Histologic characterization of coblation nucleoplasty performed on sheep intervertebral discs.

OBJECTIVE To characterize the histologic effects of coblation nucleoplasty on sheep intervertebral discs. DESIGN In vitro histologic study. METHODS Five sheep lumbar discs treated with nucleoplasty and two control discs were evaluated. Specimens were received frozen and thawed to room temperature. A segment consisting of the intervertebral disc and vertebral body above and below the disc was dissected. Using a posterolateral approach, a Perc-DLE SpineWand attached to a standard radiofrequency power generator was bluntly advanced to the annulonuclear junction of each disc. The SpineWand was advanced initially in cauterization mode 8mm into the disc and withdrawn in coagulation mode. The SpineWand was reinserted 8mm into the disc and secured in place. The specimens were fixed in 10% buffered formalin for 1-2 weeks. They were then decalcified in 10% ethylenediaminetetraacetic acid (EDTA) and embedded in paraffin. Specimens were subsequently stained with H & E, Alcian Blue, and Trichrome stain. They were examined under light microscopy and polarized light. RESULTS There were no gross changes in disc appearance. In the experimental disc, the fenestration created by the procedure left a 1mm diameter hollow channel through which tissue was cauterized leaving little visible debris or residual material. In the area immediately surrounding the channel, the fibrocartilage cells and the collagen matrix arrangement remained intact and resembled the control untreated disc tissue. There was no loss or re-distribution of proteoglycans, no alterations in collagen orientation, nor any indication of damage to the matrix surrounding the probe channel. CONCLUSION Radiofrequency nucleoplasty creates a hollow channel leaving surrounding soft tissue intact in the immediate post-procedure period. In vivo studies will be necessary to delineate the longitudinal histologic effects of radiofrequency nucleoplasty on discs.