From September 2010 until September 2011, a total of 100 patients were followed after cardiothoracic surgery at Maastricht University Medical Center (Maastricht, The Netherlands) and included in the study. A power analysis was performed using a previous pilot study,10 in which the redness of the scar after reduction mammoplasty was measured. The Medical Ethical Committee of Maastricht University Medical Center approved the study (project no. METC 10-4-009), and patients were included only after written, informed consent was obtained.
Cardiothoracic patients were contacted on postoperative day 5 before discharge. Patient inclusion criteria were age > 18 years and cardiac surgery through a median sternotomy incision. Patients with a history of hypertrophic scarring or keloid formation, diabetes mellitus, degenerative or metabolic diseases, or preexisting skin disorders and patients using corticosteroid or immunosuppressive medication were excluded from the study. Ex-smokers were defined as having quit smoking at least 1 month prior to the operation, whereas smokers had to be smoking on the day of surgery or quit smoking within 1 month prior to surgery.
Objective measurement of the scar was performed by measuring the redness of the scar at 6 weeks and at 3, 6, and 12 months postop. The exact day after surgery was documented at every time point. A Minolta CR-300 (Minolta Camera Co, Ltd, Osaka, Japan) was used for measurements. These measurements were performed under standardized conditions at 3 locations on the scar: 2 cm from the cranial end of the scar; at nipple height (or in women with ptotic breasts, a height corresponding with half the length of the humerus was used as normal nipple height); and 5 cm from the caudal end of the scar.
Coloric measurement was not performed in case of incomplete wound healing of the wound in a particular area. Normal skin color was measured near the scar at each time point and subtracted from the measured values of the different measurement points of the scar. The Patient and Observer Scar Assessment Scale (POSAS) was used to evaluate the scar at each time point. Six weeks post surgery, patients started to apply a hydrating cream (Alhydran; BAP Medical, Apeldoorn, Overijssel, The Netherlands) on the scar twice daily. In case of hypertrophic scar formation, treatment was not deferred and an alternative treatment, such as silicone dressings (Scarban Elastic; SCARPRO N.V., De Pinte, Belgium), was proposed. Hypertrophic scarring was defined as a situation in which the scar, or a part of the scar, is raised above the level of the surrounding skin. The size of the scar had to remain within the original border of the incision. If this last condition was not fulfilled, a scar was deemed as having more keloid instead of hypertrophic characteristics.
Statistical analysis
The analysis was based on patients with known smoking status (smoker, ex-smoker, nonsmoker). Four response variables were analyzed: “base redness,” which was calculated as measured redness of the scar minus the redness of the normal skin measured at the corresponding location (cranial, nipple, caudal), and 3 POSAS components (color, thickness, and irregularity). Time (6 weeks, 3 months, 6 months, 12 months) was scaled to months for computational reasons and the evolution of scar redness (with normal skin measurement subtracted) and the 3 components of the POSAS by smoking status over time was analyzed using a linear model correcting for patient age, location (only for base redness), and length and width of the scar. Time was modeled continuously in the mean evolution. The assumption that time was linear was tested by adding a squared time effect, including the interactions with smoking status and location (only for base redness), to the models and jointly testing the null hypothesis that time was linear. An unstructured variance-covariance matrix was assumed using a categorical version of time point (6 weeks, 3 months, 6 months, 12 months).
The POSAS was summarized descriptively by mean, standard deviation, median, quartiles, range of numbers, and percentage, whichever was appropriate.
A Fisher’s exact test was used to analyze the difference between location (cranial vs. middle together with the caudal part) within every patient with a hypertrophic scar.