Lower Hounsfield Units at the Planned Lowest Instrumented Vertebra Is an Independent Risk Factor for Complications Following Adult Cervical Deformity Surgery

Background: The association of Hounsfield units (HU) and junctional pathologies in adult cervical deformity (ACD) surgery has not been elucidated. Objective: Assess if the bone mineral density of the LIV, as assessed by HUs, is prognostic for the risk of complications after ACD surgery. Study Design/Setting: Retrospective cohort study. Methods: HUs were measured on preoperative CT scans. Means comparison test assessed differences in HUs based on the occurrence of complications, linear regression assessed the correlation of HUs with risk factors, and multivariable logistic regression followed by a conditional inference tree derived a threshold for HUs based on the increased likelihood of developing a complication. Results: In all, 107 ACD patients were included. Thirty-one patients (29.0%) developed a complication (18.7% perioperative), with 20.6% developing DJK and 11.2% developing DJF. There was a significant correlation between lower LIVs and lower HUs (r=0.351, P=0.01), as well as age and HUs at the LIV. Age did not correlate with change in the DJK angle (P>0.2). HUs were lower at the LIV for patients who developed a complication and an LIV threshold of 190 HUs was predictive of complications (OR: 4.2, [1.2-7.6]; P=0.009). Conclusions: Low bone mineral density at the lowest instrumented vertebra, as assessed by a threshold lower than 190 Hounsfield units, may be a crucial risk factor for the development of complications after cervical deformity surgery. Preoperative CT scans should be routinely considered in at-risk patients to mitigate this modifiable risk factor during surgical planning.