Cartilage shaping using the Holmium: YAG laser without tissue ablation

Abstract

Reshaping cartilage is a clinical problem and we are using a novel technique to solve this. Objective: To determine the mechanical, thermal, and optical changes in human cartilage in vitro during the phenomenon of ‘stress relaxation using the Holmium: YAG laser’. To define the parameters of energy intensity, pulse duration and repetition rate which produce ‘stress relaxation’ whilst minimizing chondrocyte damage. Method: Thirty-three pieces of human nasal septal cartilage were studied in vitro. Parameters including laser wavelength, pulse duration and repetition rate were measured. Tissue temperature was detected with a needle-shaped thermocouple of 30-μm diameter. The thermodynamic characteristics of the ‘bound-to-free’ phase transformation of water in cartilage were studied by FTIR spectroscopy. The structure of cartilage was examined by light and scanning electron microscopy and changes in chondrocytes were assessed using a semiquantitative method according to the degree of cell damage and the proportion of cells affected. Results: The mechanism of laser-induced stress relaxation of cartilage was found to be due to transformation and movement of the bound water in the cartilage (about 5% of the total water). There was no evidence of matrix damage although there were some microscopic changes of focal vacuolation and nuclear condensation of chondrocytes at energy levels required to produce stress relaxation. The optimum parameters were found to be a wavelength of 2.1 μm, a pulse energy of 0.5 J, a duration of 0.5 ms, a repetition rate of 5 Hz, and a spot diameter from 4.0 to 7.8 mm. An irradiation time of 4 s was needed to produce cartilage shaping. Conclusion: The conditions which produce stress relaxation using the Holmium: YAG laser show promise as a method of reshaping cartilage.