Peter F. Kelly, D.P.M., F.A.C.F.A.S. Diplomate, American Board of Podiatric Surgery Fellow, American College of Foot and Ankle Surgeons CHAPTER 37 LASER APPLICATIONS IN PODIATRIC SURGERY TABLE OF CONTENTS LASERS AND LASER PHYSICS HISTORY UNITS OF MEASUREMENT FUNDAMENTALS UNIQUE CHARACTERISTICS OF LASER LIGHT COMPONENTS OF A LASER LASER V. CONVENTIONAL PHOTONIC RADIATION THEORY of LASER OPERATION REALATION OF LASER LIGHT V. CONVENTIONAL LIGHT DELIVERY MECHANISMS TRANSMISSION MODES TISSUE INTERACTION TRANSMISSION CHARACTERISTICS THROUGH TISSUE CLINICAL TISSUE INTERACTION PHENOMENA POWER DENSITY WATTS PER CM2 Chart TIME LASERS APPLICABLE TO PODIATRIC SURGERY ----------------------------------------------------------------------------------- LASER SAFETY EYE PROTECTION HAZARDS OF THE LASER SMOKE PLUME ----------------------------------------------------------------------------------- CLINICAL LASER APPLICATIONS IN PODIATRIC SURGERY STANDARD OF CARE THE CO2 LASER PROPERTIES OF THE CO2 LASER ADVANTAGES OF USING THE CO2 LASER SELECTION OF LASER PARAMETERS DISADVANTAGES PROCEDURES PERFORMED USING THE CO2 LASER ASSIST THEORY OF CO2 LASER TISSUE INTERACTION CO2 LASER PROCEDURES TECHNIQUE OF CO2 LASER ABLATION TECHNIQUE OF CO2 LASER FOR INCISION/EXCISION HEMOSTASIS FOCUSED, FREE BEAM LASER APPLICATIONS OVERLASING CAVERNOUS HEMANGIOMA KELOID AND HYPERTROPHIC SCAR LASER ASSISTED OSSEOUS PROCEDURES BONE AND CARTILAGE LASER TREATMENT OF VERRUCA LASER NAIL MATRIXECTOMY POSTOPERATIVE CARE COMPLICATIONS PREVENTION OF COMPLICATIONS FROST AND WINOGRAD TECHNIQUE LASER TREATMENT OF ONYCHOMYCOSIS SUBTOTAL MATRIXECTOMY SUBUNGUAL HEMATOMA LASER TREATMENT OF GRANULOMAS CAUTION IN REVISIONAL PROCEDURES ----------------------------------------------------------------------------------- THE Nd:YAG LASER GENERAL DESCRIPTION MODES OF OPERATION THE CONTACT TIP SURGICAL APPLICATIONS ADVANTAGES OF Nd:YAG OVER SCALPEL Nd:YAG MEDICAL INDICATIONS PODIATRIC MEDICAL INDICATIONS FOR Nd:YAG SCALPEL CONTRAINDICATIONS INDICATIONS FOR FROSTED AND NONFROSTED CONTACT TIPS INAPPROPRIATE Nd:YAG PROCEDURES GENERAL CONSIDERATIONS IN APPLICATION OF THE Nd:YAG LASER REALISTIC EXPECTATIONS ----------------------------------------------------------------------------------- THE ARGON LASER GENERAL DESCRIPTION MECHANISM OF ACTION EYE PROTECTION SURGICAL APPLICATIONS INDICATIONS FOR THE ARGON LASER ADVANTAGES ARGON LASER DESTRUCTION OF VERRUCA POSTOPERATIVE CARE ----------------------------------------------------------------------------------- THE KTP LASER GENERAL CHARACTERISTICS FIBER PREPARATION SURGICAL APPLICATIONS KTP TREATMENT OF VERRUCA KTP APPLICATIONS TO PLANTAR FASCIOTOMY MECHANISM OF ACTION THERMAL LASER PROBLEMS INDICATING KTP LASER DISADVANTAGES OF KTP LASER ----------------------------------------------------------------------------------- OTHER SURGICAL LASERS Ho:YAG LASER COPPER VAPOR LASER Q-SWITCHED LASERS EXCIMER LASER Er:YAG LASER ----------------------------------------------------------------------------------- PHOTODYNAMIC THERAPY "PDT" MECHANISM OF OPERATION ----------------------------------------------------------------------------------- BIOSTIMULATION "BIOSTIM" ----------------------------------------------------------------------------------- BIBLIOGRAPHY SPEED-READING BIBLIOGRAPHY FURTHER READING LASER APPLICATIONS IN PODIATRIC SURGERY Applications of lasers to medicine and surgery have increased exponentially over the past decade. This technology has become established in the medical community and has become the standard of care for many procedures. Lasers have justified their utilization by the improved clinical outcome in the delivery of comparably more traumatic and invasive procedures. Some procedures are not possible without the precision or uniqueness of this modality. There are a great variety of laser types and delivery systems, each having indications unique to the desired tissue response. Fundamental to the surgeon in selecting the wavelength, power and control to produce the intended effect, with safe handling of the instrument, is a knowledge of laser physics for this tissue interaction. LASERS AND LASER PHYSICS HISTORY 1. The Quantum Theory: Max Planck 1910 Light is quantified in Photon units the basic unit of light (6.625 x 10-27 erg sec (cm2/sec)) 2. Stimulated Emission Theory: Albert Einstein 1917 Basis of laser light 3. First laser developed, demonstrated and patented Theodore Maiman Ruby Laser 1960 UNITS OF MEASUREMENT 1. Frequency Expressed in Cycles per Second (CPS) Hertz (Hz) 2. Wavelength The measurement of one crest to another of a particular frequency 3. Length Meter = the basic measurement unit Prefix centi (cm) = 1 x 10-2 meters = .01 meters mili (mm) = 1 x 10-3 meters = .001 meters micro (um) "micron" = 1 x 10-6 meters = .000001 meters nano (nm) = 1 x 10-9 meters = .000000001 meters 4. Time Second = the basic measurement unit Prefix mili (ms) = 1 x 10-3 seconds = .001 seconds micro (us) = 1 x 10-6 seconds = .000001 seconds nano (ns) = 1 x 10-9 seconds = .000000001 sec pico (ps) = 1 x 10-12 seconds = .000000000001 sec 5. Power Watts (W) = The basic measurement unit Power density = Watts per centimeter squared (W/cm2) Joules (J) = Watts x Seconds of power on tissue FUNDAMENTALS 1. The wavelength is the key to tissue absorption, laser delivery systems and to laser safety. 2. Comparison with other modalities: Scalpel --> Mechanical pressure. Local effect. Controlled crushing. Electrocautery --> Electrons. Conduction through isotherms. Global effect. Radiosurgery --> Radio Frequency transmission. Local effect. Laser --> Photon absorption. Specific to tissue content. Thermal precision. 3. The mnemonic "LASER": L ight A mplification by S timulated E mission of R adiation 4. Laser frequencies most commonly used are in the infrared and visible spectra. 5. These are non-ionizing photonic radiation. 6. No lead shielding is required. 7. Exception: Excimer (UV) lasers are ionizing. 8. Laser light is NOT a natural phenomena. UNIQUE CHARACTERISTICS OF LASER LIGHT Coherent Monochromatic Collimated Coherent = All crests of wavelengths line up. Crests and troughs are equidistant in time and space. This eliminates wavelengths canceling each other out and producing interference patterns which would decrease its intensity. This enables very efficient power production. Coherent light, (compared with incoherent, conventional light) can be focused to an exact single point. i.e.: 200 W of incoherent conventional light will illuminate a room. 200 W of coherent laser light will rapidly carve through the cement wall of the room. Monochromatic = Pure, single color. Responsible for the interaction of tissue chromophores producing a specific effect. i.e.: CO2 laser to incise and ablate amelanotic tissue, Nd:YAG for deep tissue penetration, Argon penetrates epidermis. Collimated = Emitted stream of photons is linear, and does not diverge. This also eliminates wavelengths producing interference patterns reducing power. COMPONENTS OF A LASER 1. Partially reflecting mirror 97% 2. Fully reflecting mirror 100% 3. Lasing media 4. Xenon flash lamp 5. High frequency Switching system 6. High voltage power supply 7. Delivery system - Articulating Arm, Fiberoptic, waveguide 8. Lense 9. Aiming Laser (HeNe), if required, depends on laser type LASER V. CONVENTIONAL PHOTONIC RADIATION Conventional light radiation Laser light radiation + Multiwavelength - polychromatic + Pure - monochromatic + Divergent + Collimated + Coherent + In phase + Spontaneous Emission + Stimulated Emission THEORY of LASER OPERATION 1. Spontaneous Emission (conventional) 2. Stimulated Emission (laser) CREATION OF LASER LIGHT V. CONVENTIONAL LIGHT 1. Lasers are classified by the type of active media used in the laser tube. i.e.: CO2 laser tube filled with CO2 (excitable media), N2, and He gasses.Nd:YAG is a Yttrium, Aluminum and Garnet crystal doped with Neodymium as the excitable media.2. Atoms are stimulated to rise from a lower energy shell to a higher shell, 3. Then fall back to emit a specific monochromatic wavelength of light. 4. These waves reflect in the laser media randomly at first, then become coherent together by being amplified by reflecting between the mirrors. 5. Once their energy exceeds the threshold of transmission through the partially reflecting mirror, laser radiation is emitted in a linear, collimated, array. 6. Frequency doubling media is also used to change laser wavelength. i.e.: Tunable dye or KTP (Potassium, Titanium, Phosphate) laser. The KTP crystal pumps a KTP crystal. Efficiency drops to about 30% of input. Nd:YAG Laser ----------> KTP Crystal --------> output 1060 nm 532 nm DELIVERY MECHANISMS 1. Low frequencies = longer wavelengths = far- and mid-infrared. Articulating arms, or internally reflecting waveguides are used. 2. At near-infrared, 2100 nm and above (Ho:YAG laser) fiberoptics contain these frequencies having a higher index of refraction. 3. Fiberoptics are constructed of quartz (Aluminum dioxide), silicon dioxide or silver halides, coated with a plastic sheath. 4. Lenses, or contact light scalpels of selective focal lengths, can be integrated into the terminal end of the fiberoptic system. 5. The bare fiber is also used for free beam ablation work. TRANSMISSION MODES 1. Desirable laser energy distribution energy follows a Gaussian curve. 2. Energy decay falls exponentially on either side of the curve. TEM00 has a narrow spot size TEM01 small spot 0.3 mm at best true Gaussian curve. called "near Gaussian" 0.2 mm diameter spots not desirable appropriate for cutting can be used for ablation. TISSUE INTERACTION 1. This is THE most important aspect of lasers in medical science. 2. Tissue interaction with the specific laser wavelength is the KEY to laser selection. TRANSMISSION CHARACTERISTICS THROUGH TISSUE 1. reflection 2. transmission 3. scattering 4. absorption ** Absorption of specific wavelength by specific chromophores is key. CLINICAL TISSUE INTERACTION PHENOMENA The effect on tissue by thermal lasers commonly used in Podiatry is both: 1. power and 2. time dependent: POWER DENSITY 1. Is the standard of expression in documenting laser power to tissue. 2. Expressed in W/cm2. 3. P.D. may be constant while tissue spot size and power varies. This allows physicians to communicate standard terminology, allows for preference. It is the STANDARD OF CARE: in operative reports describing laser use. It is necessary for communicating standard measurement in the scientific community. A typical example using 14 Watts with a 0.2 mm diameter contact tip or spot size (which is 0.1 mm radius) Traditional Algebraic: WATTS 14 4.46 446 ------- = -------------- = ------- = -------- = 44,600 pi x r2 0.12 0.01 0.01 3.14 x ----- ----- 102 100 where: 0.1 is the radius 10 is the conversion factor of 10 mm/cm Shortcut algebraic: WATTS 14 127 x ----------- = 127 x ------- = 44,450 d2 0.22 WATTS PER CM2 Chart TIP DIAMETER (mm) or CO2 Spot Size (mm) WATTS 0.1 0.2 0.4 0.6 0.8 1.0 2.0 3.0 --------------------------------------------------------------------- 4 50,955 12,739 3,185 1,415 796 510 127 57 5 63,694 15,924 3,981 1,769 995 637 159 71 6 76,433 19,108 4,777 2,123 1,194 764 191 85 7 89,172 22,293 5,573 2,477 1,393 892 223 99 8 101,911 25,478 6,369 2,831 1,592 1,019 255 113 9 114,650 28,662 7,166 3,185 1,791 1,146 287 127 10 127,389 31,847 7,962 3,539 1,990 1,274 318 142 11 140,127 35,032 8,758 3,892 2,189 1,401 350 156 12 152,866 38,217 9,554 4,246 2,389 1,529 382 170 13 165,605 41,401 10,350 4,600 2,588 1,656 414 184 14 178,344 44,586 11,146 4,954 2,787 1,783 446 198 15 191,083 47,771 11,943 5,308 2,986 1,911 478 212 16 203,822 50,955 12,739 5,662 3,185 2,038 510 226 17 216,561 54,140 13,535 6,016 3,384 2,166 541 241 18 229,299 57,325 14,331 6,369 3,583 2,293 573 255 19 242,038 60,510 15,127 6,723 3,782 2,420 605 269 20 254,777 63,694 15,924 7,077 3,981 2,548 637 283 21 267,516 66,879 16,720 7,431 4,180 2,675 669 297 22 280,255 70,064 17,516 7,785 4,379 2,803 701 311 23 292,994 73,248 18,312 8,139 4,578 2,930 732 326 TIME The gating of the flashlamp may be: 1. C.W. Continuous Wave - Continuously on 2. Single Pulsed - Continuous on for a preset period 3. Superpulsed - Rapid pulsing at peak power at 250 - 1000 Hz. Average power is determined by 1. pulse width and 2. repetition rate This allows tissue to undergo "thermal relaxation" 4. Ultrapulsed - Much higher RF (Radio Frequency) switching nanosecond pulse width. More thermal precision. 5. Q-switched - Very high peak power with picosecond pulse width THERMAL RELAXATION = Interval between pulses to allow dissipation of energy. Minimum interval is 1:10 ratio on:off. LASERS APPLICABLE TO PODIATRIC SURGERY WAVELENGTH USE IN PODIATRY DEPTH OF PENETRATION FUNCTION 10,600 um CO2 Noncontact: 0.1 mm Cutting Far IR Dissection Ablation Derm.Pathologies Coagulation Nail Pathologies 1,060 um Nd:YAG Bare Fiber 6-8 mm Ablation Near IR Deep tumor destr. Coagulation Nd:YAG Contact-tip: 50-200 u Cutting Dissection 2,100 um Ho:YAG Near-contact: 0.4-0.6 mm Ablation Mid IR Cartilage and bone 488/514 um Argon Noncontact Dermal vessels Photoablation Verruca 532 um KTP Noncontact: Dermal vessels Photoablation Cutaneous vascular Verruca Contact: 1-2 mm Cutting Dissection 478 um Copper- Noncontact: Dermal vessels Photoablation Vapor Cutaneous vasc. lesions i.e.: CO2 is strongly absorbed by water, therefore superficial penetration. Holmium is absorbed by water but not as much as CO2, so deeper tissue penetration. Argon and KTP are absorbed by Hb and chromophores. Nd:YAG (bare fiber) is not absorbed by anything, so it penetrates.