Characteristics. The effects of myelomeningocele, the most serious form of spina bifida, may include muscle weakness or paralysis below the area of the spine where the incomplete closure (or cleft) occurs, loss of sensation below the cleft, and loss of bowel and bladder control.pina Bifida means cleft spine, which is an incomplete closure in the spinal column. In general, the three types of spina bifida (from mild to severe) are: 1  Spina Bifida Occulta: There is an opening in one or more of the vertebrae (bones) of the spinal column without apparent damage to the spinal cord.