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

Background: We created abdominal wall defects (AWD) in fetal lambs to investigate possible causes of scoliosis.

Methods: 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.

Results: 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 59.6^o and 60.6°. Overall, 4/5 lambs with organ prolapse (80%) and both lambs without organ prolapse had scoliosis.

Conclusion: Muscle imbalance may contribute to the development of scoliosis in a fetal lamb AWD model.