Normal Heel Pad Thickness on Radiography
The heel pad is the fibrofatty soft-tissue cushion overlying the plantar surface of the calcaneus, visible on lateral foot and ankle radiographs. Accurate measurement of heel pad thickness is a simple but clinically valuable tool for screening systemic and metabolic disorders that cause soft-tissue proliferation. Because it requires only a standard lateral radiograph, it is one of the most accessible soft-tissue measurements in musculoskeletal radiology.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | <23 mm |
Clinical Significance
A heel pad thickness of 23 mm or greater on a lateral radiograph is considered abnormal in adults. The measurement is particularly associated with acromegaly, where excess growth hormone drives soft-tissue and connective-tissue hypertrophy; a heel pad exceeding 23 mm has historically been used as a screening sign for this condition. However, thickness alone is not pathognomonic, and clinical correlation is essential.
Other conditions that may increase heel pad thickness include obesity, peripheral edema, and chronic local trauma or inflammation. Conversely, an abnormally thin or atrophic heel pad can occur with aging, prolonged corticosteroid use, or plantar fasciitis-related degeneration, predisposing patients to calcaneal stress injuries.
- Acromegaly — most classic cause of diffuse heel pad thickening
- Obesity — generalized adipose hypertrophy
- Peripheral edema / myxedema — hypothyroidism-related soft-tissue infiltration
- Chronic local trauma or inflammation — reactive soft-tissue thickening
- Dilantin (phenytoin) therapy — reported soft-tissue proliferation
Reference: Reeder MM, Felson B. Reeder and Felson's Gamuts in Radiology, Comprehensive Lists of Roentgen Differential Diagnosis. Springer Verlag. (2003).
Imaging Notes
Heel pad thickness is measured on a lateral radiograph of the foot or ankle obtained in a weight-bearing or non-weight-bearing position. The measurement is taken as the perpendicular distance from the plantar skin surface to the adjacent cortex of the calcaneal tuberosity at its most inferior point. Consistent patient positioning and true lateral projection are essential; obliquity will artificially alter the apparent soft-tissue depth. Weight-bearing views are preferred when evaluating functional loading conditions, but published normative values should be matched to the acquisition technique used.
Digital radiography provides adequate soft-tissue detail for this measurement when appropriate window and level settings are applied. No advanced modality is required for routine screening, though MRI may be used to characterize heel pad composition or assess for deep soft-tissue pathology when the clinical picture is complex.