New Concepts in Management of Type IV Sacral Agenesis

Mei Fong, BSc, PT


The purpose of this paper is to describe the functional outcomes of two children with type IV sacral agenesis treated at the Alberta Children's Hospital. Our treatment goals are to achieve:

  1. hand-free sitting;
  2. upright posture;
  3. stabilised pulmonary function;
  4. improved mobility.

The surgical management in both cases included:

  1. bilateral through-knee amputation;
  2. spinal reconstruction with segmental internal fixation;
  3. vascularized autologous bone graft.



What is sacral agenesis? It is a severe congenital deficiency which is characterised by absence of a variable amount of sacrum, lumbar spine, and associated neural elements. By Renshaw classification, there are four types of sacral agenesis.

Figure 1.

Type I:
Has either total or partial unilateral agenesis of the sacrum.

Type II:
Has partial sacral agenesis with a bilaterally symmetrical defect, a normal or hypoplastic first sacral vertebra, and a stable articulation between the ilia and the first sacral vertebra.

Type III:
Has variable lumbar and total sacral agenesis, with the ilia articulating with the sides of the lowest vertebra present.

Type IV:
Has variable lumbar and total sacral agenesis with the caudal end plate of the lowest vertebra resting above either fused iliac or an iliac amphiarthrosis.

Both of our cases were the most severe type IV with abnormalities extended to the musculoskeletal and renal system. The Budda-like position (page 12) is common in these children which is that of flexed knees and crossed legs. Muscles in the legs are frail with webbed knees and often club feet. Instabilities between the spine and pelvic causes the pelvis to migrate up the abdominal cavity and affects pulmonary function.

Figure 2.

Traditional Treatment

Traditional treatment of these children was subtrochanteric amputation and a bucket-like prosthesis was used to provide sitting balance so that bilateral hand activities were possible.

Figure 3.

Current Concept of Management

Case I is an 18 year old boy who has type IV sacral agenesis. His surgical management included;

  1. Through-knee amputation at age three years. This allowed him to sit independently and freed his hands for activities.
  2. Soft tissue releases done at age four years to reduce his hip flexors and abductor contractures which were not responding to stretching and wearing of an elastic band. The releases provided good leg alignment for end-point weight bearing and fitting of prosthesis.
  3. Spine reconstruction done at age 10 years due to decreased pulmonary function with shortness of breath and inability to maintain normal activity level.

Figure 4.

His spinal reconstruction included segmental internal fixation, two vascularized ribs transposed to the lumbar region, and homologous bone graft. This stabilised his pulmonary function and allowed him to return to normal activities after recovery.

Case II is a seven year old girl. At age six, her through-knee amputation and spinal reconstruction were done at the same time. Through-knee amputation allowed her to sit independently. Spinal reconstruction included using a modified Lugue instrument for segmental internal fixation. Tibial bones were carefully transposed to the lumbar region with its own blood supplies and wired in along with autologous bone graft. This stabilised her spine and improved her mobilisation such as walking with a walker on a prosthesis one year post surgery.

Figure 5.


In these two cases, we found that through-knee amputation was more functional than subtrochantric amputation because it allowed hand-free sitting, sitting on a toilet seat without assistance, and improved appearance. All these improved quality of life and psycho-social development.

Spinal reconstruction using vascularized bone graft and segmental internal fixation had stabilised pulmonary function and improved mobilisation such as ambulation on stumps and with prosthesis.

Figure 6.


Based on these two cases, we recommend that surgical management for type IV sacral agenesis should be through-knee amputation as it provides hand-free sitting and spinal reconstruction with segmental instrumentation as it stabilised pulmonary function and improves mobility. These procedures enabled these children to be more independent and live an active lifestyle.

Please address correspondence to:

Mai Fong, BSc, P.T.
Alberta Children's Hospital
1820 Richmond Rd.,SW
Calgary, Alberta
Canada T2T 5C7

Alberta Children's Hospital