Cerclage wires and intramedullary pin

Intramedullary (IM) pin fixation with cerclage wires is an option for small to mid-sized breed dogs or cats with long oblique fractures to which at least two cerclage wires can be applied.

The fracture must be completely reducible, and the bone must share the axial load.

This technique is not recommended for dogs that cannot be adequately confined postoperatively.

Pitfall: Using this technique on the wrong fracture type or an inappropriate patient will likely lead to loss of reduction.

For this procedure, the patient is placed in lateral recumbency.

The procedure can be done through one long lateral approach for pin insertion and fracture fixation.

Alternatively, a stab incision to the greater tubercle (for IM pin insertion) and a separate approach to the fracture site can be used.

The IM pin can be inserted in either an antegrade or retrograde fashion.

If using retrograde insertion, the pin must be inserted before reducing the fracture.

If the pin is inserted in an antegrade fashion, the pin should be inserted after reduction.

In this section antegrade pin insertion will be described.

The IM pin diameter should be 70-80 % of the isthmus of the medullary canal. Alternatively, if a smaller pin diameter is used, more than one pin can be inserted.

Pitfall: If the pin is too small, it will not have adequate strength or bending stiffness to maintain stability.

A 1 cm stab incision is made directly over the craniolateral point of the greater tubercle.

Note: Care should be taken not to incise the omobrachial vein.

The IM pin enters the bone on the lateral slope of the ridge of the greater tubercle near its base.

Pearl: Cutting the sharp end of the pin reduces the risk of penetrating the supratrochlear foramen, especially in the soft bone of young animals. After having drilled the entrance hole, the pin can be retracted, the sharp end cut, and the pin reintroduced into the bone.

The pin is advanced until the fracture site.

Bone holding forceps are applied to the proximal and distal fragments for distraction.

Once distraction is achieved, the bone fragments are pulled, toggled, or levered along the fracture line into perfect anatomical reduction with the help of one or two pointed reduction forceps placed across the fracture line.

The fracture is preliminarily fixed with one or two pointed reduction forceps while the cerclage wires are applied.

Note: The forceps should not be placed at the planned cerclage sites.

The anatomical reduction and the stability of the preliminary fixation are carefully checked.

The cerclage wires should be placed at least ½ bone diameter from the tip of the fragment and ½-1 bone diameter from each other.

Read more about cerclage wire application.

Pitfall: Placing cerclage wires on a short oblique fracture will generate larger shear forces, causing loss of reduction, the fracture to shear, and collapse.

The IM pin is advanced until just proximal to the supratrochlear foramen.

Pitfall: A pin inserted too far into the supratrochlear foramen will interfere with the anconeal process. Fluoroscopic control helps control the pin positioning.

If several smaller pins are used, it might be possible to advance one pin into the medial condyle under fluoroscopic guidance.

The protruding IM pin is cut close to the greater tubercle.

The pin can also be bent, cut close, and positioned close to the greater tubercle.

In cats with smaller pins, the pin can be bent and twisted flush to the bone surface before being cut.

Final construct.

1-year-old cat with a 12-A2 fracture.

The fracture was fixed with cerclage wires and an intramedullary pin.

No follow-up was available.

The aim is to reduce edema, inflammation, and pain.

Integrative medical therapies, anti-inflammatory medication, and analgesics are recommended.

Note: Animals carry 2/3 of their weight on the front limb. Therefore, strict leash confinement or cage rest and no jumping are recommended until radiographs show signs of bone healing. Since fixation with cerclage wires and IM pin is less rigid and stable than plate fixation, strict leash confinement is essential for this treatment method.

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

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

A careful evaluation is recommended if the dog does not start to use the limb within a few days after surgery.

Early ambulation is aimed for.

Radial nerve neurapraxia may occur in some cases. This neurapraxia usually resolves within a few days.

10-14 days after surgery, the sutures are removed.

Radiographic assessment is performed every 4–8 weeks until bone healing is confirmed.

Note: It can be challenging to assess bone union on radiographs when bone healing occurs without callus formation.