Posterior longitudinal ligament status in cervical spine bilateral facet dislocations

Numerical Investigation of Spinal Cord Injury After Flexion-Distraction Injuries At the Cervical Spine

Flexion-distraction injuries frequently cause traumatic cervical spinal cord injury (SCI). Post-traumatic instability can cause aggravation of the secondary SCI during patient's care. However, there is little information on how the pattern of disco-ligamentous injury affects the SCI severity and mechanism. This study objective was to analyze how different flexion-distraction disco-ligamentous injuries affect the SCI mechanisms during post-traumatic flexion and extension. A cervical spine finite element model including the spinal cord was used and different combinations of partial or complete intervertebral disc (IVD) rupture and disruption of various posterior ligaments were modeled at C4-C5, C5-C6 or C6-C7. In flexion, complete IVD rupture combined with posterior ligamentous complex rupture was the most severe injury leading to the most extreme von Mises stress (47 to 66 kPa), principal strains p1 (0.32 to 0.41 in white matter) and p3 (-0.78 to -0.96 in white matter) in the spinal cord and to the most important spinal cord compression (35 to 48 %). The main post-trauma SCI mechanism was identified as compression of the anterior white matter at the injured level combined with distraction of the posterior spinal cord during flexion. There was also a concentration of the maximum stresses in the gray matter after injury. Finally, in extension, the injuries tested had little impact on the spinal cord. The capsular ligament was the most important structure in protecting the spinal cord. Its status should be carefully examined during patient's management.

An Experimental Study on the Safety and Mechanism of Reduction of Subaxial Cervical Facet Dislocation Using Z-Shape Elevating-Pulling Reduction Technique

OBJECTIVE

We sought to clarify the safety and unlocking mechanism of the Z-shape elevating-pulling closed reduction (ZR) technique and to analyze the differences in facet contact force and intraspinal pressure during subaxial facet dislocation reduction using the ZR technique and traditional skull traction closed reduction (SR).

METHODS

In 15 human cadaveric skull-neck-thorax specimens, reproducible unilateral and bilateral facet dislocations (UFDs/BFDs) were created at the C5-C6 level and then reduced by applying the ZR and SR techniques, respectively. Tekscan FlexiForce A-201 pressure sensors were used to measure the anterior and posterior intraspinal pressure and injured facet contact force under physiological conditions and before and after reduction. The maximum pressures during the reduction process were recorded.

RESULTS

After creation of the facet dislocation, the anterior and posterior intraspinal pressure and facet contact force were significantly increased relative to normal (P < 0.001). The UFDs and BFDs of all specimens were successfully reduced by both ZR and SR, and the intraspinal pressure and facet contact force were significantly reduced compared with before reduction (P < 0.001). Compared with SR, the maximum posterior intraspinal pressure during BFD reduction (P = 0.027) and the maximum facet contact force during UFD reduction (P < 0.001) were lower when ZR was used for closed reduction.

CONCLUSIONS

Our findings suggest that ZR and SR can both be used to reduce subaxial facet dislocation and decompress the spinal cord. However, the ZR technique appears to safer and more effective than the SR technique for closed reduction of subaxial facet dislocations.

Spinal cord injury after blunt cervical spine trauma: correlation of soft-tissue damage and extension of lesion

BACKGROUND AND PURPOSE

In patients with spinal cord injury after blunt trauma, several studies have observed a correlation between neurologic impairment and radiologic findings. Few studies have been performed to correlate spinal cord injury with ligamentous injury. The purpose of this study was to retrospectively evaluate whether ligamentous injury or disk disruption after spinal cord injury correlates with lesion length.

MATERIALS AND METHODS

We retrospectively reviewed 108 patients diagnosed with traumatic spinal cord injury after cervical trauma between 1990-2011. Plain films, CT, and MR imaging were performed on patients and then reviewed for this study. MR imaging was performed within 96 hours after cervical trauma for all patients. Data regarding ligamentous injury, disk injury, and the extent of the spinal cord injury were collected from an adequate number of MR images. We evaluated anterior longitudinal ligaments, posterior longitudinal ligaments, and the ligamentum flavum. Length of lesion, disk disruption, and ligamentous injury association, as well as the extent of the spinal cord injury were statistically assessed by means of univariate analysis, with the use of nonparametric tests and multivariate analysis along with linear regression.

RESULTS

There were significant differences in lesion length on T2-weighted images for anterior longitudinal ligaments, posterior longitudinal ligaments, and ligamentum flavum in the univariate analysis; however, when this was adjusted by age, level of injury, sex, and disruption of the soft tissue evaluated (disk, anterior longitudinal ligaments, posterior longitudinal ligaments, and ligamentum flavum) in a multivariable analysis, only ligamentum flavum showed a statistically significant association with lesion length. Furthermore, the number of ligaments affected had a positive correlation with the extension of the lesion.

CONCLUSIONS

In cervical spine trauma, a specific pattern of ligamentous injury correlates with the length of the spinal cord lesion in MR imaging studies. Ligamentous injury detected by MR imaging is not a dynamic finding; thus it proved to be useful in predicting neurologic outcome in patients for whom the MR imaging examination was delayed.

MDCT of acute subaxial cervical spine trauma: a mechanism-based approach

Injuries to the spinal column are common and road traffic accidents are the commonest cause. Subaxial cervical spine (C3–C7) trauma encompasses a wide spectrum of osseous and ligamentous injuries, in addition to being frequently associated with neurological injury. Multidetector computed tomography (MDCT) is routinely performed to evaluate acute cervical spine trauma, very often as first-line imaging. MDCT provides an insight into the injury morphology, which in turn reflects the mechanics of injury. This article will review the fundamental biomechanical forces underlying the common subaxial spine injuries and resultant injury patterns or “fingerprints” on MDCT. This systematic and focused analysis enables a more accurate and rapid interpretation of cervical spine CT examinations. Mechanical considerations are important in most clinical and surgical decisions to adequately realign the spine, to prevent neurological deterioration and to facilitate appropriate stabilisation. This review will emphasise the variables on CT that affect the surgical management, as well as imaging “pearls” in differentiating “look-alike” lesions with different surgical implications. It will also enable the radiologist in writing clinically relevant CT reports of cervical spine trauma.

Teaching Points

• Vertebral bodies and disc bear the axial compression forces, while the ligaments bear the distraction forces.

• Compressive forces result in fracture and distractive forces result in ligamentous disruption.

• Bilateral facet dislocation is the most severe injury of the flexion-distraction spectrum.

• Biomechanics-based CT reading will help to rapidly and accurately identify the entire spectrum of injury.

• This approach also helps to differentiate look-alike injuries with different clinical implications.

Head-first impact with head protrusion causes noncontiguous injuries of the cadaveric cervical spine

OBJECTIVE

To simulate horizontally aligned head-first impacts with initial head protrusion using a human cadaveric neck model and to determine biomechanical responses, injuries, and injury severity.

DESIGN

Head-first impacts with initial head protrusion were simulated at 2.4 m/s using a human cadaver neck model (n = 10) mounted horizontally to a torso-equivalent mass on a sled and carrying a surrogate head. Macroscopic neck injuries were determined, and ligamentous injuries were quantified using fluoroscopy and visual inspection after the impacts. Representative time-history responses for injured specimens were determined during impact using load cell data and analyses of high-speed video.

SETTING

Biomechanics research laboratory.

PARTICIPANTS

Cervical spines of 10 human cadavers.

MAIN OUTCOME MEASURES

Injury severity at the middle and lower cervical spine was statistically compared using a 2-sample t test (P < 0.05).

RESULTS

Neck buckling consisted of hyperflexion at C6/7 and C7/T1 and hyperextension at superior spinal levels. Noncontiguous neck injuries included forward dislocation at C7/T1, spinous process fracture and compression-extension injuries at the middle cervical spine, and atlas and odontoid fractures. Ligamentous injury severity at C7/T1 was significantly greater than at the middle cervical spine.

CONCLUSIONS

Distinct injury mechanisms were observed throughout the neck, consisting of extension-compression and posterior shear at the upper and middle cervical spine and flexion-compression and anterior shear at C6/7 and C7/T1. Our experimental results highlight the importance of clinical awareness of potential noncontiguous cervical spine injuries due to head-first sports impacts.

Inestabilidad de la columna cervical subaxial por falla de la banda de tensión posterior: artrodesis contécnica de Magerl. informe preliminar de los resultados a corto plazo

OBJETIVO: Analizar, retrospectivamente los resultados a corto plazo de las lesiones traumáticas inestables de la región subaxial, tratadas mediante fijación cervical por vía posterior con técnica de Magerl, utilizando sistema de barras y tornillos poliaxiales en las masas laterales. MÉTODOS: Se efectuó una revisión de pacientes con lesión traumática inestable cervical subaxial y afectación de la banda de tensión posterior (tipo B.1 de la AO), que hubieran sido operados con fijación posterior con barras y tornillos poliaxiales en las masas laterales, siguiendo la técnica de Magerl, utilizando criterios de selección anatómicos, diagnóstico-imagenológicos y éticos. Se valoraron, en el seguimiento, los resultados radiológicos, funcionales y neurológicos. RESULTADOS: Se incluyeron 9 pacientes (8 varones, 1 mujer), con edad promedio de 25 años (rango 21 - 34) y seguimiento promedio de 20 meses (rango 12 - 24). Tanto los resultados radiológicos, como los funcionales y los neurológicos, fueron excelentes en todos los casos, sin desviación en cifosis ni desplazamiento anteroposterior, y sin síntomas importantes en el seguimiento. Los dos casos tratados, con fijación de tres vértebras, presentaron cierta rigidez cervical esporádica. En ningún caso se extrajeron los implantes. CONCLUSIONES: Los beneficios obtenidos sugieren que es una técnica útil, segura, eficaz y versátil para las lesiones traumáticas inestables de la columna cervical baja, tipo B.1, inclusive aquellas multisegmentarias, especialmente en pacientes jóvenes.

Assessment of the posterior ligamentous complex following acute cervical spine trauma

BACKGROUND

Magnetic resonance imaging is commonly used to assess the integrity of the posterior ligamentous complex following cervical trauma, but its accuracy and reliability have not been documented, to our knowledge. The purpose of this study was to determine the diagnostic accuracy of magnetic resonance imaging in detecting injury to specific components of the posterior ligamentous complex of the cervical spine.

METHODS

Patients with an acute cervical spine injury that required posterior surgical treatment were prospectively studied. The six components of the posterior ligamentous complex were characterized as intact, incompletely disrupted, or disrupted on preoperative magnetic resonance imaging studies by a radiologist and intraoperatively by two surgeons. Correlation between the magnetic resonance imaging and intraoperative findings was determined. The percent agreement, sensitivity, specificity, negative predictive value, and positive predictive value of magnetic resonance imaging as a tool for characterizing the integrity of the posterior ligamentous complex were calculated.

RESULTS

Forty-seven consecutive patients with a total of seventy levels of injury were studied. Overall, there was moderate agreement between the magnetic resonance imaging and intraoperative findings for the supraspinous and interspinous ligaments (kappa scores of 0.46 and 0.43, respectively) and fair agreement between those for the ligamentum flavum, left and right facet capsules, and cervical fascia (kappa scores of 0.32, 0.31, 0.26, and 0.39, respectively). The sensitivity of the magnetic resonance imaging was greatest for the cervical fascia (100%) and the lowest for the facet capsules (80%). Specificity ranged from 56% (for the facet capsules) to 67% (for the interspinous ligament). The positive predictive value ranged from 42% (for the cervical fascia) to 82% (for the interspinous ligament).

CONCLUSIONS

Magnetic resonance imaging is sensitive for the evaluation of injury to the posterior ligamentous complex in the setting of acute cervical trauma. However, it has a lower positive predictive value and specificity, suggesting that injury to the posterior ligamentous complex may be "over-read" on magnetic resonance images. If magnetic resonance imaging is used in isolation to guide treatment, the high rate of false-positive findings may lead to unnecessary surgery. Other factors, including the morphology of the injury and the neurological status, should be considered as well when devising a treatment plan.

Biomechanics of cervical facet dislocation

OBJECTIVES

The goal of this study was to compute the dynamic neck loads during simulated high-speed bilateral facet dislocation and investigate the injury mechanism.

METHODS

Ten osteoligamentous functional spinal units (C3/4, n = 4; C5/6, n = 3; C7/T1, n = 3) were prepared with muscle force replication, motion tracking flags, and a 3.3-kg mass rigidly attached to the upper vertebra. Frontal impacts of increasing severity were applied to the lower vertebra until dislocation was achieved. Inverse dynamics was used to calculate the dynamic neck loads during dislocation. Average peak impact acceleration required to cause dislocation ranged between 7.6 and 11.6 g. This resulted in dynamic neck loads applied at average peak rates of 906 Nm/s for flexion moment, 8017 N/ for anterior shear, and 8100 N/s for axial compression. To determine the temporal event patterns, the average occurrence times of the load and motion peaks were statistically compared (P <0.05).

RESULTS

Among average peak loads, axial compression of 233.6 N was first to occur followed by anterior shear force of 73.1 N and flexion moment of 30.7 Nm. Among average peak motions, axial separation of 5.3 mm was first to occur followed by flexion rotation of 63.1 degrees and anterior shear of 21.5 mm. Subsequently, average peak posterior shear force of 110.3 N was observed as the upper facet became locked in the intervertebral foramina. Average peak axial compression of 6.6 mm occurred significantly later than all preceding events.

CONCLUSIONS

During bilateral facet dislocation, the main loads included flexion moment and forces of axial compression and anterior shear. These loads caused flexion rotation, facet separation, and anterior translation of the upper facet relative to the lower. The present data help elucidate the injury mechanism of cervical facet dislocation.

Mechanism of cervical spinal cord injury during bilateral facet dislocation

STUDY DESIGN

An in vitro biomechanical study.

OBJECTIVES

The objectives were to: quantify dynamic canal pinch diameter (CPD) narrowing during simulated bilateral facet dislocation of a cervical functional spinal unit model with muscle force replication, determine if peak dynamic CPD narrowing exceeded that observed post-trauma, and evaluate dynamic cord compression.

SUMMARY OF BACKGROUND DATA

Previous biomechanical models are limited to quasi-static loading or manual ligament transection. No studies have comprehensively analyzed dynamic CPD narrowing during simulated dislocation.

METHODS

Bilateral facet dislocation was simulated using 10 cervical functional spinal units (C3-C4: n = 4; C5-C6: n = 3; C7-T1: n = 3) with muscle force replication by frontal impact of the lower vertebra. Rigid body transformation of kinematic data recorded optically was used to compute the CPD in neutral posture (before dislocation), during dynamic impact (peak during dislocation), and post-impact (flexion rotation = 0(0) degrees ). Peak dynamic impact and post-impact CPD narrowing were statistically compared.

RESULTS

Average peak dynamic impact CPD narrowing significantly exceeded (P < 0.05) post-impact narrowing and occurred as early as 71.0 ms following impact. The greatest dynamic impact narrowing of 7.2 mm was observed at C3-C4, followed by 6.4 mm at C5-C6, and 5.1 mm at C7-T1, with average occurrence times ranging between 71.0 ms at C7-T1 and 97.0 ms at C5-C6.

CONCLUSION

Extrapolation of the present results indicated dynamic spinal cord compression of up to 88% in those with stenotic canals and 35% in those with normal canal diameters. These results are consistent with the wide range of neurologic injury severity observed clinically due to bilateral facet dislocation.

Cervical facet joint kinematics during bilateral facet dislocation

Previous biomechanical models of cervical bilateral facet dislocation (BFD) are limited to quasi-static loading or manual ligament transection. The goal of the present study was to determine the facet joint kinematics during high-speed BFD. Dislocation was simulated using ten cervical functional spinal units with muscle force replication by frontal impact of the lower vertebra, tilted posteriorly by 42.5 degrees. Average peak rotations and anterior sliding (displacement of upper articulating facet surface along the lower), separation and compression (displacement of upper facet away from and towards the lower), and lateral shear were determined at the anterior and posterior edges of the right and left facets and statistically compared (P < 0.05). First, peak facet separation occurred, and was significantly greater at the left posterior facet edge, as compared to the anterior edges. Next, peak flexion rotation and anterior facet sliding occurred, followed by peak facet compression. The highest average facet translation peaks were 22.0 mm for anterior sliding, 7.9 mm for separation, 9.9 mm for compression and 3.6 mm for lateral shear. The highest average rotation of 63 degrees occurred in flexion, significantly greater than all other directions. These events occurred, on average, within 0.29 s following impact. During BFD, the main sagittal motions included facet separation, flexion rotation, anterior sliding, followed by compression, however, non-sagittal motions also existed. These motions indicated that unilateral dislocation may precede bilateral dislocation.