the chihuahua breed is known to have the knee condition known as patellar luxation and is one of the most common health problems associated with chihuahuas. the knee is a complex structure consisting of muscles, ligaments, tendons, cartilage, and bones. these components must align properly and interact harmoniously in order to function properly. three bones are included in the knee: the femur, the tibia, and the patella (kneecap).
the lower front portion of the femur (thigh bone) in a normal chihuahua has two bony ridges that form a fairly deep groove in which the patella is supposed to slide up and down. these structures limit the patella’s movement to one restricted place, and in doing so, control the activity of the quadriceps muscle. the entire system is constantly lubricated by joint fluid. it works so that there is total freedom of motion between the structures.
diagram of the anatomy of a normal knee cap
patellar luxation (or trick knee, subluxation of patella, or floating patella), occurs when the patella, or kneecap, dislocates or moves out of its normal location.
when the patella is luxated in a chihuahua, the ridges forming the patellar groove are not prominent, and a too-shallow groove is created. in a chihuahua with shallow grooves, the patella will luxate (jump out of the groove) sideways, especially toward the inside. this can causes the leg to ‘lock up’ with the foot held off the ground.
chihuahua with a luxating patella on both hind legs
(like teaka the famous chihuahua has as seen in the video above)
when the patella luxates from the groove of the femur, it usually cannot return to its normal position until the quadriceps muscle relaxes and increases in length. this is why a chihuahua may be forced to hold their leg up for a few minutes after this occurs because the muscles are contracted, the patella is luxated from its correct position and the joint is held in a flexed or bent position. pain is caused by the knee cap sliding across the bony ridges of the femur.
patellar luxation in chihuahuas can have both genetic causes, or environmental causes (luxation due to injury). if it appears at an early age, it’s likely to be due to genetic causes. environmental sources of injury can include too much jumping (i.e. jumping off furniture), or too much stress on the patella and surrounding ligaments (ie. when a chihuahua dances on its rear legs). this is especially dangerous when a chihuahua is a puppy in stages of early development.
adult chihuahuas can also damage their kneecap by a forceful hit or blow. with age, looseness might also be recognized, especially in chihuahuas that are overweight as there is constant pressure on surrounding ligaments.
symptoms of patellar luxation includes skipping, yelping when in pain, holding the rear leg up for a short time as they walk or run or rear-leg weakness. if left uncorrected, the condition will result in serious wear of the patellar ridges where the groove becomes very shallow resulting in both arthritis and in the more serious cases, permanent crippling.
if your chihuahua does have patellar luxation, see your veterinarian for options to help alleviate symptoms. the use of supplements such as glucosamine may be helpful and it’s recommended that you keep your chihuahua lean and exercised to keep the leg muscles strong.
depending on how severe the condition is, it may or may not require surgery. if required, your chihuahua will recover quickly with complete recovery in as early as thirty days. breeding chihuahuas with this disorder is not recommended. chihuahuas affected still make for wonderful pets and those that do require surgery usually lead perfectly normal lives without any restrictions on activity.
references: peteducation.com/article.cfm?c=2+2084&aid=457 – drs. foster & smith, inc.