Prior to revising a scar, it is important to take a careful patient history and find out specifically what, if anything went wrong with previous surgeries. It is presumptuous to think that just because a patient has scarring, the next procedure will make it better. One should carefully review the surgical history and, if possible, speak with the original surgeon to see if there are any techniques that could be improved upon, or problems that occurred which might be avoided in future procedures.
The cause of an unacceptable scar may be due to poor healing intrinsic to the patient, such as the tendency to form keloids. It might also be caused by a genetic predisposition to poor healing because of connective tissue defects, such as Ehlers-Danlos Syndrome. Genetic or drug induced coagulopathies, or medications that interfere with healing can also result in unacceptable scars. In addition, scarring may be caused by complications such as a post-operative infection or simply from the patient not following post-op instructions, such as smoking or performing strenuous exercise too soon after the surgery.
As emphasized in the preceding discussion, a depleted donor supply is the major limitation to a successful repair. The inability to harvest additional hair is caused by two main factors. The first factor is the physical limit set by the combination of low donor density and poor scalp mobility. When donor density is low, a larger strip must be harvested to obtain an adequate amount of hair. A tight scalp, however, limits the size of the strip that can be removed. After multiple procedures, attempting to harvest additional hair is no longer worth the risk of a possible widened scar. Every hair transplant procedure simultaneously decreases donor density and scalp laxity, but poorly executed surgery does this to a greater degree and decreases the supply without making proportionate cosmetic improvements in the recipient scalp.
The second factor is the visibility of the donor scars. Once the donor scars are to the point of near visibility, the ability to harvest additional hair is severely limited, as further surgery would make the patient’s previous transplant surgery apparent. An important point to keep in mind in judging how much additional hair is available, is that coverage of donor scarring is more closely related to the amount of donor hair present than to the degree of scarring. Therefore, any process that removes hair along with the scar will run the risk of making the donor scarring more visible. The reason is that when scar and hair are both removed, the closure will further stretch the scalp and decrease the density of the remaining hair. This may prevent it from covering other scars that have not been excised or thin out the appearance of the donor fringe to an unacceptable degree.
Techniques, such as Follicular Unit Extraction, where follicular units are harvested directly from the donor area without a linear excision can be useful when the scalp is very tight. The usefulness of this technique is limited, however, as significant donor scarring makes removing hair without transection difficult and a donor zone of low density limits the amount of hair that can be removed without the area becoming too transparent