An avulsion fracture occurs when a bone breaks and a fragment of the bone is separated by the pull of an attaching muscle, tendon or ligament. The tibial tuberosity is the prominent bump on the front and top of the tibia, the shin-bone, below the knee joint. This tuberosity attaches the patella (knee-cap) via a strong thick tendon of the quadriceps muscle group. A fracture of the tibial tuberosity often results in an avulsion fracture, by virtue of the pull of the quadripceps muscles.
This fracture tends to occur in younger cats, before this area of the tibia has fully grown and fused to the rest of the bone. The fracture occurs in kittens in association with trauma, often falling from a height and landing with the knee in flexion, tearing the bone fragment from its normal position.
Untreated, the knee joint and consequently the limb function on the affected leg may be poor.
What to Watch For Sudden onset of hindleg lameness (non-weight bearing)
Swelling around the front of the knee joint
After a careful history and general physical examination, your veterinarian will perform an orthopedic evaluation of your pet. In cases of more severe trauma, life threatening injuries will be investigated and addressed before assessing for problems such as lameness. Additional tests may include: Palpation of the leg. The leg is usually painful on flexion and extension, swollen and painful on palpation over the top front portion of the tibia. The patella (knee cap) may ride higher than usual, because it is no longer firmly attached to the tibia.
Radiographs. X-rays can confirm the diagnosis, and this may require sedation or even anesthesia. Both knees may be radiographed to confirm the diagnosis as the displacement of the bone fragment can vary from small and subtle to dramatic.
In most cases, the fracture is the only medical problem and as such chest radiographs may not be necessary. There is no specific laboratory work for this type of fracture, but blood work may be obtained prior to surgical fixation and a general anesthetic.
This type of fracture is probably best treated by surgery and fixing the bone back in its correct position; otherwise, the quadriceps muscle group may continue to pull the bone fragment away.
Fixation is achieved under anesthesia by cutting the skin, exposing the fracture site and fixing the displaced piece of bone in position using pins and/or wire. In some cases, if the displacement is minimal, or finances are limited, casting the leg with the knee extended for 2-3 weeks, may be effective.
X-rays will be taken after surgery to assess the position of the implants and the realignment of the bone.
Home Care and Prevention
After surgery, a soft padded bandage may be applied to the leg to reduce swelling and offer comfort and support. This may stay in place for a few days to a week. The toes at the bottom of the bandage will need to be checked daily for swelling or pain.
The incision, if visible, will need to be checked for swelling, redness or discharge and stitches or staples removed in 10 to 14 days from surgery.
If a cast has been used, the toes should be assessed in the same way as a bandage, but the top of the cast should also be checked regularly for rubbing or chaffing.
After surgical fixation, exercise should be restricted for about 4 to 6 weeks. Passive flexion and extension of the knee may begin shortly after bandage removal to encourage good range of knee motion. This is a problem with a cast that requires longer immobilization of the knee as a whole.
Implants, pins and wires, may be removed if they are felt to interfere with normal bone growth and lengthening, or left in place if they are not causing a problem and your pet has limited growing left to do.
The prognosis for this fracture is good but there may be damage to the growth region at the top of the tibia that might not be immediately visible on x-rays, yet lead to growth deformities in the leg that are more significant and difficult to treat.
The tibial tuberosity may fuse prematurely following the repair and this could alter the conformation of the knee leading to impaired knee function.