THE LOGIC OF SINGLE STRIP HARVESTING

The use of the multi-bladed knife is incompatible with follicular unit transplantation. When one remembers follicular unit anatomy and compares it to the construction of the knife, the reason should be obvious. The multi-bladed knife has blade spacing that generally ranges from 1.5 to 3mm. When these blades pass through a donor area that has follicular units randomly distributed at 1/mm2, few follicular units will be left unscathed. Clearly, one pass of the multi-bladed knife will break up many of the naturally occurring follicular units even before they leave the scalp and immediately reduce the follicular transplant procedure to one of mini-micrografts "cut to size."8

The "lure" of the multi-bladed knife is that it quickly generates fine strips of tissue that can easily be dissected into smaller pieces, and the finer the strips, the easier the dissection. But, besides destroying the integrity of the follicular unit, the multi-bladed knife also causes transection to the follicles themselves, and the finer the strips the worse the transection. As was discussed in the first section, the multi-bladed knife is a form of "blind harvesting" that makes all of its incisions in a horizontal plane where the angle of the emerging hair is the most acute and the incisions can cause the most damage. Another issue complicating the harvesting is that follicular units actually transverse though the skin in a slightly curved path since the bulbs are random in the fat and "gathered" into bundles in the dermis.1 Regardless of the instrument, the initial incision is always going to be relatively "blind" so it makes the most sense to remove the strip with as few incisions as possible, and then perform all further cutting under direct visualization. This is the logic behind single strip harvesting.

It is argued by some, that a free hand ellipse is the preferred method for removing the strip, so that the cutting of each wound edge can be controlled separately (the upper edge should always be cut first). It is argued by others that two parallel blades offer more stability and avoid the problem of cutting through a mobile and partially distorted second edge (due to the greater contraction of the dermis relative to the epidermis and fat). Regardless of the personal preference of the surgeon, the concept is the same. Single strip harvesting is the best way to minimize transection, and the only way to provide adequate tissue for follicular unit transplantation.

THE LOGIC OF MICROSCOPIC DISSECTION

There is probably no other aspect of follicular unit transplantation that has generated more controversy than the use of the microscope. Fortunately, in no other area is the logic more straightforward. Stereo-microscopic dissection was introduced into the field of hair transplantation by Dr. Bobby Limmer17 who recognized the logic of using this tool as early as 1987. Its full value and impact is only now first being appreciated. The following three statements summarize its use:

You can only perform follicular unit transplantation if you have follicular units to transplant.
In order to dissect intact individual follicular units, you must be able to see them clearly.
Only the microscope allows their clear visualization in both normal and scarred skin, independent of the specific hair characteristics of color, hair shaft diameter, and curl.
Follicular dissection can logically be divided into two parts; the subdivision of the initial donor strip into smaller pieces and the further dissection of these pieces into individual follicular units. The first part of the procedure, the handling of the intact strip, has always been the most problematic. This is the main reason for the continued popularity of the multi-bladed knife as the multi-bladed knife, in effect bypasses the first part of the procedure by generating thin sections that can be laid on their sides. The thin sections, resting on their sides then have stability for further dissection and permit transillumination from back-lighting. The intact strip however, is difficult to stabilize and is too opaque for transillumination to be useful.

The dissecting microscope allows the strip to be divided into sections (or "slivers") by actually going around follicular units leaving them intact. The dissecting stereo-microscope is able to accomplish this because of its high resolution (usually 5x more powerful than magnifying loops) and its intense halogen top-lighting that provides continuous illumination, as one dissects through the strip. Stability can easily be achieved by applying slight traction to the free end of the strip. The thin slivers are then laid on their sides and the microscopic dissection of the individual units is completed. With stereo-microscopic dissection, except for the outer edges of the ellipse, every aspect of the procedure is performed under direct visualization, so that follicular transection can be minimized and the follicular units maintained.

In a bilaterally controlled study, 4 the dissecting microscope was compared to magnifying loops with transillumination, for the preparation of follicular unit grafts after the strip was divided into thin sections. The results showed that microscopic dissection produced a 17 % greater yield of hair as compared to magnifying loops with transillumination. This study showed an increase in both the yield of follicular unit grafts, as well as the total amount of hair. What is important to note is that this increase was observed when only the latter part of the dissecting procedure was studied i.e. after the strip has already been cut into sections. When complete microscopic dissection is used, the difference in yield is even more significant, and is probably on the order of an additional 5% to 10%.

THE LOGIC OF AUTOMATION

Although in concept, follicular unit transplantation may be the "ideal" transplant procedure, in its clinical application it poses special problems that have limited its widespread use.

Follicular unit dissection is exacting and requires special skill.
Follicular units are delicate and require special handling.
Follicular unit transplantation is labor intensive and time consuming.
One approach to these problems is to defend the status quo and rationalize the use of older techniques. The more logical solution is to solve the problems. The Rapid Fire Hair Implanter Carousel is a new instrument that has been designed to address these technological problems through automation. 21 The "Carousel" works by creating a recipient site with a specialized knife, and then "dragging" the graft into place as the knife is withdrawn. This "dragging" action is especially useful for small, delicate grafts, such as follicular units, as they normally tend to compress or bend when pushed. By combining site creation and graft placement into a single step, the extra time it would take for the grafts to be inserted separately is virtually eliminated. The cartridge, which holds 100 units at a time, is specially designed for procedures involving large numbers of grafts and may also be used in mini-micrografting techniques.

An interesting phenomena helps to explain why the Carousel places grafts into recipient sites so easily, while manual insertion is so problematic. The "finger" of the Carousel is able, in one motion, to insert the implant down to its final position in the skin. The surrounding tissues then apply a predominantly lateral force to the graft, holding it in place as the instrument is removed. In contrast, when grafts are inserted manually into a small site, the forceps allow only partial insertion on the first pass. While the forceps are being re-positioned, the vector of force on the graft is upward, and extrusion or popping occurs. Further attempts at insertion are clouded by the bloody field, and the implants, which were carefully grasped initially, are now grabbed across their growth centers and forced into the hole. This process causes crush injury and often irreversible damage. It is referred to in the literature as "H" or Human factor12, and is especially important when using small grafts that are more susceptible to mechanical trauma.

In all transplant procedures, economy of time is an essential element for success. Not only is a shorter procedure more practical for the staff and patient, but the grafts, subject to a relatively hypoxic environment once they have been removed from the body, are more quickly reunited with their oxygen supply. Although chilled holding solutions, greatly increase the survival of tissue outside the body, the sooner the grafts are re-inserted, the greater will be their chance of maximum growth. In large transplant sessions, the Carousel’s speed possibly represents its most important benefit.

Another source of injury that particularly affects small grafts is desiccation and warming. The grafts are at greatest risk while awaiting placement into the scalp, since at other times they can be held in chilled solutions. It has been recently shown that dried grafts are especially sensitive to mechanical trauma and will compound this form of injury (Gandleman M: Light and electron microscopic analysis of controlled crushing injury of micrografts. Presentation, ISHRS, Barcelona 1997). Warming will accelerate the effects of tissue hypoxia, as it speeds up the anaerobic metabolism. The enclosed cartridge of the Carousel helps to maintain a stable environment for the grafts from the time of dissection right until they are inserted into the scalp.

By reducing staffing requirements, operative time, and, most important, H-factor, automation appears to be a logical way of addressing many of the technical problems associated with the transplantation of large numbers of small grafts. Hopefully, this will allow a high quality follicular unit transplantation procedure to be more easily performed by physicians and, as a result, be available to a greater number of our patients.

* Disclosure Statement: One of the authors of this article has a proprietary interest in Rapid Fire Hair Implanter Carousel© manufactured by Apex Medical Products, LLC, Las Vegas, Nevada.

CONCLUSION

We have come full circle in our thought excursion through follicular unit transplantation. We began by showing some of the illogical events that led the field astray, and then how simple observation brought us back on track. We explained the logic of preserving the follicular unit and of using very small recipient sites. We saw the logic of using the follicular constant in the planning of the transplant and the advantage of performing it in large sessions. We saw the benefits of single strip harvesting and of microscopic dissection. Finally, we discussed problems intrinsic to the follicular unit transplantation procedure itself, and provided some logical ways to solve them.

Its seems that hair transplantation is a logical process after all! Why didn’t we notice that before?

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