Scarring occurs at a critical skin injury depth

January 1, 2008

Whether performing a chemical peel, a dermabrasion or a shave excision, just how deep can a derm surgeon go before crossing the rubicon of scar tissue formation? What is the critical depth at which a scar will form within the skin following a procedure in the skin? A recent study was able to define this critical dermal depth of no-return, making physicians more savvy to the cosmetic thorn known as fibrous scar tissue, helping them predict cosmetic outcomes prior to the intervention itself.

Key Points

Aylesbury, England - Scar formation, a well-known and clearly unwanted side effect, may follow any surgical and/or cosmetic procedure, regardless of the physician's precautions. A recent study demonstrates precisely how deep within the dermis scar formation will occur following a given procedure, helping physicians to predict cosmetic outcomes before laying hands on their patients.

"There is a depth of dermal injury that results in a fibrotic scar, as a result of a difference in dermal architecture or in the cellular phenotype of dermal constituents.

"Alternatively, the inflammatory cascade triggered by superficial dermal injury may not exceed the scarring threshold and the wound heals by regeneration rather than fibrosis," says Christopher S. J. Dunkin, M.R.C.S., M.D., of the Burns and Reconstructive Surgery Research Trust at Stoke Mandeville Hospital.

Using this method, Dr. Dunkin was able to precisely measure the critical depth at which a fibrous scar develops.

The average follow-up of patients in the study was 29 weeks. The initial length of injury was 51.3 ± 0.6 mm, which reduced to a scar of 34.9 ± 1.0 mm at 36 weeks. Dr. Dunkin found that the deep dermal end of the wound induced in study participants healed with a visible scar, and the superficial end had no visible residual mark after week 18.

Dr. Dunkin used a high-frequency ultrasound scanner as a noninvasive, quantitative technique for demonstrating the depth of injury and developing scar in microscopic resolution. The results showed a gradual reduction in scar thickness at the deep end, and no detectable scar at the shallow end. The transition point between scar and no scar marked the threshold depth for scarring, and was found to be at 0.56 ± 0.03 mm, or 33.1 percent of normal hip skin thickness.

Specialists in burns and reconstructive surgery, Dr. Dunkin says, have long recognized the association between the degree of scarring and the depth of dermal injury. He says that this relationship is a fundamental principle in the harvesting of split-thickness skin grafts and in the management of partial thickness burns. This relationship has stimulated advances in imaging, such as laser Doppler scanning, which provide objective data on depth of injury in burns.

Dr. Dunkin says that the association between depth of injury and scarring is evident from the use of lasers to treat superficial vascular malformations, and for facial resurfacing.

This study shows the precise threshold depth in the dermis at which an injury will result in detectable scar tissue. Dr. Dunkin says this newly found knowledge might prove invaluable to cosmetic surgeons, as scar tissue formation is a major issue and a feared complication in any cosmetic procedure.

"The results of our study demonstrated that scarring occurs once a threshold of depth on injury is exceeded. Clinicians should have a knowledge of the thickness of the dermis in sites of the body they treat and be aware of the depth of dermal injury they produce, whether it be with chemicals, dermabrasion, alloplastic injection or other given cosmetic intervention," Dr. Dunkin tells Dermatology Times.

"Failure to consider these factors may lead to injury that exceeds this threshold depth and results in scarring."