1. Principles of joint-bridging triangular external fixation
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.
Specific considerations for joint-bridging triangular fixation of the ankle joint are given below.
AO teaching video: Ankle-bridging delta frame
2. Patient preparation
This procedure is normally performed with the patient in a supine position.
3. Safe zones for pin placement
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.
4. Pin insertion (tibial shaft)
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, 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.
5. Frame construction (triangular external fixation)
Construction of tibial frame and insertion of Steinmann pin
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.
6. Reduction and fixation (triangular external fixation)
Reduction by manipulating the calcaneal pin
Reduce the fracture by manipulating the calcaneal pin. After checking correct reduction with image intensification, fix the reduced position by tightening all clamps.
Connecting the rods
To stabilize the construct, the two tibiocalcaneal rods may be connected with a short rod using rod-to-rod clamps.
Pearl 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
in one of the cuboids or
in the first metatarsal or
in the first and in the fifth metatarsal
and connected directly, or through a partial frame, with the tibial frame.
Alternative: Construct starting with a single tibial pin
To achieve a similar triangular construct, it is possible to start with one pin in the proximal third of the tibial crest instead of a partial frame.
Frame construction / reduction and fixation include the following steps:
Insertion of the tibial pin
Insertion of the calcaneal Steinmann pin
Connecting the two pins medially and laterally with two rods
Reduction by manipulating the calcaneal pin and fixation by tightening the clamps
Insertion of a stabilizing pin in the tibia proximal to the fracture through a rod-to-pin clamp on the medial rod
7. Aftercare following external fixation
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:
Correct placement of pins (see safe zones) avoiding ligaments and tendons, eg tibia anterior
Correct insertion of pins (eg trajectory, depth) avoiding heat necrosis
Extending skin incisions to release soft-tissue tension around the pin insertion (see inspection and treatment of skin incisions)
Pin-site care 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:
The aftercare should follow the same protocol until removal of the external fixator.
The pin-insertion sites should be kept clean. Any crusts or exudates should be removed. The pins may be cleaned with saline and/or disinfectant solution/alcohol. The frequency of cleaning depends on the circumstances and varies from daily to weekly but should be done in moderation.
No ointments or antibiotic solutions are recommended for routine pin-site care.
Dressings are not usually necessary once wound drainage has ceased.
Pin-insertion sites need not be protected for showering or bathing with clean water.
The patient or the carer should learn and apply the cleaning routine.
Pin loosening or pin tract infection In case of pin/wire loosening or pin tract infection, the following steps need to be taken:
Remove all involved pins and place new pins in a healthy location.
Debride the pin sites in the operating theater, using curettage and irrigation.
Take specimens for a microbiological study to guide appropriate antibiotic treatment if necessary.
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:
Stability of the fixator construct
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.