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  3. Diagnosis
  4. Indications
  5. Treatment

Authors of section


Bruno Peirone

Executive Editor

Amy Kapatkin

General Editor

Noel Moens

Open all credits

Interlocking nail

1. Indications

All B and C type fractures, especially the non-reconstructible types, are amenable for internal fixation with an interlocking nail (ILN). The ILN can be used with an open approach but is an excellent minimally invasive device, since it can be placed through small incisions without disturbing the fracture site.

interlocking nail

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

interlocking nail

An interlocking nail can be used for all B and C type fractures if the cat's femur is large enough for a small ILN to fit. The techniques for placing an interlocking nail are the same for a cat as the dog.

2. Principles

Illustrations of fracture types

Fracture types :

A) Comminuted, unreduced fracture
B) Comminuted fracture aligned biologically
C) Fracture aligned and biologically stabilized

interlocking nail

3. Patient positioning

This procedure is performed with the patient in lateral recumbency.

combined treatment options

4. Approach

OBDNT approach

An open-but-do-not-touch (OBDNT) approach provides direct visualization of the fracture site but the fracture fragments are minimally manipulated.

interlocking nail

MIO approach

A Minimally Invasive Plate Osteosynthesis (MIO) technique can be used. A surgical approach to the proximal and the distal femur is performed.

interlocking nail

5. Surgical technique

Preoperative planning

Diameter, length and depth of ILN insertion are determined by preoperative planning using the radiograph of the opposite intact femur if available. The nail’s largest diameter should be approximately 75% of the medullary cavity at the femoral isthmus. The longest possible nail should be selected to optimize construct stability (Dejardin et al: Interlocking nail and minimally invasive osteosynthesis Vet Clin Small Anim 42 (2012) 935–962).


In the proximal femur, the only acceptable nail insertion technique is normograde. The medullary cavity is opened using an intramedullary pin or a dedicated awl inserted from the trochanteric fossa.

Depending on the type of nail used, reaming of the medullary canal in the distal fragment may be required.

interlocking nail

The nail is coupled to an insertion handle via a nail extension. It is introduced along the anatomical axis of the femur and inserted into the medullary canal of the proximal segment by hand or gentle hammering. The fracture is aligned while the nail is further advanced into the distal segment.
The nail is directed into the distal segment using fluoroscopic guidance, closed palpation, or visualization through an open-but-do-not-touch approach to the fracture site. A mallet is used to fully impact the nail into the intramedullary canal, until deeply seated in the distal metaphysis or epiphysis.

interlocking nail

Validation of alignment and rotation

Reduction is confirmed using local landmarks and/or intraoperative fluoroscopy. Reduction is adjusted as necessary prior to locking the nail. Rotational alignment can be judged by palpation or by direct visualization of the greater trochanter and femoral trochlea or by examination of the adductor magnus muscle. The distal part of the femur is held in a true lateral position. The position of the greater trochanter is then inspected.
If the femur is correctly aligned in the axial plane the greater trochanter should be slightly caudal to the long axis of the bone.

interlocking nail

The alignment can also be checked by confirming the orientation of the femoral neck relative to the plane of the femur. This is done by inserting a small pin along side the femoral neck with the femur in a true lateral position. Orientation of the pin should be about 15°-25° in the cranial direction relative to the sagittal plane of the femur.

interlocking nail

Final application of the nail

Once adequate alingment 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 alignment guide and nail extension are removed at the end of the procedure.

interlocking nail

6. Case example

1.5 year old female domestic longhair cat with a 32-B3 fracture.

interlocking nail

The fracture was repaired with a 4mm interlocking nail and 2mm bolts.

Alignment: adequate

Apposition: not attempted

Note: The hole in the nail at the level of the fracture is a potential weak point of this repair.

interlocking nail

7. Aftercare

Phase 1: 1-3 day after surgery

Aim is to reduce the edema, inflammation and pain.
Integrative medical therapies, anti-inflammatory and analgesics.

Phase 2: 4-10 days after surgery

Aim is to resolve the hematoma, edema and control pain, and prevent muscle contracture.
Anti-inflammatory and analgesic medications may still be 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. Rehabilitation is strongly recommended to help prevent quadriceps muscle contracture.

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

10-14 days after surgery the sutures are removed.

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

~3-4 months after follow up radiographs surgery check bone healing.