[18F]-sodium fluoride PET/MR for painful lumbar facet joint degeneration - a randomized controlled clinical trial.

Background Context: [18F]-sodium fluoride (NaF) PET/MR is a modern diagnostic modality for imaging increased bone turnover. Its merits in detecting painful facet joint osteoarthritis in patients with lumbar back pain are unknown.

Purpose: To perform a prospective randomized controlled study investigating [18F]-NaF PET/MR for detecting painful facet joints in comparison to the standard of care (SOC), including clinical examination and conventional MRI.

Study Design/setting: Randomized controlled clinical study.

Patient Sample: Thirty-nine patients.

Outcome Measures: Visual analog pain scale (VAS) before and at several time points after facet joint infiltration.

Methods: Patients with low back pain and suspected facet joint osteoarthritis underwent lumbar [18F]-NaF PET/MR, besides conventional MRI and clinical examination. After randomization, they either received local anesthetics/ corticosteroid infiltration of facet joints as defined by clinical examination and conventional MRI (SOC), or according to the hot spots on PET/MR. VAS was documented at 15 minutes, 1 day, 1 week and 1 month after infiltration. Thirty-nine patients underwent PET/MR before the study was stopped due to new Good Manufacturing Practice requirement and new regulations by radiation protection authorities limiting staff radiation exposure during the production of this radiotracer.

Results: Significant pain reduction compared to baseline was shown at every timepoint in both groups, except at 1 month after infiltration in the SOC group. Pain levels did not differ between SOC (n=17) and PET/MR patients (n=12) before infiltration and at 15 minutes, 1 day, 1 week and 1 month after infiltration. No significant correlation was detected between the sum of the PET/MR activity and the initial pain scores or relative reduction of pain after 15 minutes. The constructed study groups of patients with infiltration of all facet joints being PET/MR-positive (n=18) had significantly less pain after 1 months than patients with infiltration in PET/MR-negative facet joints (n=11) (VAS: 4 [0, 9] vs. 7 [2, 10], p=.046).

Conclusions: There is no correlation of pain to NaF activity nor a relevant superiority of [18F]-NaF PET/MR for identification of painful facet joints compared to the standard of care.