Intramedullary pin fixation with cerclage wires is an option for cats with long oblique 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 those cats 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.
The dimensions of the pin should be 70-80 % of the isthmus of the medullary canal. If the pin is too small it will not have adequate strength or bending stiffness to maintain stability.
The skin incision is made along the craniolateral border of the femoral shaft from the level of the greater trochanter to the level of the patella. The subcutaneous fat and superficial fascia are incised or bluntly dissected directly under the skin incision.
The superficial fascia is retracted. The junction between the fascia lata and the biceps muscle is carefully identified by looking at the direction of the fibers.
The vastus lateralis and intermedius muscles, on the cranial surface of the femoral shaft, are retracted cranially by freeing the loose fascia between the muscle and the bone. Take care to avoid unnecessary detachment of the adductor magnus muscle as it attaches on the fascies aspera of the femur and is the major blood supply to the fractured bone.
5. Surgical technique
Bone holding forceps are applied to the proximal and distal fragment for distraction. This is necessary to counteract the strong muscles surrounding the bone.
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 sites.
Anatomical reduction and the stability of preliminary fixation are carefully checked.
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.
When it is necessary to expose the greater trochanter for implant placement, the attachment of the vastus lateralis on the neck of the femur may be partially incised.
A 1 cm skin incision is made at the level of the most proximal part of the greater trochanter.
The tip of the pin is placed against the medial aspect of the greater trochanter.
The pin is started at a 20 degree angle relative to the axis of the bone to minimize slippage in the trochanteric fossa.
As soon as the pin penetrates the fossa, the pin is redirected to align with the medullary axis of the bone. The pin is directed slightly caudally and medially to avoid the pin engaging the cranial cortex at the level of the proximal metaphysis. The pin is driven into the cancellous bone of the distal metaphysis until the tip contacts but does not penetrate the cortex.
Gently slide the pin down into the trochanteric fossa.
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. When the pin reaches the level of the distal pole of the patella, the pin is correctly placed in the medullary canal.
Note: Pin placement can be checked with intraoperative radiography if available.
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 to avoid trauma to the muscle and sciatic nerve. This level will allow pin removal if necessary in the future.
Note: If the pin is difficult to cut close with this method, it can be cut prior to seating into the distal femur.
6. Case example
9 month old DSH with an 32-A2 fracture from unknown trauma.
The fracture was repaired with a 5/64th IM pin and 2.4 LCP. At reduction, small fragment broke off and was not reduced.
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.