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Pressure profilometry of the lumbosacral disk in dogs.

OBJECTIVE
To investigate the biomechanical behavior of the lumbosacral disk under compressive load in dogs, using pressure profilometry, and to investigate the relationship between pressure profile features and background and disease variables.


SAMPLE POPULATION
23 lumbosacral disks and adjacent vertebrae harvested from medium and large breed dogs.


PROCEDURE
A 1.3-mm unidirectional needle-mounted pressure transducer was inserted into the disk in a ventral-to-dorsal manner while the disk was loaded in compression by a materials testing machine. Withdrawal of the transducer resulted in a pressure profile for cranial and lateral stress. Pressure profiles were analyzed, and relationships to age and gross evidence of degeneration were investigated.


RESULTS
There was a moderate positive correlation between age and degree of nuclear degeneration (r(s) = 0.420, P = 0.046), but no relationship between age and mean nuclear pressure was detected. Mean nuclear pressure correlated negatively with severity of degenerative changes in the nucleus pulposus. Receiver operator characteristic curves to evaluate mean nuclear pressure as a diagnostic test for nuclear degeneration revealed a sensitivity and specificity of 82 and 83%, respectively. In addition, age was moderately correlated with the magnitude of stress peaks (r(s) = -0.571, P = 0.004). Stress peaks were not related to the severity of nuclear degeneration.


CONCLUSIONS AND CLINICAL RELEVANCE
Determination of the mean nuclear pressure by disk profilometry provides information on the severity of lumbosacral disk degeneration with a high degree of sensitivity and specificity. The magnitude of single stress peaks within the dorsal annulus fibrosus is correlated with age and may not necessarily reflect advancing degeneration.