While many competent veterinarians routinely perform a complete blood count, a serum biochemistry profile and a urinalysis on dogs displaying lameness or other obvious signs of pain, the results of these tests are typically inconclusive when patellar luxation is the culprit, because displacement of the patella is not a disease or systemic disorder. This condition involves only the knee joint(s) and some form of anatomical malalignment of muscle, tendons, supporting soft tissue and bones. Manual palpation of the knee will usually reveal patellar instability in affected animals. The patella may “pop” in and out of place when manipulated. Sedation may be required during this procedure, because it can be quite painful.
Another diagnostic tool available to veterinarians is arthrocentesis, which is the surgical puncture of a joint capsule and aspiration of a synovial fluid sample for laboratory analysis. Radiographs (x-rays) usually are recommended to assess the conformation of the knee joint and of the femoral and tibial long bones of the hind legs. The attending veterinarian may want to radiograph the hip and “ankle” joints as well, especially in advanced or chronic cases. Finally, a computed tomography scan (known as a CT scan or a CAT scan) can be used to visualize the stifle joint in three dimensions; this can be helpful as an aid in formulating a treatment protocol.
Owners of limping or lame dogs are cautioned against manipulating their dogs’ legs without the guidance of a veterinarian or other competent, skilled professional. Stretching, bending, twisting, pulling and pushing on an already-damaged knee joint can worsen the pain and prognosis for a dog with luxating patellas.