Following the Example of Nature
Only in the early 1980’s was it been recognized
that hair grows not singly, but in specific anatomic units
that are called follicular units (FU’s) (see figure
1). These consist of one, two, three, four, or rarely
five terminal (mature) hairs, one or two vellus (fine)
hairs, a discrete nerve and blood vessel supply, a connective
tissue sheath, sebaceous glands, and a tiny muscle known
as the erector pili. These FU’s are the natural
groupings of the hair, the way it normally grows. It seems
intuitively obvious that a natural transplant would follow
the form of nature and use strictly FU’s. This has,
unfortunately, not been the case.
Figure 1
It would be expected that using this method would allow
us to create the most undetectable result, and also allow
us ease in following the natural angles of emergence from
the scalp. These angles at which the hairs exit the skin
are quite important, as they vary widely depending upon
the area of the scalp we are observing.
Also, improved survival may result from this technique.
Consider the old, large plug techniques. The recipient
site was actually created using the same type punch that
was used to harvest the graft. In other words, tissue
was removed. This not only created the potential for scarring
and "cobblestoning", it could compromise the
blood flow beneath the scalp as well. In addition, the
size of the grafts themselves could limit the flow of
blood and oxygen to the hairs in the center of the graft,
leading to "donutting". On the other hand, using
FU’s requires only a tiny recipient site in the
scalp; we often use only a hypodermic needle to make these
miniscule slits! Thus, healing is much quicker, there
is less post-operative evidence of the procedure (even
the next day), and there is minimal excess tissue subject
to scarring and other complications.
Minimizing Donor Hair Wastage: Mathematical Planning
Research has shown us that for Asians and Caucasians,
the density of follicular units, regardless of the number
of hairs they contain, is about one per square millimeter
(1FU/mm2). For African type hair it is less, approximately
0.6FU/mm2, although this is more than made up for by the
preponderance of three hair FU’s, versus two hair
FU’s in Asians and Caucasians.
We can directly measure not only the FU density, but the
hair density as well, by using a tool called a densitometer.
With small areas of hair clipped short, a fixed area is
observed under bright light and magnification. Then, we
can calculate the appropriate numbers, for example: we
can look at the density of FU’s and hair in the
center of the back of the head, over the ear, and halfway
in between. If the numbers average 1FU/mm2, and 2 hairs/FU,
and the patient will be receiving 1500 grafts, then we
can calculate that we will need to harvest about 15 square
centimeters (cm2) from the back and side of the head to
give us our required grafts. We can also assume that,
given a 20% occurrence of single hair grafts in those
with average density, our 20cm2 donor strip will provide
us with about 300 single hair grafts, which should be
enough for our hairline transition zone.
Moreover, we can use calculations to plan for the future.
The average, non-balding person has about 100,000 hairs
on the scalp. This would translate to 50,000 follicular
units (FU’s). The "permanent zone" comprises
about 25% of the total scalp; therefore, there would be
one-fourth, or 25% of these total 50,000 FU’s in
the permanent zone, which would equal 12,500 FU’s.
We know that about half of the hairs in an area must be
lost before there is any appearance of balding, so we
could safely harvest up to half of the permanent zone
FU’s, or 6,250 FU’s. This gives us an idea
of the viable, reasonable donor reserves that a given
patient has for current and future transplantation.
It is important to realize that the amount of coverage
and density that a given person achieves with FU transplantation
will vary not only according to their donor density and
scalp laxity, but also according to their hair characteristics.
This is another point where art meets science in the field
of hair transplant surgery.
Hair Characteristics in Follicular Unit Transplantation
The characteristics that are most cosmetically important
are: hair color (especially relative to the underlying
skin color), hair curl (or lack thereof), and hair caliber,
or cross-sectional area (in other words, is the hair shaft
itself fine, or coarse). The artful hair restoration surgeon
will take all these factors into consideration when planning
a procedure, in order to give the greatest aesthetic benefit
to the patient, with the minimal use of the limited donor
hair.
Hair caliber, or cross-sectional area is actually more
significant than density in its ability to "cover"
bald scalp. Remember that the appearance of baldness is
actually due to light penetrating past sparse or absent
hair, and then being reflected off the shiny scalp. The
more hair that is in place to block the light, the less
the appearance of baldness will be. It can be mathematically
shown that doubling the caliber of hair would do more
to block light than doubling the density. However, there
are other important factors.
One of these is the degree of curl. Generally speaking,
the more curl or wave the hair possesses, the more coverage
it will grant the scalp. An excellent example of this
phenomenon is found in African-type hair. This hair tends
to be tightly wound or kinky, which may be an evolutionary
adaptation to protect the scalp in hot climates. Although
African follicular unit density tends to be lower than
that of Caucasians or Asians, (0.6 FU/mm2 vs. 1 FU/mm2),
the curl characteristics lend this type of hair wonderful
coverage properties, as it tends to stand thick and mat-like
above the scalp, thus blocking much light. Also, an added
advantage is that African hair tends to occur predominantly
as three hair units, rather than the two hair units characteristic
of Caucasians/Asians with average density.
Hair color, especially as it relates to underlying skin
color, is also of great importance. The less contrast
there is between hair and scalp, the better the potential
for coverage. A blond person with light skin, like someone
of Scandinavian origin, appears bald only after significant
hair loss has occurred. This is because the observing
eye sees a high contrast as standing out in stark relief,
and areas of low contrast blend together. So even though
many Asians have good density and excellent hair caliber
(coarseness), they may be challenging hair transplants.
Imagine dark, straight, coarse Asian hair contrasted against
relatively light scalp skin; the eye notes the contrast,
and sees the light that has been transmitted. The eye
follows the straight hair shaft right down to the scalp,
and it appears balder than in someone with more favorable
hair characteristics.
We can see, therefore, that a combination of many factors
play a part in determining who will be a poor, good or
excellent candidate for hair transplant surgery with follicular
units. High density is great, but unfavorable hair characteristics
may attenuate some of the benefits of this density. On
the other hand, someone with curly, coarse, salt-and-pepper
hair (very good characteristics), but with poor donor
density and a tight scalp, may also not be the ideal candidate.
This is where the artistic, knowledgeable hair restoration
surgeon really shines: knowing how to work with the positive
resources the patient does have, to insure the best possible
outcome for the present and the future.
The Recipient Incisions
It is without question that, of all current graft types,
follicular units can be placed into the smallest incisions;
consequently, they can be placed in closer proximity in
the scalp. Although it is not necessary to come close
to the patient’s original density when transplanting,
there is a certain minimum required to obtain coverage;
also, the hairline especially needs closely, although
somewhat randomly, placed single hair grafts to give the
illusion of graded density.
Small incisions, moreover, simply heal more quickly than
larger ones, and the grafts placed are less likely to
suffer from blood-flow and oxygen deprivation. Any incision
can damage the circulation of the scalp, cause scarring,
and effect wound healing, hair growth, and even the potential
for subsequent transplantation. In addition, small recipient
sites, made with needles or micro blades, conserve the
normal matrix structure of the scalp’s connective
tissue. This allows the FU’s to fit snugly within
the created sites, avoiding dislodgement, and promoting
quicker healing and immediate nourishment of the grafts
from local blood supply. We discussed earlier the slow
and repetitive process of using large, standard grafts;
only so many could be placed at one time. With follicular
unit transplantation, however, sessions placing as many
as 2000 to 3000 grafts at once, and more, have become
routine for us. For many patients, this may be the only
procedure they ever need!
Large Sessions: The Rationale
Let’s talk for a moment about large sessions. As
it has become apparent that excellent growth can be realized
with large FU sessions, other benefits have become manifest.
For one thing, it advances the hair restoration process
expediently. Most patients have no desire to get ensnared
in a lengthy, repetitive series of treatments that they
might even have to terminate prior to completion. A large
session of FU’s, in some patients, can create a
natural, undetectable result; this transplant can stand
on its own, and continue to look natural even in the face
of further hair loss, and without the necessary need for
further work. In short, the process is just plain expedient
and efficient.
Also, every time a procedure is done, the donor area is
"violated". One large, single strip harvested
from the donor area will, by definition, create significantly
less scarring, hair loss, and distortion of remaining
hairs than will multiple, small strips, or, even worse,
punch grafts. Minimizing the number of harvests, careful
suturing and closure of the donor site, and close attention
to harvesting technique can be invaluable in preserving
precious donor resources; this is important not only in
the event that further transplantation is desired, but
also in preserving the cosmetic integrity of the donor
area. We will discuss the often forgotten and underappreciated
donor area at length in a subsequent section.
The possibility of telogen effluvium must also be considered
with any hair restoration surgery. This is a rapid loss
of hair that occurs in the area of the surgery, among
hairs that are in the telogen, or resting stage. These
hairs will generally grow back, unless they are severely
miniaturized hairs that would be naturally lost within
a short time anyway. Since it is not uncommon to be placing
incisions and FU’s between and around miniaturized
hairs like these, there can be significant loss. If large
numbers of FU’s are placed during a session, then
at least the patient can know that the hairs that will
grow in a few months later will be strong, solid terminal
hairs, and will compensate for the effluvium loss.
One other rationale for large sessions considers the need
for different types of FU’s (i.e., singles, doubles,
etc.). As we pointed out in the section on mathematical
planning, only a certain percentage of FU’s will
be single hair FU’s. This is quite important in
planning the hairline reconstruction, which required relatively
high numbers of singles. If too few FU’s are harvested,
then the number of singles, for example, might fall short.
In this case, the only options are an incomplete hairline,
or "creating" singles by dividing 2 or 3 hair
FU’s, which is definitely less than an ideal technique.
Indeed, if we claim the primacy of the follicular unit,
how can we then rationalize breaking them up?
Insuring the Integrity of Follicular Units
Let’s consider for a moment the other techniques
that we think are integral to the follicular unit transplantation
process. One is single strip harvesting, and the other
is stereo-microscopic dissection. Without these companion
techniques, the procedure may be called follicular unit
transplantation, but it is a pale, inefficient imitation.
As its name implies, single strip harvesting is the method
by which a single strip of hair-bearing scalp is carefully,
indeed, painstakingly, excised from the donor area; the
strip is then broken down into its smallest functional
units, or follicular units. Before single strip harvesting
came to the fore in recent years, older, infinitely more
wasteful methods were employed. The first of these was
the circular, punch grafts of yore, which have little
to recommend them save their simplicity (they are essentially
biopsy punches), and the ease with which they were directly
placed into correspondingly circular holes in the recipient
area. Next, ingenious surgeons devised multi-bladed scalpels;
three or more (sometimes many more) blades, attached to
a handle, were oriented parallel to one another, and many
thin, narrow, long strips could be excised with one pass
of the scalpel. These strips could then be placed flat
on their sides and sliced into small mini- and micro-grafts,
with little or no concern for follicular unit integrity.
This, however, was not the only drawback; transaction
rates were generally rather high, and were even higher
when more blades were used. So time was saved, but lots
of valuable follicles were wasted.
What we know as single strip harvesting overcomes many
of these disadvantages. Using two passes with a single
blade, or a single pass with a double-bladed knife, an
elongated strip is excised. It is possible, with careful
technique, to achieve transaction rates of less than 2%
(this means that fewer than two FU’s per 100 are
sliced in two). It is estimated that transaction rates
as high as 30% occur with the use of multi-bladed scalpels.
Let’s do the math. If the patient needs 1000 grafts,
then an area containing 1300 grafts would need to be removed
just to account for wastage and still produce 1000 intact
FU’s. If 2000 grafts were needed, 600 would need
to be wasted! This is of serious import when we deal with
a limited, finite amount of donor hair.
This leads us to a discussion of graft dissection. One
of the reasons many surgeons have used multiple strip
harvesting with multi-bladed scalpels, is that an intact,
single strip presents a number of difficulties in dissection.
It is too thick to place on its side or to shine light
through (transilluminate) in order to visualize the individual
FU’s. Therefore, thin, multiple strips lend themselves
to rapid, albeit inefficient, slicing of grafts. We feel,
however, that the degree of wastage is unacceptably high,
both during the strip harvest, and during graft preparation.
To avoid these problems, the techniques of stereo-microscopic
"slivering" and dissection are utilized. As
soon as the donor strip is harvested, the slivering process
begins. This is extremely painstaking; the strip is divided
into small "slivers", each one FU wide. These
are then laid flat on their sides, and, also under the
microscope, the individual FU’s are carefully sliced
out and trimmed of excess connective tissue and fat. During
this process, the grafts are suspended in a physiologic
saline solution and kept chilled; this insures their viability
and health while they are "out of body". They
are separated into one, two, three and four hair FU’s,
according to their natural occurrence, and then carefully
placed into the recipient sites.
We feel strongly that follicular unit transplantation
is the state of the art in hair restoration surgery. Older
techniques are easier and more lucrative for the surgeon,
require a smaller operative team, and may be easier to
"sell" with the false promise of higher density.
Follicular unit transplantation, done with single strip
harvesting and stereo-microscopic slivering and dissection,
requires patience, a large team, and meticulous work by
the surgeon and assistants. Despite these demanding criteria,
we are committed to using and refining this technique;
in one or two sessions, patients can achieve results that
are natural, undetectable, and will stand the dual tests
of time and of advancing baldness.
