A hydroxyapatite-based synthetic bone graft reduces intervertebral motion at 12 months, as measured by CT-RSA, in a porcine model of ACDF

Introduction: Pseudarthrosis remains a significant complication after anterior cervical discectomy and fusion (ACDF), often causing revision surgery. Synthetic bone grafts (SBGs) offer an alternative to autografts, but objective methods for assessing intervertebral motion (IVM) are needed. Computed tomography-based radiostereometric analysis (CT-RSA) enables precise measurement of cervical IVM. Research question: Does a hydroxyapatite-based SBG reduce cervical IVM compared with control in a porcine ACDF model measured by CT-RSA? Material and methods: Six adult female mini-pigs underwent two-level cervical anterior discectomy. One defect received a hydroxyapatite-based SBG, and the other served as an empty control. No instrumentation was used. The primary outcome was induced total rotation (TR) between vertebrae during flexion-extension CT at 9 and 12 months, compared using the Wilcoxon matched-pairs signed-rank test. Functional fusion was defined as TR < 1° and compared using exact McNemar test. Median (range) values are presented. Results: At 12 months, median IVM TR was significantly lower at SBG than Control levels (0.2° [0.07–0.5] vs. 1.5° [0.2–5.0], p = 0.031). At 9 months, TR was 0.3° (0.04–1.0) and 0.8° (0.1–2.7), respectively (p = 0.063). Functional fusion rates were higher at SBG levels (5/6 and 6/6 at 9 and 12 months) than at Control levels (3/6 at both time points), although the differences were not statistically significant. Discussion and conclusion: The hydroxyapatite-based SBG was associated with lower IVM at 12 months in this porcine ACDF model. CT-RSA provided an objective method for assessing cervical segmental stability and may be useful for evaluating functional spinal fusion in preclinical studies.