Comparison of Pedicle Screws Versus Hybrid Fixation With Sublaminar Polyester Bands in the Treatment of Neuromuscular Scoliosis

Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND

The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders. However, traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles (TSA). Larger TSA angles require more force to pull the muscle tissue, which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.

AIM

To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.

METHODS

Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments. A standard axial load of 500 N and a rotational torque of 10 N/m were applied. Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out, maximum stress, load-displacement ratio, maximum stress in vertebral bodies, load-displacement ratio in vertebral bodies, and the stress distribution in pedicle screws and vertebral bodies. Differences between the 0-degree and 17-degree TSA were compared.

RESULTS

At 0-degree TSA, the screw pull-out force decreased by 11.35% compared to that at 17-degree TSA (P < 0.05). At 0-degree and 17-degree TSA, the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa, separately, which were below the fracture threshold for the screw-rod system (924 MPa). At 0-degree and 17-degree TSA, the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa, separately, which were below the typical bone yield stress range for vertebral bodies (110-125 MPa). At 0-degree TSA, the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA, indicating slightly lower stability (P < 0.05).

CONCLUSION

The safety and stability of 0-degree TSA are slightly lower, but the risks of screw-rod system fracture, vertebral body fracture, and rupture are within acceptable limits.

Instrumentation of hypoplastic pedicles with patient-specific guides

PURPOSE

Hypoplastic pedicles of the thoracolumbar spine (<5 mm diameter) are often found in syndromic deformities of the spine and pose a challenge in pedicle screw instrumentation. 3D-printed patient-specific guides might help overcome anatomical difficulties when instrumenting pedicles with screws, thereby reducing the necessity for less effective fixation methods such as hooks or sublaminar wires. In this study, the surgical feasibility and clinical outcome of patients with hypoplastic pedicles following pedicle screw instrumentation with 3D-printed patient-specific guides were assessed.

METHODS

Hypoplastic pedicles were identified on preoperative computed tomography (CT) scans in six patients undergoing posterior spinal fusion surgery between 2017 and 2020. Based on these preoperative CT scans, patient-specific guides were produced to help with screw instrumentation of these thin pedicles. Postoperatively, pedicle-screw-related complications or revisions were analyzed.

RESULTS

93/105 (88.6%) pedicle screws placed with patient-specific guides were instrumented. 62/93 (66.7%) of these instrumented pedicles were defined as hypoplastic with a mean width of 3.07 mm (SD  ±0.98 mm, 95% CI [2.82-3.32]). Overall, 6 complications in the 62 hypoplastic pedicles (9.7%) were observed and included intraoperatively managed 4 cerebrospinal fluid leaks, 1 pneumothorax and 1 delayed revision due to 2 lumbar screws (2/62, 3.3%) impinging the L3 nerve root causing a painful radiculopathy. The mean follow-up time was 26.7 (SD  ±11.7) months. Complications were only noted when the pedicle-width-to-screw-diameter ratio measured less than 0.62.

CONCLUSION

Patient-specific 3D-printed guides can aid in challenging instrumentation of hypoplastic pedicles in the thoracolumbar spine, especially if the pedicle-width-to-screw-diameter ratio is greater than 0.62.

Do hypokyphotic adolescent idiopathic scoliosis patients treated with Ponte osteotomy obtain a better clinical efficacy? A preliminary retrospective study

Study design

A retrospective case–control study.

Objective

To evaluate whether Ponte osteotomy improves thoracic kyphosis and to determine its clinical efficacy in hypokyphotic adolescent idiopathic scoliosis (AIS).

Methods

Eighty consecutive Lenke type 1 AIS patients with hypokyphotic curves who underwent posterior spinal fusion by one spine surgeon at a single institution were recruited. According to whether Ponte osteotomy was performed, the patients were divided into two groups. The preoperative, immediate, one-year postoperative, and two-year postoperative radiographs were analyzed. The demographic characteristics, surgical information, radiographic parameters, Scoliosis Research Societye-22 (SRS-22) questionnaire, and complications were compared.

Results

The sagittal alignment and coronal alignment were both improved in the Ponte group and the control group postoperatively. There was no significant difference in the preoperative parameters between the two groups, except the TL/L, CB, and LL. Significant differences were found in the MT (15.18° ± 2.84° vs. 20.33° ± 3.75°, P < 0.001) and TK (24.23° ± 2.71° vs. 19.93° ± 2.38°, P < 0.001) at the two-year follow-up. The Ponte group had a longer operation time and more intraoperative blood loss. No significant difference was observed between the groups in the SRS-22 scores at the final follow-up.

Conclusions

Ponte osteotomy could obtain better coronal correction and sagittal contour restoration in AIS patients with hypokyphosis. However, Ponte osteotomies might lead to more intraoperative blood loss and longer operation time. Moreover, no discrepancy was found in the postoperative health-related quality of life of the included patients. Therefore, we considered that the Ponte osteotomy may be an alternative method to restore the desired thoracic kyphosis, which needs further study.