Yasuhiro Shono

Complications of Pedicle Screw Fixation in Reconstructive Surgery of the Cervical Spine

Study Design. Retrospective evaluation of complications in 180 consecutive patients with cervical disorders who had been treated by using pedicle screw fixation systems. Objectives. To determine the risks associated with pedicle screw fixation in the cervical spine and to emphasize the importance of preoperative planning and surgical techniques in reducing the risks of this procedure. Summary of Background Data. Generally, pedicle screw fixation in the cervical spine has been considered too risky for the neurovascular structures. There have been several reports describing the complications of lateral mass screw–plate fixation. However, no studies have examined in detail the complications associated with cervical pedicle screw fixation. Methods. One hundred eighty patients who underwent cervical reconstructive surgery using cervical pedicle screw fixation were reviewed to clarify the complications associated with the pedicle screw fixation procedure. Cervical disorders were spinal injuries in 70 patients and nontraumatic lesions in 110 patients. Seven hundred twelve screws were inserted into the cervical pedicles, and the locations of 669 screws were radiologically evaluated. Results. Injury of the vertebral artery occurred in one patient. The bleeding was stopped by bone wax, and no neurologic complication developed after surgery. On computed tomographic (CT) scan, 45 screws (6.7%) were found to penetrate the pedicle, and 2 of 45 screws caused radiculopathy. Besides these three neurovascular complications directly attributed to screw insertion, radiculopathy caused by iatrogenic foraminal stenosis from excessive reduction of the translational deformity was observed in one patient. Conclusions. The incidence of the clinically significant complications caused by pedicle screw insertion was low. Complications associated with cervical pedicle screw fixation can be minimized by sufficient preoperative imaging studies of the pedicles and strict control of screw insertion. Pedicle screw fixation is a useful procedure for reconstruction of the cervical spine in various kinds of disorders and can be performed safely.

Posterior occipitocervical reconstruction using cervical pedicle screws and plate-rod systems.

STUDY DESIGN This retrospective study was conducted to analyze the clinical results in 26 patients with lesions at the craniocervical junction that had been treated by occipitocervical reconstruction using pedicle screws in the cervical spine and occipitocervical rod systems. OBJECTIVES To evaluate the effectiveness of pedicle screw fixation in occipitocervical reconstructive surgery and to introduce surgical techniques. SUMMARY OF BACKGROUND DATA Many methods of occipitocervical reconstruction have been reported, but there have been no reports of occipitocervical reconstruction using pedicle screws and occipitocervical rod systems for reduction and fixation. METHODS Twenty-six patients with lesions at the craniocervical junction underwent reconstructive surgery using pedicle screws in the cervical spine and occipitocervical rod systems. The occipitocervical lesions were atlantoaxial subluxation associated with basilar invagination, which was caused by rheumatoid arthritis in 19 patients and other disorders in 7. The lowest cervical vertebra of fusion in 16 patients was C2, and the remaining 10 patients underwent fusion downward from C3 to C7. Flexion deformity of the occipitoatlantoaxial complex was corrected by application of extensional force, and upward migration of the odontoid process was reduced by application of combined force of extension and distraction between the occiput and the cervical pedicle screws. RESULTS Solid fusion was achieved in all patients except two with metastatic vertebral tumors who did not receive bone graft for fusion. Correction of malalignment at the craniocervical junction was adequate, and postoperative magnetic resonance imaging showed improvement of anterior compression of the medulla oblongata. There were no neurovascular complications of cervical pedicle screws. CONCLUSIONS Occipitocervical reconstruction by the combination of cervical pedicle screws and occipitocervical rod systems provided the high fusion rate and sufficient correction of malalignment in the occipitoatlantoaxial region. Results of this study showed the effectiveness of cervical pedicle screw as a fixation anchor for occipitocervical reconstruction.

Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine.

Study Design. An in vitro biomechanical analysis of three anterior instability patterns was performed using calf lumbosacral spines. Stiffness of the constructs was compared, and segmental motion analyses were performed. Objectives. To clarify the factors that alter the stability of the spinal instrumentation and to evaluate the influence of instrumentation on the residual intact motion segments. Summary of Background Data. Recently, many adverse effects have been reported in fusion augmented with rigid instrumentation. Only few reports are available regarding biomechanical effects of stability provided by spinal instrumentation and its effects on residual adjacent motion segments in the lumbar‐lumbosacral spine. Methods. Eighteen calf lumbosacral spine specimens were divided into three groups according to instability patterns‐one‐level, two‐level, and three‐level disc dissections. Six constructs were cyclically tested in rotation, flexion‐extension, and lateral bending of intact spines, of destabilized spine, and of spines with four segmental posterior instrumentation systems used to extend the levels of instability (Cotrel‐Dubousset compression hook and three transpedicular screw fixation systems). During each test, stiffness values and segmental displacements were measured. Results. The rigidity of the instrumented construct increased as the fixation range became more extensive. Although application of the instrumentation effectively reduced the segmental motion of the destabilized vertebral level, the motion at the destabilized level tended to increase as the number of unstable vertebral levels increased, and the fixation range of the instrumentation became more extensive. Instrumented constructs produced higher segmental displacement values at the upper residual intact motion segment when compared with those of the intact spine. In contrast, the instrumented constructs decreased their segmental displacement values at the lower residual intact motion segment with higher magnitude of the translational (shear) motion taking place compared with the intact spine in flexion‐extension and lateral bending. These changes in the motion pattern became more distinct as the fixation range became more extensive. Conclusions. As segmental spinal instrumentation progresses from one level to three levels, the overall torsional and flexural rigidity of the system increases. However, segmental displacement at the site of simulated instability becomes more obvious. Application of segmental instrumentation changes the motion pattern of the residual intact motion segments, and the changes in the motion pattern become more distinct as the fixation range becomes more extensive and as the rigidity of the construct increases.

Local kyphosis reduces surgical outcomes of expansive open-door laminoplasty for cervical spondylotic myelopathy.

Study Design. This retrospective study analyzed the effects of cervical alignment on surgical results of expansive laminoplasty (ELAP) for cervical spondylotic myelopathy (CSM). Objective. To determine the limitation of posterior decompression by ELAP for CSM in the presence of local kyphosis. Summary of Background Data. Several studies have reported that cervical malalignment affected surgical outcomes of ELAP. However, there has been no report to demonstrate crucial determinants of surgical outcomes of ELAP for CSM in relation to cervical sagittal alignment. Methods. The study group comprised 114 patients who underwent ELAP for CSM. All were followed up for more than 2 years. The Japanese Orthopedic Association (JOA) scoring system for cervical myelopathy (full score, 17 points) was used to evaluate surgical outcomes for each patient 2 years after surgery. Statistical analysis with multivariate logistic regression models was used to ascertain the risk factors affecting postoperative surgical outcomes. Results. The average JOA scores were 9.9 points before surgery and 14 points 2 years after surgery. The recovery rate was 60.2%. Statistical analysis showed that signal intensity change on MRI and local kyphosis were the most crucial risk factors for poor surgical outcomes. Calculated with the logistic regression model, the highest risk of poor recovery was local kyphosis exceeding 13°. Conclusions. The influence of cervical malalignment on neurologic recovery after ELAP for CSM was shown. When patients have local kyphosis exceeding 13°, anterior decompression or posterior correction of kyphosis as well as ELAP should be considered. Expansive laminoplasty for CSM is best indicated for patients with local kyphosis less than 13°.

New anterior instrumentation for the management of thoracolumbar and lumbar scoliosis. Application of the Kaneda two-rod system.

Study Design. The Kaneda multisegmental instrumentation is a new anterior two‐rod system for the correction of thoracolumbar and lumbar spine deformities. This system consists of a vertebral plate and two vertebral screws for individual vertebral bodies and two semirigid rods to interconnect the vertebral screws. Clinical results of 25 thoracolumbar and lumbar scoliosis patients treated with this new instrumentation were analyzed. Objectives. To evaluate the efficacy of the new anterior instrumentation in correction and stabilization of thoracolumbar and lumbar scoliosis. Summary of Background Data. Since Dwyer first introduced the concept of anterior spinal instrumentation and fusion for scoliosis, anterior surgery has gradually gained acceptance. In 1976, a useful modification for the anterior spinal instrumentation, which reportedly provided means of lordosation and vertebral body derotation, was described. However, some authors reported a high tendency of the implant breakage, loss of correction, progression of the kyphosis, and pseudoarthrosis as the major complications. To overcome the disadvantages of Zielke instrumentation, the authors have developed a new anterior spinal instrumentation (two‐rod system) for the management of thoracolumbar and lumbar scoliosis. Methods. Anterior correction and fusion using Kaneda multisegmental instrumentation was performed in 25 patients with thoracolumbar or lumbar scoliosis. The average follow‐up period was 3 years, 1 month (range, 2 years to 4 years, 7 months). There were 20 patients with idiopathic scoliosis (13 adolescents and seven adults) and five patients with other types of scoliosis, including congenital and other etiologies. All patients had correction of scoliosis by fusion within the major curve, and for 16 of the 25 patients, the most distal end vertebra was not included in the fusion (short fusion). Radiographic evaluations were performed to analyze frontal and sagittal alignments of the spine. Results. The average correction rate of scoliosis was 83%. Over the instrumented levels, the correction rate was 90%. Preoperative kyphosis of the instrumented levels of 7° was corrected to 9° of lordosis. Sagittal lordosis of the lumbosacral area beneath the fused segments averaged 51° before surgery and was reduced to 34° after surgery. The trunk shift was improved from 25 mm before surgery to 4 mm at final follow‐up evaluation. The average improvement in the lower end vertebra tilt‐angle was 97% in those patients whose lower end vertebra was included in the fusion and 83% in patients whose lower end vertebra was not included in the fusion. Apical vertebral rotation showed an average correction rate of 86%. At final follow‐up evaluation, all patients demonstrated solid fusion without implantrelated complications. There was 1.5° of frontal plane and 1.5° of sagittal plane correction loss within the instrumented area at final follow‐up evaluation. Conclusions. New anterior two‐rod system showed excellent correction of the frontal curvature and sagittal alignment with extremely high correction capability of rotational deformities. Furthermore, correction of thoracolumbar kyphosis to physiologic lordosis was achieved. This system provides flexibility of the implant for smooth application to the deformed spine and overall rigidity to correct the deformity and maintain the fixation without a significant loss of correction or implant failure compared with conventional one‐rod instrumentation systems in anterior scoliosis correction.

Static and Cyclical Biomechanical Analysis of Pedicle Screw Spinal Constructs

Biomechanical evaluation of twelve different spinal devices in vitro employing pedicle screws was performed using static (n = 5) and cyclical testing (n = 3) parameters. In general, the rank order of implant failures was similar between static and cyclical tests, performed, at 600 N compressive load, 5 Hz, and 1 million cycles. The mean number of cycles to failure was higher for spinal instrumentation Systems employing longitudinal rods than those using plates (ANOVA F = 16.94, P < .001). At 600 N, the compact Cotrel-Dubousset, TSRH, and ISOLA rod systems demonstrated mean cycles to failure ranging from 200,000 to 900,000 cycles. The remaining devices Including Dyna-lok, Kirschner plate, and VSP devices had failures ranging from 50,000 to 210,000 cycles, Polyethylene cylinders representing vertebral bodies were used to eliminate the problems of biologic deterioration encountered with cadaveric spines (a full cyclical test to 1 million cycles required 56 hours), and thus to provide analysis of the weak portion of each spinal system, The failure ofeleven of the twelve spinal systems occurred by fracture of a pedicle screw, most commonly at the junction of the upper screw thread and the collar (Kirschner, AO fixator, standard CD, ISOLA, and TSRH), However, in Dynalok and VSP systems, fracture of the threaded portion of the screw just posterior to the integral nuts was the most common screw fracture location. The compact CD system was the only spinal Implant that consistently failed by fracture of the longitudinal spinal member (rod). The fatigue life of rod based systems was longer than plate based systems. These studies confirm the importance of anterior column load sharing ivertebral body, corpectomy bone graft) as the mean bending strength demonstrated by these implant systems was not inordinately high using this “worst case scenario” model.

Biomechanical Analysis of Lumbosacral Fixation

Fluxion testing was performed until failure on 66 lumbosacral bovine spinal segments comparing ten different lumbosacral Instrumentation techniques. Maximum flexion moment at failure, flexural stiffness, and maximum angulation of the lumbosacral joint at failure were determined as well as strain measurements across the anterior aspect of the lumbosacral intervertebral disc using an extensometer. The maximum moment at failure was significantly greater for the only two devices that extended fixation into the ilium anterior to the projected image of the middle osteoligamentous column: ISOLA Galveston and ISOLA Iljac screws (F = 12.2, P < 0.001). The maximum stiffness at failure reinforced these findings (F = 23.7, P < 0.001). A second subset of stability showed the advantages of S2 pedicle fixation by increasing the flexural lever arm (Cotrel-Dubousset butterfly plate, and Cotrel-Dubousset Chopin block, P < 0.05). This exhaustive in vitro biomechanical study introduces the concept of a pivot point at the lumbosacral joint at the intersection of the middle osteoligamentous column (sagittal plane) and the lumbosacral intervertebral disc (transverse plane) A spinal surgeon can increase the stability of lumbosacral instrumentation by extending fixation through the anterior sacral cortex [Steffee plate group with pedicle screws that medially converge in a triangular fashion). A means of enhancing this fixation was to achieve more interior purchase by extending the fixation down to the S2 pedicle (Cotrel-Dubousset Chopin and Cotrel-Dubousset butterfly groups). However, the best fixation was achieved by obtaining purchase between the iliac cortices down into the superior acetabular bone. This extends the fixation a greater distance anterior to the projected lateral image of the middle column: ISOLA Galveston and ISOLA iliac screw techniques (P < 0.05). Crossing the SI joint with fixation is only biomechanically justified if the construct obtains purchase of the iliac creast anterior to the projected image of the middle osteoligamentous column.

Correction of cervical kyphosis using pedicle screw fixation systems

STUDY DESIGN This retrospective study was conducted to analyze the clinical results in 30 patients with cervical kyphosis that had been treated using cervical pedicle screw fixation systems. OBJECTIVES To evaluate the effectiveness of a pedicle screw fixation procedure in correction of cervical kyphosis. SUMMARY OF BACKGROUND DATA Correction of cervical kyphosis is a challenging problem in the field of spinal surgery. There have been several reports regarding surgical correction of cervical kyphosis; however, there have been no detailed reports on correction of cervical kyphosis using a pedicle screw fixation procedure. METHODS Thirty patients with cervical kyphosis underwent correction and fusion using cervical pedicle screw fixation. Seventeen of 30 patients with flexible kyphosis (Group I) were managed by a posterior procedure alone. The remaining 13 patients with rigid or fixed kyphosis (Group II) had a combined anterior and posterior procedure. RESULTS The average preoperative cervical kyphosis of 29.4 degrees improved to 2.3 degrees after surgery and was 2.8 degrees at the final follow-up. In Group I patients, preoperative kyphosis of 28.4 degrees improved to 5.1 degrees at the final follow-up. In contrast, preoperative kyphosis of 30.8 degrees in Group II patients improved to 0.5 degree at the final follow-up. Solid fusion was achieved in all patients. There were two patients with transient nerve root complications related to pedicle screw instrumentation. CONCLUSION Cervical kyphosis in 30 patients was effectively corrected using a pedicle screw fixation procedure with no serious complications. Flexible kyphosis with segmental motion can be satisfactorily corrected by a single posterior procedure using pedicle screw fixation. However, circumferential osteotomies combined with a posterior shortening procedure involving a pedicle screw system are required to achieve the best correction of fixed kyphosis by bony union. Cervical pedicle screw fixation is the most advantageous instrumentation in the correction of cervical kyphosis.

Experimental study of thoracolumbar burst fractures : a radiographic and biomechanical analysis of anterior and posterior instrumentation systems

Study Design. The efficacy of posterior instrumentations for treating thoracolumbar burst fractures to restore spinal alignment and indirectly reduce intracanal bone fragments was investigated. Also, a biomechanical study was performed to compare the mechanical stability of anterior and posterior instrumentations. Methods. Twenty-four fresh human cadaveric thoracolumbar spine segments were used. After clinically identical L1 burst fractures were created, two posterior instrumentations were used to restore spinal alignment: 1) Harrington dual distraction rods with sleeves and 2) AO internal fixator. Radiographs and computed tomography scans were obtained to assess spinal alignment and canal dimensions. Biomechanical testing was performed in axial compression, rotation, and flexionextension on all constructs, inducing anterior reconstruction with the Kaneda device. Summary of Background Data. Kyphosis averaged 14° in the injured specimens and was corrected to 1° of lordosis after posterior reduction, and vertebral body height was restored to normal in most of the specimens. Reduction rate of canal compromise was 12.3% for Harrington instrumentation and 18.5% for AO internal fixator. Anterior reconstruction with the Kaneda device was more stable than the posterior instrumentation systems in all loading conditions. Results. The posterior reduction and stabilization with posterior instrumentation provided effective restoration of the sagittal alignment. However, the reduction capability of the intracanal bone fragments was distinctly limited. Conclusions. The anterior reconstruction method permits effective decompression of the spinal canal and offers superior mechanical stability compared with the indirect decompression and stabilization of posterior instrumentation.

Biomechanical role of the posterior elements, costovertebral joints, and rib cage in the stability of the thoracic spine.

Study Design This is a biomechanical study of the thoracic spine. Various ligaments and joints were resected sequentially and nondestructive cyclic loading tests were performed. Effects of each resection were analyzed biomechanically. Objectives To investigate the role of the posterior elements, costovertebral joints, and rib cage in the stability of the thoracic spine. Summary of Background Data There have been no experimental studies concerning the mechanical interaction between the thoracic spine and rib cage. Methods Eight canine rib cage-thoracic spine complexes, consisting of the sixth to eighth ribs, sternum, and T5-T9 vertebrae, were used. Six pure moments along three axes were applied to the specimens, and angular deformation of T6-T7 was recorded. After testing the intact specimen, resection of the stabilizers was conducted incrementally in the following manner: 1) removal of the posterior elements at T6-T7, 2) resection of the bilateral seventh costovertebral joints, and finally, 3) destruction of the rib cage. The same loading tests were repeated at each stage. The ranges of motion and neutral zones were calculated by digitization. Results A large increase in the range of motion in flexion-extension was observed after resection of the posterior elements and in lateral bending and axial rotation after resection of the costovertebral joints. A significant increase in the neutral zone in lateral bending and axial rotation was observed after bilateral resection of the costovertebral joints and destruction of the rib cage. Conclusions The costovertebral joints and rib cage play an important role in providing stability to the thoracic spine. The state of the costovertebral joints and rib cage should be assessed to evaluate the stability of the thoracic spine.