Differential ¹⁸F-NaF uptake in various compartments in knee osteoarthritis: an observational study using PET/MRI

Aim: To investigate if the pattern of fluorine-18-labelled sodium fluoride (¹⁸F-NaF) uptake on integrated positron-emission tomography (PET)/magnetic resonance imaging (MRI) of bone marrow lesions (BML) and osteophytes differs between different knee compartments.

Materials and methods: Sixteen patients with no prior history of knee injury with or without pain were recruited for the study. The images of both knees were acquired on simultaneous PET/MRI. The acquisition was done after 45 minutes of intravenous injection of ¹⁸F-NaF 185-370 MBq (5-10 mCi) for 40 minutes. Each knee was divided into eight compartments patella, trochlea, medial central femur, lateral central femur, medial posterior femur, lateral posterior femur, medial tibia, lateral tibia, and cruciate ligament insertion specifically for BML. BML and osteophytes were scored using MRI Osteoarthritis Knee Score (MOAKS) criteria and their corresponding maximum standardised uptake values (SUVmax) recorded.

Results: BML and osteophytes both showed statistically significant differences among knee compartments, i.e., p-value <0.000 and < 0.043 respectively. SUVmax for BML and osteophytes was greatest in the medial tibia.

Conclusion: ¹⁸F-NaF PET/MRI showed that BML and osteophytes had differential uptake values due to bone remodelling amongst the various knee compartments and this may help to design disease-modifying osteoarthritis drugs in the future.