2025 J. Leonard Goldner Award Winner: Metabolic Activity at the Bone-Implant Interface Following Total Ankle Replacement: A Two-Year Cross-Sectional Study of Asymptomatic Patients Evaluated With 18F-NaF Positron Emission Tomography

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: Radionuclide bone scintigraphy in combination with computed tomography (CT) is often used in the evaluation of the painful total ankle arthroplasty (TAA). Increased tracer uptake around implants may indicate loosening, but there has been no work performed to define when after TAA periprosthetic activity normalizes, if at all. The majority of the arthroplasty literature has investigated use of single-photon emission computed tomography (SPECT) performed with 99mTc-labeled bisphosphonates. However, data suggest that 18F-NaF positron emission tomography (PET) may be superior for this indication, with more favorable pharmacokinetics and similar sensitivity to detect aseptic loosening. Therefore, we planned to use 18F-NaF PET/CT to establish normative data on periprosthetic metabolic activity following TAA. Methods: In this study, we used 18F-NaF PET/CT to analyze uptake ratios around TAA implants at various time intervals after surgery. Asymptomatic patients who underwent TAA with a modern fixed-bearing TAA prosthesis (either the Wright Infinity Adaptis or Exactech Vantage prosthesis) for posttraumatic arthritis were eligible for inclusion. Patients with ipsilateral hindfoot fusion or with radiographic findings potentially consistent with loosening (i.e., periprosthetic lucencies) were excluded. 8 patients were enrolled at each of four time intervals following TAA: 6, 12, 18, and 24 months, for a total of 32 patients. The average age was 66 years; 59% were male. Standard uptake values were measured at the tibial and talar bone-implant interfaces on static PET, in regions of interest (ROIs) defined on axial CT scan slices. Periprosthetic bone blood flow (K1) and bone turnover (flux) were assessed at each time interval in each periprosthetic region using dynamic PET. Results: Visually, tracer uptake in the talus increased from 6 to 12 months postoperatively, subsequently declining from 12 to 24 months. Maximal uptake in the tibia was at 6 months and steadily decreased thereafter (Figures). Uptake in both the tibia and the talus was significantly lower at 24 months than at 12 months (p < 0.05). Uptake in the talus exceeded that in the tibia in all ROIs at 6 and 12 months postoperatively (p < 0.001). At 18 months, talar uptake remained elevated compared to tibial uptake (p=0.02), but by 24 months, there was no significant difference in total tibial uptake compared to the talus (p=0.76). There was no significant change in K1 and flux between timepoints for the tibia or the talus as a whole. Conclusion: There is currently no normative data to help guide interpretation of radionuclide bone scintigraphy for the painful TAA. The present study utilizing 18F-NaF PET/CT scans demonstrates that even in asymptomatic patients, periprosthetic tracer uptake remains elevated 24 months following modern fixed-bearing TAA. Talar uptake was higher than tibial uptake at all timepoints through 18 months, but not at 24 months. Our findings suggest that radionuclide bone scintigraphy should be cautiously interpreted when performed within 2 years of TAA.