1 Indications topenlarge
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.
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.
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 topenlarge
Illustrations of fracture types
Fracture types :
A) Comminuted, unreduced fracture
B) Comminuted fracture aligned biologically
C) Fracture aligned and biologically stabilized
3 Approach topenlarge
An open-but-do-not-touch (OBDNT) approach provides direct visualization of the fracture site but the fracture fragments are minimally manipulated.
A Minimally Invasive Plate Osteosynthesis (MIPO) technique can be used. A surgical approach to the proximal and the distal femur is performed.
4 Surgical technique top
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.
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.
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.
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.
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.
5 Case example topenlarge
1.5 year old female domestic longhair cat with a 32-B3 fracture.
The fracture was repaired with a 4mm interlocking nail and 2mm bolts.
Apposition: not attempted
Note: The hole in the nail at the level of the fracture is a potential weak point of this repair.