Different Graft Sizes

Hair grafts are divided into four general categories: traditional standard grafts, minigrafts, micrografts, and follicular unit grafts. Traditional standard grafts are 3-4 mm in diameter and have 12-30 hairs per graft. Minigrafts are smaller, 1.2-2.5 mm in diameter, and have 4-12 hairs per graft. Micrografts are even smaller measuring 1.5-1.0 mm or less in diameter, with 1-3 hairs per graft. Follicular units are the naturally growing groups of hair follicles. Each follicular unit graft contains 1-4 hair follicles.

Although minigrafts and micrografts are a significant improvement over the larger grafts, they are not ideal. The idea was reasonable: to keep the number of hairs in each graft low. However, mini-micrografts were moved in unnatural arrangements and the naturally growing groups of hair were ignored. This is because in minigrafting and micrografting, the donor hair is harvested with a multi-bladed knife. This instrument that breaks up naturally occurring follicular units and causes unavoidable damage to follicles. Focusing on the number of hairs, rather than the naturally growing groups, minigrafting and micrografting damage the follicles, causing a significant transplant failure rate. Micrografts tend to produce a thin look when used exclusively over the entire head, and often produce inconsistent graft growth.
Follicular unit grafts are based upon the observation that hair emerges from the scalp in naturally occurring clusters called follicular units. Each follicular unit is comprised of one to four terminal hairs. By using the follicular unit as the base unit of the transplant, the surgeon can create hair patterns that mimic the way hair grows naturally. The art of the follicular unit approach is that the characteristics of the patient's hair dictate the size of the implant (rather than the doctor). The surgeon determines distribution and balance. By preserving both the natural physiologic and aesthetic elements of human hair, the best cosmetic results can be achieved.

There are many advantages of Follicular Unit Transplantation over micrografting. A fuller look is achieved, as the grafts can be of the same size (or even smaller) than micrografts yet contain more hair. Graft growth is more consistent than when the follicular units are split up. Recipient wounds heal more quickly because sites in the recipient area are smaller, and the results look more natural. Follicular unit transplantation allows the doctor to distribute grafts to mimic the way hair grows naturally in the patient's own scalp.

Follicular Unit Transplantation enables the surgeon to restore more hair using a smaller amount of donor tissue, as the technique is more efficient than minigrafting and micrografting. The tissue between the follicular groups is dissected away, while the vital support structures around the unit are preserved. Cobblestoning (irregularities in the surface of the scalp) and depigmentation (the appearance of whitish blemishes of the transplanted skin) can be avoided because excess skin in the grafts has been removed, making the grafts significantly smaller. The follicular units produce very small physiologic implants, that can, in turn, be inserted into very small sites. In addition, larger amounts of hair may be safely moved in one session reducing the necessity for multiple procedures. The patient benefits significantly with less time devoted to restoration, fewer procedures and, often, a lower cost per graft.

The large plugs used in the past, transplanted far too much bald skin in each graft. Minigrafts and micrografts also consist of multiple (partial or complete) follicular units along with the intervening skin. Even micrografts containing as few as two or three hairs may contain unnecessary skin if the hair was taken from two or more separate follicular units. Hair moved in these types of grafts results in transplanted tissue that has the same ratio of follicles to skin as the donor area. As healing occurs, the scar around the graft contracts, pushing the hairs in the graft together, and the density of the hair within the graft increases. The hair density within these larger grafts often exceeds the hair density in the donor area. This higher hair density within grafts is intrinsic to the principles of scar contraction, and produces the pluggy appearance of traditional grafts.

There are other problems associated with the use of the larger grafts. It takes four to six days for the buds of new capillary blood vessels to grow into the grafts from the surrounding tissue. Until these new blood vessels grow into the grafts, the graft's cells depend upon the surrounding tissue fluid seeping into them to bring them oxygen and nutrients. Hair follicle cells have a very high metabolic rate, and they require more oxygen and other nutrients than other cells. If the graft is too large, the cells of the follicles in the center of the graft may die before sufficient oxygen and nutrients can reach the center of the graft. The follicles at the periphery of the graft survive because they receive sufficient oxygen. When hair finally grows from these larger grafts, it has a doughnut configuration, with hair at the edges and a bald central area. This is one of the numerous reasons why many doctors have changed to the use of smaller grafts.