Hindfoot Nail Positioning for Tibiotalar Calcaneal Arthrodesis: Valgus Angulation of Straight Hindfoot Nails Relative to Tibial Anatomic Axis is Necessary to Maintain Appropriate Hindfoot Alignment

Research Type: Level 4 – Case series Introduction/Purpose: Hindfoot nail placement can be challenging for several reasons including normal anatomic alignment. While commonly believed that nail alignment should be parallel with the tibial axis, in theory a straight nail aligned as such has either perforated the medial calcaneal or has resulted in varus malalignment and/or foot medialization. In this investigation we examine nail/tibial angulation utilizing computer-generated nail placements overlaid on WBCT scans of individuals with normal hindfoot alignment. Second, we determine the amount of iatrogenic hindfoot malpositioning that would be required if the nail were placed parallel to the tibial anatomic axis and within the calcaneal body. We hypothesize that valgus angulation of the nail is necessary to maintain normal hindfoot alignment while ensuring proper intraosseous placement. Methods: Fifty weightbearing computed tomography (WBCT) scans were utilized from patients (mean age 43.4 years) without pathologies and with clinically normal hindfoot alignment (mean hindfoot alignment angle: 3.8°; Meary’s angle: 5.3°). After cross-referencing axial, coronal, and sagittal reconstructions, a 10 mm computer-generated hindfoot nail was superimposed on the coronal view (Figure 1). First, the virtual hindfoot nail was positioned to ensure calcaneal intraosseous placement, defined as at least 2 mm of bone between the medial border of the nail and the medial calcaneal cortex. The angle between the tibial anatomic axis and the simulated nail was then measured. Second, the hindfoot nail was then repositioned to align centrally within the tibial intramedullary canal, parallel to the tibial axis. The frequency of medial calcaneal cortex breach and the distance between the medial calcaneal cortex and the center of the simulated nail were measured. Results: The simulated hindfoot nail required an average valgus of 5.1° (standard deviation[SD] 2.3) relative to the tibial anatomic axis to (1) ensure acceptable intraosseous positioning within the calcaneal body and (2) to maintain the patient’s native normal hindfoot alignment. When the simulated nail was realigned aligned parallel to the tibial axis and centered in the tibial canal, 49 of 50 patients demonstrated medial calcaneal cortical breach. The mean distance from the nail center to the medial calcaneal cortex was 3.8 mm, suggesting that 10.8 mm of iatrogenic medial foot translation would be necessary to preserve at least 2 mm of calcaneal osseous margin. Finally, >= 7.4° (mean+1SD) of iatrogenic varus hindfoot malalignment would be needed to ensure full intraosseous calcaneal placement without medial cortical breach. Conclusion: This study demonstrates that a valgus orientation of approximately 5° is needed for a straight hindfoot nail to (1) maintain proper calcaneal intraosseous placement and (2) preserve physiologic hindfoot alignment. Strictly aligning the nail with the tibial anatomic axis risks medial calcaneal perforation and/or can lead to >= 5° of iatrogenic varus hindfoot malalignment or >= 1.0cm of inappropriate medial foot translation. Incorporating a valgus angulation of the straight hindfoot nail relative to the tibial anatomic axis appears necessary for safe intraosseous positioning and to maintain normal hindfoot alignment.