Anatomical Concepts (UK)Anatomical Concepts (UK)Heel Risk Explorer
Educational model. It does not assess or predict risk for any individual.
Quiz yourself on this scenario
support surfacetibiaAchilles tendoncalcaneusskinheel fat pad
Illustration of the mechanism, not a computed strain field. The glow shows where thin tissue is caught between bone and surface; under load the calcaneus settles into the fat pad as it creeps, and the surface gives by an amount that depends on its type.
Step 1. What is the heel resting on?

Everything starts with the surface. A softer surface spreads the same limb weight over more area, which lowers the peak pressure at the heel. It cannot make the internal loading disappear: any surface that deforms the tissue over the calcaneus loads it internally.

A softer surface spreads load and lowers peak pressure. It changes how much the tissue is deformed internally, not whether.
Heel Risk Explorer: scenario report
Anatomical Concepts (UK)
Printed from heel-risk-explorer.vercel.app
Educational model. This report illustrates published mechanisms for a scenario chosen by the reader. It does not assess or predict risk for any individual, and it does not replace clinical risk assessment or clinical judgement.

The mechanics you set

Interface pressure88 mmHg (11.7 kPa)
Support surfaceStandard hospital mattress
ShearSome (gradual migration in bed)
MoistureDry
Head of bedFlat
Unrelieved time2.0 hours
RepositioningNone
Heel floatedNo

The person you described

Age bandOlder adult
FactorsNone selected

Personal factors move this model in their documented direction only; no validated weights exist, so they never move the risk band more than one step in total.

What follows from those choices

Risk band: High
Deformation damage 50% · Ischaemic damage 37%
Illustrative index, not a probability.
In short

In this model, this load held this long is enough for the direct squashing of tissue against the heel bone to be doing real harm to the tissue.

In this model, the single change that moves the picture most is taking the heel out of contact altogether.

support surfacetibiaAchilles tendoncalcaneusskinheel fat pad
Illustration of the mechanism, not a computed strain field. The glow shows where thin tissue is caught between bone and surface; under load the calcaneus settles into the fat pad as it creeps, and the surface gives by an amount that depends on its type.
Your scenario against the damage threshold
rat muscle, Linder-Ganz 2006

The curve is the theoretical dividing line between combinations of pressure and time under load that left muscle intact and combinations that damaged it, as measured in rat muscle: a brief load is tolerated at high pressure, but after about two hours even a modest pressure crosses the line. Below the curve tissue survived; the shaded region above it is where damage occurred. The blue mark is your scenario, the effective pressure at the heel held for the time you have set.

671201802402468mmHghours
This scenario sits above the threshold curve. The solid curve is as published in rat muscle, not scaled to humans.
Tissue is not a spring
sheep adipose tissue, ex vivo, Gefen and Haberman 2007
246where a spring would stopthe tissue keeps sinking, then settlesdeformationminutes
Under a constant load, tissue deforms at once and then keeps deforming. In sheep adipose tissue tested ex vivo, tissue was roughly three times stiffer at the instant of loading than after settling, and most of the settling happened within about 2 minutes. Curve shape illustrative; at the bedside this is the heel sinking in and the pillow flattening.

Why: connecting each choice to its consequence

The surface applies about 88 mmHg (11.7 kPa) at the skin over the calcaneus. Inside, the thin tissue between bone and surface concentrates that load; the only human measurements of such concentration were made at the buttock while sitting, where stress in muscle was roughly double the surface figure, and no heel equivalent exists. This page therefore shows the concentration as an illustration only. (Linder-Ganz 2007, human buttock, n=6; Gefen 2010)

At 2.0 hours of loading, the damage threshold measured in rat muscle sits near 67 mmHg: above about 240 mmHg cells die in under an hour, and beyond 2 hours the threshold falls to about 67 mmHg. Deep damage typically develops between the first hour and 4 to 6 hours of sustained loading. (Linder-Ganz 2006, rat; Gefen 2008)

The tissue does not behave like a spring. From the moment the load goes on it creeps: in sheep adipose tissue tested ex vivo, tissue was roughly three times stiffer at the instant of loading than after settling, and most of the settling happened within about 2 minutes. The heel keeps sinking into whatever it rests on, so by the timescales on this page the deformation has already reached its full depth. (Gefen and Haberman 2007, sheep, ex vivo)

Shear is present at the interface. In human hand tissue, adding shear roughly halved the pressure needed to shut off blood flow, so the ischaemic process runs at lower pressures than pressure alone would need. (Bennett 1979, human, n=4; Gerhardt 2008, human, n=22)

Where the UK guidance points next

The same for every scenario: what exists, not advice generated for a person. NICE CG179 asks clinicians to discuss, with adults at high risk of a heel pressure ulcer, a strategy to offload heel pressure (nice.org.uk/guidance/cg179); the 2025 International Guideline’s good practice statement is the heel fully free of the support surface. For an active diabetic foot problem, NICE NG19 says refer within 1 working day to the multidisciplinary foot care service or foot protection service, and immediately to acute services if the problem threatens the limb or the person (nice.org.uk/guidance/ng19).

Sources used by this model

  1. Linder-Ganz E, Engelberg S, Scheinowitz M, Gefen A. Pressure-time cell death threshold for albino rat skeletal muscles. J Biomech 2006. PMID 16199045. Rat.
  2. Oomens CW, Bader DL, Loerakker S, Baaijens F. Pressure induced deep tissue injury explained. Ann Biomed Eng 2015. PMID 25480479.
  3. Stekelenburg A et al. Role of ischemia and deformation in the onset of compression induced deep tissue injury. J Appl Physiol 2007. PMID 17255369. Rat.
  4. Loerakker S et al. The effects of deformation, ischemia, and reperfusion on the development of muscle damage during prolonged loading. Ann Biomed Eng 2010. PMID 20232152. Rat.
  5. Gefen A. How much time does it take to get a pressure ulcer? Ostomy Wound Manage 2008. PMID 18927481.
  6. Bennett L, Kavner D, Lee BK, Trainor FA. Shear vs pressure as causative factors in skin blood flow occlusion. Arch Phys Med Rehabil 1979. PMID 454129. Human, n=4, thenar eminence.
  7. Gerhardt LC et al. Influence of epidermal hydration on the friction of human skin against textiles. J R Soc Interface 2008. PMID 18331977. Human, n=22.
  8. Linder-Ganz E, Shabshin N, Itzchak Y, Gefen A. Assessment of mechanical conditions in sub-dermal tissues during sitting. J Biomech 2007. PMID 16920122. Human, n=6, buttock; no equivalent heel measurement exists.
  9. Oomens CW et al. Can loaded interface characteristics influence strain distributions in muscle adjacent to bony prominences? Comput Methods Biomech Biomed Engin 2003. PMID 12888429. Finite element model, buttock.
  10. Oomens CW, Loerakker S, Bader DL. The importance of internal strain as opposed to interface pressure. J Tissue Viability 2010. PMID 20005716.
  11. Gefen A, Haberman E. Viscoelastic properties of ovine adipose tissue covering the gluteus muscles. J Biomech Eng 2007. PMID 18067398. Sheep, ex vivo.
  12. Hsu TC et al. Altered heel pad mechanical properties in elderly. Arch Phys Med Rehabil 1998. PMID 9749691. Human, n=33.
  13. Hsu TC et al. Altered heel pad mechanical properties in Type 2 diabetes. Diabet Med 2000. PMID 11168328. Human, n=53.
  14. Loerakker S et al. Plasticity of muscle tissue properties after spinal cord injury and its effect on internal loading. Comput Methods Biomech Biomed Engin 2013. PMID 22300480. Porcine plus finite element model.
  15. Nelissen JL et al. An advanced magnetic resonance imaging perspective on the etiology of deep tissue injury. J Appl Physiol 2018. PMID 29494291. Rat; a single 2 hour loading event remained detectable at 14 days.
  16. Coleman S, Nixon J, Keen J, et al. A new pressure ulcer conceptual framework. J Adv Nurs 2014. PMID 24684197.
  17. Gefen A. The biomechanics of heel ulcers. J Tissue Viability 2010. PMID 20584612.
  18. Gefen A, Brienza DM, Cuddigan J, Haesler E, Kottner J. Our contemporary understanding of the aetiology of pressure ulcers. Int Wound J 2022. PMID 34382331.
  19. Levy A, Gefen A. Head of bed elevation and heel loading. Ostomy Wound Manage 2016. PMID 27065218. Model.
  20. Dube A et al. Risk factors associated with heel pressure ulcer development. J Tissue Viability 2022. PMID 34742635. Systematic review.
  21. Delmore B et al. Refining heel pressure injury risk factors in the hospitalized patient. Adv Skin Wound Care 2019. PMID 31498171. Case-control, n=1,937.
  22. Allen V, Ryan DW, Murray A. Measurements of interface pressure between body sites and the surfaces of four specialised air mattresses. Br J Clin Pract 1994. PMID 8031686. Human, n=10, supine; specialised air mattresses, not standard foam.
  23. International Pressure Injury Guideline, 4th edition, heel and aetiology chapters, 2025.
Sources used by this model
  1. Linder-Ganz E, Engelberg S, Scheinowitz M, Gefen A. Pressure-time cell death threshold for albino rat skeletal muscles. J Biomech 2006. PMID 16199045. Rat.
  2. Oomens CW, Bader DL, Loerakker S, Baaijens F. Pressure induced deep tissue injury explained. Ann Biomed Eng 2015. PMID 25480479.
  3. Stekelenburg A et al. Role of ischemia and deformation in the onset of compression induced deep tissue injury. J Appl Physiol 2007. PMID 17255369. Rat.
  4. Loerakker S et al. The effects of deformation, ischemia, and reperfusion on the development of muscle damage during prolonged loading. Ann Biomed Eng 2010. PMID 20232152. Rat.
  5. Gefen A. How much time does it take to get a pressure ulcer? Ostomy Wound Manage 2008. PMID 18927481.
  6. Bennett L, Kavner D, Lee BK, Trainor FA. Shear vs pressure as causative factors in skin blood flow occlusion. Arch Phys Med Rehabil 1979. PMID 454129. Human, n=4, thenar eminence.
  7. Gerhardt LC et al. Influence of epidermal hydration on the friction of human skin against textiles. J R Soc Interface 2008. PMID 18331977. Human, n=22.
  8. Linder-Ganz E, Shabshin N, Itzchak Y, Gefen A. Assessment of mechanical conditions in sub-dermal tissues during sitting. J Biomech 2007. PMID 16920122. Human, n=6, buttock; no equivalent heel measurement exists.
  9. Oomens CW et al. Can loaded interface characteristics influence strain distributions in muscle adjacent to bony prominences? Comput Methods Biomech Biomed Engin 2003. PMID 12888429. Finite element model, buttock.
  10. Oomens CW, Loerakker S, Bader DL. The importance of internal strain as opposed to interface pressure. J Tissue Viability 2010. PMID 20005716.
  11. Gefen A, Haberman E. Viscoelastic properties of ovine adipose tissue covering the gluteus muscles. J Biomech Eng 2007. PMID 18067398. Sheep, ex vivo.
  12. Hsu TC et al. Altered heel pad mechanical properties in elderly. Arch Phys Med Rehabil 1998. PMID 9749691. Human, n=33.
  13. Hsu TC et al. Altered heel pad mechanical properties in Type 2 diabetes. Diabet Med 2000. PMID 11168328. Human, n=53.
  14. Loerakker S et al. Plasticity of muscle tissue properties after spinal cord injury and its effect on internal loading. Comput Methods Biomech Biomed Engin 2013. PMID 22300480. Porcine plus finite element model.
  15. Nelissen JL et al. An advanced magnetic resonance imaging perspective on the etiology of deep tissue injury. J Appl Physiol 2018. PMID 29494291. Rat; a single 2 hour loading event remained detectable at 14 days.
  16. Coleman S, Nixon J, Keen J, et al. A new pressure ulcer conceptual framework. J Adv Nurs 2014. PMID 24684197.
  17. Gefen A. The biomechanics of heel ulcers. J Tissue Viability 2010. PMID 20584612.
  18. Gefen A, Brienza DM, Cuddigan J, Haesler E, Kottner J. Our contemporary understanding of the aetiology of pressure ulcers. Int Wound J 2022. PMID 34382331.
  19. Levy A, Gefen A. Head of bed elevation and heel loading. Ostomy Wound Manage 2016. PMID 27065218. Model.
  20. Dube A et al. Risk factors associated with heel pressure ulcer development. J Tissue Viability 2022. PMID 34742635. Systematic review.
  21. Delmore B et al. Refining heel pressure injury risk factors in the hospitalized patient. Adv Skin Wound Care 2019. PMID 31498171. Case-control, n=1,937.
  22. Allen V, Ryan DW, Murray A. Measurements of interface pressure between body sites and the surfaces of four specialised air mattresses. Br J Clin Pract 1994. PMID 8031686. Human, n=10, supine; specialised air mattresses, not standard foam.
  23. International Pressure Injury Guideline, 4th edition, heel and aetiology chapters, 2025.