“The follicular unit hair transplant procedure has continued to evolve, becoming more refined and minimally invasive as the size of the graft incisions have become smaller. These smaller and less invasive incisions enable surgeons to place a larger number of follicular unit grafts into a given area. With the new “gold standard” of ultra refined follicular unit hair transplantation, over 50 grafts can be placed per square centimeter, when appropriate for the patient.
Surgeons have also devoted more attention to the angle and orientation of the transplanted grafts. The adoption of the “lateral slit” technique in the early 2000s, enabled hair transplant surgeons to orient 2 to 4 hair follicular unit grafts so that they splay out across the scalp’s surface. This enabled the transplanted hair to lie better on the scalp and provide better coverage to the bald areas. One disadvantage however, is that lateral incisions also tend to disrupt the scalp’s vascularity more than sagittals. Thus sagittal incisions transect less hairs and blood vessels assuming the cutting instruments are of the same size. One of the big advantages of sagittals is that they do a much better job of sliding in and around existing hairs to avoid follicle transection.”
Source – “Hair Transplantation” Wikipedia, Evidence-Based Procedural Dermatology. Springer November 2011