After Total Ankle Arthroplasty, When Does Bone Perfusion and Metabolic Activity at the Bone-Implant Interface Normalize? A PET/CT Study

CATEGORY: Ankle Arthritis INTRODUCTION/PURPOSE: Radionuclide bone scintigraphy in combination with computed tomography (CT) has been used to evaluate painful total hip and knee arthroplasties, and has also been used in the evaluation of the painful total ankle arthroplasty (TAA). Increased tracer uptake around implants may indicate loosening, but uptake characteristics of bone-seeking radiopharmaceuticals in asymptomatic total ankle patients have not been clarified. While findings of increased metabolic activity may prompt surgical intervention, there has been no work performed to define when postoperatively periprosthetic activity normalizes, if at all. In this study, we plan to establish normative data on 18F sodium fluoride (18F-NaF) positron emission tomography/CT (PET/CT) uptake ratios around TAA implants at various time intervals after surgery in asymptomatic TAA patients. METHODS: The majority of the arthroplasty literature has investigated use of SPECT/CT performed with 99mTc-labeled bisphosphonates. However, data suggest that 18F-NaF PET/CT may be superior for this indication, with more favorable pharmacokinetics and similar sensitivity to detect aseptic loosening. In the present study, 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 and with any periprosthetic lucencies or cysts were excluded. Patients were enrolled at one of four time intervals following TAA: 6, 12, 18, or 24 months. Standard uptake values were measured at the bone-implant interface for the tibial and talar components on static PET, in regions of interest 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: Sixteen asymptomatic patients underwent PET/CT: 4 patients at 6 months postoperatively, 6 at 12 months, and 6 at 24 months. We are currently still in data collection and at this time only 2 patients at 18 months have completed the scan, therefore their data were excluded. The average age was 65 years (range, 55 to 80) and 6 patients were female (38%), with individual patient data shown in the Table. Talar K1 and flux both appeared to increase from 6 to 12 months, and decrease between 12 and 24 months, although there was no statistically significant difference between timepoints. Overall tibial K1 and flux appeared to decrease slightly from 6 to 12 months, and stayed relatively stable between 12 and 24 months, again with no significant difference between timepoints (Figure). 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 bone blood flow and bone turnover remain elevated up to 24 months following modern fixed-bearing TAA. Not only do these values remain elevated at 24 months, but we found that there does not appear to be any significant decrease in either measurement over time from 6 to 24 months postoperatively. Our findings suggest that radionuclide bone scintigraphy should be cautiously interpreted when performed within 2 years of TAA.