In children with or at risk of developing Thoracic Insufficiency Syndrome, the expandable rib prosthesis devices mechanically stabilize and/or correct thoracic deformities to allow the chest and lungs to grow. The devices are attached perpendicularly to the subject's natural ribs and lumbar vertebra or pelvis. This mechanically stabilizes the chest wall and enlarges the thorax to improve respiration and lung growth. The devices allow assembly in a number of different configurations to accommodate the wide variety of anatomical deformities encountered by the clinician in treating patients with or at risk of developing Thoracic Insufficiency Syndrome.