Ununited anconeal process

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Ununited anconeal process in a young dog[1]
Ununited anconeal process in a 1 year-old female German Shepherd treated with a 3.5-mm lag screw and a dynamic proximal ulnar osteotomy[2]

Ununited anconeal process (UAP) is a genetic disease of of the canine elbow and a leading cause of elbow dysplasia, commonly seen in large-breed dogs such as the German Shepherd[3].

The condition is characterized by failure of the anconeal process to unite with the proximal ulna within the first 20 weeks of age.

Other breeds affected include several giant breeds and chondrodystrophics, especially the St. Bernard, Basset Hound and Mastiff[4].

The exceptions are the St. Bernard and Basset Hound, in which the anconeal process may fuse as late as 7 - 8 months. Males are most commonly affected, and bilateral involvement does occur.

Clinical signs are usually noted in puppies between 4 to 8 months of age. Joint effusion and varying degrees of pain on elbow manipulation may be noted.

While a presumptive diagnosis may be made upon assessment of breed and clinical examination (palpation of the shoulder is generally non-rewarding), radiography is necessary for definitive diagnosis. The presence of a lucent line on radiographs confirms the diagnosis in dogs over 6 months of age.

A differential diagnosis would include osteochondrosis, osteomyelitis, osteochondritis dissecans, fragmented coronoid process, panosteitis and hypertrophic osteodystrophy.

Treatment for young dogs is best achieved with corrective surgery, usually involving removal of the anconeal process, use of lag screws or use of dynamic proximal ulnar osteotomy to address the incongruity[5].

Removal of the anconeal process, while effective in some cases, does produce a more unstable joint, progression of degenerative joint disease, and clinical lameness in up to half of patients[6]. Anconeal process removal is primarily reserved for older patients where severe degenerative changes preclude any semblance of a normal joint after ulnar osteotomy or lag screw fixation[7].

The placement of lag screws to stabilize the anconeal process have frequently resulted in the failure of the implant by breakage.

The decision on whether to do a proximal ulnar osteotomy alone or in conjunction with a lag screw appears to be based to some extent on the patient’s age. The younger the patient when the osteotomy is done the more likely radiographic fusion will occur, even when a screw is not placed[2].

Supportive use of carprofen or meloxicam is recommended for palliative control of pain.


  1. Vet Surgery Central
  2. 2.0 2.1 Harasen G (2009) Orthopedics: Ununited anconeal process. Can Vet J 50(8):877-878
  3. Cross AR & Chambers JN (1997) Ununited anconeal process of the canine elbow. Compend Contin Educ Pract Vet 19:349–360
  4. Piermattei DL et al (2006) Handbook of Small Animal Orthopedics and Fracture Repair. 4th ed. St. Louis: Elsevier. pp:339–344
  5. Roy RG et al (1994) A retrospective long-term evaluation of ununited anconeal process excision on the canine elbow. Vet Comp Orthop Traumatol 7:94–97
  6. Sjöström L et al (1995) Ununinted anconeal process in the dog. Pathogenesis and treatment by osteotomy of the ulna. Vet Comp Orthop Traumatol 8:170–176
  7. Vezzoni A (2002) Dynamic ulna osteotomies in canine elbow dysplasia. 27th Proceedings, World Small Anim Vet Assoc Congress Granada, Spain