title: A comparison of skin expansion and contraction between one expander and two expanders: a preliminary study.
abstract: BACKGROUND
  This study aimed to compare the difference between the skin expansion and contraction rates for an expanded flap with one versus two expanders.
  
  
  METHODS
  The study cohort comprised 24 cases of two overlapping expanders and 15 cases of a single implanted expander involving 22 patients. The method of "wet-cloth sampling" was applied to measure the expanded flap area and the initial unexpanded area and to calculate the skin expansion rate. Two points 5 cm apart in the center of the expanded flap were selected before the second surgical stage. After removal of the expander, the distance between the two fixed points was measured and recorded. The contraction rate of the expanded flap then was calculated.
  
  
  RESULTS
  During the same period of expansion in the two groups (p = 0.06, >0.01), the skin expansion rate was 3.5 ± 0.9 % in the group with two overlapping expanders and 2.6 ± 0.6 % in the control group. The difference between the two groups was statistically significant (p = 0.002, <0.05). The instantly expanded flap contraction rates were 30.3 ± 0.8 and 32.3 ± 0.9 %, respectively for the two groups, and the difference was not statistically significant (p = 0.47, >0.05). We fitted a linear regression model that was Y = 0.533 − 0.003X, where Y was the contraction rate of the expanded flap and X was the period of expansion. The contraction rate of the expanded flap was negatively correlated with the period of expansion.
  
  
  CONCLUSIONS
  Compared with the traditional method of implanting a single expander, the new method of overlapping two expanders in a single cavity increased the skin expansion rate. The instantly expanded flap contraction rate did not differ significantly between the two groups, so the amount of expanded skin area absolutely increased. The clinical application of the new method is worth promoting.
  
  
  METHODS
  This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.
authors.forename: Gan-lin
authors.initials: GL
authors.lastname: Zhang
authors.forename: Jin-ming
authors.initials: JM
authors.lastname: Zhang
authors.forename: Chen-yang
authors.initials: CY
authors.lastname: Ji
authors.forename: Hong
authors.initials: H
authors.lastname: Meng
authors.forename: Jian-hua
authors.initials: JH
authors.lastname: Huang
authors.forename: He-yuan
authors.initials: HY
authors.lastname: Luo
authors.forename: Hua-sheng
authors.initials: HS
authors.lastname: Zhang
authors.forename: Xiao-tao
authors.initials: XT
authors.lastname: Liu
authors.forename: Xiao-fang
authors.initials: XF
authors.lastname: Hong
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D002681:China; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016014:Linear Models; D008875:Middle Aged; D011183:Postoperative Complications / Q000503:physiopathology; D011446:Prospective Studies; D019651:Plastic Surgery Procedures / Q000379:methods*; D018570:Risk Assessment; D012867:Skin; D013524:Surgical Flaps / Q000637:transplantation*; D015626:Tissue Expansion / Q000009:adverse effects / Q000379:methods*; D015625:Tissue Expansion Devices; D014022:Tissue Survival; D016896:Treatment Outcome; D014945:Wound Healing / Q000502:physiology; D055815:Young Adult