Hair Transplant > Hair Transplant Articles > The Hair Transplant Density Issue

The Hair Transplant Density Issue

THE DENSITY ISSUE
B.L.Limmer, M.D.
Professor of Dermatology, University of Texas Health Science Center, San Antonio, Texas; Diplomate American Board of Dermatology, Inc., Diplomate American Board of Dermatopathology, Inc., San Antonio, Texas

All hair restoration techniques should seek to mimic nature in both quality
and quantity. Results so natural that recognition as a transplant is
difficult are readily accomplished today through the use of large numbers of very small grafts. Whether density comparable to other techniques can be accomplished with small graft methodology remains a contested issue among transplant surgeons.

A review of the literature reveals a significant variation in naturally
occurring density as determined by surface anatomists, microscopic histologic studies, and the intraoperative findings of hair restoration surgeons. These findings are noted to be influenced by age, race and various alopecias including androgenetic alopecia. Using horizontal sectioning methods, Headington found terminal hair counts of 160-280 per square centimeter. Surface anatomists have found average densities ranging from 154-240 hairs per square centimeter. Using surface microscopy, Barman et al found the frontal scalp of non-balding men age 16-46 years to possess an average of 210 hairs per square centimeter. Sperling and Winton6 found the frontal scalp of patients undergoing hair transplantation for androgenetic alopecia to possess 111 hair per square centimeter of which approximately 85% were vellus and 15% terminal. Other estimates of total hair density have ranged from 435 per square centimeter for 80 year old men to 615 per square centimeter for 20-30 year old men.  Hair restoration surgeons counting terminal hair in the donor area of patients undergoing hair restoration surgery have generally found a lesser terminal hair density than surface anatomists. By counting terminal hair in 4.0-4.5 millimeter diameter donor plugs, Nordstrom found a range of 82-190 hair per square centimeter. By counting hair in an approximately 10 square centimeter elliptical donor specimen, Limmer found a range of 120-140 hair per square centimeter. Summarizing the densities encountered by these investigators it would appear with reasonable certainty that the naturally occurring density in the adult male lies in a range of 130-280 terminal hair per square centimeter with an average density estimated near 200 hair per square centimeter.

It is generally accepted that hair density must decrease approximately 50% before alopecia becomes very obvious to the naked eye. Assuming a range of 130-280 terminal hair per square centimeter as "normal", a goal of 65-140
hair per square centimeter would be required to generate the appearance of
"normal" density restoration. Based upon counts of density in cases done by both plug and mini-micrografting methods, these estimates required to produce the appearance of normal or cosmetically acceptable density hold true in this study.

Materials and Methods:

Hair restoration cases from the author's practice including former cases done
by standard plug technique and more recent cases done by mini-micrografting methods were randomly selected for counting of terminal hair density. Counts were done under 5X magnification by the author. A 1 square centimeter template was placed at the middle position of both right and left frontal hairlines and the numbers of terminal hair present within the 1 centimeter zone of the grafted hairlines counted and recorded. All cases done by plug method had been transplanted using 4.5 millimeter diameter donor plugs placed into 4.0 millimeter recipient holes and had undergone the standard 4 session replacement method. Cases done by mini- micrografting methods had undergone from 1-4 sessions of restoration along the frontal hairline using grafts bearing 1-3 hair per graft.

Densities achieved by each method and by the numbers of sessions of mini-
micrografting technique are recorded in Table 1 and Table 2. those cases done by plug technique averaged 59 terminal hairs per square centimeter. The average density among cases done by mini- micrografting technique varied by numbers of sessions done: 1 session, 41; 2 sessions, 50; 3 sessions, 63; and 4 sessions, 81 terminal hair per square centimeter. Representative pre-operative and post-operative hairlines are demonstrated in figures 1-6.

Discussion:

The issue of density achieved by various techniques remains the subject of
debate among hair restoration surgeons. Proponents of flap and plug graft
methodologies staunchly defend these approaches as essential to accomplish density in the final product. Proponents of mini-micrografting methods point out that such small graft techniques are essential to produce naturalness. In fact, most proponents of flap and plug graft techniques note that micrografting is usually if not universally used to refine the frontal
hairline the modern publications by Nordstrom and Marritt pointing out this
advantage. To date, there are no studies addressing the issue of density
achieved with mini-micrografting methodology alone.

The survival of hair in plug grafts has been studied by a number of investigators counting   terminal hair growing in 4 millimeter plugs after
transplantation. Adamson found 8-15 per plug; Muhlbauer, 11-14,
Norwood, 8-16, and Nordstrom, 20. Our counts in plug graft cases reveal a range of 10-19 hair per plug. Average density achieved among plug cases was 59 hair per square centimeter. Estimated maximum densities achievable based upon the above studies would be 50-125 hair per square centimeter (6.25 grafts of 4 millimeter diameter each per square centimeter) if perfect packing of 4 millimeter plugs were achieved which, of course, is seldom accomplished. The densities achieved using mini-micrografting methods varied with the number of sessions done. Cases undergoing one session averaged 41; 2 sessions, 50; 3 sessions, 63; and 4 sessions, 81 terminal hair per square centimeter.

The procedural technique of using the first session to establish the frontal
hairline and dense packing of 20-40 grafts per square centimeter to maximize density during the initial session accounts for the first session's
production of greater density per session. Subsequent sessions are utilized to fill between the first session's grafts and to advance transplantation to
additional zones not addressed with the initial session; therefore, fewer
grafts are generally planted per square centimeter in the frontal hairline on
second and subsequent sessions than were planted during the initial session. However, comparison of densities achieved readily reveals that under routine transplantation procedure in the author's practice densities comparable to plug procedure are accomplished with fewer sessions using mini-micrografting methodology.

In spite of mini-micrografting methodology producing densities comparable or
in excess of standard plug methodology, the appearance to the naked eye of
greater density in plug hairlines remains often a fact. Factors that may
account for this visual contradiction include the abrupt transition from an
alopecic forehead to a "wall of hair" created by a line of plugs. This
tendency to build a "wall of hair" with plug procedures contrasts with the
more gradual transition or "feathering zone" at the hairline seen in mini-
micrografting leading to the optical illusion of greater density in the plug
hairline which is not supported by actual density studies. Other factors may
include visual fixation on the density of hair in individual plugs as opposed
to the more uniform dispersal of individual hair in mini-micrografted cases.
The placement of additional rows of plugs behind the frontal line further
reinforces this line in plug grafted cases. The same level of dense
packing of mini-micrografts done in the first several centimeters of transplanted scalp often is not maintained throughout the more posterior zones. This approach has allowed the transplantation of advanced alopecias with very natural appearing coverage without donor area exhaustion which goals would never have been achievable by standard plug methodology. Therefore, the advantage of being able to cover large alopecias with a very natural but less dense coverage may be seen by the naked eye as a weakness of mini-micrografting.

Conclusion:

Comparable densities in the frontal hairline have been achieved by plug and
mini-micrografting cases in the author's practice. Such densities are
typically achieved in fewer sessions using mini- micrografting methodology.