As will be discussed later, either a single or multi-bladed knife may be employed. The first physician to describe the use of a double-bladed knife was Vallis,* but there are now various knife handles available from a host of vendors such as Ellis Instruments, A-Z Instruments, George Tiemann and Company, Robbins Instruments, Mediquip, etc., that can incorporate three or many more blades (See Chapter 20). Number 15 or 10 blades are generally utilized in these handles, with those produced by Persona preferred by most operators because of their excellent sharpness. The single or multi-bladed knife is inserted into the donor region parallel to the direction of hair growth, and is then drawn along the length of the proposed donor strip. To decrease the risk of follicle trans-section, it is advantageous to check your incision periodically, and to modify the angle of the blade to conform to the continuously changing hair angles as the strip is cut.

There are two incision surfaces you can evaluate during these assessments; the superior and inferior one. Upon close inspection of the inferior surface, should you fail to the follicular bulb, you should modify the angle of your incision so that it becomes less acute, by moving the handle of the scalpel cephalad. Should you see trans-section of the upper fractions of the hair follicle, you should move the scalpel handle more acutely or caudally. This led Kadach to propose the following pneumonic "roots angle up, no roots angle down".* Novices should ideally begin with one or no more than two blades spaced 4 or 5 mm apart. This is because when the angle of the blades is not parallel to the hair shafts, the percentage of follicle trans-section increases as the number of blades increases. A wider strip and only two blades keep the hairs in the middle of the strip "out of harm’s way" and, thereby insures, a higher yield of intact follicles. In addition, the more blades in the knife, the more resistance one can expect to encounter. Therefore, the more blades in the knife, the more important it is that they are extremely sharp. Laying the cutting edge of a five-bladed scalpel down forcefully, on a hard surface, for example, may be all that is necessary to dull the edges sufficiently that the incision is made substantially more difficult. Mangubat has also noted that downward pressure on a multi-bladed knife makes the movement of the instrument across the donor area easier.*

Various practitioners have developed quite different preferences for the type of instrument they prefer to use for excising donor strips and the widths of the latter. Using a single blade (with or without a depth guard) to excise an ellipse from the donor area is the method of harvesting demanded by those who tend to exclusively utilize FUT and who wish to define FUT stringently. It is the approach preferred by Cole, Gandelman, Hugeneck, Limmer, Sandavol, Seager, Swinehart, Ramos, Uebel, and others. Their rationale is that a single blade decreases the number of surgical margins but of course this applies only to multi-bladed knives with more than two blades. Perhaps a more important reason to employ a single blade is the variation in hair growth angles on two different planes of the curved skull. The farther apart the most superior and most inferior blades are, the greater the difference in the angle of growth will be at the incision lines.

Griffin has suggested that the trans-section rate for one strip surface should be multiplied by the number of blades on your knife to obtain the total trans-section rate for any multi-strip harvest.* In fact, the trans-section rate is almost certainly always greater than this due to the above-noted different hair growth angles in different planes of the scalp. The mean trans-section rate for a single-bladed knife, in Cole’s on-going studies, is generally between 1 to 2%. Interestingly, the trans-section rate for the first incision line is much lower than the trans-section rate for the second incision line. The mean trans-section rate for a two-bladed knife set at 1 cm to 1.2 cm between the blades is generally between 2 and 4% 2.6% of all the hairs in the strip. Pathmovitch’s trans-section rate, using his approach to elliptical excision is 1.9%.* Reed projected the trans-section rate from harvesting five, 2 mm wide strips at 8%.* Unfortunately, he determined this rate by taking a section of each strip, containing approximately 200 hairs each and counting the number of transected hairs on only one side of the strip. In this way trans-sections were not counted twice, but, as noted earlier, it is very likely the trans-section rate on the uncounted side would have been different than that on the counted side. Limmer has reported the trans-section rate with his method of elliptical harvesting and donor area dissection to be between 2 to 5% and to usually be 2 to 4%.* On the other hand, he found the trans-section rate for strip excision and graft production from two, 3 mm strips (using 3 scalpel blades) to be 13%8% to 15%16% when all transected hairs were actually counted instead of estimated.* Limmer also notes the typical trans-section rate for a single blade ellipse is 1 to 2% with a range of 1 to 4% depending patient variability.⁴⁴

Transplanting all transected, as well as intact, hairs in the donor tissue, may produce fewer, the same number, or more growing hairs depending on the study you review. This has been referred to previously in this chapter and is discussed in more detail by Reed in Chapter 12. Therefore, the importance of minimizing trans-section rates, although instinctively attractive, is not clear. All the same, those hairs that grow from transected follicles often have reduced caliber and transected hairs are also more likely to be discarded by technicians. For this reason, it is important to know how many hairs are actually transplanted into the recipient area when hair survival studies are carried out - as they periodically should be, in all offices. Limmer has studied his staff’s efficiency and believes his technician’s typically fail to return to the recipient area only 1% to 3% of all hairs removed from the donor area. *

Bernstein has reported that he can produce 3017% more FU hair from the same amount of donor tissue since switching to single bladed elliptical double blade harvesting and stereomicroscopic dissection.* Bernstein also noted a greater yield with less trans-section from the production of follicular units upon switching from a triple blade to a double blade scalpel. Bernstein et al noted the trans-section rate for a four bladed scalpel with three spacers of 3mm each ranged from 12 to 16%. Unger and Reed have questioned, at least, the size of this figure in view of the fact that a) perfectly matched original sections of donor tissue are impossible to find for comparison purposes, and were therefore not used, and b) the skill of technicians not only varies from person to person, but also in the same individual with the passage of time. He used the same technicians in the earlier studies of multi-blade harvests that he had used for studies of single-blade harvests carried out a year or more later, when they were more experienced. The study in which Bernstein based his figure was also flawed in several other important respects.* More importantly, hair counts are notoriously difficult to carry out accurately, even when stereo-microscopes are used. Two excellent and experienced technicians from each of Seager’s and Unger’s offices were unable to agree on the number of hairs in grafts being examined in a two-office hair survival study done by them in 2001, until multiple counts were carried out on the initial grafts. The hair counts nine months later, done by the same four technicians, using whatever magnification each individual thought they needed, could not be entirely agreed upon by any of the four, despite multiple counts. The results of the study were reported at the 2001 ISHRS annual meeting, and one of the conclusions of that study was that scientifically valid data is unlikely to be arrived at by these studies, even ignoring the fact that only two or three patients are being evaluated.

Beehner, Mangubat, Khan, Unger, and Shapiro use multi-bladed knives for the production of minigrafts. Unger and Shapiro obtain most of their FU from donor strips excised with a double-bladed knife, but some FU are also easily produced from the strips created by multi-bladed knives. The method of donor harvesting they use, is to some extent dependent on the type of graft they are producing. In their view, it is acceptable to use a multi-bladed knife if you are producing minigrafts, as long as all of the transected follicles are transplanted with the intact ones. It is easier to consistently make minigrafts of a specific size from narrow strips of consistent widths, as are obtained with a multi-bladed excision, than from an ellipse. A consistent minigraft size, in turn, makes the creation of the appropriate size of recipient sites easier. They also feel than an ellipse coupled with microscopic dissection is more appropriate when you want to produce predominantly FU, and therefore in this regard, they are in agreement with Cole, Gandelman, Nugenek, Limmer, etc.

Pathomvanich believes that all the current methods of donor harvesting are "blind" with regard to hair angle, in at least one dimension. Therefore, he developed a new technique based on the principle, "cut what you see, and see what you cut".*⁴⁰ First, he marks the area he plans to excise. After a tumescent anesthetic is infiltrated, he makes a superficial horizontal incision with a #15 blade, between several follicles. This incision, which is approximately 1 cm long, is then opened with skin hooks exposing the path of the hair follicles toward the subcutaneous fat. He then continues the incision with the #15 blade, first to the left and then to the right and eventually deeper, until the entire marked area is incised. Hemostasis is paramount to his technique, so that visualization of hair follicle angle and direction is optimized. Cotton swabs and a small roll of damp gauze are also utilized to keep the field clear of blood. As he dissects, he alters his course around the irregularly spaced FU and individual follicles in an effort to minimize trans-section. The ellipse may be removed in several sections or as a "block". Excision in sections, allows the remainder of the staff to begin dissecting the ellipse into smaller pieces that are1 to 3 mm wide. The procedure is more time consuming than current methods, but with experience he has learned to perform the entire excision of the donor area in 10 to 15 minutes. The additional time required for this technique is warranted in his opinion because it maximizes the reduction of follicle trans-section as the ellipse is excised, and minimizes injury to neurovascular bundles.*⁴⁰ (Pathomvanich, D., Dematol Surg 2000; 26:345-348).

Dow Stough and Parsley observed this technique at the 2001 Live Surgery Workshop in Orlando, Florida and found that the field of vision was substantially impaired by bleeding but felt that the trans-section rate was less than with other techniques. The procedure took approximately 30 minutes, rather than 10 to 15 minutes to accomplish, but most of us work better in our own offices so this was probably not representative of the time he usually needs. Stough feels that individuals with dark hair are the best candidates and excellent tumescence and vasoconstriction are more necessary than with faster techniques for obvious reasons.⁴⁷ Parsley has questioned an increased risk of desiccation because the procedure is so time consuming.⁴⁸

Because there is little margin of error for the cutting angle with a horizontal incision of the donor area with a multi-bladed knife, Blugerman proposed what he called the "vertical strip harvest".*³⁴ In this technique, he uses a non-angled multi-bladed knife with #15 blades to initially incise the donor area vertically. The blades in this knife are 1.5 to 2.0 mm apart. He limits the depth of incision to 7 or 8 mm in order to minimize nerve and vascular damage. He then removes an ellipse with a #10 blade (Fig. #). The thin strips are separated by the assistants and further dissected. (Jul-Aug 1996 Hair Transplant Forum International, pg.10). Alkek has described a similar harvesting technique* as have Al-Ghamdi and Kohn.* (Al-Ghamdi W., Kohn T., Vertical Harvesting in Hair Transplantation, Dermatol Surg. 2001; 27: 597-600). We have found that these approaches are considerably more time-consuming and in our hands produce more follicle transection than is seen with our usual method of strip harvesting. Nevertheless, the above noted authors claim lower rates of follicle trans-section.