Background and Purpose: During normal loading of the spine, the intervertebral disc (IVD) experiences large changes in hydration. Current techniques to determine IVD hydration in vitro non-destructively are costly (e.g. MRI). Here we determined the variation in hydration in loaded IVDs electrochemically using needle microelectrodes.

Methods: The relation between hydration and electrochemical current measured in the tissue at a polarising voltage of −0.65V was established in bovine caudal disc nucleus slices. Bovine caudal IVDs were then placed in a culture chamber and tissue hydration varied by applying static loads. Silver needle microelectrodes were inserted into the nucleus at defined locations and the polarising voltage applied. The electrochemical current was measured and hence hydration of the disc determined in relation to duration and magnitude of the applied load.

Results: Intradiscal current was found to correlate directly with tissue hydration, falling 45% as hydration decreased from 0.8 to 0.6. Changes in tissue hydration in response to static load were monitored at different positions in the disc in real-time by measuring electrochemical current and were found to vary spatially and in time as predicted from theory.

Conclusions: Electrochemical measurements can be used as a non-destructive and relatively inexpensive method for real-time measurements of changes in IVD hydration in response to mechanical loading in vitro.

Objectives

An experimental rabbit model was used to test the null hypothesis, that there is no difference in new bone formation around uncoated titanium discs compared with coated titanium discs when implanted into the muscles of rabbits.