Follicular Unit Hair Transplants Promote Faster Wound Healing than Traditional Hair Grafts
Posted: Thursday, December 10, 2009
by Robert M. Bernstein, MD, F.A.A.D.
Bernstein Medical - Center for Hair Restoration
There are four related benefits to recipient site wound healing when follicular implants are used instead of traditional hair grafts. These are minimizing the recipient site surgical wound size, eliminating skin surface deformity, decreasing the dermal fibroplasia associated with healing, and avoiding pigment alteration.
By limiting the implant to the follicular elements of the skin, the recipient site wound can be just slightly larger than the follicular unit itself so that the unit sits snugly in it. Because the follicular units are so compact, one and small two hair units have essentially the same footprint and can be placed in the same size site; and two, three, and four hair units have the same footprint and can be placed in the same size site. When the stretched slit contracts around the inserted follicular unit, the snug fit minimizes the space for a coagulum to form and reduces the distance for re-epithialization. In other words, the size of the wound is decreased considerably. In this situation, the fibrin "glue" will be maximally effective in securing the implant, exudate and crust formation will be reduced, and the healing time will be shortened.
On the other hand, when traditional, larger grafts (which are essentially cylinders of skin and hair) are harvested, the epithelium creates an acute angle at its superior edge and an obtuse angle on the inferior edge. Hair from the back and sides of the scalp grows at an angle of approximately 30 degrees. When the grafts are inserted into the recipient site, they must be placed at an angle that matches the angle of the original hair which varies from approximately 30 to 60 degrees. Because of this angle, mechanical forces which act on the graft immediately after placement and throughout healing, interrupt the edge-to-edge alignment of the graft with the surrounding skin causing either settling or elevation of the graft, or both. As each graft is distorted ever so slightly, the composite effect of many such grafts produces the surface irregularity (cobble stoning) of the traditional hair transplant. This surface irregularity becomes clinically more apparent as graft sizes increase and as the sites are made with punches rather than slits. This whole phenomenon is simply avoided when the implants are devoid of unnecessary skin.
Slit grafting prevents cobblestoning but often produces a dimpling or puckering at the site of the emergence of the hairs by the down growth of the epidermis alongside the graft. Although follicular units are technically placed into "slits," by reducing the perifollicular epithelium in the follicular implantation, the site required is so small (1mm) and the follicular unit so compact that this deformity does not occur.
The fibrosis that results from the healing of larger wounds causes an additional problem. Just as angulation causes surface irregularities, it also produces a distortion of the dermis that may not be readily apparent clinically. The significance of this is that grafts placed parallel do not always end up having their hair parallel under the skin surface when dermal reorganization is complete. This distortion impedes the close placement of future grafts due to the risk of damaging existing ones (even if the original angle could be exactly reproduced). This distortion of the hair shaft produced by fibrosis is easily observed each time hair is harvested and dissected from the tissue next to a previously excised donor area. Incidentally, one of the difficulties in repairing unsightly plugs by the obviously simple method of decreasing the density of the plugs with electrolysis is that the distortion of the fibrosis impedes the introduction of the electrolysis needle. The dermal changes produced by successive procedures and the difficulty in reproducing angulation are among the most compelling reasons to densely pack a given area the first time rather than to repeatedly violate a transplanted area with multiple sessions.
Another casualty of the movement of larger grafts is the melanocyte. Repigmentation after loss or disruption of the epidermis occurs by two mechanisms; migration of melanocytes from adjacent normal epidermis and migration from the follicular appendages. The presence of focal hypopigmentation at the base of larger grafts is due to the arrest of melanocyte migration into the area and attests to the fact that the grafts have produced scar tissue that has damaged both epithelial elements. The hypopigmentation at the base of the grafts often serves to accentuate any apparent "plugginess" by highlighting the resultant physical deformity with an additional contrast... that of color.
Fortunately, hypopigmentation is less common with very small grafts and has not been observed in follicular hair transplantation.
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