Expert's comment concerning Grand Rounds case entitled "Surgical management of recurrent thoracolumbar spinal sarcoma with 4-level total en bloc spondylectomy: description of technique and report of two cases" (by Claudia Druschel; Alexander C. Disch; Ingo Melcher; Tilmann Engelhardt; Alessandro Luzzati; Norbert P. Haas; Klaus-Dieter Schaser)

Quantitative in vivo fusion assessment by (18)F-fluoride PET/CT following en bloc spondylectomy

PURPOSE

The purpose of this retrospective analyses was to evaluate the bone viability in the ventral column of the spine following large segmental defect reconstructions. Osseous integration of implants following spinal fusion procedures is an essential precondition to provide adequate mechanical strength to any applied forces and subsequently satisfying patient outcomes. Although CT scan is the non-invasive gold standard for fusion assessment, it lacks the ability to visualize bone viability and, therefore, discrepancy remains about sensitivity and specificity of CT as evaluation tool of spinal fusion.

METHODS

A novel modality, (18)F Fluoride PET/CT, specifically allows quantitative in vivo evaluation of metabolic activity of the osseous integration. Bone viability following large segmental reconstructions in patients after mono- and multi-level en bloc spondylectomies (EBS) was analyzed. Spinal fusion was assessed on plain radiographs and CT scans according to the FDA fusion criteria as well as (18)F PET/CT.

RESULTS

A total of eight patients underwent (18)F PET/CT were included (one 4-level-, one 3-level, two 2-level and four 1-level EBS). The average follow-up between EBS and radiographic studies was 24.8 months. On plain radiographs and CT scans, successful fusion was confirmed in all patients. However, (18)F PET/CT showed non-union in all cases. The metabolic bone activity within the cage was fourfold decreased compared to the reference vertebra, whereas the metabolic activity of the adjacent endplates was 1.6-fold increased compared to the reference vertebra.

CONCLUSION

This study suggests a discrepancy between fusion rates assessed by plain radiographs and CT scan compared to (18)F PET/CT.