Lumbosacral agenesis is a condition in which the sacrum and some of the lumbar vertebrae, or both, fail to develop. Although the etiology is not certain, it has been noted that 14% to 18% of patients have mothers with diabetes or a strong family history of diabetes.
Clinical Manifestations. The patient’s appearance varies with the level of the vertebral lesion. Although partial sacral agenesis may not be noticeable, lumbar or complete sacral agenesis is a severe deformity.
The posture of the lower limbs has been likened to that of the “sitting Buddha” and is characterized by flexion-abduction contractures of the hips and severe knee flexion, with popliteal webbing; the feet are in equinovarus and tucked under the buttocks. Inspection of the back reveals a bony prominence, which is the last vertebral segment, and often gross motion between this and the pelvis. Flexion-extension may occur at the junction of the spine and pelvis rather than at the hips. When the patient sits unsupported, the pelvis rolls up under the thorax. Scoliosis, hemivertebrae, spina bifida, and meningocele are common associated spinal anomalies.
With low-level lesions, deformities of the foot and lower limb resemble those of resistant clubfoot or arthrogryposis. Children may be misdiagnosed for several years or until problems with toilet training call attention to the sacral anomalies. Although the clinical signs resemble those of arthrogryposis, patients with arthrogryposis have full sensation in the lower limbs, bowel and bladder control, and normal vertebral architecture.
The neurologic deficit is one of the most unusual features of this condition. Motor paralysis is profound, with no voluntary or reflex activity, and it corresponds anatomically within one level to what might be expected from the vertebral loss. Even patients with the most severe involvement have sensation to the knees and spotty hypesthesia distally. Trophic ulceration of the feet is quite uncommon, suggesting at least protective sensation.
Bladder dysfunction is a consistent finding in all patients, even those with a relatively minor hemisacral defect, but the patterns of urinary function vary. Patients exhibit individual mixtures of upper and/or lower motor neuron disorders; perineal electromyography is necessary to obtain the correct diagnosis. Severe constipation with absence of the normal sensation of rectal distention is a common bowel abnormality.
The visceral anomalies are usually confined to the anogenital region (imperforate anus is the most common) and urinary tract (e.g., bladder dysfunction, hydronephrosis, vesical reflux and diverticulum, fused or absent kidney, exstrophy of the bladder, and hypospadias).
Radiographic Findings. A lesion at the level of the lumbar spine results in the complete absence of all vertebral development below it, including the sacrum and coccyx. However, lesions of the sacrum are less consistent; and in about one third of patients the defect occurs on one side only. In lumbar or complete sacral agenesis there is usually no bony connection of the spine to the pelvis. The spinopelvic articulation should be examined with flexion-extension radiographs because its stability has important implications in treatment and rehabilitation.
Treatment. Treatment measures vary with the level of involvement; and the management plan, based on the following broad concepts, must be highly individualized.
If the sacropelvic ring is intact, the spinopelvic junction is usually stable and the patient can walk with minimal or no brace support. Patients with significant deformities of only the feet and legs requirevigorous correction, begun at birth, including serial plaster casts in conjunction with stretching and exercises to position the feet plantigrade and the knees in extension. Surgical release may be necessary if conservative measures are inadequate.
Because of the high incidence of associated defects that may lead to serious renal impairment, recognition and treatment of urinary abnormalities are an important part of management. Delay in diagnosis and treatment may lead to upper tract deterioration and severely limit therapeutic options.