External Fixator

1.Introduction

External fixation can be used to achieve “localized damage control” for fractures with severe soft tissue damage and as definitive treatment for many fractures. Bone infection is a major indication for the use of external fixation. External fixation can also be used for deformity correction and bone handling.

2 .Why use an external fixation 

2.1 Advantages of external fixation

- Little disruption of blood flow to the bone.

- Low impact on soft tissue coverage.

- Can be used quickly in emergency situations.

- Fixation of open and contaminated fractures.

- Allows redistribution and stable fixation of fractures without surgery.

- Presence of less foreign body in case of infection.

- Requires less experience and surgical skill than standard incisional reduction and internal fixation (ORIF).

- Bone handling and deformity correction can be performed.

2.2 Indications for external fixation

2.2.1 Open fractures

External fixation bracing is one of the methods of temporary or definitive immobilization of open fractures and is particularly indicated in the presence of severe soft tissue injuries. External fixation braces are useful for fractures with a high risk of infection, such as delayed attendance at the clinic and/or wound contamination. External fixation has long been a very useful method for such injuries and is still considered the gold standard.

2.2.2 Closed fractures

The indications for the application of external fixation to closed fractures are temporary immobilization of patients with severe polytrauma, and severe closed soft tissue contusions or degloving injuries. In these cases, temporary immobilization using an external fixator can be performed away from the area of injury, preferably away from the area of possible surgery, to treat the soft tissue injury while maintaining limb alignment.

2.2.3 Multiple injuries

An external fixation frame procedure should be considered when performing damage control surgery in patients with multiple injuries. The main advantages of external fixation are rapid relative stabilization of the fracture, help relieve pain, reduce bleeding, and reduce systemic inflammatory response syndrome for ease of care.

2.2.4 Intra-articular fractures

External fixation bracing is usually a temporary measure that protects the fragile soft tissue cover in unstable fractures or complex intra-articular fractures; it is also an option for joint dislocations or ligament repairs where one-stage definitive internal fixation is not possible. All major joints can be bridged in this way, but most commonly the wrist, knee, and ankle.

2.2.5 Bone or soft tissue defects

In patients with severe soft tissue and bone defects, external fixation frames can be used to shorten the limb in one stage and then restore limb length by distraction osteogenesis in the second stage.

2.2.6 External fixation frame used as a tool for indirect reset

After fracture reduction, when the internal fixation plate or intramedullary nail is placed, the position of the fracture can be maintained by locking the external fixator. Sometimes an external fixator can be retained for a period of time to provide additional fixation when the internal fixation is not strong enough. External fixators or femoral distractors have been shown to have an important role during tibial intramedullary nail placement. A Schnee pin is screwed into the dorsal side of the proximal tibial intramedullary nail entry point and into the heel bone, attached with a long rod. This provides localized balanced traction and also adjusts the length, rotation, and axis of the fracture before insertion of the intramedullary nail in either the flexed or extended knee position.

Tibial intramedullary nail placement with external fixation bracket retraction

3.Principles of external fixation brace application

3.1 Biomechanical aspects

Place at least 2 pins per major fracture block through the anatomic safety zone, with pins spaced as widely as possible. If soft tissue conditions permit, the fixation pins should be placed as close to the fracture end as possible, but should not penetrate into the fracture end hematoma or into the area of skin denudation. If extended internal fixation is planned, the fixation pins should avoid possible surgical incisions and surgical access (surgical area). The connecting rods should be placed as close to the bone as possible to increase stability. The stability of the external fixator depends on the following factors.

- Distance of the fixation pins from the fracture end: the closer the stronger.

- The spacing of the fixation pins into each fracture block: the larger the stronger.

- Distance of the longitudinal connecting rods from the bone: the closer the stronger.

- Number of connecting rods: two are stronger than one.

- Configuration of the external fixation frame (from lowest to highest strength): single plane/A-shape/biplane.

- External fixation frame combined with limited internal fixation (tension screws): rarely used because the mix of elastic and strong fixation is only temporary.

- Diameter of Schanz screws or Schnee pins: 6mm has twice the flexural strength of 5mm.

a. Unilateral single-plane single-link external fixation frame. Distance of pin from fracture end (x).

The closer, the more stable. Distance of different pins from the main fracture block (y): the further away the more stable.

The farther away, the more stable. Distance of the longitudinal connecting rods from the bone (z): the closer the more stable.

b. The unilateral, uniplanar, 3-rod combination external fixator is a useful construct for a wide range of applications, including repositioning.

model for a wide range of applications, including reset techniques.

c. Unilateral uniplanar two-link external fixation frame.

d. Unilateral biplane configuration (▲ configuration).

e. Bilateral configuration with penetrating fixation pins. Now rarely used.

Unstable external fixation delays the fracture healing process, but so does an overly rigid external fixation frame.

It is sometimes necessary to dynamize stable fixation and increase the load by partial or complete weight bearing and/or changing the configuration of the external fixation frame.

3.2 Fixed needle placement techniques

- Familiarize yourself with the anatomy to avoid injury to nerves, blood vessels and tendons.

- Do not allow fixation pins or screws to enter the joint.

- Avoid fracture ends and hematomas.

- Avoid areas of skin dehiscence or contusion.

- Pre-drill the bone cortex to avoid thermal damage (leading to ring necrosis).

- Fixation pins should be of appropriate length to construct a suitable frame.

3.2.1 Backbone

The sharper the drill or fixation pin, the less heat will be produced. The faster the screwing, the higher the temperature will rise. Thermal damage to the bone is a serious concern as this can lead to the formation of ringed dead bone, which in turn can cause early loosening and/or infection. Correctly placed fixation pins should have a good grip on both cortices, while the tip should not penetrate too far.

3.2.2 Diaphysis

In the epiphysis, heat production is not a problem. It may be safer to use self-drilling screws at this point, as it is easy to miss the pre-drilled holes when screwing in the screws. Fixation pin penetration into the joint must be avoided as there is a risk of needle tract infection seeding into the joint.

3.2.3 Safety zones

To avoid injury to nerves, blood vessels, tendons, and muscles, the surgeon must be familiar with the anatomy of the limb in all cross-sections and use the safety zone for placement of fixation pins.

Figure 3.3.3-2 Safe zone for external fixation pin placement.

a Femur.

Figure 3.3.3-2 (continued)

b Tibia.

Figure 3.3.3-2 (continued)

c Humerus, posterior view.

When used in a single plane, it is not necessary to drive the Schanz screw into the anterior tibial crest. The anterior tibial crest has a thick cortical bone and drilling will generate excessive heat, which may cause secondary osteonecrosis. In the distal tibia, there is a risk of injuring the anterior tibialis tendon and extensor digitorum muscles.

4. Components

4.1 Tube-rod system

4.1.1 Schanz screws 

Schanz screws are partially threaded fixation pins. They are available in different diameters, lengths (rod length, thread length) and different tips. The tip of the standard Schanz screw is a trocar-shaped tip (Fig. 3.3.3-3a) and usually requires pre-drilling.

Figure 3.3.3-3 Schanz screws.

a Standard socket pin-shaped tip.

b Self-drilling tip.

Self-drilling and self-tapping pins have a special sharp tip that can drill and cut threads at the same time when screwed in. They are designed for use in the metaphysis (Fig. 333-3b).

Schanz screws are available in steel, titanium or hydroxyapatite coated. Hydroxyapatite coated pins can achieve good grip in the bone, allowing early bone ingrowth and avoiding loosening. This type of pin is suitable for patients who have external fixators in place for a long time.

4.1.2 Steiner pins

Steiner pins are usually used as fixation pins that penetrate bones. Their tips are in the shape of drill sleeves and need to be pre-drilled in the cortical bone before insertion.

4.1.3 Tubes/Rods

Depending on the specifications of the tubes/rods, there are 4 different models:

• Large: 11 mm tube/rod, Schanz screws are 4~6 mm.

• Medium: 8 mm tube/rod, Schanz screws are 3~6 mm.

• Small: 4 mm tube/rod, Schanz screws 1.8 to 4 mm.

• Mini: 2 mm system for fingers, conventional design, with multi-pin clamp for fixing K-wires and 2 mm rods.

The modules of this system are supplemented with pre-shaped, curved carbon fiber rods. For difficult fixation sites such as the wrist, T-joint modules are also available.

4.1.4 Clamps

The clamps are used to connect the tube/rod and the fixation pins. The tubes/rods can also be connected to each other with a suitable clamp (tube-tube).

Figure 3.3.3-5 Clamps

a Self-locking clamp for connecting Schanz screws and tubes/rods.

b Combination clamp for connecting two rods or tubes.

c Universal multi-pin clamp.

d Tube-tube clamp for connecting two tubes.

4.2 Unilateral external fixation frame systems

The fracture block can be controlled with double-pinned clamps or customized clamps. A central threaded component can be attached for distraction or compression for bone lengthening and/or bone transportation.

Unilateral external fixation system for bone transportation

4.3 Combined External Fixation

Combined external fixation is used for fractures adjacent to the joint and requires a tensioned Kirschner pin for ring fixation and a conventional Schanz screw for the diaphysis. A 3/4 circumferential ring is usually used. Combination ring fixators are used primarily for the proximal and distal tibia.

Combined External Fixation Brace for Tibial Plateau Fractures. It can also be used for periarticular fractures of the distal tibia. the V-shaped structure provides good stability edics

4.4 Circumferential External Fixation Brace

The advantage of a fully circumferential external fixation system is that the axis of load bearing and orthopedic axis passes through the center of the circumferential external fixation system as well as the longitudinal axis of the bone. The circumferential external fixator system can be used for bone lengthening, bone handling, and the treatment of simple and complex fractures.

Tibial Ring External Fixation Brace

Clinical photograph of the tibial ring external fixation system

Application of this technique permits early weight bearing. For new fractures, we prefer a simple unilateral external fixation frame for treatment. Bone handling and lengthening can likewise be treated with a unilateral external fixation system, but it can be difficult to perform complex, sustained, multiplanar deformity corrections, for which a circumferential external fixator is recommended. When used as an external fixation, the circumferential external fixator provides relative stability. When the needle is passed through different planes for multiplanar fixation, this structure provides a high degree of stability. The strength of the structure varies depending on the configuration of the fixation, the number of rings used, and the type of pins used, such as Kirschner pins or Schanz screws. Depending on the assembly, the fracture can be retracted or compressed, and the deformity can also be corrected. Ring external fixators are usually used for distraction of osteogenesis to correct bone defects, shortening and deformities.

4.5 Hinged External Fixation Brace

Used to maintain repositioning of dislocated joints or fracture dislocations and to allow some (controlled) joint motion to prevent joint stiffness. It is most commonly used for the elbow joint.

5 Frame Construction of External Fixation Braces

5.1 Nomenclature of Frame Structures

There are different ways of categorizing frame structures, mainly based on:

- Function.

- Frame design.

- Plane of application.

- Characterization.

5.1.1 Unilateral frames

The unilateral frame is the most commonly used external fixator frame modality for the treatment of fresh diaphyseal fractures. The frame is applied in one plane, e.g. anteromedial or medial to the tibia and anterolateral or lateral to the femur. The fixation pins are inserted through the skin on one side and penetrate the double cortex. The pin must be placed away from the joint, outside the reflexed portion of the joint capsule, to avoid joint sepsis. The two rods are mounted in the same plane or in two different planes and then they are joined together.

5.1.2 Bilateral frames

The Szczecin pin is passed through the skin on one side, penetrates the bilaminar cortex, and is then passed through the skin on the opposite side. Bilateral frames are not recommended for the definitive treatment of fractures, but may be used for temporary fixation.

5.1.3 Crossed external fixation frames

Used in damage control procedures to span areas with severe soft tissue injuries or complex intra-articular fractures and fracture dislocations.

▲Pelvic fractures, proximal femur fractures, and proximal tibia fractures were immobilized using temporary external fixation braces across the knee and ankle joints.

The stability provided by the external fixation frame allows for soft tissue recovery as well as for CT scanning and preoperative planning. Unilateral frames are most commonly used, and fixation pins should be placed outside the area of injury and future performance of definitive surgery.

5.1.4 Extension frames

Ilizarov introduced this technique with a circumferential external fixation frame. Tubular external fixation frames and unilateral external fixation frames can be used to apply this principle of slow retraction, with the disadvantage that correction of both angular and rotational deformities cannot be performed at the same time unless lengthening is performed by intramedullary nailing.

5.2 Patterned Repositioning Techniques

The advantage of the combined external fixation frame is that it allows for reduction, bridging, and fixation of all long bones, areas adjacent to the joint, and the joint itself (transarticular).

Placement of the Schanz screws can be liberal, allowing the choice of the optimal anatomic fixation position for the Schanz screws or the optimal area of fixation depending on the type of fracture and soft tissue injury. Reduction of the major fracture fragments can be performed by leverage and indirect reduction techniques, while preserving the blood flow to the bone and soft tissues. Application of this technique allows readjustment of the fracture reduction at any time.

Combined reduction technique.

a Type B tibial stem fracture.

b For each major fracture block, 2 fixation pins are screwed in outside the area of injury.

c Fixation pins are secured to the connecting rods with universal clamps, making them 2 handles for indirect fracture reduction.

d After the fracture has been repositioned, the 3rd connecting rod is attached to the first 2 connecting rods with a tube-tube clamp.

▲ Demonstration of a combined external fixation brace. a Tibia. b Femur. c Trans-knee.

6 Special applications

6.1 Joint fusion

A special use of external fixators is the fusion of joints by compression with bilateral external fixators. This principle is occasionally used for fusion of the ankle, knee, and elbow joints, especially in the presence of infection .

6.2 Infection

External fixation is the ultimate treatment for acute infection or infected nonunion of a fracture, as fixation pins can usually be placed away from the site of infection.

6.3 Corrective osteotomy

Osteotomies for correction of deformities when soft tissue conditions are poor or impaired and the risk of using internal fixation is high, in which case external fixation brackets may be used for fixation. Another indication is osteotomy with simultaneous bone handling. This usually requires correction with a circumferential external fixation frame.

6.4 Bone handling - distraction osteogenesis

Bone distraction is based on Ilizarov's principle of preserving the periosteum so that carefully severed bone can be slowly distracted (0.5-1 mm/d), and new bone is formed in this gap. Slower rates of distraction result in bone healing, whereas faster rates of distraction that exceed the strain tolerance of the tissue do not result in bone formation. Carried or distracted bone scabs, like those of fractures, also go through all the stages of scab maturation until bony healing occurs. There are 3 indications for the use of this technique, and sometimes these indications may coexist:

- Limb lengthening.

- Segmental bone handling to treat bone defects.

- Corrective osteotomy.

The most suitable fixation frames for this purpose are the circumferential external fixation frame (with or without a semi-circumferential external fixation frame) and the unilateral external fixation frame.

6.5 Joint Restoration and Sustained Motion

A hinged external fixator is an important addition to a number of complex unstable elbow injuries, including chronic or unresolved elbow dislocations following incisional repositioning and ligament repair. A hinged external fixator maintains elbow reset with controlled mobilization. Maintaining repositioning is the first priority. Instability is more difficult to manage than loss of motion. The axis needs to be precisely positioned under fluoroscopy. Slight deviations in the position of the hinge can significantly affect its function.

▲ Placement of a hinged external fixator for the elbow.

7 Postoperative treatment

7.1 Pin tract care

Pin tract reaction depends on the position and stability of the fixation pin, the postoperative treatment of the nursing team and the patient. The combined reduction technique is more advantageous because it allows the selection of the best anatomical position for the fixation pin according to the type of fracture. The hospital should have a clear pin tract care process, and experienced nurses should teach patients to perform pin tract care by themselves. By avoiding thermal injury and local hematoma formation during pin insertion, and using alcohol disinfectants to clean the pin site in follow-up care, and using closed pressure dressings, the infection and loosening of the pin can be significantly reduced.

7.2 Pin tract infection 

Pin tract care must first have correct pin insertion. For conventional Schanz screws, pre-drilling is usually required and the pin is manually screwed in to reduce thermal necrosis. Inappropriate soft tissue tension around the pin must be released during surgery. Proper care of the pin tract is important to reduce the occurrence of pin tract complications. Pin tract infection and screw loosening can be solved by removing the loose pin and re-screwing a pin in another location.

7.3 Mobilization

Except for a few special cases (bridging fixation, emergency use, tension adjustment), partial weight bearing is allowed at the beginning of the external fixator. As healing progresses, full weight bearing can be gradually increased. There is no need to add additional dynamization devices to the external fixator. Partial or full weight bearing is the best and most effective method of dynamization.

8 Duration of external fixation

8.1 Change of treatment

There are 3 basic treatment options:

• Use external fixator as definitive treatment until the fracture heals.

• Early conversion to internal fixation.

• Switch to non-surgical treatment, such as plaster, orthosis, etc.

If conversion to internal fixation is expected, it must be done as early as possible (within 2 weeks) because the complication rate is significantly lower than that of late conversion.

The following rules should be followed when planning any surgery before, during, or after temporary fixation:

• If a new implant is placed around the original external fixation site, all pin tracts must be clean. Sometimes the procedure is done in two stages, with one stage to clean the original pin tract and the second stage to perform definitive fixation.

• Any pin tract site older than 10 to 14 days is considered to be colonized and should be cleaned and debrided aseptically before definitive fixation.

• If there is any doubt about the sterility of these pin tract sites or the pin tract is already infected, a “pin rest period” of at least 10 days is required after pin tract debridement before a new implant is placed.

• Antibiotics must be used prophylactically with an antimicrobial spectrum that covers bacteria from previous pin tract infections.

• Close follow-up for the first 6 weeks after replacement of the internal fixator.

If there is evidence of a problem with the pin tract, it is best to identify the bacterial species, apply antibiotics, change the pin and reposition it, and continue treatment with an external fixator. Pin tract care should involve the patient to ensure optimal results. If the external fixator must be replaced with internal fixation in the late stage, it is recommended to have a "pin rest period" of at least 10 days, that is, after removing the external fixator, the pin tract should be cleaned and debrided first, and then fixed with a splint until the pin tract problem is resolved before delaying the internal fixation surgery. Antibiotics can be used appropriately during this period.

8.2 Final fixation

Emergency external fixation can achieve temporary stability of the limb and allow soft tissue recovery. As long as the soft tissue conditions are stable, the external fixator can be replaced with the final internal fixation. Ideally, it should be replaced with internal fixation within 10 days.

If the external fixation is still stable and there are no signs of complications, replacement fixation is not necessary. If the skin coverage is poor, or there is concern about severe soft tissue damage and the risk of infection from open reduction is high, the external fixator can be retained as the final treatment of the fracture.

The progress of fracture healing must be carefully observed, and if there is no progress, other treatments should be considered.