Subtalar joint involvement with tibiotalocalcaneal intramedullary nail arthrodesis

Tibiotalocalcaneal (TTC) fusion with an intramedullary nail (IMN) has been utilized for a myriad of indications in hindfoot and ankle reconstruction. However, some controversies remain on the optimal position of the hindfoot. Previous studies have reported on the potential medialization of the rearfoot during insertion of the IMN, but few studies have examined the potential affect on the subtalar joint. We performed the present cadaveric study in order to assess the involvement of a 12-mm IMN with the posterior facet of the calcaneus. A 3-mm guide wire (for a standard TTC IMN) was inserted in an anterograde fashion beginning within the central aspect of the tibial canal in 10 fresh-frozen below knee cadaver specimens. The subtalar joint of each specimen was exposed and images of the posterior facet were collected. Utilizing an open source Java image processing program (ImageJ/Fiji), we calculated a mean native calcaneal posterior facet of 4.6 cm² with a post ream surface area of 3.6 cm², resulting in a mean of 21.4% of the posterior facet occupied by an IMN in an anterograde fashion. In conclusion, a TTC IMN placed in optimal position within the ankle and tibia is likely to occupy, on average, a fifth of the calcaneal posterior facet. Though this does leave some possibility of a medial shift of the rearfoot complex, care must be taken to not violate the lateral calcaneal or talar wall.