308 nm excimer laser ablation of cartilage

Mid-IR laser ablation of articular and fibro-cartilage: a wavelength dependence study of thermal injury and crater morphology

BACKGROUND AND OBJECTIVE

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 (lambda) evaluated were 2.79, 2.9, 6.1, and 6.45 microm 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 lambda = 6.1 microm 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, lambda = 6.1 microm produced the least thermal injury at the radiant exposure of 7.6 J/cm2. When the radiant exposure is increased to 20.4 J/cm2, both lambda = 6.1 and 6.45 microm produced less thermal injury than the ablation using lambda = 2.79 and 2.9 microm. The greatest amount of collateral thermal injury was produced by lambda = 2.79 microm 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 microm providing the largest craters at all radiant exposures. The least amount of thermal injury was created in articular cartilage using lambda = 6.1 microm at the radiant exposure of 7.6 J/cm2. Both 6.1 and 6.45 microm wavelengths demonstrated similar amount of thermal injury at 20 J/cm2 that was less than lambda = 2.79 and 2.9 microm 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.

XeCl excimer laser ablation of rabbit tibia bone: morphology of the irradiated site and self-limiting effect

OBJECTIVE

The purpose of this work is to investigate the morphological changes of the rabbit tibia bone submitted to osteotomy with XeCl excimer laser.

BACKGROUND DATA

Laser ablation of tissue is a relevant clinical application of high-power lasers. Due to the variety of laser wavelengths and properties of biological targets, the subject has not yet been completely explored.

METHODS

In this study, four tibias were irradiated with six different durations. The applied energy density was 6.7 J/cm(2) per pulse at a 4-Hz repetition rate.

RESULTS

The 24 samples had similar and well-defined craters that were free of carbonization. The ablation rates per pulse, at 60-120 seconds, were 3.8 and 1.9 microm at the compact bone and the marrow tissue, respectively. The ablation process ceased after 120 sec, with a 1.6-mm crater depth.

CONCLUSIONS

In the present study, the laser used showed a self-limiting characteristic, which is a phenomenon that can be of great value in preserving important structures close to the working area, giving a margin of safety to the surgeon, in case of over-irradiation. This self-limiting effect is attributed to liquid filling the cavity by the bleeding and irrigation process.

Free electron laser ablation of articular and fibro-cartilage at 2.79, 2.9, 6.1, and 6.45 ?m: Mass removal studies

BACKGROUND AND OBJECTIVE

The wavelength and tissue-composition dependence of cartilage ablation was examined using selected mid-infrared laser wavelengths.

STUDY DESIGN/MATERIALS AND METHODS

The mass removal produced by pulsed laser ablation of articular and fibro-cartilage (meniscus) were measured. The wavelengths examined were 2.79, 2.9, 6.1, and 6.45 microm and provided by a free electron laser (FEL) emitting 4 microsecond macropulses consisting of 1-2 picoseconds duration micropulses delivered at 350 picosecond intervals. The measurement of tissue mass removal was conducted using a microbalance during laser ablation.

RESULTS

These studies demonstrated that for articular cartilage the highest mass removal was achieved at lambda = 6.1 microm followed by, in order, lambda = 2.79, 2.9, and 6.45 microm. In comparison, the maximum mass removal for fibro-cartilage was achieved using lambda = 6.1 microm radiation with no statistically significant differences in mass removal provided by the other wavelengths. In evaluation of the comparative influence of each wavelength on tissue type, there was no difference in ablation efficiency between articular and fibro-cartilage at lambda = 6.1 microm. However, the ablation efficiency of articular cartilage was higher than that of fibro-cartilage at both lambda = 2.79 and 2.9 microm. By contrast, lambda = 6.45 microm radiation ablated fibro-cartilage more efficiently than articular cartilage at radiant exposures greater than 12 J/cm2.

CONCLUSIONS

The mass removal of articular and fibro-cartilage produced by FEL ablation at selected mid-IR wavelengths was measured as a function of incident radiant exposure. The ablation efficiency was found to depend on both wavelength and tissue type. The 6.1 microm wavelength was found to provide the highest ablation efficiency for both articular and fibro-cartilage.

Lasers in pediatric airway surgery: Current and future clinical applications

BACKGROUND AND OBJECTIVES

The smaller anatomy and limited access to instrumentation pose a challenge to the pediatric airway surgeon. The enhanced precision and ability to photocoagulate tissue while operating with the laser enhances the surgeon's ability to successfully treat unique pediatric conditions.

STUDY DESIGN/MATERIALS AND METHODS

A comprehensive literature review was performed using the Medline (1995-2004) database.

RESULTS

Due to its shallow tissue penetration and thermal effect, the carbon dioxide (CO2) laser is generally considered the laser of choice for pediatric airway applications. The potential for increased scarring and damage to underlying tissue caused by the greater penetration depth and thermal effect of the Nd:YAG and potassium-titanyl-phosphate (KTP) lasers preclude their widespread use in this population.

CONCLUSIONS

In this review, we will discuss the clinical applications of lasers in pediatric airway surgery, the current state of the art, where the current technology is deficient, and the potential applications of novel laser systems.

Cartilage shaping with the Er:YAG laser: an in vivo experimental study

Reshaping and preserving the new shape of cartilage grafts is important for reconstruction of congenital or acquired deformities. In this in vivo study the authors investigated the effect of the Er:YAG laser on cartilage reshaping in comparison with scalpel stripping. The study consisted of two groups (N = 9). After measuring the angle between two margins of the ear, the cartilage in the right ear in rabbits was reshaped using the Er:YAG laser in group I, and scalpel incisions were used to reshape the left-ear cartilage in group II rabbits. Changes in the shape of the ears were evaluated at 10 days, and 1 and 6 months. The laser-reshaped ears were flattened and preserved the new flattened shape at the end of 6 months. The ultrastructural changes in the cartilage were evaluated based on the results from histopathological examination and electron microscopy. The authors conclude that cartilage can be reshaped using the Er:YAG laser. The mechanical effect of laser ablation and the thermal effect of laser radiation caused ultrastructural changes in the cartilage tissue, resulting in permanent changes in cartilage shape.

Laser solder welding of articular cartilage: tensile strength and chondrocyte viability

BACKGROUND AND OBJECTIVE

The surgical treatment of full-thickness cartilage defects in the knee joint remains a therapeutic challenge. Recently, new techniques for articular cartilage transplantation, such as mosaicplasty, have become available for cartilage repair. The long-term success of these techniques, however, depends not only on the chondrocyte viability but also on a lateral integration of the implant. The goal of this study was to evaluate the feasibility of cartilage welding by using albumin solder that was dye-enhanced to allow coagulation with 808-nm laser diode irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Conventional histology of light microscopy was compared with a viability staining to precisely determine the extent of thermal damage after laser welding. Indocyanine green (ICG) enhanced albumin solder (25% albumin, 0.5% HA, 0.1% ICG) was used for articular cartilage welding. For coagulation, the solder was irradiated through the cartilage implant by 808-nm laser light and the tensile strength of the weld was measured.

RESULTS

Viability staining revealed a thermal damage of typically 500 m in depth at an irradiance of approximately 10 W/cm(2) for 8 seconds, whereas conventional histologies showed only half of the extent found by the viability test. Heat-bath investigations revealed a threshold temperature of minimum 54 degrees C for thermal damage of chondrocytes. Efficient cartilage bonding was obtained by using bovine albumin solder as adhesive. Maximum tensile strength of more than 10 N/cm(2) was achieved.

CONCLUSIONS

Viability tests revealed that the thermal damage is much greater (up to twice) than expected after light microscopic characterization. This study shows the feasibility to strongly laser weld cartilage on cartilage by use of a dye-enhanced albumin solder. Possibilities to reduce the range of damage are suggested.