Surgical decompression of thoracic spinal stenosis in achondroplasia: indication and outcome

Clinical article

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Object

The achondroplastic spinal canal is narrow due to short pedicles and a small interpedicular distance. Compression of neural structures passing through this canal is therefore regularly encountered but rarely described. Symptomatology, radiological evaluation, and treatment of 20 patients with achondroplasia who underwent decompression of the thoracic spinal cord are described and outcome is correlated with the size of the spinal canal and the thoracolumbar kyphotic angle.

Methods

Scores from the modified Japanese Orthopaedic Association scale, Nurick scale, European Myelopathy scale, Cooper myelopathy scale for lower extremities, and Odom criteria before and after surgery were compared. Magnetic resonance imaging was evaluated to determine the size of the spinal canal, spinal cord compression, and presence of myelomalacia. The thoracolumbar kyphotic angle was measured using fluoroscopy.

Results

Patient symptomatology included deterioration of walking pattern, pain, cramps, spasms, and incontinence. Magnetic resonance images of all patients demonstrated spinal cord compression due to degenerative changes. Surgery resulted in a slight improvement on all the ranking scales. Surgery at the wrong level occurred in 15% of cases, but no serious complications occurred. The mean thoracolumbar kyphotic angle was 20°, and no correlation was established between this angle and outcome after surgery. No postoperative increase in this angle was reported. There was also no correlation between size of the spinal canal and outcome.

Conclusions

Decompressive surgery of the thoracic spinal cord in patients with achondroplasia can be performed safely if anatomical details are taken into consideration. Spondylodesis did not appear essential. Special attention should be given to the method of surgery, identification of the level of interest, and follow-up of the thoracolumbar kyphotic angle.

Abbreviation used in this paper:mJOA = modified Japanese Orthopaedic Association.

Article Information

Address correspondence to: Carmen Vleggeert-Lankamp, M.D., Ph.D., Department of Neurosurgery, Leiden University Medical Centre, P.O. Box 9600, NL-2300 RC Leiden, The Netherlands. email: cvleggeert@lumc.nl.

Portions of this work were presented in poster form on March 23–26, 2011, at the Global Spine Congress in Barcelona, Spain. Please include this information when citing this paper: published online June 22, 2012; DOI: 10.3171/2012.4.SPINE1220.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Example of spinal cord compression of a lower thoracic (Th) level in a patient with achondroplasia. Compression of the spinal cord is maximal at T9–10 and T10–11. Myelomalacia is present at T9–10. Compression is mainly caused by hypertrophy of the yellow ligament. This sagittal MR image nicely illustrates that compression of the lower thoracic spinal cord is often combined with multilevel cauda equina compression. In this case, the thoracic compression on both thoracic levels is related to the lamina in such a way that using an interlaminar decompression technique would result in a very small bone arch. It was therefore decided to remove the entire arch and perform a laminectomy instead of a decompression between the arches on 2 levels.

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    Example of spinal cord compression at a midthoracic level in a patient with achondroplasia. Compression of the spinal cord is maximal at T8–9, which is best demonstrated by the sagittal MR image on the left. The sagittal image on the right properly demonstrates that myelomalacia is present at this level. This MR image adequately illustrates that spinal cord compression is often present on multiple levels. The decision as to which level should be decompressed can be difficult. The axial MR images can be helpful or, in this case, the level at which myelomalacia is present. In these cases a laminectomy is often preferred over an interlaminar decompression technique to accomplish a decompression on 2 levels.

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    Example of thoracolumbar kyphosis in a patient with achondroplasia. The thoracolumbar angle is 63° and reported to be constant over at least 25 years. Compression of the spinal cord was maximal at T-8, as diagnosed using MRI. The patient subsequently received a laminectomy at T-8. The overview of the spinal column is the result of sequential sagittal radiographs of the cervical, thoracic, and lumbar columns that were reconfigured into a single-image overview.

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