Ununited Anconeal Process
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 Faxitron
radiograph of a dog's elbow withan ununited anconeal process
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| Ununited anconeal process occurs primarily in
large and giant-breed dogs, most notably German shepherds. The condition is also
recognized with some frequency in chondrodystrophic breeds such as Bassett hounds and
Bulldogs, as a result of retarded ulnar growth resulting in elbow incongruency. Male dogs
are affected approximately twice as frequently as female dogs. The condition is bilateral
in 11-30% of affected dogs. Diagnosis of ununited anconeal process is confirmed by a
flexed lateral radiograph of the elbow. In breeds that are predisposed to ununited
anconeal process, the anconeal process develops as a distinct center of ossification
separate from the ulna. In German shepherd dogs, the anconeal process begins to mineralize
at approximately 12 weeks of age and fuses with the ulna at 16 to 24 weeks of age. A
definitive diagnosis of ununited anconeal process thus should not be made before 24 weeks
of age.
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| Several
radiographs (above) and histologic sections (below) demonstrating the development of the
anconeal process. A. At 10 weeks the anconeal process is completely composed of
cartilage. B. The anconeal process is beginning to mineralize at 12 weeks. C. At 16
weeks the process is nearly completely mineralized, but still separated from the rest of
the ulna. D. At 20 weeks the anconealy process is fused with the ulna. |
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| Gross specimen
and faxitron radiograph of a dog's elbow with and ununited anconeal process. Note the
proximal (abnormal) displacement of the radial head. |
Congruency of the elbow must be
assessed as many dogs (chondrodystrophic and non-chondrodystrophic) with ununited anconeal
process have proximal radiohumeral subluxation.
Secondary degenerative changes of the elbow may be present. Dogs with
ununited anconeal process typically develop an intermittent, subtle to severe lameness of
gradual onset between five and nine months of age. It should be noted, however, that
ununited anconeal process can be a serendipitous radiographic finding in mature and
middle-aged dogs with no prior history of forelimb lameness or can be a cause of acute
forelimb lameness in mature or middled-aged dogs which may not have had any previous
history of lameness.
Excision of the ununited anconeal process is still the most widely accepted treatment
for this condition. If the anconeal process is to be excised, it is removed via a
caudolateral approach to the elbow.
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| The anconeal process is generally not freely
moveable because of numerous fibrous adhesions. These adhesions must be broken down with a
periosteal elevator to remove the anconeal process. |
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Intra operative photography
of a caudo-lateral arthrotomy of the elbow and ununited anconeal process removal. |
| Following surgery the limb is placed in a soft
padded bandage for several days to limit swelling. Exercise is restricted for 21 days;
however, passive flexion and extension of the elbow should be performed during this time.
Although the prognosis for working and athletic dogs with ununited anconeal
process is guarded, many dogs obtain surprising good limb function following process
excision. A recent retrospective study evaluated the long-term (mean follow-up 65 months
following surgery) clinical results in six dogs which had ununited anconeal processes (one
bilateral) excised between five and 12 months of age.
Although degenerative joint disease progressed and range of motion was decreased in all
affected elbows, limb use was considered good to excellent in six of the seven operated
limbs. Others have reported similar results, and we have had dogs with ununited anconeal
process return to hunting, obedience and field trial work after process excision. Some
lameness after vigorous exercise, however, should be expected and medical management of
these dog’s arthritis may be necessary at some point in time.
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Stabilization of the ununited anconeal process utilizing lag
screw fixation have been suggested, but this procedure has met with technical difficulties
and complications and long-term results establishing the efficacy of lag screw fixation
are lacking. One report described radiographic union of six of 10 ununited anconeal
processes stabilized by lag screw fixation. Detail information describing limb
function in these dogs, unfortunately, was not available. |
| Recent reports describe union of the ununited anconeal
process with the olecranon following proximal diaphyseal ulnar osteotomy in young dogs
with proximal humeroradial subluxation. The proximal diaphyseal ulnar osteotomy is
performed to improve elbow joint congruency, and relieve pressure on the anconeal process.
The anconeal process fuses to the ulna in a slightly abnormal position. |
 Radiograph of
a dog that has undergone stabilization of an ununited anconeal process.
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 Proximal
ulnar diaphyseal osteotomy can be performed to treat young dogs with an ununited anconeal
process and elbow incongruity.
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| Radiographs of
a proximal diaphyseal ulnar osteotomy used to sucessfully treat a dog with an
ununited anconeal process. Pre operative (A), Immediate post op (B), 3 weeks (C) and 6
weeks (D) post op. |
| The long-term functional results associated with
proximal diaphyseal ulnar osteotomy appear to be superior in comparison to process
excision. The value of performing osteotomies to improve joint congruency at the time of
anconeal process excision in dogs with proximal humeroradial subluxation has not been
established. Empirically it would seem advantageous to restore normal joint congruency,
particular in dogs with marked subluxation; however, it is not known whether improving
joint congruency results in improved limb function any more than fragment excision alone. |
