18F-fluoride PET/CT as an early predictor of bony fusion after posterior lumbar interbody fusion- a prospective study.

Purpose: Posterior Lumbar Interbody Fusion (PLIF) is a surgical procedure in which stabilization of spinal segments is achieved by inserting interbody cages filled with bone graft. Positron Emission Tomography (PET) is an imaging modality to assess physiological processes at cellular level, well before manifestation of morphological changes on computed tomography (CT). The goal was to determine whether ¹⁸F-fluoride PET/CT findings six weeks after PLIF, can predict bony fusion one year postoperatively on CT.

Materials and methods: 20 consecutive PLIF patients (21 levels) were prospectively included. Based on diagnostic CT one year postoperatively, operated segments were classified as pseudarthrotic or fused. ¹⁸F-fluoride PET/CT scanning was performed at six weeks and one year, yielding parameters related to overall bone metabolism, bone blood flow and bone mineral incorporation. Differences in PET parameters between groups and follow-up moments were assessed. The area under the curve from the receiver operating characteristic was calculated for each PET parameter as a measure of diagnostic accuracy.

Results: 11 segments were classified as pseudarthrotic and 10 as fused. Pseudarthrotic segments showed lower intervertebral overall bone metabolism values compared to fused segments at six weeks. Pseudarthrotic segments showed lower intervertebral bone blood flow at six weeks and lower intervertebral bone mineral incorporation at one year compared to fused segments. Overall bone metabolism of the operated intervertebral disc space at six weeks had the highest diagnostic accuracy for predicting the fusion status at one year.

Conclusions: ¹⁸F-fluoride PET/CT six weeks after PLIF provides prognostic information on bony fusion at one year.