For safe pin placement make use of the safe zones and be familiar with the anatomy of the lower leg and the foot.
Choice of tibial pin placement
Drilling a hole in the thick tibial crest may be associated with excessive heat generation and there is a risk the drill bit may slip medially or laterally damaging the soft tissues. As the anteromedial tibial wall provides adequate thickness for the placement of pins, this trajectory is preferable. A trajectory angle (relative to the sagittal plane) of 20-60° for the proximal fragment and of 30-90° for the distal fragment is recommended.
Alternatively, to avoid the frame catching on the opposite leg, the pins may be placed more anteriorly. The drill bit is started with the tip just medial to the anterior crest, and with the drill bit perpendicular to the anteromedial surface (A). As the drill bit starts to penetrate the surface, the drill is gradually moved more anteriorly until the drill bit is in the desired plane (B). This should prevent the tip from sliding down the medial or lateral surface.
Pin placement in the foot
For the construction of the partial frame of the foot the following three options are used most frequently:
- one pin in the calcaneus (green circle) and one in the talus (brown circle)
- two pins in the calcaneus (green and orange circle)
- one pin in the calcaneus (green circle) and one in the cuboid (blue circle)