Kneecap problem rare for cats

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By Dr. John Koch

Question: I have a cat that has just been diagnosed as having a dislocated kneecap. I am told that she will have to have surgery to correct the problem. How serious an operation is this and how successful is the procedure?

Answer: This type of problem is more common in the smaller breeds of dogs. However, it is sometimes seen in larger breeds of dogs, but it is rarely seen in cats.

The kneecap or patella is located in the tendon of the quadriceps muscle that is located in front of the leg above the knee. The patella is a small round bone that rests in a groove between two ridges at the bottom of the femur (thighbone). The quadriceps tendon attaches to a crest of bone on the tibia below the joint. When the quadriceps contracts, the patella slides in the groove much in the same fashion of a rope sliding over a pulley. The net effect of this process is extension of the lower portion of the leg.

If the kneecap slips over the ridge to either side of the joint, the pulley arrangement is destroyed, and the lower leg cannot be properly extended without straining the structures involved. Pain is the result. Over a period of time arthritis forms and the area becomes more and more painful.

Correction of the problem may involve moving the attachment of the tendon on the tibia so that a more correct alignment with the groove is achieved. It may involve deepening the groove between the two ridges of bone located at the bottom of the femur. It may involve tightening the soft tissues holding the patella in place. Correction may involve a combination of these techniques or it may require them all.

The success of the correction is largely dependent on how severe the deformities are which led to the problem. This is a major surgery so complications are possible, but the vast majority have good results. Without question, surgery offers the best hope of a normal and functional leg.

Dr. Koch is a Cape Girardeau-area veterinarian.