Therapeutic Window of Laser Dosimetry for the Treatment of Knee Osteoarthritis.

Objectives: We propose a non-destructive laser method that uses controlled thermomechanical action to treat degenerative cartilage changes. The technique aims to reduce pain, offers a minimally invasive option for early- to mid-stage degeneration, and lessens the need for joint replacement.

Methods: An ex vivo study on laser treatment of articular cartilage involves theoretical modeling of laser-induced heating, stress relaxation, and cartilage denaturation. Theoretical model simulates the laser treatment of a multilayer system using modulated infrared radiation. It integrates the 3D heat diffusion equation with a thermomechanical model of stress relaxation and micropore formation caused by the rupture of chemical bonds. The risk of tissue denaturation is estimated with Arrhenius model. The model validation involves ex vivo temperature measurements obtained with a thermal imaging camera and experimental histological data from pig joints. This approach helps define the optimal laser dosimetry that encourages cartilage repair without causing overheating or denaturation.

Results: Experimental measurements of cartilage temperature and histological structural changes under laser irradiation confirm the model's predictions. The therapeutic window includes a lower limit marking the onset of effective stress relaxation and pore formation, while the upper limit indicates the threshold of tissue overheating and denaturation. Laser irradiation of an articular cartilage with λ = 1470 nm, pulse duration 100 ms, pulse repetition rate 1 Hz, and fiber diameter 0.6 mm shows that the therapeutic window is in the range of 0.5-0.9 W. This therapeutic window is wide enough and depends little on the parameters of cartilage defect being treated or on the conditions of laser radiation delivery for a particular patient.

Conclusion: Laser-induced heating and structural changes in cartilage verify theoretical predictions, establishing a safe and effective therapeutic window. These findings support clinical trials of the 1470 nm laser, used alongside arthroscopy, to repair degenerative cartilage and alleviate knee pain.