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Facet Loads in the Canine Lumbar Spine Before and After Disc Alteration

KAHMANN, RICHARD D., MD; BUTTERMANN, GLENN R., MD; LEWIS, JACK L, PhD; BRADFORD, DAVID S., MD

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The effect of externally applied spinal loads on facet mechanics before and after facet capsulectomy and disc alteration was investigated. Four control and four chymopapain-treated specimens were tested. Facet load and resultant load location were determined in the unaltered state, after facet capsulectomy, and after discectomy using a newly developed, noninvasive measurement technique. Resultant contact load locations shifted in a predictable manner. Caudal shift in contact locations occurred with chymopapain treatment or discectomy but was variable with capsulectomy. Facet load changed with applied load magnitude and direction; no significant change was noted after intradiscal chymopapain, discectomy, or capsulectomy. The significance of the lack of force change with disc narrowing is unknown. Perhaps, observed facet degeneration results from a change in the joint motion and contact location rather than change in facet load.

Biomechanics Laboratory, Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota.

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