Intramedullary pin fixation with cerclage wires is an option for young or small breed dogs with long oblique (the fracture line at least twice the bone diameter) or spiral simple fractures in which at least 3 cerclage wires can be applied. The fracture must be completely reconstructible and the bone must share the axial load. It is not recommended for older patients or for those dogs that cannot be adequately confined postoperatively. Failure to choose the correct fracture type and patient for this repair will likely lead to loss of reduction of the fracture.
Note: If anatomical reconstruction cannot be accomplished, then a bridging technique should be used.
The dimensions of the pin should be 50-60 % of the isthmus of the medullary canal for the tibia. A pin filling 70-80% of the medullary cavity is generally recommended for IM pinning of long bones, but due to the shape of the tibia, the pin must bend slightly during insertion to stay in the medullary cavity. If the pin is too large, it will exit the cortex; if the pin is too small it will not have adequate strength or bending stiffness to maintain stability.
Note: Retrograde pinning of the tibia should never be done because of the high probability of entering the stifle joint and damaging either the cranial cruciate ligament or the menisci.
Bone-holding forceps are applied to the proximal and distal fragments for distraction. This is necessary to counteract the muscles surrounding the bone, particularly in large breed dogs.
Once distraction is achieved, the bone fragments are pulled, toggled or levered along the fracture line into perfect anatomical reduction with the help of one or two pointed reduction forceps placed across the fracture line.
The fracture is preliminary fixed with one or two pointed reduction forceps while the cerclage wires are applied.
Note: Take care to avoid placing the forceps at the planned cerclage wire sites.
Anatomical reduction and the stability of preliminary fixation are carefully checked.
Cerclage wires application
The distance between the cerclage wires needs to be at least 1/2 diameter away from the tip of the fragment and ½-1 diameter away from each other.
A detailed demonstration of cerclage wires technique can be seen here.
Pitfall: Placing cerclage wires on a short oblique fracture will generate larger shear forces, causing loss of reduction, the fracture to shear, and collapse.
Approach for normograde insertion
This is an extra articular approach. Incision of the stifle joint capsule should be avoided. Skin incision, dissection of subcutaneous tissue, and incision of the medial stifle fascia are performed over the craniomedial aspect of the tibia plateau.
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 passing the fracture zone and reaching the distal segment.
Validation of pin placement
The location of the tip of the pin is assessed by comparing with a pin of the same length held on the outside of the bone.
Note: Pin placement can be checked with intraoperative radiography if available.
Cutting the pin
The pin is cut close to the surface of the tibia plateau to prevent irritation of the straight patellar ligament or the medial joint capsule.
4. Case example
8 month old, female, boxer cross, 23kg with a 42-A2 fracture.
The fracture was repaired with an IM pin and cerclage wires. Note the slight bending of the pin as it enters the tibia cranial to the articulation and follows the medullary cavity.
Radiographs taken one month following surgery show full healing of the bone, and incorporation of the cerclage wires into the callus.
Phase 1: 1-3 day after surgery
The aim is to reduce the edema, inflammation and pain. A Robert Jones or modified Robert Jones bandage can be used to decrease the edema and protect the surgical wound. Integrative medical therapies, anti-inflammatory medications and analgesics are recommended. In most cases, 10-20 minutes of ice therapy is recommended every 8 hours.
Phase 2: 4-10 days after surgery
The 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.
If the dog 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.