Prognostic value of NaF-PET/CT in non-instrumented posterolateral lumbar fusion

Introduction: Non-instrumented posterolateral lumbar fusion is the treatment of choice for patients diagnosed with degenerative spondylosis. Positron emission tomography (PET) with 18F-sodium fluoride (NaF) is an imaging modality capable of showing ongoing calcium deposition in vivo. We aimed to investigate the prognostic value of NaF-PET/CT performed in this category of patients one month after treatment with non-instrumented posterolateral lumbar fusion.

Method: 18 patients (median 66.5 years, range 60-78, 13 females) underwent 90-minute NaF-PET/CT one month after surgery for degenerative spondylosis. Fusion status was determined using high resolution CT within a year of surgery. Clinical characteristics including walking distance, VAS score of back pain (VAS-B), Oswestry Disability Index questionnaire (ODI), and European Quality of Life – 5 Dimensions questionnaire (EQ-5D) were assessed before surgery and 1 year after. The changes in clinical parameters between the time points were compared with the graft NaF uptake in each patient.

Results: Only 4 of 18 patients experienced fusion, which was bilateral and multilevel in all four. The graft uptake in fused patients was 1178(961-1279) SUV compared to 1333(474-27817) SUV in non-fused patients (p = 0.93). The corresponding partial volume corrected values were 1282(962-9535) SUV and 1341(481-27842) SUV (p = 0.35). Fused patients showed a median increase in walking distance of 737 (0-985) meters compared to 855(360-985) in non-fused patients (p = 0.29), a median decrease in VAS-B of 4.3(0-8.3) vs 3.8(0.1-8.5) (p=0.92), a median decrease in ODI of 25(12-54) vs 29.5(4-38) (p=0.56), and a median change in EQ-5D of 0.279(0.53-0.674) vs 0.277(0-0.611) (p = 0.56). Graft NaF uptake was not significantly correlated with walking distance (p = 0.3), VAS-B (p = 0.62), ODI (p = 0.22) or EQ-5D (p = 0.78).

Conclusion: Total NaF uptake in the graft region measured one month after surgery was not able to predict change in any of the measured clinical parameters from baseline to one year after surgical treatment. However, there was no difference either in the change of clinical parameters suggesting that the examined sample of patients and the fraction of patients with fusion were too small to allow detection of potential differences.