INTRODUCTION
Follicular Transplantation is the logical end point of over 30 years of evolution in hair restoration surgery beginning with the traditional large plugs and culminating in the movement of one, two and three hair units, which mirror the way hair grows in nature. The key to follicular transplantation is to identify the patient’s natural hair groupings, dissect the follicular units from the surrounding skin, and place these units in the recipient site in a density and distribution appropriate for a mature individual. The critical elements of follicular transplantation are an accurate estimation of the donor supply of hair, meticulous dissection of the follicular units, careful design of the recipient area to maximize the cosmetic impact of the hair transplant, the use of large numbers of implants in fewer rather than more sessions, a long-term master plan that accounts for the progression of the male pattern alopecia, and realistic expectations on the part of the patient.
FOLLICULAR UNITS
The concept of follicular transplantation is based upon the observation that, in general, hair does not grow singly, but with the exception of the hairline, emerges from the scalp in groups called follicular units. Histologically, these units are comprised of 1 to 4 terminal and 1 to 2 vellus hairs that form a distinct group bounded by a circumferential band of adventitial collagen, the perifolliculum1. Two or three hairs within this group will often merge into a common canal and protrude through a single follicular orifice (Figure 1a). The merging of the shafts usually takes place in the infra-infundibulum of the hair follicle. Variations can be seen where the shafts share some anatomic structures with their neighbors exiting through individual but adjacent pores. The importance is not the anatomic merging of the unit but the fact that the distance between the follicular groups exceeds the width of the follicular unit itself (Figure 1b). If these follicular units are ignored in dissection, then more skin will be transplanted than hair and significantly more skin will be moved than needed. If these groups are recognized, the implant can be “follicular” and the anatomic proximity of the hairs within each unit can be used to the surgeon’s advantage.
The advantages of using follicular implants in contrast to traditional grafts include:
– surgical wound size at the recipient site is minimized
– skin surface deformity is eliminated
– distortion due to fibrosis associated with healing is reduced
– natural scalp contour is preserved
– oxygen diffusion to implants is maximized
– interruption of blood supply is minimized
– post-op recovery time is reduced
– hair units may be placed extremely close together
– extensive numbers of implants may be moved per session
– hair may be distributed in a natural pattern
– great flexibility in recipient site design
NATURAL HAIR GROUPINGS
The observation of over 1,200 patients using the densitometer2 reveals that in the donor area the great majority of one’s terminal hair grows in “natural hair groupings” of two, three, four, and rarely five or more hairs. These natural hair groupings are the clinical correlate of the follicular unit and have a density of approximately 10 units per 10mm2 field, supporting the view of Headington1 that the absolute number of follicular units per unit area in man appears to be relatively constant and is around one per mm2 . The donor density (hair shafts per mm2 ), however, is quite variable and can range anywhere from 1 to 4 hairs per mm2. The number of hair shafts in each follicular unit varies for each individual and is related to the patient’s average donor density. Thus, in a patient with a high density (Figure 2a), there would be a higher proportion of groups having 3 and 4 hairs per follicular unit, but the number of follicular units per mm2 would still be around one. In a person with low density (Figure 2b), the predominant hair groupings might be of one and two. The presence of many hairs occurring singly is, therefore, the exception rather than the rule. To state it another way, an individual with high density does not have hair groupings closer together but has hair groupings with normal spacing between them. Each group, however, contains a greater than average number of hairs. Similarly, in a patient with low density, the spacing is not greater, only the hair groupings are smaller. As a patient ages, hairs randomly begin to miniaturize in each group so that each group will contain a combination of full terminal hairs, partially miniaturized terminal hairs, and vellus hairs (which are clinically insignificant) . Eventually, the miniaturized hairs are lost, and the natural hair groupings are reduced in number. In all adult patients, the donor area contains both terminal and miniaturized hair, indicating that this zone is not truly permanent but will thin gradually over time. It is not until the total hair density in the donor area falls below 1.5mm2 that some follicular units completely disappear, and the follicular density is seen to decrease.
In a person susceptible to androgenetic alopecia, the balding area thins in a way somewhat analogous to the donor area, i.e. miniaturized hairs gradually replace terminal hair, and the hair groupings initially decrease in size rather than in number. The major difference is that in the balding area, miniaturized hairs can populate entire hair grouping as the baldness progresses and can be so fine as to be indistinguishable from vellus hairs, whereas in the donor area there generally remain three rather distinct populations of hairs; terminal, miniaturized, and vellus. In some patients experiencing the early stages of what will eventuate in extensive balding (i.e., Norwood Class 6), where there is still some very light wispy coverage, the recipient density in these areas is surprisingly normal (i.e., close to the patient’s donor density). However, all the hairs in each follicular unit are extensively miniaturized. This underscores the fact that it is not only the absolute number of hairs but their diameter and character that contribute to clinical appearance of fullness. In the balding area, it is only after the alopecia becomes extensive and the follicular units are comprised of only one or two miniaturized hairs each, that the actual follicular units begin to disappear from the bald area.
The importance of understanding the concept of hair groupings and their age-related changes is that in order to have a natural looking hair transplant, hair placed in the recipient site should approximate that which would have been present there naturally had the individual not balded. Since the natural hair groupings in the donor area correspond to the original hair groupings in the recipient area before they were impacted by androgenic hormones, they reveal the appropriate way that this area should be restored. For example, in transplanting a 45 year old Norwood Class 6 with an average donor density of 2.2 hairs/mm2, one might try to restore the front and top of his scalp, leaving significant bitemporal recession and the crown bare. The distribution of natural hair groupings in this case might be 20% 1’s, 45% 2’s, 30% 3’s, and 5% 4’s. Therefore, attempting to place predominately 5 or 6 hair groups in this area would be destined to look unnatural. Similarly, all 1’s and 2’s in this situation would look too thin. In all situations, of course, the frontal hairline would be composed of single hair units. In the vast majority of restoration procedures, it would be appropriate to attempt to match these groupings, as they occur in nature, to produce an aesthetically balanced appearance.
WOUND HEALING
There are four related benefits to recipient site wound healing when follicular implants are used exclusively. These are minimizing the recipient site surgical wound size, eliminating skin surface deformity, decreasing the dermal fibroplasia associated with healing, and avoiding pigment alteration.
By limiting the implant to the follicular elements of the skin, the recipient site wound can be just slightly larger than the follicular unit itself so that the unit sits snugly in it. Because the follicular units are so compact, one and small two hair units have essentially the same footprint and can be placed in the same size site; and two, three, and four hair units have the same footprint and can be placed in the same size site. When the stretched slit contracts around the inserted follicular unit, the snug fit minimizes the space for a coagulum to form and reduces the distance for re-epithialization. In this situation, the fibrin “glue” will be maximally effective in securing the implant, exudate and crust formation will be reduced, and the healing time will be shortened. We instruct all patients to shampoo the day following their surgery, letting low pressure water flow over the transplanted area. This irrigation will allow the majority of patients to be free of crusting within 24 hours, requiring no dressings on the recipient area. We have found that by eliminating the crusting in one day, the surrounding erythema fades much more quickly. Within several days, most patients have faint erythema and the stubble of hair as the only clue to their hair restoration procedure.
Hair from the back and sides of the scalp grows at an angle of approximately 30 degrees. When larger grafts (which are essentially cylinders of skin and hair) are harvested, the epithelium creates an acute angle at its superior edge and an obtuse angle on the inferior edge. When the grafts are inserted into the recipient site, they must be placed at an angle that matches the angle of the original hair which vary from approximately 30 to 60 degrees. Because of this angle, mechanical forces which act on the graft immediately after placement and throughout healing, interrupt the edge-to-edge alignment of the graft with the surrounding skin causing either settling or elevation of the graft, or both. As each graft is distorted ever so slightly, the composite effect of many such grafts produces the surface irregularity (cobble stoning) of the traditional hair transplant. This surface irregularity becomes clinically more apparent as graft sizes increase and as the sites are made with punches rather than slits. This whole phenomena is simply avoided when the implants are devoid of unnecessary skin.
Slit grafting prevents cobblestoning but often produces a dimpling or puckering at the site of the emergence of the hairs by the down growth of the epidermis alongside the graft. Although follicular units are technically placed into “slits”, by reducing the perifollicular epithelium in the follicular implantation, the site required is so small (1mm) and the follicular unit so compact that this deformity does not occur.
The fibrosis that results from the healing of larger wounds causes an additional problem. Just as angulation causes surface irregularities, it also produces a distortion of the dermis that may not be readily apparent clinically. The significance of this is that grafts placed parallel do not always end up having their hair parallel under the skin surface when dermal reorganization is complete. This distortion impedes the close placement of future grafts due to the risk of damaging existing ones (even if the original angle could be exactly reproduced). This distortion of the hair shaft produced by fibrosis is easily observed each time hair is harvested and dissected from the tissue next to a previously excised donor area. Incidentally, one of the difficulties in repairing unsightly plugs by the obviously simple method of decreasing the density of the plugs with electrolysis is that the distortion of the fibrosis impedes the introduction of the electrolysis needle. The dermal changes produced by successive procedures and the difficulty in reproducing angulation are among the most compelling reasons to densely pack a given area the first time rather than to repeatedly violate a transplanted area with multiple sessions.
Another casualty of the movement of larger grafts is the melanocyte. Repigmentation after loss or disruption of the epidermis occurs by two mechanisms; migration of melanocytes from adjacent normal epidermis and migration from the follicular appendages. The presence of focal hypopigmentation at the base of larger grafts is due to the arrest of melanocyte migration into the area and attests to the fact that the grafts have produced scar tissue that has damaged both epithelial elements. The hypopigmentation at the base of the grafts often serves to accentuate any apparent plugginess by highlighting the resultant physical deformity with an additional contrast… that of color. Fortunately, hypopigmentation is less common with very small grafts and has not been observed in follicular transplantation.
CONTOUR AND VOLUMETRIC CHANGES
One of the rarely discussed but very significant cosmetic problems of grafts is the extra volume of tissue introduced into the recipient site. This extra tissue produces a fullness and elevation of the transplanted scalp and a clinically apparent ridge separating it from the surrounding bald scalp. (This condition in which the elevated area is relatively soft must be differentiated from the “hyperfibrotic changes” in the recipient area described by Stough3, which is a proliferative process and produces an area that is indurated.) The reason for this phenomena is that balding is not merely the absence of hair. It is an atrophic process with absence or marked diminution of entire pilosebaecous units and their associated vascularity and connective tissue support. These appendages contribute substantial volume to the normal scalp. The solution most commonly used to solve the problem of adding additional tissue to the recipient area is to cut some of the recipient area away, i.e. punch it out. Unfortunately, intact donor scalp is not the perfect match when transplanted into the bald recipient area, since it is significantly richer in each of these elements. Thus, removing skin in the recipient site is a futile attempt at compensating for the increased volume of the larger grafts, since the donor graft is much thicker than the atrophic recipient skin which it replaces. The better solution is not to transplant the intact skin in the first place, but to add only the follicular element which had been lost.
BLOOD SUPPLY AND OXYGENATION
In a “virgin scalp”, the blood supply to the recipient area is unimpeded. Each graft placed in the recipient site induces local fibrosis that interferes with normal blood flow, and every punch, large slit or ultra-pulsed laser site, has the chance to transect or seal off viable blood vessels. In subsequent procedures, the hair placed between existing grafts are implanted into scar (even though it may be microscopic) and receive the diminished flow associated with it. In follicular transplantation, the recipient site is created with a “needle like” knife that produces a minimal amount of trauma. A blood vessel that might be pierced would immediately re-seal analogous to the way a vessel heals after venipuncture. When the single hair graft is then placed into the site, the graft itself is soft and causes no additional trauma to the vessel. If it were true that a diminished blood supply would fail to support uniform graft take, then asymmetry, gaps, or areas of variable density would result from this technique and be magnified in areas of very close placement “dense packing” of grafts. However, this is not observed in spite of the fact that follicular dense packing techniques are used predominantly in the frontal hairline where any problem would be most obvious.
Since oxygen reaches the follicle by simple diffusion, oxygenation is a function of tissue mass. The larger the transplanted unit, the greater the risk that the center of the graft is impacted by the deprivation of oxygen. In contrast, the barrier to oxygen transport is at a physiologic minimum with the follicular implant. In this respect, the follicular implant should have enhanced survival and the phenomena of “doughnuting” seen with larger grafts can be avoided. In addition, since the follicular unit sits snugly in the recipient site, there is a minimum amount of coagulum impeding diffusion from the dermal blood supply to the edge of the graft.
TRANSPLANTATION IN EXTENSIVE QUANTITIES
Once the question of implant size is resolved, the corollary issue is the necessity of transplanting extensive quantities of these implants in a single or very limited number of sessions, given its medical feasibility. A simplistic answer is that when graft size decreases, the number of grafts must increase to yield the same amount of hair, which of course is true. However, there are a host of more compelling reasons to perform transplants in large sessions.
Putting aside anatomic, physiologic and technical issues for the moment, it is important to emphasize the social and practical reasons to strive toward large sessions. The majority of patients who seek hair restoration surgery feel that their balding interferes with their life either socially, professionally, or both. Until the hair restoration surgery reaches a point where there is acceptable cosmetic improvement, the patient will be focusing more on his hair loss than he did before. Multiple, small procedures spaced out over an extended period of time keeps the patient focused on the very problem he wanted to correct. During this period, his self-consciousness worsens and disappointment begins when he realizes that limited procedures fall short of his expectations. Even in the emotionally secure individual, the disruptions in daily life from the scheduling of multiple surgeries, the resultant limitations in activity, and the concern about their discovery can cause undue stress. In addition, post-operative numbness and paresthesias in the posterior scalp are constant reminders of the operation.
Multiple, partial procedures produce short-term cosmetic problems. The planning of rows of grafts that must be filled in at a later time to look normal or to be camouflaged by subsequent rows of micrografts is certainly not appreciated by the patient seeking cosmetic improvement. Flaps, multiple-staged scalp reductions, and those requiring tissue expansion certainly fit into this category as well. often the cosmetic appearance of the work is only acceptable because the patient’s own hair camouflages it. Patients undergoing multiple procedures in such a cosmetically visible area as the scalp can be so discouraged that they give up on the process entirely. In fact, many do stop until their baldness progresses and their own hair becomes unsuccessful in camouflaging the surgery. They then re-enter the population of partially treated patients shifting from doctor to doctor seeking someone who will finish the procedure. There is an important distinction between a person in the early stages of balding, undergoing a hair transplant, who has been well-informed that future procedures will be required as he balds further and a patient who begins hair restoration unaware that during an extended surgical process his appearance may be totally unacceptable to him and that he may never reach his goal.
With respect to medical feasibility, follicular transplantation is qualitatively, as well as quantitatively, different from traditional grafting; therefore, the mere extrapolation from the older techniques will not allow one to predict the outcome of the newer procedure. The physiologic limitations to transplanting large numbers of traditional grafts, such as the impediment of blood flow and interference with oxygenation as discussed above, clearly do not apply when dealing with the movement of small follicular implants. Experience has shown that up to 3600 or more follicular units may be moved safely in one session with the main limitation being the donor supply rather than the physiology of the recipient area.
The surgical issues favoring large sessions are significant. Virgin scalp has normal collagen and normal blood flow. If possible, one should transplant the total number of required grafts in the first session to take advantage of this environment. Successive implantation into a previously treated area is always hindered by the angle of the existing grafts, distortion due to fibrosis, and altered vascularity. Although follicular implantation can minimize these factors, it certainly cannot reduce them to zero. In addition, the spacing, orientation, and distribution of the implants can be planned in an unrestricted fashion without these parameters being controlled by their relationship to existing grafts.
In virgin scalp, the dermis retains its normal distensibility, therefore, implants can be placed closer together with less tendency for “popping” of adjacent units. During the post-op period, the implants will be less likely to elevate or settle as healthy collagen and elastic fibers grasp the transplanted units firmly and add to the glue-like properties of the coagulum in securing the implants.
Hair transplantation often produces varying degrees of telogen effluvium in the recipient area. This hair loss can be substantial in the young patient who is rapidly balding and whose recipient area is characterized by a high degree of miniaturization. often this lost hair does not return. Unless a significant amount of hair is transplanted in these individuals, the gain from the surgery may not even be adequate to compensate for the loss due to the telogen effluvium.
Large sessions also offer an advantage over multiple small sessions in the donor area. Each time grafts are harvested from the donor area, there is loss of potential donor hair due to destruction of hair adjacent to the wound edges from the fibrosis associated with primary intention closures. In addition, the hair follicles adjacent to the healed suture line are often distorted and more difficult to harvest on subsequent procedures causing an increased number of hairs to be transected . Minimizing the number of times the donor area is accessed will obviously minimize the distortion and wastage due to the closure.
REFERENCES
1. Headington JT: Transverse Microscopic Anatomy of the Human Scalp. Arch Dermatol 1984; 120:450.
2. Rassman WR, Pomerantz MA: The Art and Science of Minigrafting. International Journal of Aesthetic and Restorative Surgery 1993; 1:28-29.
3. Stough, DB: International Society of Hair Restoration Surgery, Third Annual Meeting 1995; Verbal Communication.
4. Haas AF, Grekin RC: Antibiotic Prophylaxis in Dermatologic Surgery. JAAD 1995; 32:155-164.
5. Salasche SJ, Bernstein G, Senkarik M. Surgical Anatomy of the Skin. Norwalk, Connecticut: Appleton and Lange, 1988 pp 176-177.
6. Rassman WR, Carson S: Micrografting in Extensive Quantities, The Ideal Hair Restoration Procedure. Dermatologic Surgery 1995; 21:306-311
7. Larson PO: Topical Hemostatic Agents for Dermatologic Surgery. J Dermatolgic Surg. Oncol. 14:6 1988.
8. Marritt E, Dzubow L: The Isolated Frontal Forelock. Dermatologic Surgery 1995;21523-538.
9. Transplant Videografting System of the Professional Hair Institute; displayed at the International Society of Hair Restoration Surgery, Third Annual Meeting 1995.
