Radial agenesis

From Dog
Radiograph of a dog with radial agenesis showing complete absence of the radius and poor congruency of the humeroulnar joint[1]

Radial agenesis (radial hemimelia) is an autosomal-recessive genetic disease of dogs characterized by abnormally deformed or absent radius.

The etiology of radial hemimelia is considered to be a combination of genetic and environmental factors[2][3]. Also different teratogenic agents have been related to congenital defects [4].

In dogs, radial agenesis usually begins to manifest at around day 23 - 35 of gestation. Both the radius and ulna can be affected[5] and affected limb(s) are usually shortened with a varus deformity and are not functional or gaiting.

If all or part of the middle bones of a limb are absent, with the proximal and distal portions being present, the hemimelia is called intercalary. Preaxial longitudinal intercalary radial hemimelia is the most common type of hemimelia in dogs and may occur unilateral or bilaterally.

A predisposition is seen in certain small breeds dogs such as the Boxer[6], Chihuahua and Shih Tzu and the genetic defect results in failure of growth-plate activity within the distal radius.

There may be complete or partial agenesis of either one or both radii with a compensatory increase in the diameter of the ulna. Congenital, bilateral, terminal anterior hemimelia in two families of Chihuahua dogs has been reported[7].

Affected dogs usually present at birth with unilateral or bilateral forelimb lameness and deformity.

Radiography and CT imaging are usually diagnostic, showing loss or absence of normal distal radial development and deformity of ulna and ulnocarpal joint[8].

A differential diagnosis would include osteogenesis imperfecta, elbow dysplasia, nutritional secondary hyperparathyroidism and hypertrophic osteodystrophy.

This condition may also observed in the polygenic disorders such as craniomandibular osteopathy[9] and polydactyly.

Depending on the severity of the defect and client compliance, surgical correction can be attempted to improve limb function and mitigate the inevitable progression of osteoarthritis in the elbow and carpus.

Numerous osteotomy and stabilization techniques have been employed, including ulnocarpal arthrodesis[10], the use of external coaptation[11], linear external fixators[12], bone plates and screws[13] and circular external fixators[14].

References

  1. Veterinary Research Institute
  2. Lenz W (1980) Genetics and limb deficiencies. Clinical Orthopedics and Related Research 148:9–17
  3. Alonso RA et al (1982) An autosomal recessive form of hemimelia in dogs. Vet Rec 110:128–129
  4. Jonson AL (1995) Growth deformities. In: Olmstead M.L. (ed.): Small Animal Orthopedics. Mosby Year Book Ink, St Louis. pp:293–309
  5. Lewis RE & Van Sickle DC (1970) Congenital hemimelia (agenesis) of the radius in a dog and a cat. J Am Vet Med Assoc 156:1892–1897
  6. McKee WM & Reynolds J (2007) Ulnocarpal arthrodesis and limb lengthening for the management of radial agenesis in a dog. J Small Anim Pract 48(10):591-595
  7. Alonso RA et al (1982) An autosomal recessive form of hemimelia in dogs. Vet Rec 110(6)':128-129
  8. Meola SD et al (2008) Validation of a technique to assess radial torsion in the presence of procurvatum and valgus deformity using computed tomography: a cadaveric study. Vet Surg 37(6):525-529
  9. Pettitt R et al (2012) Bilateral angular carpal deformity in a dog with craniomandibular osteopathy. Vet Comp Orthop Traumatol 25(2):149-154
  10. Hildreth BE & Johnson KA (2007) Ulnocarpal arthrodesis for the treatment of radial agenesis in a dog. Vet Comp Orthop Traumatol 20(3):231-235
  11. MacDonald JM & Matthiesen D (1991) Treatment of forelimb growth plate deformity in 11 dogs by radial dome osteotomy and external coaptation. Vet Surg 20:402–408
  12. Quinn MK et al (2000) Realignment of the radius in canine antebrachial growth deformities treated with corrective osteotomy and bilateral (type II) external fixation. Vet Surg 29:558–563
  13. Balfour RJ et al (2000) T-plate fixation of distal radial closing wedge osteotomies for treatment of angular limb deformities in 18 dogs. Vet Surg 29:207–217
  14. Theyse LF et al (2005) Prognostic factors in treating antebrachial growth deformities with a lengthening procedure using a circular external skeletal fixation system in dogs. Vet Surg 34:424–435