Osteoarthrosis of the facet joints resulting from anular rim lesions in sheep lumbar discs.

STUDY DESIGN: Facet joints from sheep lumbar spines were examined for histologic evidence of osteoarthrosis after anular incision.

OBJECTIVES: To describe the sequence of changes in facet joints in an animal model of disc degeneration.

SUMMARY OF BACKGROUND DATA: There are many studies with results showing a link between facet joint osteoarthrosis and disc degeneration, but the development of osteoarthrosis in facet joints has not been observed in a controlled study of disc degeneration.

METHODS: Histologic features of facet joint degeneration were compared with established descriptions of human osteoarthrosis, and the sequence of changes was documented in a controlled prospective study of disc degeneration.

RESULTS: Osteoarthrosis in sheep lumbar facet joints is similar to that described in human joints and develops in response to anular injury. Discs degenerate relatively soon after anular incision, but there is a long delay in the appearance of significant changes to the facet joints at the level of anular incision and adjacent levels.

CONCLUSIONS: The results shows that facet joints in sheep undergo osteoarthrotic changes in response to disc degeneration and confirm the sheep as a suitable model for the study of degenerative spinal disorders.