Defining pseudoarthrosis in the cervical spine with differing motion thresholds.

Study Design: Calculate the apparent pseudarthrosis rate for anteriorly plated cervical spine fusions using different threshold levels of intervertebral rotation.

Objectives: Determine whether the apparent pseudarthrosis rate depends on the amount of intervertebral rotation used to characterize a fusion as a pseudarthrosis.

Summary Of Background Data: Intervertebral 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.

Methods: Intervertebral 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 .

Conclusions: The apparent pseudarthrosis rate was highly dependent on the threshold of motion used to define a pseudarthrosis.