Direct osteosynthesis in the treatment of atlas burst fractures: a systematic review.

PURPOSE: The treatment of unstable atlas fractures remains a controversial topic. The study aims at assessing the prognosis and efficacy of osteosynthesis for unstable atlas fractures through a review of the current literature and additionally aims to compare outcomes between the transoral and posterior approaches. METHODS: A systematic review of databases including PubMed, EMBASE, Cochrane, Web of Science, CNKI, and Wanfang was conducted. Titles and abstracts were screened by two reviewers to identify studies meeting pre-defined inclusion criteria for comprehensive analysis. RESULTS: The systematic review included 28 articles, 19 employing the posterior approach and 9 utilizing the transoral approach. It covered osteosynthesis in 297 patients with unstable atlas fractures, comprising 169 treated via the posterior approach and 128 via the transoral approach. Analysis revealed high healing rates and clinical improvement in both approaches, evidenced by improvements in the visual analog scale, range of motion, atlantodens interval, and lateral displacement distance post-surgery. CONCLUSION: Osteosynthesis offers effective treatment for unstable atlas fractures. Both transoral and posterior approaches can achieve good clinical outcomes for fracture, and biomechanical studies have confirmed that osteosynthesis can maintain the stability of the occipitocervical region, preserve the motor function of the atlantoaxial and occipito-atlantoaxial joints, and greatly improve the quality of life of patients. However, variations exist in the indications and surgical risks associated with each method, necessitating their selection based on a thorough clinical evaluation of the patient's condition.

Design of a novel lateral mass screw-plate system for the treatment of unstable atlas fractures: a finite element analysis.

BACKGROUND: Osteosynthesis of unstable atlas fractures preserves joint motion and therefore has a distinct advantage over a range of treatment procedures. To prevent the potential disadvantages associated with osteosynthesis, a new atlas lateral mass screw-plate (LMSP) system has been designed. However, the biomechanical role of using the LMSP system in atlas internal fixation is not known. The aim of this study was to compare the biomechanical stability of a new LMSP with traditional posterior screw and rod (PSR) fixation techniques on the occipitocervical junction (C0-C2) through finite element analysis. METHODS: A nonlinear C0-C2 finite element model of the intact upper cervical spine was developed and validated. The unstable model using the PSR system was then compared with the model using the LMSP system for fixation. A vertical load of 40 N was applied to the C0 to simulate head weight, while a torque of 1.5 Nm was applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation. RESULTS: The range of motion of both systems was close to the intact model. Compared with the LMSP system model, the PSR system model increased flexion, extension, lateral bending, and axial rotation by 4.9%, 3.0%, 5.0%, and 29.5% in the C0-C1 segments, and 4.9%, 2.7%, 2.4%, and 22.6% in the C1-C2, respectively. In flexion, extension, and lateral bending motion, the LMSP system model exhibited similar stress to the PSR system model, while in axial rotation, the PSR system model exhibited higher stress. CONCLUSIONS: The findings of our study indicate that the two tested system models provide comparable stability. However, better stability was achieved during axial rotation with the LMSP system, and in this system, the maximum von Mises stress was less than that of the PSR one. As the atlantoaxial joint functions primarily as a rotational joint, the use of the LMSP system may provide a more stable environment for the joint that has become unstable due to fracture.

C1 anatomy and dimensions relative to pedicle screw placement.

The recent C1 pedicle screw technique for upper cervical vertebral stabilization allows longer screws to be implanted by setting the screw entry point through the posterior arch of C1, which could provide better biomechanics. However, there is controversy regarding the placement of C1 pedicle screws at different angles. We retrospectively reviewed the computed tomography (CT) scans of 300 patients. The trajectories of medial inclination of 0°, 5°, 10°, and 15° and trajectory of the maximum medial inclination angle were designed for each C1 pedicle on CT images. Screw track length at each angle, the angle of maximum medial inclination, pedicle height, distance from the screw entry point to the midpoint of the C1 posterior tubercle, and screw perforation rate at each angle were measured. The average maximum inclination angle was 17.01°, the maximum inclination angle screw track length was 31.05 mm, and the distance from the screw entry point to the midpoint of the C1 posterior nodule was 21.65 mm. The screw perforation rate was 46.73% at 15° of medial inclination, but only 5.61% at 10°, and no screw perforation at 5°. 26.47% C1 pedicle height < 4 mm. There was no significant difference between the measured data on the left and right sides(P > 0.05), and the measurement of female patients was usually smaller and significantly different from that of male patients(p < 0.05). Our data indicate that a reasonable screw inclination angle of 10° and the safety zone of screw angle can provide safety and avoid screw perforation. However, personalized measurement before surgery is essential.