UNUNITED ANCONEAL PROCESS
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
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
Topics on this Page:
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
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
Because inheritance may be important owners should have their
animals screened by XRay and they should not breed from affected individuals.
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.
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
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
Some dogs may not show any apparent sign of lameness.
ComplicationsBecause 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
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
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
Updated October 2013