In the presence of non-reducible fragments or when devitalization of the fragments is likely during reduction, indirect reduction (bridging fixation) such as a plate and rod stabilization technique is indicated.
Illustrations of fracture types
A) Comminuted, unreduced fracture B) Comminuted fracture aligned biologically C) Fracture aligned and biologically stabilized
Biomechanics of fixation construct
Plate-rod is a biological fixation technique. The intramedullary pin is used as a reduction device to align the fracture and to take the bone to its proper 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 bone plate would be subjected to high bending forces because the bone is not sharing any load.
The dimensions of the pin should be 35-40% of the isthmus of the medullary canal. This provides sufficient protection against bending forces while allowing placement of cortical screws. Bicortical screws are preferred and usually possible with this size pin. If a bicortical screw cannot be placed, monocortical screws are acceptable in a plate-rod construct as long as overall, 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 in the trochanteric fossa.
When using an OBDNT approach
Immediately after the cortex is penetrated, the pin is redirected down the medullary canal along the axis of the bone. The pin is guided through the proximal fragment until it protrudes at the level of the fracture site. The tip of the pin can be cut and then directed into the distal fragment once the fracture is aligned. Cutting the tip of the pin minimizes the risk of penetration through the distal fragment cortex when the fracture is distracted.
Alternatively, the pin is driven in a retrograde fashion into the proximal fragment retracted and cut before reinsertion into the medullary canal of the distal fragment.
When using a MIO approach
When using a MIO approach, the pin is driven into the distal fragment with a power or hand chuck under imagining guidance 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. If intraoperative imaging is not available, an incision at the distal fragment must be made to ensure proper pin placement. If that is done, the pin tip can be cut like in the OBDNT approach.
The pin is 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. Alternatively, gentle tapping with a mallet and an intramedullary pin setter until the length of the bone is restored can be used.
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 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.
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.
A bone plate is contoured to the shape of the bone. The length of the plate should allow placement at least 3-4 screws in each major fragment.
Note: ideally a plate placed in bridging fashion should span at least ¾ of the length of the bone.
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, the temporary stabilization is achieved with a push and pull device on each major fragment.
If possible, the plate is secured by inserting at least three bicortical screws in each major segment. As much as possible, the screws should be oriented is such way that does 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.
A locking plate can be used instead of a traditional bone plate. However, interference between the pin and the locking screws is likely. Using monocortical locking screws or a combination of non-locking and locking screws can provide adequate fixation. If a combination of screws is used, the plate must be anatomically contoured and the non-locking screws should be placed and tightened first because they will compress the plate to the bone.
6. Case example 1
2 year old cat with a 32-C3 femoral fracture from being hit by a car.
The fracture was repaired with a 12 hole 2.4 mm LCP plate and a 2.0 mm pin with MIPO.
Apposition: not attempted
7. Case example 2
4 year old DSH outdoor cat with a 32-C3 fracture from gunshot injury.
The fracture was repaired with a 5/64 IM pin and a 2.4 LCP.
Apposition: not attempted
The patient did well on follow up but never returned for radiographs.
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.