Quantitative changes in spinal canal dimensions using interbody distraction for spondylolisthesis.
STUDY DESIGN: An experimental study was performed using cadaveric lumbar spines to evaluate the effect of anteriorly or laterally placed interbody distraction implants on the alteration of spinal canal and neuroforaminal dimensions. OBJECTIVES: To quantify changes in the spinal canal and neuroforaminal dimensions using interbody fusion devices inserted at various configurations in cadaveric lumbar spines exhibiting degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: Although several clinical studies have demonstrated successful treatment of degenerative spondylolisthesis with anterior interbody fusion, no study has shown the role of interbody distraction in improving lumbar spinal canal and foraminal stenosis. METHODS: Five fresh cadaver lumbar spines exhibiting a degenerative spondylolisthesis or retrospondylolisthesis were used for the study. Computed tomography scans of each specimen and a silicon mold of the left intervertebral foramens were repeated in a consistent manner after pure compressive load (150 lb) was applied to simulate physiologic load (intact case), after two BAK (Sulzer SpineTech Inc., Minneapolis, MN) distraction plugs were anteriorly inserted into the intervertebral disc space (anterior distraction cases), and after one long BAK cage was laterally inserted from the left side (lateral distraction case). The cross-sectional area of the spinal canal was measured from computed tomography images using National Institutes of Health image software (Bethesda, MD). The spinal canal volume was calculated using the cross-sectional area and total scan thickness. Left intervertebral foraminal volumes were calculated from the weight of the silicon mold injected into the foramen. Descriptive statistics and a Student's t test were used to detect statistical differences in the spinal canal and neuroforaminal volumes before and after interbody distraction. RESULTS: The cross-sectional canal area was significantly increased after anterior distraction (35.11%) and lateral distraction (33.14%). The spinal canal volume was markedly increased with anterior distraction (19.92%) and lateral distraction (21.96%). Left foraminal volume was also enhanced by 40.25% for anterior distraction and 41.03% for lateral distraction. CONCLUSIONS: Interbody distraction either by anteriorly inserted plugs or laterally inserted threaded cagescan immediately improve the narrowed canal area and increase spinal canal, as well as foraminal volume for lumbar degenerative spondylolisthesis or retro- spondylolisthesis.