Radiographic changes in patients with pseudarthrosis after posterior lumbar interbody arthrodesis using carbon...

The aim of this study was to demonstrate longitudinal radiographic changes at up to five years in patients with pseudarthrosis after posterior lumbar interbody arthrodesis using carbon interbody cages.

From 2003 to 2006, prospective longitudinal radiographic and CT (computed tomography) scan evaluations were made at up to five years after posterior lumbar interbody arthrodesis using carbon interbody cages at one or two levels in 153 consecutive patients. At the one-year evaluation, seventeen patients with early pseudarthrosis at nineteen levels were selected as subjects on the basis of one or more of the following characteristics: complete absence of osseous bridging between the upper and lower vertebrae, angular motion of ≥5°, and/or radiolucent zones surrounding the implant. Angular motion, continuity of osseous bridging, grafted bone quantity, and radiolucent zones around the pedicle screws and cages were observed annually until five years.

The mean angular motion of five levels that exhibited ≥5° of motion at one year began to decrease significantly thereafter (p = 0.046), and no level showed movement of ≥5° at five years. The mean grade of the radiolucent zones around the screws on CT showed significant improvements at two years (p = 0.039) and three years (p < 0.01). The radiolucent zones around the screws disappeared at twelve of sixteen levels by five years, and the radiolucent zones around the cages disappeared in eleven of seventeen levels by five years. Of eighteen levels with early pseudarthrosis, seven (39%) were assessed as successfully fused at three years and twelve (67%) at five years. Four (80%) of five patients with a radiolucent zone of >1 mm around the entire cage on CT at one year showed continuing pseudarthrosis at five years, whereas only two (15%) of thirteen patients without this finding did (crude relative risk = 5.2; 95% confidence interval, 1.35 to 20.02). A radiolucent zone of >1 mm around the entire cage on CT at one year could be an early predictor of permanent pseudarthrosis (odds ratio = 123; 95% confidence interval, 1.03 to 14,680).

The interbody arthrodesis site in patients with early pseudarthrosis may begin to change to a successful fusion one or two years after surgery, with two-thirds of such patients exhibiting successful fusion five years after surgery. Final assessment of pseudarthrosis should be performed at least three years after surgery. A radiolucent zone of >1 mm around the entire interbody cage on CT at one year may require early additional surgery.

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.