Musings on Hair Density

drcole

When discussing hair transplant surgery, it is useful to consider various ways of counting hairs or follicular units. This is often done when a patient comes in for an evaluation; we examine the donor area and document what the follicular density is (number of FU’s per unit area, usually a square centimeter), and also the hair density (number of hairs per square centimeter).
This is useful because it gives us an idea of the amount of hair that may potentially be transferred from the donor region to the recipient area, where thinning or balding has taken place. Some physicians use various tools such as the so called densitometer, or even the trichograph, capillicare, or folliscope to calculate densities. This may give fallacious results, as hair counting is much more difficult than it seems.
Let us consider a case in point. Look at the photo below and see if you can count the number of FU’s present (count only the groups where you can see the base of the hairs emerging from the scalp). Not to tough, eh? Did you get 28 groups? Maybe you were off by a couple. As you can see, it’s not TOO hard.

Fig 1

Now, try counting the number of hairs. This gets a little more difficult. One way to do it is to classify all the groups as ones, twos, threes, fours, etc. Then add all these up and you have the hair density. Then divide the number of hairs by the number of FU’s and you have the calculated density, or CD. This is an important number, for a variety of reasons, as we’ll see later.
The point I’d like to make here is this: it is extremely difficult to get an accurate hair count using optical machinery. It is difficult to do with the human eye just observing the hairs in a single plane; it is most accurate when one can move the instrument around or even use forceps to “tease” the hairs apart. This is because often two hairs will sit adjacent to one another and appear as one. Let’s go back to the photos and see. The second photo is the same as the first, but we have written in by hand the number of hairs per FU. Some of them will fool you. Look, for instance, at the big fat “two hair” unit at about “3 o’clock”, a little toward the center. It’s actually a three! And the “one hair” just up and to it’s right? It’s a two. Fooled ya!

Fig 2

Seriously, however, this is a problem with counting hairs, unless there is a “real-time” ability to move the viewer or the hairs themselves, one can easily be misled. And there is another issue here in terms of the calculated density (CD).
We have noted in our work with FIT that we have a higher CD than that usually obtained with strip surgeries. Why? Well it’s easy. With strip surgery, what you see is what you get. If the strip has a high percentage of ones and twos, then that is what you have to work with. There is no way around that fact. Look back at the photos; the patient has a high percentage of ones and twos, and no fours or fives at all, at least in this sample. A strip taken from here is a low yield strip in terms of total numbers of hairs available (unless you’re working on his hairline only Wink

With FIT, however, we can decide as we harvest, which FU’s to take and which to leave behind. If the patient DOES have a higher percentage of ones and twos, then we “cherry pick”. The threes and fours are right there, calling to us, just begging to be harvested. Which method would YOU want in order to maximize the results for coverage on top of your head?
Or, conversely, if the work is all being done on the hairline, and ones and twos are the preferred grafts, well… you guessed it. We can “selectively harvest” for those as well! So my point is this: FIT is convertible, that is, it has a built in flexibility that only works in the patient's best interest. Whatever types of grafts we want, we can get. And this is not only a matter of follicular unit size. If finer, more delicate hairs are needed for the exacting work on the leading edge of the hairline, where that soft, feathered transition zone is a must, then are the coarser, thick hairs from the middle of the head the best choice? Absolutely not. This is the ONLY area that strip surgeons can harvest from (without risking a grossly widened scar). This is why we see so many unnatural looking hairlines from elsewhere; even if ones and twos are placed appropriately at the front, the CALIBER of the hair is to large. There is nothing natural about big fat, highly pigmented hairs, even singles, sticking out like sore thumbs on the front of the hairline. It’s supposed to be soft and feathered!
How can we use FIT to avoid this pitfall? Go low on the nape of the neck. Go over the ears. Go wherever we need to go to get the appropriately fine hairs for that all-important hairline; the hairline that everybody sees, as soon as they meet you, and that you see every time you look into a mirror.
We have some interesting data that we plan to publish soon, that deals with the changes in density in different areas of the donor region, and all over the head for that matter. But that’s for another time. Adios, amigos.

wassup

very interesting Dr. Cole - great stuff!

it also looks like there are some hairs just under the skin as well. are those hair cycling back into a growing phase or am I just seeing things and these have already broken through already (around 2 o'clock and a couple around 7-8 o'clock as well)?