Interlocking nail

Humeral shaft fractures, which are not too close to the supratrochlear foramen, are amenable for internal fixation with an interlocking nail (ILN).

The distal fragment should be long enough to hold the ILN with its tip proximal to the supratrochlear foramen, and the locking holes should lay at a safe distance from the fracture area. These requirements can be judged based on preoperative x-rays.

The ILN provides good relative stability for the fractured bone. Because of its large diameter and intramedullary location, the ILN is highly effective in counteracting bending forces. Unlike intramedullary pins, they effectively counteract axial compression and torsion due to their interlocking mechanisms.

This procedure is performed with the patient positioned in lateral recumbency.

The ILN can be introduced either in an antegrade or retrograde fashion.

For retrograde insertion, a small approach over the fracture zone can be used with two separate small approaches for screw/bolt placement, proximal and distal. Alternatively, one long lateral approach over the whole length of the bone is possible.

For antegrade insertion, a small approach to the greater tubercle is necessary.

The diameter, length, and depth of ILN insertion are determined during preoperative planning using x-rays of the opposite intact humerus if available.

The nail’s largest diameter should be approximately 75% of the medullary cavity. The longest possible nail should be selected to optimize construct stability.

Note: The distal tip of the ILN must be above the supratrochlear foramen.

Antegrade nail insertion can be done in a closed fashion not touching the fracture site and with a small incision for bolt placement. Alternatively, it can be done using an “open-but-do-not-touch” approach.

The medullary cavity is opened using an intramedullary pin or a dedicated awl inserted from the greater tubercle of the humerus.

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

The nail is directed to the fracture site and then, after reducing the fracture using fluoroscopic guidance, closed palpation, or visualization through an “open-but-do-not-touch” approach, directed into the distal fragment. The nail is seated just proximal to the supratrochlear foramen.

Reduction is confirmed using local landmarks and/or intraoperative fluoroscopy. Reduction is adjusted as necessary before locking the nail. The rotational alignment can be judged by fluoroscopy or visual judgment by extending or flexing the elbow.

Once adequate alignment and proper nail insertion are confirmed, placement of the bolts or locking bolts is achieved by using an alignment guide coupled to the nail. The bolts can be inserted through small stab incisions.

The alignment guide and nail extension are removed at the end of the procedure.

A small lateral approach to the fracture site is made.

The medullary cavity is opened using an intramedullary pin or a dedicated awl. The ILN is introduced retrograde exiting at the greater tubercle. It is withdrawn until the end of the nail is at the fracture site.

The fracture is reduced manually or with the help of reduction forceps.

The nail is advanced into the distal fragment until just proximal to the supratrochlear foramen.

The fracture is checked for reduction and alignment.

Once adequate alignment and proper nail insertion are confirmed, placement of the bolts or locking bolts is achieved through the use of an alignment guide coupled to the nail. The bolts can be inserted through small stab incisions or by extending the lateral approach.

The alignment guide and nail extension are removed at the end of the procedure.

11-month-old German Shepherd dog with a 12-B1 fracture.

The fracture was fixed with an interlocking nail. The wedge was adapted with suture in cerclage manner.

Follow-up radiographs six weeks postoperative. Elevated periosteum shows beginning callus formation.

No further follow-up radiographs showing healed fracture were 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. Strict leash confinement or cage rest and no jumping is, therefore, 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.

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.