Unusual aspiration during genicular nerve radiofrequency ablation after total knee arthroplasty

Case Diagnosis: Unexpected synovial fluid aspiration during genicular nerve radiofrequency ablation in a post-total knee arthroplasty patient.

Case Description or Program Description: A 77-year-old female presented with chronic left knee pain. She had a left total knee arthroplasty (TKA) 14 months prior followed by revision surgery 6 months later. Despite improved range of motion, her pain persisted, leading her to seek interventional management. Two diagnostic genicular nerve blocks were performed without any complications nor unusual findings, and both temporarily provided 100% pain relief. She then proceeded with therapeutic genicular nerve radiofrequency ablation (RFA) under fluoroscopic guidance. Once the superomedial needle was appropriately positioned, the stylet was removed, and there was an immediate return of clear, viscous liquid. The fluid was sent for cytology, the needle was successfully repositioned, and the RFA was completed without complications.

Setting: Academic ambulatory care center procedure suite

Assessment/Results: Ultrasound of the same area of the knee was then performed. There was a small fluid pocket that was distinct and not communicating with any bursae. Cytology confirmed synovial fluid.

Discussion (relevance): This case underscores the need to recognize the possibility of synovial tissue presence or regrowth along with synovial fluid production in post-TKA patients. While synovectomies were historically common with TKA, evidence now suggests no clinical benefit. Even with a synovectomy, synovial tissue can regenerate to allow adequate lubrication of artificial joints, and this can occur outside of known bursae. During genicular nerve procedures, clinicians should recognize potential synovial pockets and ensure negative aspiration before proceeding. Injecting or placing RFA needles in a synovial pocket should also be avoided, as the synovial fluid may act as a heat sink and affect impedance during the procedure.

Conclusions: This case highlights an unusual finding and important considerations for genicular nerve procedures in a post-TKA patient.