¹⁸F-Naf PET/CT in pseudarthrosis after anterior cervical discectomy and fusion

Background context: Pseudarthrosis is a well-known cause of persistent or recurrent pain after anterior cervical discectomy and fusion (ACDF). Numerous radiographic criteria to determine the fusion status has been described in the literature, but their accuracies in clinical practice vary considerably and no 1 single method has proved superior. Fluorine-18 sodium fluoride (¹⁸F-NaF) positron emission tomography/computed tomography (PET/CT), depicting osteoblastic activity, might be useful to identify pseudarthrosis after ACDF.

Purpose: To investigate the ability of ¹⁸F-NaF PET/CT to identify pseudarthrosis after ACDF using surgical revision as the reference standard.

Study design: Retrospective observational study.

Patients sample: A total of 30 patients consisting of 40 surgical levels.

Outcome measures: For each level, the presence or absence of intragraft uptake (InGU) and extragraft uptake (ExGU) were recorded, as well as adjacent segment uptake (ASU). CT part of the scan was rated as "fused" or "nonfused." Results were correlated to the gold-standard of revision surgery.

Methods: We retrospectively included consecutive patients who underwent revision surgery for suspicion of symptomatic pseudarthrosis after ACDF following ¹⁸F-NaF PET/CT performed between July 2019 and march 2023. ¹⁸F-NaF PET/CT results were compared with the gold standard of surgical evaluation of the stability of the fusion material. All patients underwent a systematic CT scan to evaluate the success of revision surgery 1 year postoperatively. We also investigated whether some patients underwent a repeated ¹⁸F-NaF PET/CT for persistent or recurrent pain after revision surgery.

Results: Revision surgery demonstrated pseudarthrosis in 37 levels (93%) and excluded pseudarthrosis in 3 levels (7%). In the pseudarthrosis group (n=37), InGU was observed in all levels (100%) while ExGU was present in only 10 levels (27%). Fifteen levels (41%) with confirmed pseudarthrosis were rated as "fused" on CT scan preoperatively. In the non-pseudarthrosis group (n=3), InGU was observed in 2 levels (67%) while ExGU was never present. Two levels (67%) were rated as "fused" on fusion CT scan. One year postoperatively, fusion was successfully achieved on CT scan in 39 levels (98%). Seven patients (consisting of 8 levels) had been subsequently re-explored by ¹⁸F-NaF PET/CT for persistent or recurrent pain following revision surgery. PET/CT did not reveal any uptake (InGU or ExGU) in 7 levels, rated as "fused" on follow-up CT scan. PET/CT showed InGU in the only level rated as "nonfused" on CT scan.

Conclusions: ¹⁸F NaF PET/CT may be a useful adjunctive diagnostic tool to detect pseudarthrosis after ACDF surgery, especially in case of high clinical suspicion with standard conventional imaging not suggestive of non-union. In our cohort, all levels (100%) with confirmed pseudarthrosis on revision surgery demonstrated InGU on PET/CT, while 41% of these levels were rated as "fused" on CT scan preoperatively. ¹⁸F NaF PET/CT might also be helpful after revision surgery to rule out re-pseudarthrosis and identify the pain generator. These promising data need to be confirmed in larger prospective studies.