Do plantar calcaneal spurs make the plantar aponeurosis enthesis stronger? A biomechanical analysis

Calcaneal spurs are shown to be increasingly prevalent in modern populations and often contribute to forming heel and foot pain. There are multiple hypotheses for their formation, including exercise, prolonged standing and obesity. The impact of these spurs on foot biomechanics remains unclear; it is suggested that their presence may contribute to enthesial avulsion forces. This study aimed to determine the avulsion properties of the plantar aponeurosis enthesis with and without spurs. Twenty-four feet from 15 cadavers donated to the Department of Anatomy at the University of Otago were used for this study. Tissues were X-rayed to determine the presence of spurs. The donor feet were dissected to isolate the calcanei. These were then mounted in a custom-developed 3D-printed clamping rig to perform tensile testing of the plantar calcaneal enthesis to determine pull-out forces of the central band of the plantar fascia. Biomechanical testing showed no statistically significant differences in avulsion properties between the spur (n = 7) and non-spur (n = 14) samples in any of the avulsion parameters investigated: F_max (1121 ± 358 N vs. 953 ± 283 N, mean ± SD, p = 0.302) and εF_max (53 ± 11% vs. 51 ± 13%, mean ± SD, p = 0.660). Despite this, the avulsion parameters were highly variable. The results of this study indicate that the pull-out force of the central band of the plantar fascia is unrelated to the presence of spurs. Therefore, it is less likely that plantar spurs fulfill a biomechanical function within the plantar fascia complex.