A joint-bridging triangular external fixator consists of a Steinmann pin running through the calcaneal tuberosity. A rod is fixed to each end of the pin and connected to the partial frame on the tibial crest.
This triangular frame is extended into the foot to stabilize soft tissues, to fix the foot in a neutral position and to reduce the risk of secondary equinus deformity.
A joint-bridging frame is usually used for temporary stabilization, but may be used for definitive treatment if necessary.
Details of external fixation are described in the basic technique for application of modular external fixator.
Specific considerations for joint-bridging triangular fixation of the ankle joint are given below.
AO teaching video: Ankle-bridging delta frame
Inserting percutaneous instrumentation such as pins or transfixion wires through safe zones reduces the risk of damage to neurovascular structures.
For safe pin placement make use of the safe zones and be familiar with the anatomy of the lower leg and the foot.
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, in order 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.
Insert two pins in the sagittal plane and slightly medial to the anterior tibial crest at an adequate distance above the fracture zone. Connect them with a short rod and tighten the rod-to-pin clamps. Placement more proximally gives room for later definitive open fixation and avoids damaged soft tissue in the fracture zone. Place the pins far enough apart to ensure adequate stability.
Then insert a Steinmann pin, or a threaded pin, from medial to lateral through the calcaneal tuberosity. Take care to avoid damage to the posterior tibial neurovascular bundle.
Connect each end of the calcaneal pin to one of the tibial pins with a rod using rod-to-pin clamps applied loosely enough to allow reduction of the fracture.
Reduce the fracture by manipulating the calcaneal pin. After checking correct reduction with image intensification, fix the reduced position by tightening all clamps.
To stabilize the construct, the two tibiocalcaneal rods may be connected with a short rod using rod-to-rod clamps.
A bent Steinmann rod can be used as an alternative to a straight rod if needed.
To keep the foot in a neutral position, one or two small pins should be inserted
and connected directly, or through a partial frame, with the tibial frame.
External fixation of distal tibial fractures is often extended to include the foot, to avoid an equino-varus deformity. Otherwise consider a splint to support the foot and ankle.
Proper pin insertion
To prevent postoperative complications, pin-insertion technique is more important than any pin-care protocol:
Various aftercare protocols to prevent pin tract infection have been established by experts worldwide. Therefore no standard protocol for pin-site care can be stated here. Nevertheless, the following points are recommended:
Pin loosening or pin tract infection
In case of pin/wire loosening or pin tract infection, the following steps need to be taken:
Before changing to a definitive internal fixation an infected pin tract needs to heal. Otherwise infection will result.
The timing and how much weight may be taken through the fracture will be influenced by:
See patient 7-10 days after surgery for a wound check. X-rays are taken to check the reduction.
Once the fracture is deemed to be sufficiently stable for the external fixator to be removed, the surgeon may choose to apply a cast or functional brace before leaving the ankle completely unsupported.
At 3 months, if there are symptoms of lateral instability, either inversion stress x-rays or MRI can be used to investigate lateral ligament integrity.