Do Native Breasts Move During Pectoralis Major Contraction in Unoperated Women? A Quantitative 3D Analysis

The dynamic behavior of unoperated native breasts during pectoralis major contraction remains poorly defined. This study aimed to quantitatively assess native breast displacement during pectoralis major contraction using three-dimensional (3D) imaging.

Healthy, unoperated adult women underwent 3D surface scanning at rest and during maximal pectoralis major contraction. Six anatomical landmarks were identified per breast: nipple midpoint (Nm), inframammary fold midpoint (IMFm), and midpoints of the superior, inferior, medial, and lateral boundaries. For each point, spatial coordinates (X, Y, Z) and distance from the sternal notch (D) were extracted. Repeated-measures ANOVA compared displacement among landmarks. Sagittal contour profiles were graded: A, complete overlap; B, localized displacement without crossover; C, crossover displacement; D, distorting displacement. Visual assessment of breast motion was performed independently.

Thirty-eight women (76 breasts) were included. All landmarks showed superior displacement, largest at IMFm (ΔY = 2.689 ± 2.331 mm). Displacement differed significantly among landmarks (F = 4.326, P = 0.004, partial η² = 0.105). Sagittal contour analysis classified 42.1% of breasts as Grade B and 57.9% as Grade C; none were Grade A or D. Slight motion was observed in 28.9% of breasts. Only IMFm displacement differed significantly between breasts with and without perceptible motion (3.808 ± 2.063 mm vs 1.875 ± 2.211 mm, P = 0.010).

Native breasts exhibit mild superior displacement during pectoralis major contraction, greatest at the inframammary fold, with minimal clinical perceptibility. These data provide a physiological baseline for understanding native breast movement and animation deformity following subpectoral implant placement.

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