Diagnostic Genicular Nerve Block Prior to Radiofrequency Ablation for Knee Osteoarthritis Pain

Knee osteoarthritis (OA) is one of the most common conditions and causes of disability in
older adults, with an estimated prevalence of symptoms in 20-30% of individuals over 65 years
of age. Pain associated with knee OA may have a central nervous system component, but
intra-articular chemical pain mediators such as Substance P and Calcitonin-gene related
peptide, possible intra-articular ischemic pain due to vasospasm, mechanical compression or
irritation of the richly innervated subchondral bone, periosteum, synovium, and joint
capsule, as well as peripheral genicular nerve sensitization have largely been implicated.

Knee OA, in general, is treated conservatively with weight loss (when indicated), physical
therapy, oral analgesic medications, and intra-articular corticosteroid or hyaluronic acid
injections. If this approach fails to provide adequate pain relief and functional
restoration, patients may be offered total knee arthroplasty (TKA), if they are surgical
candidates. While, TKA is generally a safe procedure, like any major open surgery, it is
associated with a risk of serious complications; a large cohort study of 83,756 patients
demonstrated the annual incidence of venous thromboembolism (0.6%), myocardial infarction
(0.5%), stroke (0.5%), and a 90 day mortality (0.7%) to all be significantly higher than the
general population. Furthermore, some patients are not candidates for TKA due to
co-morbidities such as morbid obesity or cardiopulmonary disease.

Radiofrequency ablation (RFA) for knee joint denervation represents a promising intervention
for patients with chronic painful knee osteoarthritis who have failed conservative management
and are either not willing or not eligible for TKA. During RFA a thermal lesion is created by
applying radiofrequency energy through an electrode placed at a target structure. RFA has
been used to disrupt sensory afferent nociceptive nerve fibers supplying the zygapophyseal
(facet) joints of the spine as well as the sacroiliac joint with excellent pain reduction and
functional improvement when performed appropriately.

To date, there are only two published studies that have investigated knee joint denervation
by RFA for the treatment of chronic painful OA. In a randomized prospective study (n=35),
Choi et al. found that genicular nerve RFA resulted in clinically meaningful pain improvement
in approximately 60% of patients at 6 month follow-up. Improvement in function was also
observed. Bellini and Barbieri report a series of 3 patients with chronic painful knee OA,
two of whom who experienced meaningful pain and functional improvement after genicular nerve
RFA.

There is no evidence-based algorithm established which provides a means of properly selecting
which patients would benefit from genicular nerve RFA. In the study performed by Choi et al.,
only one set of diagnostic genicular nerve blocks with a threshold of 50% pain relief to be
considered a "positive response" was used. In contrast, a well developed literature regarding
selection of patients for medial branch RFA for facet-mediated pain indicates that two sets
of diagnostic medial branch nerve blocks with a threshold of >80% pain reduction to be
considered a "positive response" increased positive predictive value for both meaningful pain
and functional outcomes to 80-90%. While the diagnosis of facet-mediated pain can be
challenging given the variety of potential pain generators in the spine, diagnostic
uncertainly is far less likely when evaluating the knee as a pain generator. In fact, it is
unclear that any diagnostic blocks of the genicular nerves are needed given that this
increase the potential for complications and healthcare costs compared to proceeding directly
to the ablation procedure. It is vital that evidence-based selection criteria are developed
for genicular nerve RFA in order to optimize clinical outcomes and minimize healthcare costs.

Inclusion Criteria:

1. All patients ages 30-80 with chronic painful knee osteoarthritis who would undergo
treatment by genicular nerve radiofrequency ablation.

2. Knee pain for at least 6 months.

3. Kellgren-Lawrence knee osteoarthritis of 2 or greater.

4. Pain resistant to conventional therapy including NSAIDs, opioids, muscle relaxants,
oral steroids, physical therapy, and intra-articular injection therapy.

5. No pain referral beyond the expected distribution for knee osteoarthritis.

Exclusion Criteria:

1. NRS pain score of 4 or more

2. Focal neurologic signs or symptoms.

3. Previous radiofrequency ablation treatment for similar symptoms.

4. Intra-articular knee corticosteroid or hyaluronic acid injection in the past 3 months.

5. Concomitant radicular pain.

6. Previous knee surgery.

7. Patient refusal.

8. Lack of consent.

9. Active systemic or local infections at the site of proposed needle and electrode
placement.

10. Coagulopathy or other bleeding disorder, current use of anticoagulants or
anti-platelet medications.

11. Allergy to medications being used for injection procedures (contrast, local
anesthetic).

12. Inability to read English, communicate with staff, or participate in follow-up.

13. Pregnancy.

14. Pacemaker.

15. Cognitive deficit.

16. Unstable medical or psychiatric illness.