Biomechanical evaluation of surgical constructs for stabilization of cervical teardrop fractures

Conundrum in surgical management of three-column injuries in sub-axial cervical spine: a systematic review and meta-analysis

STUDY DESIGN

Systematic Review and Meta-analysis.

PURPOSE

Three-column injuries making the spine unstable require adequate fixation which can be achieved by anterior alone, posterior alone or combined anterior-posterior approach. There is no general consensus till date on a single best approach in sub-axial cervical spine trauma. This study comparing the three approaches is an attempt to establish a firmer guideline in this disputed topic.

MATERIAL AND METHODS

The protocol was registered with PROSPERO. PubMed, Embase and Google Scholar were searched for relevant literature. For each study, pre-defined data were extracted which included correction of kyphosis, loss of correction, hospital stay, operative time, blood loss during surgery as the outcome variables. Studies were also screened for the complications.

RESULTS

Eleven studies were evaluated for qualitative analysis and quantitative synthesis of the data in our review. The result demonstrated significant difference with most correction achieved in combined approach subgroup. Though no significant difference was found, the anterior group was having maximum loss of correction. Combined approach showed significantly more operative time and blood loss followed by posterior approach and then anterior approach alone. The improvement in VAS was significantly more in anterior subgroup when compared to combined approach.

CONCLUSION

Cervical alignment is best restored by combined approach compared to the other two. Anterior only approach showed more correction than posterior approach. However, there is no significant difference between all three approaches in loss of correction at long-term follow-up. Anterior only approach is superior to posterior and combined approach on basis of intraoperative and perioperative parameters.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.

C2-C3 Anterior Cervical Diskectomy and Fusion for Hangman's Fractures with C2 Posterior Dislocation: Technical Notes

BACKGROUND

The overwhelming majority of hangman's fractures cause anterior dislocation of C2. Hangman's fracture with C2 posterior dislocation is extremely rare; only 1 pediatric case was reported in 2018 to date. This kind of injury cannot be cataloged using current classification schemes, and no established treatment recommendations exist. The purpose of this article is to report a rare case of a hangman's fracture with C2 posterior dislocation, which does not fit into existing classification systems and discuss management technical notes to avoid pitfalls.

METHODS

We describe this case, review relevant literature, and share our experience.

RESULTS

A 31-year-old male sustained a hangman's fracture with C2 posterior dislocation after he fell into a 50-cm deep roadside ditch when riding a motorcycle. Radiograph and computed tomography on admission showed fractures through both pars of C2 and C2 posterior dislocation. Magnetic resonance imaging on admission showed high T2-weighted signal intensity of cervical spinal cord and compression of the cervical spinal cord by posterior dislocation of the C2 vertebral body. A C2-3 anterior cervical diskectomy and fusion was performed. At 6 months after operation, bony fusion was achieved and magnetic resonance imaging showed the T2-weighted signal hyperintensity of cervical spinal cord before surgery disappeared.

CONCLUSIONS

C2-C3 anterior cervical diskectomy and fusion is recommended for hangman's fractures with C2 posterior dislocation. Traction before surgery is not recommended.

Surgical Outcomes for C2 Tear Drop Fractures: Clinical Relevance to Hangman's Fracture and C2-3 Discoligamentous Injury

Objective

To analyze characteristics of surgically managed tear drop (TD) fractures of the C₂ axis associated with other injuries such as hangman's fracture and C_2‐3 discoligamentous injury as well as treatment outcomes.

Methods

A total of 14 patients (eight men and six women) with TD fractures of the C₂, who were surgically treated at four national trauma centers of tertiary university hospitals from January 2000 to December 2017, were included in this retrospective study. The mean age of the patients was 45.5 years (ranging from 19 to 74 years). The characteristics, surgical treatment methods (anterior fusion vs posterior fusion), and results of 14 TD fractures of the C₂ were analyzed retrospectively. And the clinical relevance between C₂ TD fracture and hangman's fracture and C_2‐3 discoligamentous injury was investigated through the co‐occurrence between injuries. The mean follow‐up time after surgery was 22.6 months (ranging from 12 to 60 months).

Results

Among 14 patients with TD fracture of the C₂, four patients (28.6%) had anterior TD fracture and 10 patients (71.4%) had posterior TD fracture. All 10 posterior TD fracture patients had anterior C_2‐3 displacement. While two of four anterior TD fracture patients had posterior C_2‐3 displacement, the remaining two did not. All 14 patients of TD fracture had at least two or more other associated C₂ injuries as well as C_2‐3 discoligamentous injuries. About 92.9% (13/14) of the patients had typical or atypical hangman's fracture; 100% (10/10) of the posterior TD fracture patients had hangman's fracture, but 75% (3/4) of the anterior TD fracture had hangman's fracture. At admission, 13 patients were neurologically intact. However, the remaining patient had spinal cord injury with American Spinal Injury Association (ASIA) impairment scale B with C_2‐3 bilateral facet dislocation. All four anterior TD fracture patients underwent posterior C_2‐3 fusion. While four of 10 posterior TD fracture patients underwent C_2‐3 anterior fusion, the remaining six underwent posterior fusion. At last follow‐up, 100% (14/14) of the patients achieved solid fusion, and visual analog scale for neck pain was significantly improved (5.9 vs 2.2, P < 0.001). One patient with ASIA impairment scale B had significantly improved to scale D. No major complications occurred.

Conclusion

Our study showed that surgically managed TD fractures of the C₂ showed a high incidence of other associated spine injuries including hangman's fracture and C_2‐3 discoligamentous injury. Therefore, special attention and careful radiologic evaluation are needed to investigate the presence of other associated spine injuries including hangman's fracture and C_2‐3 discoligamentous injury, which are likely to require surgery.

Reduction and Open Fixation of a Cervical Teardrop Fracture: A Technical Note

BACKGROUND

Cervical teardrop fractures are hyperflexion and axial loading injuries associated with significant ligamentous disruption. Patients sustaining these types of injury are classically treated with a cervical corpectomy and anterior fusion. However, there are notable disadvantages of this approach, namely, disruption of the patient's true anatomic alignment and a reduction in the number of fixation points available for cervical fusion. Here we present a novel method of open reduction and internal fixation in a neurologically intact patient with cervical teardrop fracture.

CASE DESCRIPTION

A 34-year-old man presented to Ryder Trauma Center after a helmeted motorcycle accident. The patient was found to be neurologically intact on arrival, and imaging demonstrated a C5 teardrop fracture without bony retropulsion. The patient was taken to the operating room for an open reduction and internal fixation of the fracture using a novel technique. This technique used traditional diskectomies at the C4-5 and C5-6 levels, along with a temporary, unicortical screw into the C5 body to capture the anteriorly displaced fragment. A bicortical screw was then placed into the contralateral side, and now, having fully reduced the fracture, the first (temporary) screw was replaced with a bicortical screw. The patient was neurologically intact postoperatively, with 2-month follow-up computed tomography scan demonstrating stable reduction of the fracture.

CONCLUSIONS

Here we present a novel technique for open reduction and internal fixation of a cervical teardrop fracture that does not require cervical corpectomy. This technique is particularly useful in patients with an anteriorly displaced fragment and without neurologic deficit or compromise.

Anterior reduction and fusion for treatment of massive tear drop fracture of axis combining with inferior endplate serious traversed lesion: A retrospective study

BACKGROUND

Tear drop fracture of axis represents a very small percentage of injuries of the cervical spine, but there is controversy about the treatment method for tear drop fracture of axis, especially when a large avulsed fragment is significant displacement, which combined with the inferior endplate serious traversed lesion of axis.

OBJECTIVE

To evaluate the clinical outcome of anterior reduction, graft fusion of C2-3 and plate fixation in the management of massive tear drop fracture of axis combining with inferior endplate serious traversed lesion of axis.

METHODS

There were 7 patients with a massive tear drop fracture of axis combining with inferior endplate serious traversed lesion. The avulsed ratio of inferior endplate of axis was 46.8 ± 13.4%, the average angle of rotation of the avulsed fragment was 30.4 ± 11.7, and the average displacement was 7.7 ± 2.8 mm. The posterior displacement of axis body was observed with three patients. All patients underwent anterior reduction, graft fusion of C2-3 and plate fixation with high anterior cervical retropharyngeal approach. The follow-up ranges from 2 years to 5 years.

RESULTS

In all cases, tear drop fracture was reduced completely, avulsed fragment got bony healing, and bone graft achieved bony fusion at C2-3. There were no local angle deformity and rotated deformity in all patients, and there were normal physiological lordosis and good stabilization of upper cervical spine. The neurological function of one patient with American Spine Injury Association (ASIA) impairment scale type D was improved to type E postoperatively. Six patients without neurological lesion had no neurological syndrome after operation.

CONCLUSIONS

Anterior surgical procedures would be an effective treatment of massive tear drop fracture of axis combining with inferior endplate serious traversed lesion. Complete reduction, sufficient stabilization and normal physiological lordosis of upper cervical spine could be achieved postoperatively.

Anterior Surgical Fixation for Cervical Spine Flexion-Distraction Injuries

BACKGROUND

Optimal surgical management for flexion-distraction cervical spine injuries remains controversial with current guidelines recommending anterior, posterior, and circumferential approaches. Here, we determined the incidence of and examined risk factors for clinical and radiographic failure in patients with 1-segment cervical distraction injuries having undergone anterior surgical fixation.

METHODS

A retrospective review of 57 consecutive patients undergoing anterior fixation for subaxial flexion-distraction cervical injuries between 2008 and 2012 at our institution was performed. The primary outcome was the number of patients requiring additional surgical stabilization and/or radiographic failure. Data collected included age, gender, mechanism and level of injury, facet pattern injury, and vertebral end plate fracture.

RESULTS

A total of 6 patients failed clinically and/or radiographically (11%). Four patients (7%) required additional posterior fixation. Although 2 other patients identified met radiographic failure criteria, at follow-up they had fused radiographically, were stable clinically, and no further treatment was pursued. Progressive kyphosis and translation were found to be significantly correlated with need for revision (P < 0.05 and P = 0.02, respectively). No differences were identified for all other clinical and radiologic factors assessed, including unilateral or bilateral facet injury, facet fracture, and end plate fracture.

CONCLUSION

This study contributes to the growing body of evidence supporting anterior fixation alone for flexion-distraction injuries. Findings suggest that current measurements of radiographic failure including segmental translation and kyphosis may predict radiographic failure and need for further surgical stabilization in some patients. Future follow-up studies assessing for independent risk factors for anterior approach failure with a validated predictive scoring model should be considered.

Anterior Reduction, Discectomy, and Three Cortical Iliac Bone Grafting With Instrumentation to Treat A Huge Tear Drop Fracture of the Axis: A Case Report and Literature Review

Fractures of the axis body have been little reported and treatment strategies remain controversial and individualized. Not more than 10 cases of huge tear drop fracture of the axis (HTDFA) have been reported in previous studies and the treatment method varies from conservative treatment to an anterior, or posterior, approach surgery. Considering the sparse knowledge of HTDFA, we present a special case report to share our experience and to explore the safety and effectiveness of anterior reduction and fusion to treat HTDFA. A 24-year-old man was referred to our department; he presented with neck pain lasting for 12 h since being involved in a roll-over motor vehicle accident. His neck movement was limited but there was no neurological compromise. Physical examination of the patient showed myodynamia of four limbs Grade 5, Hoffmann sign (-), and Babinski sign (-). Three-dimensional reconstruction computed tomography (CT) confirmed a huge tear drop fracture of the anterior-inferior corner of the axis and discontinuity of the cortex of the axis. After discussion with the spinal surgeon team in the department and an effective conversation with the patient, surgery involving anterior reduction, discectomy, and three cortical iliac bone grafts with instrumentation after transnasal induction of general anesthesia was performed. The patient was instructed to wear a cervical collar until he returned to our department for a follow-up examination some 3 months after surgery. The 3-month postoperative x-ray and CT scan showed a good position of the implant and bony fusion at the C2/3 segment. Anterior reduction, discectomy, and three cortical iliac bone grafts with instrumentation to treat HTDFA are effective, safe, and simple. Of course, longer follow-up duration and more cases are warranted to verify this procedure. Anterior reduction, discectomy, and bone grafting with instrumentation are warranted for most HTDFA cases. However, if HTDFA incorporates other complex fractures, such as fracture of the posterior structure, an anterior and posterior union surgery is recommended.

Conservative and Operative Treatment in Extension Teardrop Fractures of the Axis

STUDY DESIGN

A retrospective case series describing teardrop fracture of the axis.

OBJECT

The purpose of the study was to clarify the clinical features, the mechanism of injury, and the potential instability of extension teardrop fractures of the axis, so as to emphasize the importance of recognizing this injury as a separate entity.

SUMMARY OF BACKGROUND DATA

Teardrop fractures of the axis are rare spinal fractures, comprising only a small percentage of all injuries of the cervical spine. The stability of this fracture pattern has been a matter of debate leading to controversy regarding treatment strategies and the need for stabilization.

METHODS

We retrospectively reviewed data collected from 16 patients to document the mechanism of injury, neurological deficit, treatment and clinical outcome, and imaging findings.

RESULTS

Extension teardrop fractures accounted for approximately 8.9% of the upper cervical spinal injuries and 12.7% of axis fractures at the authors' institution over the same period. Six patients (4 males and 2 females) underwent surgery (4 by an anterior approach, 2 by a posterior approach). Ten cases underwent Halo-vest immobilization for a period between 6 and 12 weeks. At final follow-up, 14 cases achieved excellent results, whereas 2 patients complained of mild residual neck pain. Maximum cranial-caudal dimensions of the fragments were between 5 and 24 mm (average, 12.9 mm), and the transverse dimensions were between 5 and 22 mm (average, 11.1 mm). Fragment displacement ranged from 1 to 9 mm (average, 3.5 mm), whereas fragment rotation ranged from 10 to 52 degrees (average, 24.4 degrees) in the sagittal plane.

CONCLUSIONS

Most patients with an extension teardrop fracture of the axis can be treated conservatively. On the basis of this case series, the authors suggest that large fragment size, displacement or angulation, intervertebral disk injury, neurologic deficit, or signs of instability are reasonable indications for surgical treatment.

Treating Huge Tear-Drop Fracture of Axis With Trapezoidal Bone: A Case Report and Literature Review

STUDY DESIGN

Case report and review of relevant literature.

OBJECTIVE

To discuss the surgical strategies and clinical outcome of managing huge tear drop fracture of axis.

SUMMARY OF BACKGROUND DATA

Teardrop fracture of axis is rarely seen, especially the huge type. The surgical technique is demanding because of the special anatomical structure and difficulty with bone grafting. Moreover, the surgical approach is controversial in the literature.

METHODS

A 51-year-old male patient suffered from neck pain after falling from the bicycle, neck movement was limited with no neurological compromise. X-ray suggested huge tear-drop fracture of anterior-inferior corner of axis, narrowing of C2/3 intervertebral disc. Fusion with self-designed tricortical trapezoidal iliac bone was performed.

RESULTS

Treating huge teardrop fracture of axis by anterior bone grafting with self-designed tricortical trapezoidal iliac bone is effective and stable. A 3-month follow-up showed fusion was achieved, upper cervical curvature was restored, and neck pain disappeared.

CONCLUSION

Self-designed tricortical trapezoidal iliac bone provided adequate fusion area of bone grafting, restoring the normal intervertebral height and cervical alignment, and the midterm outcome is satisfactory.

LEVEL OF EVIDENCE

5.

Biomechanical evaluation of the impact of various facet joint lesions on the primary stability of anterior plate fixation in cervical dislocation injuries: a cadaver study

Object

Injuries of the subaxial cervical spine including facet joints and posterior ligaments are common. Potential surgical treatments consist of anterior, posterior, or anterior-posterior fixation. Because each approach has its advantages and disadvantages, the best treatment is debated. This biomechanical cadaver study compared the effect of different facet joint injuries on primary stability following anterior plate fixation.

Methods

Fractures and plate fixation were performed on 15 fresh-frozen intact cervical spines (C3–T1). To simulate a translation-rotation injury in all groups, complete ligament rupture and facet dislocation were simulated by dissecting the entire posterior and anterior ligament complex between C-4 and C-5. In the first group, the facet joints were left intact. In the second group, one facet joint between C-4 and C-5 was removed and the other side was left intact. In the third group, both facet joints between C-4 and C-5 were removed. The authors next performed single-level anterior discectomy and interbody grafting using bone material from the respective thoracic vertebral bodies. An anterior cervical locking plate was used for fixation. Continuous loading was performed using a servohydraulic test bench at 2 N/sec. The mean load failure was measured when the implant failed.

Results

In the group in which both facet joints were intact, the mean load failure was 174.6 ± 46.93 N. The mean load failure in the second group where only one facet joint was removed was 127.8 ± 22.83 N. In the group in which both facet joints were removed, the mean load failure was 73.42 ± 32.51 N. There was a significant difference between the first group (both facet joints intact) and the third group (both facet joints removed) (p < 0.05, Kruskal-Wallis test).

Conclusions

In this cadaver study, primary stability of anterior plate fixation for dislocation injuries of the subaxial cervical spine was dependent on the presence of the facet joints. If the bone in one or both facet joints is damaged in the clinical setting, anterior plate fixation in combination with bone grafting might not provide sufficient stabilization; additional posterior stabilization may be needed.

Subaxial cervical spine trauma: evaluation and surgical decision-making

Study Design Literature review. Objective To discuss the evaluation and management of subaxial cervical spine trauma (C3-7). Methods A literature review of the main imaging modalities, classification systems, and nonsurgical and surgical treatment performed. Results Computed tomography and reconstructions allow for accurate radiologic identification of subaxial cervical spine trauma in most cases. Magnetic resonance imaging can be utilized to evaluate the stabilizing discoligamentous complex, the nerves, and the spinal cord. The Subaxial Injury Classification (SLIC) is a new system that aids in injury classification and helps guide the decision-making process of conservative versus surgical treatment. Though promising, the SLIC system requires further validation. When the decision for surgical treatment is made, early decompression (less than 24 hours) has been associated with better neurologic recovery. Surgical treatment should be individualized based on the injury characteristics and surgeon's preferences. Conclusions The current state of subaxial cervical spine trauma is one of great progress. However, many questions remain unanswered. We need to continue to account for the individual patient, surgeon, and hospital circumstances that effect decision making and care.

Relationships between joint motion and facet joint capsule strain during cat and human lumbar spinal motions

OBJECTIVE

The lumbar facet joint capsule (FJC) is innervated with mechanically sensitive neurons and is thought to contribute to proprioception and pain. Biomechanical investigations of the FJC have commonly used human cadaveric spines, whereas combined biomechanical and neurophysiological studies have typically used nonhuman animal models. The purpose of this study was to develop mathematical relationships describing vertebral kinematics and FJC strain in cat and human lumbar spine specimens during physiological spinal motions to facilitate future efforts at understanding the mechanosensory role of the FJC.

METHODS

Cat lumbar spine specimens were tested during extension, flexion, and lateral bending. Joint kinematics and FJC principal strain were measured optically. Facet joint capsule strain-intervertebral angle (IVA) regression relationships were established for the 3 most caudal lumbar joints using cat (current study) and human (prior study) data. The FJC strain-IVA relationships were used to estimate cat and human spine kinematics that corresponded to published sensory neuron response thresholds (5% and 10% strain) for low-threshold mechanoreceptors.

RESULTS

Significant linear relationships between IVA and strain were observed for both human and cat during motions that produced tension in the FJCs (P < .01). During motions that produced tension in the FJCs, the models predicted that FJC strain magnitudes corresponding to published sensory neuron response thresholds would be produced by IVA magnitudes within the physiological range of lumbar motion.

CONCLUSIONS

Data from the current study support the proprioceptive role of lumbar spine FJC and low-threshold mechanoreceptive afferents and can be used in interpreting combined neurophysiological and biomechanical studies of cat lumbar spines.

The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping

Clinical studies reported frequent failure with anterior instrumented multilevel cervical corpectomies. Hence, posterior augmentation was recommended but necessitates a second approach. Thus, an author group evaluated the feasibility, pull-out characteristics, and accuracy of anterior transpedicular screw (ATPS) fixation. Although first success with clinical application of ATPS has already been reported, no data exist on biomechanical characteristics of an ATPS-plate system enabling transpedicular end-level fixation in advanced instabilities. Therefore, we evaluated biomechanical qualities of an ATPS prototype C4-C7 for reduction of range of motion (ROM) and primary stability in a non-destructive setup among five constructs: anterior plate, posterior all-lateral mass screw construct, posterior construct with lateral mass screws C5 + C6 and end-level fixation using pedicle screws unilaterally or bilaterally, and a 360° construct. 12 human spines C3-T1 were divided into two groups. Four constructs were tested in group 1 and three in group 2; the ATPS prototypes were tested in both groups. Specimens were subjected to flexibility test in a spine motion tester at intact state and after 2-level corpectomy C5-C6 with subsequent reconstruction using a distractable cage and one of the osteosynthesis mentioned above. ROM in flexion-extension, axial rotation, and lateral bending was reported as normalized values. All instrumentations but the anterior plate showed significant reduction of ROM for all directions compared to the intact state. The 360° construct outperformed all others in terms of reducing ROM. While there were no significant differences between the 360° and posterior constructs in flexion-extension and lateral bending, the 360° constructs were significantly more stable in axial rotation. Concerning primary stability of ATPS prototypes, there were no significant differences compared to posterior-only constructs in flexion-extension and axial rotation. The 360° construct showed significant differences to the ATPS prototypes in flexion-extension, while no significant differences existed in axial rotation. But in lateral bending, the ATPS prototype and the anterior plate performed significantly worse than the posterior constructs. ATPS was shown to confer increased primary stability compared to the anterior plate in flexion-extension and axial rotation with the latter yielding significance. We showed that primary stability after 2-level corpectomy reconstruction using ATPS prototypes compared favorably to posterior systems and superior to anterior plates. From the biomechanical point, the 360° instrumentation was shown the most efficient for reconstruction of 2-level corpectomies. Further studies will elucidate whether fatigue testing will enhance the benefit of transpedicular anchorage with posterior constructs and ATPS.

Mid- to long-term outcome of instrumented anterior cervical fusion for subaxial injuries

The management of patients with subaxial cervical injuries lacks consensus, particularly in regard to the decision which surgical approach or combination of approaches to use and which approach yields the best clinical outcome in the distinct injury. The trauma literature is replete with reports of surgical techniques, complications and gross outcome assessment in heterogeneous samples. However, data on functional and clinical outcome using validated outcome measures are scanty. Therefore, the authors performed a study on plated anterior cervical decompression and fusion for unstable subaxial injuries with focus on clinical outcome. For the purpose of a strongly homogenous subgroup of patients with subaxial injuries without spinal cord injuries, robust criteria were applied that were fulfilled by 28 patients out of an original series of 131 subaxial injuries. Twenty-six patients subjected to 1- and 2-level fusions without having spinal cord injury could be surveyed after a mean of 5.5 years (range 16-128 months). The cervical spine injury severity score averaged 9.6. Cross-sectional outcome assessment included validated outcome measures (Neck pain disability index, Cervical Spine Outcome Questionnaire, SF-36), the investigation of construct failure and successful surgical outcome were defined by strict criteria, the reconstruction and maintenance of local and total cervical lordosis, adjacent-segment degeneration and intervertebral motion, and the fusion-rate using an interobserver assessment. Self-rated clinical outcome was excellent or good in 81% of patients and moderate or poor in 19% that corresponded to the results of the validated outcome measures. Results of the NPDI averaged 12.4 +/- 12.7% (0-40). With the SF-36 mean physical and mental component summary scores were 47.0 +/- 9.8 (18.2-59.3) and 52.2 +/- 12.4 (14.6-75.3), respectively. Using merely non-constrained plates, construct failure was observed in 31% of cases and loss of local lordosis, expressed as a mean injury angle of 14 degrees, postoperative angle of -5.5 degrees and follow-up angle of -1 degree, was significant. However, total cervical lordosis was within the limits of normalcy (-24.3 degrees +/- 13.3) and fusion-rate was 88.5%. The progression of adjacent-level degeneration was shown to be significantly influenced by a decreased plate-to-disc-distance. Adjacent-level intervertebral motion was not altered due to the adjacent fusion, but reduced in the presence of advanced adjacent-level degeneration. Patients were more likely to maintain a high satisfaction level if they succeeded to maintain segmental lordosis (<0 degree), had a solid fusion, an increased plate-to-disc distance, and if they were judged to have a successful surgical outcome that included the absence of construct failure and reconstruction of lordosis within +/-1 SD of normalcy. Using validated outcome vehicles the interdependencies between radiographical, functional and clinical outcome parameters could be substantiated with statistically significant correlations. The use of validated outcome vehicles in a subgroup of patients with plated anterior cervical fusions for subaxial injuries is recommended. With future studies, it enables objective comparison of surgical techniques and related radiographical, functional and clinical outcome.

Micro-structure and mechanical properties of annulus fibrous of the L4-5 and L5-S1 intervertebral discs

BACKGROUND

Nowadays, the study on the structure of the annulus fibrous of intervertebral discs centers on the overall and microscopic structure. There are, however, few investigations about the structures and mechanical properties of the annulus fibrous of intervertebral discs in each point and layer.

METHODS

We observed the tiny anatomical structures and mechanical properties of the adult annulus fibrous of intervertebral discs (L4-5, L5-S1) at the fibrous layer level. Each annulus fibrous of intervertebral disc was delaminated through microsurgical technique. Eight testing points were evenly taken at every layer, and the angles between the fabric direction and the horizontal plane were measured. Meanwhile, five testing specimens were taken from each testing point on every layer along the fabric direction angle, with length (l)=15-20mm, width (b)=1-1.5mm, and thickness (t)=0.1-0.5mm.

FINDINGS AND INTERPRETATION

Through tension tests, we first measured the stress/strain curves to obtain the fitting curves and equations. Thus, mechanical property parameters such as the elastic moduli, damage strain, and damage stress of the testing points were obtained along with relevant equations. The results are as follows: first, there was no obvious difference between the micro-structures and mechanical properties of the annulus fibrous of intervertebral discs L4-5 and L5-S1. Second, the fiber orientation angle at each measurement point gradually increases with the increase of the fibrous layer from the outside to the inside along the radial direction in the horizontal plane. The minimum fiber orientation angle was 25-30 degrees . The fiber orientation angle at the same layer gradually increases from front to back. Furthermore, the fiber orientation angle was 70-90 degrees right in the middle of the back of the annulus fibrous of the lumbar intervertebral disc. The fiber orientation is basically consistent with the posterior longitudinal ligament going. Through the normalized equation and normalized line, the fiber orientation angle alpha at any point in any layer can be easily obtained. Lastly, the elastic moduli of each testing point decreased with the layers increasing along the radius from the outside to the inside. The damage stress decreased linearly from the outside to the inside.

The surgical approach to subaxial cervical spine injuries: an evidence-based algorithm based on the SLIC classification system

STUDY DESIGN

Systematic review of literature and expert clinical opinions of the members of the Spine Trauma Study Group were combined to develop and refine this algorithm.

OBJECTIVE

To develop an evidence-based algorithm for surgical approaches to manage subaxial cervical injuries using a systematic review of the literature, expert opinion, and anticipated patient preferences.

SUMMARY OF BACKGROUND DATA

There is lack of consensus in the management of subaxial cervical spine trauma, in part, because of the lack of a clinically relevant system for classifying these injuries. The newly developed Subaxial Injury Classification scoring system categorizes injury morphology into 3 broad groups, includes an assessment of the integrity of the discoligamentous soft tissue structures and the patient's neurologic status, and thus guides surgical or nonsurgical treatment. The choice of a specific surgical technique and approach is currently not evidence based, and this gap in knowledge is one which the current article seeks to address.

METHODS

A literature review followed by a consensus of experts approach was used to develop the algorithm and to ensure face and content validity.

RESULTS

An algorithm is presented to guide the choice of surgical approach in cervical subaxial burst fractures, distraction injuries, and translation or rotation injuries. The burst or compression injuries and distraction injuries are more likely to be treated with a single anterior approach, whereas the more severe translation or rotation injuries may more commonly be approached posteriorly or with combined anterior and posterior surgery.

CONCLUSION

This algorithm; derived from the Subaxial Injury Classification scoring system, will assist surgeons in answering the 2 most common questions they face when managing subaxial cervical spine trauma: "Should I operate?" and "Which surgical approach should I select?"