title: Bulk compressive properties of the heel fat pad during walking: a pilot investigation in plantar heel pain.
abstract: BACKGROUND
  Altered mechanical properties of the heel pad have been implicated in the development of plantar heel pain. However, the in vivo properties of the heel pad during gait remain largely unexplored in this cohort. The aim of the current study was to characterise the bulk compressive properties of the heel pad in individuals with and without plantar heel pain while walking.
  
  
  METHODS
  The sagittal thickness and axial compressive strain of the heel pad were estimated in vivo from dynamic lateral foot radiographs acquired from nine subjects with unilateral plantar heel pain and an equivalent number of matched controls, while walking at their preferred speed. Compressive stress was derived from simultaneously acquired plantar pressure data. Principal viscoelastic parameters of the heel pad, including peak strain, secant modulus and energy dissipation (hysteresis), were estimated from subsequent stress-strain curves.
  
  
  RESULTS
  There was no significant difference in loaded and unloaded heel pad thickness, peak stress, peak strain, or secant and tangent modulus in subjects with and without heel pain. However, the fat pad of symptomatic feet had a significantly lower energy dissipation ratio (0.55+/-0.17 vs. 0.69+/-0.08) when compared to asymptomatic feet (P<.05).
  
  
  CONCLUSIONS
  Plantar heel pain is characterised by reduced energy dissipation ratio of the heel pad when measured in vivo and under physiologically relevant strain rates.
authors.affiliation: Health QWest and Bioengineering Unit, University of Strathclyde, 106 Rottenrow, Glasgow, Scotland G40NW, UK. scott.wearing@strath.ac.uk
authors.forename: Scott C
authors.initials: SC
authors.lastname: Wearing
authors.forename: James E
authors.initials: JE
authors.lastname: Smeathers
authors.forename: Bede
authors.initials: B
authors.lastname: Yates
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Urry
authors.forename: Philip
authors.initials: P
authors.lastname: Dubois
mesh_terms: D000328:Adult; D015331:Cohort Studies; D019245:Compressive Strength; D004548:Elasticity; D005260:Female; D005471:Fluoroscopy / Q000379:methods; D005528:Foot / Q000503:physiopathology*; D005684:Gait; D006365:Heel / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000503:physiopathology*; D010865:Pilot Projects; D011312:Pressure; D016138:Walking