The foot is the foundation of the body. The stability of the osseous hindfoot structure is crucial in bipedal locomotion. The subtalar joint is responsible for conversion of the rotatory forces of the lower extremities and dictates the movements of the midtarsal joints and the forefoot. In a hyperpronated foot, excessive abnormal pronation results in partial to full obliteration of the sinus tarsi. The hypothesis is that the HyProCure device will prevent obliteration of the sinus tarsi, thereby stabilizing the subtalar joint complex and eliminating the excessive forces to the proximal and distal musculoskeletal system that occur with every step.
Five fresh-frozen human foot cadaver specimens that represented pathologic hindfoot and midfoot instability and partial to full obliteration of the sinus tarsi were axially compressed to 2,000 N and internally rotated by 15° to produce maximum pronation of the subtalar joint using a biaxial materials testing machine. The forces were measured across the posterior and anterior talocalcaneal joint facets before and after placement of the HyProCure stent.
The subtalar joint stabilized after placement of the HyProCure sinus tarsi stent. The mean ± 1 SD forces in the posterior talocalcaneal joint increased from 795.88 ± 106 N to 1,004.86 ± 72.41 N (P < 0.05, two-tailed paired t test). The mean ± SD forces at the anterior talocalcaneal joint decreased from 520.15 ± 127.18 N to 394.56 ± 73.83 N (P < 0.05), shifting the contact area posteriorly.
Placement of the HyProCure subtalar stabilization stent in a hyperpronated foot prevents excessive talar subluxation and assists in proper distribution of the axial loads on the subtalar facet joints. (J Am Podiatr Med Assoc 101(5): 390–399, 2011)