Hindfoot Nail Positioning: WBCT-Based Simulation Indicates Valgus Angulation of Straight Nails Is Necessary to Obtain...

Hindfoot nail placement, whether for tibiotalocalcaneal (TTC) arthrodesis or as the index procedure for geriatric ankle fractures or comminuted pilon fractures, is challenging because of anatomical constraints. Although it may be assumed that a straight hindfoot nail should align parallel with the tibial axis, this can lead to either medial calcaneal cortical perforation, varus hindfoot malalignment, or iatrogenic medialization of the foot. This simulation study aims to quantify the angulation required for a straight hindfoot nail to achieve both intraosseous calcaneal placement and preserve native hindfoot alignment in patients without significant coronal plane malalignment.

We retrospectively analyzed 61 weightbearing computed tomography (WBCT) scans from patients (mean age 43.6 years) with radiographically physiologic hindfoot alignment (mean hindfoot alignment angle: 1.3 degrees, Meary angle: 4.9 degrees). Using multiplanar reconstruction of CT images, 10-mm and 12-mm virtual hindfoot nails were superimposed on each coronal scan. First, the virtual nail was positioned to ensure calcaneal intraosseous placement, defined as ≥2 mm of bone between the nail and the medial calcaneal cortex. The angle between the virtual nail and the tibial anatomic axis was recorded. Second, the virtual nail was repositioned to be parallel to the tibial axis and centered within the tibial canal; medial cortical breach and distance to the medial cortex of the calcaneus were then assessed.

To maintain proper intraosseous calcaneal placement and alignment, a mean valgus angulation of 4.0 degrees (95% CI, 3.5-4.4) for 10-mm nails and 4.9 degrees (95% CI, 4.4-5.4) for 12-mm nails relative to the tibial axis was required. When the nail was aligned strictly parallel to the tibial axis, 60 of 61 scans demonstrated medial calcaneal breach. To avoid this breach, an average medial foot translation of 9.2 mm or iatrogenic hindfoot varus ≥5.8 degrees would be necessary.

This WBCT-based simulation suggests that a valgus orientation of approximately 4 degrees is needed for a straight hindfoot nail to (1) maintain proper calcaneal intraosseous placement and (2) preserve physiologic hindfoot alignment.

Level III, retrospective cohort study.