Presentation
Prsents with an abnormal gait.
Patient Data
Left thoracic limb: The radius is absent and the ulna is hypertrophied to approximately 2-3x its normal width. The proximal radius forms a good articulation with the distal humerus. Although there is no visible proximal radius, there may be a remnant of radius fused to the proximal ulna creating a relatively normal articulation (compare to left). There is carpal varus due to the lack of radiocarpal articulation. The radiocarpal bone is absent.
Right thoracic limb: There is a small triangular bone representing a vestigial radius near the elbow. The elbow joint is less congruent compared to the left. The ulna is hypertrophied similar to the left thoracic limb. There is caudal bowing of the ulna on the lateral projection and marked carpal varus on the craniocaudal projection. The radiocarpal bone is absent.
Developmental disorder involving agenesis of the radius and absent radiocarpal bones.
Case Discussion
Radial agenesis may also be termed intercalary hemimelia. In the absence of the radius, the ulna remodels according to Wolff's law, becoming larger and altering shape to best distribute the forces along the limb and stabilize the elbow joint.
Radial hypoplasia is often accompanied by absent radiocarpal bone and polydactyly. Cardiomegaly and vertebral anomalies have also been reported. It is most likely to be a heritable condition although nutritional and toxic disorders are also possibilities.
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