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19 Articles in Volume 20, Issue #4
20/20 with Dr. Nathaniel Katz: Pain Research and Future Therapeutics
A 20-Year Timeline: Pain Therapeutics and Regulations
A Comparison of the Alpha-2-Adrenergic Receptor Agonists for Managing Opioid Withdrawal
A Pain Assessment Primer
After the Task Force: A Conversation with Vanila A. Singh, MD
Ask the PharmD: Can opioids and benzodiazepines ever be used together?
Cognitive Strategies and Mindful Awareness for Integrative Pain Care
COVID: Clinical Considerations for Acute and Post-Infection Symptoms
Editorial: Fudin and Gudin Tackle Pain Care History – Asking, Have We Done a 180?
From Hands-On to Home-Based Care: Physical Therapy Undergoes a Paradigm Shift Due to Pandemic
MS-Related Pain and Spasticity: Are Cannabinoids an Option?
New Biological Agents for Psoriatic Arthritis: A Monoclonal Antibody Primer
Pandemic Presents Unexpected Opportunity to Embrace Multimodal Analgesia and the Integrative Care Team
Provider Perspective on Knee OA: Injections and RFA Options
Redefining the “Pain Specialist” of Today
Resident’s Corner: Climbing the Learning Curve in Pain Management
The Evolution of Pain Management: Experts Weigh In
Tips from the Field: How to Enhance Practice Efficiency
Tumor Necrosis Factor (TNF) Inhibitors: A Clinical Primer

Provider Perspective on Knee OA: Injections and RFA Options

Orthopaedic surgeon Antonia F. Chen contends that cooled radiofrequency ablation fills an existing treatment gap in the management of painful knee osteoarthritis.

As a practicing orthopaedic surgeon, I often see patients with knee osteoarthritis (OA) referred to me by their primary care physicians. Many patients think that seeing an orthopaedic surgeon is the end of the road and that they will immediately need to undergo surgery, which I understand can be scary for them. As a surgeon, I enjoy operating on patients – but that’s not always the best option for everyone and, in my opinion, is why nonsurgical options for knee OA exist.

Clinically speaking, knee OA is the gradual degradation of cartilage in the knee joint. We know that cartilage provides the lubrication and shock absorption for the knee joint to function properly – without it, there can be painful bone-on-bone rubbing.


Conventional Approaches to Knee OA Pain

Non-operative management of knee pain caused by OA has developed over the past several decades. Conservative methods include diet and weight loss. I tell my patients that 1 pound of weight loss is equivalent to 4 pounds of weight off the knee. By reducing the load on their knees, they can reduce their pain.

Exercise, including physical therapy, can improve knee function by reducing swelling and stiffness.1 Strengthening exercises can make activities of daily living easier, while flexibility exercises can increase range of motion. Many PT exercises can be done by the patient on their own once they receive a proper demonstration. 

Increased physical activity, however, can be somewhat of a catch-22 for some patients. As they are moving around more, their knee pain can increase. Over-the-counter medications such as acetaminophen and NSAIDS may help to reduce this pain, but patients often need to progress to other treatments to alleviate such pain and/or to avoid side effects that may arise with chronic use (ie, bleeding of the stomach, kidneys, or liver).

More recently, the treatment paradigm for knee OA has moved into “the age of injections.” These localized procedures often help to fill the gap between conservative modalities and surgery, providing pain relief and improving function.

The Age of Injections

The first injection to rise to prominence was corticosteroids, used by Miller in 1958.2 Since osteoarthritis of the knee is often associated with inflammation of the knee joint that leads to progression of cartilage damage, it was initially believed that suppressing the inflammatory processes could help slow its progression. In a clinical trial comparing intra-articular (IA) injections of the corticosteroid triamcinolone to saline, administered every 3 months over 2 years, researchers found that the corticosteroid offered no significant difference in knee pain.3 Further, subjects who received the corticosteroid had significantly greater cartilage volume loss secondary to the associated numbing agents used, especially lidocaine. However, it is useful for some patients, as some individuals get relief for longer than 3 months, and others get relief for less than 3 months.

Another commonly used injection is hyaluronic acid, also referred to as viscosupplementation. Knee OA is associated with changes in the synovial fluid, a viscous fluid that reduces friction between the articular cartilage in the knee joint during movement. These changes can affect the mechanical forces placed on the knee, making it susceptible to wear and tear.4 Viscosupplementation involves the injection of hyaluronic acid, a viscous polymer, that is believed to provide lubrication and shock absorption in the knee joint. However, FDA5 has recently brought into question the mechanism of action of this treatment, and clinical practice guidelines for orthopaedic surgeons do not currently recommend this treatment for knee OA.6

Platelet-rich plasma (PRP) injections have become popular as well. This treatment involves the extraction and concentration of a patient’s platelets from blood that are then reinjected into the affected area. It is hypothesized that these platelets accelerate healing processes.7 Because of how the treatment is prepared, there is an inherent variability and lack of standardization for the injection. Additionally, clinical evidence for its efficacy is contradictory, with some studies demonstrating efficacy and others not.8

PRP therapy is often not covered by insurance, so patients commonly pay for this treatment out-of-pocket. In my experience, PRP injections do not provide any relief for some patients, while for others, a series of injections do provide a great deal of pain relief and improved function. Still, the beneficial effects of repeat injections tend to fade, leaving many patients to face surgery as the next step.

Radiofrequency Ablation’s Time to Shine

Enter radiofrequency ablation (RFA) as another non-pharmacological option. Instead of targeting the inflammatory factors within the knee, this nonsurgical treatment targets the nerves outside of the knee that contribute to the pain associated with knee OA. Through a process known as ionic heating, RF probes deliver targeted thermal damage to these nerves, creating what are known as lesions. When the nerve structure is damaged, it interrupts the transmission of pain signals. Pain is attenuated while the nerve structure heals. Clinical data has shown that traditional radiofrequency probes can provide up to 3 months of pain relief.9


Example of a cooled radiofrequency ablation generator, pump, and probes (COOLIEF, by Avanos).


Cooled radiofrequency ablation (CRFA) is an evolution of traditional RF technology and is the only type of RFA treatment cleared by the FDA for the management of osteoarthritis of the knee. During a CRFA procedure, water is circulated through a RF probe. The internal cooling of the probe results in a larger lesion area and more extensive damage to the nerve structure. Robust anatomical studies have identified four core sensory nerves around the knee to determine CRFA protocols.10

A case series by Bellini  demonstrated the efficacy of CRFA, with participants’ knee pain shown to be diminished for up to 12 months.11

A separate multicentered RCT of 151 patients who were unresponsive to other conservative modalities compared the effectiveness of CRFA to IA steroid injections. Those who received CRFA reported significant improvements in pain, as measured by numeric rating scale (NRS) and function, as measured by Oxford Knee Score (OKS).10,12

Subjects reported their improvements at both the 6- and 12-month timepoints, again suggesting extended clinical durability of CRFA. Those who received steroid injections did not report similar outcomes, with pain returning and function worsening at approximately 3 months after treatment. Interestingly, this study also recorded the patient’s overall impression of treatment success, as measured by Global Perceived Effect (GPE). At the 6-month timepoint, 91% of subjects who underwent CRFA reported improved condition, while at 12 months, 75% of CRFA subjects reported improved condition.

Together, these results demonstrated that patients who underwent CRFA reported decreased pain, improved function, and improved overall health that could last as long as 12 months. An extension of this clinical study followed enrolled subjects for a longer period of time.13 Subjects receiving CRFA reported pain relief extending to the 18- and 24-month time periods.

Having well designed clinical trials is paramount to any practicing doctor considering a new technology.  I had the opportunity to be part of another very recent multicentered RCT study comparing the effectiveness of CRFA to hyaluronic acid injections in the management of knee OA.14 At the 6-month timepoint, those who received CRFA had significantly better outcomes than hyaluronic acid injection related to pain and knee function. At the time of this writing, the 12-month results from this study have been submitted for publication and confirm the extended clinical durability of CRFA.


Patient Identification for RFA Procedures

As with any medical procedure, there are opportunities to optimize CRFA treatment with regard to patient selection. Subjects undergoing radiofrequency ablation (both standard and cooled) receive diagnostic blocks, the injection of a local, short-acting anesthetic to the target genicular nerves. If a patient experiences pain relief following these temporary blocks, it is posited that they will receive benefit from an RFA procedure.

Researchers are currently working to determine if these blocks can be used prognostically, that is, to determine what level of response from a block will ensure treatment success. This is an exciting field of research that will help practicing physicians provide the best recommendations for their patients.

It is also important to consider the value of a particular treatment to a patient. As noted, diet, exercise, and OTC medications can improve the quality of life for many patients suffering chronic pain from osteoarthritis of the knee, and for little cost. When they turn to injections, corticosteroids tend to be the lowest in cost and represent a valuable procedure if the patient responds to treatment. Hyaluronic acid and PRP injections cost significantly more and their improvement in patient outcome is variable. Cooled radiofrequency ablation is a more resource intensive-procedure than an injection and comes at a cost similar to hyaluronic acid and PRP injections.  

However, because of the significant and clinically validated improvements to a patient’s quality of life, seen in both the literature and my own practice, I consider this to be a valuable treatment option for many patients.  

Overall, each of these treatment options has a role in the patient journey. Despite my career as a surgeon, if a partial or total knee replacement can be avoided, I am glad to have other options on the table.


Disclosure: Dr. Chen is a consultant for Avanos, which provides cooled radiofrequency ablation technology, but she does not use any of the products mentioned in this piece.

Last updated on: August 3, 2020
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