Introduction: Although osteoporosis and low bone mineral density is thought to lead to poor fusion outcomes, few studies have adequately addressed the correlation, and they were limited by small sample size at a single institution.
Methods: We completed a secondary analysis of 182 patients enrolled at 26 spine centers across the United States in the EXO-SPINE FDA-approved clinical trial with 12-month CT-based fusion status determined by two independent, blinded radiologists. Using previously described CT-based techniques, we measured local and global Hounsfield units (HU) and examined the relationship with radiographic and clinical outcomes.
Results: CT scans were available for review from 95 patients, with a mean age of 56.2 years and mean global density of 153.0 HU. No relationship was observed between HU and radiographic fusion status or clinical outcomes. Although 12% of patients had lumbar vertebral body HU measurements consistent with osteoporosis, this classification had no relation with fusion or clinical outcomes. Patients with pseudarthrosis had higher Oswestry Disability Index (22.2 vs. 16.6, P = 0.037) and back pain visual analog scale (7.0 vs. 4.9, P = 0.014) scores than patients with at least unilateral fusion at the 12-month follow-up.
Discussion: In this large, multicenter study, lower vertebral body HU was not associated with worse fusion status after single-level instrumented posterolateral lumbar fusion using only local autologous bone graft. However, there was an association between radiographic fusion status and clinical outcomes, validating the importance of determining predictors of successful fusion. Assessment of fusion status with CT scans yielded a much lower fusion success rate with local bone graft than previously reported and may warrant additional investigation.
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