The plate-rod configuration can be an option for the treatment of comminuted, non-reducible A3 fractures. This fixation requires that there is enough bone stock in the neck fragment to allow pin insertion and that the fracture does not involve the greater trochanter.
Although the pin-plate combination increases the strength and fatigue life of the fixation, the pin makes the placement of the cervical screw difficult. The benefit of the pin must be balanced with the potential loss of screw purchase.
Proximal plate fixation may be challenging due to the reduced bone stock present. The plate must be precisely contoured to the lateral aspect of the greater trochanter to achieve optimal bone purchase.
Biomechanics of the fixation construct
Plate-rod is a biological fixation technique. The intramedullary pin is used as a reduction device to align the fracture and restore bone length. The two implants work together; the pin protects the repaired 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 because the bone is not sharing any load.
The length of the incision will depend on the extension of the fracture.
4. Surgical technique
The dimensions of the pin should be 35-40% of the isthmus of the medullary canal. This provides sufficient protection against bending forces and allows placement of cortical screws. Bicortical screws are preferred and usually possible with this pin size. If a bicortical screw cannot be placed, monocortical screws are acceptable in a plate-rod construct as long as a sufficient number of cortices are engaged.
The pin is started at a 20 degree angle relative to the axis of the bone to minimize slippage into the trochanteric fossa.
Because of the very small fragment size, orientation of the pin is critical. A maloriented pin may cause significant coxa valga or coxa vara deformity.
The pin is passed through the fragmented section and driven into the distal fragment with a power or hand chuck until the tip of the pin reaches the bone of the distal metaphysis. The femur is distracted to its full length by pushing the pin against the distal femoral cortex.
Spatial alignment is achieved without disturbing the bone fragments within the zone of comminution.
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. The distal part of the femur is held in a true lateral position. The position of the greater trochanter and alignment of the adductor magnus muscle are then inspected.
If the femur is correctly aligned in the axial plane, the adductor magnus muscle should be aligned and 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 alongside 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 lateromedial 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.
Plate selection and preparation
The plate is perfectly contoured over the lateral aspect of the greater trochanter.
Note: the plate bending is difficult and needs to be well preplanned. Make sure that one screw hole is positioned to allow screw placement up to femoral head and neck.
The plate is secured to the bone with bone clamps and/or bone holding forceps. Rotational alignment is verified again.
If a locking plate is used temporary k-wires through drill guides can be inserted in the proximal and distal fragments instead of bone holding forceps to achieve temporary plate stabilization.
If possible, the plate is secured by inserting at least two bicortical screws in each major segment. One screw is positioned into the femoral head and neck.
As much as possible, the screws should be oriented in such a way that they do not interfere with the intramedullary pin.
If the drill contacts the intramedullary pin, a monocortical screw can be used instead of a bicortical screw. Forcing a drill bit against the pin will likely result in breakage of the drill bit and potentially the screw hole will be unusable.
Fixation with a locking plate
A locking plate can be used instead of a traditional bone plate. Interference between the pin and the locking screws is likely. Using monocortical locking screws or a combination of cortex and locking screws can provide adequate fixation. If a combination of screws is used, the plate must be anatomically contoured and the cortex screws should be placed and tightened first because they will compress the plate to the bone.
Cutting the pin
The protruding part of the pin is cut as close as possible to the level (or below the level) of the greater trochanter.
Validation of fixation
Postoperative orthogonal radiographs are taken to assess fixation.
5. Case example
8-year-old domestic shorthair cat with an A3 fracture from being hit by a car. The cat also had an acetabular fracture
The fracture was repaired using a plate and rod configuration with a 1.4 mm pin and a locking ALPS 8 plate. The acetabular fracture was repaired using a locking ALPS 6.5 plate.
Activity restriction is indicated until radiographs indicate bone healing of the fracture.
Phase 1: 1-3 day after surgery
Aim is to reduce the edema, inflammation and pain.
Integrative medical therapies, anti-inflammatory and analgesic medications.
Note: Nonsteroidal anti-inflammatory medications can be toxic in the cat and should only be used as labeled for the cat.
Phase 2: 4-10 days after surgery
Aim is to resolve the hematoma, edema and control pain, and prevent muscle contracture.
Anti-inflammatory (see nonsteroidal warning) 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 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.
Implants may cause discomfort of the adjacent soft tissue. If this occurs, implants can be removed after bone healing is observed. In case of infection, implants must be removed after healing.
If there is no implant failure or infection, there is no need for implant removal.