Thermal side effects of fiber-guided XeCl excimer laser drilling of cartilage

Ablation of articular cartilage with an erbium:YAG laser: an ex vivo study using porcine models under real conditions-ablation measurement and histological examination

BACKGROUND AND OBJECTIVES

The use of an erbium:YAG laser in arthroscopic surgery has the advantage of a precise treatment of soft tissue. Due to the high absorption in water, the laser energy is perfectly matched to smoothing the hydrous, fibrillated articular cartilage surface. In minimal invasive surgery, the workspace is filled with aqueous liquids for enlargement. This appears contrary to the absorption characteristics of erbium:YAG laser radiation in water. The purpose of this study was to evaluate the ablated volume per pulse of cartilage lesions and the potential side effects including thermal damage and tissue necrosis.

STUDY DESIGN/MATERIALS AND METHODS

Twenty-four osteochondral specimens of porcine knee joints were irradiated with an Er:YAG laser completely submerged in water, with distances to the cartilage surface of 1, 3 and 5 mm and pulse durations of 75 and 100 microseconds. To keep a constant peak power of approximately 6 kW, pulse energies of 450 and 580 mJ were used at a pulse repetition rate of 15 Hz. After a histological preparation, ablated volumes, depths, and widths of the cuts were investigated. Additionally, laser protocols were correlated with different markers of cartilage tissue damage and apoptosis.

RESULTS

Ablation could be observed for every measurement. The influence of the distance showed a statistical significance (P < 0.001) for the volume, depth, and width of the cuts. For the pulse duration, statistical significance (P < 0.001) was found only for the volume and the depth. We observed no loss of proteoglycan or collagen type II. The total cell number, cell morphology, and number of apoptotic cells in an area close to the cutting edge and in a corresponding unaffected area of the same specimens revealed no differences regardless of the applied protocol.

CONCLUSION

The use of an Er:YAG laser demonstrates the successful application in liquid environments for cartilage removal without any damage of the surrounding tissue.

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.

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.

Laser light delivery systems for medical applications

For medical applications, the choice of a delivery system will be governed by the characteristics of the laser system on the one hand and the tissue application on the other. The most important parts are the beam guide and the target optics. Most lasers have wavelengths in the visible and near-infrared and can be transported by silica fibres. For the mid- and far-IR other fibre materials or hollow waveguides are used. At the end of the waveguide or fibre, an optically active component is present to direct the beam and to control the power density on the target tissue. The laser beam can be delivered either by focusing handpieces and scanning devices to treat superficial areas or through microscopes, endoscopes and flexible fibres to treat areas almost anywhere inside the human body. The characteristics of the delivery systems can be determined looking at beam properties, transmission and thermal properties. The delivery of continuous wave or pulsed laser energy, contact or non-contact, will determine the contribution of optical, thermal and mechanical effects to the tissue. The practical use of laser delivery systems is illustrated by various clinical applications.

Real time monitoring of laser-induced thermal changes in cartilage in vitro by using snapshot FLASH

Snapshot FLASH imaging has been applied to study the spatial and temporal spreading of thermal changes caused by a Holmium:YAG laser in patella cartilage in vitro at 7 T. The temperature dependence of the proton resonance frequency was used to demonstrate the thermal energy deposition. A series of cartilage images, with a time resolution of 512 ms and a spatial resolution of 400 x 200 microm, showed dynamic changes of the temperature-related image phase in the regions irradiated by the laser.

Holmium: YAG laser-induced aseptic bone necroses of the femoral condyle

In laser-controlled cartilage-ablation arthroplasties, the attention focuses more and more on the depth effects of the various lasers, especially as heat necroses of the cartilage and even in places of the bone were found in animal experiments. For the first time, two cases of holmium: YAG laser-induced aseptic bone necrosis of the femoral condyles after cartilage ablation are described.

Effects of excimer laser on healing of articular cartilage in rabbits

This study examined healing of 1.0 mm diameter defects in rabbit knee articular cartilage for as long as 14 weeks after creation of the defects by either laser or drilling. The purpose of the research was to determine the effects of laser debridement of cartilage on the intrinsic biomechanical properties of the repair tissue. We therefore imitated chondral shaving and subchondral abrasion of cartilage by creating partial-thickness and full-thickness cartilage defects of standardized size with both excimer laser and drilling. Light and scanning electron microscopic examinations of the repair tissue showed that healing of osteochondral defects created by laser may be delayed compared with defects created by drilling, for at least 6 weeks postoperatively. Even though there initially was a considerable delay in healing in the laser group, neither laser nor drilling had any appreciable effects on the mechanical properties of the repair tissue, as demonstrated by biomechanical testing at 14 weeks. Specifically, the repair cartilage in the defects in the laser group had the following material properties (mean +/- SD): aggregate modulus, 0.40 +/- 0.24 MPa; Poisson's ratio, 0.37 +/- 0.08; permeability, 3.72 +/- 4.28 x 10(-15) m4/N.s; and thickness, 0.20 +/- 0.06 mm. The corresponding values for the defects in the drilling group were 0.39 +/- 0.23 MPa, 0.34 +/- 0.09, 3.82 +/- 3.44 x 10(-15) m4/N.s, and 0.22 +/- 0.09 mm. The repair tissue from both types of defects was pooled, and the values were compared with those for contralateral (control) tissue.(ABSTRACT TRUNCATED AT 250 WORDS)