Periprosthetic Metabolic Activity After Total Ankle Arthroplasty: Cross-Sectional 18 F-NaF PET/CT Data From Asymptomatic Patients at 6-24 Months

Background: Radionuclide bone scintigraphy in combination with computed tomography (CT) is increasingly used as a diagnostic tool to evaluate the painful total ankle arthroplasty (TAA). However, uptake patterns following uncomplicated TAA have not been investigated. In this study, we aimed to establish normative data on periprosthetic metabolic activity following TAA. Methods: Thirty-two asymptomatic patients who underwent TAA with a modern fixed-bearing prosthesis for posttraumatic arthritis were included. Patients underwent 18 F-NaF positron emission tomography (PET) at 1 of 4 time intervals following TAA: 6, 12, 18, or 24 months, with 8 different patients enrolled at each time point. Standard uptake values (SUVs) were measured at the bone-implant interface in regions of interest (ROIs) defined on axial CT scan slices. Periprosthetic bone blood flow ( K 1 ) and bone turnover ( k i , flux) were quantified from dynamic 18F-NaF PET/CT. Results: Tracer uptake in the talus increased from 6 to 12 months postoperatively, subsequently declining from 12 to 24 months. Uptake in the tibia was similar at 6 and 12 months, and steadily decreased thereafter. SUVs, K 1 , and k i in both the tibia and talus decreased significantly between 12 and 24 months ( P -adj < .05). SUVs, K 1 , and k i in the talus exceeded those measures in the tibia at 12, 18, and 24 months postoperatively ( P -adj < .05). Conclusion: The present study demonstrates that in asymptomatic patients, periprosthetic tracer uptake peaks at 12 months and remains elevated up to 24 months following modern fixed-bearing TAA. In both the tibia and talus, uptake decreased between 12 and 24 months. Talar uptake was higher than tibial uptake at 12, 18, and 24 months. Our findings suggest that radionuclide bone scintigraphy should be cautiously interpreted especially when performed within 2 years of TAA.