Patellar Luxation
PATELLAR LUXATIONWhat is Patellar Luxation?The patella, or kneecap, is part of the stifle joint (knee). In patellar luxation, the kneecap luxates, or pops out of place, either in a medial or lateral position. Patellar Luxation CategoriesPatellar luxations fall into several categories: Medial Luxation in Toy, Miniature BreedsAlthough the luxation may not be present at birth, the anatomical deformities that cause these luxations are present at that time and are responsible for subsequent recurrent patellar luxation. Patellar luxation should be considered an inherited disease. Clinical SignsThree classes of patients are identifiable: Signs vary dramatically with the degree of luxation. In grades 1 and 2, lameness is evident only when the patella is in the luxated position. The leg is carried with the stifle joint flexed but may be touched to the ground every third or fourth step at fast gaits. Grade 3 and 4 animals exhibit a crouching, bowlegged stance (genu varum) with the feet turned inward and with most of the weight transferred to the front legs. Permanent luxation renders the quadriceps ineffective in extending the stifle. Extension of the stifle will allow reduction of the luxation in grades 1 and 2. Pain is present in some cases, especially when chondromalacia of the patella and femoral condyle is present. Most animals; however, seem to show little irritation upon palpation. Lateral Luxation in Toy and Miniature BreedsLateral luxation in small breeds is most often seen late in the animal’s life, from 5 to 8 years of age. The heritability is unknown. Skeletal abnormalities are relatively minor in this syndrome, which seems to represent a breakdown in soft tissue in response to, as yet, obscure skeletal derangement. Thus, most lateral luxations are grades 1 and 2, and the bony changes are similar, but opposite, to those described for medial luxation. The dog has more functional disability with lateral luxation than with medial luxation. Clinical SignsIn mature animals, signs may develop rapidly and may be associated with minor trauma or strenuous activity. A knock-knee or genu valgum stance, sometimes described as seal-like, is characteristic. Diagnosing Patellar LuxationExamination and CertificationThe dog is examined awake (chemical restraint is not recommended) and classified by the attending veterinarian according to the application and general information instructions. The veterinarian then completes the application form indicating the the results of the dog’s patella evaluation. The application and fee can then be mailed to OFA. The attending veterinarian and owner is encouraged to submit all evaluations, whether normal or abnormal, for the purpose of completeness of data. There is no OFA fee for entering an abnormal evaluation of the patella in the data bank. A breed database number will be issued to all dogs found to be normal at 12 months of age or older. The breed database number will contain the age at evaluation and it is recommended that dogs be periodically reexamined as some luxations will not be evident until later in life. Preliminary EvaluationsEvaluation of dogs under 12 months of age is encouraged if the owner desires to breed at this age. The most opportune time to gather breeding data is at 6-8 weeks of age prior to the puppy’s release to the new owner. Grades of Patellar LuxationThe Patellar Luxation Database is for dogs 12 months and over. Examinations performed on dogs less than 12 months will be treated as Consultations and no OFA breed numbers will be assigned. Grade 1Manually the patella easily luxates at full extension of the stifle joint, but returns to the trochlea when released. No crepitation is apparent. The medial, or very occasionally, lateral deviation of the tibial crest (with lateral luxation of the patella) is only minimal, and there is very slight rotation of the tibia. Flexion and extension of the stifle is in a straight line with no abduction of the hock. Grade 2There is frequent patellar luxation, which, in some cases, becomes more or less permanent. The limb is sometimes carried, although weight bearing routinely occurs with the stifle remaining slightly flexed. Especially under anesthesia it is often possible to reduce the luxation by manually turning the tibia laterally, but the patella reluxates with ease when manual tension of the joint is released. As much as 30 degrees of medial tibial torsion and a slight medial deviation of the tibial crest may exist. When the patella is resting medially the hock is slightly abducted. If the condition is bilateral, more weight is thrown onto the forelimbs. Many dogs with this grade live with the condition reasonably well for many years, but the constant luxation of the patella over the medial trochlear ridge of the trochlea causes erosion of the articulating surface of the patella and also the proximal area of the medial lip. This results in crepitation becoming apparent when the patella is luxated manually. Grade 3The patella is permanently luxated with torsion of the tibia and deviation of the tibial crest of between 30 degrees and 50 degrees from the cranial/caudal plane. Although the luxation is not intermittent, many animals use the limb with the stifle held in a semi flexed position. The trochlea is very shallow or even flattened. Grade 4The tibia is medially twisted and the tibial crest may show further deviation medially with the result that it lies 50 degrees to 90 degrees from the cranial/caudal plane. The patella is permanently luxated. The patella lies just above the medial condyle and a space can be palpated between the patellar ligament and the distal end of the femur. The trochlea is absent or even convex. The limb is carried, or the animal moves in a crouched position, with the limb flexed. Medial and lateral patellar luxationProvided by:VetCentric.com
It is much more common for the kneecap to ride on the inside than on the outside surface of the knee. This condition typically affects small and miniature breeds such as the poodle, Pomeranian, Chihuahua, Schipperke, Bichon Frise, and pug. It is also seen in the cocker spaniel, golden retriever, Labrador retriever, and mixed breeds. 1. Patella Outside dislocation of the kneecap, or lateral patellar luxation, occurs more often in large breeds such as the Great Dane, Saint Bernard, and Bernese mountain dog. Lateral luxation is often accompanied by malformation of the femur, the large bone in the thigh. In these cases the prognosis is more uncertain, as major limb reconstructive surgery may be needed. Clinical SignsLameness that is often intermittent, and may be unilateral or bilateral; thick, swollen stifles; pain on range-of-motion; crepitus; palpable luxation; inability to jump or walk normally; medial displacement of quadriceps muscle group; lateral bowing of the distal third of the femur. SymptomsIntermittent or consistent lameness; bowlegged stance; reluctance to walk or jump; occasionally holding a rear leg out to the side when walking. DescriptionMedial patellar luxation, or MPL, is a very common disease of small and miniature breeds in which the kneecap occasionally rides on the inside of its normal groove. Primarily congenital, although occasionally acquired through trauma, MPL causes lameness in one or both rear limbs. The degree of lameness is determined by the severity and duration of the disease, as well as the extent of existing arthritis. DiagnosisThe examining veterinarian will often make a diagnosis from a physical examination and history. However, x-rays are needed to determine the degree of arthritis, and evaluate for any malformation of the femur and tibia, the two major bones in the leg, which are joined together at the knee. PrognosisThe prognosis for a Grade I patellar luxation is very good. These dogs may not need surgery. However close observation for signs of worsening is important. If surgery is indicated and performed early on, most animals regain normal functionality. Transmission or CauseThe congenital condition is probably genetic in nature, and as such, affected animals should not be bred. Trauma or injury can also cause patella luxation. TreatmentTreatment involves replacing the kneecap into the groove, and preventing it from popping in and out. The following procedures can be used alone or in combination as necessary to maintain the proper function of the knee. ImbricationTightening the joint capsule, known as imbrication, is done on the opposite side of the luxation to prevent the kneecap from having enough slack to pop out of the trochlear groove. Thus a medial patellar luxation is treated with a lateral imbrication, and vice-versa. Additionally, the joint capsule can be loosened on the side of the luxation; this is called a release incision. This procedure relieves the tension that the joint capsule is placing on the patella, thus allowing it to ride in the trochlea. TrochleoplastyDeepening of the trochlear groove, or trochleoplasty, can be accomplished with a variety of techniques. A chondroplasty technique involves cutting out a taco-shaped wedge of cartilage, removing a small portion of bone beneath it, and then replacing the cartilage. The result is a deeper groove. This procedure can only be performed on very young dogs, because their cartilage is thicker. Tibial Tuberosity TranspositionThe kneecap attaches to the lower leg via its patellar tendon at a bony site called the tibial tuberosity. Many times this site forms abnormally on the inside, as with MPL, or on the outside, as with LPL. In this procedure, the surgeon moves the tibial tuberosity back into proper alignment and secures it in place with a pin or wire. Realigning the joint, kneecap, and tendon prevents dislocation from reoccurring. OsteotomyIn severe cases, with malformation of the tibia or femur, corrective bone cuts known as osteotomies may be required. Prevention:Early detection and correction is the best way to prevent severe lameness and dysfunction. Breeding affected animals should be discouraged; however, the disease is so prevalent in some breeds that this may not be practical. |