If you've ever suffered a knee injury, you can commiserate with a Chihuahua with luxating patellas. When the dog's patella, or kneecap, does not fit neatly in a track with the femur or thighbone, the off-kilter or misaligned patella can luxate, or literally slip off to the side of the joint, causing the knee to dislocate. A dog's patella may be misaligned due to trauma to the area, or it can stem from a malformed kneecap.
Regardless of why the kneecap is not tracking correctly, a luxating patella is extremely painful. The patella does tend to right itself — or “pop” back in — but the aftermath leaves the entire joint sore, tender, and inflamed. If you happen to catch your Chihuahua when she dislocates her knee, you may notice her slip and then hop a few steps before gingerly putting weight back on the rear leg.
In more severe cases, the patella doesn't realign itself, and the Chi's rear leg locks and becomes stiff. When the patella remains misaligned, it is necessary for your veterinarian to move the patella back into place.
Regardless of the reason, when the knee dislocates, the supporting tendons and ligaments are stretched and pulled and are now even less equipped to hold the kneecap in place. With everything loose in the joint, the Chi is likely to dislocate her knee repeatedly on an intermittent basis — or with a severely misaligned patella, the situation could be chronic. With a joint problem such as this, arthritis is more likely to appear at an earlier age, too.
In addition to hopping (temporary dislocation) or a stiff rear leg (requiring veterinary assistance to realign), symptoms that your Chihuahua has suffered a dislocation include stiffness in either or both rear legs, difficulties rising from the floor, limping, tenderness in the knee, and a reluctance to exercise. The severity of the situation usually dictates what treatments might be prescribed, but in general, moderate to severe cases benefit greatly from surgery.