Elbow Dysplasia and Surgical Correction

April 21, 2019

Ununited Anconeal Process or UAP in Dogs

The elbow joint is made up of 3 separate bones, the radius, the ulna, and the humerus. A problem called elbow dysplasia is a developmental abnormality that occurs in the elbow joint of dogs, mostly of the medium to large breeds. There are 3 developmental problems that may be called elbow dysplasia, namely a fragmented coronoid process (FCP), an ununited anconeal process (UAP), and osteochondritis dissecans (OCD). Dogs with elbow dysplasia typically have only one of the three conditions, and it is rare for a single dog to have all three components of elbow dysplasia.

What is an Ununited Anconeal Process?

The anconeal process is a small projection of bone on the ulna, the longer of the two bones of the forearm. The anconeal process forms part of the back surface of the elbow joint. There is a growth plate between the anconeal process and the rest of the ulna.

Growth plates are found at the ends of the bones in growing animals, and are the sites of bone growth during development. Normally, as the dog reaches puberty, the growth plates close, fusing the parts of the bone together. The growth plate between the anconeal process and the ulna normally fuses by about 5 months of age. If the anconeal process does not fuse to the rest of the ulna correctly, it causes a condition called Ununited Anconeal Process (UAP). This condition is one of three conditions that are sometimes also called “elbow dysplasia”. 

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Is this condition hereditary?

This problem does appear to be hereditary in certain breeds, mostly large breeds. In affected animals, there appears to be an abnormality in the growth plate and the anconeal process fails to fuse or unite to the main part of the ulna. German Shepherds seem to be particularly affected by the problem, although it does occur in other breeds, and males are more commonly affected. There may be dietary factors involved in the development of this condition, since there is a correlation between diets that contain too much energy and calcium and the development of elbow dysplasia. 

What are the symptoms of UAP?

When this part of the ulna does not fuse, the elbow joint becomes unstable, causing lameness and pain. The instability causes inflammation, and eventually the inflammation and instability will lead to the development of degenerative joint disease or arthritis. In some cases, the bone fragment floats freely in the joint, causing further discomfort.

Dogs with this disease are lame on the affected leg or legs and they may cry when the elbow is extended. Often the affected elbow joint has a decreased range of motion.

How is the condition diagnosed?

The results of a physical examination are often highly suggestive of this problem. However, other conditions can cause elbow dysplasia, including fragmented coronoid process (FCP) and osteochondritis dissecans (OCD). UAP can be diagnosed by means of radiographs of the elbow. In some cases, this may require a short-acting anesthetic or sedative in order to achieve the optimal positioning for diagnostic purposes. In some cases, it may be necessary to have the x-rays examined by a veterinary radiologist for confirmation of the diagnosis.

How is UAP treated?

Treatment requires surgery. The traditional treatment is removal of the anconeal process from the joint. A more recent approach to surgery is to use screws to reattach the anconeal process to the ulna. Your veterinarian may recommend a referral to an orthopedic surgeon for surgical correction, depending on the case. In all cases, surgery should be performed as soon as possible, and results are much better if surgery is done before secondary arthritis affects the joint.

What is the prognosis with and without surgery?

If the ununited anconeal process is not treated surgically, the lameness will progress rapidly and the dog will be in severe pain. If surgery to reattach the UAP is delayed, or if the condition is severe, the fragment edges may not match well because of the erosion of bone and cartilage, so the piece may not be easily fixed in place. Since the condition is caused by a developmental defect, it is also possible that healing will be slow.

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In all cases, some degree of arthritis will develop in the elbow joint, but with surgical treatment, the arthritis will usually be less severe and there will be less pain involved. Medical treatment such as joint protective supplements and/or anti-inflammatory medications may be recommended to delay progression of degenerative joint disease.  

What is a fragmented coronoid process?

“FCP is a developmental defect of one of the coronoid processes…”

FCP is a developmental defect of one of the coronoid processes, two small bony protrusions on the end of the ulna within the elbow joint. In this condition, one of the coronoid processes develops a fissure or crack and separates from the rest of the bone. It most commonly occurs on the inner, or medial, process. This separation causes pain and joint instability.

Is this condition hereditary? 

A genetic component is likely involved, and males appear to be more commonly affected. The problem is usually seen in large breed dogs such as Bernese Mountain Dogs, Golden Retrievers, Labrador Retrievers, Rottweilers, and German shepherds. Some researchers believe that this condition is another manifestation of OCD. FCP has also been associated with excessive calcium levels in the diet and/or with excessively high calorie diets. 

What are the symptoms of FCP?

With this condition, lameness usually develops in the foreleg of young dogs that are between 5 and 11 months of age. The dog will have a mild to moderate weight-bearing lameness. Dogs with this disease are lame on the affected leg or legs and they may cry when the elbow is palpated (felt and manipulated). In many cases, the affected joint will be swollen and warm to the touch. The elbow joint will have a decreased range of motion, or decreased mobility, on an orthopedic examination. It is relatively common for the condition to develop in both elbows, although it is usually worse on one side than the other.

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How is FCP diagnosed?

Because of the possibility of permanent lameness, your veterinarian will recommend diagnostic testing, in the form of radiographs (x-rays) if any lameness lasts more than 2 weeks in a young, large breed dog. Several radiographs of each affected leg, with the leg in different positions, are necessary in order to get an accurate assessment of various bones and joints. In many cases, this will require a short-acting anesthetic or sedative in order to achieve the optimal positioning for diagnostic purposes. In dogs under 6-7 months of age, x-rays can be challenging to interpret due to the presence of “growth plates.” To reach the diagnosis, it may be necessary to have the x-rays examined by a veterinary radiologist.

In some cases, the FCP may not be seen on standard radiographs. Rather, secondary signs associated with degenerative joint disease are seen. With FCP, a diagnosis may be made relatively early in the course of the condition using computerized tomography (a “CT scan”).

What is the recommended treatment for FCP?

Surgery is the treatment of choice for this condition, and its aim is to remove any abnormal cartilage or bone and attempt to return the joint to a more normal anatomy and function. The procedure may involve a surgical exploration of the joint or an arthroscopic repair. Arthroscopic repair may be the preferable technique because the smaller incision means that there is less damage done to the supporting structures (the joint capsule and ligaments). Your veterinarian may recommend referral to an orthopedic surgeon for this procedure.

What is the prognosis with and without surgery?   

If the joint is not treated surgically, degenerative changes will rapidly develop and the dog will suffer from chronic pain. Surgical treatment of FCP should be performed as soon as possible after diagnosis to minimize the development of degenerative joint disease.

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In all cases, some degree of arthritis will develop in the elbow joint, but with surgical treatment, the arthritis will usually be less severe and there will be less pain involved. Medical treatment such as joint protective supplements and/or anti-inflammatory medications will usually be recommended to delay progression of degenerative joint disease.

Will my dog need rehabilitation?

Some form of rehabilitation will improve your dog’s chances of making a full recovery from surgery, and minimize lameness problems. You will need to restrict your dog’s exercise for the first few weeks to months after surgery, which usually means that your dog will only be allowed to go for controlled leash walks. If the UAP is reattached to the ulna with a screw, it is recommended that weight-bearing activities be restricted until healing is complete, for up to 8 to 12 weeks in some cases.

Your veterinarian will design the appropriate program for your dog, or if a canine rehabilitation program is available in your area, may refer your dog for treatment.

My veterinarian has recommended surgically sterilizing my dog. Why is this?

Since the condition appears to be hereditary, affected dogs should not be used for breeding.

If your dog is a purebred, you should notify your breeder. Many breeders of large breed dogs have their breeding stock cleared for this condition (called elbow certification) prior to using them in a breeding program.

Cheryl Yuill, DVM, MSc, CVH

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