The effect of partial removal of the nucleus pulposus from the intervertebral disc on the response of the human annulus fibrosus to compression.
OBJECTIVE
To determine how partial removal of the nucleus changes the response of the annulus to compression.


METHODS
The deformation of the annulus in the mid-sagittal plane, during compression, was determined from digital video images.


BACKGROUND
Several studies have shown that removal of the nucleus changes the external behaviour of the intervertebral disc, but few studies have investigated changes to internal behaviour.


METHODS
Six frozen human lumbar discs were bisected in the sagittal plane to produce 12 specimens. The cut surfaces were marked with seven dots of Alcian blue stain. The specimens were sealed, enabling their internal structure to be viewed directly by a digital video recording system, and thawed. The video system recorded the response of each specimen as it was compressed by up to 1.8 mm at a rate of 0.2 mm s(-1). The displacements of the Alcian blue marks were measured using an image analysis program. Magnetic resonance imaging was used to investigate the validity of this technique.


RESULTS
Partial removal of the nucleus changed the way that the disc deformed under compression. A highly significant change in direction of movement was seen in the inner posterior region of the annulus.


CONCLUSIONS
Partial removal of the nucleus changes the response of the annulus to compression.


CONCLUSIONS
Partial denucleation of the human intervertebral disc is shown to change the direction of bulging of the inner annulus when the disc is compressed. Increases in shear stress, arising from these changes, may lead to further disc degeneration in the form of circumferential tears.
Meakin
J R
JR
Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK. j.meakin@biomed.abdn.ac.uk
Redpath
T W
TW
Hukins
D W
DW
D001696:Biomechanical Phenomena; D017586:Diskectomy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007403:Intervertebral Disc / Q000503:physiopathology* / Q000601:surgery*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000503:physiopathology*