Aims

Mechanical stimulation is a key factor in the development and healing of tendon-bone insertion. Treadmill training is an important rehabilitation treatment. This study aims to investigate the benefits of treadmill training initiated on postoperative day 7 for tendon-bone insertion healing.

Summary

Neurological deficits resulting from spinal cord compression occur infrequently. When presented with neurological compromise, the most common management was radiotherapy, with surgery only being offered to patients who developed neurological deficit or pathological fracture resulting in unresolved severe pain post radiotherapy.

A biomechanical study assessing pedicle screw fixation with three different augmentation methods was performed in human cadaveric vertebrae. Precision opto-electronic measurement of screw motion assessed motion magnitude and patterns, ie translation and/or rotation. Physiological cyclic loads were applied as opposed to the simple pull out test. Augmentation with wires, hook or cement decreased overall motion. There were no significant differences in motion magnitude between the three augmentation methods. Motion patterns for screws with cement augmentation were mainly rotational and differed from the other two methods. Rigid body translations were observed with wires or hook augmentation, suggesting a loosening behaviour. Augmentation with cement resulted in better fixation than wires or hook.

Augmentation of loosened pedicle screws in poor quality bone is often necessary. The purpose of this study was to contrast the kinematics of loosened pedicle screws augmented with laminar hooks, sublaminar wires or calcium phosphate cement.

Cyclic tests of pedicle screws with compressive force and bending moment were carried out on forty-eight screws in twenty-four cadaveric vertebrae (L3-L5) augmented with hooks, wires or cement. Motion at the screw tip and screw head were measured using an optoelectronic camera system and the magnitudes compared in a paired manner using non-parametric statistics. Motion patterns of the screws were determined for each augmentation method.

Augmentation with hook, wire or cement decreased screw motion. There was no significant difference between augmentation methods when the magnitudes of motion, described as ranges and offsets, were compared. Augmentation with cement resulted in mainly rotations of the screws while there were rigid body translations with wires or hooks.

Comparing magnitudes of motion at the screw head and screw tip were insufficient. The screw head and screw tip could be moving in synchronous, indicating rigid body translations. Using simple pull out tests would not detect such differences.

The method used in this study contrasted pedicle screws motion with different augmentations. While there was no detected significant difference in motion magnitude of the pedicle screws, the motion pattern of the screws suggested better augmentation with cement.

Motion of pedicle screws in situ had not been described in the literature. Previous work comparing pedicle screws fixation used the pull out test, while the current method applied physiological loads.

Funding: Funding from the Canadian Institutes for Health Research, Funding from Synthes

Spine Please contact author for diagrams and/or graphs.

Purpose: The objectives of this study were to determine the effect of posterior instrumentation extension and/or cement augmentation on immediate stabilization of the instrumented level and biomechanical changes adjacent to the spinal instrumentation.

Methods: This study was designed for repeated measures comparison, using 12 T9-L3 human cadaveric segments, to test the effects of posterior rod extension and cement augmentation following T11 corpectomy. The spine was stabilized with a vertebral body replacement device and with posterior instrumentation from T10 to T12. The T12 pedicle tracts were over-drilled to simulate loosened screws in an osteoporotic spine. The T10 screws were not over-drilled but cemented so as to keep the superior segments constant. Flexibility tests were first carried out on the intact specimen, followed by 3 randomized surgical conditions without cement and lastly the 3 conditions after cement augmentation. The 3 conditions were: 1) no posterior extension rods to L1, 2) flexible extension rods, and 3) rigid extension rods. A combined testing/analysis protocol that used both the traditional flexibility method and a hybrid technique [Panjabi 2005] was adopted. Flexibility tests with +/−5 Nm pure moments in flexion-extension, axial rotation and lateral bending were carried out and vertebral bodies’ motion in 3-D were collected. Two-way repeated measures ANOVA analyses were carried out on ROM between cement augmentation (factor 1) and the posterior rod extension (factor 2) on each flexibility test direction. An alpha of 0.05 was chosen. Newman-Keuls post-hoc analyses were carried out to compare between surgical techniques.

Results: Using the flexibility protocol, a reduction in ROMs at the destabilized level was observed with cement augmentation of screws or extension with rigid or flexible posterior rods to adjacent distal level. With the hybrid protocol, ROMs at adjacent level (T12-L1) were reduced with rod extension, but not with cement.

Conclusions: The results of this study suggest that cement augmentation would enhance stabilization, but create possible adjacent level effects due to increased motion and strain, while additional flexible extension rods would reduce biomechanical changes at the level of extension. Funding: 2 Funding Parties: CIHR

A biomechanical study assessing compressive failure load, strength and stiffness with three different interbody device shapes was performed in human cadaveric vertebrae. The custom-made interbody devices had similar cross-sectional areas and specimens were tested with 20% or 40% coverage of indentor to endplate area. Axial compressive load was applied at 0.2mm/s to a depth equivalent to 20% of the vertebral height. The clover-leaf shaped device resulted in significantly higher failure load, strength and stiffness over the elliptical and the kidney shaped devices for both areas of coverage. The clover-leaf shaped devices extended over stronger periphery regions of the endplates and resulted in stronger interface properties.

To determine if two novel interbody cage shapes, the kidney and the clover-leaf, are biomechanically superior to a standard elliptical shape of similar cross sectional area.

Uniaxial compression tests with unrestricted rotations were carried out on the superior endplates of forty-eight thoracolumbar (T9-L2) vertebrae with one of three shaped indentors covering 20% or 40% of the endplate area. Compressive load was applied using a servohydraulic testing machine at 0.2mm/s, to depth equivalent to 20% of the vertebral height. Failure load, strength and stiffness were compared.

The clover-leaf shaped indentors resulted in higher failure load (53% average increase), higher strength (67% average increase) and higher construct stiffness (43% average increase), and these results were significant (p< 0.05). Larger indentor coverage area of 40% also resulted in significantly higher failure loads over 20% coverage (75% average increase).

Current elliptical interbody devices are placed over the central region of the endplate, which is also the weakest. A clover-leaf shaped device extended over the stronger peripheral regions of the endplates and resulted in improved bone-implant interface properties. This implant if implemented in vivo could potentially reduce implant subsidence and lead to better long-term outcomes in osteoporotic patients.

The novel clover-leaf shaped indentor displayed superior bone-implant interface properties. Larger interbody devices should be used when possible to improve interface properties.

Implant subsidence in osteoporotic patients could be significantly reduced with a clover-leaf shaped device, leading to better long-term outcomes.

Funding: Funding from the Canadian Institutes for Health Research.