Intervertebral motion after incremental damage to the posterior structures of the cervical spine

Photoacoustic Characterization of Cortical and Cancellous Bone in The Vertebrae

To date, spinal problems are not rare, and relevant therapies are always required. Although the combination of photoacoustic imaging (PAI) and spinal fusion surgery, a widely applied operation for spinal cures, is unprecedented, we assume that such combination might improve the accuracy and safety of the surgery. This paper aims to testify that PAI is effective in monitoring and navigating during spinal fusion surgery. Specifically, we examined the optical absorption spectrum of bones to determine the optimal laser wavelength as 532nm. Afterwards, we measured the photoacoustic signals of this bone samples, discovering that the signals of two kinds of samples, cortical bone and cancellous bone, differ considerably in frequency domain. It demonstrated the feasibility that PAI is effective enough to distinguish different bone tissues during the spinal fusion surgery.

Biomechanical evaluation of the ProDisc-C stability following graded posterior cervical injury

OBJECTIVEThere are limited data regarding the implications of revision posterior surgery in the setting of previous cervical arthroplasty (CA). The purpose of this study was to analyze segmental biomechanics in human cadaveric specimens with and without CA, in the context of graded posterior resection.METHODSFourteen human cadaveric cervical spines (C3-T1 or C2-7) were divided into arthroplasty (ProDisc-C, n = 7) and control (intact disc, n = 7) groups. Both groups underwent sequential posterior element resections: unilateral foraminotomy, laminoplasty, and finally laminectomy. Specimens were studied sequentially in two different loading apparatuses during the induction of flexion-extension, lateral bending, and axial rotation.RESULTSRange of motion (ROM) after artificial disc insertion was reduced relative to that in the control group during axial rotation and lateral bending (13% and 28%, respectively; p < 0.05) but was similar during flexion and extension. With sequential resections, ROM increased by a similar magnitude following foraminotomy and laminoplasty in both groups. Laminectomy had a much greater effect: mean (aggregate) ROM during flexion-extension, lateral bending, and axial rotation was increased by a magnitude of 52% following laminectomy in the setting of CA, compared to an 8% increase without arthroplasty. In particular, laminectomy in the setting of CA introduced significant instability in flexion-extension, characterized by a 90% increase in ROM from laminoplasty to laminectomy, compared to a 16% increase in ROM from laminoplasty to laminectomy without arthroplasty (p < 0.05).CONCLUSIONSForaminotomy and laminoplasty did not result in significant instability in the setting of CA, compared to controls. Laminectomy alone, however, resulted in a significant change in biomechanics, allowing for significantly increased flexion and extension. Laminectomy alone should be used with caution in the setting of previous CA.

Digital tracking algorithm reveals the influence of structural irregularities on joint movements in the human cervical spine

BACKGROUND

Disc height loss and osteophytes change the local mechanical environment in the spine; while previous research has examined kinematic dysfunction under degenerative change, none has looked at the influence of disc height loss and osteophytes throughout movement.

METHODS

Twenty patients with pain related to the head, neck or shoulders were imaged via videofluoroscopy as they underwent sagittal-plane flexion and extension. A clinician graded disc height loss and osteophytes as "severe/moderate", "mild", or "none". A novel tracking algorithm quantified motions of each vertebra. This information was used to calculate intervertebral angular and shear displacements. The digital algorithm made it practical to track individual vertebrae in multiple patients through hundreds of images without bias.

FINDINGS

Cases without height loss/osteophytes had a consistent increase in intervertebral angular displacement from C2/C3 to C5/C6, like that of healthy individuals, and mild height losses did not produce aberrations that were systematic or necessarily discernable. However, joints with moderate to severe disc height loss and osteophytes exhibited reduced range of motion compared to adjacent unaffected joints in that patient and corresponding joints in patients without structural irregularities.

INTERPRETATION

Digitally-obtained motion histories of individual joints allowed anatomical joint changes to be linked with changes in joint movement patterns. Specifically, disc height loss and osteophytes were found to influence cervical spine movement in the sagittal plane, reducing angular motions at affected joints by approximately 10% between those with and without height loss and osteophytes. Further, these joint changes were associated with perturbed intervertebral angular and shear movements.

Motion and dural sac compression in the upper cervical spine during the application of a cervical collar in case of unstable craniocervical junction-A study in two new cadaveric trauma models

Background

Unstable conditions of the craniocervical junction such as atlanto-occipital dislocation (AOD) or atlanto-axial instability (AAI) are severe injuries with a high risk of tetraplegia or death. Immobilization by a cervical collar to protect the patient from secondary damage is a standard procedure in trauma patients. If the application of a cervical collar to a patient with an unstable craniocervical condition may cause segmental motion and secondary injury to the spinal cord is unknown.

The aim of the current study is (i) to analyze compression on the dural sac and (ii) to determine relative motion of the cervical spine during the procedure of applying a cervical collar in case of ligamentous unstable craniocervical junction.

Methods and findings

Ligamentous AOD as well as AOD combined with ligamentous AAI was simulated in two newly developed cadaveric trauma models. Compression of the dural sac and segmental angulation in the upper cervical spine were measured on video fluoroscopy after myelography during the application of a cervical collar. Furthermore, overall three-dimensional motion of the cervical spine was measured by a motion tracking system.

In six cadavers each, the two new trauma models on AOD and AOD combined with AAI could be implemented. Mean dural sac compression was significantly increased to -1.1 mm (-1.3 to -0.7 mm) in case of AOD and -1.2 mm (-1.6 to -0.6 mm) in the combined model of AOD and AAI. Furthermore, there is a significant increased angulation at the C0/C1 level in the AOD model. Immense three-dimensional movement up to 22.9° of cervical spine flexion was documented during the procedure.

Conclusion

The current study pointed out that applying a cervical collar in general will cause immense three-dimensional movement. In case of unstable craniocervical junction, this leads to a dural sac compression and thus to possible damage to the spinal cord.

A videofluoroscopy-based tracking algorithm for quantifying the time course of human intervertebral displacements

The motions of individual intervertebral joints can affect spine motion, injury risk, deterioration, pain, treatment strategies, and clinical outcomes. Since standard kinematic methods do not provide precise time-course details about individual vertebrae and intervertebral motions, information that could be useful for scientific advancement and clinical assessment, we developed an iterative template matching algorithm to obtain this data from videofluoroscopy images. To assess the bias of our approach, vertebrae in an intact porcine spine were tracked and compared to the motions of high-contrast markers. To estimate precision under clinical conditions, motions of three human cervical spines were tracked independently ten times and vertebral and intervertebral motions associated with individual trials were compared to corresponding averages. Both tests produced errors in intervertebral angular and shear displacements no greater than 0.4° and 0.055 mm, respectively. When applied to two patient cases, aberrant intervertebral motions in the cervical spine were typically found to correlate with patient-specific anatomical features such as disc height loss and osteophytes. The case studies suggest that intervertebral kinematic time-course data could have value in clinical assessments, lead to broader understanding of how specific anatomical features influence joint motions, and in due course inform clinical treatments.

Efficacy of MRI for assessment of spinal trauma: correlation with intraoperative findings

STUDY DESIGN

Observational diagnostic study on consecutive patients.

OBJECTIVE

To assess the efficacy of magnetic resonance imaging (MRI) for detecting spinal soft tissue injury after acute trauma using intraoperative findings as a reference standard.

SUMMARY OF BACKGROUND DATA

Recognizing injuries to spinal soft tissue structures is critical for proper decision making and management for blunt trauma victims. Although MRI is considered the gold standard for imaging of soft tissues, its ability to identify specific components of soft tissue damage in acute spine trauma patients is poorly documented and controversial.

METHODS

Intraoperative findings were recorded for 21 acute spinal trauma patients (study group) and 14 nontraumatic spinal surgery patients (control group). Preoperative MRI's were evaluated randomly and blindly by 2 neuroradiologists. MRI and intraoperative findings were compared. By using the intraoperative findings as the reference standard, sensitivity, specificity, positive and negative predictive values of MRI in detecting spinal soft tissue injury were determined.

RESULTS

MRI was 100% sensitive and specific in detecting injury to the anterior longitudinal ligament. MRI was moderately sensitive (80%) but highly specific (100%) for injury to the posterior longitudinal ligament. In contrast, MRI was highly sensitive but less specific in detecting injury to paraspinal muscles (100%, 77%), intervertebral disk (100%, 71%), and interspinous ligament (100%, 64%). MRI was moderately sensitive and specific in detecting ligamentum flavum injury (80% and 86.7%) but poorly sensitive for facet capsule injury (62.5%).

CONCLUSIONS

MRI demonstrated high sensitivity for spinal soft tissue injuries. However, MRI showed a definite trend to overestimate interspinous ligament, intervertebral disk, and paraspinal muscle injuries. On the basis of these results, we would consider MRI to be a useful tool for spine clearance after trauma. Conversely, caution should be applied when using MRI for operative decision making due to its less predictable specificity.

Development of a novel radiographic measure of lumbar instability and validation using the facet fluid sign

BACKGROUND

Lumbar spinal instability is frequently referenced in clinical practice and the scientific literature despite the lack of a standard definition or validated radiographic test. The Quantitative Stability Index (QSI) is being developed as a novel objective test for sagittal plane lumbar instability. The QSI is calculated using lumbar flexion-extension radiographs. The goal of the current study was to use the facet fluid sign on MRI as the "gold standard" and determine if the QSI is significantly different in the presence of the fluid sign.

METHODS

Sixty-two paired preoperative MRI and flexion-extension exams were obtained from a large FDA IDE study. The MRI exams were assessed for the presence of a facet fluid sign, and the QSI was calculated from sagittal plane intervertebral rotation and translation measurements. The QSI is based on the translation per degree of rotation (TPDR) and is calculated as a Z-score. A QSI > 2 indicates that the TPDR is > 2 std dev above the mean for an asymptomatic and radiographically normal population. The reproducibility of the QSI was also tested.

RESULTS

The mean difference between trained observers in the measured QSI was between -0.28 and 0.36. The average QSI was significantly (P = 0.047, one-way analysis of variance) higher at levels with a definite fluid sign (2.3±3.2 versus 0.60±2.4).

CONCLUSIONS

Although imperfect, the facet fluid sign observed may be the best currently available test for lumbar spine instability. Using the facet fluid sign as the "gold standard" the current study documents that the QSI can be expected to be significantly higher in the presence of the facet fluid sign. This supports that QSI might be used to test for sagittal plane lumbar instability.

CLINICAL RELEVANCE

A validated, objective and practical test for spinal instability would facilitate research to understand the importance of instability in diagnosis and treatment of low-back related disorders.

In vitro biomechanics of the craniocervical junction-a sequential sectioning of its stabilizing structures

BACKGROUND CONTEXT

Occipitocervical dislocations involve translations of the craniocervical joints. The relative contributions of each ligament to overall stability and the effects of the occipitoatlantal joint capsules on the pathologic translation are unknown. Although incidences of occipitocervical dislocations are rare after blunt trauma, they are usually fatal. When patients do survive these dislocations, the proper diagnosis is difficult, which in turn may increase the fatality rate. A biomechanical model may provide a greater pathologic understanding of craniocervical subluxation.

PURPOSE

The purpose of the study is to build an in vitro biomechanical model to determine which stabilizing ligament(s) of the craniocervical junction are most important in restraining rotation and translations during these rotations. This may guide clinical diagnosis, which could assist in treatment options.

STUDY DESIGN/SETTING

The study design includes a biomechanical cadaveric test.

METHODS

Seven cadaveric specimens were tested using a 6-degree-of-freedom spine simulator under the following conditions: intact, clivus/alar removal (CR), transverse ligament destruction (TLD), occipitoatlantal (OA) joint capsulotomyoccipitoatlantal (OA) joint capsulotomy (C0-C1 JC), and C1-C2 joint capsulotomy (C1-C2 JC). Flexion-extension (FE), lateral bending (LB), and axial rotation (AR) were applied (2.5 Nm) to a C0-C2 segment, whereas anterior-posterior (AP) and cranial-caudal (CC) translations were recorded. Average motions were normalized to intact (100%) for each joint.

RESULTS

Increases in C0-C1 angular and translational motions occurred after TLD and C0-C1 JC. At the atlantoaxial joint, there were significant (p<.05) increases from intact in FE (TLD=154%, C0-C1 JC=174%) and in AR (TLD=178%, C0-C1 JC=224%). Anterior-posterior translation during applied LB increased significantly after TLD (248% intact). Cranial-caudal translation during applied FE increased significantly after TLD (188%) and C0-C1 JC (361%). Increases in C1-C2 angular motion occurred after TLD and C1-C2 JC and in translation after CR and TLD. At the C1-C2 joint, there were significant increases from intact in FE (TLD=172%, C1-C2 JC=160%) and in LB (TLD=286%, C1-C2 JC=332%); in AR, there were no statistical differences. Anterior-posterior translation increased significantly after CR (280%). Cranial-caudal translation also increased significantly after CR (205%) and TLD (298%) during LB.

CONCLUSIONS

Transverse and alar ligaments appear to be the main stabilizers of the craniocervical junction. The vertical structures attached to the clivus and OA joint capsules function as secondary stabilizers. Craniocervical dislocations seem to affect FE and lateral bending the most, whereas increased translation seems to occur primarily in the AP and CC directions. Models of craniocervical trauma should section all three restraining structures for the future studies.

Stabilization of the craniocervical junction after an internal dislocation injury: an in vitro study

BACKGROUND CONTEXT

Reconstructive surgeries at the occipitocervical (OC) junction have been studied in treating degenerative conditions. There is a paucity of data for optimal fixation for a traumatically unstable OC joint. In clinical OC dislocations, segmental fixation may be impossible because of vertebral artery injury or fracture. Segmental fixation of the occiput, C1, and C2 demonstrated maximum biomechanical stability in fixation of an unstable craniocervical dislocation. A biomechanical study comparing various points of cervical posterior screw fixation after recreating traumatic injury would illuminate relative advantages between the various techniques.

PURPOSE

To determine the rigidity lost, if any, of segmental C0-C2 posterior screw fixation versus fixation skipping C1 at the OC junction, with or without a cross-connector.

STUDY DESIGN

This study is a cadaveric biomechanical investigation.

METHODS

Intervertebral motions and translations were recorded in seven specimens under conditions in the following order: intact, OC dislocation model with complete disruption of the cruciate ligaments, alar ligaments, and occipitoatlantal/atlantoaxial capsules (injury), segmental posterior fixation (SPF) with posterior instrumentation (ELLIPSE; Globus Medical, Inc., Audubon, PA, USA) at occiput, C1, and C2 levels, endpoint fixation (EPF) with posterior instrumentation at occiput and C1 level skipping C1, and endpoint fixation with a cross-connector (EPFC). Motion was applied through a custom spine simulator with a pure moment load of 2.5 Nm and measured with motion capture markers attached to occiput (C0), anterior C1 ring, and C2. Flexion-extension (FE), lateral bending (LB), axial rotation (AR), and cranial-caudal (CC) motions were recorded in terms of C0-C2. Results were reported as a percentage of injured motion (injury=100%), unless otherwise stated.

RESULTS

The injury significantly increased the motion to 165%, 263%, and 130%, during FE, LB, and AR, respectively, of intact. The CC translations increased to 164%, 254%, and 121% during FE, LB, AR, respectively, of intact. Segmental posterior fixation significantly reduced motion to 7%, 8%, and 1%, during FE, LB, and AR, respectively, of injury. Endpoint fixation significantly increased motion in FE, resulting in 12%, 6%, and 4% during FE, LB, and AR, respectively, of injury when compared with SPF. The EPFC construct decreased the motion compared with its counterpart to 8.6%, 5.7%, and 3.2% during FE, LB, and AR, respectively.

CONCLUSIONS

All fixation constructs significantly reduced motion in all loading modes and CC translations, compared with intact and injury. The construct with the greatest stability against craniocervical dislocation included SPF with instrumentation at the occiput, C1, and C2. By skipping C1 using the EPF, FE and cephalad-caudal translations significantly increased compared with posterior fixation at every level. The addition of a cross-connector increased the stability but was not statistically significant.

Intraobserver and interobserver reliability of measures of cervical sagittal rotation

BACKGROUND

Diagnosis and treatment decisions of cervical instability are made, in part, based on the clinician's assessment of sagittal rotation on flexion and extension radiographs. The objective of this study is to evaluate the intraobserver and interobserver reliability of three measurement techniques in assessing cervical sagittal rotation.

METHODS

Fifty lateral radiographs of patients with single-level cervical degenerative disc were selected and measured on two separate occasions by three spine surgeons using three different measurement techniques. Cervical sagittal rotation was measured using three different techniques.

RESULTS

Intraclass correlation coefficients were most consistent for Method 2 (ICC 0.93-0.96) followed by Method 1 (ICC 0.88-0.91) and Method 3 (ICC 0.81-0.87). Intraobserver agreement (% of repeated measures within 0.5° of the original measurement) ranged between 76% and 96% for all techniques, with Method 2 showing the best agreement (92%-96%). Paired comparisons between observers varied considerably with interobserver reliability correlation coefficients ranging from 0.54 to 0.89. Method 2 showed the highest interobserver reliability coefficient (0.82, range 0.73-0.88). Method 2 was also more reliable for the classification of "instability". Intraobserver percent agreements ranged from 94 to 98% for Method 2 versus 84% to 90% for Method 1 and 78% to 86% for Method 3, while interobserver percent agreements ranged from 90% to 98% for Method 2 versus 86% to 94% for Method 1 and 74% to 84% for Method 3.

CONCLUSIONS

Method 2 (measuring the angle from the inferior endplate of the vertebra above the degenerative disc and the inferior endplate of the vertebra below the degenerative disc) showed the best intraobserver and interobserver reliability overall in assessing cervical sagittal rotation.

Measurement of intervertebral cervical motion by means of dynamic x-ray image processing and data interpolation

Accurate measurement of intervertebral kinematics of the cervical spine can support the diagnosis of widespread diseases related to neck pain, such as chronic whiplash dysfunction, arthritis, and segmental degeneration. The natural inaccessibility of the spine, its complex anatomy, and the small range of motion only permit concise measurement in vivo. Low dose X-ray fluoroscopy allows time-continuous screening of cervical spine during patient's spontaneous motion. To obtain accurate motion measurements, each vertebra was tracked by means of image processing along a sequence of radiographic images. To obtain a time-continuous representation of motion and to reduce noise in the experimental data, smoothing spline interpolation was used. Estimation of intervertebral motion for cervical segments was obtained by processing patient's fluoroscopic sequence; intervertebral angle and displacement and the instantaneous centre of rotation were computed. The RMS value of fitting errors resulted in about 0.2 degree for rotation and 0.2 mm for displacements.

Hidden discoligamentous instability in cervical spine injuries: can quantitative motion analysis improve detection?

PURPOSE

Recent literature shows that occult discoligamentous injuries still remain difficult to diagnose in the first instance. Thresholds as indicators for discoligamentous segmental instability were previously defined. But, since supine radiodiagnostic is prone to spontaneous reduction of a displaced injury, and even some highly unstable injuries reveal only slight radiographic displacement, these criteria might mislead in the traumatized patient. A highly accurate radiographic instrument to assess segmental motion is the computer-assisted quantitative motion analysis (QMA). The aim was to evaluate the applicability of the QMA in the setting of a traumatized patient.

METHODS

Review of 154 patients with unstable cervical injuries C3-7. Seventeen patients (male/female: 1:5, age: 44.6 years) had history of initially hidden discoligamentous injuries without signs of neurologic impairment. Initial radiographs did not fulfill instability criteria by conventional analysis. Instability was identified by late subluxation/dislocation, persisting/increasing neck pain, and/or scheduled follow-up. For 16 patients plain lateral radiographs were subjected to QMA. QMA data derived were compared with normative data of 140 asymptomatic volunteers from an institutional database.

RESULTS

Data analysis of measurements revealed mean spondylolisthesis of -1.0 mm (-3.7 to +3.4 mm), for segmental rotational angle mean angulation of -0.9° (-11.1° to +17.7°). Analysis of these figures indicated positive instability thresholds in 5 patients (31.3 %). Analysis of center of rotation (COR)-shifts was only accomplishable completely in 3/16 patients due to limited motion or inadequacy of radiographs. Two of these patients (12.5 %) showed a suspect shift of the COR.

CONCLUSIONS

Our data show a high rate of false negative results in cases of hidden discoligamentous injuries by using conventional radiographic analysis as well as QMA in plain lateral radiographs in a trauma setting. Despite the technical possibilities in a modern trauma center, our data and recent literature indicate a thorough clinical and radiographic follow-up of patients with cervical symptoms to avoid secondary complications from missed cervical spine injuries.

Three-dimensional kinematic stress magnetic resonance image analysis shows promise for detecting altered anatomical relationships of tissues in the cervical spine associated with painful radiculopathy

For some patients with radiculopathy a source of nerve root compression cannot be identified despite positive electromyography (EMG) evidence. This discrepancy hampers the effective clinical management for these individuals. Although it has been well-established that tissues in the cervical spine move in a three-dimensional (3D) manner, the 3D motions of the neural elements and their relationship to the bones surrounding them are largely unknown even for asymptomatic normal subjects. We hypothesize that abnormal mechanical loading of cervical nerve roots during pain-provoking head positioning may be responsible for radicular pain in those cases in which there is no evidence of nerve root compression on conventional cervical magnetic resonance imaging (MRI) with the neck in the neutral position. This biomechanical imaging proof-of-concept study focused on quantitatively defining the architectural relationships between the neural and bony structures in the cervical spine using measurements derived from 3D MR images acquired in neutral and pain-provoking neck positions for subjects: (1) with radicular symptoms and evidence of root compression by conventional MRI and positive EMG, (2) with radicular symptoms and no evidence of root compression by MRI but positive EMG, and (3) asymptomatic age-matched controls. Function and pain scores were measured, along with neck range of motion, for all subjects. MR imaging was performed in both a neutral position and a pain-provoking position. Anatomical architectural data derived from analysis of the 3D MR images were compared between symptomatic and asymptomatic groups, and the symptomatic groups with and without imaging evidence of root compression. Several differences in the architectural relationships between the bone and neural tissues were identified between the asymptomatic and symptomatic groups. In addition, changes in architectural relationships were also detected between the symptomatic groups with and without imaging evidence of nerve root compression. As demonstrated in the data and a case study the 3D stress MR imaging approach provides utility to identify biomechanical relationships between hard and soft tissues that are otherwise undetected by standard clinical imaging methods. This technique offers a promising approach to detect the source of radiculopathy to inform clinical management for this pathology.

The importance of the posterior osteoligamentous complex to subaxial cervical spine stability in relation to a unilateral facet injury

BACKGROUND CONTEXT

Unilateral facet disruptions are relatively common in the cervical spine; however, the spectrum of injury is large, and little is known regarding the magnitude of instability expected to be present in an isolated posterior osteoligamentous injury.

PURPOSE

To quantify the contribution of the posterior osteoligamentous structures to cervical spine stability during simulated flexion-extension (FE), lateral bend (LB), and axial rotation (AR).

STUDY DESIGN

An in vitro biomechanical study.

METHODS

Eight cadaveric C2-C5 spines were used in this study. A custom-developed spinal loading simulator applied independent FE, LB, and AR to the specimens at 3°/s up to ±1.5 Nm. Using an optical tracking system, data were collected for the intact specimen and after sequential surgical interventions of posterior ligamentous complex (PLC) disruption, unilateral capsular disruption, progressive resection of the inferior articular process of C3 by one-half, and finally complete resection of the inferior articular process of C3. The magnitude of segmental and overall range of motion (ROM) for each simulated movement along with the overall neutral zone (NZ) was analyzed using two-way repeated-measures analyses of variance and post hoc Student-Newman-Keuls tests (α=.05).

RESULTS

An increase in ROM was evident for all movements (p<.001). Within FE, ROM increased after cutting only the PLC (p<.05). For AR, sectioning of the PLC and complete bony facet fracture increased ROM (p<.05). Lateral bend ROM increased after facet capsular injury and complete articular facet removal (p<.05). There was an overall effect of injury pattern on the magnitude of the NZ for both FE (p<.001) and AR (p<.001) but not for LB (p=.6); however, the maximum increase in NZ generated was only 30%.

CONCLUSIONS

The PLC and facet complex are dominant stabilizers for FE and AR, respectively. The overall changes in both ROM and NZ were relatively small but consistent with an isolated posterior osteoligamentous complex injury of the Stage I flexion-distraction injury.

Motion within the unstable cervical spine during patient maneuvering: the neck pivot-shift phenomenon

BACKGROUND

Cervical extrication collars are applied to millions of blunt trauma victims despite the lack of any evidence that a collar can protect against secondary injuries to the cervical spine. Cadaver studies support that in the presence of a dissociative injury, substantial motion can occur within the occipitocervical spine with collar application or during patient transfers. Little is known about the biomechanics of cervical stabilization; hence, it is difficult to develop and test improved immobilization strategies.

MATERIALS

Severe unstable injuries were created in seven fresh whole human cadavers. Rigid collars were applied with the body in a neutral position. Computed tomographic examinations were obtained before and after tilting the body or backboard as would be done during patient transport or to inspect the back. Relative displacements between vertebrae at the site of the injury were measured from the Computed tomographic examinations. The overall relative alignment between body and collar was assessed to understand the mechanisms that may facilitate motion at the injury site.

RESULTS

Intervertebral motion averaged 7.7 mm±6.8 mm in the axial plain and 2.9 mm±2.5 mm in the cranial-caudal direction. The rigid collars appeared to create pivot points where the collar contacts the head in the region under the ear and where the collar contacts the shoulders.

DISCUSSION

Rigid cervical collars appear to create pivot points that shift the center of rotation lateral to the spine and contribute to the intervertebral motions that were measured. Immobilization strategies that avoid these neck pivot-shift phenomena may help to reduce secondary injuries to the cervical spine. The whole cadaver model with simulation of patient maneuvers may provide an effective test method for cervical immobilization.

Kinematics of progressive circumferential ligament resection (decompression) in conjunction with cervical disc arthroplasty in a spondylotic spine model

STUDY DESIGN

Benchtop biomechanics study examining kinematic effects of progressive resection in a human cadaveric spine model.

OBJECTIVE

To determine the effects of posterior longitudinal ligament (PLL) resection, unilateral and bilateral foraminotomy, and laminectomy on cervical intervertebral rotation and translation after cervical disc arthroplasty (CDA).

SUMMARY OF BACKGROUND DATA

Although the clinical results after CDA have been studied, there remain unanswered questions regarding the surgical techniques used at the time of device insertion. For example, it is unclear whether a surgeon should retain or resect the PLL and uncinate processes at the time of primary surgical intervention. Further, the effect of a subsequent posterior decompression (foraminotomy or laminectomy) on the stability of a motion segment containing a disc arthroplasty is unknown.

METHODS

Three-dimensional intervertebral motion was measured by biplanar videography in human cadaveric spines at C4-C5 or at C5-C6 subjected to a 1.5-Nm moment applied to induce motion in the sagittal plane. Coupled motions were not constrained. After measuring intact spine motion, disc arthroplasty with bilateral ventral foraminotomy was performed without PLL resection. Sequentially, rotations and translations were measured after PLL resection, unilateral foraminotomy, bilateral foraminotomy, and laminectomy.

RESULTS

CDA with bilateral ventral foraminotomy increased sagittal rotation by 0.4 degrees (16%) compared with the intact spine. The addition of PLL resection increased rotation by 0.5 degrees (14% increase). Unilateral and bilateral foraminotomy had negligible effects on sagittal rotation or anteroposterior (AP) translation. Laminectomy resulted in an additional sagittal plane rotation of 2 degrees. The sagittal-plane interverterbal rotation resultant after all interventions was 6 degrees , with 1.5 mm of AP translation occurring only.

CONCLUSION

Given that a greater degree of motion was seen with PLL resection combined with ventral foraminotomy, we recommend that PLL resection be performed when performing CDA. In our benchtop model, unilateral and bilateral posterior foraminotomies were not associated with the creation of significant sagittal rotational or AP translational instability.

Reference data for assessing widening between spinous processes in the cervical spine and the responsiveness of these measures to detecting abnormalities

BACKGROUND CONTEXT

Traumatic injury to the spine is evaluated and treated based on the perceived stability of the spine. Recent classification schemes have established the importance of evaluating the discoligamentous complex to fully comprehend stability. There are a variety of techniques to evaluate the discoligamentous complex, including assessment of interspinous distance. However, there currently are no clinically validated methods to define and assess abnormal interspinous widening.

PURPOSE

The purpose of the study was to provide reference data and evidence to support the objective use of spinous process widening in the diagnosis of cervical spine injury and instability.

STUDY DESIGN

The study was designed to be biomechanical and observational.

METHODS

Distances between spinous processes were measured from lateral flexion-extension X-rays of 156 skeletally mature asymptomatic subjects who reported never having had neck symptoms as well as 12 whole human cadavers before and after creating increasingly severe damage to posterior structures. Cervical interspinous distances were measured and then normalized to the width of the C4 vertebral end plate. The change in the distance from flexion to extension was also calculated.

RESULTS

Descriptive statistics, including the 95% confidence intervals for each cervical level were tabulated for 863 levels in 149 analyzable asymptomatic volunteers. In the simulated cadaver model, interspinous widening was highly specific and mildly sensitive for detecting damage to the posterior structures of the cervical spine.

CONCLUSIONS

This study provides reference data that can be used to quantitatively assess interspinous process widening in the cervical spine. Application of the reference data to a cadaver model of cervical trauma suggests that although objective evidence of abnormal widening may be uncommon, when present, it is suggestive of extensive damage to the cervical spine. Derived from this data were two "rule of thumb" criteria to identify abnormal interspinous widening in flexion X-rays; when greater than 30% relative to an adjacent level (40% between C1-C2 and C2-C3) or greater than 50% of the anterior-posterior width of the C4 vertebral body (30% for C2-C3).

Cervical spinal disc replacement

Cervical spinal disc replacement is used in the management of degenerative cervical disc disease in an attempt to preserve cervical spinal movement and to prevent adjacent disc overload and subsequent degeneration. A large number of patients have undergone cervical spinal disc replacement, but the effectiveness of these implants is still uncertain. In most instances, degenerative change at adjacent levels represents the physiological progression of the natural history of the arthritic disc, and is unrelated to the surgeon. Complications of cervical disc replacement include loss of movement from periprosthetic ankylosis and ossification, neurological deficit, loosening and failure of the device, and worsening of any cervical kyphosis. Strict selection criteria and adherence to scientific evidence are necessary. Only prospective, randomised clinical trials with long-term follow-up will establish any real advantage of cervical spinal disc replacement over fusion.

Anterior cervical discectomy and fusion with a locked plate and wedged graft effectively stabilizes flexion-distraction stage-3 injury in the lower cervical spine: a biomechanical study

STUDY DESIGN

An in vitro three-dimensional (3D) flexibility test of human C3-C7 cervical spine specimens.

OBJECTIVE

To test the hypothesis that anterior cervical fusion with a wedged graft and a locked plate can effectively stabilize the cervical spine after complete anterior and posterior segmental ligamentous release.

SUMMARY OF BACKGROUND DATA

Distraction-flexion Stage 3 injuries of the lower cervical spine (bilateral facet dislocations) are usually reduced under awake cranial traction. When the magnetic resonance imaging reveals a traumatic disc prolapse, anterior cervical discectomy and fusion (ACDF) is usually recommended. Most authors advise combining ACDF with posterior instrumentation to address the insufficiency of the posterior elements. However, there is clinical evidence that ACDF with a locked plate alone suffices for the treatment of these injuries, especially in young patients. Still, there are no biomechanical studies on the effect of a locked plate on the complete anterior and posterior ligamentous-deficient young cervical spine under physiologic preload.

METHODS

Eight fresh frozen human lower cervical spines (C3-C7) from young donors (age, 44.5 years; range, 21-63 years) were used. A 3D flexibility test was conducted using a moment of 0.8 Nm without preload. Flexion-extension was additionally tested using a moment of 1.5 Nm under 0 and 150 N follower preload. Spines were tested first intact, then after complete C5-C6 discectomy with posterior longitudinal ligament resection and ACDF with a wedged bone graft and a rigid locked plate, and finally after complete release of the supraspinous, interspinous, and intertransverse ligaments; the facet capsules; and ligamentum flavum. RESULTS.: When tested under 0.8 Nm moment without preload, complete posterior and anterior ligamentous release did not significantly increase the ROM of the ACDF construct in flexion-extension (P > 0.025), lateral bending (P > 0.025), and axial rotation (P > 0.025). When tested under 1.5 Nm moment with or without a compressive preload, the complete posterior and anterior ligamentous release did not significantly affect the ROM of the ACDF construct (P > 0.01). The application of preload significantly reduced the motion at the C5-C6 ACDF construct with ligamentous disruption in comparison with the motion in the absence of a preload (P < 0.01).

CONCLUSION

Anterior cervical fusion with a wedged graft and a rigid constrained (locked) plate can effectively stabilize the nonosteoporotic cervical spine after complete posterior element injury when excessive ROM is prevented (for example, by the use of postoperative external immobilization). Even when the construct is subjected to higher moments, adequate stability can be achieved when physiologic preload is present. Osteoporosis and lack of sufficient preload due to poor neuromuscular control may affect long-term screw stability, and additional external immobilization may be needed until fusion matures.

Threshold cervical range-of-motion necessary to detect abnormal intervertebral motion in cervical spine radiographs

STUDY DESIGN

Whole human cadaver model to assess a common diagnostic test for cervical spine stability.

OBJECTIVE

Determine criteria that can be used to determine if sagittal plane angular motion of the head/neck during a cervical spine flexion/extension study is adequate to reliably assess intervertebral motion (IVM).

SUMMARY OF BACKGROUND DATA

Flexion/Extension radiographs of the cervical spine are commonly used to help identify specific abnormalities in IVM. Several authors have recognized that inadequate patient effort can make flexion/extension studies unreliable, but validated guidelines for assessing the adequacy of these studies are not available.

METHODS

Increasingly severe anterior-to-posterior (N = 6), and posterior-to-anterior (N = 6) soft tissue injuries were simulated in the cervical spines of 12 human cadavers. Sagittal plane radiographic images were taken with 4 gradually increasing amounts of overall flexion and extension motion of the head. IVM was measured for each level of sagittal plane rotation of the head/neck using previously validated computer-assisted methods.

RESULTS

With less than 60 degrees of sagittal plane rotation of the head/neck, intervertebral rotation or displacement was almost never greater than the 95% confidence interval previously established for asymptomatic people. Even with 60 degrees or more motion, intervertebral rotation and displacement were within normal limits after extensive damage to the soft-tissues. The center-of-rotation was the most sensitive measure for detecting soft tissue damage.

CONCLUSION

The results of this study suggest that clinicians should make sure patients can flex and extend their head/neck to a minimum range of 60 degrees before evaluating them for a dynamic motion study to assess cervical spine stability. Even with adequate motion, interverterbral rotation and translation can remain within normal limits in the presence of extensive soft tissue damage. The most sensitive measure for detecting soft tissue damage was center-of-rotation although it lacks specificity, particularly in the presence of underlying degenerative changes, and is not readily assessed in most clinical situations.

Observer agreement in assessing flexion-extension X-rays of the cervical spine, with and without the use of quantitative measurements of intervertebral motion

BACKGROUND CONTEXT

Flexion-extension X-rays are commonly used to identify abnormalities in intervertebral motion, despite little evidence for the reliability of the information that clinicians derive from these test.

PURPOSE

Quantify observer agreement on intervertebral motion abnormalities assessed with and without the use of computer-assisted technology.

STUDY DESIGN

Assess interobserver agreement among clinicians when they evaluate cervical flexion-extension X-rays using the methods they now use in clinical practice, and compare this to observer agreement when the same clinicians reassess the X-rays using computer-assisted technology.

METHODS

Seventy-five flexion-extension X-rays of the cervical spine, obtained from several clinical practices, were assessed by seven practicing physicians who routinely assess these X-rays. Observers assessed the studies using the methods they routinely use, and then reassessed the studies, at least a month later, using validated computer-assisted methods. Agreement among clinicians with and without computer-assisted technology was assessed using kappa statistics.

RESULTS

Agreement was poor (kappa=0.17) with methods routinely used in clinical practice. Computer-assisted analysis improved interobserver agreement (kappa=0.77). With computer-assisted methods, disagreements involved cases with severe degeneration or static misalignment where motion was within normal limits, or in fusion cases where there was between 1 and 1.5 degrees of motion at the fusion site.

CONCLUSIONS

This study suggests that commonly used methods to assess flexion-extension X-rays of the cervical spine may not provide reliable clinical information about intervertebral motion abnormalities, and that validated, computer-assisted methods can dramatically improve agreement among clinicians. The lack of definitions of instability and fusion acceptable to all the clinicians was likely a primary source of disagreement with both manual and computer-assisted assessments.

Radiographic assessment and quantitative motion analysis of the cervical spine after serial sectioning of the anterior ligamentous structures

STUDY DESIGN

Cadaveric study of a diagnostic test for cervical spine instability.

OBJECTIVE

Determine if flexion-extension (FE) radiographs can be used to detect incremental damage to anterior cervical structures.

SUMMARY OF BACKGROUND DATA

Prior studies have shown that damage to cervical structures can alter motion between vertebrae, and FE radiographs are sometimes used to detect this damage. However, no study has determined if FE radiographs are sensitive and specific for acute injury.

METHODS

FE radiographs were taken of the intact neck and after each incremental increase in damage to the anterior structures. Intervertebral motion was quantified using previously validated methods. The sensitivity and specificity of intervertebral motion measurements were assessed.

RESULTS

Motion within the intact spines was within normal ranges. Although intervertebral rotation changed significantly after certain anterior structures were damaged, rotation frequently remained within normal ranges, even after extensive damage. A center of rotation that was posterior to the 95% confidence interval for normal motion was 100% sensitive and specific for damage to the anterior structures of the spine.

CONCLUSIONS

The results suggest that extensive damage to the anterior cervical spine could be missed if instability assessment was based on intervertebral rotation or displacements measured from FE radiographs. In contrast, a center of rotation that was located posterior to normal was both sensitive and specific for damage to anterior structures.