Sacral agenesis

Sacral agenesis is a genetic condition which affects the sacrum, which is the part of the spine just around the ‘tailbone’.

The sacrum is formed by five bones (vertebrae) that are joined together. Children with sacral agenesis are born with part or all of their sacrum missing. The sacrum gives the buttock it’s rounded shape, which is important for the placement of the pelvis and acts as passageway for some of the nerves from the spinal cord.

Sacral agenesis is a rare type of spina bifida and is also known as caudal regression syndrome or caudal dysplasia. Sometimes parts of the vertebrae higher up in the spine can be missing too. When it extends to the lower back region it is called lumbo-sacral agenesis. Sacral agenesis can extend further again into the middle section of the spine, but this is very rare.

Signs and symptoms

  • A shorter body in comparison to other children.
  • A flattened buttock due to missing muscle bulk.
  • An abnormal curvature of the spine.
  • An irregular shaped chest and/or small hip bones.
  • Missing lower limbs or lower limb differences.

Having some or all of these bones missing may lead to disruptions of the nerve supply to the lower half of the body. This is because the nerves leading from the sacral spine deliver messages to and from the bowel, bladder and muscles of the lower limbs and provide feedback to the brain.

These disruptions to the lower body nerve supply can lead to bowel, bladder and walking problems such as:

  • Urinary problems which may involve incontinence, urinary tract infections and kidney damage due to bladder dysfunction.
  • Bowel problems can include constipation and faecal incontinence.
  • Lower limb paralysis and decreased muscle strength can also occur, affecting mobility.
  • Lower limb complications can range from very minor walking difficulties to complete paralysis of the lower limbs requiring the use of a wheelchair.

Some children with sacral agenesis may also have lower leg deformities which may require orthoses (specialised footwear) or corrective surgery.

What causes sacral agenesis?

The cause of sacral agenesis is not well understood. There is no cure for the condition and no known way to prevent it. It is believed that sacral agenesis forms during the third to eighth week of pregnancy possibly because of genetic variation, or toxic/infective damage when this part of the spine is starting to develop in the womb. Parents who have spina bifida, scoliosis, or maternal diabetes are more likely to have a baby with sacral agenesis.


Sometimes sacral agenesis may be detected by ultrasound during the second trimester of pregnancy. At birth it can usually be detected by a physical examination of the lower spine. If the condition is mild, it may not be detected until the child presents for a medical examination for urinary incontinence – usually between four and five years of age.

Early detection is a key factor as it can prevent harmful kidney damage and recurrent urinary tract infections. It also helps enable a child to grow up to be more independent, achieve continence from an early age, and maximise their mobility.

Contact your child’s care team if you notice your child is experiencing a change in their bladder or bowel habit, signs of a urine infection, change in mobility or pain in their back.


The treatment of sacral agenesis will vary depending on how a child is affected. Treatment includes physiotherapy to maximise mobility and treatment of urinary or bowel problems.

Developed by the Queensland Paediatric Rehabilitation Service, Queensland Children's Hospital. We acknowledge the input of consumers and carers.

Resource ID: FS371.   Reviewed: Dec 2023

Disclaimer: This information has been produced by healthcare professionals as a guideline only and is intended to support, not replace, discussion with your child’s doctor or healthcare professionals. Information is updated regularly, so please check you are referring to the most recent version. Seek medical advice, as appropriate, for concerns regarding your child’s health.

Last updated: March 2024