Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P40. 18F-Fluoride PET/CT as an early predictor of bony fusion after posterior lumbar interbody fusion

BACKGROUND CONTEXT The clinical success of posterior lumbar interbody fusion (PLIF) may be limited by pseudarthrosis (PA), defined as the absence of solid fusion 1 year after surgery. At present, no noninvasive technique is available to reliably assess bone graft incorporation in the early phase after PLIF. Positron emission tomography (PET) is a nuclear imaging modality that is able to identify changes at the cellular and molecular level in an early stage, well before manifestation of anatomical changes. PET/CT with the bone seeking tracer 18F-fluoride allows localization and quantification of bone metabolism. PURPOSE This study investigates whether an 18F-fluoride PET/CT scan early after PLIF is able to predict the fusion status on CT at 1 year postoperative. METHODS Twenty patients were enrolled after PLIF and gave written informed consent. At 6 weeks and at 1 year after PLIF, intravenous injection of 18F-fluoride was followed by a static scan at 60 minutes (Philips, Gemini TF PET/CT). Processing of images resulted in a bone metabolism parameter that is standardized uptake value (SUV). This parameter was determined for 3 regions of interest (ROIs): the intervertebral disc space (IDS) and the upper and the lower endplate (UE and LE, respectively) of the operated segment.Interbody fusion was scored on a diagnostic CT scan made 1 year postoperative and was defined as the amount of complete bony bridges between vertebrae i.e 0, 1 or 2. Based on these scores, patients were divided in either the PA group (score 0) or the fusion group (scores 1 and 2). Differences between groups were analyzed using the independent samples Mann-Whitney U -test. RESULTS Ten patients were classified as PA (0 bridges: n=10) and 10 patients as fused (1 bridge: n=5, 2 bridges: n=5).Patients in the PA group showed significantly lower bone metabolism values in the IDS on the 6 weeks PET/CT scan compared to patients in the fusion group (SUVIDS=13.3±5.62 for PA and SUVIDS=22.6±6.42 for the fusion group, p=.003), whereas values at the endplates were similar (SUVUE=20.3±5.85 for PA and SUVUE=21.6±4.24 for the fusion group, p=.282). Furthermore, only in the PA group, bone metabolism in the IDS was significantly lower than at the endplates (p=.006). In the fusion group, bone metabolism in the IDS and at the endplates was similar (p=.470).The PET/CT scan at 1 year postoperative showed that in the PA group, bone metabolism of the IDS remained lower compared to the endplates (SUVIDS=13.2±4.37, SUVUE=16.4±5.33, p=.004), while in the fusion group, IDS and endplate bone metabolism was similar (SUVIDS=13.6±2.91, SUVUE=14.4±3.14, p=.397). CONCLUSIONS This study shows that lower bone metabolism values in the intervertebral disc space of the operated segment as seen on 18F-fluoride PET/CT 6 weeks after PLIF, is related to development of PA 1 year postoperatively. These results suggest that 18F-fluoride PET/CT might be an early diagnostic tool to identify patients prone to develop PA after PLIF.