Bone allografts used for interbody spinal fusion are often preserved through either freeze drying or lowtemperature freezing, each having disadvantages related to graft preparation time and material properties. In response, a glycerol preservation treatment has been developed to maintain the biomechanical properties of allografts at ambient temperatures, requiring no thawing or rehydration and minimal rinsing prior to implantation. The authors conducted a prospective randomized study to compare the clinical results of glycerol-preserved Cloward dowels and those of freezedried Cloward dowels in anterior cervical discectomy and fusion. The primary outcome measures were evidence of fusion and graft subsidence, and the secondary outcome measures included adverse events, pain, and neck disability scores.
Of 106 patients, 53 (113 levels of surgery) were randomly assigned to the glycerol-preserved graft group and 53 (114 levels of surgery) to the freeze-dried graft group. Subsidence was assessed at 3 and 6 months after implantation. Evidence of fusion was evaluated radiographically at 6 months postimplantation. Subsidence was quantitatively assessed based on physical measurements obtained from radiographs by using calibrated comparators, whereas fusion was also evaluated visually. Surgeons were blinded to treatment type during visual and physical assessments of the patients and the radiographs.
No one in either group had evidence of complete nonunion according to radiographic evaluation at the 6-month follow-up. Average subsidence for all graft-treated levels was 2.11 mm for the glycerol-preserved group and 2.73 mm for the freeze-dried group at the 3-month follow-up and 2.13 and 2.83 mm at the 6-month follow-up, respectively. The 2 treatment groups were statistically equivalent (p = 0.2127 and 0.1705 for the 3- and 6-month follow-up, respectively). No differences were noted between the graft types in terms of adverse event incidence or severity.
Glycerol-preserved bone allografts exhibit fusion results and subsidence values similar to those of their freeze-dried counterparts, potentially more favorable biomechanical properties, and significantly shorter preparation times.