Signalment & History
- This patient presents to your clinic to evaluate an angular limb deformity in the left thoracic limb.
- You order left radial/ulnar radiographs.
Findings
- The radius is absent. There is moderate incongruity and osteophyte formation associated with humeroulnar joint.
- The distal ulna is irregularly shaped and the cuboidal bones or the carpus are disorganized.
- There is 90 degrees lateral angulation of the metacarpal bones relative to the ulna and there is luxation of the radiocarpal joint.
Diagnosis
- This patient is diagnosed with radial agenesis (radial hemimelia) with severe carpal valgus, antebrachiocarpal luxation and humero-ulnar osteoarthrosis.
Radial Agenesis
- Radial agenesis is defined as the congenital underdevelopment or absence of the radial structures of the forearm. It is the most frequent hemimelia reported in the dog and cat. The involvement of a single limb is most common, however, bilateral cases have been reported.
- There may be complete or partial agenesis of either one or both radius.
- The total absence of the radius is often accompanied by complete or partial absence of the radial carpal bone and first digit.
- The radial absence usually results in severe deformity and impaired function
- The ulna becomes thickened and curved due to increased load bearing, and the paw develops a varus deformity because of loss of medial support structures and contracture of extensor tendons
- The elbow joint is also affected due to the presence of humeroulnar subluxation secondary to lack of support from the radial head. Secondary fractures can also occur.
- It has also been reported less common in the tibia. In this case, the fibula is markedly enlarged.
- It has been considered as possible causes the presence of a trait may be heritable in some cases. Another hypothesis is that hemimelia results from an injury to the neural crest by a teratogen in utero and that the pattern of deformity follows the distribution of sensory nerves. The sensory nerve tissue may exert a trophic effect on the developing embryonic limb tissues, and therefore in their absence, normal development does not occur.
- Various aetiological factors have been also proposed, including inflammatory or infectious conditions, vaccines maternal disease, malnutrition and various drugs, for example, Thalidomide.
- Treatment of choice for unilaterally affected animal is considered to be limb amputation.
- Euthanasia may be necessary if limb function is severely affected bilaterally.
References
- Winterbotham. E. Johnson, A. Francis. D. Radial agenesis in a cat. Journal of small animal practice. (1985) 26, 393-398.
- Jezyk, P. Constitutional Disorders of the Skeleton in Dogs and Cats. Textbook of Small animal Orthopedics, C.D. Newton and D.M. Nunamaker (Eds). Publisher by International Veterinary Information Service, Ithaca, New York. USA.
- O’Brien, CR. Malik, R. Ncoll, RG. What is your diagnosis? Journal of Feline Medicine and Surgery 92002) 4, 112-113.
