Lasers in orthopaedic surgery

Laser-induced micropore formation and modification of cartilage structure in osteoarthritis healing

“…Crucial for optimizing therapeutic effects is the choice of the laser parameters, including the irradiation wavelength and power, pulse duration and repetition rate, beam spot diameter, and exposure time. 15,20,23 Specifically, the wavelength is taken as 1.56 μm, guaranteeing the penetration depth 0.5 mm, which is defined by the coaction of the light adsorption by the interstitial water and light scattering. 29 The effective length of the beam action results from the interplay of the optical penetration depth and the distance of the heat propagation depending on the time of irradiation t. This distance is estimated as ðatÞ 1∕2 ¼ 0.4 mm, where a is cartilage thermal diffusivity 0.0014 cm 2 ∕s.…”

“…15 The possible mechanisms that can explain the influence of laser-induced pores and bubbles on the singular phases of the multistep process of cartilage regeneration are: (1) the acceleration of liquid and mass transfer within the areas containing laser-induced pores promotes cell nutrition, breath, and transport of signaling molecules; 23 (2) the formation of gas bubbles decreases oxygen concentration in interstitial liquid, and therefore, stimulates cell reparation activity. It is known that synthetic activity of chondrocytes increases with the lowing oxygen concentration; 3 (3) the oscillation of the bubbles under the pulse-periodic laser radiation mechanically affects the chondrocytes stimulating their synthetic activity 23 (the mechanical effect on the cell proliferation and synthesis was studied in Refs. [34][35][36]; and (4) the bubble and pore formation accelerates decomposition of the dead cells, thereby creating free space for the living cells and the growth of the newly synthesized matrix, which is of great importance for cartilage regeneration.…”

“…Laser-induced formation of the gas bubbles and nanosize pores in the ECM stimulates cascade processes of cellular transformations like differentiation and dedifferentiation of chondrocytes, resulting in the formation of well-organized HC. 15,23 Importantly, pores appear not only within the hottest zones but also in the regions of the minimal Young modulus, i.e., near the cell surfaces, and in the regions in the neighborhood of the laser spot boundary, where the temperature gradient is maximal. In the absence of inhomogeneities, the heating of the tissue leads to formation of large pores in the area of maximal temperatures, which usually results in the growth of the FC.…”

“…In the absence of inhomogeneities, the heating of the tissue leads to formation of large pores in the area of maximal temperatures, which usually results in the growth of the FC. 23 Morphological images in Fig. 3 show various stages of formation of the HC starting with transformation of cellular structures toward the structural modification of the ECM.…”

“…The detailed description of such defect modeling is provided in our previous work. 23 In the course of this (secondary) surgery, all defects were irradiated by the laser with the wavelength of 1.56 μm using the parameters described in the cartilage ex vivo section. Half of the defects (right or left) were left intact.…”