This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Note for Pet Owners:
In the UK the British Veterinary Association and the Kennel Club have launched a grading system based up on Guidelines drafted by the International Elbow Working Group to screen and identify dogs with Elbow Dysplasia (of which Ununited Anconeal Process is one of the causes). Because genetic inheritance is an important factor, owners should not breed from affected dogs. Your veterinarian can provide you with more information on the Scheme- or Provet will be pleased to send you more information email 

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The anconeal process is a bony protrusion which forms part of the ulna bone at the back of the elbow joint. In very young animals this part of the ulna is still cartilage and bone is laid down from within it's own ossification centre. Sometimes, the anconeal process does not fuse on to the main body of the ulna, in which case it forms a separate bone and is called an ununited anconeal process.

On this XRay of the  flexed elbow of a young dog with the condition, you can clearly see a dark line like a fracture line (labelled DL) which separates the ununited anconeal process (labelled AP) from the ulna (labelled U)


A genetic predisposition to develop ununited anconeal process is thought to exist in the German Shepherd Dog, Bassett Hound and St Bernard. A genetic basis has not yet been confirmed for other breeds. The disorder is not caused by a single gene- it is controlled by the combined effect of many genes (called polygenic) 

Because inheritance may be important owners should have their animals screened by XRay and they should not breed from affected individuals.

Other possible causative factors include :

  • Trauma to the anconeal process which might cause a fracture along the line separating the developing process from the ulna bone. 
  • Other orthopaedic conditions such as short radius disease may play a role, as pressure put on the lower part of the humerus by the radius may push the humerus backwards causing sheering forces along the line along which the anconeal process should fuse to the ulna.

Breed Occurrence
Ununited anconeal process usually affects large and giant breeds of dog including the Afghan, Bullmastiff, French Bulldog, Great Dane, Irish Wolfhound, Labrador Retriever, Pointer, Pyrenean Mountain Dog, St Bernard and Weimeraner. It has also been reported in achondroplastic breeds - the Bassett Hound and the Dachshund. However, by far the most frequent number of reported cases come from German Shepherd Dogs.

The elbow is a hinge joint, and having a piece of bone (the ununited anconeal process) free at the back of the hinge makes the joint unstable. In addition, chemicals that cause inflammation are released into the joint from the fracture surface. 

Signs usually appear as an intermittent lameness at 5-9 months of age. The condition most often only affects one elbow - but it can affect both.

Some dogs may not show any apparent sign of lameness.

Because an ununited anconeal process is in effect a fracture within a joint, it causes the release of inflammatory products into the joint, and it results in abnormal wear within the elbow joint. Both of these result in degenerative changes (osteoarthrosis) as an inevitable consequence - which can cause long term joint pain and lameness.

Flexing.and extending  the elbow joint usually causes a grating feeling (crepitus), and the animal may feel moderate pain. Sometimes the elbow joint is swollen with fluid.

The diagnosis is confirmed by taking XRays of the elbow joint. The flexed lateral view is best as this throws the anconeal process away from the other bony structures of the elbow - making it easier to see.

Strict rest with external support can result in fusion in very young animals. However, because of the potential for secondary osteoarthritic change most orthopaedic specialists prefer to operate early to either :

  •  Fix the anconeal process in place (using a lag screw technique) to try to achieve healing across the non-union, or
  • Remove the bony fragment from the joint.

Fixing the process back to the ulna can only be carried out if there is little or no evidence of osteoarthrosis in the joint. Removal of the fragment is a very rewarding procedure and is the one most often performed in first opinion practice.

The long term prognosis for these cases is generally good, although some dogs will have a reduced range of movement within the joint, and some will develop chronic degenerative joint disease.  

Long term problems
Osteoarthritis and intermittent lameness can be a permanent sequele.


Updated October 2013