Bayne classified ulnar dysplasia according to the morphology of the ulna and elbow:
- I - hypoplasia:
- ulna hypoplastic with presence of distal and proximal ulnar epiphyses
- frequently minimal deformity or shortening
- slight ulnar deviation of hand
- minimal bowing of radius
- II - partial aplasia:
- absent distal or middle third of ulna
- fibrous anlage distally that may cause progressive ulnar deviation
- progressive radial bowing
- stable elbow
- III - complete aplasia:
- total agenesis of ulna with often a fibrous anlage in its place
- radius often straight
- unstable elbow
- severe deficiencies of hand and carpus
- IV - synostosis:
- entire limb is shortened
- fusion of radius to humerus produces a stable elbow
- progressive ulnar deviation due to a distal ulnar anlage
Type II is the most common abnormality.
Ref: Bayne LG (1985); Hand Clin 1(3): 457-465.