Disclosures: Seema Parikh: No financial relationships or conflicts of interest

Case Diagnosis: A 75-year-old male patient with severe, diffuse tricompartmental osteoarthritis in the left knee.

Case Description or Program Description: The patient was scheduled for fluoroscopy-guided genicular nerve radiofrequency ablation (RFA) after failed prior conservative management. The pre-procedure MRI of the left knee showed a moderate suprapatellar joint effusion. During the procedure, an 18-gauge, 100mm, 10mm active tip venom RFA needle was inserted towards both the superior medial (SM) and superior lateral (SL) portions of the femoral condyle. Subsequently, a 22-gauge, 100mm, 10mm active tip RFA needle was inserted towards the inferior medial (IM) portion of the tibial condyle. Correct placement of the needles was confirmed using fluoroscopy. Unexpectedly, the RFA needle targeting the SM genicular nerve was persistently leaking synovial fluid. Despite multiple attempts at repositioning the needle, it continued to leak synovial fluid, and the needle was removed to reduce infection risk. Afterwards, the radiofrequency probes were inserted at the SL and IM regions. However, the temperature at each region failed to rise to the desired 70°C despite troubleshooting the RFA machine and changing the probes.

Setting: Same Day Surgery

Assessment/Results: The RFA procedure was not performed. Instead, genicular nerve blocks with steroids were done to provide the patient with pain relief. The patient reported about 80% pain relief with the nerve blocks immediately after the procedure was over.

Discussion (relevance): Blood flow in large vessels near RFA probe tips causes a cooling effect, which increases impedance and prevents heat from the ablation from reaching the targeted nerves; this phenomenon is known as the heat-sink effect. The large joint effusion in this patient caused a heat-sink effect, resulting in failure of the RFA procedure. Patients should have large effusions aspirated prior to the RFA to prevent excess synovial fluid from causing high impedance.

Conclusions: Radiofrequency ablation procedures may fail in joints with large effusions due to the heat-sink effect.

Level of Evidence: Level V

« Back to AAPM&R Annual Assembly 2022

PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/heat-sink-effect-causing-unsuccessful-radiofrequency-ablation-of-left-knee-a-case-report/