Facet loads in the canine lumbar spine before and after disc alteration.

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.