What is a Follicular Unit Hair Transplant?
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). 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.
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.
Credits
- Information Provided by John P. Cole, MD - International Hair Transplant Institute
Hair Transplant Adviser Blog
Provided by The International Alliance of
Hair Restoration Surgeons,
the Hair Transplant Adviser blog provides the opportunity for prospective
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