Osmotic Pressure Alters Time-dependent Recovery Behavior of the Intervertebral Disc.
- Author(s): Bezci, Semih E
- O'Connell, Grace D
- et al.
Published Web Locationhttps://doi.org/10.1097/brs.0000000000002354
STUDY DESIGNDisc recovery behavior under hypo- and hyperosmotic pressure.OBJECTIVETo evaluate the effect of osmotic pressure on the unloaded recovery response of healthy discs.SUMMARY OF BACKGROUND DATAThe intervertebral disc is a poroviscoelastic material that experiences large fluctuations in water composition throughout a diurnal loading cycle. Fluid flow out of the disc occurs through mechanical loading, whereas fluid flow into the disc occurs through passive diffusion because of an imbalance of ions between the disc and its surrounding environment. Osmotic pressure has been used to alter water uptake and tissue hydration.METHODSMotion segments were prepared from the caudal spine sections of the skeletally mature bovines. A 300-N compressive load was applied for 2 hours before unloaded recovery for 12 hours. Hypo- and hyperosmotic pressure was used to alter the rate of water uptake and disc height recovery during unloaded recovery. A 5-parameter rheological model was used to describe the disc's time-dependent recovery behavior.RESULTSThe elastic response was not altered by changes in osmotic pressure; however, viscoelastic recovery was highly dependent on saline osmolarity and recovery time. The fast response of viscoelastic recovery was not dependent on osmotic pressure. The time constant for the slow response decreased whereas the slow response stiffness increased as osmotic pressure increased.CONCLUSIONThe fast response of viscoelastic recovery is governed by flow-independent recovery, whereas the slow response is related to flow-dependent recovery. The rate and magnitude of flow-dependent recovery are highly sensitive to changes in osmotic pressure of the saline bath. There is an osmotic pressure that reduces disc recovery behavior to an elastic response or flow-independent recovery.LEVEL OF EVIDENCEN/A.