Modified Posterior Short-Segment Pedicle Screw Instrumentation for Lumbar Burst Fractures with Incomplete Neurological Deficit

Finite element study on whether posterior upper wall fracture is a risk factor for the failure of short-segment pedicle screw fixation in the treatment of L1 burst fracture

PURPOSE

To establish the finite element model of T12 and L2 (T12-L2) pedicle screw fixation for severe L1 burst fracture, and quantitatively simulate and analyze the screw stress and vertebral displacement in different degrees of L1 posterior upper wall fracture (PUWF), and evaluate whether PUWF degree is a risk factor for fixation failure.

METHODS

The data of 6 healthy volunteers were used to establish a finite element model of T12-L2 pedicle screw fixation for type A severe burst fractures. The stress and displacement of the conventional and Schanz pedicle screws for the different degrees of PUWF (including the anterior upper wall of the vertebral canal and the bipedicle) were evaluated.

RESULTS

The maximum stress and L1 displacement of conventional and Schanz pedicle screws were positively correlated with the severity of the PUWF (P<0.05). During anterior flexion, the maximum stress of conventional pedicle screws for 70% type I were 538.3±59.75MPa and the maximum stress of Schanz pedicle screws for 90% type Ⅱ, 90% type Ⅲ and 70% type IV fractures were close to the fatigue threshold. The maximum stress during anterior flexion were significantly higher than those during posterior extension, bending and rotation (P<0.05).

CONCLUSION

The posterior upper wall fracture of vertebral body (VB) of type A burst fracture is not an independent risk factor for the failure of short-segment pedicle screw fixation (SSPSF). Anterior flexion of type A fractures combined with severe PUWF of VB was a risk factor for the failure of SSPSF.

The feasibility of short-segment Schanz screw implanted in an oblique downward direction for the treatment of lumbar 1 burst fracture: a finite element analysis

Background

To evaluate the biomechanical properties of short-segment Schanz screw implanted in an oblique downward direction for the treatment of lumbar 1 burst fracture using a finite element analysis.

Methods

The Universal Spine System (USS) fixation model for adjacent upper and lower vertebrae (T12 and L2) of lumbar 1 vertebra burst fracture was established. During flexion/extension, lateral bending, and rotation, the screw stress and the displacement of bone defect area of the injured vertebrae were evaluated when the downward inserted angle between the long axis of the screws and superior endplate of the adjacent vertebrae was set to 0° (group A), 5° (group B), 10° (group C), and 15°(group D). There were 6 models in each group.

Results

There were no significant differences in the maximum screw stress among all the groups during flexion/extension, lateral bending, and rotation (P > 0.05). There were no significant differences in the maximum displacement of the bone defect area of the injured vertebrae among all the groups during flexion/extension, lateral bending, and rotation (P > 0.05).

Conclusion

Short-segment Schanz screw implanted in an oblique downward direction with different angles (0°/parellel, 5°, 10°, and 15°) did not change the maximum stress of the screws, and there was a lower risk of screw breakage in all groups during flexion/extension, lateral bending, and rotation. In addition, the displacement of the injured vertebra defect area had no significant changes with the change of angles.

Percutaneous pedicle screw fixation combined with selective transforaminal endoscopic decompression for the treatment of thoracolumbar burst fracture

Background

The objective of this study was to evaluate the feasibility, safety, efficacy, and indications of percutaneous pedicle screw fixation (PPSF) combined with selective transforaminal endoscopic decompression (TED) in the treatment of thoracolumbar burst fracture (TBLF).

Methods

From August 2015 to October 2018, a total of 41 patients with single-segment TLBF (28 men and 13 women) were enrolled in this study. X-ray and computed tomography were obtained before surgery, 1 week after surgery, and 1 year after surgery to evaluate spinal recovery. In addition, we used the visual analog scale (VAS), the Oswestry Disability Index (ODI), the Japanese Orthopedic Association score (JOA), and the Frankel classification of neurological deficits to evaluate the effectiveness of the treatments.

Results

The average follow-up time was 22.02 ± 8.28 months. The postoperative Cobb angle, vertebral body compression ratio, vertebral wedge angle, mid-sagittal canal diameter compression ratio, and Frankel grade were significantly improved. There were also significant improvements in the VAS (7.61 ± 1.41 vs. 1.17 ± 0.80, P < 0.001), ODI (89.82 ± 7.44 vs. 15.71 ± 13.50, P < 0.001), and JOA (6.90 ± 2.91 vs. 24.90 ± 3.03, P < 0.001).

Conclusions

Our results showed that PPSF combined with selective TED in the treatment of TLBF had excellent efficacy, high safety, less secondary injury than other treatments, and a wide range of indications and that it could accurately distinguish patients who did not need spinal canal decompression after posterior fixation. PPSF combined with selective TED is therefore a good choice for the treatment of TLBF.

Treatment of Thoracolumbar Fractures Through Different Short Segment Pedicle Screw Fixation Techniques: A Finite Element Analysis

Objective

To compare the von Mises stresses of the pedicle screw system and the displacement of injured vertebrae using 3‐D finite element analysis, and to evaluate the curative effect of the pedicle screw system.

Methods

Finite element methods were used for biomechanical comparison of four posterior short segment pedicle screw fixation techniques. The different pedicle screw models are traditional trajectory (TT), Universal Spine System (USS), cortical bone trajectory (CBT), and CBT at the cranial level and pedicle screw (PS) at the caudal level (UP‐CBT). The stress distribution of the screws and connecting rods under different working conditions and the displacement of the injured vertebrae were compared and analyzed.

Results

After the pedicle screw system was fixed, the stress under vertical compression was mainly concentrated at the proximal end of the screw, while the stress was mainly concentrated on the connecting rod during flexion, extension, lateral flexion, and rotation. The TT group had the greatest stress during the flexion, extension, and left and right rotation. The UP‐CBT group was most stressed when the left and right sides were flexed; the stress of the USS screw system was less than that of the other three models during flexion, lateral flexion, and rotation. The maximum von Mises stress values of pedicle screws in all exercise states were 556.2, 340.7, 458.1, and 533.4 MPa, respectively. In the USS group, the displacement of the injured vertebra was small in the flexion, and the left and right lateral flexion and the right rotation were higher than in the TT group and the CBT group. The maximum displacements of the injured vertebrae in all motion states were 1.679, 1.604, 1.752, and 1.777 mm, respectively.

Conclusion

Universal Spine System pedicle screws are relatively less stressed under different working conditions, the risk of breakage is small, and the model is relatively stable; CBT screws do not exhibit better mechanical properties than conventional pedicle screws and USS pedicle screws.