Biomechanical Effects of Fixation of Different Segments of Goat Lumbar Spine on Adjacent Segmental Motion and Intradiscal Pressure Change

Establishment of a Rabbit Model of Adjacent Intervertebral Disk Degeneration After Lumbar Fusion and Fixation and Evaluation of Autophagy Factor Expression in Nucleus Pulposus Cells

BACKGROUND

The objectives of this research were to establish an animal model of adjacent segment degeneration (ASD) bordering lumbar fusion and to investigate the expression of autophagy factors in nucleus pulposus cells of adjacent intervertebral disks.

MATERIALS AND METHODS

Twenty-four adult New Zealand white rabbits were enrolled and divided into two groups: group A (n=12) and group B (n=12). Posterolateral fusion and fixation were performed after intervertebral disk degeneration occurred in group A, and the rabbits were monitored for 6 months. Group B was the control group and did not undergo fusion surgery. These rabbits were monitored for 6 months. Real-time quantitative polymerase chain reaction and immunohistochemistry were performed to detect the mRNA and protein expressions of PTEN-induced kinase 1 (PINK1), Parkin, ADAMTS-4, and MMP-3. An external database, the GEO database, was used to examine the expression of these genes and analyze them for differential expression.

RESULTS

After lumbar fusion in rabbits, the animal model of ASD exhibited gradual degeneration of adjacent intervertebral disks over time. Group A displayed significantly higher mRNA and protein expressions of PINK1 and MMP-3 but lower expression of ADAMTS-4 compared with group B (P<.05). The results analyzed in the GEO database showed that the expression of PINK1 was higher in group A than in group B, while the expression of ADAMTS-4 was lower in group A than in group B.

CONCLUSION

After posterolateral lumbar fusion in rabbits, the animal ASD model showed gradual deterioration of adjacent intervertebral disks with prolonged follow-up. The findings indicate the important role of autophagy in the apoptosis of nucleus pulposus cells in adjacent intervertebral disks. [Orthopedics. 202x;4x(x):xx-xx.].

In Vitro Studies for Investigating Creep of Intervertebral Discs under Axial Compression: A Review of Testing Environment and Results

Creep responses of intervertebral discs (IVDs) are essential for spinal biomechanics clarification. Yet, there still lacks a well-recognized investigation protocol for this phenomenon. Current work aims at providing researchers with an overview of the in vitro creep tests reported by previous studies, specifically specimen species, testing environment, loading regimes and major results, based on which a preliminary consensus that may guide future creep studies is proposed. Specimens used in creep studies can be simplified as a “bone–disc–bone” structure where three mathematical models can be adopted for describing IVDs’ responses. The preload of 10–50 N for 30 min or three cycles followed by 4 h-creep under constant compression is recommended for ex vivo simulation of physiological condition of long-time sitting or lying. It is worth noticing that species of specimens, environment temperature and humidity all have influences on biomechanical behaviors, and thus are summarized and compared through the literature review. All factors should be carefully set according to a guideline before tests are conducted to urge comparable results across studies. To this end, this review also provides a guideline, as mentioned before, and specific steps that might facilitate the community of biomechanics to obtain more repeatable and comparable results from both natural specimens and novel biomaterials.

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment

Objectives

The purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.

Methods

Fifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.

Results

As the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.

Conclusions

Adjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.