The Logic of Follicular Unit Transplantation

Robert M. Bernstein, MD*
William R. Rassman, MD

*Assistant Clinical Professor of Dermatology, College of Physicians and Surgeons, Columbia University, New York, NY

From the College of Physicians and Surgeons, Columbia University, New York, New York (RMB) and the New Hair Institute, New York, New York (RMB and WRR
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Follicular Unit Transplantation is a method of hair restoration surgery where hair is transplanted exclusively in its naturally occurring, individual follicular units. The evolution and rational for follicular unit transplantation will be discussed, as well as the logic for the various techniques used in its implementation. Specifically, the logic for single strip harvesting, stereo-microscopic dissection, automated graft insertion, and large transplant sessions will be reviewed. The central role of the follicular unit constant in the surgical planning will also be discussed.

Progress in modern medicine is often the result of sophisticated technology that allows us to quietly probe into the deepest regions of the human body or to analyze its actions at the molecular level. Rarely is a field of medicine dramatically changed by simple observation. After more than three decades of relative inertia, surgical hair restoration is undergoing such a change. This writing discusses the logical applications of these observations to clinical practice, a logic that has literally revolutionized hair transplantation in just a few short years. It will also touch upon some of the illogical judgments that contributed to its delay.

HISTORICAL ASPECTS
A donor (graft) is better if it is as small as possible. The reason is that if a donor is big, hairs grow in … a very unnatural appearance.

- Hajime Tamura - 19431

If we had only heeded the advice of the pioneering Japanese hair transplant surgeons in the first half of this century, we could have avoided years of unsightly surgical results that caused dismay to thousands of unwary patients, and literally tarnished an entire field of medicine. Unfortunately, the "Japanese insight" was lost to us during World War II and when we tried to "reinvent the wheel, " we did it wrong.

The Punch Graft Technique
After the "rediscovery" of hair transplantation by Dr. Norman Orentreich in 1952, the excitement that hair actually grew, and continued to grow after it was transplanted, clouded the very essence of hair restoration surgery i.e., that it was a cosmetic procedure whose sole purpose was to improve the appearance of the balding patient. The 4-mm plug that had been ordained as the optimal vehicle for moving hair was actually of a size that had no counterpart in nature.

The initial problem was that the decision to use 4-mm plugs was based mainly upon technical rather than aesthetic considerations. In the original, ingenious experiments performed by Dr. Orentreich, published in the Annals of the New York Academy of Science in 1959, which established the concept of "Donor Dominance, " 6 to12-mm punches (trochars) were used to create the grafts.18 At these sizes, there was an unacceptably high rate of hair loss in the center of the grafts due to the difficulty oxygen has diffusing over such large distances. The initial effort to decrease graft size was thwarted by the concern that much smaller grafts would not move enough hair to make the procedure worthwhile. Eventually a compromise was reached, and the 4mm graft was born.

In addition, a logic developed which postulated that, by replacing bald skin with hair bearing skin, most of the balding area could eventually be replaced with hair. No adjustments for scar contraction were accounted for, and no changes in the size of the newly transplanted grafts were expected, despite observations to the contrary. More important, these assumptions were based upon the mathematically impossible feat of covering a large area of balding with a much smaller donor supply, while maintaining the same density.

The punch-graft, open-donor technique was developed with tools in routine use by dermatologists of the time. In the "open-donor method" devised by Dr. Orentreich, the same trochar that was used to make the recipient sites was also used to harvest the hair. Since hair in the donor area emerges from the scalp at rather acute angles that vary in different regions, the physician was required to have the angle of the trochar exactly parallel to the angle of the hair. If there was even the slightest deviation from a perfectly parallel orientation, significant wast of hair would occur from follicular transection. In fact, in many patients, so much transection would occur that the potentially "pluggy" appearance was reduced to a thinner look by the inadvertent reduction in the number of hairs per graft.

The hidden problem, of course, was that this harvesting technique reflected a grossly inefficient use of the donor supply, and patients often became depleted of donor hair long before the transplant process was completed. These problems were compounded by the fact that in the "open donor method" the wounds were left to heal by secondary intention and the resulting fibrosis further altered the direction of the remaining donor hair, making subsequent harvesting even more difficult.

The large donor and recipient wounds created by these punches necessitated that the procedure be performed in small sessions, usually 20 to 50 grafts at a sitting, with the sessions spaced apart in time due to the prolonged healing. As a result, one of the truly unfortunate problems intrinsic to the early techniques was that neither the long-term cosmetic issues, nor the ultimate depletion of the patient’s donor supply, could be appreciated for many years. Possibly because of Dr. Orentreich’s deservedly high esteem in the medical community (he also did pioneering work in dermabrasion, intra-lesional corticosteroids, injectable silicon, and the hormonal treatment of hair loss (to name just a few), the 4mm size went unchanged for years.

Early attempts at reducing the size of the grafts were largely unsuccessful. A reasonable approach to making these large plugs cosmetically more acceptable was to divide them into smaller grafts i.e. to produce split grafts or quarter grafts from the larger plugs.10 Unfortunately, these only resulted in further manipulation and damage to grafts that already contained populations of transected follicles. Simply reducing the size of the punches20 was also problematic since a decreased radius greatly exaggerated the damage caused by even the slightest deviation in the harvesting angle. It seemed that a relative impasse had been reached in trying to create a smaller size graft that would be cosmetically acceptable, contain enough hair to make the procedure worthwhile, and not be too wasteful of the donor supply. Fortunately, new techniques in harvesting the donor tissue provided solutions to these problems.

The Donor Supply
Some hair transplant surgeons, conscious of the finite donor supply, noticed that there were islands of hair bearing skin left behind after the initial rows of plugs were harvested. However, subsequent attempts to harvest the intervening tissue, and leave the wounds open resulted in confluent areas of scarred scalp devoid of hair, and lacking adequate camouflage. Suturing the open donor wounds seemed to be a logical solution to decrease the scarring, but this further altered the hair direction and made the remaining scalp less amenable to successful punch harvesting.

A more creative attempt to deal with this problem was to totally excise the tissue between the rows of punches and then suture the "serrated" upper edge to the serrated lower edge. The wound edges would then neatly come together if the punches were aligned properly.14, 19 There were two important consequences of this procedure. The first was that it produced a piece of "free standing" donor tissue that could be cut into smaller pieces under direct visualization prior to transplantation. The second was that the sutured incision left a single line in the donor area (although somewhat squiggly). After looking at the result of this procedure even the casual observer would have to question the necessity of the punch graft aspect of the process. After all, why not just remove an intact strip of tissue and suture the wound edges closed, obviating the problems of the punches, i.e. the open donor wounds and the punch transection of hair follicles. After a number of years, this is the procedure that was eventually adopted.

The double- and then multi-bladed knifes11, 24, 28 were born out of an attempt to avoid the open donor scars produced by the punch-graft method, and to decrease the transection produced by this "blind" harvesting technique. Unfortunately, it solved only the first of these two problems. As with the punches, the multi-bladed knife was also a form of "blind-harvesting" since the surgeon would still have to match the angle of hair to avoid follicular transection, and the visual cues needed to perform this accurately were either hidden below the surface of the skin or covered with blood. As a result, the necessary fine-tuning of the blade angle, while making the incision, always came too late, i.e. after the transection of hair follicles had occurred.

In addition to the difficulty in following the curve of the skull, as one moved across the donor area horizontally, the fixed relationship between the multiple blades did not allow for any adjustments in the vertical plane. To compound the problem, pressure from one blade would distort the direction of hair near the others. The surgeon could adjust one blade (usually the upper) to follow the changing hair direction as he moved around the scalp, but since the angle of hair changed in the vertical dimension as well, transection caused by the other blades would be unavoidable. In addition, as one tried to angle the knife, in order to follow the vertical curve of the scalp, some blades might be too superficial, while others were too deep. The superficial wound required a second incision which ran the risk of further transection. The deeper wound risked cutting fascia, or larger nerves and blood vessels, increasing the morbidity of the procedure.

An obvious solution would be to take a single strip of tissue from the donor area. The problem with that was, in all but the smallest procedures, one was left with a large, three dimensional piece of tissue that defied further sectioning. In addition, with the trend to perform larger sessions, the fine slivers produced by the multi-blade knife grew more appealing, and the cumbersome nature of the single strip proved a hindrance to completing the surgery in a reasonable period of time.

There was still one last important issue with the multi-bladed knife, i.e. that the blades moved in random planes though the donor tissue. As we will soon discuss, hair doesn’t grow randomly in the donor area, nor in the rest of the scalp for that matter, but in tightly organized bundles called follicular units. In effect then, the multi-bladed knife, even if it passed though the scalp perfectly aligned with, and parallel to, the growing hair, would still break up the integrity of these naturally occurring structures and reduce hair yield.

The significance of this last problem was not initially known, but it became apparent that transplanting very small grafts in large quantities, produced a thin look, and that this look was thinner than one would have anticipated based solely upon the amount of hair transplanted. The role of the multi-bladed knife in contributing to this problem is still in dispute, but it is felt by these authors, as well as others, to be very substantial. Other factors will be covered in later sections.

The recognition that square inch for square inch replacement of bald scalp with hair would not be possible with transplantation, posed a frustrating dilemma to the surgeon, and allowed a number of other procedures to proliferate, namely scalp reductions, lifts, and flaps. However, when working toward the elusive goal of restoring original density, the mathematics of these procedures made no more sense than the plugs they were supposed to complement or replace. Regardless of the choice, the precious donor supply was still being consumed, and the patient’s long-term results compromised. In retrospect, it seems that the popularity of these procedures was not based upon their intrinsic value, but upon the fact that the alternatives were so poor. When the quality of the transplantation procedures finally improved, the frequency of these surgeries declined.

This is the position that the field of hair transplantation found itself in as it entered the 1990’s, and for the most part stayed in until 1996, when follicular unit transplantation caught on, and everything changed. As we will discuss, the logic of using follicular units is quite inseparable from the technique itself, and many of these techniques had their foundation as far back as 1982 in the "Punctiform" procedure of Carlos Uebel26 that later evolved into the "Megasession", and in the work of Dr. Bobby Limmer who began using microscopic dissection and single strip harvesting as far back as 1988.17 Surprisingly, the fact that hair grows in discrete bundles was largely unknown to most hair transplant surgeons for almost forty years, and it was the general revelation that these naturally occurring groups could be used to the patient’s advantage that changed the hair transplant procedure forever.

THE LOGIC OF PRESERVING THE FOLLICULAR UNIT
The underlying premise of follicular unit transplantation is that the intact, individual follicular unit is sacred. It should neither be broken up into smaller units, nor combined into larger ones.5, 7, 9

This simple idea may not seem like a radical approach to hair transplantation, but when viewed in the context of how the surgery has been performed over the past forty years (when the very existence of the follicular unit went generally unrecognized), it is radical indeed. Even now when its existence is widely known, there is a trend in hair transplantation to not only ignore the importance of the follicular unit, but to ignore the integrity of the follicle itself.

Figure 1: The follicular unit

The follicular unit (see figure 1) was first defined by Headington in his landmark 1984 paper "Transverse Microscopic Anatomy of the Human Scalp".13 The follicular unit includes:

1 to 4 terminal follicles
1, or rarely 2, vellus follicles
associated sebaceous lobules
insertions of the arrector pili muscles
perifollicular vascular plexus
perifollicular neural net
perifolliculum – cirumferential band of fine adventitial collagen that defines the unit

This rather dry definition belies the fact that the follicular unit is a physiologic entity rather than just an anatomic one. As we will see, the obvious reason to preserve the integrity of the follicular unit is economy of size, i.e. it is a way to get the most hair into the smallest possible site, and create the smallest wound. The ingenious hair transplant surgeon, Dr. David Seager, gave us another.23 In a bilateral controlled study, matched for the number of hairs, he showed that when single-hair micrografts were generated from breaking up larger follicular units, their growth was less than when the follicular units were kept intact. In his study, he showed that at 5 ½ months the single-hair micrografts only had an 82% survival rate, whereas the intact follicular units had a survival of 113%, presumably due to the fact that hairs in telogen, that were not initially counted, also began to grow.

Clearly this is an example where "the whole is greater than the sum of its parts, " supporting the concept of the follicular unit as a physiologic entity. More work is certainly needed to pinpoint the mechanism for the decreased yield of this "divided unit." Determining whether it is due to factors intrinsic to the unit itself, increased susceptibility to environmental events during the transplant, or both, will have an important impact upon the direction of future research when trying to find techniques that will maximize growth.

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