Excellent surgical results and high patient satisfaction with hair transplantation depend on attaining optimal growth. Unfortunately, even experienced surgeons acknowledge that graft survival often is not as high as is commonly stated. Hair transplant surgeons should be thoroughly familiar with the many variables that affect graft survival and refine their surgical techniques accordingly. This article provides a brief overview of the key factors that most significantly influence graft survival, including graft trauma, vascular/oxygenation factors, and biochemical injury.
Key points
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Achieving optimal growth in hair transplantation is a critical part of obtaining excellent results and high patient satisfaction.
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The most important factors determining graft survival are avoiding physical trauma to the grafts and ensuring that the oxygenation needs of transplanted follicles are met.
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Hair follicles that are physically intact have a much higher chance of survival than transected ones.
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Graft dehydration from loss of intracellular water is very damaging to cells of the hair follicle.
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Grafts that have been roughly handled and crushed by forceps have a significantly lower growth rate than grafts that have been handled gently.
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Variation in scalp oxygenation may be the single biggest factor explaining variability in graft survival.
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The use of liposomal adenosine triphosphate may help replace graft oxygen needs that are not fully met by patients’ vascular beds.
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Biochemical injury may occur to the graft tissue while it is outside the body or after it has been transplanted.
Introduction
Achieving optimal growth in hair transplantation is a critical part of obtaining excellent results and high patient satisfaction. For the purposes of this review, optimal growth refers to the highest possible percent survival of implanted hair follicles as well as the quality (eg, caliber) of the resulting hair that grows. Obviously other factors are also critical to the quality of the result, such as hairline design, graft angle and direction, and graft distribution. These concepts are discussed in other articles in this publication.
Many experienced surgeons quietly acknowledge among themselves that graft survival is not consistently as high as is publicly stated, partly because of the natural tendency to avoid publicly admitting to suboptimal results. Furthermore, in the era of follicular unit transplantation (FUT) in which a typical case is 2000 grafts and often more, it can be very difficult to accurately establish the percentage of grafts that survive. Nevertheless, all surgeons should be aware of the factors related to graft survival and develop their surgical technique accordingly.
This article provides a brief overview of the factors related to graft survival. Relatively little is available in the way of valid, controlled scientific studies. This point may seem surprising to novice surgeons given the advanced stage of development of modern hair transplantation techniques. It is worthwhile to consider the reasons for this lack of quality evidence-based research. Perez-Meza and Shapiro discussed the reasons why tracking hair transplant outcomes is so difficult, and the reader is referred to this excellent review. These reasons include the long time period until a final result is achieved, difficulty in counting hairs among the thousands planted to determine survival rates, and spotty follow-up by patients.
Over the years, surgeons have attempted to study factors that might affect growth by performing small study boxes on patients’ scalps. Although well intended, these studies lack the proper size and design to eliminate bias and chance as chief reasons for the observed results. Parsley and colleagues have reviewed some of these prior studies.
Nevertheless, important principles can be identified based on the science of transplantation as well as case reports and the opinions of experienced surgeons. The most important factors determining graft survival are avoiding physical trauma to the grafts (transection, crushing, dehydration) and ensuring that the oxygenation needs of transplanted follicles are met. There are other factors that may also be important, and these factors are discussed later ( Table 1 ).
| Problem | Solution |
|---|---|
| Physical Trauma | |
| Transection | Microscopic dissection |
| Dehydration | Hydration, humidifier (?) |
| Crushing | Careful, gentle technique |
| Vascular/Oxygenation Factors | |
| Baseline blood flow & vascular reserve | Effect of sites on blood flow: size, depth, density of incisions |
| Postoperative treatments (?) | |
| Liposomal ATP | |
| Other: vasodilators, hyperbaric oxygen | |
| Optimized holding solution (eg, HypoThermosol [BioLife Solutions, Bothell, WA]/ATP) |
| Infection | Clean technique, patient hygiene, antibiotics (?) |
| Patient disruption | Postoperative instructions |
| Idiopathic (X factor) | |
Introduction
Achieving optimal growth in hair transplantation is a critical part of obtaining excellent results and high patient satisfaction. For the purposes of this review, optimal growth refers to the highest possible percent survival of implanted hair follicles as well as the quality (eg, caliber) of the resulting hair that grows. Obviously other factors are also critical to the quality of the result, such as hairline design, graft angle and direction, and graft distribution. These concepts are discussed in other articles in this publication.
Many experienced surgeons quietly acknowledge among themselves that graft survival is not consistently as high as is publicly stated, partly because of the natural tendency to avoid publicly admitting to suboptimal results. Furthermore, in the era of follicular unit transplantation (FUT) in which a typical case is 2000 grafts and often more, it can be very difficult to accurately establish the percentage of grafts that survive. Nevertheless, all surgeons should be aware of the factors related to graft survival and develop their surgical technique accordingly.
This article provides a brief overview of the factors related to graft survival. Relatively little is available in the way of valid, controlled scientific studies. This point may seem surprising to novice surgeons given the advanced stage of development of modern hair transplantation techniques. It is worthwhile to consider the reasons for this lack of quality evidence-based research. Perez-Meza and Shapiro discussed the reasons why tracking hair transplant outcomes is so difficult, and the reader is referred to this excellent review. These reasons include the long time period until a final result is achieved, difficulty in counting hairs among the thousands planted to determine survival rates, and spotty follow-up by patients.
Over the years, surgeons have attempted to study factors that might affect growth by performing small study boxes on patients’ scalps. Although well intended, these studies lack the proper size and design to eliminate bias and chance as chief reasons for the observed results. Parsley and colleagues have reviewed some of these prior studies.
Nevertheless, important principles can be identified based on the science of transplantation as well as case reports and the opinions of experienced surgeons. The most important factors determining graft survival are avoiding physical trauma to the grafts (transection, crushing, dehydration) and ensuring that the oxygenation needs of transplanted follicles are met. There are other factors that may also be important, and these factors are discussed later ( Table 1 ).
| Problem | Solution |
|---|---|
| Physical Trauma | |
| Transection | Microscopic dissection |
| Dehydration | Hydration, humidifier (?) |
| Crushing | Careful, gentle technique |
| Vascular/Oxygenation Factors | |
| Baseline blood flow & vascular reserve | Effect of sites on blood flow: size, depth, density of incisions |
| Postoperative treatments (?) | |
| Liposomal ATP | |
| Other: vasodilators, hyperbaric oxygen | |
| Optimized holding solution (eg, HypoThermosol [BioLife Solutions, Bothell, WA]/ATP) |
| Infection | Clean technique, patient hygiene, antibiotics (?) |
| Patient disruption | Postoperative instructions |
| Idiopathic (X factor) | |
Physical trauma
Hair follicles that are physically intact have a much higher chance of survival than transected ones. This fact is a major rationale for microscopically controlled FUT, first described by Limmer. By using a single scalpel blade for donor excision, transection is minimized along the wound edge. The strip is then slivered and dissected using stereomicroscopes, whereby a 10 × magnification provides for superior visualization of the follicle. A study performed by the author involving multiple experienced surgeons showed that those who used microscopes had half as many transected hair follicles in random samples of grafts than those who did not use microscopes.
Microscopic Dissection
Without the use of microscopes, follicular transection is very likely to occur to varying degrees in all cases. Some individuals have claimed that this is not that important because transected follicles sometimes grow anyway. The probability of follicle regeneration is directly related to the level of transection. If less than half of the follicle is present, regeneration rarely occurs. The author thinks that follicle regeneration is an unpredictable process and that the best way to ensure good growth is to transplant physically intact follicles. In the author’s practice, the change to follicular unit grafting with all microscopic dissection has been the biggest factor in increased graft survival.
There are situations in which microscopic dissection is especially critical:
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In patients with extremely curly hair (eg, black patients)
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In those with extensive scarring in the donor tissue from prior procedures
Many of the follicles will be transected if they are not carefully dissected under the stereomicroscope.
There are situations in which the patients’ hair characteristics allow for easier dissection and may not require stereomicroscopes. Asians, for example, generally have dark, straight hair, allowing for easier visualization.
Many surgeons think that they can have consistently low transection rates with simple loupes and backlighting for all cases. On the other hand, most practices see patients from a variety of backgrounds, and using microscopic dissection on all cases eliminates trying to guess beforehand whether use of microscopes will be necessary. Even in cases when the hair is easy to dissect, the use of the microscope allows closer dissection and sorting of fine hairs for the hairline.
Patients with gray or white hair also present challenges in visualization. Even with the use of the microscope, visualization can be difficult. Some surgeons have found that injecting or soaking the donor strip with methylene blue can be helpful in increasing the contrast between follicles and the surrounding tissue. Others have found that dying the donor hair before harvesting with over-the-counter mustache dye is a useful aid. The author has found the latter approach to be particularly helpful. Many find it helpful to leave more tissue around the follicles to avoid transection. However, this then requires larger recipient sites to ensure a proper fit.
Graft Dehydration
Graft dehydration from loss of intracellular water is very damaging to cells of the hair follicle. With increasingly larger sessions of increasingly more grafts, there is more opportunity for these small grafts to be exposed to the air during dissection and while awaiting placement. There is widespread consensus for the need to keep grafts well hydrated. Achieving this requires constant monitoring of the staff. Some staff, in an effort to cut quickly, leave dissected grafts piled up before putting them in holding solution, increasing exposure time to the air and increasing the risk of dehydration. One factor that can affect graft drying is the ambient humidity in the operatory environment, having an impact especially when forced air conditioning or heat is in use. In the author’s experience, having a humidifier running constantly during the surgery helps add moisture to the air and reduces graft drying.
There is some controversy as to whether grafts should be submerged in graft-holding solution or placed at the air-liquid interface on moistened gauze pads. Some strongly advocate the former, whereas other successful surgeons use the latter, both with excellent results.
Graft Crush Injury
Crushing of the grafts during placement is another potentially lethal factor. Given the small size of today’s grafts, it is not surprising that the forceps may crush them during placement into small recipient sites, such as 22-gauge needle or 0.6-mm incisions. One point worth highlighting is that the bulb is very sensitive to crush injury. Because of its melanin content, the bulb is often the darkest part of the follicle and may seem sturdy. However, formation of the keratinized hair shaft does not occur until just above the bulb. Grasping the bulb with forceps too aggressively can easily rupture the dermal sheath and cause the dermal papilla to be lost. Grafts that have been roughly handled and crushed by forceps have a significantly lower growth rate than grafts that have been handled gently.
Techniques to minimize crush injury during placement include the following:
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Site dilators
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Implantation devices
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Special forceps
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The 2-forceps technique
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The stick-and-place technique
The last technique, developed by Dr Bobby Limmer, consists of placing the graft immediately after each site is made by a hypodermic needle. Dr David Seager was also a strong advocate of this approach. The author uses a modified stick-and-place technique whereby all incisions are premade. Then the placers will have their forceps in their dominant hand and a dull hypodermic needle (eg, 22 gauge) in their nondominant hand. The dull needle can be used to reopen the incision, if necessary, as the graft is gently placed into the site. The tip of the needle also acts as a tiny fingertip to hold the graft in place as the forceps are withdrawn, which reduces manipulation by the forceps.
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