Knee Surgery for Dogs

Tibial Plateau Leveling Osteotomy (TPLO) Surgery

TPLO is a technique to compensate for knees that ``give out". ``Giving out" results from instability after the cruciate ligament is torn. The force generated by weightbearing results in drawer motion or ``giving out" of the knee which is called cranial tibial thrust. There is very little of this force in people due to the fact that our tibial plateau is parallel to the ground and perpendicular to the tibia bone. However, the top of the dog tibia (shin bone) is sloped caudally. The tibial plateau slope allows a constant forward thrust or ``give" to the shin. The cranial cruciate ligament counteracts this force. When the ligament is torn, the tibia ``gives" out into a forward or drawer position. Without surgery to stabilize the knee, the instability causes tearing of the meniscus, loss of cartilage and decreased movement of the knee in the forward position. Larger dogs, require stronger repair techniques.

The goal of surgery is to stabilize the knee so cranial thrust is neutralized. The repair must be strong enough to counter the force that caused the ligament to tear. A suture placed to offset the force may be enough for a dog <50 lbs but would likely break in a larger dog. When the repair fails, the stifle laxity returns and allows arthritis.

TPLO does not involve replacing the ligament but creates a flat surface so the ligament is no longer necessary. By changing the top of the tibia so it is level, the slope is gone and the force of cranial tibial thrust is neutralized. The instability during weight-bearing is gone. 

TPLO requires special xray positions to allow measurements of the slope. A circular cut in the tibia allows easier rotation and positioning of the cut ends. The cut is bridged with a metal bone plate and screws. If the medial meniscus is torn, the torn piece is removed. The bone takes 8 weeks to heal across the cut. The muscles need another month or two to regain strength before the pet can have normal activity. Cutting the bone also allows correction of angulation of the leg if the dog is slightly bow-legged for example.

Complications of surgery include infection, pain, fluid accumulation under the skin, implant failure, slow or nonhealing of bone, persistent joint laxity, angulation of the leg, and inflammation of the patella ligament.   

Young, active, large breed dogs over 60 lbs should not have a weak repair performed that will stretch or break. TPLO may take longer to perform and cost more but the end result would be more long-lasting.