Keijiro Isobe

MECHANICAL STABILITY OF THE PEDICLE SCREW FIXATION SYSTEMS FOR THE LUMBAR SPINE

Five different pedicle screw systems: AO Fixator Interne, VSP Steffee plate, Luque ISF, modified Zielke, and Chibatype plate screw system (experimental device), were evaluated for biomechanical strength. A fatigue test for the screw, compressive, and torsional tests for the pedicle screw systems and a pull-out test of the pedicle screw were done. Even the Schanz screw, which showed the highest endurance limit, may be broken under the continuous loading condition in the body. The AO Fixator Interne and Steffee plate system themselves are rigid and are indicated for injuries that need reduction. The Luque ISF, modified Zielke, and Chiba-type plate screw systems, however, are indicated for degenerative lumbar disease requiring in situ fusion. There was a linear positive correlation between the bone mineral density of the vertebral body and the pull-out strength of the pedicle screw (correlation coefficient, 0.68). The fixation strength of the pedicle screw to the bone decreased remarkably in osteoporosis.

Preoperative MRI analysis of patients with idiopathic scoliosis. A prospective study

Study Design. A prospective trial of preoperative MRI study in patients with “idiopathic” scoliosis. Objectives. To investigate the prevalence of neural axis malformations and the clinical relevance of MRI in the evaluation of patients with idiopathic scoliosis undergoing surgical intervention. Summary of Background Data. With the development of MRI, neural axis abnormalities such as syringomyelia or Chiari malformations are increasingly being found in patients with “idiopathic” scoliosis. The risk of neurologic complications during correction of scoliosis without prior decompression surgery for syringomyelia has been documented; however, there have been no prospective studies for identifying the risk of neurologic complications as a result of scoliosis surgery in patients with asymptomatic neural axis malformations. Methods. A total of 250 patients who were classified as having “idiopathic” scoliosis at first presentation and admitted for spinal surgery were evaluated. All patients were examined for neural axis abnormalities using MRI. The presence of neurologic symptoms and abnormal neurologic signs was also examined before and after surgical intervention. Neurologic complications during scoliosis surgery were reviewed in patients with neural axis abnormalities. Results. There were 44 (18%) patients (13 males and 31 females) who had neural axis abnormalities on MRI, including syringomyelia with Chiari malformations in 22 patients, syringomyelia with tonsillar ectopia in 2, Chiari malformations in 13, tonsillar ectopia in 6, and low conus medullaris in 1. On clinical examination, 44 (18%) patients had abnormal neurologic signs and 26 (7%) patients complained of headache or back pain. There were significant differences between patients with and without neural axis abnormalities regarding the age at first visit, gender, curve pattern, sagittal profile of thoracic spine, presence of neurologic deficit, and complaint of pain. Only 12 of 44 patients needed neurosurgical treatment for foramen magnum decompression before correction of scoliosis. Neurologic status temporarily worsened in 3 patients, including 2 patients with neurosurgical treatment and 1 patient without neurosurgical treatment; however, there were no permanent neurologic complications as a result of scoliosis surgery. All patients without neurologic deficits or complaints of pain did not receive neurosurgical treatment, while they had no permanent neurologic complications. Conclusions. Foramen magnum decompression for neural axis malformations could prevent permanent neurologic complications during scoliosis surgery. There is little risk of neurologic complications in patients with “idiopathic” scoliosis whose neurologic status is normal, even if these patients have a neural axis malformation on MRI.

Vertebral decancellation for severe scoliosis

STUDY DESIGN The results of staged surgery including vertebral decancellation were reviewed retrospectively for 21 patients with severe scoliosis. OBJECTIVES To evaluate the benefits and limitations of vertebral decancellation as new anterior surgical procedure. SUMMARY OF BACKGROUND DATA The curvatures of severe scoliosis are often very rigid, and surgical correction using the anterior or posterior approach may not achieve the desired correction. Some studies reported neurologic complications might appear due to the aggressive approach or excessive correction force. METHODS Twenty-one patients (average age, 17.0 years) with severe scoliosis, in whom Cobb angle was over 80 degrees (average angle, 107 degrees), underwent staged anterior and posterior spinal reconstruction. Vertebral decancellation was performed as anterior procedure, and until posterior instrumentation, halo traction was carried out. The transition of curvatures in coronal and sagittal planes was assessed in this series. RESULTS The average correction rate of lateral curvature at the final follow-up was 46%. The average loss of correction was 2.5 degrees. Kyphosis, measured between T5 and T12, changed from 41 degrees to 36 degrees. Lordosis, measured between L1 and S1, changed from 56 degrees to 45 degrees. Transient neurologic deficit was seen in one case after vertebral decancellation. CONCLUSIONS Staged surgery including vertebral decancellation is an effective surgical method for patients with severe scoliosis, where an inflexible rigid curve or the risk of occurrence of neurologic complications due to temporary correction may exist.

Long-term results of spinal instrumentation surgery for scoliosis five years or more after surgery, in patients over twenty-three years of age.

From 1967 to 1981, 311 scoliotic patients treated at Chiba University, with a minimum follow-up of 5 years and aged more than 23 years, were selected for this study. Seventy-two were males and 239 were females, whose age at operation ranged from 9 to 44 years, with an average of 16.5 years. The operative procedures were one-stage Harrington procedure in 179 cases, staged procedure in 108 cases, anterior procedure in 20 cases, and combined anteroposterior fusion in four cases. Including 198 patients examined physically, a total of 263 patients (54 males and 209 females) have responded to a questionnaire or were interviewed by telephone. In general, 85% of the patients were satisfied with the result of the operation for the control of spinal deformity, improvement of the cosmesis, and increase in physical and social activity.