Cryoneurolysis for the Management of Chronic Pain in Patients With Knee Osteoarthritis

BACKGROUND Pain is the principal symptom in knee osteoarthritis (OA) and results in a considerable amount of years lived with disability, emotional distress and has significant socioeconomic consequences. Knee OA in particular, has a high prevalence rate compared to other types of OA, and is also present in the younger working age population. The treatment of knee OA typically focuses on pain relief, however the effects of current conservative treatment options remain small to moderate and most are associated with side effects. In many cases patients alternatively may be subjected to partial/total knee arthroplasty (TKA). TKA is considered to be an effective treatment for end-stage knee osteoarthritis however more than 20% of patients receiving TKA, experience persistent and unchanged pain post-surgery. Reviewing these results, focus should be on low-risk, minimally invasive therapies. Novel advances in the field of cryoneurolysis are in that respect promising. Cryoneurolysis has made it possible to apply low temperatures to a target percutaneous peripheral nerve, causing Wallerian degeneration. This has been shown to provide pain relief in a variety of chronic pain conditions. Recently, Radnovich et al. (2017) targeted the genicular nerves to reduce pain in patients with knee OA. The authors reported significant pain relief in patients with knee OA for up to 150 days. The authors reported expected adverse effects, that were transient, with mild severity, requiring no further intervention. These results might suggest that cryoneurolysis treatment is a safe procedure, that may reduce both pain and symptoms in patients with knee OA. Further prospective randomized controlled studies, with adequate power are needed to confirm the efficacy and safety of cryoneurolysis treatment in patients with knee OA.

In Denmark, a neuromuscular exercise program (GLA:D) has been implemented, for the treatment of knee and hip OA in clinical practice. Recent studies show that exercise reduce pain and improve function in people with knee or hip OA. Despite of these reports the beneficial effects remains moderate with difficulties in maintaining these effects at long-term follow-up and includes a significant discontinuation rate for patients reporting high pain levels. In this line, pain and muscle weakness, among others, have been reported to be major barriers for physical exercise. The application of cryoneurolysis treatment as an effective pain reducing treatment prior to a standardized exercise program could perhaps provide significant pain relief, resulting in improved adherence, exercise effectiveness and long-term benefits of both therapies.

The primary objective of the current project is to determine the effectiveness of cryoneurolysis in its proposed ability to decrease pain in patients with knee osteoarthritis. The secondary objective is to evaluate the safety and effectiveness of cryoneurolysis in its ability to improve outcomes in the GLA:D program to potentially delay or avoid surgical intervention.

We hypothesize that cryoneurolysis in combination with GLA:D will be a safe and effective therapeutic option with few side effects to reduce pain in patients with knee osteoarthritis and may post pone surgical intervention.

TRIAL DESIGN This study is a randomized, controlled, trial (RCT) designed to test the efficacy of cryoneurolysis treatment in patients with knee osteoarthritis followed by a neuromuscular exercise program (GLA:D). The patients will be randomly allocated in either a cryoneurolysis intervention group (CRYO) or a sham group (SHAM) and will be assessed at baseline, 2 weeks post cryoneurolysis, post GLA;D and at 6, 12 and 24 month follow-up. The tests will include both patient-reported outcomes (PRO) and objective functional measurements.

RECRUITMENT AND SAMPLE SIZE Patients with pain and knee OA confirmed by radiography, are referred to GLA:D by their general practitioner prior to assessment of surgery eligibility at the hospital. The current project will recruit these patients in collaboration with selected general practitioners in the Region of Southern Denmark. According the Region of Southern Denmark, an average of 270 patients participate in the GLA:D program every year. Based on this estimation and considering the eligibility criteria to participate in the current project, recruitment will continue for up to 1 year.

The planned number of trial participants is based on the assumed superiority of the cryoneurolysis treatment over control. Estimating the sample size for a two-sample means test with a level of significance at 0.05, assuming a common standard deviation (SD) of 30 in VAS pain intensity scores indicates that for the intention-to-treat (ITT) population, 74 individuals is required to obtain a power of at least 80% to establish a minimal clinically significant difference (MCSD) of 20 in VAS pain scores. The MCSD and common standard deviation is based on previous findings with a similar patient group and intervention. With an expected drop-out rate of 20%, a total of 94 individuals will be included in the project, 47 in each group.

ALLOCATION AND BLINDING Randomization will be performed as computer-generated block randomization with a 1:1 allocation ratio using random block sizes of 2, 4 and 6 in either group CRYO or group SHAM. The randomization restrictions will not be disclosed to ensure allocation concealment and the sequence will be performed by an external co-investigator.

To account for the placebo effect and reduce the risk of bias, the patients, therapists and data-manager will be blinded to the allocation. Blinding will be assured using a sham trial that includes the same procedures as cryoneurolysis treatment but without any freezing temperatures. Thus, visible marks as a result of the procedures in both groups will be similar.

INTERVENTIONS Diagnostic nerve block. All patients reporting a decrease of ≥ 50 % in VAS pain scores at least 15 min after a diagnostic nerve block of the genicular nerves.

Cryoneurolysis. The current project involves the novel application and test of cryoneurolysis, in the treatment of OA related pain. The rationale behind this method, is based on previous reports showing that low temperature conditions can alter nerve function. This technology allows for reversible destruction of nerves, also known as Wallerian degeneration, that prevents nerve signaling and potentially alleviate pain and motor dysfunction in a number of medical conditions. A probe will be inserted percutaneously at the target anterior femoral cutaneous nerve and infrapatellar branch of the saphenous nerve guided by ultrasound visualization to accurately determine the location of the nerve and to account for adjacent neurovascular structures and variations in anatomical structures. The target locations are drawn directly on the patients' skin prior to treatment along which a dose of local anesthetic will be injected subcutaneously before treatment. Cryoneurolysis at each target site requires 2-4 freeze cycles with a duration of 3 mins, and with thaw cycles between 20-40 seconds. A temperature probe will be inserted adjacent to the target nerve and cryoneurolysis-probe to ensure a controlled cooling effect and to control nerve damage. The sham intervention includes a similar procedure but using a sham probe.

GLA:D. SHAM and CRYO will both participate in the GLA:D program, which is a standard education and exercise program for patients with osteoarthritis in Denmark. The program is performed in groups and with the supervision of an experienced physiotherapist specialized in training of musculoskeletal disorders and has a duration of 8 weeks.

STATISTICAL METHODS The treatment groups will be examined for comparability based on baseline demographic and prognostic measures. An Intention-To-Treat (ITT) analysis will be used for all allocated patients and a mixed effects model will be used on the continuous outcome measures to determine the effects of cryoneurolysis treatment from baseline to post treatment and follow-ups [Between groups factor: CRYO vs SHAM, within groups factor: time]. The model will use robust estimation methods to account for outliers. Finally, a multiple imputation approach will be used in case of missing data. All P-values < 0.05 will be considered statistically significant.

ETHICS AND SIGNIFICANCE The project will be conducted according to the declaration of Helsinki and will be registered in ClinicalTrials.gov. The Project has been approved by the Regional Committee on Health Research Ethics for Southern Denmark (S-20180089).

Cryoneurolysis could potentially provide an effective, safe and minimally invasive option to treat pain in OA patients. The potential benefits include increased functional capacity and quality of life as a result of significant pain relief and improved benefits of physical exercise, ultimately postponing or making surgical intervention unnecessary. Finally, an important perspective, is the application of cryoneurolysis in other areas - such as managing pain, related to surgery, to improve rehabilitation.