Principles of external fixation AOTrauma External Fixation Education Working Group (February 2018): Main author: Dankward Hoentzsch (Germany) Reviewers and contributors: J Spence Reid (US), Vajara Phiphobmongkol (Thailand), Andrey Volna (Russia) AOTrauma External Fixation Working Group (February 2018)

Learning objectives Describe the types of external fixators Describe the indications for external fixation Explain the “spectrum of stability” that can be achieved Describe how to determine the stability of the frame by the method of construction Describe how a modular frame is constructed and used to reduce and stabilize a fracture Explain how to place anatomically safe and stable pins in the tibia

Types of external fixation Monolateral fixator Ring fixator Types of external fixation: Modular, a versatile pin clamp system: with pin or screws; tubes or rods: 4, 6, and 11 mm versatile. Unilateral but V shape or bilateral possible and more construction possible Monotube systems: Clamps with defined pin placement connected with one large tube/ “body“ (monotube) Ring: tensioned wires on a full or partial ring, pins are possible; mixture between wires and pins (recommended today) Some name it hybrid because of the mixture of wires and pins: Hybrid: official name for the mixture between unilateral and full or mostly partial rings (also referred to as Combination) Hexapod: between rings are 6 oblique rods named struts, which can be lengthened and shortened. Technique well known with flight simulators. Known under the name “Taylor frame” from first medical use.

Why external fixation? Minimally invasive—protects the local biology Damage control—can be quick to apply Easy Anywhere, any time, by anyone Wide range of indications Very successful outcome for management of fractures and soft-tissue handling Good result if done properly With “easy” we mean – easy to apply or to handle, forgiving (no second surgery required if changes are necessary), no internal surgery (external manipulation) , minimal invasive, short learning curve etc.

Why not external fixation? Risk of pin infection No or minimal experience with method Equipment unavailable Uncomfortable for the patient Managing the patient in an external fixator can be challenging

1. Modular system Any limb Any joint Partial frames for each main fragment then Reduction and fixation/stabilization with third rod The modular system can be applied anywhere—for an individual bone fracture or for joint bridging fractures. First, two pins are inserted in each segment of the fractured bone. In each segment, a rod will be fixed with clamps parallel to the bone segment. This is repeated for the other segment. The clamps in these partial constructs must be fixed very well. Often this is forgotten (it is extremely important to teach this). Finally a third rod will be loosely fixed (once again with clamps) from rod to rod. Now you can use these partial frames as a handle to reduce the fracture and or joint with any maneuver and ligamentotaxis. Once the reduction is performed the clamps of the third rod will be tightened so that the fracture is fixed. This method should be used from the beginning, not as a salvage procedure. And very important: this is the “AO recommended method”, evaluated and recommended by all experts in this field and the Expert Group.

Corrective procedures 2. Monotube system Corrective procedures Lengthening of shortened limbs Segmental bone transport Correction of simple deformities Corrective procedures can be performed in order to perform: Lengthening of shortened limbs Segmental bone transport (in this case as mentioned up to 6 cm) Correction of simple deformities

3. Ring/Ilizarov system Corrective procedures can be performed in order to perform: Lengthening of shortened limbs Correction of rotational deformities Segmental bone transport (in this case as mentioned up to 6 cm)

4. Combination system Combined use of Periarticular fractures Partial ring or full ring with Unilateral system Periarticular fractures Secondary procedures (eg, septic cases) Alone In combination with other implants Hybrid fixators refer to combinations of 2 types of fixator, such as a half ring fixator plus unilateral external fixation systems.

5. Hexapod system Ring fixation system that uses six angled struts to provide six axes of movement between bone segments Allows correction of complex deformity Requires computer assisted manipulations to guide strut adjustments Sometimes the Hexapod system is called “Taylor Frame”

Indications for external fixation Fractures with soft-tissue damage Polytrauma—damage control surgery Skeletal infection Corrective surgery (deformity or nonunion) Definitive fracture care (pediatric and adult patients) The external fixator can be used for many reasons and in many ways. The two areas in which the fixator is used are traumatology and elective orthopedic surgery. In this presentation only use of the external fixator in traumatology will be discussed.

Indications Fractures with soft-tissue damage Indications for external fixation are fractures with severe soft-tissue damage: Closed fractures with soft-tissue compromise Open fractures with soft-tissue wounds Closed fractures with soft-tissue compromise Open fractures with soft-tissue wound

Indications Polytrauma—damage control Multiple fractures… In a polytrauma, the external fixator has to be applied as fast as possible to stabilize the patient and save life and limb. A polytrauma patient is often treated in different stages: Application of (an) external fixator(s) The definitive treatment is done later depending on the condition of the patient. Multiple fractures… …often resulting from road traffic accidents

Indications Infection When the wound, bone and/or implant is infected: Debridement will remove all dead and infected tissue—including bone Remove or reduce all implants The fracture will then be stabilized temporarily by external fixation Final osteosynthesis is done later, once the infection is cured

Indications Corrective surgery Limb lengthening segment transport with callus distraction EX Fix can be used for Corrections, Limb lengthening Segment transport with callus distraction or modulation (called Ilizarov technique) One example: Limb lengthening with callus distraction 6.5 cm can be achieved to restore the full length of the limb (2.5 plus 4.0 cm) But this should not be a topic of focus for this lecture. 2.5 4.0

Indications V. Definitive fracture care In children: avoid second operation for removal Soft-tissue complication: cannot use cast Avoid epiphyseal plate Indications V. Definitive fracture care In this case with a child a single tube has achieved a good reduction and the single rod was stable enough. This picture only shows that it is possible, however, the modular technique is not the only solution. The AO and AO EX FIX groups recommend in this case for you to use a modular system.

Spectrum of external fixation stability Damage control (optimize soft tissue) Motion at Fracture (Strain) Relative stability Temporary – fracture healing not intended: DCO: within a bone segment and across joints Position a joint after internal fixation Definitive application for fracture union: Achieve relative stability in a fracture setting Protection of a lag screw Achieve primary bone healing via compression Create bone via distraction osteogenesis Absolute stability Stiffness of bone-frame construct

Stiffness of external fixator Distance between tube (ring) and bone Number of tubes (rings and threaded rods or struts) Separation of tubes (rings) from each other Number and diameter of pins (very relevant) Relationship between pins and the fracture and between pins themselves The system configuration The surgeon cannot manipulate all parameters. The distance from tube to bone is limited by soft tissue, eg, femur or not too near the skin because of secondary swelling and/or dressing. Diameter of pins is very relevant and not well known. Do not forget the 6 mm Schanz screws, especially for the femur and pelvis & for heavy patients: see the next slides Stiffness of bone-frame construct

Stiffness µ (diameter)4 Frame stiffness: pins Pin diameter The larger the diameter of the pin, the greater the stiffness Stiffness µ (diameter)4

Frame stiffness: pins Stiffness ratio: pin diameters 4 mm vs 5 mm 1: 2.44 4 mm vs 6 mm 1: 5.06 5 mm vs 6 mm 1: 2.07 6 mm pin is more than twice as stiff as a 5 mm pin 256/625 = 2.44

Factors influencing stiffness of construct Diameter and number of rods Distance between clamps, rods and bone Distance between pins and fracture site Distance between pins in a fragment Diameter of screws Go through all of the factors. Here, it is shown firstly with the modular technique because you should learn this recommended method. The factors are independent of the frame—modular or conventional (old one tube system). Holding strength in bone

Factors influencing stiffness of construct Additional rod Distance between clamps, rods and bone Distance between pins and fracture site Distance between pins in a fragment Diameter of screws Go through all of the factors. Here, it is shown firstly with the modular technique because you should learn this recommended method. The factors are independent of the frame—modular or conventional (old one tube system). Holding strength in bone

Modular external fixation recommended The modular external fixation technique is recommended by the AO for reduction and stabilization Detailed poster available Animations of the previous few slides are also available

Modular technique Pin insertion Fix rods/tubes to pins Create a “partial” frame for each main fragment Tighten all clamps very well Apply third rod using two rod-to-rod clamps, yet loosely Reduce fracture Tighten clamps Mount the third short rod using two tube-to-tube clamps: leave the two tube-to-tube clamps loose. The fracture is then reduced and finally fixed by tightening the nuts.

Modular technique The modular method allows the external fixator to become a reduction tool Now we want to explain the “MODULAR TECHNIQUE” This is the key point of this lecture—this is the first choice! Proven and recommended by AO TK AO EX FIX Experts and Experts Group AO Principles book 3rd and next 4th editions. This is the “AO recommended method”, evaluated and recommended by all experts in this field and the Expert groups.

Modular technique Why use a technique with three rods? Gentle fracture reduction is performed in a second step The fixator becomes a gentle, efficient fracture reduction tool The modular technique with three rods allows the first two rods to be attached, one to each fragment, and when the reduction has been gained, the third rod locks the first two in that position.

Additional neutralization rod Modular technique Even with the modular technique, a “second rod” is possible if greater stability/neutralization of forces is required Add additional rod The modular technique with 3 rods allows the first two rods to be attached, one to each fragment, and when the reduction has bee gained, the third rod locks the first two in that position. Even with the modular technique an “additional neutralisation rod” is possible. If more stability/neutralization of forces is required, add an additional rod. Additional neutralization rod

Modular technique Pin insertion independent of fracture reduction Safe position of pins in tibial midshaft Avoid tethering soft tissue Less pain, better pins Insert two pins on the proximal and distal parts of the bone in the safe zones.

Schanz screws placement in diaphyseal bone The bicortical pin placement is very important. When the tip of the pin is not fixed in the far cortex the pin can dangle. Conventional: penetrate the far cortex 1–6 mm Self-drilling in the cortex but not penetrating—why? The self-drilling tip is very sharp and dangerous. No! Conventional bicortical Self-drilling

Schanz screws/half pins AO principles: example, tibial safe zones Must avoid anatomical structures Avoid tethering soft tissue Less pain Fewer pin-track infections For the safe and recommended zones for the pins, look at the different instructions. In this basic lecture it is not possible to teach all, only the tibia, as a main indication can be shown with one or two pictures.

Polytrauma—damage control external fixation An example of polytrauma with femur, tibia and ankle fractures. Treated with damage control external fixation. The modular technique has been used for the femur. The modular technique was used for reduction and fixation. The basic construct was completed with an additional rod for neutralization. This rod can be curved, like in this example. Similarly the modular technique has been used on the tibia and ankle bridging. With external fixation in place initial physiotherapy can be done in the intensive care unit.

Postoperative care to prevent pin infection Controversial—no clear consensus Removal of crusts Saline or disinfectant solution Cleaning The goal is to remove any debris, such as crusts or exudates. There is no evidence to suggest how best to do this. Less is more.

Take-home messages External fixators have broad indications Many types of fixators are available with specific functions The stability of a fixator is surgeon-controlled The modular technique is the standard for damage control applications Technique and location of pin placement is important to minimize infection and pain