Effect of Spinal Fixation in Rabbits With Metastatic Tumor Using a Novel Spinal Fusion Model

Posterior fixation without debridement for pyogenic spondylodiscitis can promote infection control: initial evaluation of a pyogenic spondylodiscitis posterior fixation rat model

PURPOSE

Pyogenic spondylodiscitis is a significant health concern, particularly in older individuals. Minimally invasive surgical techniques, such as posterior fixation, are promising for infection control; however, their mechanisms remain unclear. This study aimed to clarify how posterior fixation promotes infection control in an animal model.

METHODS

Thirty female Wistar rats were used to create a pyogenic spondylodiscitis model by injecting methicillin-sensitive Staphylococcus aureus into the intervertebral space between the 6th and 7th coccygeal vertebrae. Three days post-injection, rats were divided into fixation and control groups. The fixation group underwent posterior fixation with an external fixator, whereas the control group underwent screw insertion alone. Bone destruction was assessed via microcomputed tomography on postoperative days (POD) 7, 14, and 21. Immunohistochemistry for cathepsin K and receptor activator of nuclear factor-kappa B ligand (RANKL) was performed on POD 7 samples to assess osteoclast activity.

RESULTS

The fixation group showed less bone destruction than the control group at POD 14 (35% vs. 56%, p = 0.0007) and POD 21 (30% vs. 52%, p < 0.0001). The cathepsin K-positive area was significantly reduced in the fixation group (p = 0.027). RANKL expression was localized within the intervertebral disc in the fixation group, whereas RANKL was strongly expressed on the bone surface adjacent to the disc in control. The RANKL-positive area was also reduced in the fixation group (p = 0.041).

CONCLUSIONS

Our combined model of pyogenic spondylodiscitis and posterior fixation supports the theory that posterior fixation stability suppresses RANKL and osteoclast expression, promoting infection control.

Mechanical stress induces elastic fibre disruption and cartilage matrix increase in ligamentum flavum

Lumbar spinal stenosis (LSS) is one of the most frequent causes of low back pain and gait disturbance in the elderly. Ligamentum flavum (LF) hypertrophy is the main pathomechanism of LSS, but the reason for its occurrence is not clearly elucidated. In this study, we established a novel animal model of intervertebral mechanical stress concentration and investigated the biological property of the LF. The LF with mechanical stress concentration showed degeneration with elastic fibres disruption and cartilage matrix increase, which are similar to the findings in hypertrophied LF from patients with LSS. By contrast, decreased Col2a1 expression was found in the LF at fixed levels, in which mechanical stress was strongly reduced. These findings indicate that mechanical stress plays a crucial role in LF hypertrophy through cartilage matrix increase. The findings also suggest that fusion surgery, which eliminates intervertebral instability, may change the property of the LF and lead to the relief of patients' symptoms.

Establishing a rabbit spinal tumor model for nonvascular interventional therapy through CT-guided percutaneous puncture inoculation

BACKGROUND AND PURPOSE

An animal spinal tumor model is needed to better simulate the clinical situation and to allow percutaneous puncture, which may provide an experimental platform for the new nonvascular interventional therapies. We established a rabbit spinal tumor model through a CT-guided percutaneous puncture inoculation technique for nonvascular interventional therapy.

MATERIALS AND METHODS

VX2 tumor cells were inoculated into the lumbar vertebrae of 32 rabbits through a CT-guided percutaneous puncture technique; then, the development of hind limb paraparesis was observed in the rabbits twice a day. MR imaging and CT were performed on days 14, 21, and 28 postinoculation and at the development of hind limb paraparesis. On days 21 and 28 postinoculation, 2 rabbits, whose imaging suggested successful modeling without hind limb paraparesis, were chosen on each day. The lumbar vertebrae were sampled from 1 rabbit for histopathologic examination, and the other rabbit underwent PET-CT examination before percutaneous vertebroplasty. Finally the lesion vertebrae were sampled for histopathologic examination.

RESULTS

The success rate of modeling was 90.6% (29/32) in our study. On day 21 postinoculation, successful modeling was achieved in 21 rabbits, with 19 having no hind limb paraparesis. On day 28 postinoculation, another 7 achieved successful modeling, and only 1 developed hind limb paraparesis. Percutaneous vertebroplasty treatment was successful for the 2 rabbit models.

CONCLUSIONS

Establishment of a rabbit spinal tumor model through a CT-guided percutaneous puncture technique and inoculation of VX2 tumor is easy and has a high success rate. The established model can be used to study nonvascular interventional therapies for spinal tumor, including percutaneous vertebroplasty.