title: Changes in bone mineral density in the intertransverse fusion mass after instrumented single-level lumbar fusion: a prospective 1-year follow-up.
abstract: METHODS
  Prospective cohort.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate changes in bone mineral density (BMD) in the intertransverse fusion mass as representative for the process of bone remodeling after spinal fusion.
  
  
  BACKGROUND
  Intertransverse bone graft is frequently applied to facilitate bony fusion between 2 spinal levels. The biological process of bone graft remodeling leading to eventual fusion is, however, poorly understood.
  
  
  METHODS
  In 20 patients with a single-level instrumented posterolateral lumbar fusion for low-grade spondylolisthesis, radiographs, and clinical outcome scores (visual analogue scale for back and leg pain, Oswestry Disability Index, Short Form-36) were obtained. Locally harvested laminectomy bone was used as intertransverse bone graft. The BMD in selected "regions of interest" at both intertransverse fusion areas was assessed on days 4 and 3, after a period of 6 and 12 months after surgery using dual-energy x-ray absorptiometry scans. Eventual fusion status was assessed on computed tomographic scan at 12 months.
  
  
  RESULTS
  All clinical outcome scores significantly improved at the final follow-up (P < 0.05). Baseline BMD in both paraspinal fusion areas was expressed as 100%, which significantly decreased from 81% to 75% and 77% to 70% at 3 and 6 months, for regions of interest 1 and 2, respectively (P < 0.001). From 6 to 12 months, there was an increase in BMD from 90% to 80%, for regions of interest 1 and 2 (P = 0.296). On computed tomography scan a complete fusion was noticed in 70% of the patients.
  
  
  CONCLUSIONS
  Repeated dual-energy x-ray absorptiometry was able to elucidate the biological process of bone graft remodeling in the intertransverse fusion mass. An active bone remodeling process was quantified with profound resorption or demineralization of the graft during the first 6 months, followed by subsequent bone apposition and restoration of BMD at the final follow-up. No difference in trend in BMD change between patients with and without fusion could be established; however, no firm conclusions can be drawn from small patient numbers.
authors.affiliation: Department of Orthopaedics, Rijnstate Hospital, Arnhem, The Netherlands.
authors.forename: Femke
authors.initials: F
authors.lastname: Hagenmaier
authors.forename: Dennis
authors.initials: D
authors.lastname: Kok
authors.forename: Annemiek
authors.initials: A
authors.lastname: Hol
authors.forename: Ton
authors.initials: T
authors.lastname: Rijnders
authors.forename: F Cumhur
authors.initials: FC
authors.lastname: Oner
authors.forename: Job L C
authors.initials: JL
authors.lastname: van Susante
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D001416:Back Pain / Q000175:diagnosis; D015519:Bone Density; D016025:Bone Transplantation / Q000379:methods; D004185:Disability Evaluation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007866:Leg / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000175:diagnosis; D010147:Pain Measurement / Q000379:methods; D011446:Prospective Studies; D013123:Spinal Fusion / Q000379:methods*; D013168:Spondylolisthesis / Q000601:surgery*; D011795:Surveys and Questionnaires; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome