Background and Objectives: The aim of this study was to evaluate areas of collateral thermal injury and crater morphology for evidence of wavelength-dependent effects on the ablation of articular cartilage and fibro-cartilage (meniscus) using selected mid-IR wavelengths produced by a free electron laser. Study Design/Materials and Methods: Two types of cartilage, articular cartilage and fibro-cartilage were used in the study. The wavelengths (l) evaluated were 2.79, 2.9, 6.1, and 6.45 mm generated by a free electron laser (FEL) using a 4 microseconds macropulse configuration. The zone of thermal injury and crater morphology produced by laser ablation were examined by light microscopy following standard histologic processing. Results: The zone of thermal injury and crater morphology created in cartilage by the FEL at selected mid-IR wavelengths were examined as a function of incident radiant exposure. Ablation using l ¼ 6.1 mm provided the largest crater size for both articular and fibro-cartilage at all radiant exposures. For the zones of collateral thermal injury in articular cartilage, l ¼ 6.1 mm produced the least thermal injury at the radiant exposure of 7.6 J/cm 2 . When the radiant exposure is increased to 20.4 J/cm 2 , both l ¼ 6.1 and 6.45 mm produced less thermal injury than the ablation using l ¼ 2.79 and 2.9 mm. The greatest amount of collateral thermal injury was produced by l ¼ 2.79 mm for both tissue types.
Conclusions:
The results demonstrate that crater depth and collateral thermal injury produced in articular cartilage and fibro-cartilage are wavelength-dependent with 6.1 mm providing the largest craters at all radiant exposures. The least amount of thermal injury was created in articular cartilage using l ¼ 6.1 mm at the radiant exposure of 7.6 J/cm 2 . Both 6.1 and 6.45 mm wavelengths demonstrated similar amount of thermal injury at 20 J/cm 2 that was less than l ¼ 2.79 and 2.9 mm at similar fluences. These observations are explained based on the absorption by water and protein in the tissue types studied. It is further observed that the use of crater dimensions may not provide a reliable estimate for the amount of tissue removal provided by an ablation procedure.