Graft size and angle
During a hair transplant, a hair surgeon always studies the
orientation of the hair follicles so that he can graft them in
the recipient site as necessary so that the natural flow of hair
is retained like the patient originally had. This success of this
approach was mainly due to the artistic abilities of the surgeon.
Using mathematical modeling, Alhaddab and his colleagues have
arrived at a workable proportion in which they have used the size,
angle of the graft and the distance between one graft from the
other or the intergraft distance as the parameters with 1sq cm
area as the working area.
In an adult male, the number of hairs per sq cm ranges between
130-280 with an average of 200 hairs / sq cm. If the man is diagnosed
to have alopecia and is visibly seen to have thin hair, then he
must have lost at least 50% of his original hair density which
means he will have only 65-140 hairs/ sq cm. In order to restore
normalcy the patient has to be transplanted with as many hairs
lost. But in most of the hair transplants carried out so far,
this has not been possible and if at all possible, the final result
is not as pleasing. In terms of number of follicular units, 40
follicular units / sq cm with 2-3 hairs each give a hair density
of 80-120 hairs.
The following assumptions have been made before embarking upon the calculation-
1. The angle of hair transplant – 0 deg means vertical to the skin or
at 90 deg to the skin surface; 75 deg is horizontal or 15 deg from the skin
surface. [Imagine a protractor with 90 deg as 0 and 0 as 90 !]
2. 1 mm is the standard hair graft diameter.
3. 5 mm is the length of the hair graft along with the shaft
4. The depth at which the graft is to be inserted is equal to the length of
the graft multiplied by cosine alpha. This makes the length and width of the
recipient site 10 mm each and the depth of the site 5 mm.
5. The interslit distance – maintained at 1 mm in the anterior and posterior
sides of the slit. 1.5 mm is maintained at the lateral distance so that when
the graft is inserted, the wound will heal and the distance would close in
by 0.5 mm during the healing bringing the grafts closer. All the mentioned
distances will be halved to calculate for either side of the graft.
6. Volume wasted is not taken into consideration but is presented as the areas
in continuation with the adjacent grafts.
Keeping these parameters as standard a mathematical expression
has been formulated that will help calculate the number of hair
follicles necessary for a sq cm of hair transplant.
By this mathematical expression what is very clear is that depending
on the angle of the hair follicle the number of hairs that go
into a recipient site is delineated. Another significant advantage
is in determining the use of nerve blocks to anesthetize patients
depending on the surface area of the skin available for the procedure.
Size and angle of the grafts play very important roles in achieving higher
hair density. At an angle of 90 deg, maximum number of hairs (33) can be inserted
while at an angle of 15 deg only 8 can be inserted. The actual density of
the hair depends on the inter distance variability and this depends on the
thickness of the shaft too. When the shaft is less dense, closer packing of
the grafts would result in better density, but the availability of donor hair
for closer packing needs to be decided prior to the procedure. In order to
minimize surgical wound, the grafts have to be dissected to near perfection.
In 1998 Dr. Meyer reported the following results he achieved
in terms of density in all the hair transplant procedures he carried
out. A 10 follicular unit/sq. cm had a survival rate of 97.5%,
20 with 92.5%, 30 with 72.5% and 40 with 78.1% which shows that
achieving higher density results in decrease in the survival rate.
Use of this mathematical formula might help in evaluating patients to help
them achieve greater hair density even if it is filling of thinned down mane
and not necessarily high degree alopecia.
Graft size and angle references
- Alhaddab M, Kohn T, Sidloi M. Effect of
graft size, angle, and intergraft distance on dense packing
in hair transplant. Dermatol Surg. 2005 Jun;31(6):650-3;
discussion 654.
PMID: 15996414
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