Efficacy and Safety of Atlantoaxial Fluoroscopy-guided Pedicle Screw Fixation in Patients Younger Than 12 Years: A Radiographic and Clinical Assessment

Posterior intra-articular distraction technique to treat pediatric atlantoaxial instability

PURPOSE

Surgical treatment for atlantoaxial instability in pediatric patients is challenging. We report our experience with posterior intra-articular distraction technique in treating this disorder.

METHODS

This is a retrospective descriptive study which included 15 patients of atlantoaxial instability whose age was less than 16 years at the time of clinical presentation. All patients underwent anterior soft tissue released through a posterior-only approach, followed by intra-facet cage implantation, cantilever correction, and instrumentation. Clinical results were measured using the Japanese Orthopedic Association (JOA) scale and radiographic measurements including the atlantodental interval (ADI), posterior atlantodental interval (pADI), the distance of odontoid tip above Chamberlain's line, clivuscanal angle (CCA), and triangular area (TA) of craniovertebral junction.

RESULTS

The follow-up period ranged from 18 to 72 months, with an average of 41.2 ± 15.2 months. The JOA score increased from 13.6 ± 2.3 to 16.6 ± 0.8. ADI decreased from 4.31 ± 2.37 to 1.85 ± 1.09 mm, and TA decreased from 261.96 ± 107.99 to 197.12 ± 72.37 mm2. pADI increased from 12.89 ± 3.52 to 18.25 ± 3.89 mm, and CCA improved from 132.19 ± 16.34 to 144.35 ± 13.91°. All changes in measurements showed statistically significant. There were no evidence of surgery-related complications or iatrogenic secondary cervical deformity during follow-up. Radiological evaluation showed satisfactory corrections and bony fusions of C1-2 facet joint in all cases.

CONCLUSION

Posterior intra-articular distraction followed by cage implantation and cantilever correction can be one of the safe and effective ways to solve atlantoaxial instability in pediatric patients.

Effect of High-Riding Vertebral Artery on the Accuracy and Safety of C2 Pedicle Screw Placement in Basilar Invagination and Related Risk Factors

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate the effect of HRVA on the intrapedicular accuracy of C2PS placement through the freehand method in patients with BI and analyse the possible risk factors for C2PS malpositioning.

METHOD

A total of 91 consecutive patients with BI who received 174 unilateral C2PS placements through the freehand method were retrospectively included. The unilateral pedicles were assigned to the HRVA and non-HRVA groups. The primary outcome was the intrapedicular accuracy of C2PS placement in accordance with the Gertzbein-Robbins scale. Moreover, the risk factors that possibly affected intrapedicular accuracy were assessed.

RESULTS

The rate of intrapedicular accuracy in C2PS placement in patients with BI was 23.6%. Results showed that the non-HRVA group had remarkably higher rates of optimal and clinically acceptable C2PS placement than the HRVA group. Nevertheless, the HRVA group exhibited similar results for grade B classification as the non-HRVA group. Moreover, in the HRVA and non-HRVA groups, the most common direction of screw deviations was the lateral direction. Furthermore, the multivariate analyses showed that the obliquity of the lateral atlantoaxial joint in the sagittal plane ≥15°, and that in the coronal plane ≥ 20°, isthmus height < 4.3 mm, and distance from the skin to the spinous process ≥ 2.8 cm independently contributed to a high rate of screw malpositioning in BI patients.

CONCLUSION

The presence of HRVA in BI patients contributed to the high rate of malpositioning in C2PS placement via the freehand method. However, the rates of intrapedicular accuracy in patients with BI with and without HRVA were considerably low.

Posterior Atlantoaxial Fusion With C1-2 Pedicle Screw Fixation for Atlantoaxial Dislocation in Pediatric Patients With Mucopolysaccharidosis IVA (Morquio a Syndrome): A Case Series

OBJECTIVE

To investigate the efficacy and safety of posterior atlantoaxial fusion (AAF) with C1-2 pedicle screw fixation for atlantoaxial dislocation (AAD) in pediatric patients with mucopolysaccharidosis IVA (MPS IVA).

METHODS

This study included 21 pediatric patients with MPS IVA who underwent posterior AAF with C1-2 pedicle screw fixation. Anatomical parameters of the C1 and C2 pedicle were measured on preoperative computed tomography (CT). The American Spinal Injury Association (ASIA) scale was used to evaluate the neurological status. The fusion and accuracy of pedicle screw was assessed on postoperative CT. Demographic, radiation dose, bone density, surgical, and clinical data were recorded.

RESULTS

Patients reviewed included 21 patients younger than 16 years with an average age of 7.4 ± 4.2 years and an average of 20.9 ± 7.7 months follow-up. Fixation of 83 C1 and C2 pedicle screws was performed successfully and 96.3% of them were identified as being safe. One patient developed postoperative transient disturbance of consciousness and one developed fetal airway obstruction and died about 1 month after the surgery. Out of the remaining20 patients, fusion was achieved, symptoms were improved, and no other serious surgical complications were observed at the latest follow-up.

CONCLUSIONS

Posterior AAF with C1-2 pedicle screw fixation is effective and safe for AAD in pediatric patients with MPS IVA. However, the procedure is technically demanding and should be performed by experienced surgeons with strict multidisciplinary consultations.

Ideal entry point and trajectory for C2 pedicle screw placement in children: a 3D computed tomography study

PURPOSE

To identify the ideal entry point for pediatric C2 pedicle screw and to obtain parameters of it for the indication of pediatric atlantoaxial fusion arthrodesis.

METHODS

The pediatric cervical CT images were reconstructed into the 3D digital models and the C2 vertebrae were separated. The location of ideal entry point and screw placement related linear and angular parameters were assessed on the 3D digital models.

RESULTS

A total of 214 pedicles from 107 C2 digital models were analyzed. The average entry point for C2 was 3.80 ± 2.78 mm medial to the lateral notch (LN) and 2.57 ± 1.70 mm superior to the LN. The average pedicle diameter (PD) was 6.02 ± 1.31 mm, and the average pedicle screw length (PSL) was 25.63 ± 3.46 mm. Statistical differences were found between different sex for PD and PSL (P < 0.05). As patient age increases, using the most lateral and inferior edge of the lateral mass as a reference marker, the entry point tends to move medial and cephalad, when using the LN as a reference marker, the entry point tends to move medial and slightly caudad. Univariate linear regression analysis suggested that these linear parameters were associated with age (P < 0.01).

CONCLUSION

In this study, we found that the measurement results of C2 pedicle screw varied based on sex, laterality, and ages for children younger than 18 years. The entry point of the screws facilitating ideal trajectory tends to change in a linear way as a function of age. This information helps the surgeon to establish the specific anatomy related to C2 pedicle screw placement to facilitate fixation in the pediatric patients.

The feasibility and efficacy of computer-assisted screw inserting planning in the surgical treatment for severe spinal deformity: a prospective study

Background

The objective of the study was to explore the feasibility and efficacy of computer-assisted screw inserting planning (CASIP) in the surgical treatment for severe spinal deformity.

Methods

A total of 50 patients participated in this prospective cohort study. 25 patients were allocated into CASIP group and 25 patients were in Non-CASIP group. The demographic data, radiological spinal parameters were documented and analyzed. Each pedicle screw insertion was classified as satisfactory insertion or unsatisfactory insertion based on Gertzbein-Robbins classification. The primary outcome was the accuracy of pedicle screw placement. The secondary outcomes were the rate of puncturing screws, estimated blood loss, surgical time, correction rate and other radiological parameters.

Results

A total of 45 eligible patients completed the study. 20 patients were in CASIP group and 25 patients were in Non- CASIP group. The accuracy of pedicle screw placement in CASIP Group and Non-CASIP Group were (92.0 ± 5.5) % and (82.6 ± 8.3) % (P < 0.05), and the rate of puncturing screws were (0 (0–0)) % and (0 (0-6.25)) % (P < 0.05). The median surgical time were 280.0 (IQR: 260.0–300.0) min and 310 (IQR: 267.5–390.0) min in two group and showed significant statistic difference (P < 0.05).

Conclusions

CASIP has good feasibility and can gain a more accurate and reliable instruments fixation, with which spine surgeons can make a detailed and personalized screw planning preoperatively to achieve satisfying screw placement.

The technique of using three-dimensional and multiplanar reformatted computed tomography for preoperative planning in pediatric craniovertebral anomalies

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Surgical planning of pediatric craniovertebral anomalies is requires multiplanar CT reconstructions.

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Screw trajectories can be planned in 4 steps using an open-source DICOM manipulation software.

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This method gives more anatomical information compared to studying conventional PACS images.

Background

Computed tomography (CT) images provided by the radiology department may be inadequate for planning screws for rigid craniovertebral junction (CVJ) instrumentation. Although many recommend using multiplanar reconstruction (MPR) in line with screw trajectories, this is not always available to all surgeons. The current study aims to present a step-by-step workflow for preoperative planning for pediatric CVJ anomalies.

Methods

Twenty-five consecutive children (<12 years) were operated for atlantoaxial instability between 2014 and 2019. Preoperative CT angiograms were transferred to an open-source software called Horos™. The surgeon manipulated images in this viewing software to determine an idealized path of screws. Three-dimensional volume rendering of the pathoanatomy was generated, and anomalies were noted. The surgeon compared the anatomical data obtained using Horos™ with that from the original imaging platform and graded it as; Grade A (substantial new information), Grade B (confirmatory with improved visualization and understanding), Grade C (no added information). The surgeon then executed the surgical plan determined using Horos™.

Results

Surgeries performed were occipitocervical (n = 18, 72%) and atlantoaxial fixation (n = 7, 28%) at a mean age of 7.2 years, with 72% of etiologies being congenital or dysplasias. In 18 (72%) patients, the surgeon noted substantial new information (Grade A) about CVJ anomalies on Horos™ compared to original imaging platform. Concerning planning for fixation anchors, the surgeon graded A in all patients (100%). In 4 (16%) patients, the surgery could not be executed precisely as planned. There were three (12%) complications; VA injury (n = 1), neurological worsening (n = 1), and loss of fixation (n = 1).

Conclusion

In our experience, surgeon-directed imaging manipulation gives more anatomical information compared to studying original imaging planes and should be incorporated in the surgeon's preoperative workup. When image reformatting options are limited, open-source software like Horos™ may offer advantages.

Biomechanical design and analysis of auxetic pedicle screw to resist loosening

BACKGROUND

Pedicle screws are widely used in fusion surgery, while screw loosening often occurrs. An auxetic structures based pedicle screw was proposed to improve the bone-screw fixation by radial expansion of the screw body under tensile force to resist pulling out. It was optimized to obtain excellent anti-pullout ability for a particular bone based on the biomechanical interaction between screw and surrounding bone.

METHODS

The screw was designed based on re-entrant unit cells. The mechanical properties of it were adjusted by the wall thickness (t) and re-entrant angle (θ) of the unit cell, and characterized using finite element (FE) method. The designed screws were manufactured using 3D-printing, and Ti6Al4V as the materials. Subsequently, the pullout FE models were established, and verified by pulling the fabricated screws out of Sawbone blocks. The pulling out processes of screws from bone were simulated to explore the optimizing design of the screw.

RESULTS

The mechanical properties of the screw could be adjusted in a wide range. The biomechanical interaction between the screw and bone can affect the anti-pullout performance of the screw. With an identical elastic modulus (E), better auxiticity of the screw, resulted in a better anti-pullout performance; while an appropriate E is the necessary condition for its excellent anti-pullout performance for a particular bone.

CONCLUSION

Appropriate mechanical properties are necessary for the auxetic pedicle screw with excellent screw-bone fixation performance for a particular bone, which can be obtained by rationally designing the wall thickness and re-entrant angle of the unit cells.

Accuracy and safety of C2 pedicle or pars screw placement: a systematic review and meta-analysis

Study design

Systematic review and meta-analysis.

Aim

The purpose of this study was to compare the safety and accuracy of the C2 pedicle versus C2 pars screws placement and free-hand technique versus navigation for upper cervical fusion patients.

Methods

Databases searched included PubMed, Scopus, Web of Science, and Cochrane Library to identify all papers published up to April 2020 that have evaluated C2 pedicle/pars screws placement accuracy. Two authors individually screened the literature according to the inclusion and exclusion criteria. The accuracy rates associated with C2 pedicle/pars were extracted. The pooled accuracy rate estimated was performed by the CMA software. A funnel plot based on accuracy rate estimate was used to evaluate publication bias.

Results

From 1123 potentially relevant studies, 142 full-text publications were screened. We analyzed data from 79 studies involving 4431 patients with 6026 C2 pedicle or pars screw placement. We used the Newcastle-Ottawa Scale (NOS) to evaluate the quality of studies included in this review. Overall, funnel plot and Begg’s test did not indicate obvious publication bias. The pooled analysis reveals that the accuracy rates were 93.8% for C2 pedicle screw free-hand, 93.7% for pars screw free-hand, 92.2% for navigated C2 pedicle screw, and 86.2% for navigated C2 pars screw (all, P value < 0.001). No statistically significant differences were observed between the accuracy of placement C2 pedicle versus C2 pars screws with the free-hand technique and the free-hand C2 pedicle group versus the navigated C2 pedicle group (all, P value > 0.05).

Conclusion

Overall, there was no difference in the safety and accuracy between the free-hand and navigated techniques. Further well-conducted studies with detailed stratification are needed to complement our findings.