitations of our study. We have not selected any control group for comparison and our study is not a randomized control trial. We have not taken into account the emotional status of the patient. Furthermore, our sample size was relatively small.
CONCLUSIONS
CRFA of the genicular nerve in chronic knee OA provides long-term pain relief and improved function for at least 12-month duration without any significant complications.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal for academic purposes. The patients understand that their name and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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