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

Background and Objective: Recent studies have indicated that chondrocyte vi ability decreases with prolonged or repeated laser irradiation. To optimize laser-mediated cartilage reshaping, the heating process must be finely con trolled. In this study, we use high-power Nd:YAG laser irradiation (lambda = 1.32 mum) combined with cryogen spray cooling (CSC) in an attempt to resh ape porcine septal cartilage while enhancing chondrocyte viability. Study Design/Materials and Methods: Chondrocyte viability was determined af ter high-power (50 W/cm(2)) Nd:YAG-mediated cartilage reshaping with and wi thout 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 relaxat ion) was observed in both laser only and laser with CSC specimens. After 2 seconds of laser exposure, specimens in both groups retained the curved sha pe for up to 14 days. After one laser exposure, chondrocyte viability was 9 4.35 +/- 6.1% with CSC and 68.17 +/- 20.1% (P < 0.05) without CSC. After tw o 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 wh ile minimizing extreme front surface temperature elevations and axial therm al gradients. Laser irradiation with CSC can be used to effectively reshape cartilage tissue with the additional advantage of increasing chondrocyte v iability. Lasers Surg. Med. 28:1-10, 2001. (C) 2001 Wiley-Liss, Inc.