IR Laser and Heat‐induced Changes in Annulus Fibrosus Collagen Structure

Abstract

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.

Effects of laser irradiation on collagen organization in chemically induced degenerative annulus fibrosus of lumbar intervertebral disc

“…The values of T d and DH d are summarized in Table 2. The denaturation temperature for enzyme digested samples (H, T1, and T2 groups) was consistent in the value of 65.58C reported for intact AF collagen [16,21]. Glyceraldehyde cross-linking resulted in a material with a high T d (74.58C).…”

“…Previously we observed this effect on intact AF and obtained high values of extents of denaturation (a$60% and 90% for 0.5 and 1 W, respectively) [21]. We offered the consistency of occurrences in AF matrix which described laser-induced response of AF collagen based on the mechanisms for mechanical damage in an intervertebral disc [57], thermo-mechanical damage of collagenous tissues [15] and biphasic theory introduced in 1980 to model cartilage as a mixture of an incompressible fluid phase and an incompressible solid porous and permeable phase (see review article [58]).…”

“…Two groups of laser treatment tests were performed. The radiometric subsurface temperature distribution during laser irradiation was monitored by thermograph IRTIS-2000 (IRTIS Ltd., Moscow, Russia) at 1 Hz frame rate [21]. The laser energy settings and matching maximal radiometric temperature (T max ) are listed in the Table 1.…”

“…Moreover, a local disturbance zone in tissues can be detected by this technique. In our previous work PS-OCT was used to characterize essential changes in AF structure after hydrothermal and non-ablative laser treatment [21]. Our data has demonstrated quantitative difference between results of laser and hydrothermal heating of discs in motion segments.…”

“…PS-OCT has been used to quantify the birefringence properties of AF. A birefringence value Dn ¼ 6.0 Â 10 À3 at 1.3 mm [19], 3.0-4.5 Â 10 À3 at 0.83 mm [20] and 5.5 Â 10 À3 at 0.98 mm [21] was obtained. This technique has been reported to be a useful tool for an assessment of collagen organization within intact AF including fiber orientation and lamella thickness assessment based on the semiempirical models [19,20].…”