Preoperative Hounsfield Units Predict Pedicle Screw Loosening in Osteoporotic Patients Following Short-Segment Lumbar Fusion
Rajkishen Narayanan, Omar H. Tarawneh, Delano Trenchfield, Matthew Meade, Yunsoo Lee, Olivia Opara, Michael A. McCurdy, Nathaniel Pineda, lan David Kaye, Fatimah Alhassan, M. Vo, John J. Mangan, José A. Canseco, Alan S. Hilibrand, Alexander R. Vaccaro, Christopher K. Kepler, Gregory D. Schroeder
Abstract
STUDY DESIGN: Retrospective Cohort. OBJECTIVE: (1) To determine if vertebral HU values obtained from preoperative CT predict postoperative outcomes following one to three level lumbar fusion and (2) to investigate whether decreased BMD values determined by HU predict cage subsidence and screw loosening. SUMMARY OF BACKGROUND DATA: In light of suboptimal screening for osteoporosis, vertebral computerized tomography (CT) Hounsfield Units (HU), have been investigated as a surrogate for bone mineral density (BMD). MATERIALS AND METHODS: In this retrospective study, adult patients who underwent one to three level posterior lumbar decompression and fusion (PLDF) or transforaminal lumbar interbody and fusion (TLIF) for degenerative disease between the years 2017 and 2022 were eligible for inclusion. Demographics and surgical characteristics were collected. Outcomes assessed included 90-day readmissions, 90-day complications, revisions, patient-reported outcomes (PROMs), cage subsidence, and screw loosening. Osteoporosis was defined as HU of ≤110 on preoperative CT at L1. RESULTS: We assessed 119 patients with a mean age of 59.1, of whom 80.7% were white and 64.7% were nonsmokers. The majority underwent PLDF (63%) compared with TLIF (37%), with an average of 1.63 levels fused. Osteoporosis was diagnosed in 37.8% of the cohort with a mean HU in the osteoporotic group of 88.4 compared with 169 in nonosteoporotic patients. Although older in age, osteoporotic individuals did not exhibit increased 90-day readmissions, complications, or revisions compared with nonosteoporotic patients. A significant increase in the incidence of screw loosening was noted in the osteoporotic group with no differences observed in subsidence rates. On multivariable linear regression osteoporosis was independently associated with less improvement in visual analog scale (VAS) scores for back pain. CONCLUSIONS: Osteoporosis predicts screw loosening and increased back pain. Clinicians should be advised of the importance of preoperative BMD optimization as part of their surgical planning and the utility of vertebral CT HU as a tool for risk stratification. LEVEL OF EVIDENCE: 3.