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Chapter: 1 | 2 | 3 | 4 |
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| There are several functions of the
physical examination: (a) It should support the diagnosis of androgenetic
alopecia, (b) It should qualify the patient for hair restoration surgery, (c) It
should allow you to estimate the total amount of movable hair, the maximum width
of excision for any particular procedure and the amount of donor tissue required
for a particular procedure, (d) It gives you the opportunity to assess the
impact of prior hair restoration surgery. The evaluations should ideally
include, donor hair density (one or more areas), hair shaft diameter (one or
more areas), scalp laxity, thickness of the scalp, degree of hair loss, color of
the hair, skin color, hair wave, appearance of existing grafts, and results from
any previous AR, percentage of miniaturized hairs and percentage of telogen
hairs. The percentage of telogen and miniaturized hairs is obtained when a strip
of hair bearing scalp is excised from the scalp and examined with 6 to 10x
magnification. These percentages may, in future, prove to have practical value
but at present their significance in hair restoration surgery is unknown.
Recording all of the above parameters will allow for the development of the most
scientific evaluation of donor tissue potential but, unfortunately at present,
is carried out in its entirety by few practitioners. Each will be discussed
separately below.
In addition, the size and symmetry of the head can impact the procedure
significantly. Asymmetry, for example, may have a positive, negative or neutral
impact. A head, which is large in the donor area relative to the recipient area,
may have a positive effect on the donor to recipient area ratio. A head, which
has a broad forehead without a correspondingly large donor area, would have a
negative influence on the donor to recipient area ratio. It should be clear from
the preceding that although this is a chapter on the donor area, examination of
the donor area alone without an examination of the recipient area at the same
time, clearly does not provide sufficient information. Therefore, if one wants
to accurately predict what can be accomplished with hair restoration surgery, a
careful examination of the recipient area must also be conducted. This
examination should include, like the donor area examination, such things as the
shape, size, and asymmetry of the recipient areas as well as the degree of hair
loss and the state of any previous hair restoration surgery. In this regard, it
is important to also note that a circle and a square with the same circumference
have markedly different surface areas. The circle’s surface area is much larger.
Therefore, as you increase a more or less round or oval alopecic area’s
circumference, it has an exponential effect on its surface area. While
predicting coverage, with 100% accuracy is not currently possible, a thorough
examination establishes realistic expectations. Future work should, therefore,
focus on improving our methods of objective evaluations and calculations of
donor and recipient areas.
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» Donor Area Hair Density
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There are three different densities we should consider in
donor area assessments. The first is the number of hairs in a given surface area
of scalp, the hair density. The second is the number of hairs per FU, the
calculated density (See Chapters 6 & 11) for a description of the
FU). The third is the number of FU in a given surface area, the Follicular
Unit Density (FUD). Each parameter reveals specific information and will
assist you in customizing your procedure to the individual patient.
Hair Density:Many physicians subjectively assess the amount of donor
area hair by simply combing the hair apart at various points in the proposed
donor area and making an estimate based on previous experience. However, it
obviously is much more accurate and meaningful to objectively measure the
previously noted hair densities. There area several commercially available
instruments that can help you in this taskto measure hair density. These include
the Rassman Densitometer, the Welch Allyn Trichoscope, and the Kahn
Densitometer. The viewing surface area of the Rassman Densitometer is
approximately 10 mm2; while the Welch Allyn and Kahn are 12.56
mm.2 It is therefore easier to convert the density to hairs per
mm2 with the Rassman Densitometer. The number of visible hairs in the
10 mm2 surface area is simply divided by 10. For instance, if 21
terminal hairs are counted, the density is 2.1 hair/mm2. The Rassman
Densitometer also contains a light source and magnification, making it is easier
to count hairs. This same instrument is available at Radio Shack (30x
Microscope,Cat No. 63-851). The Kahn Densitometer has the same magnification as
the Rassman Densitometer. However, it has no light source and because the
viewing area is larger, there are more hairs to count. The latter two factors
reduce the probability of an accurate hair count. It should be noted that all
densitometers are commercially produced and not subject to strict scientific
standards in their manufacturing. Therefore, it is possible that the viewing
orifice is slightly different than presumed. The physician should verify the
surface area of his/her densitometer prior to its incorporation into his/her
practice. More recently, a number of other dermatological instruments have been
developed and can be used to measure density. The most expensive and
technologically advanced instruments use light electromagnetic waves and
advanced computer programming to count surface structures.
Over the years, many physicians have attempted to determine the average hair
density in the donor area. Unfortunately, there is a wide variation in their
findings. The difference in values results from the difficulty in counting
hairs, the extreme difficulty in measuring a defined surface area and a lack of
standardization in the method -- for example, how many sites are examined and
their locations. Table 4 notes the differences in hair densities reported by
various investigators:
TABLE 45
Hair Densities according to Different
Physicians
Wilson 1.54 hairs per mm
Pecoraro et al. 1.75 to 3.0 (Occiput 2.4 hairs
per mm2)8.
Cottington et al. 2.11 hairs per mm2 in the left temporal
area8.
Nordstrom 1to 2.4 hairs per mm2 (average 1.8 hairs per
mm2)8.
Stough and Haber 1.44 to 1.76 hairs per mm2 (Average)
Rassman and
Carson 2.0 hairs per mm2 (average density) Range 1 to 4 hairs per mm2.3Jimenez
and Ruifernandez 1.24 to 2.00.
Cole 1.9 to 2.1 hairs per mm2 (average mastoid
density).
Hair density usually decreases as we move toward the ear and increases as we
move toward the occipital area in most individuals. (See below). Excising a
donor area exclusively from the occipital area would, therefore, theoretically
contain much more hair than the usual pattern of donor area harvesting.
Bernstein recommends we measure density 5 cm lateral to the mid-occipital
regions. Cole recommends measurement of density over the "mid-mastoid" area if a
single site is assessed. This region is roughly half way between the occipital
protuberance and the auricle. The measurement assumes you will remove a donor
strip extending from near the ear to a line drawn vertically through the
occipital protuberance (either unilaterally or bilaterally). However, because
hair density varies from the mid-occipital region to the supra-auricular area,
it is more accurate to measure density in more than one location along the
proposed strip; a minimum of three locations is recommended. These three points
are called reference points(Figure 3). With the head in the Franklin plane, they
are located a) in the mid-sagittal plane at the occipital protuberance, b) three
centimeters superior to the reflection of the helix on a line drawn superiorly
from the external auditory meatus, and c) at a point half-way along the line
connecting points a) and b) over the ipsilateral mastoid. This line is generally
between 14 and 15 cm long, putting the mid-point between 7 and 7.5 cm from
either endpoint. The three reference points serve as sites for all density
measurements and are an attempt to standardize the examination of the donor
area.
Using a Rassman Densitometer, Cole measured the hair density, hair
diameter, and FU density in the aforementioned three reference points in 40
patients. He then calculated the hair densityhairs per follicular unit,
calculated density, in each region. Table #5 6summarizes his findings, which
confirm that hair density and FU density in "virgin" donor areas is generally
highest in the mid-occipital region and least in the supra-auricular area. The
density in the mid-mastoid area is usually somewhere between these two
measurements. (Table 56).
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Left Auricle |
Left Mastoid |
Inion |
Right Mastoid |
Right Auricle |
| Density in mm2 |
1.8 |
2.1 |
2.4 |
2.1 |
1.8 |
| Follicular Groups / 10 mm2 |
8.2 |
8.7 |
9.9 |
8.6 |
8.1 |
| Diameter in m m |
73.5 |
78.5 |
72 |
76.6 |
73.5 |
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Table 6.
Rassman and Bernstein suggest the "safe donor area" consists of approximately
25% of the scalp and that only half the donor area can be removed without
over-depleting it. They also contend the hair-bearing scalp is 80 inches2 or
51,613 mm2 and that the average scalp contains approximately two hairs per
mm2.12 Thus, the average scalp contains approximately 100,000 hairs (51,613 mm2
x hairs per mm2).12 Based on these contentions, they have proposed Table 76 for
quantifying the effect of donor area hair density on the number of hairs that
are available for transplanting. This table is useful in helping the physician
and his patients to understand the limitations of their donor areas and to
customize the approach for each individual. It should, however, not be construed
as absolutely accurate or obligatory since it is based on several assumptions
and averages. In addition, as discussed previously, great variations exist with
regard to the size and shape of the scalp, the size of the "permanent" donor
area and even the number of hairs/mm2.
|
Donor
Density hairs/mm2 |
Total Hair in Permanent Zone |
Hair Must Remain in Permanent Zone |
Moveable Hair |
% Change in Density |
% Change in Moveable Hair |
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1.0
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12,500
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12,500
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0
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-50%
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-100%
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1.3
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16,250
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12,500
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3750
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-35%
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-70%
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1.5
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18,750
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12,500
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6,250
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-25%
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-50%
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1.8
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22,500
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12,500
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10,000
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-10%
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-20%
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2.0
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25,000
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12,500
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12,500
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0
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0
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2.2
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27,500
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12,500
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15,000
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+10%
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+20%
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2.5
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31,250
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12,500
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18,750
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+25%
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+50%
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2.7
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33,750
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12,500
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21,250
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+35%
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+70%
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3.0
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37,500
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12,500
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25,000
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+50%
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+100%
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Table 7The effect of changes in donor area hair density on
movable hair. |
Table 7.
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» Calculated Density (CD)
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| The average number of hairs in each FU or calculated
density is an important quotient. The method used in obtaining or
"calculating" it is described later. This number represents the mean number of
hairs a person will receive with each FU, with each graft containing multiple FU
and therefore with each procedure. For instance, if a person averages 2.3
terminal hairs per FU and you transplant 1000 FU, the patient will receive
approximately 2300 hairs. The average 2 mm2 graft with a 2mm diameter
contains between four and six FU. Hence, 100 grafts that are 2 mm2 in
size2 mm in diameter, averaging 2.3 hairs per follicular unit and an average of
5 FU, would transfer 1150 hairs. The calculated density also helps to
define the size of each graft. As the number of hairs in each FU increases, the
size of the FU graft increases while if grafts containing multiple FU are being
used to transplant a specific number of hairs per graft, this type of graft can
contain fewer FU in order to reach that number, and can, therefore, be
smaller. Grafts containing more than one FU can also be smaller than
average if they are "cherry-picked" to include only sections of skin in which FU
are closer together than average. (See Chapters 11 & 12). Furthermore, in
FUT it allows the surgeon to customize the transplant by using FU containing
different numbers of hairs in different locations. The calculated density
combined with a determination of the FUD (see below) also assists you in
predicting the amount of tissue you will require from the donor area.
The calculated density also predicts the ratio of follicular units with a
particular hair count. Table 8 outlines how the percentage of natural 1, 2, 3,
4, 5, and 6 hair follicular units changes as the calculated density changes.
Knowledge of the calculated density allows the surgeon to customize the size of
his receptor sites based on the anticipated number of natural follicular units
of a particular size. A low calculated density predicts fewer grafts containing
four or more hairs. In this case the surgeon would need to cut grafts containing
multiple follicular units if a larger number of more dense grafts is desired.
Conversely, the surgeon might consider single follicular units more appropriate
when the calculated density is higher.
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Table 8.
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