There may be asymmetry of the chest and the sternum may be rotated.
Most patients have a slim chest, a slouching posture and younger children commonly have potbellies.
The deformity is thought to be caused by excessive growth of the costal cartilages although the reason for this is unknown. This overgrowth causes the ribs and cartilages to 'buckle' and pushes the sternum either inwards or outwards. The deformity is often noticeable at birth but becomes more apparent during the period of rapid skeletal growth in early adolescence. After the age of approximately 18 years of age the deformity remains the same.