Intervertebral foramen size and volume changes in low grade, low dysplasia isthmic spondylolisthesis.
METHODS
Anatomic study.


OBJECTIVE
The purpose of this study is to determine the effect of the slip amount, slip angle, and disc height on the geometry of the L5 foramen in low-grade, low-dysplasia isthmic L5 spondylolisthesis using a human cadaveric model.


BACKGROUND
Radicular pain and varying degrees of nerve root dysfunction are present in many adult isthmic spondylolisthesis patients and can be the result of compression of the L5 root within its foramen.


METHODS
The intervertebral foramens of six L5 vertebra and sacrum cadaver specimens had a standardized pars defect created and were mounted on an adjustable frame. Plasticene molds of the foramens were made by varying sagittal translocation (0%, 12.5%, 25%, and 50%), slip angle (kyphotic 10° and lordotic 0°, 10°, 20°, and 30°), and disc height (0, 5, and 10 mm). The volume of each mold was measured. The surface area was determined by sagittally slicing on a microtome the mold and each section's face was measured by computer image analysis.


RESULTS
The area and volume of the foramen at a sagittal slip of 0%, slip angle of 0°, and 0 mm disc height were used as a control. As disc height decreased from 10 to 5 mm, 10 to 0 mm, and 5 to 0 mm, the foramen area and volume significantly decreased (P < 0.05). Incremental slip percentage from 0% to 12.5%, 25%, and 50% produced significantly reduced foramen area and volumes (P < 0.05). As slip angle increased from 10° kyphosis to 0°, 10°, 20°, and 30° lordosis, foramen area and volume decreased (P < 0.05).


CONCLUSIONS
Disc height and slip percentage had the largest effect on intervertebral foramen area and volume in this model of low-grade, low-dysplasia isthmic spondylolisthesis. Slip angle changes affected foramen area to a lesser degree. Surgical treatment strategies should consider restoration of disc height in cases with foraminal stenosis.
Spivak
Jeffrey M
JM
Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, NY, USA. jeffrey.spivak@nyumc.org
Kummer
Frederick J
FJ
Chen
Deyu
D
Quirno
Martin
M
Kamerlink
Jonathan R
JR
D002102:Cadaver; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007403:Intervertebral Disc / Q000473:pathology*; D007738:Kyphosis / Q000473:pathology; D008141:Lordosis / Q000473:pathology; D008159:Lumbar Vertebrae / Q000473:pathology*; D008954:Models, Biological; D013168:Spondylolisthesis / Q000473:pathology*