As noted earlier, it is possible to calculate hair surface area and hair volume and predict coverage based on this calculation. Patients with mean hair diameters greater than 70 m m and a Norwood Classification less than or equal to V are generally much better candidates for the illusion of full coverage from hair restoration surgery. When treating patients with a mean hair diameter less than 70 m m, it is often better to limit transplanting to only the frontal area or the frontal and midscalp areas because they have less total hair mass to move and, therefore, one is often unable to achieve the illusion of as much coverage. A number of variables can affect this generalization: (a) a high FUD and calculated density improve the potential coverage (b) wavy, curly or kinky hair can improve the illusion of coverage (c) a smaller color contrast between the hair and skin create the illusion of denser hair (see also below) and (d) hairs sometimes change their characteristics after transplanting – for example, becoming more wavy – and thus, may increase the impression of greater than actual hair density.

Despite the foregoing, Unger has pointed out at several medical meeting, that one of the most remarkable phenomenon in hair transplanting is the fact that one is actually usually transferring a very small amount of hair per session and yet, one can achieve the appearance of full, or nearly full coverage, over a relatively large portion of the area of MPB. The reasons for this are discussed later in this chapter. The photo shown in Fig.8# demonstrates the amount of hair clipped from a typical donor area by Unger (approximately 1.2 cm x 24 cm), prior to excising most, but not all, of the area. (Usually, the tissue actually excised is only 8 to 10 mm wide). This relatively small amount of hair is typically expected to produce acceptable coverage after two or three sessions to the frontal area of a man with, for example, type V or sometimes, even type VI MPB. As noted in Chapter 6 it will also be used to treat not only presently evident thinning but also areas that currently have hair that is expected to be lost in the future. Examples of the type of coverage that can be expected with this approach are shown in Figure #Y,9 and elsewhere in this text.

As an extreme example, the patient shown in Fig. #Y9 had type VI MPB and a donor area with dense hair, but that was only approximately 5 cm wide before transplanting began. A wide zone of very sparse hair was present inferior to the area with dense hair, but was totally unusable for transplanting because of both its sparseness and the fine texture of the hair within it. A single donor area was used, with the scar from previous sessions being excised as part of each new harvest. He is shown in Fig. # after five sessions (and two AR's) with light, but effective, coverage over the anterior three-quarters of his original area of MPB (his chosen objective). How was it possible to create this illusion with so little hair? For that matter, how is it possible to do so much better in most patients who have better donor/recipient area ratios but in whom we are, in fact, only transplanting per session, the hair shown in Fig. #8. A small amount of hair somehow goes a long way. As noted in Chapter 6, part of the reason so much apparent coverage is possible is because the hair in the recipient area will usually be grown longer than the hair that is clipped in a typical donor area. This extra length not only results in more hair volume, but also because of its length, can be layered hair over hair in the same way as one shingles a roof. Wherever such layering is not present, for example, at the "part" or center of the whorl of the vertex, the illusion falls apart and the area must be treated more often to create an appearance of coverage equal to that of adjacent areas that are layered. Patients who complain of being able to "see the scalp" at such sites must be reminded of this fact, but of course should be forewarned of it during the initial consultation.

SCALP LAXITY

Scalp "laxity" and elasticity are not synonymous although these terms are frequently misused in that fashion. Gerard Seery has described, "scalp laxity" as being composed of two distinct components. His description of these and their implications are worthwhile quoting:

"The first component of scalp laxity is the ability of the scalp to slide or glide on the underlying pericranium. This is possible because the loose fibroareolar tissue in the subgaleal compartment allows the scalp to be moved on the cranium. This has nothing to do with the stretching or the elastin content of the skin and is simply a mechanical movement of the scalp on the pericranium. In a scalp with a high capacity to slide/glide, an excision of 4 cm or more (if made parallel to Langer’s lines) may be possible and closure easily effected. Operations that take advantage of the scalp’s capacity to glide, rather than stretch, are virtually complication-free and result in negligible topographical distortion of tissues. (The analogy of pulling a carpet over a polished floor comes to mind. The carpet and the furniture are moved but their topographical relationships to each other are not changed nor are the physical components of the carpet altered). Scalp surgery that utilizes the scalps facility to glide is highly effective and minimally traumatic to tissues. The relatively restricted width of donor strip excision in the temporal area is the result of the lateral extremity of the subgaleal space not extending that far laterally i.e. the galea blends with the temporalis fascia and results in only three layers of tissue being present in the temporal area.

The second property of scalp laxity is its extensibility or ability to stretch. It is reiterated that this is independent of the sliding phenomena. Some scalps are highly elasticized and reasonably wide strips can be removed by undermining and stretching but this is relatively much more detrimental to tissue viability, and often the formation of fine scars, than sliding.

The net consequence of the above is that notably wider horizontal strips can be taken from the superior donor area (because the subgaleal fibroareolar layer allows the gliding described above) than in the lower area. As much as a 2 cm width or more may be taken in the higher regions of the occipital scalp and closure effected without difficulty. In the inferior donor area, where there is no subgaleal fibroareolar layer, the width of the strip taken is determined by the skin extensibility (loosely termed elasticity) and subcutaneous tissue. Here a horizontal strip as narrow as 1 cm may result in difficulty with closure. It must also be remembered that some scalps have relatively poorly developed fibroareolar layers i.e. are "tight scalps" in which the gliding phenomenon is minimal. This is easily determined by simply placing the pulps of the examining fingers on the scalp and moving them on the underlying pericranium. The orientation of the lines of minimum tension (Langer’s lines) also play a part in determining the width of the strip that can be taken.*

At the midscalp, crown and going down into the scalp’s upper donor area, Langer’s lines are largely vertical and allow generous excision of tissue taken in a vertical axis. Conversely, there is an associated relative limitation in excision widths in the horizontal axis (because here Langer’s lines proceed are cross-cut), but this is more than compensated by the tissue laxity provided by the fibroareolar layer in the upper donor region. As Langer’s lines proceed inferiorly into the mid donor area, they increasingly assume a too horizontal orientation and in the inferior part of the donor area are entirely horizontal. This facilitates a relatively wider donor strip excision in the inferior donor area than would otherwise be the case but this does not nearly compensate for the absence of the "gliding" subgaleal fibroareolar layer present in the upper donor area.

Bosley outlined a method of objectively assessing scalp laxity for AR. He quantified the decrease in distance between two dots on either side of the alopecic area following manual compression between both thumbs and index fingers. * Norwood proposed a somewhat similar means of evaluating scalp laxity. He counted the number of folds created on the alopecic scalp as a result of manually compressing the temporal regions of the scalp toward one another*.

Scalp laxity of the donor area, unfortunately, still remains entirely subjective. One can estimate scalp laxity at that site by manually compressing two anatomically different regions toward one another, or the skin can be moved up and down to get a sense of laxity, but a standard and objective method of assessing laxity in the donor area is still required. Until one has evolved, we can, at least, suggest grading scalp laxity as "tight, moderately tight, slightly tight, average, slightly loose, moderately loose, or loose".

In general, a tight scalp requires a longer, narrower incision to move a given amount of hair than a loose one because the donor wound should ideally be closed with minimum tension. Limitations in the width of donor area excisions are reduced further with multiple excisions in the same donor region as part of subsequent sessions (see below). Failure to recognize a tighter than average scalp may compromise the surgeon’s ability to close the donor area without significant tension. If the excision width exceeds the combined laxity and elasticity of the donor region, it may even be impossible to approximate the margins of the wound. Such instances may require undermining of one or both wound flaps and/or the use of mechanical creep by approximating the wound edges as closely as possible with towel clips or staples, for 30 to 60 minutes or longer, before attempting final closure. In the worst scenario, even with undermining and the use of mechanical creep, it may not be possible to approximate the margins with reasonable tension. Galeal sutures or "deep plane fixation" described by Seery, at the end of this chapter, should then be used. If necessary, the edges must be left with a slight gap at one or more points along the course of the wound closure. The gap(s) will fill in by secondary intention and the resulting scar(s) may be cosmetically improved at a later time. It is, of course, wise to err on the side of a conservative assessment of what is a reasonable maximum width for the donor strip and to avoid such situations.

It follows from the preceding, that a tight donor scalp limits the amount of donor area, which may safely be moved to the recipient region during each session. In a patient with a greater degree of hair loss, it may not be possible to achieve the coverage both the patient and physician desire or it may require unacceptable numbers of sessions. In patients with more severe degrees of MPB, it may be possible to produce the coverage objectives, but not without multiple smaller than usual sessions. Thus, it is imperative that the patient and physician understand the consequences of limited scalp laxity prior to beginning hair restoration surgery, in order to prevent unrealistic expectations. Scalp laxity nearly always varies from area to area, and frequently is greater on one side of the head than the other. Thus, the maximum width of any donor strip can be greater or smaller at various points along its length. Most commonly, from a scalp laxity point of view, it can be wider in the temporal and occipital areas. However, because the "permanent" donor hair zone in the occipital and temporal areas are not as wide as in the parietal area (Fig. #10), you may not want to excise maximum widths at those sites, despite adequate laxity to do so. One of the disadvantages of the elliptical donor strips used by many hair replacement surgeons is that it is typically widest in the occipital area, where the "permanent" rim hair is approximately 10 mm narrower than in the parietal area. Most of the parietal area is usually lax enough for quite wide donor strips, however, the post-auricular areas nearly always are the least lax and donor strips should accordingly be narrowed – sometimes substantially – in that region. Taking into account both scalp laxity and the varying widths of the "safe donor area": a) if elliptical donor strips are employed, it would seem wisest to use ellipses whose widest points are in the mid-parietal region and narrow as they approach the post-auricular and occipital areas, with the tapered ends overlapping each other in the midline (Fig. #), b11) if the strip extends from ear to ear, a single bladed knife can be used to excise the strip in an undulating pattern that is wider at some points than others. Alternately, two-bladed knives of various widths (according to scalp laxity) can be used along the length of the donor area, with gaps of intact skin between them. The gaps can then be incised with a single-bladed knife to join the sections (Fig. #12). This approach is discussed later in the chapter.