Current Concepts in Laser Assisted Shoulder Surgery

Wesley M. Nottage, M.D.
The Sports Clinic
Orthopaedic Medical Associates, Inc.
Laguna Hills, California, USA

January 1997

Summary
The application of laser/thermal energy in arthroscopic shoulder surgery remains controversial. Laser proponents tout the benefits of coagulation and vaporization of tissue, while opponents cite costs, complications and the fact that the laser has not yet demonstrated superior results to presently available mechanical techniques. A lack of basic science studies and disinclination by many physicians toward the marketing aspects of laser technology has undermined the widespread orthopaedic acceptance of laser techniques. Newer applications, such as "capsular shrinkage" are just now being evaluated as to effect and efficacy. Orthopaedists should be assured that at present they have not been demonstrated to be compromising patient care by using laser techniques.

Background
"Laser" is an acronym for Light Amplification by Stimulated Emission of Radiation, a unique type of light energy produced by man. Laser light is different than visible light in its characteristics of collimation (all emitted light is almost perfectly parallel), coherent (light waves are all in phase in both time and space) and monochromatic (one specific wave length).

Development of the laser followed Neil Bohr's description of the atom in 1913 and Albert Einstein's hypothesis of stimulated versus spontaneous emission of radiation (1917). The laser, however, was created in 1960 by Maiman, while employed in the aerospace industry. The CO2 laser was first applied in arthroscopy in the early 1980s which led to considerable controversy as to both efficacy and benefit beyond the normal mechanical techniques.

It was the Holmium 2.1 nanometer laser which was introduced experimentally in 1987 as the first fiber optic delivered free energy laser beam for arthroscopic application in a water medium. The FDA approved a the Holmium 2.1 laser following in 1989 for all peripheral joint applications.

Principles
Laser light is created in a lasing cavity which must contain a lasing medium, such as Holmium doped crystal rod of yttrium, aluminum and garnet (Ho:YAG). The crystal rod is excited by high intensity flash lamp (commonly Krypton) causing release of photons which become trapped in the lasing cavity. This "optical resonator" is composed of the rod internally and at each end a precisely aligned parallel mirror. One mirror is 100% reflective of the wave length while the opposite mirror reflects a predetermined amount of photons (light energy) allowing a percentage of the impinging photons to pass through the mirror and become the usable output or "laser beam."

The principle of lasing phenomena is the ability of photons to stimulate the emission of other photons, each having the same wave length and direction of travel. When a photon passes close to an excited electron, the electron will become stimulated to emit a photon that is identical in both wave length, phase and spatial coherence to the impinging photon. This process can be amplified between the two mirrors of the optical resonator. A photon can be defined as an energy or particle packet released by excited electrons.

A laser must include three fundamental elements, a lasing medium which provides the source of photons that support the light amplifications, such as carbon dioxide or a Holmium doped YAG crystal; an energy source to excite the medium, commonly a Krypton flash lamp; and an optical resonator, or chamber containing parallel mirrors to amplify the laser effect.

Changing the lasing medium will change the characteristic of the laser light by altering the wavelength produced, each wavelength having specific properties and tissue effects, generally determined by experimentation.

The common laser pointer is prepared using a helium neon 630 nanometer wavelength laser (visible), neodymium:YAG is 1064 nanometers, in the infrared spectrum which commonly penetrates 4-6 mm in avascular tissue. Holmium:YAG at 2100 nanometers is in the near infrared(invisible) with a depth of penetration of 0.5 mm in avascular tissue, and carbon dioxide at 10,600 nanometers in the far infrared penetrates approximately 0.2 mm in tissue.

Applications
Laser light is just one form of energy, in this case photons. When absorbed by tissue, the light energy is converted to heat energy much like the sun when illuminating the earth. This will then raise the tissue temperature; it is ultimately the thermal effect of the laser energy which produces the surgical effect we see rather than a specific unique characteristic of the laser beam itself.

Laser tissue interaction may cause reflection, scattering, transmission, conduction or absorption. The visible effect we see of the laser is, therefore, to cut, coagulate or vaporize.

The laser tissue effect of most interest medically is that of absorption. Tissue absorption is dependent upon the type of laser utilized and the characteristics of the tissues to which it is exposed. Laser impact on tissue can instantly boil the intracellular water by heat transfer, causing a cellular explosion such as seen with tissue ablation.

The effect of a laser beam on given tissue can be varied by adjusting the laser energy, the spot size and the exposure time or dwell. The correct exposure time for desired tissue effect is controlled by the operator and generally learned by experience.

The combination of spot size (beam diameter) and laser energy, is expressed as joules/cm2, or "energy density." The energy density varies directly with the energy level and adversely with the spot size or will vary inversely with the square of the beam diameter. Energy density is one of the most important operating parameters to understand at a given wavelength and reflects the amount of energy actually delivered per unit area.

The development of pulsed as opposed to continuous laser application of energy allows the operator optimized specific tissue effects and minimizing thermal damage. The pulse frequency can vary from 150 to 350 nanoseconds which optimizes tissue absorption and minimizes char or burning by eliminating the amount of heat delivered at any one time.

The delivery of laser energy can be via free beam (noncontact) or direct contact (hot tip). Contact tips commonly will accumulate debris upon them which block the laser energy and ultimately lead to a cautery tip effect. The Holmium YAG is produced as a free beam unit.

A wavelength useful in orthopaedics today is that of the Holmium 2.1 laser, an invisible beam of light in the infrared zone of radiation directed by a helium neon visible aiming beam aligned with the treatment beam.

The Holmium 2.1 laser is well-absorbed by water and because of this absorption when the beam is fired a small amount of laser energy at the tip of the free beam will boil immediate water adjacent to it (in an aqueous medium) creating a vapor bubble, which allows the laser energy to pass through this bubble and reach the tissues to be absorbed. Although the 2.1 Holmium laser is used in a contact mode, it is actually a free beam spaced back slightly from the tip of the probe, to operate as described.

The common settings for the Holmium 2.1 laser: pulse power is 0-6 kilowatts, pulse duration of 100-350 nanoseconds, energy level of 0.6-2.0 joules/pulse, repetition rate of 8-20 per second (hertz) and a spot size of 0.5 mm. Application of thermal energy from the Holmium YAG laser will commonly produce thermal damage in an area of 25-50 microns with an area of adjacent thermal change from 250-300 microns with a normal depth of penetration of approximately 0.5 mm.

Laser Controversy
AANA Advisory Statement 1993:

AANA recognizes that the use of lasers in arthroscopic surgery is an alternative to mechanical techniques. There is no proven advantage of laser techniques over other techniques. There is, however, the issue of cost effectiveness to be considered.

Common Opinion
The laser has been called "the most expensive solution to a nonproblem."

The history of laser use in arthroscopy has been quite controversial, clouded by both anecdotal clinical reports both pro and con and coupled with the high cost and potential for advertising, marketing, promotion and abuse, has led many to adopt a "wait and see" position, while the public continues to enthusiastically embrace the concept of "laser surgery," which by definition MUST BE BETTER.

Orthopaedic Laser Applications
The specific characteristics of the Holmium 2.1 laser allow it to be a useful adjunct to arthroscopy. It is best used for the ablation of hypertrophic synovium such as with synovectomy utilizing it's characteristics to both ablate tissue and create hemostasis.

The laser in the shoulder, however, has been applied in the subacromial space and glenohumeral joint for the debridement of labral lesions, release of the coracoacromial ligament and chondroplasty.

The clinical results and benefits, however, have not been demonstrated as superior to conventional cautery and mechanical techniques, making the high cost and safety use issues hard to justify in most facilities. Fanton2 has reported "Treatment of Impingement Syndrome in the Left Shoulder and Torn Glenoid Labrum Using the VersaPulse® Surgical Laser: A Case Report." He described the apparent hemostatic benefits while continuing to use conventional mechanical devices to assist and complete the procedure.

Carbon dioxide laser has largely been abandoned due to the problems in maintaining gas environment in the shoulder for any period of time and the potential problems of fatal gas emboli as well as subcutaneous emphysema.

Fanton and Dillingham3 (1995) reported their experience in "2.1 nanometer Holmium:YAG Arthroscopic Laser Surgery of the Shoulder" article describing over 200 arthroscopic shoulder surgical procedures and a minimal of 24 months follow-up. They noted, "95% percent of the patients expressed satisfaction with the procedures," but also noted, "The benefits of its use intraoperative and high patient satisfaction justifies continued application. However, direct comparison studies with mechanical techniques are needed."

Laser Assisted Capsular Reduction (LACS)
Anecdotal reports of laser treatment for glenohumeral instability which "shrinks" the capsular tissue of the shoulder has led to the development of the phrase "laser assisted capsular shift" (LACS), a laser induced change in the morphological characteristics of the shoulder capsule dependent upon the laser used, time exposed and intensity of the heat exposure.

It should be remembered that the laws of thermodynamics apply to laser tissue effects which are achieved through radiation and heat conduction. The transfer of energy by photons of light create a warming effect of the intracellular water and it is the amount of heat produced and its conduction through the tissues which becomes important.

Basic Science
The shoulder capsule is composed of mostly type I collagen which normally contains a triple helical polypeptide stabilized by intramolecular and intermolecular bonds. Thermal energy application to this collagen molecule will disrupt the molecular bonds stabilizing the triple helix which leads to the decrease in the overall length of the molecule or "shrinkage." This shrinkage is associated with a DECREASE in capsular tissue tensile strength and an INCREASE in stiffness.

Tissue shrinkage commonly occurs in the narrow temperature range between 55-80 degrees centigrade, ideally between 60-70 degrees centigrade, but the shrinkage is tempered by the loss of biomechanical and tensile strength.

Vangsness Mitchell, et al.9, have reported it was the heat effect and not the laser effect alone which produced collagen shrinkage and that the shrinkage was precise and dose-related.

Naseff, et al.6, reported tissue shrinkage was dependent upon the temperature and time utilized. Tissue heated below 57 degrees centigrade did not shrink and over 75 degrees for five minutes showed complete loss of fibrillar structure and capsular architecture.

The Holmium YAG laser current thermal delivery system, however, has no specific feedback mechanism that exists for the surgeon to carefully identify the amount of heat exposure and temperature within the tissue for clear definition of the amount of collagen shrinkage which would be produced.

Hayashi, Markel, et al.5, (1995) reported the thermal effects on rabbit patellar tendon noted at seven days dead cells at the lased site and disrupted collagen lattice, however, noting at 30 days, the tissue remained shorter having been shrunk and suggestion of a healing response was noted.

Hayashi, Thabit, et al.4, (1995) reported the effects of the Holmium YAG laser on rabbit patellofemoral joint capsule and noted on electron microscopy the heat induced alteration of collagen fibular architecture seemed to produce the shrinkage as previously noted.

Shields, Tokito, et al.8, (1996) reported ten human cadaveric shoulder ligaments subjected to laser energy (5 watts and 10 hertz) and concluded in a lax model that laser energy at a non-ablative setting noting the strength and stiffness of the lased ligaments were only 24% and 40% of the intact ligaments.

In summarizing the presently available clinical basic science, the data seems to clearly demonstrate that the heat induced effect does alter the collagen architecture and capsular contracture does indeed occur. The control as to the degree and amount of shrinkage, however, becomes speculative and results generally are neither predictable or controllable in the true scientific sense. The healing response and the recovery of tissue following thermal damage is also unknown.

Clinical Series
The first clinical series of laser assisted capsular shrinkage was reported in 1993/1994 as a combined study of five orthopaedic practices using a Coherent lasers, the VersaPulse® Holmium laser. This multicenter study addressed unidirectional or multidirectional instability without evidence of Bankart lesions. The treatment parameters included 1 joule, 10 hertz defocused beam, tangential application with a 30 degree probe. The review prepared thereafter noted patients followed an average of six months with results reported as 93% good or excellent, 5% fair and 2% poor. Better results were noted in younger patients, subluxers did better than dislocators, and nondominant arms did better than dominant arms.

This article, however, was not peer reviewed.

Overall, application of laser energy to produce capsular shrinkage must be considered INVESTIGATIONAL since the ultimate fate of the tissue remains unknown (does it heal? does the shrinkage remain permanently?) and standardized studies with defined end point evaluations, standardized rehabilitation potentials and standardized outcome studies measuring function on both SF36 and joint specific studies have yet to be presented.

The ORATEC Company in Menlo Park, California has developed a surgical tool which heats tissue by using radio waves (RF) rather than a laser. This application of radio frequency will oscillate electrolytes in and around cells and produce a heating phenomenon which is controlled at the tip of the probe with a thermocouple constantly monitoring and adjusting the amount of energy supplied maintaining a narrow treatment range temperature of 67 degrees C. This probe has just been developed and has been coined the "ORATEC Tac Probe" and is designed for radio frequency capsular tightening procedures. This unit is still considered experimental and in the developmental stages; human and clinical trials have yet to be reported. The unit has demonstrated thermal change for a depth of 2 mm and a heat effect for 3 more millimeters. The approximate cost of the unit is anticipated to be $9,000.

Summary
Most surgeons, if they are using thermal capsular shrinkage techniques, are presently using lasers, the Holmium 2.1 in conjunction with established mechanical arthroscopic techniques. Multidirectional instability, however, has seemed a good candidate for laser application and currently Dr. Lonnie Paulos is conducting an ongoing clinical trial using laser thermal capsular management only to produce capsular shrinkage and manage shoulder pain in this population. Results have yet to be reported, and we await these results.

References

  1. Berend ME, Glisson RR, Seaber AV, Speer, et al. Soft tissue shortening with the Ho:YAG laser: Experimental model, structural effects, and histologic and ultrastructural analysis. Am J Sports Med. In press.
  2. Fanton, GS. Treatment of impingement syndrome of the left shoulder and torn glenoid labrum using the VersaPulse® surgical laser: A case report. Update in Orthopaedic Laser Surgery. 1991:2(4).
  3. Fanton, GS, Dillingham MF. 2.1 mm Holmium:YAG arthroscopic laser surgery of the shoulder. In: Brillhart A, ed. Arthroscopic Laser Surgery. New York: Springer-Verlag; 1995:239-251.
  4. Hayashi K, Markel MD, Thabit G, Bogdanske JJ, Thielke RJ. The effect of non-ablative laser energy on joint capsular properties: An in vitro mechanical study using a rabbit model. Am J Sports Med 1995; 23:482-487.
  5. Hayashi K, Markel MD, Thabit G, Bogdanske JJ, Thielke RJ. The effect of non-ablative laser energy on the ultrastructure of joint capsular collagen. Arthroscopy 1996; 12:474-481.
  6. Naseff G, Foster TE, Solhpon BA, Zarns B. The thermal properties of Type I collagen: The basis science of the laser assisted capsular shift. Presented at AANA 1st Annual, December 1996.
  7. Selecky MT, Vangsness CT, Hedman TP, Liao WL, Saadat V. The effects of laser induced collagen shortening on the biomechanical properties of the inferior glenohumeral ligament complex. 1996. In press.
  8. Shields CL, Tokito SE, Park SH. Efficacy of laser treatment on a "pathologically-induced" lax ligament model. Presented at Tahoe Sports Medicine, December 1996.
  9. Vangsness CT, Mitchell W, Saadat V, Nimni M, Schmotzer H. Collagen shortening: An experimental approach with heat. CORR 1996. In press.