title: Diagnosing the Undiagnosed: Osteoporosis in Patients Undergoing Lumbar Fusion.
abstract: METHODS
  Retrospective analysis.
  
  
  OBJECTIVE
  The aim of the study was to report the incidence of undiagnosed osteoporosis in patients undergoing lumbar spine fusion using computed tomography (CT) Hounsfield units (HU).
  
  
  BACKGROUND
  We used a recent technique utilizing HU to estimate bone mineral density (BMD) of the lumbar spine and hypothesized that this technique would reveal a high percentage of undiagnosed osteoporotic patients undergoing transforaminal lumbar interbody fusion (TLIF).
  
  
  METHODS
  We reviewed patients older than 50 years undergoing TLIF from a single-center and multiple surgeons. We determined the mean HU of L4 on axial CT. Average HU values for patients with diagnosed lumbar osteoporosis (DEXA BMD <0.75 g/cm) were compared to patients with osteopenia and normal BMD (between 0.75 and 0.9 g/cm and >0.9 g/cm, respectively). The percentage of patients with HU values consistent with osteoporosis, but without any formal evaluation, was also calculated.
  
  
  RESULTS
  Over 10 years, 143 patients older than 50 years underwent TLIF, and 128 had available perioperative lumbar CT scans. Men and Women comprised 60.2% and 39.8% of the population, respectively. Average age was 61.5 years (range: 50.0-83.5 years). Twenty-nine patients had both dual-energy X-ray absorptiometry and CT data available for analysis. There was a significant association with decreased HU in patients with lumbar BMD less than 0.75 g/cm (105.6 HU, 95% confidence interval [CI] 6.76) in comparison to patients with osteopenia (146.0 HU, 95% CI 4.09) and with normal BMD (165.9, 95% CI 21.35). Ten men (7.8%) and 15 women (11.7%) had HU values consistent with osteoporosis. Sixty-four percent of patients with osteoporotic HU values had never been formally evaluated for the disease.
  
  
  CONCLUSIONS
  HU may be an alternative to screening preoperative dual-energy X-ray absorptiometry scan and can minimize costs and resource utilization. We found a large proportion of patients older than 50 years undergoing TLIF had HU levels consistent with undiagnosed osteoporosis of the lumbar spine.
  
  
  METHODS
  4.
authors: Department of Orthopedics, Walter Reed National Military Medical Center, Bethesda, MD.
authors: Scott C
authors: SC
authors: Wagner
authors: Department of Orthopedics, Walter Reed National Military Medical Center, Bethesda, MD.
authors: Peter M
authors: PM
authors: Formby
authors: Department of Orthopedics, Walter Reed National Military Medical Center, Bethesda, MD.
authors: Melvin D
authors: MD
authors: Helgeson
authors: Department of Orthopedic Surgery, Madigan Army Medical Center, Tacoma WA.
authors: Daniel G
authors: DG
authors: Kang
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D015519:Bone Density / Q000502:physiology; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D013123:Spinal Fusion; D014057:Tomography, X-Ray Computed