Muscle imbalance as a cause of scoliosis: a study in a fetal lamb abdominal wall defect model.

We created abdominal wall defects (AWD) in fetal lambs to investigate possible causes of scoliosis. We incised the upper abdominal wall (including Rectus) in 60-day gestation fetal lambs, from the midline to either the right (Group A) or left (Group B) costal margin, in 14 lambs carried by 7 ewes. They were delivered by cesarean section at term (about 145 days). Scoliosis was evaluated by anterio-posterior X-rays, determining the Cobb angle. Four fetuses in Group A and 3 in Group B survived. There were 3 successful AWD lambs Group A and 2 in Group B. One lamb in each group survived with the AWD covered with a thick capsule. The convexity of spinal curve was the direction of scoliosis. Right scoliosis was only seen in the 4 Group A lambs. Left scoliosis was only seen in Group B lambs (2/3, 67%). The mean Cobb angle was 41.7 ± 11.5° in Group A and in Group B the Cobb angles were 59.6o and 60.6°. Overall, 4/5 lambs with organ prolapse (80%) and both lambs without organ prolapse had scoliosis. Muscle imbalance may contribute to the development of scoliosis in a fetal lamb AWD model.