Heel spur formation and the subcalcaneal enthesis of the plantar fascia.

OBJECTIVE: To describe the structure and significance of subcalcaneal heel spurs associated with the plantar fascia.
METHODS: The enthesis of the plantar fascia was removed from 17 elderly cadavers by sagittal saw cuts either side of the medial tuberosity, radiographs were taken, and the tissue was processed for routine histology. Sagittal sections were stained with toluidine blue, Masson's trichrome, or alcian blue, and sections were matched with the corresponding radiographs.
RESULTS: Spurs develop on the deep surface of the plantar fascia but their formation is heralded by degenerative changes that occur within it. According to differences between small and large spurs, we propose that there are 3 stages in their development: (1) an initial formation of cartilage cell clusters and fissures at the plantar fascia enthesis; (2) thickening of the subchondral bone plate at the enthesis as small spurs form; (3) development of vertically oriented trabeculae buttressing the proximal end of larger spurs. The spurs grow by a combination of intramembranous and chondroidal ossification.
CONCLUSION: Contrary to popular belief, subcalcaneal heel spurs cannot be traction spurs as they do not develop within the plantar fascia itself. They are thus fundamentally different from heel spurs in the Achilles tendon. We suggest instead that they develop as a consequence of degenerative changes that occur in the plantar fascia enthesis.