For at least 4 years, Dr. Wong has tried to talk me in to using lateral incisions. I had experimented with them in the past and found the sites hard to see, hard to transplant, and had problems with popping- so I dismissed it. His results were outstanding and, in 2002, I invited him to write an article in the Hair Transplant Forum. In that article, he pointed out that hairs in a follicular unit tended to line up perpendicular to the exit angle. I focused in close on the donor strip and....he was right! After that, everything started to fall in to place. With lateral sites, the grafts lay more naturally and the curl is correctly aligned. There is no squeeze on the hairs which allows them to keep there separation. I noticed that they make their incisions in a laterally oriented line and, after checking, most donor follicular units tended to line up the same way. It convinced me to give it another try. Lateral grafting is not new. Several have tried it, but with minigrafts and slots. There was a lot of compromise to the circulation, some necrosis, and it fell out of favor. No one thought that the lateral alignment of hairs in a small unit such as the follicular unit would make much difference- until H&W. However, multiply the effect by 5000 or more and a significance occurs. My fears of circulatory compromise were aided by 1)H&W dense packed with small incisions with no compromise 2)Limmer and Seager, without thinking of the implications, had been using lateral slits, because they were easier to plant, with their stick&place for years with dense packing and outstanding results. With the cut razor blades, the sites are easier to work with and, with experience, popping is much less of a problem for me. The sites are still more difficult to see, but staying in a pattern pretty much corrects that problem.
Also- take the curl. With sagittal sites, the tendency is to put the grafts in so the hairs are aligned parallel with the desired hair angle. Not only do the grafts not seat quite as well, but the curl is 90 degrees off the desired curl angle. Angling is more difficult with the multihaired grafts using sagittal incisons (I still don't think lateral sites make any difference with single haired grafts).
Of course, many centers get wonderful results with sagittal sites. But these technique modifications add up and give better and better results. There is a learning curve, but for someone experienced, it is not too great.
No- I don't work for H&W, but I do recognize good work and progress.
One note about circulation. There is a supragaleal plexus that connects to the subdermal plexus by vessels that run vertically. The subdermal plexus connects via vertical vessels to the subepidermal plexus. A plexus probably looks like a spider web sitting horizontally in the skin. Created sites with sag or lateral blades have to penetrate thru the subepidermal and the subdermal plexus in order to get the bulbs into the fat layer where they naturally lie. If the incisions stops in the dermis the bulbs won't be where they should be, the grafts will be harder to plant, may fold on themselves, or sit to high. The damage to the subdermal plexu with either orientation is probably about the same.
The difference is that a lateral incision will cut thru more of the dermal vessels than a sagittal incision. With larger lateral blades this is definitely significant. Limmer, Seager, and H&W, however, have show pretty well that smaller sites (1.2mm or less) do not cause a problem. It is true that lateral sites do not penetrate as far into the fat layer and are logically less damaging to the the subcutaneous vessels. If one stays above the important supragaleal plexus, the sagittal sites aren't very damaging. This is where tumescence helps.
All in all, this is probably a push and, correctly used, neither orientation should have signficant impact on the circulation. Scientific studies would be helpful here.
1.) Why does the lateral slit method allow increased density of FU packing? Is it really because of the way the FU can be angled to exit the skin Or I am simply confusing FU packing with cosmetic density.
Well, it's actually the opposite end of the angle that makes dense packing easier. You see, when the incisions are made in the recipient scalp they are made at an angle parallel to the native hair growth. This is determined best by buzzing the native hair very short,(2mm to 3mm), so that the hair will not be encumbered by it's own weight. The angle is free to stand at it's natural angle.
When the incisions are made at this angle they are more shallow than had they been made in a saggital manner. A more shallow incision allows for less vascular damage to the recipient scalp which leads to faster healing. More importantly, the nature of the incisions significantly reduces the amount of pressure exherted by the neighboring grafts. The pressure from saggital incisions is cumulative with each additional incision thereby preventing dense packing.
Furthermore, when the Hasson & Wong Lateral Slit Technique is employed the blades that are used to make these incisions are custom cut to the size of the grafts. This means that the incisions are the same width AND depth of the grafts thereby preventing excessive damage to the recipient scalp. When the grafts are inserted into sites that are the same size then there is no risk of compression. When doctors place grafts into sites that are not customized then it is similar to placing a square block into a round hole.
2.) Is this now the 'industry standard' in FU surgery, i.e. should most HT candidates seeking FU transplant of good density (equal to or greater than 40 FU / cm2) in 1 session only go with surgeons offering lateral slit ?
We think so but more importantly go with a doctor that you feel fits your situation the best. Don't get caught up in shear density numbers as they are misleading and may not apply to your situation. One patient that gets 40 per cm2 may look more dense than another that has 60 per cm2 due to his hair characteristics.
