Authors of section


Mary Sarah Bergh

Executive Editor

Amy Kapatkin

General Editor

Noel Moens

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External skeletal fixator

1. Principles

Proper alignment of the femur must be obtained with special attention to angulation and torsion. Comparison with the contralateral unaffected bone can be useful.

The use of this technique is limited by the morbidity associated to external fixators in very muscular areas.

Note: Careful attention to alignment of the limb is important, to avoid torsional or angular deformities which can affect patellar tracking and limb function.

External skeletal fixator used to repair a distal femoral fracture in a dog

Biomechanics of the fixation construct

ESF-tie-in is a biological fixation technique. The intramedullary pin is used as a reduction device to align the fracture and to restore bone length. The two implants work together; the pin protects the repaired fracture against bending forces, while the external fixator resists axial collapse, rotation and shear. Without the pin, the external fixator is subjected to high bending forces because the bone is not sharing any load in the fractured area.

Note: This will be a less rigid stabilization than a bone plate. It is important to assess the ability of this type of stabilization to counteract all the forces that will be placed on it. Safe zone ESF pin placement is difficult in the femur because of the large muscle mass on the lateral surface. In addition, the intramedullary pin will cause interference with the gluteal muscles.

2. Positioning and approach

This procedure is performed with the patient placed in lateral recumbency and through stab incisions for the external fixator.

lateral recumbency position

3. Surgical technique

Pin selection

The dimensions of the intramedullary pin should be 30-50% of the isthmus of the medullary canal. This provides sufficient protection against bending forces and allows placement of threaded bicortical transfixation pins.

Dimensions of the intramedullary pin for external skeletal fixator used to repair a distal femoral fracture in a dog

Pin insertion

The intramedullary pin is inserted in a proximal to distal direction. The pin is started at a 20 degree angle relative to the long axis of the femur to minimize slippage into the trochanteric fossa.

Intramedullary pin insertion for external skeletal fixator used to repair a distal femoral fracture in a dog

The pin is passed through the proximal femur and driven into the distal fragment through the region of comminution with a power or hand chuck until the tip of the pin reaches the bone of the distal metaphysis. The femur is distracted to its full length by pushing the pin against the distal femoral metaphyseal bone.

Spatial alignment is achieved without disturbing the bone fragments within the zone of comminution.

Note: It is very important not to penetrate through the articular surface with the tip of the pin. Using a hand chuck while seating the pin distally helps avoid joint penetration.

Intramedullary pin insertion for external skeletal fixator used to repair a distal femoral fracture in a dog

Validation of alignment and rotation

Once the bone length has been restored, it is necessary to check for correct alignment and rotation. Rotational alignment can be judged by palpation or by direct visualization of the greater trochanter and femoral trochlea. The distal part of the femur is held in a true lateral position. The position of the greater trochanter and alignment of the adductor magnus muscle are then inspected.

If the femur is correctly aligned in the axial plane, the adductor magnus muscle should be aligned and the greater trochanter should be slightly caudal to the long axis of the bone.

Validation of alignment and rotation

Application of the external fixator

A positive profile threaded pin is applied in the proximal fragment in a lateral to medial direction. The most distal ESF pin is placed across the femoral condyles in a similar fashion, taking care not to penetrate the articular surfaces. The connecting bars and clamps are assembled, and the remaining pins are positioned creating a type IA external fixator. Two or three pins per fragment should be used.

Note: A positive profile pin should always be predrilled with a drill bit that is slightly smaller than the diameter of the positive profile pin. Negative profile pins should never be used because they break at the thread- no-thread interface. Smooth pins have poor holding power.

Note: Care must be taken to avoid perforating the articular surface.

The proximal part of the IM pin, protruding from the gluteal region, is connected with the connecting bar of the external fixator creating a tie-in configuration.

Application of external skeletal fixator used to repair a distal femoral fracture in a dog

Validation of fixation

Postoperative orthogonal radiographs are taken to assess fixation. If acceptable the pins are cut close to the connecting bar.

4. Aftercare

The pin-skin interface should be cleaned and adequately protected.

Frequent rechecks are recommended in the early postoperative period to access stability of the frame and the pin-skin interface.

external skeletal fixator

Phase 1: 1-3 day after surgery

The aim is to reduce the edema, inflammation and pain using anti-inflammatory and analgesic medications.

Passive range of motion of the hip and stifle joint can be initiated to promote mobility and joint health.

Phase 2: 4-10 days after surgery

The aim is to resolve the hematoma, edema and control pain, and prevent muscle contracture.

Anti-inflammatory and analgesic medications are still needed. Rehabilitation and integrative medical therapies can be used.

Special attention should be given to patients less than 1 year of age with a femoral fracture, as they are at risk for developing quadriceps contracture. Early controlled activity and passive range of motion is strongly recommended to help prevent this complication.

If the patient is not starting to use the limb within few days after surgery, a careful evaluation is recommended.

cross pinning

Implant removal

Complete removal of ESF and the IM pin is indicated once the fracture is healed.