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The holmium:YAG laserin knee arthroscopy
THE HOLMIUM:YAG LASER IN KNEE ARTHROSCOPY BENJAMIN SHAFFER, MD
The Holmium:YAG (Ho:YAG) laser is effective in the arthroscopic treatment of common knee conditions, including resection of inaccessible posterior meniscal tears, smoothing irregular chondral disease, and ablation of hypertrophic synovium. Understanding the multiple parameters that influence energy delivery will facilitate appropriate and effective use of the laser. Clinical outcome data does not demonstrate the laser to be superior to mechanical instrumentation. Complications of osteonecrosis and chondral sloughing have been reported after use of the holmium laser, but critical review suggests these may be a consequence of inappropriate surgical technique rather than the laser itself. When used properly, the holmium laser is safe and provides a convenient and multipurpose tool in the arthroscopic treatment of common conditions of the knee. KEY WORDS: knee, arthroscopy, laser, holmium, meniscectomy
With its clinical introduction in the late 1980s, use of the holmium laser garnered enthusiastic application for arthroscopically treating a variety of common knee disorders, including meniscal, chondral, and synovial pathologic conditions. 1-7 The use of a single tool that, depending on specific setting and technique of use, could ablate, contour, caul:erize, or shrink tissue held widespread appeal, but, with the emergence of reports linking use of the laser to osteonecrosis and chondral sloughing 8-1° and the introduction of alternative thermal devices, interest in the laser has waned. Nevertheless, it continues to be useful clinically. The purpose of this article is to review the potential advantages, operative techniques, clinical indications and outcomes, and reported complications associated with use of the Holmium:YAG (Ho:YAG) laser during knee arthroscopy.
WHY HOLMIUMI? THE HOLMIUM:YAG LASER The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. When applied to any tissue or surface, this light energy can be reflected, transmitted, scattered, or absorbed. In principle, the greater the absorption of light by the target tissue, the more precise and efficient the intended effect. In practice, the evolution of laser technology has been based on developing lasers with wavelengths that are optimally absorbed by the musculoskeletal tissues, including the CO2, the neodynium, and the holmium lasers. Lasers must achieve energy levels that are sufficient to achieve tissue ablation while minimizing collateral thermal damage to adjacent tissues. The laser must also be From the Department of Orthopaedics, Georgetown University Medical Center, Washington, DC. Address reprint requests to Benjamin Shaffer, MD, Department of Orthopaedics, Georgetown UniversityMedical Center, 3800 Reservoir Rd, NW, Washington, DC 20007. Copyright © 1998 by W.B. Saunders Company 1060-1872/98/0603-000658.00/0
deliverable by reliable fiberoptic technology in an arthroscopic environment. The Ho:YAG laser is the only laser that is capable of achieving all of these goals and for that reason is the only laser currently of practical value in knee arthroscopy. Named for the rare element holmium, into which crystals of yttrium, argon, and garnet have been doped, the Ho:YAG laser generates a wavelength of 2.1 ~m, which is well absorbed by water and easily transmitted by fiberoptic delivery systems. Since the late 1980s it has served as the definitive laser tool used in arthroscopic surgery.
POTENTIAL ADVANTAGES OF THE HOLMIUM:YAG LASER There are three potential advantages to the Holmium laser. The greatest is the ability to treat certain conditions that have not been otherwise treatable with conventional arthroscopic instrumentation. These include some meniscus tears, partial-thickness chondral damage, and synovial disease.
Articular Cartilage The lack of regenerative potential in treating partial thickness chondral lesions is well documented. ~1,12Traditional methods of mechanical debridement, with removal of generous amounts of both pathologic and healthy surrounding tissue, have been practiced routinely, with little concern about collateral damage. Treatment of partialthickness chondral damage (Outerbridge grades II and III) with laser technology seems advantageous. Instead of relying on conventional mechanical shavers to convert irregular chondral surfaces from long to short hair, or having to remove healthy surrounding normal cartilage to stabilize some lesions, laser debridement allows smoothing and contouring of the chondral surface and sealing of fissures or cracks. It may even be more selective in removal of pathologic chondromalacic tissue, which has been shown to have a greater content of water compared to normal cartilage.
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Meniscus Some meniscus tears are difficult to remove. In the posterior body and horn, access, even with small mechanical instruments, may be compromised, leading to inadequate resection, iatrogenic chondral scuffing, or both. The small 1.7-mm diameter laser tip facilitates entry into the occasionally tight and inaccessible areas of the posterior medial meniscus and horn, allowing successful excision and contouring with less chance of iatrogenic fingerprinting.
Synovial Disorders The laser probe can both ablate tissue and achieve hemostasis and do so without requiring pinpoint targeting of bleeding vessels. This prevents constant arthroscopic equipment exchange and reduces procedure time.
OTHER ADVANTAGES The Ho:YAG laser is a multipurpose tool and can ablate, cut, contour, shrink, and cauterize tissue. In the stand-by mode, it provides tactile feedback as a probe, preventing redundant instrument introduction and exchange. It also offers surgical precision. With a spot beam of 0.4 mm, the surgical cut is potentially more precise than that achieved with mechanical instrumentation. According to several studies, the depth of thermal injury is limited to 0.6 ram, with minimal damage to adjacent tissues. 13,14More recent research suggests that the extent of thermal injury may in fact be greater. 15-17
OPERATIVE TECHNIQUE-GENERAL COMMENTS Using the laser is relatively simple, but requires attention to precautionary details. Before use, the surgeon must be certified in a laser safety course. Protection from eye injury mandates prophylactic eyewear by everyone in the surgical suite, including the patient. The basic instrumentation includes the laser generator and the probes, which are either reusable or disposable. A variety of different angle tips are available, including 0 °, 15°, 30 °, and 70 ° handpieces (Fig 1). Selection is to some degree individual and depends on the location, accessibility, type of tissue targeted, and the intended effect (ablation, contouring, or hemostasis). The tissue effect is influenced by four factors: energy setting, frequency setting, probe-target tissue distance, and the duration of energy application.
ENERGY SETTING--JOULES The laser must be preset to a specific amount of energ~ measured in joules (J). The selected setting is dictated by the effect desired. For example, lower energy settings (such as 1 J) are effective in heating tissue for the purposes of shrinkage or hemostasis, whereas higher settings (2 J and higher) are chosen for tissue ablation (Table 1). Current laser models are powerful enough to generate more than sufficient energy for any arthroscopic application.
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Fig 1. Laser probes are available in a variety of angles. This photo shows the straight (0 °) and 30 ° angle tips. Note their small size (1,7 mm diameter tip),
ENERGY SETTINGmHERTZ The laser must also be set for the rate of energy delivery, measured in pulses per second and known as hertz (Hz). This parameter determines the speed of delivery and ranges from a slow, deliberate thermal effect (eg, 10 Hz used during hemostasis) to rapid energy delivery (20 Hz during synovial ablation). I will usually begin at a slower speed, particularly when precision is critical (tight posterior hom meniscus tear), setting the rate at 5 to 10 Hz. Conversely, when ablating easily targeted tissue, I will adjust the rate to a higher setting (20hz) to more efficiently remove tissue. Early in the learning curve, using the laser on a lower "speed" will prevent inadvertent delivery of too much energy too quickly. As the comfort level with using the laser increases, the frequency can be increased.
ENERGY SETTINGmPROBE-TO-TARGET TISSUE DISTANCE By setting the energy and frequency levels, the amount of energy available has been established. But this is not the same as the amount of energy delivered to the tissue. The amount of energy imparted is also significantly influenced by two other factors, one of which is the laser probe's proximity to the target tissue. The energy density (the actual calculated energy seen by the affected tissue) has been shown to be exponentially affected by this target distance. The closer to the tissue, the higher the energy delivered. The highest energy delivery occurs when the laser is used in the contact mode, during which the laser probe is in actual physical contact with the target tissue, TABLE 1. Guidelines for Energy Settings in Use of Holmium:YAG Laser During Knee Arthroscopy Intended Tissue Effect
Energy (J)
Frequency ( H z )
Cut Ablate Coagulate Smooth/Contour
1.6-3.0 1,8-3.0 0.8-1.0 1.4
10 10 16 16
Power (W) 16-30 18-30 12.8-16 22.4
BENJAMINSHAFFER
allowing tissue ablation or cutting. Conversely, the farther awa~ the more likely the energy will be absorbed by the surrounding irrigation fluid and have little or no thermal effect on the tissue. Such use is known as noncontact or defocused, because, with the probe away from the tissue and[ the beam not sharply focused, the energy actually delivered is much less and the "ablation threshold" usually not reached. This mode of delivery is effective for achieving hemosta sis and contouring tissues.
ENERGY SETTING--TIME OF APPLICATION Regardless of the level of energy set and the mode of application, the amount of heat energy imparted to the tissues will naturally depend on the amount of time the laser is in contact with the tissue. The laser is used until the goal of tissue ablal.~on or contouring has been achieved or desired tissue response is no longer elicited. Because tissue manipulation relies on the absorption of water, when the cells to which file laser is applied are vaporized or desiccated, there is no target tissue left for further manipulation. Continuing to lase in this circumstance invites carbonization of tissue and thermal transmission to adjacen'~ areas.
OPERATIVE TI--CHNIQUE Once the energy settings have been established, the selected laser probe is introduced gently into the knee. Ensure the soft tissue portal has been sufficiently established, using a clamp to open it up if necessary. The probe can easily get entangled in the portal's soft tissue, leading to inadvertent plunging and chondral damage, probe damage, or both. A disposable cannula allows easy introduction and removal of the laser probe, although I have not found this routinely necessary. As with any arthroscopic tool initial practice placing the instrument in the desired position is a reasonable and appropriate step. Particularly with the laser, performing this step first while the laser is still in the "stand-by" mode will prevent accidental laser delivery to adjacent structures. Turning on the red guide beam (inert helium argon laser) that parallels; the otherwise invisible Holmium laser can help targeting as well. When ready to proceed, turn the laser from stand by to active mode and begin the delivery of laser energy. Regardless of the intended, target tissue, remember to always start the laser at least 4 to 5 mm away from the tissue. When the laser is fired, a small vapor bubble forms at the tip of the probe. If the bubble cannot form because it is surrounded by or against tissue, the probe may flame out and be damaged. Althoug!h not dangerous, it does deliver energy in an imprecise manner, and is expensive to replace the subsequently ineffectual probe, which will no longer deliver energy in a precise fashion. The probe is then advanced towards the target tissue and used in either a contact (directly touching tissue) or "noncontact" mode (probe is maintained at a distance of up to several millimeters from the tissue). In general the contact mode is most useful during tissue ablation (menis-
THE HOLMIUM:YAG LASER IN KNEE ARTHROSCOPY
cus and synovium). The noncontact defocused mode is useful for tissue contouring (such as in meniscus and chondral sculpting) and synovial hemostasis.
SPECIFIC INDICATIONS AND OPERATIVE TECHNIQUE Brillhart 1provided the first published broad indications for use of the laser during arthroscopic surgery of the knee. However, these remain somewhat empiric, and there are no universally agreed-upon criteria. Indications depend on perceptions of convenience, decreased morbidity, and experience rather than scientifically proven data.
Meniscus I do not routinely use the laser for arthroscopic meniscectomies, although one can do so. Removal with standard mechanical instrumentation is effective in most cases. I reserve use of the laser during meniscal work for two specific circumstances: a tight posterior b o d y / h o r n tear and a symptomatic discoid meniscus. Arthroscopic resection of a torn medial meniscus in a tight knee jeopardizes the chondral surfaces and challenges even experienced arthroscopists who are using small instrumentation. The laser probe's small size (1.7 mm tip diameter) facilitates posteromedial access. If I am unable to remove or properly debride a torn meniscus in a tight compartment, I use a laser. Using a 15 ° or 30 ° probe, with the energy set on 1.5 to 2.0 J and 10 to 15 Hz, I will start away from the meniscus, advance toward it, and in a contact mode, resect the torn fragment(s). I will then decrease the energy setting to 1.5 J and in a more defocused (noncontact) mode sculpt the meniscal remnant (Fig 2). I have also found the laser useful during contouring of a symptomatic discoid lateral meniscus after mechanical resection. Articular
Cartilage
The laser is useful in treating partial-thickness chondral disease. In partial-thickness chondral disease (Outerbridge grade II or III lesions), the laser can stabilize and smoothly contour the irregular and loose chondral surface better than its mechanical counterparts. I first use mechanical instruments and a shaver to debulk the loose debris and then use the laser for touch-up work. Set on 1.5 to 1.8 J, the laser must be used in a noncontact mode, the probe just close enough to elicit a response. Inappropriate proximity or persistence after tissue response will be penalized by a plasma flash, in which normal cartilage will light up. The angle at which the tip delivers the beam is also an important consideration. Although any angle probe can be effective, the energy should be delivered tangentially to the chondral surface. For this reason, I prefer a 30 ° tip introduced through an inferomedial or parapatellar portal. By keeping the guide beam on, you can see the targeting effect and maintain a safe distance from the surface. By observing the tissue response to the laser energy as you approach the chondral surface, you can visually titrate the area to be targeted and the duration of treatment (Fig 3).
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Fig 2. (A) A probe anteriorly translates a complex tear of the posterior body and horn of a medial meniscus. The medial compartment was tight and barely permitted excision of the body, Access to the posterior horn was difficult. (B) This view of the posterior horn shows the small 1,7-mm diameter laser tip being used in a noncontact mode to smooth the posterior horn remnant not accesible with conventional instrumentation. The red guide light is an inert argon beam useful in targeting,
The laser is also effective in stabilizing the periphery of full-thickness lesions, in which there is progressive delamination, like paint peeling from a wall. In such cases, I will use mechanical instruments to remove loose debris and then rely on the laser to smooth and seal the periphery of the lesion. I am careful not to apply the laser energy to the exposed subchondral bone itself.
Synovium/Retinaculum Although effective in removing proliferative synovium, fat pad, and soft tissue, the laser is inefficient by itself and is used in conjunction with mechanical shaving. The laser is a very effective tool for achieving hemostasis. In the noncontact mode, with the energy set at 1.0 J, the affected synovium can be "spray painted" with obvious blanching as the vascularized synovium is essentially cauterized over a widespread area. After this maneuver is performed, the laser energy can be increased to a level of 2 to 3 J and the tissue ablated (Fig 4). However, debulking considerable amounts of synovium is inefficient with the laser, despite its substantial power. The generated plume of vaporized debris requires irrigation and clearance anyway, usually with a mechanical shaver. First I use the laser to achieve hemostasis, and then I use the shaver to debulk the synovium. I have found this technique to be very effective for performing a substantial synovectomy without requiring tourniquet inflation or resulting in postoperative hemarthroses. The advantage of the broad application of energy to achieve hemostasis rather than the pinpoint direct contact mode required when using other thermal devices is striking in these cases. The laser can also be used for arthroscopic lateral release, achieving cutting and hemostasis simultaneously. Conventionally, with the scope positioned in the inferomedial portal the 70 ° laser can be used to directly release the retinaculum as it is withdrawn inferolaterally under direct visualization. I prefer to place the arthroscope superomedially and use a 0 ° or 15 ° probe through a small percutaneous midmedial parapatellar portal. Under direct visualization the lateral retinaculum is released. The energy setting is placed at 2.0 J at a rate of 15 to 20 Hz. The laser should be
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used in the contact mode. If defocused, the laser energy may shrink the tissue rather than ablate and release it.
OTHER LESS COMMON INDICATIONS Predictably, the laser has been tried for almost every conceivable application during knee arthroscopy, including notchplasty during anterior cruciate ligament reconstructions and osteophyte removal during debridement for arthritis. Although it is powerful enough to ablate bone, it is not particularly efficient at doing so because of the relatively low water content of bone (approximately 45%), which can result in heat transmission and thermal necrosis of bone. Such a potential has been demonstrated in a porcine m o d e l in which drill holes were made by the laser. ~s The holmium laser should not be used for drilling, ablating, or removing bone. Some surgeons have described using the laser to tighten up tissues, currently applicable in the treatment of shoulder laxity. Animal models with patellofemoral retinaculum have demonstrated a clear, dramatic, and reproducible shrinkage in response to laser energy. 19,2° This effect has been exploited in plicating the medial retinaculum in patients with patellofemoral instability and those with lax but intact anterior cruciate ligaments. Although appealing, no outcome data are available on either strategy.
CLINICAL OUTCOMES OF HOLMIUM:YAG LASER DURING KNEE ARTHROSCOPY Meniscus Little clinical data are available to corroborate claims of the Holmium laser's purported advantages. Several studies have examined the use of the laser in meniscectomy. In the first reported clinical outcome, Fanton and Dillingham claimed quicker recovery among patients randomized to the laser rather than the conventional group, a Lane et al were unable to confirm this in their comparative series. 3 Siebert et al, in a multicenter study involving 401 patients undergoing laser surgery for a variety of knee conditions, found no inherent advantage for meniscal lesions. 4
BENJAMIN SHAFFER
Articular Cartilage Pathology No comparison studies have been published regarding treatment with laser versus mechanical debridement. In their multicenter study, Siebert et al were unable to find any clinically detectable difference in outcome. 4 In a recent
review of 504 knee arthroscopies in which the laser was used to perform chondroplasties of the medial femoral condyle, 88% were satisfied. However, there was no control group, al Lateral Release Two studies have examined outcome following lateral release, with a split decision regarding the superiority of the laser. According to Shapiro et al, a retrospective review comparing use of the Holmium laser to cautery found significantly reduced morbidity in the laser group. 5 However, in a prospective study, Carter and Edinger found no clinical difference. 22 Synovitis With the exception of the retrospective multicenter review by Siebert, 4 no clinical studies have documented outcome after use of the laser for treatment of synovial disease. CONTRAINDICATIONS
Just as there are no absolutes in terms of appropriate clinical indications, there are few absolute contraindications and those that exist are based more on reason and experience than clinical or research outcomes. The contraindications are basically those in which thermal energy thwarts the biological process of healing, causes inadvertent soft tissue shrinkage, or potentially risks bone necrosis. The laser should not be used when treating meniscal lesions with healing potential on which vascularity depends. Ablation or cautery of such vascular access is an invitation to healing failure. The Holmium laser has not been shown to stimulate healing, and, because it compromises the endosteal blood supply (in addition to causing thermal necrosis), it should not be used in treating fullthickness chondral lesions. DISADVANTAGES/COMPLICATIONS
There are several disadvantages to the use of the laser. First, although it has proven useful in treating specific conditions (tight medial meniscus, chondromalacia, synovial hypertrophy), few studies corroborate its superiority over mechanical instrumentation. Its clinical benefits remain largely unproven. Second, the laser is expensive. There are additional costs incurred in using the (usually) disposable probes. Training of surgeons and nurses, and compliance with Occupational Safety and Health Administration safety standards, make use of the laser somewhat inconvenient. Third, several reports have been published
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Fig 4. (A) Marked proliferative synovium in the anteromedial region of the right knee in a 28-year-old patient with recurrent atraumatic effusions. (B) The same area as in Figure 4A, after ablation with the holmium laser and simultaneous hemostasis. This patient had inflammatory arthritis, which was confirmed by biopsy and histological examination.
i m p l i c a t i n g the laser in c a u s i n g either c h o n d r a l s l o u g h i n g o r o s t e o n e c r o s i s after its u s e in k n e e arthroscopy. 8-1°,23-25 Critical r e v i e w of e a c h of these articles reveals little scientific e v i d e n c e of a true direct relationship b e t w e e n u s e of the H o l m i u m laser a n d the d e v e l o p m e n t of these complications. H o w e v e r , o n e a n i m a l m o d e l h a s clearly s h o w n the d e v e l o p m e n t of t h e r m a l necrosis after the laser w a s u s e d to m a k e drill h o l e s in the bone. 18 W h e n u s e d properly, the H o l m i u m laser is a safe a n d effective tool. W h e n u s e d i m p r o p e r l y , it c a n be as d a n g e r o u s as a n y i n s t r u m e n t u s e d d u r i n g a r t h r o s c o p i c surgery.
SUMMARY The H o l m i u m laser is a n effective a n d m u l t i p u r p o s e tool, c a p a b l e of ablating, cutting, c o n t o u r i n g , a n d cauterizing. It has p r o v e n to be a n effective tool in the a r t h r o s c o p i c t r e a t m e n t of several c o m m o n k n e e conditions, i n c l u d i n g inaccessible p o s t e r i o r b o d y a n d h o r n m e n i s c a l tears, partial thickness c h o n d r a l disease, a n d s y n o v i a l h y p e r t r o p h y . U n d e r s t a n d i n g the v a r i o u s p a r a m e t e r s i n f l u e n c i n g delive r y of laser e n e r g y will facilitate its u s e d u r i n g k n e e arthroscopy. L i m i t e d clinical o u t c o m e d a t a d o n o t a p p e a r to p r o v e the s u p e r i o r i t y of the laser o v e r c o n v e n t i o n a l m e c h a n i c a l i n s t r u m e n t a t i o n . C o m p l i c a t i o n s h a v e b e e n rep o r t e d , b u t w h e n u s e d properly, the H o l m i u m laser is a n effective a n d safe a d j u n c t in a r t h r o s c o p i c s u r g e r y of the knee.
REFERENCES 1. Brillhart AT:Avascular Necrosis, Chondrolysis, Hemarthrosis, Synovitis, and Arthroscopic Laser Surgery. Tech Orthop 10:346-351, 1995 2. Fanton GS, Dillingham MF: The use of the holmium laser in arthroscopic surgery. Seminars in Orthopaedics 7:113, 1992 3. Lane GJ, Sherk HH, Mooar PA, et al: Holmium:YAG laser versus carbon dioxide laser versus mechanical arthroscopic debridement. Seminars in Orthopaedics 7:95-101, 1992
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4. Siebert WE, Saunier J, Gerber B, et al: Two-year follow-up results of arthroscopic laser surgery of the knee: European multicenter study. Tech Orthop 10:309-317, 1995 5. Shaprio GS, Fanton GS, Dillingham MF, et al: Lateral retinacular release: The Holmium:YAG laser versus electrocautery. Clin Orthop 310:42-47,1995 6. Abelow SP: Use of lasers in orthopedic surgery: Current concepts. Orthopedics 16:551-556, 1993 7. Dillingham MF, Price JM, Fanton GS: Holmium laser surgery. Orthopedics 16:563-566, 1993 8. Garino JP, Lotke PA, Sapega AA, et al: Osteonecrosis of the knee diagnosed following laser-assisted arthroscopic surgery: A report of six cases. Arthroscopy 11:467-474, 1995 9. Fink B, Schneider T, Braunstein S, et al: Holmium:YAG laser-induced aseptic bone necrosis of the femoral condyle. Arthroscopy 12:217-223, 1996 10. Thal R, Danziger MB, Kelly A: Delayed articular cartilage slough: Two cases resulting from Holminm:YAG laser damage to normal articular cartilage and a review of the literature. Arthroscopy 12:92-94, 1996 11. Newman AP: Current concepts: Articular cartilage repair. AJSM 26:309-324, 1998 12. Campbell CJ: The healing of cartilage defects. CORR 64:45-63, 1969 13. Sherk HH, Black JD, Prodoehl, JA, et al: The effects of lasers and electrosurgical devices on human meniscal tissue. CORR 310:14-20, 1995 14. Vangsness CT, Ghaderi B, Brustein M, et al: Ablation rates of human meniscal tissue with the Ho:YAG laser: The effects of varying fluences. Arthroscopy 13:148-150, 1997 15. Lane JG, Amiel ME, Moosov AZ, et al: Matrix assessment of the articular cartilage surface after chondroplasty with the Holmium: YAG laser. Am J Sports Med 25:560-569, 1997 16. Bernard M, Grothues-Spork M, Hertel P, et al: Reactions of meniscal tissue after arthroscopic laser application: An in vivo study using five different laser systems. Arthroscopy 12:441-451, 1996 17. Trauner KB, Nishioka NS, Flotte T, et al: Acute and chronic response of articular cartilage to Holmium:YAG laser irradiation. CORR 310:52-57, 1995 18. Truaner KB, Parekh S, Naseef G, et al: Ho:YAG laser-induced osteonecrosis in a porcine model. Presented at the 23rd Annual Meeting of the AOSSM; Sun Valley, Idaho June 24,1997 19. Hayashi K, Markel MD, Thabit IlI G, et al: The effect of nonablative laser energy on joint capsular properties: An in vitro mechanical study using a rabbit model. AJSM 23:482-487, 1995
BENJAMIN SHAFFER
20. Hayashi K, Thabit III G, Vailas AC, et al: The effect of nonablative laser energy on joint capsular properties: An in vitro histologic and biochemical study using a rabbit model. AJSM 24:640-646, 1996 21. Janecki C, Perry M, Bonati A, et al: Safe parameters for laser chondroplasty of the knee. Presented at 17th annual meeting of the Arthroscopy Association of North America, Orlando, FL, April 30, 1998 6 22. Carter TR, Edinger SK: Arthroscopic lateral release of the knee: ]-tolmium laser vs. electrocautery. Presented at American Orthopedic Society for Sports Medicine Specialty Day, Atlanta, GA, February 25, 1996
THE HOLMIUM:YAG LASER IN KNEE ARTHROSCOPY
23. Rozbruch SR, Wickiewicz TL, DiCarlo EE et al: Osteonecrosis of the knee following arthroscopoic laser rneniscectomy.Arthroscopy 12:245250, 1996 24. Drucker M, Forman S, Venuto R, et al: Osteonecrosis of the knee following conventional and laser-assisted arthroscopy. Presented at the 15th Annual AANA Meeting, Washington, DC, April 14, 1996 Published in Arthroscopy, Vol. 12, No. 3, June, 1996, pp. 375-376. 25. Bonutti PM, Gray T, Stewart D: Osteonecrosis and chondrolysis after arthroscopic laser chondroplasty of the knee. Presented at the International Society of Arthroscop~ Knee Surgery and Orthopaedic Sports Medicine, Buenos Aires, Argentina, May 1997
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The Holmium:YAG (Ho:YAG) laser is effective in the arthroscopic treatment of common knee conditions, including resection of inaccessible posterior meniscal tears, smoothing irregular chondral disease, and ablation of hypertrophic synovium. Understanding the multiple parameters that influence energy delivery will facilitate appropriate and effective use of the laser. Clinical outcome data does not demonstrate the laser to be superior to mechanical instrumentation. Complications of osteonecrosis and chondral sloughing have been reported after use of the holmium laser, but critical review suggests these may be a consequence of inappropriate surgical technique rather than the laser itself. When used properly, the holmium laser is safe and provides a convenient and multipurpose tool in the arthroscopic treatment of common conditions of the knee. KEY WORDS: knee, arthroscopy, laser, holmium, meniscectomy
With its clinical introduction in the late 1980s, use of the holmium laser garnered enthusiastic application for arthroscopically treating a variety of common knee disorders, including meniscal, chondral, and synovial pathologic conditions. 1-7 The use of a single tool that, depending on specific setting and technique of use, could ablate, contour, caul:erize, or shrink tissue held widespread appeal, but, with the emergence of reports linking use of the laser to osteonecrosis and chondral sloughing 8-1° and the introduction of alternative thermal devices, interest in the laser has waned. Nevertheless, it continues to be useful clinically. The purpose of this article is to review the potential advantages, operative techniques, clinical indications and outcomes, and reported complications associated with use of the Holmium:YAG (Ho:YAG) laser during knee arthroscopy.
WHY HOLMIUMI? THE HOLMIUM:YAG LASER The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. When applied to any tissue or surface, this light energy can be reflected, transmitted, scattered, or absorbed. In principle, the greater the absorption of light by the target tissue, the more precise and efficient the intended effect. In practice, the evolution of laser technology has been based on developing lasers with wavelengths that are optimally absorbed by the musculoskeletal tissues, including the CO2, the neodynium, and the holmium lasers. Lasers must achieve energy levels that are sufficient to achieve tissue ablation while minimizing collateral thermal damage to adjacent tissues. The laser must also be From the Department of Orthopaedics, Georgetown University Medical Center, Washington, DC. Address reprint requests to Benjamin Shaffer, MD, Department of Orthopaedics, Georgetown UniversityMedical Center, 3800 Reservoir Rd, NW, Washington, DC 20007. Copyright © 1998 by W.B. Saunders Company 1060-1872/98/0603-000658.00/0
deliverable by reliable fiberoptic technology in an arthroscopic environment. The Ho:YAG laser is the only laser that is capable of achieving all of these goals and for that reason is the only laser currently of practical value in knee arthroscopy. Named for the rare element holmium, into which crystals of yttrium, argon, and garnet have been doped, the Ho:YAG laser generates a wavelength of 2.1 ~m, which is well absorbed by water and easily transmitted by fiberoptic delivery systems. Since the late 1980s it has served as the definitive laser tool used in arthroscopic surgery.
POTENTIAL ADVANTAGES OF THE HOLMIUM:YAG LASER There are three potential advantages to the Holmium laser. The greatest is the ability to treat certain conditions that have not been otherwise treatable with conventional arthroscopic instrumentation. These include some meniscus tears, partial-thickness chondral damage, and synovial disease.
Articular Cartilage The lack of regenerative potential in treating partial thickness chondral lesions is well documented. ~1,12Traditional methods of mechanical debridement, with removal of generous amounts of both pathologic and healthy surrounding tissue, have been practiced routinely, with little concern about collateral damage. Treatment of partialthickness chondral damage (Outerbridge grades II and III) with laser technology seems advantageous. Instead of relying on conventional mechanical shavers to convert irregular chondral surfaces from long to short hair, or having to remove healthy surrounding normal cartilage to stabilize some lesions, laser debridement allows smoothing and contouring of the chondral surface and sealing of fissures or cracks. It may even be more selective in removal of pathologic chondromalacic tissue, which has been shown to have a greater content of water compared to normal cartilage.
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Meniscus Some meniscus tears are difficult to remove. In the posterior body and horn, access, even with small mechanical instruments, may be compromised, leading to inadequate resection, iatrogenic chondral scuffing, or both. The small 1.7-mm diameter laser tip facilitates entry into the occasionally tight and inaccessible areas of the posterior medial meniscus and horn, allowing successful excision and contouring with less chance of iatrogenic fingerprinting.
Synovial Disorders The laser probe can both ablate tissue and achieve hemostasis and do so without requiring pinpoint targeting of bleeding vessels. This prevents constant arthroscopic equipment exchange and reduces procedure time.
OTHER ADVANTAGES The Ho:YAG laser is a multipurpose tool and can ablate, cut, contour, shrink, and cauterize tissue. In the stand-by mode, it provides tactile feedback as a probe, preventing redundant instrument introduction and exchange. It also offers surgical precision. With a spot beam of 0.4 mm, the surgical cut is potentially more precise than that achieved with mechanical instrumentation. According to several studies, the depth of thermal injury is limited to 0.6 ram, with minimal damage to adjacent tissues. 13,14More recent research suggests that the extent of thermal injury may in fact be greater. 15-17
OPERATIVE TECHNIQUE-GENERAL COMMENTS Using the laser is relatively simple, but requires attention to precautionary details. Before use, the surgeon must be certified in a laser safety course. Protection from eye injury mandates prophylactic eyewear by everyone in the surgical suite, including the patient. The basic instrumentation includes the laser generator and the probes, which are either reusable or disposable. A variety of different angle tips are available, including 0 °, 15°, 30 °, and 70 ° handpieces (Fig 1). Selection is to some degree individual and depends on the location, accessibility, type of tissue targeted, and the intended effect (ablation, contouring, or hemostasis). The tissue effect is influenced by four factors: energy setting, frequency setting, probe-target tissue distance, and the duration of energy application.
ENERGY SETTING--JOULES The laser must be preset to a specific amount of energ~ measured in joules (J). The selected setting is dictated by the effect desired. For example, lower energy settings (such as 1 J) are effective in heating tissue for the purposes of shrinkage or hemostasis, whereas higher settings (2 J and higher) are chosen for tissue ablation (Table 1). Current laser models are powerful enough to generate more than sufficient energy for any arthroscopic application.
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Fig 1. Laser probes are available in a variety of angles. This photo shows the straight (0 °) and 30 ° angle tips. Note their small size (1,7 mm diameter tip),
ENERGY SETTINGmHERTZ The laser must also be set for the rate of energy delivery, measured in pulses per second and known as hertz (Hz). This parameter determines the speed of delivery and ranges from a slow, deliberate thermal effect (eg, 10 Hz used during hemostasis) to rapid energy delivery (20 Hz during synovial ablation). I will usually begin at a slower speed, particularly when precision is critical (tight posterior hom meniscus tear), setting the rate at 5 to 10 Hz. Conversely, when ablating easily targeted tissue, I will adjust the rate to a higher setting (20hz) to more efficiently remove tissue. Early in the learning curve, using the laser on a lower "speed" will prevent inadvertent delivery of too much energy too quickly. As the comfort level with using the laser increases, the frequency can be increased.
ENERGY SETTINGmPROBE-TO-TARGET TISSUE DISTANCE By setting the energy and frequency levels, the amount of energy available has been established. But this is not the same as the amount of energy delivered to the tissue. The amount of energy imparted is also significantly influenced by two other factors, one of which is the laser probe's proximity to the target tissue. The energy density (the actual calculated energy seen by the affected tissue) has been shown to be exponentially affected by this target distance. The closer to the tissue, the higher the energy delivered. The highest energy delivery occurs when the laser is used in the contact mode, during which the laser probe is in actual physical contact with the target tissue, TABLE 1. Guidelines for Energy Settings in Use of Holmium:YAG Laser During Knee Arthroscopy Intended Tissue Effect
Energy (J)
Frequency ( H z )
Cut Ablate Coagulate Smooth/Contour
1.6-3.0 1,8-3.0 0.8-1.0 1.4
10 10 16 16
Power (W) 16-30 18-30 12.8-16 22.4
BENJAMINSHAFFER
allowing tissue ablation or cutting. Conversely, the farther awa~ the more likely the energy will be absorbed by the surrounding irrigation fluid and have little or no thermal effect on the tissue. Such use is known as noncontact or defocused, because, with the probe away from the tissue and[ the beam not sharply focused, the energy actually delivered is much less and the "ablation threshold" usually not reached. This mode of delivery is effective for achieving hemosta sis and contouring tissues.
ENERGY SETTING--TIME OF APPLICATION Regardless of the level of energy set and the mode of application, the amount of heat energy imparted to the tissues will naturally depend on the amount of time the laser is in contact with the tissue. The laser is used until the goal of tissue ablal.~on or contouring has been achieved or desired tissue response is no longer elicited. Because tissue manipulation relies on the absorption of water, when the cells to which file laser is applied are vaporized or desiccated, there is no target tissue left for further manipulation. Continuing to lase in this circumstance invites carbonization of tissue and thermal transmission to adjacen'~ areas.
OPERATIVE TI--CHNIQUE Once the energy settings have been established, the selected laser probe is introduced gently into the knee. Ensure the soft tissue portal has been sufficiently established, using a clamp to open it up if necessary. The probe can easily get entangled in the portal's soft tissue, leading to inadvertent plunging and chondral damage, probe damage, or both. A disposable cannula allows easy introduction and removal of the laser probe, although I have not found this routinely necessary. As with any arthroscopic tool initial practice placing the instrument in the desired position is a reasonable and appropriate step. Particularly with the laser, performing this step first while the laser is still in the "stand-by" mode will prevent accidental laser delivery to adjacent structures. Turning on the red guide beam (inert helium argon laser) that parallels; the otherwise invisible Holmium laser can help targeting as well. When ready to proceed, turn the laser from stand by to active mode and begin the delivery of laser energy. Regardless of the intended, target tissue, remember to always start the laser at least 4 to 5 mm away from the tissue. When the laser is fired, a small vapor bubble forms at the tip of the probe. If the bubble cannot form because it is surrounded by or against tissue, the probe may flame out and be damaged. Althoug!h not dangerous, it does deliver energy in an imprecise manner, and is expensive to replace the subsequently ineffectual probe, which will no longer deliver energy in a precise fashion. The probe is then advanced towards the target tissue and used in either a contact (directly touching tissue) or "noncontact" mode (probe is maintained at a distance of up to several millimeters from the tissue). In general the contact mode is most useful during tissue ablation (menis-
THE HOLMIUM:YAG LASER IN KNEE ARTHROSCOPY
cus and synovium). The noncontact defocused mode is useful for tissue contouring (such as in meniscus and chondral sculpting) and synovial hemostasis.
SPECIFIC INDICATIONS AND OPERATIVE TECHNIQUE Brillhart 1provided the first published broad indications for use of the laser during arthroscopic surgery of the knee. However, these remain somewhat empiric, and there are no universally agreed-upon criteria. Indications depend on perceptions of convenience, decreased morbidity, and experience rather than scientifically proven data.
Meniscus I do not routinely use the laser for arthroscopic meniscectomies, although one can do so. Removal with standard mechanical instrumentation is effective in most cases. I reserve use of the laser during meniscal work for two specific circumstances: a tight posterior b o d y / h o r n tear and a symptomatic discoid meniscus. Arthroscopic resection of a torn medial meniscus in a tight knee jeopardizes the chondral surfaces and challenges even experienced arthroscopists who are using small instrumentation. The laser probe's small size (1.7 mm tip diameter) facilitates posteromedial access. If I am unable to remove or properly debride a torn meniscus in a tight compartment, I use a laser. Using a 15 ° or 30 ° probe, with the energy set on 1.5 to 2.0 J and 10 to 15 Hz, I will start away from the meniscus, advance toward it, and in a contact mode, resect the torn fragment(s). I will then decrease the energy setting to 1.5 J and in a more defocused (noncontact) mode sculpt the meniscal remnant (Fig 2). I have also found the laser useful during contouring of a symptomatic discoid lateral meniscus after mechanical resection. Articular
Cartilage
The laser is useful in treating partial-thickness chondral disease. In partial-thickness chondral disease (Outerbridge grade II or III lesions), the laser can stabilize and smoothly contour the irregular and loose chondral surface better than its mechanical counterparts. I first use mechanical instruments and a shaver to debulk the loose debris and then use the laser for touch-up work. Set on 1.5 to 1.8 J, the laser must be used in a noncontact mode, the probe just close enough to elicit a response. Inappropriate proximity or persistence after tissue response will be penalized by a plasma flash, in which normal cartilage will light up. The angle at which the tip delivers the beam is also an important consideration. Although any angle probe can be effective, the energy should be delivered tangentially to the chondral surface. For this reason, I prefer a 30 ° tip introduced through an inferomedial or parapatellar portal. By keeping the guide beam on, you can see the targeting effect and maintain a safe distance from the surface. By observing the tissue response to the laser energy as you approach the chondral surface, you can visually titrate the area to be targeted and the duration of treatment (Fig 3).
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Fig 2. (A) A probe anteriorly translates a complex tear of the posterior body and horn of a medial meniscus. The medial compartment was tight and barely permitted excision of the body, Access to the posterior horn was difficult. (B) This view of the posterior horn shows the small 1,7-mm diameter laser tip being used in a noncontact mode to smooth the posterior horn remnant not accesible with conventional instrumentation. The red guide light is an inert argon beam useful in targeting,
The laser is also effective in stabilizing the periphery of full-thickness lesions, in which there is progressive delamination, like paint peeling from a wall. In such cases, I will use mechanical instruments to remove loose debris and then rely on the laser to smooth and seal the periphery of the lesion. I am careful not to apply the laser energy to the exposed subchondral bone itself.
Synovium/Retinaculum Although effective in removing proliferative synovium, fat pad, and soft tissue, the laser is inefficient by itself and is used in conjunction with mechanical shaving. The laser is a very effective tool for achieving hemostasis. In the noncontact mode, with the energy set at 1.0 J, the affected synovium can be "spray painted" with obvious blanching as the vascularized synovium is essentially cauterized over a widespread area. After this maneuver is performed, the laser energy can be increased to a level of 2 to 3 J and the tissue ablated (Fig 4). However, debulking considerable amounts of synovium is inefficient with the laser, despite its substantial power. The generated plume of vaporized debris requires irrigation and clearance anyway, usually with a mechanical shaver. First I use the laser to achieve hemostasis, and then I use the shaver to debulk the synovium. I have found this technique to be very effective for performing a substantial synovectomy without requiring tourniquet inflation or resulting in postoperative hemarthroses. The advantage of the broad application of energy to achieve hemostasis rather than the pinpoint direct contact mode required when using other thermal devices is striking in these cases. The laser can also be used for arthroscopic lateral release, achieving cutting and hemostasis simultaneously. Conventionally, with the scope positioned in the inferomedial portal the 70 ° laser can be used to directly release the retinaculum as it is withdrawn inferolaterally under direct visualization. I prefer to place the arthroscope superomedially and use a 0 ° or 15 ° probe through a small percutaneous midmedial parapatellar portal. Under direct visualization the lateral retinaculum is released. The energy setting is placed at 2.0 J at a rate of 15 to 20 Hz. The laser should be
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used in the contact mode. If defocused, the laser energy may shrink the tissue rather than ablate and release it.
OTHER LESS COMMON INDICATIONS Predictably, the laser has been tried for almost every conceivable application during knee arthroscopy, including notchplasty during anterior cruciate ligament reconstructions and osteophyte removal during debridement for arthritis. Although it is powerful enough to ablate bone, it is not particularly efficient at doing so because of the relatively low water content of bone (approximately 45%), which can result in heat transmission and thermal necrosis of bone. Such a potential has been demonstrated in a porcine m o d e l in which drill holes were made by the laser. ~s The holmium laser should not be used for drilling, ablating, or removing bone. Some surgeons have described using the laser to tighten up tissues, currently applicable in the treatment of shoulder laxity. Animal models with patellofemoral retinaculum have demonstrated a clear, dramatic, and reproducible shrinkage in response to laser energy. 19,2° This effect has been exploited in plicating the medial retinaculum in patients with patellofemoral instability and those with lax but intact anterior cruciate ligaments. Although appealing, no outcome data are available on either strategy.
CLINICAL OUTCOMES OF HOLMIUM:YAG LASER DURING KNEE ARTHROSCOPY Meniscus Little clinical data are available to corroborate claims of the Holmium laser's purported advantages. Several studies have examined the use of the laser in meniscectomy. In the first reported clinical outcome, Fanton and Dillingham claimed quicker recovery among patients randomized to the laser rather than the conventional group, a Lane et al were unable to confirm this in their comparative series. 3 Siebert et al, in a multicenter study involving 401 patients undergoing laser surgery for a variety of knee conditions, found no inherent advantage for meniscal lesions. 4
BENJAMIN SHAFFER
Articular Cartilage Pathology No comparison studies have been published regarding treatment with laser versus mechanical debridement. In their multicenter study, Siebert et al were unable to find any clinically detectable difference in outcome. 4 In a recent
review of 504 knee arthroscopies in which the laser was used to perform chondroplasties of the medial femoral condyle, 88% were satisfied. However, there was no control group, al Lateral Release Two studies have examined outcome following lateral release, with a split decision regarding the superiority of the laser. According to Shapiro et al, a retrospective review comparing use of the Holmium laser to cautery found significantly reduced morbidity in the laser group. 5 However, in a prospective study, Carter and Edinger found no clinical difference. 22 Synovitis With the exception of the retrospective multicenter review by Siebert, 4 no clinical studies have documented outcome after use of the laser for treatment of synovial disease. CONTRAINDICATIONS
Just as there are no absolutes in terms of appropriate clinical indications, there are few absolute contraindications and those that exist are based more on reason and experience than clinical or research outcomes. The contraindications are basically those in which thermal energy thwarts the biological process of healing, causes inadvertent soft tissue shrinkage, or potentially risks bone necrosis. The laser should not be used when treating meniscal lesions with healing potential on which vascularity depends. Ablation or cautery of such vascular access is an invitation to healing failure. The Holmium laser has not been shown to stimulate healing, and, because it compromises the endosteal blood supply (in addition to causing thermal necrosis), it should not be used in treating fullthickness chondral lesions. DISADVANTAGES/COMPLICATIONS
There are several disadvantages to the use of the laser. First, although it has proven useful in treating specific conditions (tight medial meniscus, chondromalacia, synovial hypertrophy), few studies corroborate its superiority over mechanical instrumentation. Its clinical benefits remain largely unproven. Second, the laser is expensive. There are additional costs incurred in using the (usually) disposable probes. Training of surgeons and nurses, and compliance with Occupational Safety and Health Administration safety standards, make use of the laser somewhat inconvenient. Third, several reports have been published
THE HOLMIUM:YAGLASER IN KNEEARTHROSCOPY
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Fig 4. (A) Marked proliferative synovium in the anteromedial region of the right knee in a 28-year-old patient with recurrent atraumatic effusions. (B) The same area as in Figure 4A, after ablation with the holmium laser and simultaneous hemostasis. This patient had inflammatory arthritis, which was confirmed by biopsy and histological examination.
i m p l i c a t i n g the laser in c a u s i n g either c h o n d r a l s l o u g h i n g o r o s t e o n e c r o s i s after its u s e in k n e e arthroscopy. 8-1°,23-25 Critical r e v i e w of e a c h of these articles reveals little scientific e v i d e n c e of a true direct relationship b e t w e e n u s e of the H o l m i u m laser a n d the d e v e l o p m e n t of these complications. H o w e v e r , o n e a n i m a l m o d e l h a s clearly s h o w n the d e v e l o p m e n t of t h e r m a l necrosis after the laser w a s u s e d to m a k e drill h o l e s in the bone. 18 W h e n u s e d properly, the H o l m i u m laser is a safe a n d effective tool. W h e n u s e d i m p r o p e r l y , it c a n be as d a n g e r o u s as a n y i n s t r u m e n t u s e d d u r i n g a r t h r o s c o p i c surgery.
SUMMARY The H o l m i u m laser is a n effective a n d m u l t i p u r p o s e tool, c a p a b l e of ablating, cutting, c o n t o u r i n g , a n d cauterizing. It has p r o v e n to be a n effective tool in the a r t h r o s c o p i c t r e a t m e n t of several c o m m o n k n e e conditions, i n c l u d i n g inaccessible p o s t e r i o r b o d y a n d h o r n m e n i s c a l tears, partial thickness c h o n d r a l disease, a n d s y n o v i a l h y p e r t r o p h y . U n d e r s t a n d i n g the v a r i o u s p a r a m e t e r s i n f l u e n c i n g delive r y of laser e n e r g y will facilitate its u s e d u r i n g k n e e arthroscopy. L i m i t e d clinical o u t c o m e d a t a d o n o t a p p e a r to p r o v e the s u p e r i o r i t y of the laser o v e r c o n v e n t i o n a l m e c h a n i c a l i n s t r u m e n t a t i o n . C o m p l i c a t i o n s h a v e b e e n rep o r t e d , b u t w h e n u s e d properly, the H o l m i u m laser is a n effective a n d safe a d j u n c t in a r t h r o s c o p i c s u r g e r y of the knee.
REFERENCES 1. Brillhart AT:Avascular Necrosis, Chondrolysis, Hemarthrosis, Synovitis, and Arthroscopic Laser Surgery. Tech Orthop 10:346-351, 1995 2. Fanton GS, Dillingham MF: The use of the holmium laser in arthroscopic surgery. Seminars in Orthopaedics 7:113, 1992 3. Lane GJ, Sherk HH, Mooar PA, et al: Holmium:YAG laser versus carbon dioxide laser versus mechanical arthroscopic debridement. Seminars in Orthopaedics 7:95-101, 1992
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4. Siebert WE, Saunier J, Gerber B, et al: Two-year follow-up results of arthroscopic laser surgery of the knee: European multicenter study. Tech Orthop 10:309-317, 1995 5. Shaprio GS, Fanton GS, Dillingham MF, et al: Lateral retinacular release: The Holmium:YAG laser versus electrocautery. Clin Orthop 310:42-47,1995 6. Abelow SP: Use of lasers in orthopedic surgery: Current concepts. Orthopedics 16:551-556, 1993 7. Dillingham MF, Price JM, Fanton GS: Holmium laser surgery. Orthopedics 16:563-566, 1993 8. Garino JP, Lotke PA, Sapega AA, et al: Osteonecrosis of the knee diagnosed following laser-assisted arthroscopic surgery: A report of six cases. Arthroscopy 11:467-474, 1995 9. Fink B, Schneider T, Braunstein S, et al: Holmium:YAG laser-induced aseptic bone necrosis of the femoral condyle. Arthroscopy 12:217-223, 1996 10. Thal R, Danziger MB, Kelly A: Delayed articular cartilage slough: Two cases resulting from Holminm:YAG laser damage to normal articular cartilage and a review of the literature. Arthroscopy 12:92-94, 1996 11. Newman AP: Current concepts: Articular cartilage repair. AJSM 26:309-324, 1998 12. Campbell CJ: The healing of cartilage defects. CORR 64:45-63, 1969 13. Sherk HH, Black JD, Prodoehl, JA, et al: The effects of lasers and electrosurgical devices on human meniscal tissue. CORR 310:14-20, 1995 14. Vangsness CT, Ghaderi B, Brustein M, et al: Ablation rates of human meniscal tissue with the Ho:YAG laser: The effects of varying fluences. Arthroscopy 13:148-150, 1997 15. Lane JG, Amiel ME, Moosov AZ, et al: Matrix assessment of the articular cartilage surface after chondroplasty with the Holmium: YAG laser. Am J Sports Med 25:560-569, 1997 16. Bernard M, Grothues-Spork M, Hertel P, et al: Reactions of meniscal tissue after arthroscopic laser application: An in vivo study using five different laser systems. Arthroscopy 12:441-451, 1996 17. Trauner KB, Nishioka NS, Flotte T, et al: Acute and chronic response of articular cartilage to Holmium:YAG laser irradiation. CORR 310:52-57, 1995 18. Truaner KB, Parekh S, Naseef G, et al: Ho:YAG laser-induced osteonecrosis in a porcine model. Presented at the 23rd Annual Meeting of the AOSSM; Sun Valley, Idaho June 24,1997 19. Hayashi K, Markel MD, Thabit IlI G, et al: The effect of nonablative laser energy on joint capsular properties: An in vitro mechanical study using a rabbit model. AJSM 23:482-487, 1995
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20. Hayashi K, Thabit III G, Vailas AC, et al: The effect of nonablative laser energy on joint capsular properties: An in vitro histologic and biochemical study using a rabbit model. AJSM 24:640-646, 1996 21. Janecki C, Perry M, Bonati A, et al: Safe parameters for laser chondroplasty of the knee. Presented at 17th annual meeting of the Arthroscopy Association of North America, Orlando, FL, April 30, 1998 6 22. Carter TR, Edinger SK: Arthroscopic lateral release of the knee: ]-tolmium laser vs. electrocautery. Presented at American Orthopedic Society for Sports Medicine Specialty Day, Atlanta, GA, February 25, 1996
THE HOLMIUM:YAG LASER IN KNEE ARTHROSCOPY
23. Rozbruch SR, Wickiewicz TL, DiCarlo EE et al: Osteonecrosis of the knee following arthroscopoic laser rneniscectomy.Arthroscopy 12:245250, 1996 24. Drucker M, Forman S, Venuto R, et al: Osteonecrosis of the knee following conventional and laser-assisted arthroscopy. Presented at the 15th Annual AANA Meeting, Washington, DC, April 14, 1996 Published in Arthroscopy, Vol. 12, No. 3, June, 1996, pp. 375-376. 25. Bonutti PM, Gray T, Stewart D: Osteonecrosis and chondrolysis after arthroscopic laser chondroplasty of the knee. Presented at the International Society of Arthroscop~ Knee Surgery and Orthopaedic Sports Medicine, Buenos Aires, Argentina, May 1997
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