INTRODUCTION: Intradiscal pressure (IDP) generation contributes to compressive mechanics of the disc. Disc degeneration leads to altered tissue hydration and biomechanical function. The impact of these changes on IDP generation has previously been investigated in human discs. This study sought to determine whether trends in IDP changes are similar in a rat animal model of degeneration.
METHODS: Sprague‐Dawley rats were anesthetized and caudal discs punctured with an 18g needle to induce degenerative changes. After 8 weeks, rats were euthanized, and healthy and degenerate motion segments were harvested. Specimens were mounted on a materials testing system, and a custom Fabry‐Perot fiber optic pressure sensor was guided into the nucleus pulposus (NP). Step loads of 0.05, 0.25 and 0.45 MPa were applied for 30s with 30s of rest between, ending with an additional 300s hold at 0.5 MPa. Independent t‐tests were used to compare IDPs generated between healthy and degenerate groups.
RESULTS: Comparisons of IDP at each loading step revealed significantly higher pressure in healthy versus degenerate groups at 0.25 and 0.45MPa (p<0.05). (cont'd) Linear fits also showed significantly better pressurization in healthy discs (p<0.05). Importantly, the trends in IDP changes in this animal model closely resembled that observed in human degenerate discs.
DISCUSSION: This study confirms that the ability for the NP to pressurize is compromised following degeneration, likely due to breakdown of the extracellular matrix in both the NP and annulus fibrosus (AF) as well as decreased tissue hydration. To compare with past studies, the ratio of healthy: degenerate IDPs in our study was 1.71 while Adams and colleagues measured a healthy: degenerate (Grade I:IV) ratio of 1.45 in human discs. Our results suggest that there may be important parallels in the biochemical and structural changes in the NP and AF between age‐related human disc degeneration and injury‐induced degeneration in rats.