Intradiscal electrothermal therapy can alter compressive stress distributions inside degenerated intervertebral discs

Mechanical testing of cadaveric motion segments.

To test the hypothesis that intradiscal electrothermal therapy (IDET) can affect the internal mechanical functioning of lumbar discs.

The clinical efficacy of IDET is variable, and its mode of action uncertain.

Eighteen lumbar motion segments (64-97 years old) were incubated at 37 degrees C. A miniature pressure transducer, side mounted in a 1.3-mm diameter needle, was used to measure the distribution of compressive "stress" along the midsagittal diameter of each disc while it was compressed at 1.5 kN. Measurements were repeated in 3 simulated postures. Standard IDET was performed using biplanar radiography to confirm the placement of the heating element and an independent thermocouple to measure temperature in the inner lateral anulus. Stress profilometry was repeated immediately after IDET.

Peak temperatures in the inner lateral anulus during IDET averaged 40.0 degrees C (standard deviation [STD] 2.3). Stress measurements repeated before IDET differed by less than 8%, and a sham IDET procedure produced no consistent changes. After IDET, pressure in the nucleus decreased by 6% to 13% (P < 0.05), and stress concentrations in the anulus were reduced by an average 0.28 MPa (P < 0.004). In 12 of the 18 specimens, anulus stress concentrations were reduced by more than 8%, and in these "responders," mean reduction was 78%. Stress concentrations were increased by more than 8% in 2 specimens.

IDET has a significant but inconsistent effect on compressive stresses within intervertebral discs. These results may partly explain the variable clinical success of IDET.