title: Lower preoperative Hounsfield unit measurements are associated with adjacent segment fracture after spinal fusion.
abstract: METHODS
  Retrospective case-control study.
  
  
  OBJECTIVE
  To determine the association of Hounsfield unit (HU) measurements with adjacent segment fractures after spinal fusion.
  
  
  BACKGROUND
  Adjacent segment fracture is a potentially devastating complication after spinal fusion surgery in osteoporotic patient. Recently, a technique for assessing bone mineral density using HU measurements from computed tomography was described and correlated with both dual-energy x-ray absorptiometry-assessed bone mineral density and compressive strength in an osseous model.
  
  
  METHODS
  Patients with adjacent segment fractures after spinal fusion were identified from a prospectively collected patient database and matched 1:1 with nonfracture controls on the basis of age, sex, and fusion construct. Minimum follow-up was 6 months. Patients with metabolic bone disease other than osteoporosis or those taking medications known to negatively alter bone strength were excluded. HU assessment was done according to the previously published protocol using the preoperative computed tomography.
  
  
  RESULTS
  Twenty patients had complete imaging data and could be matched to nonfracture controls. The groups were well matched with respect to age, sex, body mass index, and number of levels fused. Following the index surgical procedure, the fracture group had more positive sagittal balance than the control group (10.7 cm vs. 9.1 cm). Analysis of HU values at the fracture level showed a significantly lower value in the fracture group than in the controls (145.6 vs. 199.4, P = 0.006). Similarly, global assessment of HU across the thoracic and lumbar spines was significantly lower in the fracture group (139.9 vs. 170.1, P = 0.032).
  
  
  CONCLUSIONS
  HU was significantly lower both locally and globally in the fracture cohort. Because computed tomographic scans are frequently part of preoperative planning for spinal fusion, this information should be incorporated in preoperative planning. Studies to prospectively validate HU as a predictor of adjacent segment fracture risk and to assess the effect of increasing HU preoperatively with medications for osteoporosis are needed.
  
  
  METHODS
  3.
authors.affiliation: Department of Orthopedic Surgery, Spine and Scoliosis Service, Hospital for Special Surgery/Weill Cornell Medical Center, New York, NY 10021, USA. dsm@stanfordalumni.org
authors.forename: Dennis S
authors.initials: DS
authors.lastname: Meredith
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Schreiber
authors.forename: Fadi
authors.initials: F
authors.lastname: Taher
authors.forename: Frank P
authors.initials: FP
authors.lastname: Cammisa
authors.forename: Federico P
authors.initials: FP
authors.lastname: Girardi
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D019245:Compressive Strength; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011300:Preoperative Care; D012189:Retrospective Studies; D012307:Risk Factors; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D013123:Spinal Fusion / Q000009:adverse effects*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging* / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D014057:Tomography, X-Ray Computed