How Hair Is Harvested From the Scalp in a Hair Transplant

How Hair is Harvested from the Scalp in a Hair Transplant

There are two processes that occur simultaneously in the balding individual. One is androgenetic alopecia — the patterned balding or hair loss programmed to affect only certain hair follicles in susceptible individuals. The other is hair loss due to aging itself, which to some degree affects all hair in everyone.

The donor region in the back of the scalp where hair is traditionally harvested from has been optimistically called the “permanent zone;” however, this zone is far from permanent. It may be spared from the process of genetic balding, but it is surely affected by the aging process itself. It seems that, on average, the donor site thins at least 30% over one’s lifetime due to simple aging.

In some men with extensive balding, the permanent hair seems to be affected by the genetic process as well. When these two processes occur together, the decrease in donor density can be marked with counts occasionally falling below one hair/mm2. This process is probably analogous to the extensive diffuse thinning seen occasionally in women. The continued loss of hair in the permanent zone over time must, of course, be accounted for in the planning of the hair transplant and in giving a realistic prediction to the patient of the long-term stability of the transplanted hair.

Two major factors determine the amount of hair that can be safely removed from the donor area. The first is donor density, and the second is scalp laxity.

The importance of accurately assessing donor density cannot be over emphasized. At the initial consultation, density determinations are made from a representative area in the permanent zone where the donor strip might be harvested. If there is significant clinical variability in the donor density or scarring due to prior surgery, then multiple measurements are taken. These numbers are used in the initial planning of the procedure. At the time of surgery, the density is measured again, calculations are taken to determine the length and width of the donor strip and the area is then prepped and shaved. The shaved donor site is then inspected for irregularities of density due to natural variability and those resulting from scarring due to past procedures. Multiple determinations are made again and averaged to accurately assess the density. Our experience has shown that the gross visual impression of density is often at variance from the true density by a factor of up to 35% and is far too imprecise to be useful in surgical planning.

Scalp laxity is a more subjective measurement, but with experience can be estimated with a reasonably high degree of accuracy. Judging scalp mobility by simply moving the scalp up and down with the hand or tenting of the skin between the fingers are the two obvious means of assessing laxity. Also useful is noting the thickness of the scalp (an abundance of subcutaneous fat makes for a mobile scalp) and observing the configuration (contour) of the cranial bones. Prominent mastoid processes and occipital notches decrease the ability to easily close a horizontal incision.

Many hair restoration facilities use a Rassman knife that, when fully loaded with 8 blades, produces a donor strip 21mm in width. By removing blades, hair restoration surgeons can harvest strips of 18mm, 15mm, 12mm, 9mm and so on. Generally, the widest strip that can be harvested without producing undue tension during closure should be used.

If a donor strip is too narrow, then its length must be increased to yield the same amount of hair and a longer incision produces more donor site scarring and distortion. If a strip is too wide, then tension on the wound edge may result in dehiscence, infection, excessive post-operative discomfort, prolonged wound healing or a hypertrophic or spread scar. In general, the greatest degree of tension occurs over the mastoid processes, and great care should be taken when estimating scalp mobility in this location. If it is anticipated that this area will be a limiting factor in the harvest, then it is best to use a more conservative width and excise a longer strip.

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In patients having a very prominent occipital protuberance, the greatest tension may be at the midline. In this situation the surgeon may remove a blade to narrow the width as he or she extends medially. Or, the hair transplant surgeon may harvest an additional strip on one or both sides freehand. On occasion, when a patient with a prominent ridge has had multiple previous surgeries, the strip is harvested in two separate pieces neither extending to the midline.

The plane of dissection should be just below the hair follicles in the superficial fat to avoid damaging the larger nerves and blood vessels which lie deep in the subcutaneous layer, just above the galea apounurotica. If possible, the galea should not be violated as this fibrous band serves as the structural support of the wound closure and prevents its spread. Suturing a transected galea will never approach the strength of the membrane left intact. In addition, dissection in the subcutaneous layer avoids the necessity of a layered closure and its associated foreign body reaction.

In very large hair transplant sessions where up to 50 square centimeters of scalp may be removed and the incision length can be 30 cm, the importance of superficial dissection and leaving the galea intact cannot be over emphasized. In addition, a hair restoration surgeon must never undermine. In the rare instance where the wound edges cannot be approximated, it is better left to heal by secondary intention rather than to risk damaging hair follicles, blood vessels or nerves. It is important to remember that, during a hair transplant, any cosmetically unacceptable scar can easily be removed in the future after the scalp tension has decreased.

Additionally, many hair restoration facilities are abandoning the process of electrodessication: a process using a small electrode to seal lesions, vessels or wounds. Bleeding generally occurs at the wound edges and is controlled with a running cutaneous suture. On rare occasion, a larger vessel is ligated using 4-0 Vicryl, if it would not be incorporated easily in the closure.

As a licensed dermatologist and clinical professor of dermatology, I recommend using a single running suture of 2-0 polypropylene. The sutures are generally left in place for two weeks. However, if there is significant tension during the closure then these sutures may be left in place for three or more weeks as polypropylene produces little tissue reactivity. The entire length of the suture line is kept covered continually with a topical antibiotic in an ointment base (Bacitracin).

At the time of suture removal, the sutures should protrude slightly above the scalp surface which indicates that edema and inflammation have significantly subsided. This is in sharp contrast to sutures left in glaborous skin, which become progressively more embedded the longer they are left in place. In patients without penicillin sensitivity, I recommend pre-medicating with Dicloxacillin 1gm PO, 1 hour prior to surgery, and then a second dose of 500mg PO 6 hours later if there was excessive bleeding, or wound tension.

In determining the position of the donor incision, it is best to assume that the patient may become a Norwood Class VII (class VII patients have extensive hair loss with only a wreath of hair remaining in the back and sides of the scalp). Therefore, the hair transplant surgeon should place the upper blade of the rake at least 1cm below the lowest point of possible hair loss. This will allow for coverage of the scar in the worst case scenario. As the incision extends laterally, it should be at least 1 cm superior to the top of the ear. It is important to stay very superficial in this area, especially as one extends the incision towards the temples, as the parietal branch of the superficial temporal artery and vein as well as branches of the auriculotemporal nerve lie very close to the undersurface of the dermis in this location. The excision should not extend anteriorly to a position closer than 3 cm from the hairline. Some patients may have extensive bitemporal recession, and this should be anticipated by carefully assessing the extent of the patient’s current recession, the degree of miniaturization at the free edge, and the family history of balding and hair loss.

Traditional surgical techniques have often left a “step-ladder” pattern of scarring in the donor area. When there is a preexisting horizontal linear scar (or scars), the scar may be totally avoided, totally incorporated into the new strip, or incorporated into one edge of the new incision. If the scar is in a position where it is already placed too high and may possibly be exposed with further balding, it is best avoided. If the scar had been placed too low, it is also best avoided to reduce the chance of hypertrophic scarring. Also if the donor area is relatively tight from prior surgery and if the scar is not visible, it may be left in place, as removing it will only increase wound tension.

Avoiding the scar will maximize the yield of hair for that particular hair restoration procedure. One may totally incorporate the scar if it is clinically visible and if there is enough laxity to remove it and still obtain the desired amount of hair. It is critically important to ascertain why the patient scarred in the first place. If the scar was a result of poor surgical technique and the problem can be identified and corrected, then excising it may be appropriate. If the scar (either stretched or hypertrophic) was due to the intrinsic healing properties of the individual (as seen in Ehlers-Danlos syndrome), then the scar is best avoided, because removing it will further increase wound tension, and the problem will most likely reoccur.

It is important to assess the impact of the scarring on the average donor density as small amounts of scarring can significantly decrease hair yield due to distortion of follicles in the surrounding area. In the majority of instances, I recommend hair restoration surgeons opt for the third choice (i.e., using the previous scar as the upper or lower boarder of the new excision). The surgeon will remove all but approximately 1.5 mm of the width of the scar to allow the suturing to be limited to the scarred area and not to extend into viable hair bearing scalp. In this way the amount of distortion and possible damage to existing hair is limited to only one free edge.

Dr. Bernstein is Clinical Professor of Dermatology and is recognized worldwide for pioneering Follicular Unit Hair Transplantation. Dr. Bernstein’s hair restoration center in Manhattan performs hair transplants and other hair restoration procedures. To read more publications on balding and hair loss, visit http://www.bernsteinmedical.com/.

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