• John A Hipp, Charles A Reitman, and Nicholas Wharton.
• Baylor College of Medicine, Department of Orthopedic Surgery, Houston, Texas, USA. jhipp@bcm.tmc.edu
• Spine. 2005 Jan 15; 30 (2): 209-10.

Study DesignCalculate the apparent pseudarthrosis rate for anteriorly plated cervical spine fusions using different threshold levels of intervertebral rotation.ObjectivesDetermine whether the apparent pseudarthrosis rate depends on the amount of intervertebral rotation used to characterize a fusion as a pseudarthrosis.Summary Of Background DataIntervertebral motion at a spine fusion site is an important outcome measure in most spine fusion research studies. Intervertebral motion measures are used to determine if a device can be sold for use in spine fusion surgery. There is no consensus on how much motion is too much motion at a spine fusion site, and the intervertebral motion threshold that is used to define a pseudarthrosis is arbitrary. There are only limited data on the dependence of the pseudarthrosis rate on the threshold used to define a pseudarthrosis.MethodsIntervertebral motion at the fusion site was measured from flexion extension radiographs taken 1 year after cervical spine fusion using anterior plates and allograft in 200 patients. The number of cases where intervertebral motion at the fusion site exceeded thresholds between 1 degrees and 4 degrees were calculated. RESULTS.: The apparent pseudarthrosis rate varied from 6% when the intervertebral motion threshold was 4 degrees to 44% when the intervertebral motion threshold was 1 degrees .ConclusionsThe apparent pseudarthrosis rate was highly dependent on the threshold of motion used to define a pseudarthrosis.

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