Pedicle Screw-rod System Research Articles

Usefulness of 3-Dimensional Full-Scale Modeling for Preoperative Simulation of Surgery in a Patient With Old Unilateral Cervical Fracture-Dislocation

Case report. We describe the usefulness of 3-dimensional full-scale modeling for preoperative simulation of surgery in a patient with old cervical fracture-dislocation. Many different surgical procedures have been used in the treatment of unilateral cervical fracture-dislocation. However, consistent protocols and procedures for the surgical correction of old fracture-dislocations associated with nerve root lesions have not been established. Two months after an automobile accident, a 50-year-old man developed symptoms of left C5 palsy. Four months after the accident, he was diagnosed with a fracture-dislocation at left C4-C5 facet with impingement of the left C5 root at the neural foramen. In addition, his left vertebral artery was completely occluded. Spontaneous bony fusion had progressed around the left facet and the anterior aspect of the vertebrae at C4-C5. Before surgery, a 3-dimensional full-scale model in the patient's cervical spine was made in order to simulate the planned surgical reconstruction. Through this simulation, we were able to accurately evaluate the deformed bony structures around the fractured C4-C5 facet. During the actual surgery, all the planned procedures were successfully achieved, including anterior release, insertion of pedicle screws at left C4 and C5, unroofing of the left C5 root, reduction of the displaced facet with the pedicle screw-rod system, and spinal fusion at C4-C5. After surgery, the patient's left C5 palsy was dramatically relieved and the spinal fusion went on to successful healing. The surgical simulation made possible by the 3-dimensional full-scale model appeared to simplify the surgical procedure and may enhance the safety of the complex spinal reconstruction.

Anatomical measurements of porcine lumbar vertebrae

Porcine spines are frequently used as an alternative to human specimens for spinal implant testing. Morphometric data of the normal porcine lumbar vertebrae are lacking at this time, yet these data are crucial for application to such studies. This study provides such a database and highlights the differences between porcine and human specimens. All the lumbar vertebrae (L1-L6) from six adult (18-24 month old, 60-80 kg) male porcine spines were used in our study (n=36). A total of 15 anatomical parameters from each vertebra were measured by two observers. Linear parameters were measured using digital calipers. The mean, standard deviation and standard error of mean were calculated using Microsoft Excel. Results from our study were compared with available data on human vertebra. Compared to the human vertebrae, there were several anatomical differences in the porcine thoracolumbar vertebrae including smaller end plate area, larger pedicles, taller and narrower vertebral bodies, narrower spinal canals and smaller spinous process lengths. Our results provide a database of anatomical measurements for porcine lumbar vertebrae and highlight their differences with human vertebrae. Porcine vertebrae may be used as an alternative to human specimen if these differences are taken into account. Studies which involve testing implants such as interbody cages, disc replacements and pedicle screw-rod systems in porcine spines should match implant size appropriately.

Effect of Lumbar Interbody Cage Geometry on Construct Stability: A Cadaveric Study

Biomechanical study to investigate three-dimensional motion behavior of cadaveric spines in various surgical simulations. To determine the effect of cage geometry on the construct stability. There is a wide variety of cage/spacer designs available for lumbar interbody fusion surgery. These range from circular, tapered, and rectangular with and without curvature. However, the effectiveness of cages with different designs and materials to stabilize a decompressed intervertebral space has not been fully studied. Six fresh ligamentous lumbar spine specimens (L1-S2) were subjected to pure moments in the six loading directions. The resulting spatial orientations of the vertebrae were recorded using Optotrak Motion Measurement System. Measurements were made sequentially for intact, bilateral spacer placements across L4-L5 using a posterior approach, supplemented with pedicle screw-rod system fixation, and after the cyclic loading in flexion-extension mode. The stability tended to decrease after the bilateral cage placement as compared with the intact for all loading cases except flexion. In flexion, the angular displacement decreased to 80% of the intact. However, there was no significant statistical difference seen in stability between intact and after bilateral spacer placement. Following the addition of posterior fixation using pedicle screw-rod system, the stability significantly increased in all directions. Cyclic loading did not have any significant effect on the stability. Stand-alone cages restore motion to near-intact levels at best, and supplement instrumentation is essential for significantly increasing the stability of the decompressed segment. The effects of cage geometry and Young's modulus of the cage material do not seem to influence the stability, as compared with the other cagedesigns, especially after supplemental fixation with a posterior system.

Mechanical stability of thoracolumbar pedicle screw fixation. The effect of crosslinks.

Pedicle screw fixation for unstable thoracolumbar spine injuries is relatively new. The effect of one or two crosslinks on rotational and lateral bending stiffness was studied. To determine the rotational and bending stiffness values of thoracolumbar fractures fixed by the AO's internal fixation system with zero, one, or two crosslinks. Eight embalmed thoracolumbar spine segments. (T12-L2) were instrumented at T12 and L2 with a pedicle screw-rod system. Rotational stiffness was determined for 10 cycles to 2.5 degrees, 3.5 degrees, and 5 degrees of rotation, with and without one or two crosslinks, and lateral bending stiffness for 10 cycles to 0.25, 0.40, and 0.50 inch. The results showed a clear trend toward increased stiffness with crosslinks. The stiffness values of the two-crosslink construct at 2.5 degrees and 3.5 degrees of rotation were significantly higher than those of the zero-crosslink system. Also, the bending stiffness of the two-crosslink construct was significantly higher than that of no-crosslink system at all of the displacements. Rotational stiffness values of the two-crosslink construct were significantly higher than those of the zero-crosslink system, at 2.5 degrees and 3.5 degrees of rotation. Lateral bending stiffness of the two-crosslink system was higher than that of the zero-crosslink system at all levels of displacement.

Experience with the “Fixateur Interne”

Impressive clinical reports have come from several major spinal research centers regarding the results of using the AO spinal internal fixator, a recently released pedicle screw rod system. A retrospective review of the first 2 years of clinical results from a diverse group of orthopedic surgeons using this device at a Canadian University center may provide some insight into potential clinical outcomes in general use. These results contrast with the outcome data provided to date, which have been presented by expert academic spinal surgeons. The results suggest that there may be room for considering limited release of this device, perhaps with the requirement for special certification in its application.

Operative Treatment of Spinal Fractures with the AO Internal Fixator

A multicentered prospective trial to investigate the usefulness of the AO spinal internal fixator for the treatment of thoracolumbar fractures and fracture-dislocations was undertaken. This pedicle screw-rod system was effective in stabilizing a variety of unstable fracture patterns. It was effective in decompressing the canal of retropulsed bony fragments associated with burst fractures. By the use of this implant, sagittal plane deformity was easily corrected.