Advances in Laser Technology

Two major potential drawbacks of conventional "cold steel" created slit recipient sites that have been voiced are graft compression and decreased hair density when comparable amounts of donor material are transplanted into recipient sites in which bald tissue is not removed.

1. With "cold steel", whether needle, knife or other sharp instruments, the slit recipient site represents a stab wound during which the skin merely "pops open", since recipient tissue is not removed. Laser assisted hair transplantation sought to address these shortcomings. Unfortunately, the "Laser" is often considered synonymous with the carbon dioxide (CO2) laser, which produces a significant thermal burn in the process of creating the recipient site. The advantage of the laser’s ability to rapidly create uniform recipient sites with less bleeding than conventional cold steel techniques has been overshadowed by the tissue injury it causes. This article will serve to introduce the reader to the Erbium: YAG Laser as a new means of creating recipient sites without the thermal consequences of CO2 lasers.
   
   The carbon dioxide laser was first invented by Bell Laboratories in 1964 and offered the advantage of hemostasis while "cutting." This laser emits light in the far infrared portion of the electromagnetic spectrum at 10, 600 nm, a wavelength that is highly absorbed by water. Because approximately 70% to 80% of skin tissue is composed of water, this absorption is nonspecific and is the basis for the use of the CO2 laser as a cutting tool. Cutting is achieved by focusing the CO2 laser beam to a 0.1 – 0.2-mm spot size, resulting in a focal impact generating temperatures > 300 degrees Celsius at the immediate zone of injury.
   
   
2. This results in various zones of thermal damage (burn wound) depending on the laser used. This burn wound creates a locus minoris resistensiae (an area of decreased resistance) in the skin, the skin "pops open" about this zone of thermal damage, and minimal amounts of bald tissue, corresponding to the tiny CO2 laser spot sizes employed, are removed. The spot size was 0.2 mm emitted by one CO2 laser in the creation of slits, 1 and a 0.15mm spot size from another in which punctiform sites were created.
   
   
3. Equally, if not more importantly, the use of the CO2 laser to create hair transplant recipient sites introduced additional, if not more, drawbacks than its use was intended to solve. The zone of thermal damage compromises blood flow and decreases the fibrin network that acts as a "biologic glue" to hold the grafts in place. Not surprisingly, some grafts were reported to "fall out".
   
   
4. This zone of thermal damage also compromises the proper oxygenation and nutritive flow to the grafts, thus compromising graft survival. Moreover, a zone of thermal necrosis during the acute phase of wound healing must first be removed by the body. This led to reports of impaired graft revascularization, increased inflammation and prolonged crusting of up to two weeks, delay onset of growth by up to eight weeks, as well as sparse growth and scarring. 3, 5, 6

Dr. Walter Unger, who has been studying the use of CO2 lasers in hair transplantation since 1993, has generated an impressive body of work that is admirable for the scientific approach brought to these studies. Because Dr. Unger came to the conclusion that the cosmetic results were not superior when the Sharplan laser was used, and superior cosmetic results were inconsistent with the Ultrapulse CO2 Laser (Coherent), this prominent hair transplant surgeon announced in early 1998 that he had abandoned the use of the CO2 laser for hair transplantation.7

Imagine a technological advance in which bald tissue is actually removed, yet there is no burn at the wound edges to compromise the building of the fibrin network, the "biological glue" that holds the transplants in place, or compromising blood flow that delivers the crucial oxygenation and nutritive flow essential for graft survival prior to graft revascularization. The Erbium: YAG Laser represents such a technological advance. This laser (Er:YAG) has an emission line at 2940nm coincident with the strongest absorption peak of water (at least ten times greater than CO2!). Equally, if not more importantly, the Erbium: YAG Laser’s wavelength is near a local collagen absorption peak at 3030nm. The result on impact is much greater precision of tissue removal, almost nonexistent thermal damage, and "actual removal" of tissue! For example, by using the Erbium:YAG Laser to create 1000 recipient sites we are also now performing 1000 "mini alopecia reductions", without the longitudinal scars inherent to alopecia reduction surgery. With the 1mm spot size we have used over the past two years this represents 785mm2 of bald tissue removed (pie r2 = 3.14 x 0.5mm2 x 1000 = 785mm2) per 1000 grafts.

Graft compression is a separate issue we have all at one time or another encountered. When grafts are trimmed to fit into very small recipient sites ("skinny" grafts"), they may be more subject to injury and, in addition, some telogen hairs may be trimmed away.8 Importantly, one study showed up to 24%, 9 and another presented by Dr. Beehner showed a loss of up to 33% of hairs, 10 when such "skinny" as opposed to "chubby" grafts were prepared. "Skinny" grafts may also result in finer and frizzy hair growth as opposed to hair growing from "chubby" grafts.10 The advantage of bald tissue removal in not compressing such "chubby" grafts which also contain viable telogen hairs, as might be the case in a narrow slit, should be apparent.

In the initial studies using an Erbium:YAG Laser (Candela\Fotona) for hair transplantation, a total of 35 laser created recipient site scalp specimens were evaluated histologically by two "blinded" dermatopathologists. It was shown that, at the level of the lower reticular dermis and in the fat at the level at which a transplanted follicle would reside, the skin exhibited 0 to less than 10 microns of thermal damage as measured by an ocular micrometer on a microscope.11, 12

An update on the original patient group who underwent hair transplantation with micro- and minigrafting with 2001 recipients sites created by Erbium:YAG Laser alone, and in combination with 1934 "cold steel" created slit recipient sites12 showed that bleeding from the Erbium:YAG Laser (a "cold laser") created recipient sites was not a clinical problem and was easily controlled with tumescent local anesthesia. Oozing was similar between the Erbium:YAG Laser and cold steel created recipient sites and there was no apparent difference in the "take." In addition, unlike the experience that has been reported with some CO2 laser created recipient sites, no grafts were known to "fall out." Equally important, because of the similarity between the Erbium:YAG Laser and cold steel, there seemed to be no detectable compromise of oxygenation and nutritive flow to the grafts, as witnessed by similar "yields" in the growth of the grafts, and no infection or scarring has, as yet, been noted.

These observations are further underscored by the following: when the Erbium:YAG Laser was used as a "warm" laser to emulate the properties of a CO2 laser, we did note prolonged crusting by up to five days and a delay in the onset of hair growth by up to three weeks. An Er:YAG laser functions as a "warm" laser when very high pulse repetition rates are programmed into the Erbium:YAG Laser’s computer. These clinical observations cast strong doubt concerning any advantage of a recently introduced laser that combines CO2 and Erbium:YAG Laser beams into one. In fact, clinical experience suggests that the advantages of an Erbium Laser for hair transplantation would be, at least partially, abrogated utilizing such a device since it would limit the ability to create scalp recipient sites in which our goal is to preserve graft oxygenation and nutritive flow during one of the follicles’ most vulnerable periods.

Although the Erbium:YAG Laser used (Candela\Fotona) created slits, Erbium made slits are cumbersome and time-consuming to produce with the present technology. This is why circular recipient sites were the ones performed over the past two years in the majority of patients.

"Nirvana" in Erbium:YAG Laser hair transplantation has not yet been achieved and there have already been exciting advances since the initial group of patients was treated. Present power outputs from Erbium Lasers are less than ideal, unnecessarily slowing the procedure while leaving the door open to the inadvertent introduction of unnecessary thermal damage by laser users turning up the pulse repetition rate in an effort to compensate for the inadequate power output provided by some Erbium:YAG Laser manufacturers. A new 2500 mJ Erbium:YAG Laser seems to be clinically superior to the original 1000 mJ output.

It is important for the reader to realize that the beam profile of the laser beam emitted by some laser manufacturers is far from ideal. Indeed, some beam profiles have been reported to be in the shape of a "doughnut, " i.e. the energy is greatest at the sides with the central area possessing the lowest energy. This is not desired in a beam profile and leads to markedly increased zones of thermal damage at the wound edges, as has been noted by some investigators using such lasers.

There are a number of other advances that have recently been introduced. One manufacturer (Dornier Med Tech) already offers a telescopic handpiece capable of altering the beam diameter with a simple sliding bar built into the handpiece. Another laser manufacturer (ConBio) offers a variety of 0.5, 0.75 and 1mm spot sizes for use in hair transplantation. Most importantly, another manufacturer (Dornier Med Tech) is already in the final stages of releasing a "slit hand piece" truly capable of making slits of various dimensions quickly. This hand piece should be usable with a computer-generated scanner, as well as manually, to appropriately adapt to many transplant situations.

The ability of the new Erbium: YAG Laser to rapidly create uniform recipient sites, and its ability to create a slit while at the same time removing recipient tissue without causing significant thermal injury to the recipient bed, represents a significant advance over CO2 lasers. The Erbium:YAG Laser is an important new addition to the hair transplant surgeon’s armamentarium.

REFERENCES
Unger W.P.: Laser Hair Transplantation IIII. Computer-assisted Laser Transplanting. Dermatol Surg 1995; 21: 1047-1055.
Nemeth A.J.: Lasers and Wound Healing. In: Nemeth A.J. (ed.): Dermatologic Clinics – Wound Healing. W.B. Saunders Co. Vol. II No. 4; 1993, pp 783-789.
Villnow M.M., Fenduni B: Update on Laser-assisted Hair Transplantation. Dermatol Surg 1998; 24: 749-754.
Bernstein R.J., Rassman W.: Laser Hair Transplantation: Is It Really State of the Art? Lasers Surg Med 1996; 19: 233-238.
Fitzpatrick R.E.: Laser Hair Transplantation. Tissue Effects of Laser Parameters. Dermatol Surg 1995; 21: 1042-1046.
Unger WP: Update On Lasers. Hair Transplant Forum Intl. 1997; 7(2): 19
Unger WP: Presentation on Laser and Controversial Hair Transplantation. Am Soc for Dermatol Surg in Portland, Oregon, May 13-17, 1998.
ISHRS Washington D.C. September 16-20, 1998
Seager D.J.: Micrograft Size and Subsequent Survival. Dermatol Surg 1997; 23: 757-761
Beehner M.: Two Research Studies on Follicular Unit Growth. ISHRS in Washington, D.C. September 16-20, 1998
Nemeth A.J., Miller I, Messina J.L., Glass F, Rehnke R.D: Erbium:YAG Laser-assisted Hair Transplantation: A Clinical and Histological Study. ISHRS in Barcelona, Spain, October 15-19, 1997.
Nemeth A.J.: Erbium Laser Hair Transplantation: Update and Present Status. ISHRS in Washington, D.C., September 16-20, 1998

COMMENTARY

There is no doubt that the new Erbium: YAG Laser offers substantial improvement over traditional CO2 lasers in eliminating thermal injury. For those practitioners who use minigrafts and larger grafts containing multiple follicular units, the ability to rapidly create recipient slits and cause less graft compression, is a significant advantage. For those of us who use individual follicular units to keep the wound sizes to a minimum, the usefulness of the laser is less obvious. It is a concern to some of these authors that the wounding produced when recipient tissue is removed is not equivalent to a small "cold steel"slit. Well controlled studies are much needed to resolve this important issue.

Robert M. Bernstein, MD

Splitting Hairs

Not a hair transplant procedure is performed without at least implanting a few transected follicles. What happens if grafts with transected follicles are planted?

To answer this question, a study was performed in which excised skin from the human occipital scalp was cut by a surgical blade along the direction of hair growth. Intact individual human anagen hair follicles were isolated with a scalpel. Implants were prepared from follicles as follows:

The upper one-third and lower two-thirds of the follicle were obtained by horizontal section just below the pilo-sebaceous junction.
The upper and lower halves of the follicle were obtained from a transverse cut at the middle portion of the follicle
The upper two-thirds and lower one-third of the follicle were obtained from the transection of the follicle at the lower one-third of the follicle.
Both upper and lower follicle grafts were transplanted onto the forehead or leg. Histologic examinations were performed for each successive biopsy after grafting. Lower half follicles and intact (non-transected) follicles were cultured in Philpott´s medium1. Follicles were measured daily using inverted microscopes with a calibrated eyepiece graticule.

Eight months after grafting, 13 of the 20 grafted upper two-thirds, 25 of the 30 grafted lower two-thirds, 10 of the 25 grafted upper half, and 4 of the 15 lower half follicles have regenerated complete hair follicles. However, no hair follicles were regenerated from the grafted lower one-third and upper one-third follicles. The regenerated hairs from upper follicle implants were thinner than those from lower follicle implants.

A histologic examination showed that the regenerated hair follicle from the upper half follicle implant revealed the presence of a reformed small dermal papilla and a matrix. Lower half follicle implants reconstituted the complete hair follicle. Sebaceous glands were also completely regenerated. Some lower half grafts formed epithelial cysts.

Dissected hair follicles will grow and retain their morphology for 8 days in culture. Intact follicles show prominent naked shaft outgrowth. In contrast, the outer and inner root sheath grows concomitantly with the shaft in lower half follicles (1.5 mm after 8 days).

The results of this study showed that if the bulb containing the dermal papilla is removed, the hair will usually regrow. If the papilla is necessary for hair growth, how will hair regrow without it? A new papilla appears to be reformed from the connective tissue sheath2. However, the higher up in the follicle that transection occurs, the smaller will be the papilla that is reformed and hence the smaller and finer the hair is which is produced. The papilla determines the caliber of the hair shaft3. And if transection occurs above the midpoint of the follicle, a new papilla is not formed and hence no hair grows.

Thus, loss of the bulb region during graft dissection and placement is a clinically significant problem, which can contribute to incomplete and fine hair growth. However, this problem may be useful for the eyebrows, pubic hair, and female hairline reconstruction. In contrast to males, the female hairline is generally made up of fine vellus hairs that give it its "soft" character. One can successfully graft single hair follicles after removal of the bulb for the reconstruction of these regions. This technique can provide the best possible cosmetic result.

If the follicle is transected in its upper portion and is planted so that it is stranded in the dermis, cyst formation is likely4. Our results showed that some grafts formed epithelial cysts, but 25 of the 30 grafted lower two-thirds and 4 of 15 lower half follicles regenerated complete hair follicles. The sheath components grew out at the same rate as the shaft (1.5 mm for 8 days) in culture. This result suggests that the outer and inner root sheath grew out and could connect with epidermal invagination in vivo. If grafted hair follicles were located too deep, the re-grown sheath could not reach the epidermal layer. In this situation, the formation of an epidermal cyst is likely.

REFERENCES
Philpott MP, Kealey T. Effects of EGF on the morphology and patterns of DNA synthesis in isolated human hair follicles. J Invest Dermatol 1994;102:186-191.
Kim JC, Choi YC. Regrowth of grafted human scalp hair after removal of the bulb. Dermatol Surg 1995;21:312-313.
Oliver RF. Whisker growth after removal of the dermal papilla and lengths of follicle in the hooded rat. J Embryol Exp Morphol 1966;15:331-347.
Cooley J. Rat whiskers, follicle transection, and hair transplantation. Hair Transplant Forum 1997;7(2):20-21.

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