Sohei Ebara

The prognosis of surgery for cervical compression myelopathy. An analysis of the factors involved

We have studied the morphometry of the spinal cord in 50 patients with cervical compression myelopathy. Computed tomographic myelography (CTM) showed that the transverse area of the cord at the site of maximum compression correlated significantly with the results of surgery. In most patients with less than 30 mm2 of spinal cord area, the results were poor; the cord was unable to survive. Several factors, such as chronicity of disease, age at surgery and multiplicity of involvement are said to influence the results of surgery, but the transverse area of the cord at the level of maximum compression provides the most reliable and comprehensive parameter for their prediction.

The lumbar spine in spastic diplegia. A radiographic study

Some radiological features of the lumbar spine of 84 patients with spastic diplegia were compared with 50 control subjects. The average age of the patients was 20.1 years (3 to 39). Spondylolysis of the fifth lumbar vertebra was found in 21%, four times more frequently than in normal subjects. No patient under nine years of age had spondylolysis and the frequency increased with age. The average angle of lumbar lordosis in spastic patients in the standing position was greater than in normal subjects, and increased with age. The patients had a decreased sacrofemoral angle which caused an increase in Fergusons angle and explained the increased angle of lumbar lordosis.

THE CERVICAL SPINE IN ATHETOID CEREBRAL PALSY: A RADIOLOGICAL STUDY OF 180 PATIENTS

We have reviewed the cervical spine radiographs of 180 patients with athetoid cerebral palsy and compared them with those of 417 control subjects. Disc degeneration occurred earlier and progressed more rapidly in the patients, with advanced disc degeneration in 51%, eight times the frequency in normal subjects. At the C3/4 and C4/5 levels, there was listhetic instability in 17% and 27% of the patients, respectively, again six and eight times more frequently than in the control subjects. Angular instability was seen, particularly at the C3/4, C4/5 and C5/6 levels. We found a significantly higher incidence of narrowing of the cervical canal in the patients, notably at the C4 and C5 levels, where the average was 14.4 mm in the patients and 16.4 mm in normal subjects. The combination of disc degeneration and listhetic instability with a narrow canal predisposes these patients to relatively rapid progression to a devastating neurological deficit.

Experimental spondylosis in the rabbit spine : overuse could accelerate the spondylosis

It has been suggested that overuse can accelerate the progression of cervical spondylosis. This assumption was derived from a study examining premature onset of cervical spondylosis in patients with athetoid cerebral palsy. To clarify the relationship between overuse and structural abnormalities of the spine, repetitive extension-flexion movement was loaded onto young rabbit spines through electric stimulation of the trapezius muscle. Repetitive loads of 200,000 cycles caused more severe delamination of the anulus fibrosus than control at the lower cervical spine. In addition, it was associated with early osteophyte formation at the same disc level. No severe degeneration of the nucleus pulposus, however, occurred through repetitive loading. It was found that repetitive movement could accelerate the progression of structural abnormalities, such as cervical spondylosis. This result suggests that overuse is an important factor in the pathogenesis of spondylosis.

Surgical Treatment of Bone Tumors Arising from Pelvic Ring

Six patients with periacetabular pelvic tumors were treated with a new type of constrained total hip replacement without reconstruction of pelvic continuity later wide resection. Five of six patients were able to walk with the supporting aids without pain after a follow-up of 6 months to 3 years. There was one local recurrence and one metastasis. No prosthetic failure and symptomatic loosening were found. Pelvic tumors away from the acetabulum were resected with wide margins and had no local recurrence. They had almost normal function. In sacral tumors (11 cases), there were two local recurrences and two deep infections. The preservation of the S2 nerve root appears to be adequate for normal control bladder and bowel functions. Moreover, stability of the spinal column can be obtained with complete preservation of the body of the S1 vertebra.

Intraoperative Measurement of Lumbar Spinal Stiffness

Spinal instability has been assessed according to certain physiological or radio-graphic abnormalities of the spine [1–5]. A quantitative assessment of spinal instability is, however, essential for justification of lumbar fusion or stabilization and this has actually been conducted by few researchers [6] (D.C. Holmes, M.D. Brown, E.C. Eckstein, et al. 1989, In Vitro and In Vivo Measurement of Lumbar Spine Motion Segment Unit Stiffness; unpublished work, University of Miami School of Medicine). We attempted to develop a method of measuring spinal instability that could be carried out during lumbar spine surgery [7–10]. This method enabled us to measure the alterations of lumbar spinal instability in each step of surgical decompression, stabilization, or bone grafting. The final aim of this research was to establish an objective criterion for fusion and stabilization [6,11–14].

Instability of the Spinal System with Focus on Degeneration of the Intervertebral Disk

The intervertebral disk is a cartilaginous tissue. It is organized with a concentrated proteoglycan solution, which is the central nucleus pulposus, held within the strong collagen network, the outer anulus fibrosus. The disk exhibits a viscoelastic response when subjected to loads and deformations. Disk degeneration introduces a less stiff segment in the spinal column and is generally considered to be an age-dependent change. However, in the cervical spine of cerebral palsy patients who exhibit athetotic movements in the neck, there is a very early onset of disk degradation. Acceleration of disk degeneration occurs in the spines of animals subjected to excessive extension—flexion of the head and neck or to spinal instability induced by surgery. Repetitive torsion of the disk may lead to structural regression in in vitro studies using animal spines. Delamination or disruption of the anulus fibrosus is always recognized as the beginning stage of destruction of intervertebral disk structure. This disruption of the collagen network may result from fatigue failure by repetitive loadings, which cause high tensile stresses in the anulus fibrosus because large hydrostatic pressures develop within the nucleus pulposus. Loosening of the collagen network may be responsible for the loss of proteoglycans and water, and also may be a key factor leading to the development of disk degeneration. A “degenerated disk” can be induced through pure mechanical fatigue failure of the tissue as an age-independent change of the cartilaginous tissue.

Biomechanical Properties of the Rabbit Disc Body Unit Under Cyclic Torsional Loading

To understand the biomechanical effect of repetitive torsional loading to the spine, fresh cadaveric lumbar disc body units from Japanese white rabbits were tested. The specified angular displacement was loaded to the specimen in a cyclic manner. The amplitude of axial rotation ranged from 10° to 19°, and the average rate of loading was 24°/s. The peak values of torque were monitored as a time series. The torque angle curves were recorded intermittently during cyclic loading, which was continued until failure of the specimen occurred. As the number of torsional cycles increased, the peak torque decreased. It was represented as two portions of a linear segment plotted against the logarithm of the number of torsional cycle. The decrease of peak torque showed the two phases, which were, first, the gradual decrease phase and second, the sudden decrease phase. The torque angle curves showed that the stiffness decreased and the initial toe part of the curve increased after repetition of the load. Histological examination after testing showed that the failure site was a growth plate at the upper vertebral body. However, distortion of stratification and rupture of the laminated bands were also observed at the intervertebral disc. These were considered as the accumulation of damage resulting in the failure caused by the cyclic load. These findings suggest that the response to the repetitive loading, in other words, the fatigue phenomenon, is strongly associated with the etiology of disc degeneration and spondylosis.

Prosthetic Replacement Surgery for Spine Metastasis

In the early 1970s, we began to find an increasing number of patients with metastatic disease of the spine, primarily cervical, presenting with constant pain. Subsequently neural deficits associated with vertebral collapse occurred and there was, according to professionals in the field, “nothing to do with them” or because “they don’t have long to go.” When we looked more carefully at these patients, it became obvious that they had all gathered together in one group and were generally treated in one or two ways; either only supportive care was provided or they were subjected to radio-therapy and/or laminectomy. Under more careful scrutiny, it became apparent that this was not a homogenous group. There were differences in these patients based on the primary tumor, location and number of metastatic sites, their general conditions, and, considering these factors, their long-term prognoses. We began to select those patients with a reasonable remaining life span of over 6 months who have pain due to instability and/or neural compression from vertebral collapse and carried out instrument replacement supplemented by methyl-methacrylate posteriorly and, in some instances, methyl-methacrylate replacement of vertebral bodies anteriorly. We were pleased with the pain relief and return of neural function achieved in these patients. Through similar experiences in subsequent years, we developed a metal prosthesis for replacement of the metastatic tumor-affected vertebra [1] (Fig. 1).