Yorkie Haven Rescue is pleased to present the below article regarding Patellar Luxation which was superbly written and graciously provided by Dr. Brian S Beale of Gulf Coast Veterinary specialists in Houston, TX. He has also written and provided us with another article about Patellar Luxation.

Yorkie Haven has entrusted all of our orthopedic cases in the Houston area to Dr. Beale's expertise. He has been a wonderful surgeon; and he and Kate Lawrence, Client/Patient Service Coordinator, have been a valuable resource for our rescue pups as well as some of our own. It is our hope that these articles will be a resource for many yorkie owners (and other breeds as well).

The most common injury of the hind limb we see in dogs is a tear of the cranial cruciate ligament (CrCL). On average, we see 
20 patients with this injury every week at Gulf Coast Veterinary Surgery. Cranial cruciate ligament tears occur in dogs of 
all sizes and all ages. Toy breed dogs such as the Yorkshire Terriers, Maltese, Shih Tzus and Toy Poodles are commonly 
affected. Many tears begin as a partial tear and gradually progress to a complete tear. Other tears occur acutely as a 
complete tear. The tear can occur as a result of acute trauma or more commonly as a result of chronic repetitive injury.  
The chronic repetitive injury is influenced by the degree of angulation of the top of the shin bone (slope of the tibial 
plateau). Tears of the CrCL are also common in toy breeds having long-standing medial patellar luxation. This is due to the 
increased stress placed on the CrCL when the patella is luxated. Other risk factors that increase the chance of CrCL tear 
include genetic factors, excessive weight and high-risk exercise.

Consequences of a CrCL tear
Tearing of the cranial cruciate ligament leads to instability of the knee joint. The instability causes the joint surfaces 
to slide excessively against each other, leading to damage to the joint.  This damage includes arthritis, cartilage erosion, 
meniscal tears, joint capsule thickening and bone spurs.  Even dogs with partial tears and minimal instability develop 
progressive arthritis. Arthritis cannot be reversed so it is important to stabilize the knee to prevent progression of 
arthritis and the pain and decreased function that occurs as a result. A delay in treating a dog with a CrCL tear can also 
lead to an increased chance of tearing the CrCL in the opposite hind limb due to the increased forces placed on the “good” 
leg.  We have many patients who come in for treatment with CrCL tears of both knees at the same time. I cannot stress enough 
the importance of treating this condition early to increase the chance of preserving normal function of the knee and 
decreasing the chance of the same injury in the opposite knee.

Clinical Signs
Clinical signs of CrCL injury vary depending on the type of tear, chronicity and the size of the patient. The most obvious 
clinical sign is sudden lameness of the hind leg. This lameness may appear to improve over 4-5 days, but this is only 
because the acute inflammation has subsided. The knee continues to be unstable and the arthritic time bomb begins to tick! 
Other clinical signs that your dog may be have a tear of the CrCL include unwillingness to sit squarely (hind legs may splay 
to side slightly), difficulty rising from a laying position, reluctance to jump or go up stairs and pain on extension of the 
knee.  Arthritis progresses much more rapidly in dogs than in man. As arthritis becomes more severe, the clinical signs 
mentioned above become more obvious and the joint also starts to thicken and become stiff.

Diagnosis
A tear of the cranial cruciate ligament can be diagnosed quickly and with minimal expense. Most patients can be diagnosed 
with a simple orthopedic examination. Your veterinarian will look for cranial drawer instability, swelling and pain of the 
stifle. A radiograph (x-ray study) will help to confirm the diagnosis and is used to help plan the surgical treatment. The 
radiograph is used to assess the slope of the tibial plateau. The greater the slope the more stress on the CrCL.  Dogs with 
a steep slope are best treated with a method that lowers the slope to prevent a recurrent CrCL tear. The radiograph is also 
helpful in assessing the amount of arthritis that is already present prior to stabilizing the stifle.

Treatment Strategy
Some veterinarians and pet enthusiasts recommend conservative treatment of CrCL tears for a period of time, but this is 
rarely successful and is not a good course of action to follow. Conservative treatment leaves the knee unstable for a long 
period of time allowing the onset of progression of osteoarthritis and meniscal tears.  Osteoarthritis can progress very 
insidiously in the early stages, giving the impression that the dog is improving. This is because the lameness may appear to 
improve as the acute inflammation inside the knee joint subsides. However, as the arthritis progresses over the months and 
years to follow, lameness and stiffness ensue. Many pet owners have difficulty recognizing this and believe their dog has 
recovered.  An orthopedic specialist can alert owners to the decreased function and pain the dog is actually experiencing. 
Dogs are very clever at modifying their posture, gait and activity level to lessen the pain and functional deficit they are 
experiencing. These clinical signs become more obvious when arthritis becomes severe. Unfortunately, surgical treatment of 
the CrCL may be less successful at this time due to the presence of irreversible arthritis and fibrosis of the joint. The 
best recommendation is surgical stabilization of the joint as soon as possible. It has been shown that early treatment of 
partial tears leads to preservation of the CrCL, minimal to no arthritis and a very low chance of future meniscal tears.

Surgical Treatments
Several surgical options are routinely performed at Gulf Coast Veterinary Surgery to treat toy breed dogs with CrCL tears.  
The most common procedures used are the extracapsular prosthetic ligament repair (EPLR), the tibial plateau leveling 
osteotomy (TPLO) and the tibial tuberosity advancement (TTA).  An orthopedic specialist will evaluate each dog to determine 
the surgical method that will most likely to lead to a permanent repair, minimal chance of future arthritis and meniscal 
tears and result in the most normal long term function in that particular individual.  Many criteria are evaluated to reach 
the correct decision for the dog.  The surgeons of Gulf Coast Veterinary Surgery are particularly concerned about selecting 
a technique that will last the lifetime of the dog and have a lower chance of failure. We have had the opportunity to see 
many dogs present to us with failed repairs performed elsewhere due to selection of a technique that was not optimal for 
that particular patient. If medial patellar luxation is also present, this condition can be repaired at the same time 
through the same incision.  Most patients are limited to walking exercise for 6-8 weeks postoperatively. Prognosis is 
excellent after surgical repair. The patient is expected to return to normal activity and function as long as the condition 
is treated prior to the onset of substantial arthritis. 

What About Arthroscopy?
Arthroscopy is the gold standard for repair of tears of the anterior cruciate ligament (synonymous to the CrCL in the dog) 
in humans. It is now the gold standard in dogs and cats as well. Arthroscopic treatment of CrCL tears has been performed on 
a routine basis in dogs and cats at Gulf Coast Veterinary Surgery for the past 15 years.
Arthroscopy of the knee can be performed on dog and cats of all sizes. The most obvious advantage to the pet and pet owner 
is the much smaller incision, quicker recover and less pain following surgery. Arthroscopy is a minimally-invasive method of 
treating the dog with CrCL tears and can be used with EPLR, TPLO and TTA. The greatest advantage for the surgeon is the 
magnification provided by the scope which allows more accurate assessment and precise treatment of the damaged ligament and 
meniscus. The arthroscope is very small (1.9-4.0 mm diameter) and can be easily inserted into inaccessible areas of the 
joint allowing a more complete evaluation and treatment of damage that may have been left behind with a traditional open 
incision.

Key Take Home Points:
1.	CrCL tears lead to instability of the knee, resulting in pain, arthritis and meniscal tears.
2.	Dogs often tear their opposite CrCL, especially if the treatment of the first leg is delayed.
3.	Medial patellar luxation increases the chance of CrCL in toy breeds.
4.	Surgical stabilization of the knee is recommended as soon as possible after a tear of the CrCL to avoid irreversible 
arthritis
5.	The TPLO is the only procedure shown thus far to result in minimal osteoarthritis, minimal chance of meniscal tears 
and prevention of further tearing of the CrCL in dogs that have a partial CrCL tear.