Nail technicians should know as much about the inside of the nail as the outside. Here’s an anatomy lesson on the onychium. Pay attention – there’s going to be a test at the end.
While a nail technician’s job is focused primarily on the exterior surfaces of the nail, the supporting structures are just as important, as they dictate how the nails grow. This short lesson will give you the basics of nail anatomy, starting with how the nail is formed in a developing fetus.
The earliest sign of nail development in the embryo occurs at about 10 weeks. On the far end of the finger or toe, there is a pushing in of skin cells, known as an invagination, whereupon a structure called the matrix primordium is found. It is from this source that the true nail matrix develops and begins to manufacture the nail plate, which proceeds to grow outward.
The nail plate, of course, is the external structure. The nail matrix grows underneath the proximal nail fold, which extends back from the cuticle for 1/8 inch to ¼ inch. The matrix ends underneath the nail plate in the lunula – which is not always visible on all nails. Where the lunula ends, the nail bed begins. The nail bed is constructed in longitudinal grooves and ridges and extends distally to where the nail plate just begins to separate from it. This is the site of the hyponychium, which may be seen on an unpolished thumbnail as a very narrow red area that extends from side to side. The hyponychium ends in the normal skin of the finger or toe.
At about 20 weeks, the embryo’s entire nail unit will be fully developed. Underneath the cuticle on top of the nail plate is a very important space called the proximal nail groove. The purpose of the cuticle is to seal off this space and thereby prevent all the outside world hazards from getting in – including bacteria, fungi, and viruses as well as harmful chemicals, soaps, detergents, and so on. That’s why it’s so important no to remove or abuse the cuticle by pushing, cutting, or trimming it.
Sometimes on the nail a thin piece of skin come out from beneath the proximal nail groove and is deposited on the surface of the nail plate. This structure is referred to as the eponychium. It is often confused with the cuticle itself, which is not actually deposited on the nail plate. On both sides of the nail is also a depression into which the nail plate fits snugly. These are known as the laternal nail grooves. They are important as fungus can often enter the nail from those locations.
Finally, the portion of the nail plate beneath the proximal nail fold is called the nail root. It is thinner and softer than the rest of the nail and is easily damaged, particularly by over-manipulation of the cuticle. It is very important to remember that, unlike the skin which has fat underneath it, there is no fatty tissue under the nail. Just beneath the nail unit is bone, called the distal phalanx. The total distance from the surface of the nail plate of the covering (periosteum) of the underlying bone is only about ¼ inch. It is essential to keep in mind that what affects the nail may affect the bone, and what affects the bone may produce an abnormal nail. Consequently, in some cases, an X-ray of the finger or toe can be very helpful in assessing and diagnosing nail disorders.
At the near end of the distal phalanx is a joint known as the distal interphalangeal joint. Old age arthritis (osteoarthritis) can involve this joint, and since it is situated so close to the nail matrix, the nail may be abnormal in clients with this condition. Likewise, the arthritis occurring with psoriasis (psoriasis arthritis) may also affect this joint. The end result is that almost all patients with distal interphalangeal joint psoriatic arthritis have abnormal nails as well.
Fingernails grow at a rate of about 3 mm, or 1/8 inch per month. Toenails grow at about ½ or 1/3 that rate, which is 1-1.5 mm, or 1/16 inch per month. It takes about six months to totally replace a fingernail and 12-18 months to replace a toenail. Nail growth is slower in the elderly, in nails infected by fungus, and during a systemic illness such as a viral infection with fever. Nails grow faster during the summer, pregnancy, menstruation, and in the presence of psoriasis. Frequent trauma or injury may also make the nails grow faster. Because it takes the nails so long to grow, it used to take antifungal medication six months to clear a fingernail and 12 months or more to clear a toenail. With the new treatments available, however, fingernails can be cleared in as few as six weeks, and toenails in only three to four months. This is because the new medications reach the nail very early – one to three weeks – and remain in the nail much longer after the treatment is stopped – three to nine months.
Thus, the anatomy of the nail unit and its adjacent joint and bone structures have a profound effect on nail development and nail disease. Nail growth is also influenced by outside forces that may either speed up or slow down growth according to the particular insult.
Problems with fingernails don’t just happen to adults. Children have nail problems as well, and whether they’re coming to you for services for themselves, or if it’s the child of one of your adult clients, understanding the nail problems of children makes you a more well-rounded nail technician. Nail problems in children and adolescents may often mirror those disorders found in adults. However, there are a number of situations when differences exist.