STUDY DESIGN

Radiologic study for patients with athetoid cerebral palsy (CP), and a biomechanical study using the finite-element model (FEM).

OBJECTIVES

To understand the lumbar disorders of athetoid CP patients and the etiology based on the results from the FEM study.

SUMMARY OF BACKGROUND DATA

Cervical spondylotic myelopathy is a well-identified spinal disorder associated with cerebral palsy, especially in athetoid type. One can rationalize that the athetoid involuntary trunk movement may induce stress-related lumbar disorders. Until now, very few investigations have been conducted on lumbar disorders that could occur in patients with CP.

METHODS

Sixty-one cases with athetoid cerebral palsy were clinically reviewed. Radiographs of the lumbar spine in 30 cases with low back pain were taken. From these radiographs, the incidence of lumbar spondylolysis and endplate lesion was analyzed. The biomechanical study was conducted using a three-dimensional FEM of the ligamentous lumbar spine. Axial compression of 400 N was applied to simulate preload on the spine during the standing position followed with 10.6 Nm moment to simulate extension and axial rotation. The combined motion of extension and axial rotation was also simulated. During supine position, pure extension and rotation were simulated, and no preload was applied. The von Mises stresses were computed at the pars interarticularis at the each level and compared for different motions.

RESULTS

Among the 61 patients, 41 complained of symptoms such as low back and leg pain. Thirty of these 41 patients gave their consents to undergo radiographic evaluation. Twenty-eight of the 30 patients (93.3%) showed stress-related disorders such as the spondylolysis and/or vertebral endplate lesions. Spondylolysis was found in 18 of the 30 patients (60.0%). Spondylolysis was observed at the multiple levels in 4 patients involving two levels in 2 cases and three levels in the other 2 cases. Vertebral endplate lesions (deformity) were seen in 26 (86.7%) of the 30 patients. Overall, the lesions (deformity) were found in 109 of 330 endplates (33.0%) out of all lumbar endplates in the 30 patients. The FEM based results showed that stresses at pars interarticularis of L5 were the highest of all levels in all loading modes, with or without preload. However, compared with the extension or axial rotation alone modes, the combined motion of extension and rotation showed higher stresses at the pars interarticularis.

CONCLUSIONS

The athetoid involuntary movements in CP patients may cause stress-related lumbar disorders. Especially, combined extension and rotation due to the involuntary trunk motion may contribute to the high incidence of spondylolysis.