Clinical Characteristics Of Follicular Units In Hair Transplants

June 13th, 2010

Follicular Unit Constant

One of the interesting aspects of hair transplants with follicular units is that nature was kind to space them at approximately one per mm2. This has been observed clinically using densitometry and stereomicroscopic dissection and histologically using transverse microscopic sections of the skin this was first described by Headington in 1984. Not only does a follicular unit constant of 1 unit/mm2 make the math easy but it makes accurately estimating the donor harvest possible and gives a logical basis for planning the density and distribution of the grafts.

The constancy of follicular unit density has been studied but inconsistent study designs prevent accurate conclusions. There is general agreement on the following:

1. Follicular unit density generally decreases as work moves laterally from the midocciput at the level of the occipital protuberance towards the temples.

2. Follicular unit density varies among races such that the darker skinned races tend to have the lowest follicular unit densities and lightskinned races the highest.

3. Within the same race and same location on the scalp there is significant persontoperson variation in follicular unit density.

4. Given points 13 above the constancy of the follicular unit density is still rather striking so that patients with high hair density have more hairs per follicular unit rather than follicular units spaced closer together and those with low hair density for the most part have fewer hairs per follicular unit than units spread further apart.

Although the follicular unit density is not exactly 1/mm2 it is close enough to this number that it can be extremely useful in the surgery. Once it is realized that the follicular unit density is relatively constant and that hair density varies it follows that the number of hairs per follicular unit largely determines hair density. The implications of this in hair transplantation can be summarized as follows:

Since the follicular unit density is relatively constant the same number of follicular units should generally be used to cover a specificsized bald area regardless of the hair density of the patient.

With low hair density using the same number and spacing of follicular units as in a patient with high density will help to ensure that there is proper conservation of donor hair for the long term.

Hair density is a characteristic of the follicular unit specific to each individual and together with hair shaft diameter color and wave will determine the cosmetic impact of the transplant.

Hair characteristics

The results of a hair transplantation procedure are determined as much by the characteristics of the individual hairs as the number of hairs per follicular unit. Since hair counts are easily measurable the more subjective hair characteristics or the ones more difficult to measure are often discounted. Many characteristics including hair shaft diameter hair color texture wave curl kink and other factors such as the emergent angle of the hair static oiliness or sheen all contribute to the appearance of fullness however hair shaft diameter probably has the greatest impact.

The total volume of hair determines the visual impact. Doubling the hair density doubles the hair volume while doubling the hair diameter quadruples the hair volume remember pi r2. Hair density varies from 1.53.0 hairs/mm2 while hair shaft diameter varies from 0.060.14 mm. Therefore hair shaft diameter plays a greater role than absolute hair numbers in determining overall cosmetic impact.

Conclusion

The introduction of follicular unit transplantation created a literal revolution in hair restoration surgery with doctors discarding their multibladed knives buying stereomicroscopes and training their staff in the dissection of individual follicular units. However the belief that in order to get the best results only naturally occurring individual follicular units should be transplanted has not been universally accepted.

With the new harvesting method of extracting follicular units directly from the donor area new technical issues are challenging the wisdom of always keeping follicular units intact. In particular if the object is to minimize the number of recipient wounds when performing follicular unit extraction it may pay to split larger units into single hairs to create a soft hairline rather than making separate punch holes to harvest each onehair graft. This and other technical issues of follicular unit extraction where only partial units are removed require fresh thinking about what should constitute follicular unit transplantation.

About the writer: Dr. Bernstein is recognized worldwide for pioneering Follicular Unit Hair Transplantation. Dr. Bernstein’s hair restoration center in Manhattan is devoted to the treatment of hair loss using his stateoftheart hair transplant techniques. Dr. Bernstein has been named “Best Doctor” in New York Magazine for 10 consecutive years. Read more at http://www.bernsteinmedical.com/.

Finer Hair

Clinical Characteristics Of Follicular Units In Hair Transplants