Butt (gluteal region)

Gluteal-region morphology: shape, size, projection, gluteal-fold definition, and transitions to surrounding regions. Dimensions are drawn from gluteal-aesthetic-surgery literature (Cuenca-Guerra, Mendieta, Roberts) which has produced the contemporary classification systems for buttock shape and proportions. Significant ethnic and individual variation; the Mendieta four-class system is the most-cited classification for buttock shape in plastic-surgery literature.

Dimensions

• Buttock shape (Mendieta)

  photo-observable

  categorical · mendieta_four_class

  Four-class buttock-shape classification developed for gluteal-aesthetic surgery, based on the silhouette from a posterior view.

  Mendieta CG (2007). Classification system for gluteal evaluation. Clinics in Plastic Surgery, 34(3): 333-346.

  Valid values (4)

  • round_A_shapeA-shape (square below, narrow above)— Wider at the lower buttock; trapezoidal silhouette with the wider edge inferior.
  • v_shapeV-shape (wide above, narrow below)— Wider at the upper buttock; trapezoidal silhouette with the wider edge superior.
  • roundRound— Approximately circular silhouette; aesthetic-surgery reference shape.
  • squareSquare— Approximately rectangular silhouette with similar width across upper and lower.

• Buttock size (relative)

  photo-observable

  ordinal · buttock_size_qualitative

  Overall buttock size relative to body proportions.

  Aligned with gluteal-aesthetic descriptors used in body-contouring literature (Roberts TL et al. Aesthetic Surgery Journal).

  Valid values (4)

  • smallSmall— Limited gluteal mass; minimal projection from the trunk silhouette.
  • moderateModerate— Average gluteal mass.
  • fullFull— Pronounced gluteal mass.
  • very_fullVery full— Substantial gluteal mass; dominant feature of the trunk silhouette. Constitutional, athletic, or augmented.

• Buttock projection (lateral view)

  photo-observable

  ordinal · buttock_projection_qualitative

  Posterior projection of the buttock from the sacral plane in lateral view.

  Aligned with gluteal-aesthetic descriptors used in lateral-view-based aesthetic assessment.

  Valid values (3)

  • flatFlat— Minimal posterior projection.
  • moderateModerate— Standard posterior projection.
  • high_projectionHigh projection— Pronounced posterior projection; 'shelf-like' silhouette in lateral view.

• Gluteal fold definition

  photo-observable

  ordinal · gluteal_fold_qualitative

  Sharpness of the gluteal fold (the crease between the buttock and the posterior thigh).

  Aligned with descriptors used in gluteal-aesthetic-surgery literature on the gluteal-thigh transition.

  Valid values (3)

  • sharp_definedSharp / defined— Clear, crisp gluteal fold as a discrete landmark.
  • moderateModerate
  • soft_blendedSoft / blended— Gradual buttock-to-thigh transition; reduced fold definition.

• Lateral hip concavity (hip dip)

  photo-observable

  categorical · trochanteric_depression_qualitative

  Visible depression at the lateral hip ('hip dip' / 'violin hip') between the iliac crest and the greater trochanter.

  Aligned with descriptors used in gluteal-augmentation literature on lateral hip morphology.

  Valid values (3)

  • absentAbsent— Smooth lateral hip silhouette without visible depression.
  • subtleSubtle— Slight visible depression.
  • pronouncedPronounced— Distinct depression; common skeletal-anatomy variant.

• Buttock-to-hip silhouette

  photo-observable

  categorical · gluteal_hip_silhouette_qualitative

  Relationship between buttock width and hip width in the posterior silhouette.

  Aligned with descriptors used in BBL (Brazilian Butt Lift) aesthetic literature.

  Valid values (3)

  • hourglass_pronouncedHourglass (pronounced waist)— Buttock projection substantially wider than waist creating an hourglass posterior silhouette.
  • balancedBalanced
  • narrow_continuousNarrow / continuous— Minimal buttock-to-hip transition; rectangular silhouette.

• Buttock asymmetry

  photo-observable

  ordinal · buttock_symmetry_qualitative

  Degree of left-right buttock asymmetry.

  Aligned with surgical-gynecology and gluteal-aesthetic descriptors of bilateral asymmetry.

  Valid values (4)

  • symmetricSymmetric
  • mild_asymmetryMild
  • moderate_asymmetryModerate
  • marked_asymmetryMarked