[Imaging study of "shell" phenomenon of thoracolumbar fractures after posterior reduction]

A Finite Element Study on the Treatment of Thoracolumbar Fracture with a New Spinal Fixation System

Objective

In this study, the mechanical properties of the new spinal fixation system (NSFS) in the treatment of thoracolumbar fractures were evaluated by the finite element analysis method, so as to provide a mechanical theoretical basis for the later biomechanical experiments and clinical experiments.

Methods

T12-L2 bone model was constructed to simulate L1 vertebral fracture, and three models of internal fixation systems were established on the basis of universal spinal system (USS): Model A: posterior short-segment fixation including the fractured vertebra (PSFFV); Model B: short-segment pedicle screw fixation (SSPF); Model C: new spinal fixation system (NSFS). After assembling the internal fixation system and fracture model, the finite element analysis was carried out in the ANSYS Workbench 18.0 software, and the stress of nail rod system, fracture vertebral body stress, vertebral body mobility, and vertebral body displacement were recorded in the three models.

Results

The peak values of internal fixation stress, vertebral body stress, vertebral body maximum displacement, and vertebral body maximum activity in Model C were slightly smaller than those in Model B.

Conclusions

Compared with the traditional internal fixation system, the new spinal internal fixation system may have the mechanical advantage and can provide sufficient mechanical stability for thoracolumbar fractures.

[Surgical treatment strategy for the "shell" phenomenon after thoracolumbar fracture]

Objective

To explore the surgical treatment strategy of the vertebral "shell" after thoracolumbar fracture, and provide clinical reference for the intervention and treatment of "shell".

Methods

Between June 2015 and January 2017, 53 patients with high risk of vertebral "shell" after thoracolumbar fracture surgery were enrolled in a prospective study according to the selection criteria. All patients were randomly divided into two groups according to the order of treatment, 27 cases in the treatment group were treated with short-segment fixation combined with vertebral reconstruction, 26 cases in the control group were treated with short-segment fixation. There was no significant difference in gender, age, injury cause, Denis classification, fracture segment, the degree of injured vertebra compression, bone mineral density, and American Spinal Cord Injury Association (ASIA) classification between the two groups ( P>0.05). The degree of injured vertebra compression, visual analogue scale (VAS) score, and Oswestry disability index (ODI) score at preoperation, immediate after operation, and last follow-up were calculated and compared between the two groups. The "shell" phenomenon and surgery complications were observed at the same time.

Results

All patients were followed up 12-18 months with an average of 14.4 months. There were 5 cases of "shell" phenomenon in the treatment group and 4 cases of nonunion at last follow-up, 23 cases of "shell" phenomenon in the control group and 19 cases of nonunion at last follow-up; there was a significant difference between the two groups ( P<0.05). In the treatment group, 1 case had incision fat liquefaction and 4 cases had bone cement leakage; in the control group, 2 cases had screw loosening and 1 case had unilateral connecting rod rupture; there was no significant difference in the incidence of complications between the two groups ( χ2=0.504, P=0.478). The degree of injured vertebra compression, VAS score, and ODI score were significantly improved in both groups at immediate after operation and last follow-up ( P<0.05). There was no significant difference in the degree of injured vertebra compression between the two groups at immediate after operation ( P>0.05), but which was significantly higher in the control group than that in the treatment group at last follow-up ( P<0.05). Except that the ODI score of the control group was significantly higher than that of the treatment group at last follow-up ( P<0.05), there was no significant difference in VAS score and ODI score between the two groups at the other time points ( P>0.05).

Conclusion

The treatment of thoracolumbar fracture with short-segment fixation combined with injured vertebral reconstruction can effectively prevent the "shell" phenomenon, which is conducive to maintaining the height of injured vertebral and improving the long-term function. The effectiveness is satisfactory.