Posterolateral lumbar fusion: Relationship between computed tomography Hounsfield units and symptomatic pseudoarthrosis

Background: Assessment of bone quality can guide spinal surgery. However, surgeons infrequently evaluate bone quality in a quantitative manner. Recent literature suggests a role for computed tomography (CT) Hounsfield units (HUs) as a marker for bone quality. Limited data exist regarding its utility with respect to posterolateral lumbar fusion (PLF). Methods: From fall 2010 to winter 2012, 10 patients underwent revision surgery for symptomatic pseudoarthrosis (defined as intractable pain associated with either radiographic evidence of nonunion or intraoperative evidence of nonunion) after a prior L4–S1 PLF. These patients were age-matched (±5 years) to 10 patients who underwent L4–S1 PLF with no clinical signs of pseudoarthrosis at 1-year follow-up. Available CT imaging (with or without instrumentation) was evaluated from L1 to L5 for the averaged HU. Data were pooled among L1–L3 values and between L4 and L5 values. Results: Within the pseudoarthrosis group, the pooled L1–L3 HU value was similar to the pooled L4–L5 HU value (168.39 ± 22.84 HU vs. 166.98 ± 23.20 HU respectively, P = 0.89). The same pattern was observed for the control group (190.24 ± 37.13 HU vs. 201.89 ± 36.59 HU respectively, P = 0.44). On the other hand, the pooled L1–L3 and L4–L5 HU values were larger for the control group compared to the pseudoarthrosis group, with the pooled L4–L5 HU demonstrating statistical significance, P = 0.01. Conclusion: Currently, CT imaging is typically not obtained prior to lumbar fusion. Results demonstrated that CT HU values were significantly larger for patients who did not exhibit symptomatic pseudoarthrosis at 1-year follow-up compared to those who required revision surgery. As such, CT HU values may serve as a predictor for bony fusion to guide surgical management of patients under consideration for PLF.