Medial & Lateral Patellar Luxation
Patellar (knee cap) luxation, a frequent occurrence in dogs manifests in different types of luxation and varying grades of severity. Understanding
the causes and effects of this problem, allows dog owners to make educated decisions about the care of pets.
Help is available for dogs affected by patellar luxation. Good diagnostic and surgical practices have produced a 90-95% success rate for
achieving active and pain free use of the patient's affected limbs.
Early detection of patellar luxation is critical for providing a good quality of life. In addition to the pain and suffering caused by the knee
abnormalities, approximately 95% of dogs with patellar luxation have a related structural abnormality. If these conditions are treated when the
dog is young, progressive deformities can be avoided. Routine veterinary examinations should include evaluation of the joints with particular
attention paid to those dog breeds known to be predisposed to orthopedic abnormalities.
Medial Patellar Luxation is the most common stifle problem seen. Toy and miniature breeds have 4-8 times the incidence of this disease than
other dogs. Medial patellar luxation is most often a congenital (inherited) problem which occurs early in life (4-6 months of age). Usually trauma is
not associated with medial luxation, but anatomical deformities result in the luxation. In middle to older aged pets, 15-20% of the cases presented
exhibit concurrent rupture of the cranial cruciate ligament of the stifle joint.
Clinical signs of medial luxation of the patella depend on the degree and duration of deformity, and if one or both joints are involved. Neonates
and young puppies may be seen with abnormal hind leg carriage and function (grades 3-4). Young to mature dogs with a grade 2-3 will have an
abnormal or intermittently abnormal gait. These will usually only be presented for examination when the gait visually worsens.
Older dogs with a grade 1-2 luxation exhibit sudden signs of lameness due to breakdown of the soft tissue in the joint resulting from trauma or
degenerative joint disease. Many dogs with medial patellar luxation will not show pain on palpation. The treatment for this dislocation is aimed at
reducing the anatomic defects causing the secondary luxation as well as repair of the patella.
Trauma-induced Medial Luxation
Lateral Patellar Luxation is typically seen in small dogs. Symptoms arc slow to develop, exhibiting problems in the dog later in life (5-8 years).
Usually these are grade 1-2 luxations, which have a greater function in degree of disability, but still may result in a breakdown of soft tissue
response. Clinical signs may develop rapidly, usually associated with minor trauma or strenuous activity. A "knock-knee" or seal-like stance often
characterizes the condition, and pets with sudden luxation occurring in both legs, may not be able to stand, simulating a neurologic disease.
Lateral Luxation in Large Dogs is often seen in the breeds that are affected by hip dysplasia, including Rottweilers, Golden Retrievers. Labrador
Retrievers, Chow Chows, and German Shepherd Dogs. Research has shown that congenital hip dysplasia deformities may cause this condition.
Lateral patellar luxation can cause deformation of the femoral head, due to the rapid growth seen in large breeds. Genetic (and possibly
nutritional) factors are keys to the development of this condition. Clinical signs occur around 5-6 months of age with a thickening of tissues of the
stifle joint, a "knock-knee" and/or a cow hocked stance with the toes pointed out. In cases with associated hip dysplasia, the correction of both
abnormalities is necessary to prevent progressive deformities.
Preliminary classification of the degree of patellar luxation is important in evaluation of the patient. These grades (1 being the least severe, to 4
being the most severe) are based on the pets' stance, movement (gait) and how easily the veterinarian can manipulate the patella.
" Grade 1: Occasional carrying of the leg is seen, often described as skipping or hopping, which may be transient, often returning to normal by
itself. Your veterinarian may easily luxate the patella manually and return it to its normal position. Pain may be evident only when the knee cap is
" Grade 2: The frequency of luxation increases, becoming more or less permanent. The pet will usually carry its leg, but will occasionally bear
weight on it. When palpated by the veterinarian, a dry, crackling sensation (crepitation) may occur in the joint. A grade 2 luxation can increase in
severity, and if not surgically treated, can develop into degenerative joint changes.
" Grade 3: Permanent dislocation that occurs though weight bearing may still be possible, however the stance will appear somewhat crouching or
bowlegged. Surgical intervention should not be delayed, especially if this is found in a young, growing dog. Rapid growth of abnormalities results
in progressive deformities.
" Grade 4: Permanent luxation, with the affected limb always being carried, creates a bowlegged / crouching stance. Early surgery is strongly
recommended at this state for bony deformities of the femur and tibia.
In early to mild stages, soft tissue reconstruction may be sufficient to correct the problem. Complications such as increasing degrees of luxation,
duration and multiple joint involvement require a variety of bone reconstruction techniques, with soft tissue repair often being necessary.
Luxating patellas can be surgically corrected to allow a dog to lead a pain free, productive life. The key to successful treatment lies in early
diagnosis and therapy.