Causes of rib notching:

Superior rib notching

Polio
Restrictive lung disease
Neurofibromatosis
Connective tissue disease
Osteogenesis imperfecta
Hyperparathyroidism

Inferior rib notching

Thrombosis of aorta
Coarctation of arota
Blalock Taussig shunt
Occlusion of subclavian artery
Pulmonary AV malformation