1 Indications topenlarge
32-B3, 32-C3 and usually 32-B2 fractures are not reducible fractures; therefore, biological fracture repairs are recommended.
A plate with a bridging function can under certain conditions be used alone for internal fixation of these fractures. If a bone plate is used alone, it must be able to withstand all the weight bearing forces during healing, as the bone will not initially be sharing the load.
A bridging plate used alone is acceptable in light weight, young cats in which bone healing is fast.
For larger patients, stronger fixation such as plate and rod or an interlocking should be used. Double plating could be considered as an alternative.
2 Principles topenlarge
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 topenlarge
Indirect reduction is achieved by distracting and aligning the major bone segments using bone clamps, or other distraction techniques.
Validation of alignment and rotation
Once the bone length has been restored, it is necessary to check for correct alignment and rotation. Rotational alignment can be judged by palpation or by direct visualization of the greater trochanter and femoral trochlea or by verifying the alignment 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.
Correct alignment and rotation can be checked with intraoperative imaging. The latero-medial projection is used and the whole bone, including the proximal and distal joints, must be visible.
If the femur is properly aligned in the transverse plane, about 1/3 of the femoral head should be visible cranially to the cranial femoral cortex. (Image A). Image B shows excessive internal rotation and C shows excessive external rotation of the distal femur.
Comparison with the contralateral unaffected limb can be useful.
In a properly aligned leg, manual manipulation of the femur, will allow 90° of external rotation and 45° of internal rotation of the hip. This method can only be used if the plate has been temporarily secured to the bone.
A large plate must be selected because it must be able to withstand all the weight bearing forces because the bone will not be sharing the load. A lengthening plate (a plate without holes in the central part) can be used.
The plate is contoured and placed on the lateral side of the femur, in bridging function.
If possible, the plate is applied by inserting at least three bicortical screws in each major segment. The plate should bridge at least 75% of the length of the femur.
A locking plate can be used instead of a traditional bone plate.
5 Case example topenlarge
1 year old male cat with a 32-C3 fracture from being hit by a car.
The fracture was repaired with a 92 mm plate 2.0 mm thick.
Postoperative radiographs at 8 weeks.
6 Alternative surgical technique: Double plating topenlarge
Double plating can be an alternative to plate rod or interlocking nail fixations in some cases; for example, in very active, large patients or when a single plate is not considered to be strong enough.
Application of plates
The first plate is applied on the lateral surface of the femur. A second plate is secured to the cranial surface.
During the cranial plate placement, care must be taken to avoid interference with the quadriceps mechanism. The distal plate end should be placed safely above the most proximal part of the trochlear ridge. Placement of the cranial plate and screw orientation should be carefully planned to minimize interference with the lateral plate and screws.