Biomechanical comparisons of spinal fracture models and the stabilizing effects of posterior instrumentations

A new instrumentation system for the reduction and posterior stabilization of unstable thoracolumbar fractures

An innovative instrumentation and stabilization system was used for the treatment of unstable thoracolumbar fractures. The new osteosynthesis apparatus employs pedicle screw fixation, plate application, and a mechanical device for dynamic reduction in stable posterior fixation. Sixteen patients were treated with this operative technique that included a decompressive laminectomy, an arthropedunculectomy, and the removal of vertebral canal bone fragments. In most patients, three vertebral bodies, rather than four or five, were immobilized. All patients were studied pre- and postoperatively with plain radiographs and computed tomography. Pre- and postoperative examinations demonstrated no alteration in neurological status. All patients, however, with incomplete lesions showed improvement in neurological function at a mean follow-up period of 12 months. The authors' experience suggests that the new system offers ease and versatility of application, restoration of vertebral alignment through mechanical reduction, and enhanced spinal stability. The new system, moreover, enables the reduction of lateral dislocation.

Biomechanical stability of five pedicle screw fixation systems in a human lumbar spine instability model

In this study, the three-dimensional biomechanical stabilizing capabilities of five pedicle screw fixation systems and facet screw fixation were determined. These systems were the Ace device without and with transverse wiring, AO device, CD device, Steffee plate, Wiltse device with single and double rods, and facet screw fixation. All systems were applied to the L5S1 level in a human in vitro spine rendered unstable by transection of the posterior ligaments and transverse holes drilled through the intervertebral disc. There were no statistically significant differences in the biomechanical stability provided by any of the pedicle screw devices, where stability was defined as the average stiffness from the load-displacement curve. All devices restored motion to less than 50% of intact levels under flexion moments. In extension, all devices, except the facet screw method, restored motion to below intact levels. In lateral bending, all devices restricted motion to less than 50% of intact motion. Under axial torque, the CD device provided the least motion while the AO device did not restore motion to the intact level.

Bone graft translation of four upper cervical spine fixation techniques in a cadaveric model

The goal of spinal fixation is to promote bony fusion by restricting motion at the site of the bone graft. Therefore, in order to evaluate the efficiency of various cervical fixation techniques, we determined the translations at the posterior arch of C1 for four C1-C2 posterior techniques: Gallie, Brooks, Magerl, and Halifax. Our model was the cadaveric specimen, with extensive soft tissue injury: transection of the alar, transverse, and capsular ligaments. Under three-dimensional physiological loading, we recorded the motion of C1 relative to C2, and calculated the translations at the surface of the graft in three dimensions, 10 specimens being tested intact, injured, and instrumented with each of the techniques. We assumed that translational laxity or neutral zone was the critical motion parameter and evaluated it, quantified herein as the neutral zone, at seven points at the graft site. The three-dimensional neutral zone translations were analyzed by their axial and shear components. We found that there was no significant difference with the fixation techniques in the average axial translation (Brooks: 1.1 mm; Magerl: 1.3 mm; Gallie: 1.5 mm; and Halifax: 0.5 mm). In shear, the Magerl averaged 1 mm, which was significantly less than the Gallie (2.1 mm). The Brooks (1.6 mm) and Halifax (1 mm) were not different from each other, Magerl, or Gallie. We propose that evaluation by translational laxity (neutral zone) at the graft site is a noteworthy concept in biomechanical analysis.

Percutaneous interbody osteosynthesis in the treatment of thoracolumbar traumatic or tumoural lesions. A review of 51 cases

The authors describe a technique of percutaneous interbody osteosynthesis applicable to the dorsal and lumbar spine. 51 patients were so treated for different aetiologies: traumatic conditions (35 cases) and tumoural lesions (16 cases). The material used consisted of special instruments that are positioned in double obliquity by a percutaneous posterolateral approach. A posterior approach limited to the pathological focus was used jointly whenever a graft or a decompression was necessary (19 cases). Several types of anaesthesia were used (local, local-regional, general, neuroleptanalgesia). The patients benefited by the advantages that usually accompany percutaneous techniques. The advantages and limitations of the method are discussed.