Adjacent-level biomechanics after single versus multilevel cervical spine fusion: Laboratory investigation

Mark L. Prasarn, Dinah Baria, Edward Milne, Loren Latta, William Sukovich

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


Object. Previous studies have demonstrated that patients with spinal fusion are at greater risk for adjacentsegment disease and require additional surgery. It has been postulated that excessive motion of a given motion segment unit (MSU) leads to an increased risk of disc degeneration. It is the authors' hypothesis that a greater increase in adjacent-segment motion will be observed following a 2-level versus a single-level anterior cervical discectomy and instrumented fusion (ACDF). Therefore, they undertook this study to determine the effect of single-level versus 2-level ACDF on the biomechanics of adjacent MSUs. Methods. Ten fresh-frozen human cervical spines were used in this study. The specimens were potted at C-4 and T-1 and tested in flexion and extension. Range of motion (ROM) was 30° of flexion and 15° of extension at a maximum load of 50 N. The specimens were tested intact and then were randomized into 2 groups of 5 specimens each. Group 1 underwent a single-level ACDF at the C5-6 level first, and Group 2 underwent the procedure at the C6-7 level. After testing, both groups had the fusion extended to include the C5-7 levels, and the testing was repeated. Changes in overall ROM, stiffness, and segmental motion were calculated and statistically analyzed using a paired Student t-test. Results. An increase in sagittal ROM of 31.30% above (p = 0.012) and 33.88% below (p = 0.066) the fused MSU was found comparing a 2-level with a 1-level ACDF. The overall stiffness of the entire spinal construct increased 37.34% (p = 0.051) in extension and 30.59% (p = 0.013) in flexion as the second fusion level was added. As expected, the overall sagittal ROM of the entire spinal construct decreased by 13.68% (p = 0.0014) with a 2-level compared with a 1-level fusion. Conclusions. This study has shown that the biomechanics at adjacent levels to a cervical spine fusion are altered and that there is increased adjacent-segment motion at the levels above and below, after a 2-level compared with a 1-level ACDF.

Original languageEnglish (US)
Pages (from-to)172-177
Number of pages6
JournalJournal of Neurosurgery: Spine
Issue number2
StatePublished - Feb 2012


  • Adjacent level disease
  • Arthrodesis
  • Biomechanics
  • Cervical spine
  • Fusion
  • Multilevel fusion
  • Segmental motion

ASJC Scopus subject areas

  • Clinical Neurology
  • Surgery
  • Neurology


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