THE DONOR AREA

The punch autograph technique of Orentreich2, the multi-bladed knife excision method of Vallis3, and the single bladed donor harvest of Uebel4 have individual advantages and disadvantages. Simple mathematical analysis of the length of the surgical excision required to harvest 10 cm square area of donor tissue clearly reveals that the punch technique requires 5 times as much surgical margin as a single ellipse, and the multi-bladed knife (utilizing four blades with 3 mm spacing) requires 2.5 times as much excisional margin as a single bladed knife5. When the mathematical advantages of such significantly less surgical margins are combined with the advantage of direct intra-operative visualization of the single bladed knife excision throughout the excision process, the use of single-bladed knife for the donor harvest obviously becomes the most follicular sparing method.

It has been the experience of some of these authors that when comparing the percentage of hair follicles that are transected by multi-bladed vs. single bladed knife harvest reveals a significant difference in follicular transection rate. The single bladed knife will transect approximately 2-3% of all follicles in total donor tissue harvested compared with 12-16% follicular transection rates for multi-bladed knives utilizing 4 blades spaced at 3 mm widths between blades. When the blade spacing is decreased, the amount of transection increases dramatically.

GRAFT DISSECTION

Historically, grafts for transplantation have typically been "cut to fit" specific recipient site and sizes. Such "cut to fit" methods ignore the natural growth pattern of follicular units as they occur within the donor’s scalp. Microscopic dissection and implantation of naturally occurring follicular units as the basic graft methodology used since 1988 by Limmer6 has the advantage of not only preserving the maximum number of undamaged hair follicles for transplantation but also has the advantage of generating small, clean grafts which allow for much denser packing. In the hands of an experienced assistant, the transection rate during graft production is characteristically less than 3% of all follicles in the donor tissue.

Cooley and others7 found the transection rate to be approximately twice as high when utilizing back lighting and loupe magnification techniques compared with the dissecting microscope. Additionally, Bernstein and Rassman8 have shown that even partial microscopic dissection of the donor tissue produces a 17% greater yield of hair for transplantation when compared with loupe dissection with transillumination. If total microscopic dissection were compared, certainly the percentages of hair available for transplantation would be significantly increased above this 17% figure, probably on the order of an additional 5-10%. Most importantly, the high resolution and intense illumination of the microscope allows for the dissection of an intact donor strip and obviates the need to "pre-cut" the strip with a multi-bladed knife in order to make the subsequent dissection easier and thus eliminate this source of follicular injury as well.

REFERENCES
Limmer BL: Survival of Micrografts. In: Hair Replacement. Stough DB, Haber R. St Louis Mosby Press 1996; 147-149.
Orentreich N: Autografts in Alopecias and Other Selected Dermatological Conditions. Ann. N.Y. Acad. Sci. 1959; 83: 463.
Vallis CP: Surgical Treatment of the Receding Hairline. Plast Reconstr Surg 1968; 33: 247.
Uebel CO: Micrografts and Minigrafts: A New Approach for Baldness Surgery. Ann Plast Surg 1991; 27: 476-487.
Limmer BL: The Donor. In: Hair Replacement. Stough DB, Haber R. St Louis: Mosby Press 1996; 142-143.
Limmer BL: Elliptical Donor Stereoscopically Assisted Micrografting as an Approach to Further Refinement in Hair Transplantation. Dermatol Surg Oncol 1994; 20: 789-793.
Cooley JE: Follicle Trauma in Hair Transplantation: Prevalence and Prevention. Presented at Int Soc Of Hair Restor Surg, 5th Annual Meeting, Barcelona, Spain. Oct 15-19, 1997.
Bernstein RM, Rassman WR: Dissecting Microscope vs Magnifying Loupes with Transillumination in the Preparation of Follicular Unit Grafts. A Bilateral Controlled Study. Dermatol Surg Dermatologic Surgery 1998; 24: 875-880.
New Ways to Quantify Hair Movement
Francisco Jimenez, MD and Jose M. Ruifernandez

Since hair transplantation is essentially a redistribution of a limited amount of hairs from one circumscribed area of the scalp (donor area) to another (recipient zone), the whole process of hair movement can be mathematically modeled. The advantages of this mathematical analysis are:

To develop an objective method of surgical planning that is reproducible.
To evaluate the efficiency of a hair transplant by comparing the final result with the proposed theoretical estimations.
To save as much donor hair as possible due to its finite supply.

DISTRIBUTION OF HAIR IN THE DONOR AREA

Human hair emerges from the scalp in groupings containing one to four and rarely five hairs. In the average Caucasian individual, most of the hair follicles emerges from the scalp as two hair follicular units (approximately 55% are two hair follicular units, 35% are three, four and five hair follicular units, and 10% are one hair follicular units). However, there is a clear correlation between the hair density (number of hairs per square centimeter) and the relative proportion of one to four hair follicular units. For instance, individuals with average and high hair density have more numbers of three hair follicular units than one hair follicular units, but individuals with low hair density (less than 130 hairs/cm2) have more one hair units than three hair units.

These correlations can be expressed with the following mathematical equations, which are explained in greater detail elsewhere1:

n = 0.29 x d + 27
n1= -0.16 x d + 36
n2= 0.19 x d + 9
n3= 0.26 x d – 18

Where,

d = hair density (number of hairs /cm2)
n = follicular unit density (total number of follicular units / cm2)
n1= number of one hair follicular units / cm2
n2= number of two hair follicular units / cm2
n3 = number of three, four, and five hair follicular units /cm2

Note: Due to the scarcity of four and five hair follicular units and for the sake of simplification, all four and five hair follicular units are considered as three hair units.

After measuring the hair density with a densitometer, or an equivalent quantifying instrument, the hair transplant surgeon can use these equations to calculate the follicular unit density and the expected proportions of the hair groupings. The results obtained by the former equations are "most probable median values" for a specific hair density. As occurs with any statistical mathematical model applied to a biological system, a small percentage of error can be expected. Significant variations in the hair distribution (hair density and follicular density) have been noted among different races2, which make the above equations useful only for Caucasians.

The distribution of the hair in one- to four-hair follicular units is what mainly determines the great genetic variability in hair density, rather than the actual spacing of follicular units, which is relatively constant. There is also a dynamic change in the proportion of follicular units due to the progressive hair loss pattern associated with androgenetic alopecia.

The early stages of androgenetic alopecia are marked by the progressive diminution of hair shaft diameter and a decrease in length, caused by a shortening of the hair growth cycle. These changes seem precede actual hair loss. It appears that as male pattern baldness progresses, the hair is lost as single hairs from all types of follicular units, in the same proportion. Therefore, the three hair units will be converted into two hair units, the two hair units into one-hair units, and some of the one-hair units gradually disappear, although new one-hair units will be formed from preexisting two hair units. As a result (although the hair density varies significantly), the total number of follicular units per square centimeter remains between certain limits until the individual reaches a significant degree of alopecia3.

EVALUATION OF THE RECIPIENT SITE

To measure the recipient area is very important for planning a hair transplant session. Depending on the area in square centimeters to be transplanted, the surgeon can predict the number of recipient sites to be made and, subsequently, the number of follicular units needed from the donor area.

A simple method to measure the recipient area is to use a flexible and transparent calibrated reticula that accommodates to the curved shape of the scalp. A more accurate instrument, however, could be an electronic planimeter, which by outlining the borders of the recipient zone can give us the exact measurement of the area. As far as we know, this instrument has not yet been adapted for use in hair transplantation.

The density of a hair transplant (number of hairs transplanted per square centimeter) is always an object of debate in meetings and scientific journals. We believe it is a mistake to link density exclusively with graft size (the argument is made in favor of larger grafts producing more density than smaller grafts), and that a much more critical factor is the number of recipient sites made per unit area (or how close the follicular units are placed)4. A recent in vivo study by Limmer5 compared the density achieved using the mini-micrografting technique with that accomplished by standard grafts, showing that comparable or even better density could be obtained with the mini-micrografting approach (average density of 64 hairs/cm2 after four plug sessions versus an average density of 61 hairs/cm2 along the first centimeter of frontal hairline after only 1 session of mini-micrografting).

To achieve densities in the order of 60 hairs/cm2 with randomly placed follicular units, it is necessary to create from 25 to 40 recipients sites per square centimeter depending upon the donor density of the patient and the size of follicular units used in a specific area. In adition, when using follicular units, the surgeon can dictate the density not only by changing the number of recipient sites made per square centimeter, but also by planning the distribution of the follicular units. For example, larger follicular units might be placed in those areas where maximum density is desired, such as in the central forelock. If the larger 3- and 4-hair follicular units are sorted and used in select areas, it is relatively easy for an experienced surgical team to achieve these densities with only 20 sites/cm2.2

When discussing hair transplant density, an effort should be made to always present numerical data (number of recipient sites made per square centimeter and the average number of hairs placed in each site), while avoiding nonspecific terms such us "dense packing, " which only adds confusion.

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