I was asked to update my comments from what I said before about hair growth and follicle survival in high densities, but for the most part would pretty much say the same thing now in late 2008.
There was a nice study published in the journal, Dermatologic Surgery, by Coalition members Dr. Tom Nakatsui and Dr. Jerry Wong about a year ago or so, in which they used small lateral slits and created study boxes of between 23 and 72 slits per square cm of surface area, and obtained a 95.6% survival in the 23/cm2 box and 98.6% in the 72/cm2 box. These results are outstanding, although we have to keep in mind that the study was done on only one hair transplant patient and the same results may or may not occur with another person. Also, as I recall, these boxes were around the periphery of the area transplanted and I don’t believe any were actually in the center, which I think would be the area most at risk for possible less-than-optimal hair regrowth. I have noticed in past studies I have conducted that, even though I did everything exactly the same, I often would see marked variation in hair follicle survival a year out. Every hair surgeon that I have spoken with acknowledges that there is an individual patient “X factor” that we can’t totally put our finger on, but does in fact exist.
There are a number of factors that I think definitely play a role in worsening the survival of densely packed grafts: Among these are: cigarette smoking; a very thin scalp with little subcutaneous tissue; a scalp that has had a lot of past surgery performed on it;
Another factor that I think makes a huge difference in a hair surgeon’s ability to create density and obtain good hair growth at the same time is the size of the recipient site. There is no question that the custom-made lateral slits allow us to place a larger number of recipient sites in a given square area than ever before. Then the limiting factor becomes the safety with which the placers can insert the follicular unit grafts without traumatizing them. With extremely dense sites, this is much more difficult with the hair left long.
I will again make the statement that I believe the biggest factor in getting good dense hair growth is not necessarily the density with which the sites are made, but rather the skill and conscientiousness of the assistants who are placing the grafts. If they do their work in a rough, slipshod manner, there is going to be terrible growth. If they are gentle and meticulous with each placement, then the growth will probably be wonderful.
I haven’t gotten around to doing any further survival studies on 1-hair follicular units (FU) but would welcome others doing so, to see how they compare. The 3-4 studies I have performed comparing 1-hair grafts with 2-hair grafts would suggest that there is 10-15% less growth with the 1-hair grafts. This is simply a function of their slim build and inherent vulnerability to desiccation (drying) and trauma with handling.
Mike Beehner, M.D.