What is a Graft?
A graft is a generic term for any piece of hair-bearing tissue that is transplanted into the scalp. Whether it is a modern follicular unit, a mini-micro, or one of the large 4-millimeter “plugs” of yesteryear, they are all technically considered grafts. Grafts can be harvested from all over the body, but they are usually selected from the occipital scalp (the back of scalp known as the donor zone) due to the hair’s high levels of sustainability in that region. Their overall size and shape are determined by the technology, tools, and surgical approach.
How is a Graft Created?
In general, hair grafts are created by removing tissue from the donor zone. The ultimate goal is to remove a small amount of tissue that can grow hair and transplant it to the area of the scalp that needs to grow hair (recipient scalp). Hair-bearing tissue from the donor zone can be removed either in a fleshy strip all out once (known as follicular unit strip surgery, or FUSS), or by removing the follicular units directly from the donor zone one at a time (known as follicular unit extraction, or FUE).
With FUSS (sometime incorrectly referenced as "FUT"), grafts are harvested from the donor strip. After the strip is removed from the occipital scalp, the physician's team must dissect the follicular units from the donor strip using stereoscopic dissecting microscopes. These follicular units are then preserved and prepared for insertion into the recipient scalp as individual hair grafts. A follicular unit typically yields 2-3 hairs, though this is not universal. Next, the physician makes incisions on the recipient scalp that are the exact same size as the graft (called recipient sites). The grafts are then inserted one by one into each recipient site at the appropriate depth and angle with the goal or replicating nature.
With FUE, the physician does not need to remove a donor strip. Instead, the follicular units are individually extracted directly from the recipient scalp itself. These follicular units are then preserved and transplanted into the scalp in the same fashion as FUSS.
What Determines Graft Survivability?
It is crucial that as many of the hair grafts survive the transplant from their original area into the recipient scalp as possible. Unfortunately, a number of factors can go awry:
- Dehydration – studies have shown that a graft can survive over 16 minutes in a dry environment before “significant death occurs”. Storing them in a liquid solution such as saline or HypoThermosol adresses this problem.
- Temperature – one of the primary contributing factors to dehydration. A 2007 study showed that chilling the follicular units to 1°C can drastically prolong their survival rates by hours, especially when compared to storing them in room temperature. In fact, a study in 2002 revealed that grafts frozen for 14 days at negative 20°C showed no damage.
- Oxygen supply – ATP is a process in which the body breaks down oxygen from the blood and converts it into energy. This occurs virtually everywhere that energy is expended, even in the hair. When the follicular units are removed from the donor zone, they are deprived of oxygen; the ATP process is interrupted. For this reason, if the follicular units are deprived of oxygen for too long, they will fail.
- Proper selection – the occipital scalp provides the sturdiest donor hairs. If the physician selects hairs from other areas of the scalp or body, however, they may not be as durable. In worst case scenarios, the donor hairs themselves are susceptible to degradation over time.
A Quick Warning about Follicular Units
The average follicular unit is considered to have 2 to 4 hairs, but some clinics will further divide follicular units into even smaller grafts with even fewer hairs. This step allows for an additional layer of refinement during the procedure, but also artificially inflates the graft numbers. Always ask your hair physician for a hair count evaluation before your surgery and compare this to your hair counts that are documented after your surgery.