Hello, I am Dr RB and I am a licensed veterinarian. I am so sorry to hear Gracie hasn't been feeling well! A few things first.. Does Gracie like to jump on and off of furniture? Most Chihuahua's are pretty active and it can be difficult to keep them still but when I hear of a sudden reluctance to use a limb, traumatic injury is usually at the middle of it. Being 9 years old, Gracie may have some of the early signs of arthritis in her joints. This may make her not as agile as before and more prone to injury herself! When dogs do not want to put weight down in a rear leg, the source is either hip injury pain or knee injury pain. Hip pain in an older dog can be from arthritis and can be worsened by injury. Knee pain in small breed dogs is usually due to a patellar luxation or an partial or complete tear to the cruciate ligament in the knee.
Patella luxation occurs when the knee cap will temporary pop in and out of the groove in the larger bone of the knee (tibia). Dogs that have a luxating patella will often run with one leg up and skip; sometimes you will see them kick one leg out to the side and then place weight back on the limb. It can become painful when the patella won't "pop" into place or if arthritic changes in the knee occur. Sometimes surgery is needed to help this.
The cruciate ligaments in our knee are involved in holding out knee in the proper placement. An injury can partial tear or completely tear one or more of these ligaments, thus making it painful to put weight on the affected limb. A partial tear usually results in less severe pain and can be treated with pain medication and anti-inflammatory medications in addition to rest. A complete tear in a cruciate ligament may require surgery.
My advice to you in the short term is to allow Gracie strict rest for several days. Keep her in a small room or crate for most of the day with only short walks outside to use the restroom. Don't allow her to run, jump on/off furniture or climb stairs, or any rough play. This will prevent her from furthering injury herself until you can make an appointment with your regular veterinarian. Once she is examined by her vet, he/she will be able to determine from the exam what area of the leg is likely the source of the pain. They may or may not recommend x-rays of the limb. Gracie may need some anti-inflammatory medications in addition to rest to help her feel better. Since she is 9 years old, I would also talk to your vet about starting her on a daily joint supplement to slow any progression of arthritis:)
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