Skin displacement analysis (SDA): a tool for the quantitative evaluation of skin movements elicited by underlying muscles in the face and neck area

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). CONCLUSION: 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.