Journal of Spine

Abstract
Purpose: To compare the pullout loads of variable versus fixed angle screws in anterior lumbar interbody fusion (ALIF) plate/screw constructs in both foam and cadaveric models.
Methods: An ALIF plate was secured to a 0.160 g/cm3 polyurethane foam block (N = 10) with fixed or equivalently positioned variable angle screws and pulled out at 1 mm/min to failure. Embalmed human vertebral pairs (N = 10) were similarly utilized to compare fixed versus variable angle plate/screw constructs for pullout strength.
Results: There was no statistically significant difference between fixed and variable angle plates for either foam (p = 0.6) or vertebral specimens (p = 0.3) based on maximum load or stiffness. The maximum load for the vertebral specimens was on average 39% of that for the foam (p = 0.001) and the stiffness was about 55% of that for the foam (p = 0.001).
Conclusions: In this study, no statistically significant difference in pullout strength or stiffness was found between fixed and variable angle ALIF plate/screw constructs. However, the embalmed cadaveric bone model was shown to be statistically weaker in pullout strength and stiffness when compared to the foam model. This study suggests that the foam model may not always be representative of the cadaveric model in the magnitude of load, but may still provide good comparative results between different designs.

Abstract Objective: To illustrate a hybrid technique that involves a combination of open decompression and Posterior Lumbar Interbody Fusion (PLIF) and percutaneously placed pedicle screws. This technique allows for PLIF via a midline incision and approach, and decompression without compromise in operative time and visualisation. Furthermore, this approach is proposed to reduce post-operative wound pain by: smaller midline incision, significantly reduced muscle trauma by not dissecting the paraspinal muscles off the facet joint complex, avoidance of a posterolateral fusion to facilitate limited lateral muscle dissection off the transverse processes. Summary of background data: PLIF fusion rates are comparable to posterolateral fusion rates, as well as providing greater sagittal and coronal balance. There is positive evidence that degenerative spondylolisthesis with canal and/or foraminal stenosis requires stabilisation when decompressed via laminectomy. Methods: Patients with Grade I-II spondylolisthesis at L4/5 with moderate - severe canal/foraminal stenosis undergo a midline PLIF at L4/5, with closure of the midline incision. Percutaneous pedicle screws are inserted, therefore minimising local muscle trauma, with reduction of the spondylolisthesis performed using the pedicle screw construct. Rods are inserted percutaneously to link the L4 and L5 pedicle screws. Image intensification is used to confirmed satisfactory screw placement and reduction of the spondylolisthesis. Conclusion: Percutaneous lumbar pedicle screws can be combined with a standard midline PLIF to reduce postoperative wound pain while allowing for satisfactory screw placement.

Abstract Study Design: Biomechanical study using a finite element model of the lumbar functional spinal unit (FSU). Objectives: To compare the biomechanics of a novel in situ expandable posterior lumbar interbody fusion (PLIF) device, with a traditional rigid cage used in a stand-alone fashion. Methods: An experimentally validated intact finite element (FE) model of the L4-L5 FSU was altered to model expandable VariLift-L and BAK devices in a stand-alone fashion. A follower compressive pre-load of 400 N plus 8.0 Nm of flexion, extension, lateral bending, and axial rotation moments were applied to the model to simulate the physiological loadings. The kinematics and load sharing among various models were compared. Results: Range of motion analyses showed that fusion utilizing VariLift-L expandable stand-alone device was more effective in limiting motion of the spinal column than the BAK device. The normal load at the device/endplate interface for the VariLift-L was similar to that of the BAK in all loading modes. The A-P shear load for the stand-alone VariLift-L model was higher than the BAK model under flexion. Conclusions: Due to predicted forces along the A-P direction, axial contact loads in flexion and extension, the lordotic slope of the device and the presence of intact annulus in the anterior region of the disc, the tendency of the VariLift-L device to migrate into the canal and subside into the endplate may be lower, despite the higher A-P shear force predicted for the VariLift-L device. This shape and lordotic expandability act to resist A-P shear forces in the flexion mode. The expandable device has the  advantage of adjusting its outer profile to the lordotic angle of the treated segment, ensuring a better contact between the device and endplates. Biomechanically, the VariLift-L interbody fusion device is a good solution for fusion surgery of the lumbar spine segment.

Abstract Purpose: Venous thrombotic events remain a common problem following both spinal cord injury and elective spinal surgery. Recent guidance has been issued by the National Institute of Clinical Excellence (NICE) on the use of prophylaxis for these patients. This study was designed to show how spinal units in the United Kingdom (UK) are managing this risk for their patients. Method: We conducted a telephonic survey of 30 spinal units which were identified from a NHS website. We asked about their current method of thromboprophylaxis in spinal patients and asked if they had changed their practice based on the recommendations by NICE Results: 13.3% of the centres had changed their practice based on these updated clinical guidelines. 93% centres used mechanoprophylaxis only in the elective setting and 10% of centres reported increased wound complications with their new practice. Conclusion: Our results show that the majority of spinal centres are compliant with the recommendations of NICE. However, there remains a lack of good quality clinical evidence for thromboprophylaxis and more research should be conducted in this area.

Background: In previous reports, the patients are described to have transient symptoms from physiologic rotation or extension of the cervical spine, resulting from a cervical osteophyte compressing the vertebral artery and causing vertebral artery insufficiency, known as Bow Hunter syndrome.

Methods: An 85-year-old female presented with new onset occipital headaches, nausea, vomiting and vertigo that were not precipitated by change in head position. Patient had bilateral cerebellar infracts. Patient underwent decompression and instrumented stabilization of the cervical spine from the posterior approach.

Results: At one-year follow-up, patient remained stroke free with patent vertebral artery.

Conclusion: To our knowledge, this is the first report of bilateral infraction from a vertebral artery insufficiency caused by cervical osteophytes without history of transient symptoms from movement of the head or neck, a variant of the Bow Hunter syndrome. Anterior versus posterior approach for vertebral artery insufficiency from osteophytic compression should be primarily based on location of the pathology and not the cervical level of involvement.