Follicular Unit Transplantation: the State of the Art

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.