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.

Upper Cervical Trauma

Craniocervical injuries (CCJs) account for 10% to 30% of all cervical spine trauma. An increasing number of patients are surviving these injuries due to advancements in automobile technology, resuscitation techniques, and diagnostic modalities. The leading injury mechanisms are motor vehicle crashes, falls from height, and sports-related events. Current treatment with urgent rigid posterior fixation of the occiput to the cervical spine has resulted in a substantial reduction in management delays expedites treatment of CCJ injuries. Within CCJ injuries, there is a spectrum of instability, ranging from isolated nondisplaced occipital condyle fractures treated nonoperatively to highly unstable injuries with severely distracted craniocervical dissociation. Despite the evolution of understanding and improvement in the management of cases regarding catastrophic failure to diagnose, subsequent neurologic deterioration still occurs even in experienced trauma centers. The purpose of this article is to review the injuries that occur at the CCJ with the accompanying anatomy, presentation, imaging, classification, management, and outcomes.

3D-Printed Screw-Rod Auxiliary System for Unstable Atlas Fractures: A Retrospective Analysis

Objective

To develop and validate the efficacy of a 3D‐printed screw‐rod auxiliary system for unstable atlas fractures.

Methods

This research is a retrospective analysis, and a total of 14 patients, including 11 males and three females, were enrolled in our hospital from January 2017 to March 2019 who underwent occipitocervical fusion assisted by the 3D‐printed screw‐rod auxiliary system were reviewed, and with an average age of 53.21 ± 14.81 years, an average body mass index (BMI) of 23.61 ± 1.93 kg/m². The operation time, blood loss and radiation times during the operation were recorded. The maximum fracture displacement values of pre‐ and post‐operation were measured based on CT imaging. All screw grades were evaluated after surgery. The occipital‐cervical 2 (O‐C₂) angle and occipitocervical inclination (OCI) angle of pre‐operation, post‐operation and the last following‐up were measured. The dysphagia scale 3 months after surgery and at the last follow‐up, the Neck Disability Index (NDI) 3 months after surgery and at the last follow‐up were assessed.

Results

All patients were completed the surgery successfully. There was no patient with severe dysphagia or aggravation of nerve injury. The follow‐up was from 12 to 14 months, and with an average of 12.5 months. The average surgery time, average blood loss and average radiation times for the 14 patients were 112.14 min, 171.43 mL and 5.07 times, respectively. There was a significant difference in maximum fracture displacement between pre‐ and post‐operation values (P < 0.05). A total of 56 screws were inserted in 14 patients, among them, three screws were classified as grade 1, and the other screws were classified as grade 0. There was a significant difference in the O‐C₂ between pre‐operation and 3 days after operation (P = 0.002); There was a significant difference in OCI angles between pre‐operation and 3 days after operation (P < 0.05); there was no significant difference in the O‐C₂ or OCI angle between 3 days after the operation and the last follow‐up (P = 0.079; P = 0.201). The dysphagia scales of two patients were assessed as mild at 3 months after surgery, and the others were assessed as normal at 3 months after surgery. All patients' dysphagia scores returned to normal at the last follow‐up. The average NDI and average neck Visual Analogue Scale (VAS) scores at the last follow‐up were 2.53 and 8.41, respectively.

Conclusion

It can objectively restore the OCI to normal with few post‐operative complications under the assistance of a screw‐rod auxiliary system to perform occipitocervical fusion for unstable atlas fractures and atlantooccipital joint instability.

Posterior osteosynthesis with monoaxial lateral mass screw-rod system for unstable C1 burst fractures

BACKGROUND CONTEXT

Surgical treatment for unstable atlas fractures has evolved in recent decades from C1-C2 or C0-C2 fusion to motion-preservation techniques of open reduction and internal fixation (ORIF). However, regardless of a transoral or a posterior approach, the reduction is still not satisfactory.

PURPOSE

The article describes and evaluates a new technique for treating unstable atlas fractures by using a monoaxial screw-rod system.

STUDY DESIGN

This is a retrospective study.

PATIENT SAMPLE

The sample includes adult patients with unstable C1 fractures treated with a posterior monoaxial screw-rod system.

OUTCOME MEASURES

The outcome measures included a visual analog pain scale, radiographic reduction (lateral mass displacement [LMD]), maintenance of reduction, C1-C2 instability (anterior atlantodens interval), and complications.

MATERIALS AND METHODS

From August 2013 to May 2016, nine consecutive patients with unstable atlas fractures were retrospectively reviewed. All patients were treated with posterior ORIF by using a monoaxial screw-rod system. The medical records and the preoperative and postoperative radiographs were reviewed. Preoperative and postoperative computed tomography scans were used to specify the fracture types and to assess the reduction.

RESULTS

All nine patients with a mean age of 50.3 years successfully underwent surgery with this technique, and a follow-up of 17.4±9.3 months was performed. Transverse atlantal ligament (TAL) injury was found in eight of the nine patients: one of type I and seven of type II. The preoperative LMD averaged 7.0±2.2 mm and was restored completely after surgery; all the fractures achieved bony healing without loss of reduction or implant failure. None of the patients had complications of neurologic deficit, vertebral artery injury, or wound infection associated with the surgical procedure. Two patients complained of greater occipital nerve neuralgia after the operation, which gradually disappeared in 1 month. All patients had a well-preserved range of motion of the upper cervical spine at the final follow-up.

CONCLUSIONS

Posterior osteosynthesis with a monoaxial screw-rod system is capable of an almost anatomical reduction for the unstable atlas fractures. The TAL incompetence may not be a contraindication to ORIF for C1 fractures, but the long-term effect of C1-C2 instability remains to be further investigated.

Epidemiology of atlas fractures--a national registry-based cohort study of 1,537 cases

BACKGROUND CONTEXT

The epidemiology of fractures of the first cervical vertebra-the atlas-has not been well documented. Previous studies concerning atlas fractures focus on treatment and form a weak platform for epidemiologic study.

PURPOSE

This study aims to provide reliable epidemiologic data on atlas fractures.

STUDY DESIGN

This was a national registry-based cohort study.

PATIENT SAMPLE

A total of 1,537 cases of atlas fractures between 1997 and 2011 from the Swedish National Patient Registry (NPR).

OUTCOME MEASURES

The outcome measures were annual incidence and mortality.

METHODS

Data from the NPR and the Swedish Cause of Death Registry were extracted, including age, gender, diagnosis, comorbidity, treatment codes, and date of death. The Charlson Comorbidity Index was calculated and a survival analysis performed.

RESULTS

A total of 869 (56.5%) cases were men, and 668 (43.5%) were women. The mean age of the entire population was 64 years. The proportion of atlas fractures of all registered cervical fractures was 10.6%. In 19% of all cases, there was an additional fracture of the axis, and 7% of all cases had additional subaxial cervical fractures. Patients with fractures of the axis were older than patients with isolated atlas fractures. The annual incidence almost doubled during the study period, and in 2011, it was 17 per million inhabitants. The greatest increase in incidence occurred in the elderly population.

CONCLUSIONS

Atlas fractures occurred predominantly in the elderly population. Further study is needed to determine the cause of the increasing incidence.

Self-designed posterior atlas polyaxial lateral mass screw-plate fixation for unstable atlas fracture

BACKGROUND CONTEXT

Most atlas fractures can be effectively treated nonoperatively with external immobilization unless there is an injury to the transverse atlantal ligament. Surgical stabilization is most commonly achieved using a posterior approach with fixation of C1-C2 or C0-C2, but these treatments usually result in loss of the normal motion of the C1-C2 and C0-C1 joints.

PURPOSE

To clinically validate feasibility, safety, and value of open reduction and fixation using an atlas polyaxial lateral mass screw-plate construct in unstable atlas fractures.

STUDY DESIGN

Retrospective review of patients who sustained unstable atlas fractures treated with polyaxial lateral mass screw-plate construct.

PATIENT SAMPLE

Twenty-two patients with unstable atlas fractures who underwent posterior atlas polyaxial lateral mass screw-plate fixation were analyzed.

OUTCOME MEASURES

Visual analog scale, neurologic status, and radiographs for fusion.

METHODS

From January 2011 to September 2012, 22 patients with unstable atlas fractures were treated with this technique. Patients' charts and radiographs were reviewed. Bone fusion, internal fixation placement, and integrity of spinal cord and vertebral arteries were assessed via intraoperative and follow-up imaging. Neurologic function, range of motion, and pain levels were assessed clinically on follow-up.

RESULTS

All patients were followed up from 12 to 32 months, with an average of 22.5±18.0 months. A total of 22 plates were placed, and all 44 screws were inserted into the atlas lateral masses. The mean duration of the procedure was 86 minutes, and the average estimated blood loss was 120 mL. Computed tomography scans 9 months after surgery confirmed that fusion was achieved in all cases. There was no screw or plate loosening or breakage in any patient. All patients had well-preserved range of motion. No vascular or neurologic complication was noted, and all patients had a good clinical outcome.

CONCLUSIONS

An open reduction and posterior internal fixation with atlas polyaxial lateral mass screw-plate is a safe and effective surgical option in the treatment of unstable atlas fractures. This technique can provide immediate reduction and preserve C1-C2 motion.