Laser‐mediated cartilage reshaping with feedback‐controlled cryogen spray cooling: Biophysical properties and viability

Abstract

Background and Objective:Recent studies have indicated that chondrocyte viability decreases with prolonged or repeated laser irradiation. To optimize laser-mediated cartilage reshaping, the heating process must be finely controlled. In this study, we use high-power Nd:YAG laser irradiation ( ‫ס‬ 1.32 m) combined with cryogen spray cooling (CSC) in an attempt to reshape porcine septal cartilage while enhancing chondrocyte viability. Study Design/Materials and Methods: Chondrocyte viability was determined after high-power (50 W/cm 2 ) Nd:YAG-mediated cartilage reshaping with and without cryogen spray cooling (CSC) and correlated with dynamic measurements of tissue optical and thermal properties. Results: After 1.5 to 2.0 seconds of laser exposure, characteristic changes in diffuse reflectance (indicating the onset of accelerated stress relaxation) was observed in both laser only and laser with CSC specimens. After 2 seconds of laser exposure, specimens in both groups retained the curved shape for up to 14 days. After one laser exposure, chondrocyte viability was 94.35 ± 6.1% with CSC and 68.77 ± 20.1% (P < 0.05) without CSC. After two laser exposures, a similar trend was observed with CSC (70.18 ± 16.44%) opposed to without CSC (28 ± 45%; P < 0.05). Conclusion: CSC during high-power laser irradiation allows rapid heating while minimizing extreme front surface temperature elevations and axial thermal gradients. Laser irradiation with CSC can be used to effectively reshape cartilage tissue with the additional advantage of increasing chondrocyte viability. Lasers Surg.

Analysis of Nd:YAG laser‐mediated thermal damage in rabbit nasal septal cartilage

“…Instead, these findings suggest that in order to produce clinically relevant shape change in cartilage tissue using the Nd:YAG, significant cellular damage will occur within the region of energy deposition and heat conduction [2]. The success of LCR procedures reported in both animal studies [2,12] and clinical trials [11] likely depends upon spatially selective heating where reshaping may result from deposition of energy into well-defined layers within a specimen or graft leading to mechanical relaxation of this region alone [8]. Cartilage tissue beneath this level likely undergoes little temperature elevation and thus remains viable and may participate in the remodeling process.…”

“…LCR is a potential improvement over classic surgical techniques that rely on incisions, morselization, or suturing to balance the elastic forces in cartilage that resist deformation [2]. While some animal [11,12] and human studies [1,2,11] have demonstrated promising results, the clinical relevance of LCR still depends on its ability to minimize and/or limit thermal injury in irradiated regions [2,13]. In order to better understand the safety of LCR, both shape change and resultant tissue viability must be determined as a function of laser dosimetry.…”

“…Previous studies from this laboratory empirically determined the relationship between shape change and the temperature and duration of heating using porcine and rabbit nasal septal cartilage, and also identified the set of laser parameters that produced clinical relevant shape change [9]. The Nd:YAG laser (l ¼ 1.32 mm) was used because it has low absorption in cartilage and thus produces a relatively uniform axial fluence distribution [12]. The net effect is the elimination of significant axial temperature gradients, which ensures uniformity of temperature within the optical zone [14,15].…”

Shape retention in porcine‐septal cartilage following Nd:YAG (λ = 1.32 μm) laser‐mediated reshaping

“…Next, specimens were irradiated for 15 seconds with a Nd:YAG laser (l 1.32 mm, 50-Hz PPR, 5W, 6-mm spot diameter, New Star Lasers, Auburn, CA). These laser parameters are similar to those used in previous investigations by our group [13,16] . The laser beam was directed at the center of the specimen along the center of the bend specimen ( Fig.…”

Characterization of temperature dependent mechanical behavior of cartilage

“…The alteration in internal stress during laser irradiation results in accelerated stress relaxation and represents a fundamental biophysical change that results in cartilage reshaping [18,23,24]. Preliminary studies using diffuse light scattering and calorimetric measurements have identified changes in cartilage tissue, thermal and optical properties that are consistent with this phase transformation hypothesis [11][12][13]15,19,20,[25][26][27][28][29][30][31][32].…”