Virtual pathology of cervical radiculopathy based on 3D MR/CT fusion images: impingement, flattening or twisted condition of the compressed nerve root in three cases.

BACKGROUND: There have been several imaging studies of cervical radiculopathy, but no three-dimensional (3D) images have shown the path, position, and pathological changes of the cervical nerve roots and spinal root ganglion relative to the cervical bony structure. The objective of this study was to introduce a technique that enables the virtual pathology of the nerve root to be assessed using 3D magnetic resonance (MR)/computed tomography (CT) fusion images that show the compression of the proximal portion of the cervical nerve root by both the herniated disc and the preforaminal or foraminal bony spur in patients with cervical radiculopathy. FINDINGS: MR and CT images were obtained from three patients with cervical radiculopathy. 3D MR images were placed onto 3D CT images using a computer workstation. The entire nerve root could be visualized in 3D with or without the vertebrae. The most important characteristic evident on the images was flattening of the nerve root by a bony spur. The affected root was constricted at a pre-ganglion site. In cases of severe deformity, the flattened portion of the root seemed to change the angle of its path, resulting in twisted condition. CONCLUSIONS: The 3D MR/CT fusion imaging technique enhances visualization of pathoanatomy in cervical hidden area that is composed of the root and intervertebral foramen. This technique provides two distinct advantages for diagnosis of cervical radiculopathy. First, the isolation of individual vertebra clarifies the deformities of the whole root groove, including both the uncinate process and superior articular process in the cervical spine. Second, the tortuous or twisted condition of a compressed root can be visualized. The surgeon can identify the narrowest face of the root if they view the MR/CT fusion image from the posterolateral-inferior direction. Surgeons use MR/CT fusion images as a pre-operative map and for intraoperative navigation. The MR/CT fusion images can also be used as educational materials for all hospital staff and for patients and patients' families who provide informed consent for treatments.

Circumspinal decompression with dekyphosis stabilization for thoracic myelopathy due to ossification of the posterior longitudinal ligament.

STUDY DESIGN: Circumspinal decompression with dekyphosis stabilization was prospectively performed with thoracic myelopathy due to ossification of posterior longitudinal ligament (OPLL). Neurologic outcome was reviewed. OBJECTIVE: To evaluate how easily, safely, and completely the thoracic OPLL can be removed or floated by circumspinal decompression with dekyphosis stabilization. SUMMARY OF BACKGROUND DATA: Anterior decompression is the best for the spinal cord recovery to treat thoracic myelopathy caused by OPLL on the concave side of the spinal cord. However, anterior approach for removal of OPLL plaque is technically demanding. METHODS: This is an operative procedure. Wide laminectomy is performed. Bilateral gutters along the dural tube are made using a diamond drill into the vertebral body covering the extent of the OPLL to be removed anteriorly. Posterior instrumentation is applied for stabilization of the spine and reducing thoracic kyphosis by approximately 5 to 10 degrees (dekyphosis stabilization). Four weeks after the first step, anterior decompression is performed with direct vision with the landmark of gutters using an operative microscope, followed by interbody fusion. Fifteen patients with thoracic myelopathy due to OPLL had the first-step operation, and 11 patients underwent circumspinal decompression (both the first and second operation). RESULTS: Kyphosis in the stabilization area reduced from 30.7 to 24.7 degrees on average in 15 patients. In 2 of the 15 patients, the spinal cord was shifted posteriorly and completely decompressed by only the first-step operation in the postoperative myelography or magnetic resonance imaging. The second-step operation was cancelled, and their Japanese Orthopedic Association scores improved from 6 to 10 points and from 4 to 10.5 point, respectively at final follow-up. In other 13 patients, the spinal cord was still compressed by the OPLL plaque. In 2 of the 13 patients, the second-step operation was cancelled because their general condition was impaired. Their preoperative Japanese Orthopedic Association scores were 2.0 and 2.5, and final scores were 5.5 and 5.5 points, respectively. Remaining 11 patients who underwent circumspinal decompression (both the first and second operation) neurologically improved and maintained from 4.0 points to 9.1 points on average at final follow-up. CONCLUSION: The OPLL plaque in the thoracic spine might be most easily, safely, and completely removed or floated, and the spinal cord is circumferentially decompressed through circumspinal decompression with dekyphosis stabilization.

Finite-element analysis on closing-opening correction osteotomy for angular kyphosis of osteoporotic vertebral fractures.

BACKGROUND: Closing-opening correction (COC) osteotomy is a useful procedure for severe angular kyphosis. However, there is no previous research on the reconstructed vertebrae with kyphotic malalignment in the presence of osteoporosis. Finite-element (FE) analysis was performed to estimate the biomechanical stress with both osteoporotic grades and corrective kyphotic angles during COC osteotomy for osteoporotic angular kyphosis. METHODS: FE models of COC osteotomy were created by changing three major parameters: (1) grade of osteoporosis; (2) kyphotic angle; and (3) compensated posture when standing still. Osteoporosis was graded at four levels: A, normal (nonosteoporotic); B, low-grade osteoporosis; C, middle-grade osteoporosis; D, high-grade osteoporosis. The kyphotic angle ranged from 0 degrees as normal to 15 degrees and 30 degrees as moderate and severe kyphosis, respectively. FE analyses were performed with and without assumed compensated posture in kyphotic models of 15 degrees and 30 degrees . Along each calculated axis of gravity, a 427.4-N load was applied to evaluate the maximum compressive principal stress (CPS) for each model. RESULTS: The CPS values for the vertebral element were the highest at the anterior element of T10 in all FE models. The maximum CPS at T10 increased based on the increases in both the grade of osteoporosis and the kyphotic angle. Compensated posture made the maximum CPS value decrease in the 15 degrees and 30 degrees kyphotic models. The highest CPS value was 40.6 MPa in the high-grade osteoporosis (group D) model with a kyphotic angle of 30 degrees . With the normal (nonosteoporotic) group A, the maximum CPS at T10 was relatively low. With middle- and high-grade osteoporosis (groups C and D, respectively), the maximum CPS at T10 was relatively high with or without compensated posture, except for the 0 degrees model. CONCLUSIONS: Lack of correction in osteoporotic kyphosis leads to an increase in CPS. This biomechanical study proved the advantage of correcting the kyphotic angle to as close as possible to physiological alignment in the thoracolumbar spine, especially in patients with high-grade osteoporosis.

The transmission of stress to grafted bone inside a titanium mesh cage used in anterior column reconstruction after total spondylectomy: a finite-element analysis.

STUDY DESIGN: A finite-element study of posterior alone or anterior/posterior combined instrumentation following total spondylectomy and replacement with a titanium mesh cage used as an anterior strut. OBJECTIVES: To compare the effect of posterior instrumentation versus anterior/posterior instrumentation on transmission of the stress to grafted bone inside a titanium mesh cage following total spondylectomy. SUMMARY OF BACKGROUND DATA: The most recent reconstruction techniques following total spondylectomy for malignant spinal tumor include a titanium mesh cage filled with autologous bone as an anterior strut. The need for additional anterior instrumentation with posterior pedicle screws and rods is controversial. Transmission of the mechanical stress to grafted bone inside a titanium mesh cage is important for fusion and remodeling. To our knowledge, there are no published reports comparing the load-sharing properties of the different reconstruction methods following total spondylectomy. METHODS: A 3-dimensional finite-element model of the reconstructed spine (T10-L4) following total spondylectomy at T12 was constructed. A Harms titanium mesh cage (DePuy Spine, Raynham, MA) was positioned as an anterior replacement, and 3 types of the reconstruction methods were compared: (1) multilevel posterior instrumentation (MPI) (i.e., posterior pedicle screws and rods at T10-L2 without anterior instrumentation); (2) MPI with anterior instrumentation (MPAI) (i.e., MPAI [Kaneda SR; DePuy Spine] at T11-L1); and (3) short posterior and anterior instrumentation (SPAI) (i.e., posterior pedicle screws and rods with anterior instrumentation at T11-L1). The mechanical energy stress distribution exerted inside the titanium mesh cage was evaluated and compared by finite-element analysis for the 3 different reconstruction methods. Simulated forces were applied to give axial compression, flexion, extension, and lateral bending. RESULTS: In flexion mode, the energy stress distribution in MPI was higher than 3.0 x 10 MPa in 73.0% of the total volume inside the titanium mesh cage, while 38.0% in MPAI, and 43.3% in SPAI. In axial compression and extension modes, there were no remarkable differences for each reconstruction method. In left-bending mode, there was little stress energy in the cancellous bone inside the titanium mesh cage in MPAI and SPAI. CONCLUSIONS: This experiment shows that from the viewpoint of stress shielding, the reconstruction method, using additional anterior instrumentation with posterior pedicle screws (MPAI and SPAI), stress shields the cancellous bone inside the titanium mesh cage to a higher degree than does the system using posterior pedicle screw fixation alone (MPI). Thus, a reconstruction method with no anterior fixation should be better at allowing stress for remodeling of the bone graft inside the titanium mesh cage.