Local bone metabolism during the consolidation process of spinal interbody fusion

Although computed tomography (CT) can identify the presence of eventual bony bridges following lumbar interbody fusion (LIF) surgery, it does not provide information on the ongoing formation process of new bony structures. 18F sodium fluoride (18F-NaF) positron emission tomography (PET) could be used as complementary modality to add information on the bone metabolism at the fusion site. However, it remains unknown how bone metabolism in the operated segment changes early after surgery in uncompromised situations. This study aimed to quantify the changes in local bone metabolism during consolidation of LIF. Six skeletally mature sheep underwent LIF surgery. 18F-NaF PET/CT scanning was performed 6 and 12 weeks postoperatively to quantify the bone volume and metabolism in the operated segment. Bone metabolism was expressed as a function of bone volume. Early in the fusion process, bone metabolism was increased at the endplates of the operated vertebrae. In a next phase, bone metabolism increased in the center of the interbody region, peaked, and declined to an equilibrium state. During the entire postoperative time period of 12 weeks, bone metabolism in the interbody region was higher than that of a reference site in the spinal column. Following LIF surgery, there is a rapid increase in bone metabolism at the vertebral endplates that develops towards the center of the interbody region. Knowing the local bone metabolism during uncompromised consolidation of spinal interbody fusion might enable identification of impaired bone formation early after LIF surgery using 18F-NaF PET/CT scanning.