Authors of section

Special Author

Dankward Höntzsch

Executive Editors

Peter Trafton, Rick Buckley

Hybrid external fixator (definitive)

1. Principles of hybrid external fixation

By bridging from the epiphysis to the diaphysis, the fixator stabilizes the metadiaphyseal region.

Intraarticular fractures should be anatomically reduced and held with lag screws or reduction wires.

More complex fracture patterns, with articular fragment displacement, may require a separate open reduction. Interfragmentary fixation, typically with lag screws, should be added in a way that also permits wire placement.

A ring fixator may be useful to hold complex proximal fractures, and 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 and the proximal tibia are given below.

hybrid external fixator definitive

2. Patient preparation

This procedure is normally performed with the patient in a supine position.

bridging external fixator temporary

3. Reduction of the articular fracture

Ligamentotaxis

Ligamentotaxis helps to achieve preliminarily reduction of the fracture fragments and helps to maintain length during the operation. It is also used preoperatively to maintain provisional reduction.

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Use of distractors and external fixators

In order to reduce the fracture it may be helpful to use a femoral distractor. This is usually applied on the lateral side, with the knee in slight flexion.

The same effect may be achieved with the use of an external fixator.

hybrid external fixator definitive

A distractor, because it applies the force directly to the bone, is very powerful and makes distraction easy. The distractor may be used on the side with more comminution. If only an external fixator is available, place one on the medial and one on the lateral side or span the knee joint anteriorly with a unilateral frame.

A bilateral distractor may also be used but may interfere with a later ring implementation.

Note: If a distractor is not available the goal of ligamentotaxis and reduction is still achievable using other techniques such as manual traction.

hybrid external fixator definitive

Use of a reduction forceps for articular fracture reduction

Reduce the articular fracture and preliminarily secure it with large pointed reduction forceps. Check the reduction under image intensifier control.

hybrid external fixator definitive

4. Wire placement

Planning of wire placement

2 mm diameter wires are recommended.

Placement of wires for proximal tibial fixation must be carefully planned. The fracture planes must be determined. Wires must support rather than prevent reduction. Provisional reduction and temporary K-wires might be required.

Interfragmentary compression may be achieved using reduction wires perpendicular to the fracture plane.

Alternatively, lag screws may be placed before the fixator.

Note: If opposed reduction wires will be used for fracture compression, their location must be planned with regard to both fracture anatomy and local structures.

In addition to proximal ring and tensioned wires, the distal pins and frame, and its connection to the ring, must be planned for maximal stability.

hybrid external fixator definitive

Safe wire placement in the proximal tibia

A thorough knowledge of the anatomy is mandatory to perform the correct placement of the K-wires as they go through both cortices (see the safe zones). All the important neurovascular structures run in the posterior half of the cross section. Therefore the wire corridors must be chosen carefully.

hybrid external fixator definitive

Wires should be positioned as proximal as possible but not through the joint. The most proximal wire should be at least 14 mm below the articular surface because of the distal capsular insertion. If a wire is passed within this area, any infection tracking along the wire may lead to a septic arthritis.

hybrid external fixator definitive

With only two wires, stability is limited. Maintaining an overall arc of 60-80° between the wires improves stability. Adding a third wire or a threaded pin gives greater stability.

5. Ring placement

Insertion of wires

At least two wires must be used.

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 knee 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.

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Attaching ring to wires

A bilateral distractor may sometimes interfere with ring implementation. In these cases, if possible, it should be removed before ring application.

Connect the wires to the ring and tighten the clamps. This secures the articular fracture component.

After the wires are tightened, the pointed reduction forceps can be removed.

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Wire tensioning

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.

hybrid external fixator definitive

Pearl: Reduction wires

Reduction wires have small beads called “olives”.

hybrid external fixator definitive

Articular fracture fragments may be held with interfragmentary lag screws.

Alternatively, when the fracture configuration is appropriate, this may be achieved using reduction wires (with “olives”), which will be inserted and tensioned as first wires.

Applying reduction wires with olives is demanding, and should only be performed by surgeons trained in this technique.

hybrid external fixator definitive

6. Pin insertion (tibial shaft)

Pin placement

For safe pin placement make use of the safe zones and be familiar with the anatomy of the lower leg.

hybrid external fixator definitive

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.

hybrid external fixator definitive

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.

hybrid external fixator definitive

7. Finalizing the hybrid external fixator

Ring-to-rod connection

Choose safe locations for pin insertion on the anteromedial side of the tibia.

Place the proximal pin as close as possible to the fracture. The second pin must be positioned as distally as possible. The further the pins are apart, the more stable the construction will be.

hybrid external fixator definitive

Connect the pins with one rod and tighten the rod-to-pin clamps. Then, connect the rod to the ring. The rod-to-ring clamp is left loose enough to allow for manipulation.

hybrid external fixator definitive

Reduction and fixation

Reduce the segments using ring and rod as reduction handles. Restore length, alignment and rotation. Check reduction clinically and with image intensification.

Before manipulation, loosen the distractor.

hybrid external fixator definitive

If reduction is satisfactory, tighten the rod-to-ring clamp.

Take off the distractor.

hybrid external fixator definitive

For additional stability of the frame, at least one or preferably two tubes should be added to the construct.

hybrid external fixator definitive

For additional stability of the tibial head frame, one or two Schanz pins may be added and connected with the ring.

hybrid external fixator definitive

8. Aftercare following nonbridging external fixation

Compartment syndrome and nerve injury

Close monitoring of the tibial compartments should be carried out especially during the first 48 hours to rule out compartment syndrome.

The neurovascular status of the extremity must be carefully monitored. Impaired blood supply or developing neurological loss must be investigated as an emergency and dealt with expediently.

Pin-site care

Various aftercare protocols to prevent pin track 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/wire-insertion sites should be kept clean. Any crusts or exudates should be removed. The pins/wires 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/wire-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/wire loosening or pin track infection

In case of pin/wire loosening or pin track infection, the following steps need to be taken:

  • Remove all involved pins/wires and place new pins/wires 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 track needs to heal. Otherwise infection will result.

Mobilization

Unless there are other injuries or complications, mobilization may be performed on day 1. Static quadriceps exercises with passive range of motion of the knee should be encouraged. Early active range of motion of knee and ankle is encouraged.

Following any injury, and also after surgery, the neurovascular status of the extremity must be carefully monitored. Impaired blood supply or developing neurological loss must be investigated as an emergency and dealt with expediently. See (compartment syndrome) for more details.
The goal of early active and passive range of motion is to achieve as full range of motion as possible within the first 4 - 6 weeks.
Optimal stability should be achieved at the time of surgery, in order to allow early range of motion exercises.

Weight bearing

Partial weight bearing may be allowed only in extraarticular metaphyseal fractures. Weight bearing is usually avoided in the treatment of articular fractures.

The timing and how much weight may be taken through the fracture will be influenced by:

  • Patient factors
  • Fracture configuration
  • Stability of the fixator construct

Follow up

See patient 7-10 days after surgery for a wound check. X-rays are taken to check the reduction.

Frequency of outpatient follow-up depends on the complexity of the injury and on the compliance of the patient. The follow-up visits should not be spaced more than three weeks apart.