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.
2. Patient preparation
This procedure is performed with the patient placed in either:
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 in the proximal and distal parts of the tibia. 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 overall, sufficient cortices are engaged.
Normograde pin insertion in the tibia
The appropriate size pin is inserted in a normograde fashion without entering the stifle joint.
The pin is started at a point on the tibia plateau just inside the medial cortex and halfway between the straight patellar tendon and the medial collateral ligament.
The pin is directed very slightly caudally in the direction of the tibial shaft and parallel to the medial cortex. The caudal angle must be shallow to allow the pin to bend slightly as it contacts the caudal cortex and aligns with the medullary cavity.
The pin is advanced through the proximal fragment. When using an open but do not touch approach, 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.
If a MIPO approach is performed, it is not necessary to cut the tip of the pin.
The pin is advanced passing the fracture zone and reaching the distal segment.
Note: The pin tip is not always cut before advancing it. Placing the pin with a hand chuck instead of a power drill is advised.
The fracture is aligned and stabilized with bone-holding forceps, while the pin is advanced into the distal metaphyseal area.
Entering the talocrural joint with the tip of the pin must be avoided.
A second pin of the same length or fluoroscopy can be used to judge insertion length.
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 relation between the tarsus and the stifle.
Flexing and extending the tarsus and stifle will help to check the alignment of the repair.
Note: Position of the cat in dorsal recumbency permits a better three-dimensional view of the tibia, thus it helps in the verification of alignment.
Cutting the pin
The pin is cut close to the surface of the bone to prevent irritation of the straight patellar ligament or the medial joint capsule.
A bone plate is contoured to the shape of the bone. The length of the plate should allow placement at least three to four screws in each major fragment.
Note: Ideally a plate placed in bridging fashion should span at least 75% 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 and corrected if necessary.
If a locking plate is used, temporary stability is achieved using K-wires through the locking drill guide in each of the fragments.
If possible, the plate is secured by inserting at least three bicortical screws in each major segment. This is easier to achieve proximally and distally because the bone tends to be larger in those locations.
The screws should be oriented in such 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.
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.
Phase 1: 1-3 day after surgery
The aim is to reduce the edema, inflammation and pain and to protect the surgical wound. A compressive bandage or modified Robert Jones bandage can be used. Integrative medical therapies, anti-inflammatory medications (note in the cat that many are toxic; only use drugs labeled for cats) and analgesics are recommended. In most cases, 10-20 minutes of ice therapy is recommended every 8 hours, but maybe challenging in cats.
Phase 2: 4-10 days after surgery
The aim is to resolve the hematoma, edema and control pain, and prevent muscle contracture. Analgesic medications may still be needed. Anti-inflammatory medications used in the cat are not labeled for continued use after a few days and should be avoided. Rehabilitation and integrative medical therapies can be used.
If the cat is not starting to use the limb within a few days after surgery, a careful evaluation is recommended.
10-14 days after surgery the sutures are removed.
Phase 3: 10 day-bone healing
Radiographic assessment is performed every 4-8 weeks until bone healing is confirmed.
More information about implant removal can be found here.