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.

Novel method for selecting slices of the same cross-sectional view from digital tomosynthesis for monitoring posterior spinal instrumentation

BACKGROUND

A method to evaluate pedicle screw loosening on digital tomosynthesis images is yet to be established owing to lack of methods for selecting slices of the same cross-sectional view. We aimed to develop an objective method for selecting slices of the same cross-sectional view on digital tomosynthesis images.

METHODS

First, an objective method of pixel selection was developed by measuring the size of glass disk and titanium alloy screw on digital tomosynthesis images followed by comparison with the actual sizes. Second, a method for selecting slices of the same cross-sectional view was explored on a bone model with posterior spinal instrumentation using the screw centerline and rod curvature as indicators of the same cross section. The angle between the screw centerline and rod was calculated to verify the accuracy in obtaining the same cross-sectional view. Third, the method for selecting slices of the same cross-sectional view was applied to six patients after posterior lumbar spinal instrumentation.

RESULTS

The pixel selection method enabled objective determination of a pixel on the peripheral lines of objects with an error as low as 200 μm in distance measurements on titanium alloy and glass. The mean differences of rod-screw angles between two slices were less than 1° and were not statistically significant in the bone model and patient images.

CONCLUSION

A method for selecting slices of the same cross-sectional view on digital tomosynthesis images was successfully developed. This method can enable objective and quantitative evaluations of pedicle screw loosening.

Bilateral fracture of the superior articular process of S1 - An unusual fracture seen in a speed skater

Background Fractures of the superior articular process are rarely seen in clinical practice. Repetitive spinal movements may lead to fractures of the pars interarticularis, resulting in spondylolysis. Traumatic spinal fractures often involve the vertebral body, transvers and/or the spinous processes. The superior articular processes, however, are seldom involved in both traumatic and stress-induced fractures. Purpose The purpose of this report is to present an unusual case of symptomatic bilateral fracture of the superior articular process of the sacrum in a 21-year-old speed skater. Study design This is a case report. Methods The patient was admitted for close observation after complaining of excruciating lower back pain and bilateral dysesthesia along the L5 nerve root. Post-myelography computed tomography (CT) revealed a bilateral facet joint deformity at L5/S1 and a bilateral fracture of the superior articular process of the sacrum. A facet joint block at the L5/S1 joint alleviated the pain, and a nerve root block at the L5 nerve root improved the dysesthesia. The patient underwent an L5/S1 decompression, whereby the nonunion bone fragments were removed, followed by a posterior lumbar inter-body fusion (PLIF) at L5/S1. Results The patient showed immediate improvement and returned to training six months post-operatively. Conclusion We have presented a case of bilateral fractures of the superior articular process of the sacrum in a speed skater. His presenting symptoms were similar to those found in patients with spondylolysis and the etiology appears to be similar. Surgical treatment was opted given his symptomatic relief from nerve root and facet joint blocks.

Thoracolumbar burst fractures requiring instrumented fusion: Should reducted bone fragments be removed? A retrospective study

BACKGROUND

Thoracolumbar burst fractures are common clinical entity encountered in neurosurgical practice, accounting for 10-20% of all spinal fractures. Clinical picture could be devastating due to severe neurological deficits which lead the patients dependent both socially and emotionally.

MATERIALS AND METHODS

This study compared two groups of patients who were operated because of thoracolumbar burst fracture secondary to spinal trauma in terms of neurologic deficits, degree of improvement, and radiologic measurements at one-year follow-up. The first group (group I) included the patients who underwent posterior total laminectomy, peroperative reduction of intracanal bone fragments, and posterior spinal instrumentation and the second group (group II) included the patients who underwent total laminectomy, and spinal instrumentation without reduction of free bone fragments.

RESULTS

Neither group showed significant correlation with any measurement parameter. Radiological assessments and clinical improvements did not disclosed significant difference between the two groups at one-year follow-up.

CONCLUSION

Retropulsion of free bone fragments extend the time of surgery and causes complications. This study found that there is no need to retropulse the bone fragments in the spinal canal in patients with unstable burst fractures who underwent total laminectomy and posterior long segment stabilization.