Predictors of conservative treatment for pyogenic spondylitis.

INTRODUCTION: Although initial treatments for pyogenic spondylitis include conservative approaches such as rest and antibiotics, some cases are refractory to conservative therapy. The objective of this study was to clarify the predictors for achievement of C-reactive protein (CRP) normalization in pyogenic spondylitis by conservative therapy. METHODS: In the present study, we enrolled 83 patients (51 men and 32 women) with conservatively treated pyogenic spondylitis from 2006 to 2015. Multiple logistic regression analysis was used to examine the association of achievement of CRP normalization with the number of infected vertebrae, bacterial strain, blood data, and the expansion of abscess to the epidural space by using functional magnetic resonance imaging. RESULTS: We found significant differences in the subjects with and without achievement of CRP normalization with respect to age, the number of affected vertebrae, ratio of resistant pathogenic bacteria, ratio of expansion of abscess to the epidural space, and blood data such as Hb, ALB, eGFR, Cr, and ALP levels. After adjustment for age and sex, the number of infected vertebral bodies, resistant bacteria, expansion of abscess to the epidural space, and Hb level showed significant associations with the normalization of CRP. In addition, we used multiple logistic regression analysis with age, sex, number of infected vertebral bodies, resistant bacteria, expansion of abscess to the epidural space, and serum Hb level as explanatory variables. We found that expansion of the abscess to the epidural and paravertebral spaces was significantly associated with the normalization of CRP level. CONCLUSIONS: The number of infected vertebral bodies, resistant strains of pathogenic bacteria, expansion of abscess to the epidural and paravertebral spaces, and serum Hb level predicts the prognosis of patients with pyogenic spondylitis. Particularly, expansion of abscess to the epidural and paravertebral spaces was strongly associated with the achievement of CRP normalization.

A Comparative Biomechanical Analysis of Stand Alone Versus Facet Screw and Pedicle Screw Augmented Lateral Interbody Arthrodesis: An In Vitro Human Cadaveric Model.

STUDY DESIGN: Cadaveric biomechanical study. OBJECTIVE: To investigate the kinematic response of a stand-alone lateral lumbar interbody cage compared with supplemental posterior fixation with either facet or pedicle screws after lateral discectomy. SUMMARY OF BACKGROUND DATA: Lateral interbody fusion is a promising minimally invasive fixation technique for lumbar interbody arthrodesis. The biomechanical stability of stand-alone cage placement compared with supplemental posterior fixation with either facet or bilateral pedicle screws remains unclear. METHODS: A 6-degree of freedom spine simulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral-bending, and axial-rotation were tested in the intact condition, followed by destabilization through a lateral discectomy at L2-L3 and L4-L5. Specimens were then reconstructed at both operative segments in the following sequence: (1) lateral interbody cage placement; (2) either Discovery facet screws or the Viper F2 system using a transfacet-pedicular trajectory randomized to L2-L3 or L4-L5; and (3) removal of facet screw fixation followed by placement of bilateral pedicle screw instrumentation. Acute range of motion (ROM) was quantified and analyzed. RESULTS: All 4 reconstruction groups, including stand-alone interbody cage placement, bilateral Discovery facet screws, the Viper F2 system, and bilateral pedicle screw-rod stabilization, resulted in a significant decrease in acute ROM in all loading modes tested (P<0.05). There were no significant differences observed between the 4 instrumentation groups (P>0.05). Although not statistically significant, the Viper F2 system resulted in greatest reduction of acute ROM in both flexion-extension and axial rotation versus all other treatments (P>0.05). CONCLUSIONS: Stand-alone interbody cage placement results in a significant reduction in acute ROM at the operative segment in the absence of posterior supplemental fixation. If added fixation is desired, facet screw placement, including the Viper F2 facet screw system using an integrated compression washer and transfacet-pedicular trajectory, provides similar acute stability to the spinal segment compared with traditional bilateral pedicle screw fixation in the setting of lateral interbody cage deployment.

Comparative in vitro biomechanical analysis of a novel posterior cervical fixation technique versus conventional posterior-based constructs.

STUDY DESIGN: Comparative in vitro, cadaveric biomechanical study. OBJECTIVE: To compare the kinematic response of a new posterior cervical midline surgical technique versus that of conventional fixation techniques. SUMMARY OF BACKGROUND DATA: A new method was designed using alternating bilateral intralaminar screws connected with a single midline rod. This technique provides the theoretical benefits of less operative dissection and reduced implant cost, but the acute flexibility properties remain unknown. Using an in vitro cadaveric model, the study objective was to define the operative level(s) changes in multidirectional flexibility after posterior destabilization/reconstruction from C3 to C6. METHODS: A 6 degree of freedom spine stimulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral bending, and axial rotation were tested in the intact condition, followed by destabilization by a simulated posterior column injury from C3 to C6. Specimens were then reconstructed from C3 to C6 and tested in the following sequence: sublaminar hook rod (SH), lateral mass screw rod (LMR), midline laminectomy from C3 to C6 with LMR (MLR), and midline posterior fixation from C3 to C6 (SMF). Range of motion (ROM) and neutral zone were quantified and analyzed. RESULTS: Significant increases in ROM and neutral zone at C3 to C6 were found under all loading conditions for the destabilized condition and intact spine versus all other treatments (P<0.05). The conventional treatments: SH, LMR, and MLR resulted in significantly less ROM than the proposed SMF in flexion-extension and lateral bending (P<0.05). Axial rotation provided similar results; however, no differences were observed between the SH and SMF (P>0.05). Notably, LMR and MLR provided significantly more stability than SH in axial rotation (P<0.05). CONCLUSIONS: Data produced suggest that the new, midline rod fixation approach provides less biomechanical stability than conventional posterior cervical reconstruction techniques. In addition, the high incidence of laminar fracture during screw placement and close proximity of the screw trajectory and polyaxial heads to the dura suggest a practical limitation as well.

Adjacent-level range of motion and intradiscal pressure after posterior cervical decompression and fixation: an in vitro human cadaveric model.

STUDY DESIGN: This in vitro human cadaveric study measured adjacent-level kinematics after posterior cervical decompression and fixation. OBJECTIVE: Quantify adjacent-level changes in range of motion (ROM) and intradiscal pressure after posterior cervical decompression and fixation. SUMMARY OF BACKGROUND DATA: Optimal length of instrumentation after posterior decompression is unclear. Longer posterior cervical fixation constructs may increase the risk of adjacent-segment degeneration. METHODS: Eight cervicothoracic spines were evaluated intact, with C3-C6 laminectomy, C3-C6 laminectomy + C3-C6 fixation, C3-C6 laminectomy + C3-C7 fixation, C3-C7 laminectomy, C3-C7 laminectomy + C3-C7 fixation, C3-C7 laminectomy + C2-C7 fixation, C3-C7 laminectomy + C3-T2 fixation, and C3-C7 laminectomy + C2-T2 fixation. Testing included intact moments (± 2.0 N·m) in flexion/extension, axial rotation, and lateral bending, with quantification of ROM at C2-C3, C6-C7, and C7-T1 normalized to the intact spine. Intradiscal pressures were also measured at each level. RESULTS: For the C3-C6 laminectomy group, there were no differences in adjacent-level flexion/extension ROM or intradiscal pressure based on construct length, except at C6-C7, where ROM was significantly decreased when fixation was extended to C7 (P < 0.05). After C3-C7 laminectomy and reconstruction, the greatest increase in C2-C3 flexion/extension ROM and intradiscal pressure occurred in the C3-T2 fixation subgroup (ROM: 348% [P < 0.05]; intradiscal pressure: 319 ± 243 psi [pounds per square inch] vs. 65 ± 41 psi intact [P < 0.05]). At C7-T1, the greatest increase in flexion/extension ROM and intradiscal pressure occurred after C2-C7 fixation (ROM: 531% [P < 0.05]; intradiscal pressure: 152 ± 83 psi vs. 21 ± 14 psi intact [P < 0.05]). CONCLUSION: For C3-C6 laminectomy, instrumentation to C7 significantly decreased flexion/extension ROM and intradiscal pressure at C6-C7 without significantly increasing either measure at C2-C3 or C7-T1 relative to C3-C6 fixation. In the setting of a C3-C7 laminectomy, when instrumenting to either C2 or T2, consideration should be given to including both levels within these constructs.

The effect of spinal instrumentation on kinematics at the cervicothoracic junction: emphasis on soft-tissue response in an in vitro human cadaveric model.

OBJECT: Thoracic pedicle screw instrumentation is often indicated in the treatment of trauma, deformity, degenerative disease, and oncological processes. Although classic teaching for cervical spine constructs is to bridge the cervicothoracic junction (CTJ) when instrumenting in the lower cervical region, the indications for extending thoracic constructs into the cervical spine remain unclear. The goal of this study was to determine the role of ligamentous and facet capsule (FC) structures at the CTJ as they relate to stability above thoracic pedicle screw constructs. METHODS: A 6-degree-of-freedom spine simulator was used to test multidirectional range of motion (ROM) in 8 human cadaveric specimens at the C7­T1 segment. Flexion-extension, lateral bending, and axial rotation at the CTJ were tested in the intact condition, followed by T1­6 pedicle screw fixation to create a long lever arm inferior to the C7­T1 level. Multidirectional flexibility testing of the T1­6 pedicle screw construct was then sequentially performed after sectioning the C7­T1 supraspinous ligament/interspinous ligament (SSL/ISL) complex, followed by unilateral and bilateral FC disruption at C7­T1. Finally, each specimen was reconstructed using C5­T6 instrumented fixation and ROM testing at the CTJ performed as previously described. RESULTS: Whereas the application of a long-segment thoracic construct stopping at T-1 did not significantly increase flexion-extension peak total ROM at the supra-adjacent level, sectioning the SSL/ISL significantly increased flexibility at C7­T1, producing 35% more motion than in the intact condition (p < 0.05). Subsequent FC sectioning had little additional effect on ROM in flexion-extension. Surprisingly, the application of thoracic instrumentation had a stabilizing effect on the supra-adjacent C7­T1 segment in axial rotation, leading to a decrease in peak total ROM to 83% of the intact condition (p < 0.05). This is presumably due to interaction between the T-1 screw heads and titanium rods with the C7­T1 facet joints, thereby limiting axial rotation. Incremental destabilization served only to restore peak total ROM near the intact condition for this loading mode. In lateral bending, the application of thoracic instrumentation stopping at T-1, as well as SSL/ISL and FC disruption, demonstrated trends toward increased supraadjacent ROM; however, these trends did not reach statistical significance (p > 0.05). CONCLUSIONS: When stopping thoracic constructs at T-1, care should be taken to preserve the SSL/ISL complex to avoid destabilization of the supra-adjacent CTJ, which may manifest clinically as proximal-junction kyphosis. In an analogous fashion, if a T-1 laminectomy is required for neural decompression or surgical access, consideration should be given to extending instrumentation into the cervical spine. Facet capsule disruption, as might be encountered during T-1 pedicle screw placement, may not be an acutely destabilizing event, due to the interaction of the C7­T1 facet joints with T-1 instrumentation.