The anconeal process is found in the elbow. It is a “keel” of bone on the ulna (one of the bones of the forearm) which slots into the back of the humerus (the bone of the upper arm) and which gives stability to the elbow when that joint is in extension.
The anconeal process develops as a separate area of bone from the rest of the ulna, and should fuse with it by 5 months of age. Sometimes this doesn’t occur and the anconeal process is said to be “un-united”. The un-united anconeal process (UAP) is loose and floating within the joint, and occasionally we have seen this associated with the development of infection in the joint. The floating UAP causes lameness, pain and discomfort, especially on elbow extension.
Certain breeds are predisposed to UAP. These include German Shepherd dogs and Wolfhounds, and sometimes UAP occurs because the ulna growth is retarded because of growth plate issues at the bottom of the forearm which (amongst other things) causes the anconeal process to impinge on the back of the humerus.
The UAP can be addressed in one of two ways. It can be treated as a fracture and fixed with metal work or it can be removed.
Fixation presents some problems:
The fragment is small
It is soft bone
It doesn’t always “fit” very well onto the adjacent ulna
There is only room for one implant so the fragment can move on the implant to some degree
Implant placement requires very accurate drilling
If the implant is too long, it will penetrate into the joint
The ulna often needs to be cut to prevent the fixed UAP from impinging on the humerus which would predispose to fixation failure (see separate article on dynamic ulna osteotmy
The patient (a puppy) needs to be strictly confined in the early post-operative period.
Removal of the fragment has some advantages:
It is a cheaper and easier procedure
There is no metalwork to create technical problems
There is no need to cut the ulna
The need for exercise restriction post-op is less critical
The outcome is more predictable.
On the other hand, the keel stability usually provided by the AP is missing if the fragment is removed, and the missing stability must then be provided by the development of fibrosis and thickening of the periarticular structures.
In both scenarios, some degenerative joint disease, commonly called osteoarthritis, is to be expected in the long term.
25th June 2014