Ankle-spanning external fixation, aka “Delta Frame”
The ankle-spanning external fixator is a versatile external fixation construct that is useful for fractures of the tibial plafond (pilon), unstable ankle fractures, and talus fractures. It can be adapted for other injuries including midfoot fractures. CPT Code 20692 – Application of multiplanar external fixator.
Tibial Schanz Pins
- Mark out the tibial tubercle. The most proximal pin will go 2-4 finger breadths distal to this point.
- Make a mark 1 cm medial to the tibial tubercle. Make a 1cm incision with a scalpel through the skin.
- Use a tonsil to bluntly dissect to the bone.
- Insert the trocar directly to the bone, and then insert the drill bit. It is ok to walk the drill bit up to the tibial crest and then back down about 1 cm.
- Start drilling at about 45 degrees to the floor (which is more perpendicular to the medial side of the tibia, and then slowly raise your hand as you progress through the first cortex. This will ensure proper pin alignment for your external fixation.
- By the time you reach the first cortex, you should be exactly perpendicular to the long axis of the tibia and the floor.
[error]Be careful not to plunge as you progress through the second cortex of the tibia. [/error]
- After drilling bicortically, remove the drill while holding the trocar in place with your left hand. Have the scrub tech hand you a 170mm x 5.5mm partially threaded Schanz pin (e.g. Synthes Large Ex-Fix pin) preloaded on a T-handle chuck. Advance the pin until you feel the second cortex. Turn 8 more half turns after engaging the far cortex.
- Take a 4-pin multipin clamp, and attach it loosely to the pin. Mark your incision for the 2nd pin, and then repeat the pin placement technique described above. Make sure to keep this pin exactly parallel to the proximal pin.
Calcaneal Transfixion Pin
- Obtain a perfect lateral of the calcaneus with the C-arm. Have an assistant hold the foot dorsiflexed near neutral. Identify the “safe zone.”
- Use a #15 blade scalpel to make a 5mm incision through the skin. Use C-arm to assist in placing a drill at the medial cortex of the calcaneus in the safe zone. Drill through the near cortex only.
- Have the C-arm tech “left-to-right” the previous image. Use that as a guide to make sure your pin is in the same starting point. Advance a centrally threaded calcaneal transfixion pin through the near cortex and out again through the far cortex. Advance the pin until it is centered perfectly in the calcaneus.
- Gather 2 pin-to-bar clamps as well as the 4-pin multi-pin clamp, and two carbon fiber rods.
- Apply the multi-pin clamp to the two tibial Schanz pins. [box type=”download”]The closer the clamp is to the bone, the stronger the construct will be. However, this has to be balanced with the risk of skin breakdown, especially if significant swelling occurs. A good rule of thumb is to place the multi-pin clamp 2 finger-breadths away from the skin.[/box]
- Provisionally tighten the clamp to the pins, and make sure there is an articulating arm on each side of the clamp.
- Loosely tighten pin-to-bar clamps on each side of the calcaneal pin.
- Measure out a carbon fiber rod of the proper length to reach from the articulating arm on the multipoint clamp to the pin to bar clamp on the calcaneal pin. Make sure to leave 2-3 cm of extra length at the calcaneal end so there will be enough rode left after pulling traction.
- Place two folded towels over the distal shin, such that they are located between the carbon fiber rods and the skin.
- Obtain gross alignment of the ankle, and tighten the tibial construct with a T-handle wrench. The only thing left loose should be the calcaneal pin-to-bar clamps.
- Use two blue towels wrapped around the calcaneal pin to pull traction, while at the same time keeping your hands out of the x-ray beam. Tighten external fixation frame as necessary.