title: Skin displacement analysis (SDA): a tool for the quantitative evaluation of skin movements elicited by underlying muscles in the face and neck area.
abstract: BACKGROUND
  Quantitative numerical analysis of skin displacement triggered by muscles inserting the overlaying skin would be useful for monitoring the inhibition of mimetic muscles.
  
  
  METHODS
  By using removable grid markings and digital photographs, skin displacement analysis (SDA) was performed on 13 patients pre-treatment and on Days 1, 2, 3, and 7 after injection of 18 units of botulinum toxin type A (BoNT/A) in the fronto-glabellar area.
  
  
  RESULTS
  At baseline, amplitudes of horizontal skin displacement with fronto-glabellar contraction showed a linear increase along the eyebrow laterally from the midline; mean values (±standard deviation [SD]) 15 and 30 mm lateral to the midline were 3.2 ± 1.0 mm (range, 1.9-4.9 mm) and 6.5 ± 1.4 mm (range 4.0-8.5 mm), respectively. After injection of BoNT/A, maximum horizontal skin displacement 30 mm lateral to the midline showed a mean reduction (±SD) to 62% ± 23% at Day 2 and to 17% ± 16% at Day 7; corresponding values 15 mm lateral to the midline were 62% ± 29% and 15% ± 20%, respectively. In all cases, the reduction in horizontal skin displacement compared with pre-injection levels was statistically significant (P < 0.001).
  
  
  CONCLUSIONS
  SDA is a feasible method for the quantitative evaluation of skin movements elicited by muscles inserting the overlaying skin in the face and neck area.
authors.affiliation: Department of Dermatology, University Clinic of Mainz, Mainz, Germany.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Proebstle