Hidenori Inoue

Long-Term Results of the Anterior Cervical Spondylodesis

From 1974 to 1992, anterior cervical spondylodesis was performed in 163 patients of cervical spondylotic myelopathy, cervical spondylotic radiculopathy, traumatic spinal injury, ossification of the posterior longitudinal ligament, or cervical spondylitis. Forty-five of these patients were followed for more than 4 years. To analyze the long-term results of anterior cervical spondylodesis, a radiological examination was performed in these 45 patients and magnetic resonance imaging was conducted in 41 of them. Postoperative spondylotic changes were observed radiologically in 23 (51.1%) of the 45 patients. Anterior bony spur was more frequently observed than posterior bony spur in these postoperative spondylotic changes. Postoperative canal stenosis caused by the bulging of the discs and the ligamentum flavum was frequently demonstrated with hypo- or isointense signal on T2-weighted images by magnetic resonance imaging in patients followed long term after surgery and in patients with malalignment of the cervical spine due to kyphosis of the fused vertebrae and multisegmental fusion. Neurological improvement was less in patients with bulge of the discs and the ligamentum flavum seen in magnetic resonance imaging than in patients without it. The bulge of the ligamentum flavum was histopathologically defined as hypertrophy of the ligament.

Radiographic classification of L5 isthmic spondylolisthesis as adolescent or adult vertebral slip

Study Design. A radiographic and morphologic study was conducted to investigate low-grade spondylolisthesis in cases with preexisting isthmic spondylolysis of L5. Objective. To distinguish radiographically between vertebral slips before and after skeletal maturity as determined by deformities of the sacral endplate. Summary and Background Data. Very few reports have shown that spondylolisthesis with preexisting isthmic defects of L5 develops frequently in adulthood. The prognostic factors of the vertebral slip have remained unclear. It is hard to determine the onset time of low-grade spondylolisthesis. Methods. This study examined plain radiographs of 367 adult patients with pars defects of L5 (213 without slippage and 154 with Grade 1 or 2 spondylolisthesis) and 310 control subjects, ages 20 to 59 years at the first visit. The following parameters were measured and analyzed for each age decade: the sacral table index (anteroposterior width of the sacral endplate expressed as a percentage of the anteroposterior diameter of the upper L5 endplate), the sacral table angle (formed by the sacral endplate with the posterior wall of S1), the relative thickness of the L5 transverse process, and the iliac crest height. Results. The prevalence of patients with slippage who met deformity criteria (sacral table index > 102% [the mean plus 2 standard deviations of the controls] and sacral table angle ≤97° [the mean of the controls]) remained almost one fourth during all decades. On the contrary, the prevalence of patients with slippage who met normal-shape criteria (sacral table index ≤102% and sacral table angle ≥89° [mean minus 2 standard deviations of the controls]) was 0% in the third decade, but increased remarkably in the fifth and sixth decades. Of the 213 patients without slippage, 8 patients in whom new slippage developed during long-term follow-up evaluation all had a normally-shaped sacral table. The prevalence of patients without slippage decreased gradually with age, and elderly patients had relatively broader transverse processes and a higher iliac crest line. Conclusions. The authors considered that the slips with and those without deformities of the sacral table had developed in adolescence and adulthood, respectively. Using new radiographic parameters that indicate widening and tilting of the sacral table, low-grade isthmic spondylolis thesis can be categorized into “adolescent and adult vertebral slips.”

Radiological study of cervical ossification of the posterior longitudinal ligament.

The rate of progression of cervical ossification of the posterior longitudinal ligament (OPLL) was radiologically studied during a 3-year period in three patient populations: (a) after laminoplasty (25 patients), (b) after laminectomy (16 patients), and (c) in patients who were managed without surgery (56 patients). There appeared to be no significant difference between these two surgical procedures in postoperative progression of OPLL. When progression of OPLL was compared between patients treated surgically and nonsurgically, posterior surgery accelerated progression of OPLL.

Vertebral slip in lumbar spondylolysis and spondylolisthesis. Long-term follow-up of 22 adult patients

We studied the aetiology of vertebral slip in a long-term follow-up of 22 adult patients with isthmic spondylolysis or spondylolisthesis of L5. Of the 18 with spondylolysis without slip, 13 showed no slip after ten years, but five developed displacement of over 5%. All four patients with spondylolisthesis showed progression of the slip. We found that the vertical thickness of the transverse process of L5 was significantly greater (p < 0.01) in the 13 patients with no slip than in the other two groups. The relationship of vertebral slip to the shape of the transverse processes of L5 may be explained by differences in the bulk or physiological strength of the posterior bands of the iliolumbar ligament.

Redundant nerve roots of the cauda equina caused by lumbar spinal canal stenosis

To investigate pathogenesis of redundant nerve roots of the cauda equina, which were concomitant with severe lumbar spinal canal stenosis, six cadavers were examined anatomically and histopathologically, and quantitative analysis of nerve fibers was performed. In this anatomic study, it was observed that all the redundant nerve roots passed through the constriction of the spinal canal. No significant pathologic change was detected in the spinal ganglia and in the spinal cords except for the posterior column, in which dorsal redundant roots were entering. Redundant nerve roots of unequal length also were observed in the anatomic study. The spatial distribution of redundant nerve roots and the extent of degeneration of nerve fibers in them were established by these histopathologic and quantitative studies. These facts indicated a close causal relationship between redundant nerve roots and constriction of the spinal canal, and that the pathogenesis of redundant nerve roots was a squeezing force acting on the nerve roots at the area of spinal canal constriction.

Analysis of dural configuration for evaluation of posterior decompression in cervical myelopathy.

OBJECTIVE The goal of this study was to establish the criteria for sufficient decompression of the cervical spinal cord in laminoplastic surgery. METHODS Radiological examinations and neurological evaluations were conducted for 63 patients with cervical spondylotic myelopathy (CSM) and 31 patients with ossification of the posterior longitudinal ligament (OPLL) of the cervical spine who underwent suspension laminotomy. RESULTS The dural configuration in computed tomographic myelograms was evaluated in comparison with the critical value for the dural configuration established from 36 control subjects. Seventy-six of 94 patients were judged to have achieved full decompression. The neurological improvement of patients with full decompression was significantly better than that of patients with insufficient decompression (P<0.01). The postoperative sagittal diameter of the spinal canal was more than 14 mm in most of the sufficiently decompressed cases of CSM and more than 17 mm in OPLL cases. The laminotomy width was more than 70% of the transverse diameter of the spinal canal in both CSM and OPLL cases. There were four OPLL cases with insufficiently decompressed dura mater in the well-enlarged spinal canal after surgery. In these cases, the ossified posterior longitudinal ligament continuously occupied more than 25% of the preoperative spinal canal area over three or more segments. CONCLUSION The following conditions were considered critical for sufficient decompression of the spinal cord in laminoplastic operations: postoperative sagittal diameter of the spinal canal of more than 14 mm in CSM cases and more than 17 mm in OPLL cases and laminotomy width of more than 70% of the transverse diameter of the spinal canal in both CSM and OPLL cases. However, in cases of extensive OPLL, sufficient decompression could not be obtained through posterior enlargement of the spinal canal.

Delayed vertebral slip and adjacent disc degeneration with an isthmic defect of the fifth lumbar vertebra

We reviewed the radiographs of 325 unselected patients with defects in the pars interarticularis of L5 to study whether the incidence of vertebral slip in spondylolysis of L5 remained unchanged after the age of 20 years. MRI was also carried out on 111 of the patients to investigate the relationship between the shape of the transverse process of L5 and the degeneration of the discs adjacent to this level. The incidence of spondylolisthesis increased with age from 17% in the second decade to 51% in the sixth. The transverse process was significantly more slender in patients with less degeneration at L4/5 and advanced degeneration at L5/S1 than in patients with advanced degeneration at L4/5 and less degeneration at L5/S1. Vertebral slip secondary to an isthmic defect of L5 after the age of 20 years was confirmed and the adjacent disc degeneration was significantly related to the vertical thickness of the transverse process of L5.

Finite element analysis of the lower lumbar neural arch under facet loading

To evaluate the mechanical effect of the direction of facet load on the isthmus stresses of the lower lumbar neural arch, stress analyses were performed by using three-dimensional finite element models of isolated L4 and L5 vertebrae with particular emphasis on accurate discretization of the posterior elements. The bilateral symmetric or unilateral facet loads, with a constant magnitude, were applied within the sagittal and transverse planes. The largest maximal principal stress in the neural arch (the largest sigma(max)) tended to be qualitatively similar in L4 and L5. At the physiologic range, the largest sigma(max), observed on the anterior surface of the isthmus, was relatively insensitive to the sagittal plane loadings but sensitive to the transverse plane loadings. The values of the largest sigma(max) of L4 and L5 were low at the more frontally directed facet load. The magnitude and direction of the largest sigma(max) depended upon the facet loadings mainly on the ipsilateral side and partly on the opposite side. The results suggest that the direction of facet load, which may be characterized by the facet orientation, can have mechanical effects on the occurrence and direction of isthmic crack.

Finite Element Stress Analyses of the Fifth and Fourth Single Lumbar Vertebrae.

Separation of an interarticular portion of human vertebra, or spondylolysis, is often observed in the fifth (L5) and the fourth (L4) lumbar vertebra. The present study investigates Spondylolysis from a mechanical point of view. For this purpose, finite element models of L5 and L4 are constructed by reproducing the shape of typical vertebral specimens of a 44-year-old man as accurately as possible. Then the upper and the lower surface of the vertebral disk are constrained, and constant loads are applied to the inferior facet faces of L5 and L4 in various directions. The dependence of the maximum principal stress in the interarticular portion on the load direction and the point of load application is discussed. The results show that the maximum principal stress in the interarticular portion in L5 is higher than that in L4 in most cases. This result agrees with the clinical observation that 80% of spondylolysis occurs in L5. It is also observed that the principal direction of maximum stress in the interarticular portion is Independent of the direction of the applied load, and is perpendicular to the surface of the separation observed clinically.