Postoperative decrease of regional volumetric bone mineral density measured by quantitative computed tomography after lumbar fusion surgery in adjacent vertebrae.

ABSTRACT

We investigated the effect of posterior lumbar fusion surgery on the regional volumetric bone mineral density (vBMD) measured by quantitative computed tomography. Surgery negatively affected the regional vBMD in adjacent levels. Interbody fusion was independently associated with vBMD decline and preoperative epidural steroid injections (ESIs) were associated with less postoperative vBMD decline. INTRODUCTION: Few studies investigate postoperative BMD changes after lumbar fusion surgery utilizing quantitative computed tomography (QCT). Additionally, it remains unclear what preoperative and operative factors contribute to postoperative BMD changes. The purpose of this study is to investigate the effect of lumbar fusion surgery on regional volumetric bone mineral density (vBMD) in adjacent vertebrae and to identify potential modifiers for postoperative BMD change. METHODS: The data of patients undergoing posterior lumbar fusion with available pre- and postoperative CTs were reviewed. The postoperative changes in vBMD in the vertebrae one or two levels above the upper instrumented vertebra (UIV+1, UIV+2) and one level below the lower instrumented vertebra (LIV+1) were analyzed. As potential contributing factors, history of ESI, and the presence of interbody fusion, as well as various demographic/surgical factors, were included. RESULTS: A total of 90 patients were included in the study analysis. Mean age (±SD) was 62.1 ± 11.7. Volumetric BMD (±SD) in UIV+1 was 115.4 ± 36.9 mg/cm3 preoperatively. The percent vBMD change in UIV+1 was - 10.5 ± 12.9% (p < 0.001). UIV+2 and LIV+1 vBMD changes showed similar trends. After adjusting with the interval between surgery and the secondary CT, non-Caucasian race, ESI, and interbody fusion were independent contributors to postoperative BMD change in UIV+1. CONCLUSIONS: Posterior lumbar fusion surgery negatively affected the regional vBMDs in adjacent levels. Interbody fusion was independently associated with vBMD decline. Preoperative ESIs were associated with less postoperative vBMD decline, which was most likely a result of a preoperative decrease in vBMD due to ESIs.