Non-fusion Surgeries of Lumbar Spine
In developed nations, a significant portion of the population (70-85%) suffers from low back pain at some stage in their lives. Spinal fusion is a popular treatment option when conservative therapies prove ineffective, but it can lead to accelerated degeneration in neighboring spinal segments. Nonfusion methods, on the other hand, focus on decreasing mobility in a specific spinal segment to prevent degeneration in the adjacent levels.
Dynamic spine stabilization devices, used for nonfusion purposes, can be categorized as anterior and posterior implants. The Dynesys device is a commonly employed posterior option that limits motion more during flexion than extension. On the other hand, the recently developed Elaspine device focuses on achieving consistent load distribution.
A study examined the impact of Elaspine on the range of motion and compared it to other nonfusion devices. Additionally, the study assessed the strength of Elaspine’s pedicle screws in terms of anchorage, comparing them to alternative designs mentioned in existing literature.
The study investigated the impact of a newly introduced posterior motion preservation device on the stiffness of a motion segment, both with and without a surgically induced structural defect in the intervertebral disc. The device significantly reduced the range of motion in flexion, extension, and lateral bending compared to intact segments. However, its effect on restricting motion in axial rotation was comparable to other non-fusion devices examined in previous studies.
The objective of motion preservation techniques is to achieve a balance between segmental motion and protecting the structural integrity, thus bridging the gap between segmental reconstruction and rigid fusions. Nevertheless, biomechanical studies have revealed limitations in these techniques, especially when it comes to restricting axial rotation.
Clinical application should be limited to early stages of degeneration without significant instability. However, the challenge lies in effectively matching the appropriate level of motion restriction with the individual’s segmental instability.
There have been reports of increased pedicle screw loosening and failure in a commonly used motion preservation system. This may be attributed to altered screw loading observed in experimental and Finite Element studies. Pull-out tests showed that the pedicle screws in the Elaspine device performed comparably to values reported in the literature, indicating good resistance to pull-out forces.
Comparing the effects of various non-fusion devices on range of motion (RoM) after additional surgical interventions is difficult. In vitro studies differ in the surgical techniques used and the extent of decompressions or defects created, leading to varying levels of instability. The stabilizing capability required of a device depends on the magnitude of RoM increase resulting from these interventions.
To facilitate comparisons with previous studies on non-fusion devices, the range of motion (RoM) data reported in those studies was adjusted to reflect the intact state.
After undergoing surgical destabilization, the Elaspine device, which was the subject of this investigation, demonstrated similar outcomes to the StabilimaxNZ (manufactured by Applied Spine Technology in New Haven, CT, USA) and a hinged pedicle screw system (Safinaz, Algorithma AS, Turkey) in terms of lateral bending (ranging from 60% to 79% of the intact state) and flexion/extension (ranging from 55% to 66% of the intact state).
Nevertheless, in terms of axial rotation, none of these devices achieved a reduction in range of motion (RoM) of previously destabilized levels to a level lower than that of the intact state.
In analyzing the outcomes of various in vitro experiments, it was observed that the Dynesys device exhibited a range of motion (RoM) between 20% and 40% of the intact specimen in lateral bending and flexion/extension. In axial rotation, the RoM of the Dynesys device ranged from 90% to 101% of the intact state.
However, one study reported a reduced motion restricting effect for the Dynesys device, which could be attributed to a larger increase in RoM caused by the simulated surgical intervention. To accurately assess the device’s effect after surgical intervention, it is essential to consider the disparity between the instability induced by the surgery and the resulting RoM after device instrumentation. This disparity provides a clearer understanding of the device’s impact.
When comparing the impacts of various devices, the Elaspine, StabilimaxNZ, and hinged pedicle screw design produced comparable motion restrictions in lateral bending and flexion/extension.
Conversely, the Dynesys consistently demonstrated a greater level of motion restriction in these movements across multiple studies. Regarding axial rotation, the Elaspine and StabilimaxNZ had a relatively modest effect, whereas the hinged pedicle screw design showed motion restriction similar to the lower range reported for the Dynesys.
Factors such as specimen age, bone mineral density, pedicle geometry, and cortical thread purchase can contribute to variations in maximum force and displacement. There was no observed correlation between bone mineral density and the maximum pull-out force.
At lower loads, the initial fixation of the screw in the trabecular structure of the vertebra and pedicle enhances stiffness. Nevertheless, as the loads escalate, the fracturing of trabeculae causes a decline in pull-out stiffness.
The Elaspine motion preservation device investigated in a study falls within the range of other devices studied in the literature and clinical trials. Compared to the widely used Dynesys device, Elaspine offers greater flexibility and more natural motion in lateral bending and flexion/extension.
However, it is less effective in limiting motion in axial rotation. The pull-out force of Elaspine pedicle screws is comparable to other reported screw designs. The optimal clinical application of these devices is still a subject of debate.
I am Vedant Vaksha, Fellowship trained Spine, Sports and Arthroscopic Surgeon at Complete Orthopedics. I take care of patients with ailments of the neck, back, shoulder, knee, elbow and ankle. I personally approve this content and have written most of it myself.
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