Bridging plate and pin

Plate and rod fixation can be used for all types of humeral shaft fractures. It is, however, mainly used for multiple wedges and complex fractures.

Plate and rod fixation is a fixation technique with the intention of secondary bone healing.

The two implants work together; The pin protects the fracture against bending forces while the plate resists axial collapse, rotation, shear, and bending. Without the pin, the plate would be subjected to high bending forces since the bone does not share any load.

The intramedullary pin is used as a reduction device for aligning the fracture. The pin can also be used for distracting the main fragments. The fracture distraction and alignment are maintained by the plate.

Locking screws give more stability than cortical screws. In axial locking systems, the screws can often not be directed past the intramedullary pin. In these cases, monocortical screws can be used. Otherwise, polyaxial-locking systems or non-locking systems can be used to direct the screws past the intramedullary pin.

The patient is placed in lateral recumbency with the affected leg up.

The intramedullary pin is usually introduced through a lateral approach over the greater tubercle. Therefore, a lateral approach is used most often for bridging plate and pin fixation.

The diameter of the pin should be 30-40% of the isthmus of the medullary canal. This diameter provides sufficient protection against bending forces while still allowing the placement of bicortical screws. If a bicortical screw cannot be placed, monocortical screws may be used if enough cortices are engaged.

Pearl: Cutting the sharp end of the pin reduces the risk of penetrating the supratrochlear foramen, especially in the soft bone of young animals. A more blunt end is also helpful for distracting the fragments.

The pin is usually inserted in an antegrade fashion from the proximal end. The pin enters the bone on the lateral slope of the ridge of the greater tubercle near its base. It is directed distal medially in the direction of the fracture area and driven across the fracture site.

Note: If a blunted pin is used, an initial entry hole must be made with a pointed pin.

The fracture is reduced using reduction forceps or by maneuvering the distal fragment over the intramedullary pin. By further introducing the pin, alignment of the long axis and fragment distraction can be achieved.

The pin is advanced to just proximal to the supratrochlear foramen. In dogs, it sometimes is possible to advance the pin into the medial condyle.

The protruding part of the pin is cut close to the bone level, so it is still possible to remove it later.

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

The plate's length should allow placement of at least two, preferably three or more, screws in each major fragment.

The selected bone plate is contoured to the shape of the bone.

Read more about plate preparation.

The plate is fixed with one proximal screw.

The alignment (especially the rotational alignment) is verified, and a screw is inserted in the distal fragment.

Alternatively, the plate can be secured to the bone with bone clamps or bone-holding forceps.

If possible, the plate is secured to the bone by inserting at least two bicortical screws into each major fragment. The screws should, whenever possible, be oriented in such a way that they do not interfere with the intramedullary pin. Alternatively, three or more monocortical screws can be used.

The most proximal and distal screws should preferably be bicortical screws. Often this is only possible if non-locking screws are used.

The remaining screws should preferably be locking screws to increase the stability of the repair. Depending on the position and plate system used, the remaining screws can be either monocortical or bicortical screws.

Note: If a combination of locking and non-locking screws is used, the plate must be anatomically contoured, and the non-locking screws should be placed and tightened first since they will compress the plate to the bone.

The number of screws needed depends on whether monocortical or bicortical screws are used. The use of locking screws will reduce the number of screws required.

Pitfall: There is a high risk of the drill bit hitting the pin, which may lead to the screw hole becoming unusable. Drilling must, therefore, be done carefully. If increased resistance is felt, drilling should be stopped, and a monocortical screw should be used.

12-year-old cat with a 12-A3 fracture.

The fracture was repaired with an IM pin and a craniolateral plate.

In this case, a slightly bigger pin would have been preferable.

Follow-up radiographs were taken after pin removal nine months postoperatively.

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

Integrative medical therapies, anti-inflammatory medications, 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.

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.

Radial nerve may occur in some cases. This 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.