1 Principles of hybrid external fixation topenlarge
By bridging from the epiphysis to the diaphysis, the fixator stabilizes the metadiaphyseal region.
A ring fixator may be useful to hold complex distal fractures and can be attached to the tibial shaft with pins and rods (hybrid fixation).
Details of external fixation are described in the basic technique for application of modular external fixator.
Specific considerations for hybrid external fixation in the distal tibia are given below.
2 Wire placement top
Planning of wire placement
2 mm diameter wires are recommended.
Placement of wires for distal tibial fixation must be carefully planned.
Note: In addition to distal ring and tensioned wires, the proximal pins and frame, and its connection to the ring, must be planned for maximal stability.
Safe wire placement in the distal tibia
Many important structures surround the ankle and must not be injured by the wires. Good knowledge of anatomy is mandatory.
No consistently safe zones for pin or wire insertion in the distal tibia have been identified. A small skin incision is performed. Tissues are spread to expose the bone, avoiding nerves and vessels. If a tendon is impaled, the offending wire must be changed.
Intraarticular placement of the wires should be avoided, if possible, to reduce the risk of joint infection. Pins that are inserted less than 20 mm proximal to the tibiotalar joint may enter the joint capsule.
To improve and reach appropriate stability, it is important to:
- Maintain an overall arc of 60-80° between the wires
- Add a third wire or a threaded pin
3 Ring placement topenlarge
Insertion of the first wire
Make a stab incision and use blunt dissection down to the bone.
Insert the protection sleeve until it reaches the bone. Place the wire parallel to the tibiotalar joint under image intensification until it penetrates the far cortex. Finish wire insertion by hand, until the wire extends an equal length on both sides of the tibia. Make sure that the wire does not impale tendons or neurovascular structures.
Option for insertion of first wire
A non-olive wire placed through the fibula to emerge from the anteromedial tibia is often a good first wire. It is inserted from posterolateral (avoiding peroneal tendons) to anteromedial, parallel to the ankle joint.
Attaching ring to first wire
Place a wire-to-ring clamp on either end of the wire and attach these clamps to the ring, keeping the wire straight.
Tighten the clamps to the ring and then provisionally to the wire.
Option: Some surgeons place two wires initially and then attach the ring to both.
Insertion of additional wires
The wire-to-ring clamps may serve as guides for insertion of additional wires. The angle between the first and the second wire should be as wide as possible. Confirm that the articular reduction is satisfactory.
It is advisable to use at least three distal wires, or two with a supplementary threaded pin.
Flexible wires must be under tension for mechanical stability. Generally, a tension of 100 kg force is appropriate.
Pearl: While tensioning the second wire, the tension in the first may decrease due to ring deformation. Both wires should be retensioned to obtain better stability. If two tensioning devices are available, they can be used simultaneously to ensure equal tension in the two wires.
4 Pin insertion (tibial shaft) topenlarge
For safe pin placement make use of the safe zones and be familiar with the anatomy of the lower leg.
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.
5 Ring-to-rod connection top
An anteromedial rod is placed and attached to the ring to hold the provisional reduction. Then an anterolateral rod and cross brace is added for mechanical stability, with supplementary diaphyseal pins in multiple planes.
Placement of the first rod
Place an anteromedial proximal pin first. Choose a rod that is long enough to connect the pin to a clamp on the medial side of the ring. Place a rod-to-rod clamp and then a second rod-to-pin clamp on the rod.
Then attach the distal end of the rod to the ring, with a rod-to-ring clamp, with approximate fracture reduction. Angular alignment, length, and rotation must each be restored.
Next, insert a pin in the distal shaft through the rod-to-pin clamp.
6 Reduction and fixation topenlarge
Loosen the rod-to-ring clamp. Reduce the segments using ring and rod as reduction handles. Restore length, alignment and rotation. Check reduction clinically and with image intensification. If reduction is satisfactory, tighten the ring-to-rod clamp.
7 Frame completion topenlarge
Second and third rod
Attach the anterolateral rod to the proximal pin and to the ring laterally, using a rod-to-ring clamp. A rod-to-rod clamp is first placed on the rod.
Once the anterolateral rod is positioned, and reduction reconfirmed, connect the two rods with a short cross-brace using the previously placed clamps. If reduction remains satisfactory, tighten all frame clamps.
Additional pin from ring (option)
A pin from the ring may be used for fixation to the distal shaft. This is placed through a ring-to-pin clamp, directed proximally, towards the anteromedial tibial shaft, proximal to the fracture zone. (An alternative supplementary pin must be chosen if comminution extends too far proximally.)
Predrill if necessary for thick cortex. Place the pin, using the previously described technique, and tighten the clamp.
Once again, confirm the reduction. If satisfactory, tighten all the clamps. If necessary, readjust the reduction first.
Bending the wires
Cut and bend the wires. The sharp end can be bent into a space on the clamp. Alternatively, the sharp end can be covered with a protective cap and bent to avoid prominence.
Example of final construct.