Anatomical reconstruction of the fragments is mandatory for the correct placement of screws in lag fashion and/or cerclage wires.
Note: If anatomical reconstruction cannot be accomplished, then a bridging technique should be used.
Lag screws vs. cerclage wires
In order to achieve compression and counteract the shearing forces, either screws in lag fashion, cerclage wires or a combination of both can be used depending on fracture configuration.
Although the indications for screws in lag fashion in cats are the same as in the dog, the size of the bones and the thinness of the cortices make the application of screws in lag fashion more difficult.
Cerclage wires should only be used if the fracture configuration allows for placement of at least two wires and should not be used on short oblique fractures.
A singular screw in lag fashion can be used on short oblique fractures as long as it is directed at a right angle to the fracture plane.
Bone-holding forceps are applied to the proximal and distal fragment for distraction. This is necessary to counteract the muscles surrounding the bone.
Alternatively, a bone distractor can be used for this purpose.
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 screw(s) in lag fashion or cerclage wires are applied.
Note: Take care to avoid placing the forceps at the planned lag screw or cerclage wire sites.
Anatomical reduction and the stability of preliminary fixation are carefully checked before applying the implants.
Lag screw fixation
The screws are inserted in lag fashion. To achieve maximal interfragmentary compression, the screws must be directed perpendicular to the fracture plane.
Depending on the fracture configuration, one or two additional screws are inserted in the same fashion.
Note: The screws should be evenly spaced and care should be taken to avoid placing them too close to each other. Safe distance is at least one screw diameter away from any fracture line and two screws should be separated by two times their diameter.
Cerclage wires application
Indications for the use of cerclage wires are long oblique fractures, in which at least two wires can be applied.
Pitfall: Placing cerclage wires on a short oblique fracture will generate larger shear forces and will cause the fracture to shear and collapse.
The length of the plate should allow the placement of at least three screws in each major fragment.
Note: A traditional non-locking or locking plate (DCP, LCDCP or the LCP) can be used.
The contoured plate is applied to the medial surface (tension surface) of the bone and secured with at least three bicortical screws in each of the major fragments. Avoid screw insertion close or at the level of the fracture line. All screws are placed in a neutral mode.
When using a locking plate, locking screws or a combination of cortex and locking screws can be used. All cortex screws must be placed before the locking screws are used.
Pitfall: In spiral fractures it may be difficult to determine the exact location of the fracture line once the bone is reduced. Careful examination of the fracture configuration and pre-planning is necessary to avoid placing a screw too close to or at the level of a fracture line.
4. Alternative surgical technique
Lag screws through the plate
In cases where independent lag screws would interfere with the placement of the plate, the lag screws can be placed through the plate holes to achieve compression.
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.