Bilateral Facet Joints Research Articles

Effects of posterior lumbar spinal fusion on the stability of unstable lumbar segment and biomechanical properties of adjacent segments: a finite element study

To explore the effects of posterolateral lumbar fusion (PLF) and posterior lumbar interbody fusion (PLIF) on the stability of postoperative unstable single lumbar segment and the biomechanical alterations of the adjacent segments. A finite element model of L3-S1 segments with a single segmental degeneration at the L4-5 level was established, and the model of L4-5 segmental instability after posterior laminectomy and facetectomy was also established, in which laminar and interior 2/3 area of bilateral facet joints were resected. Physical loads were applied to the models and the changes of the range of motion (ROM) at L4-5 level in different models were recorded at the condition of flexion, extension, lateral bending and rotation. PLF and PLIF were performed on postoperative unstable model respectively, the changes of the ROM at L4-5 level, the ROM and the stress on the adjacent discs in different models were recorded. Compared to the unstable model, the L4-5 segmental stability was restored after PLF or PLIF. The ROMs of L3-4 and L5-S1 levels were similar to the preoperative unstable model. The stress on adjacent discs (L3-4 and L5-S1) was increased significantly, and maximum stress distribution changed and concentrated in the anterior annulus fiber in the two fusion models. There was no significant difference of the maximum stress on adjacent discs between PLF and PLIF models [(1.056 ± 0.061) mPa vs (1.070 ± 0.075) mPa; (1.147 ± 0.055) mPa vs (1.162 ± 0.075)mPa, P>0.05]. Lumbar segmental stability after posterior laminectomy and facetectomy can be recovered by both PLF and PLIF. Both PLF and PLIF may increase the possibility of adjacent segment degeneration because of the augmentation of maximum stress on adjacent discs.

Osseous associated cervical spondylomyelopathy at the C2-C3 articular facet joint in 11 dogs

In dogs, vertebral canal stenosis at C2-C3 due to articular facet joint degeneration is only sporadically identified. The authors’ aims were to review the clinical presentation, MRI characteristics, treatment and...

Critical Values of Facet Joint Angulation and Tropism in the Development of Lumbar Degenerative Spondylolisthesis: An International, Large-Scale Multicenter Study by the AOSpine Asia Pacific Research Collaboration Consortium.

Study Design An international, multicenter cross-sectional image-based study performed in 33 institutions in the Asia Pacific region.Objective The study addressed the role of facet joint angulation and tropism in relation to L4–L5 degenerative spondylolisthesis (DS).Methods The study included 349 patients (63% females; mean age: 61.8 years) with single-level DS; 82 had no L4–L5 DS (group A) and 267 had L4–L5 DS (group B). Axial computed tomography and magnetic resonance imaging were utilized to assess facet joint angulations and tropism (i.e., asymmetry between facet joint angulations) between groups.Results There was a statistically significant difference between group A (left mean: 46.1 degrees; right mean: 48.2 degrees) and group B (left mean: 55.4 degrees; right mean: 57.5 degrees) in relation to bilateral L4–L5 facet joint angulations (p < 0.001). The mean bilateral angulation difference was 7.4 and 9.6 degrees in groups A and B, respectively (p = 0.025). A critical value of 58 degrees or greater significantly increased the likelihood of DS if unilateral (adjusted OR: 2.5; 95% CI: 1.2 to 5.5; p = 0.021) or bilateral facets (adjusted OR: 5.9; 95% CI: 2.7 to 13.2; p < 0.001) were involved. Facet joint tropism was found to be relevant between 16 and 24 degrees angulation difference (adjusted OR: 5.6; 95% CI: 1.2 to 26.1; p = 0.027).Conclusions In one of the largest studies assessing facet joint orientation in patients with DS, greater sagittal facet joint angulation was associated with L4-L5 DS, with a critical value of 58 degrees or greater increasing the likelihood of the condition for unilateral and bilateral facet joint involvement. Specific facet joint tropism categories were noted to be associated with DS.

Traumatic L4 –L5 Spondylolisthesis with Vertical Shear Fracture of Pelvis

We report a case of traumatic listhesis of L4 over L5 vertebra with vertical shear fracture of pelvis in a 45 year old male. The patient was treated surgically immediately after the injury. His radiological and operative findings showed anterior listhesis of L4 over L5 vertebra with dislocation of bilateral facet joints at L3-L4 and L4-L5 level and fracture of spinous processes of L4-L5 vertebra with fracture of right lamina of L4 vertebra. There was also evidence of diastasis of pubic symphysis with displaced communited fracture of right iliac bone. Surgically he was treated by decompression and reduction, L3-L5 pedicular screw fixation along with L3 to L4 laminectomy, L3-L4 and L4-L5 discectomy and reconstruction plating for pubic diastasis and right iliac bone fracture. Key-words: Traumatic Spondylolisthesis, Pubic Diastasis, Vertical Shear fracture

Outcomes of extended transforaminal lumbar interbody fusion for lumbar spondylosis

This study aims to assess the results of extended transforaminal lumbar interbody fusion (TLIF) for a two surgeon, single institution series. In total, extended TLIF with bilateral decompression was performed in 57 patients. Pain, American Spinal Injury Association scores, patient demographics, body mass index (BMI), perioperative indices and radiographic measurements were recorded and analysed. The surgeries were performed between February 2011 and January 2014 on 38 women and 19 men. The mean patient age was 62.86years, and the mean BMI was 30.31kg/m2. In 49 patients, spondylolisthesis was the primary indication. The mean intraoperative time was 284.65min, and this decreased as the series progressed. The median length of stay was 5days (range: 2–9). The surgical complication rate was 19.3%. Two patients died from cardiopulmonary complications. Single level TLIF was performed in 78.9% of the cohort, with L4/5 the most commonly fused level. Significant pain reduction was achieved from a mean (±standard deviation) preoperative visual analogue scale (VAS) of 8.28±1.39 to 1.50±1.05 at 12months postoperatively. No patients deteriorated neurologically. Spondylolisthesis was significantly corrected from a preoperative mean of 6.82mm to 2.80mm postoperatively. Although there is a learning curve associated with the procedure, extended TLIF with bilateral facet joint removal and decompression appeared to be a safe and effective alternative to other fusion techniques, and our results were comparable to other published case series. The stabilisation and correction of spinal deformity reduces pain, aids neurologic recovery and improves quality of life.

How to Reduce Bilateral Cervical Facet Joint Dislocation in Anterior Approach: A Trick to Avoid Anterior-Posterior-Anterior Surgical Procedures

Introduction Cervical facet joint dislocation is a common injury of the lower cervical spine. These flexion distraction lesions in cervical spine occur as a subluxation or unilateral/bilateral dislocation of the facet joints, which often be accompanied by direct spinal cord and nerve root injury. The presence of herniated intervertebral disc requires an anterior approach to decompress the spinal cord. Because often it is not possible to reduce facet joint dislocation while performing anterior surgery an additional posterior approach and then the fixation trough an anterior approach again is necessary. This method (supine-prone-supine) creates difficulties for surgeons because of the prolonged operation time; the need for frequent changes in patient position; and a subsequent high incidence of complications. Materials and Methods On the basis of a case, we present a maneuver to use pins such as joysticks in vertebral body during anterior approach to reduce dislocated facet joints in cervical spine fractures. After cervical discectomy/corpectomy, we use the pins to put the vertebral body in kyphotic position following rotational motion to reduce the facet joints. Results and Conclusion: Since we implemented this procedure, we had no more to perform posterior approach in surgical treatment in the last 15 cases of bilateral facet joint dislocation with herniated intervertebral disc in cervical trauma.

The Risk Factors of Pedicle Screws Loosening after Spinal Instrumentations

Introduction Implant instability has a relatively low rate of incidence, however revision interventions in those cases are expensive, difficult to perform and have a considerable frequency of poor results. Even though various novel technologies are available, this problem is not resolved yet and it is essential to assess risk factors that may lead to this complication. The objective of this study is to determine risk factors for the pedicle screw instability development after spinal instrumentations. The objective of this study is to assess risk factors in relation to pedicle screw instability development. Materials and Methods This is a prospective randomized study of 120 spinal instrumentations performed in case of traumatic injuries and spinal degenerative diseases of lumbar and thoracolumbar spine. Preoperatively patients underwent CT examination and bone density was measured in Hounsfield units. CT scans utilized slice thickness 0.5 mm. Tube voltage was 120 kV, current 300 mA, auto mA range 180 to 400; 1.0 s/3.0 mm/0.5 × 32, and helical-pitch 21.0. Transpedicular fixation was used to treat patients either as standalone technique or in combination with various types of interbody fusion, also if indicated, decompression of nerve roots and spinal cord was performed. Patients with suboptimal screws placement were excluded from this study. The duration of follow-up was 1 year; cases with screws loosening were registered. Logistic regression analysis was utilized to assess the relationship between expected risk factors (extension of decompression, bone density, extension of fixation), and the rate of screws loosening. Results Extensive decompression resulting in a total or subtotal bilateral facet joints total resection results in the considerable increase in frequency of pedicle screws instability. The parameters of the logistic regression model were chi-square = 14.78227, p = 0.0001209; В0 = −0.9360933, р = 0.0005580619; В1 = 1.479709, р = 0.0002964492; OR (odds ratio) = 4.391667 (2.001693; 9.635212). It was estimated that the rate of implant instability has a strong inverse relation to the bone density measured in HU during CT investigation. The parameters of the logit regression model were chi-square = 12.32050, p = 0.0004486; B0 = −1.846886, p = 0.007698078; B1 = 0.01737968, p = 0.00169618; OR = 56.7059 (4.706; 683.2748). Even though the extension of fixation in general turned out to be irrelevant to a screw loosening, it was pointed out that S1 vertebra included into a fixed area is an additional risk factor for implant instability formation. The estimated parameters of logistic regression model were chi-square = 4.882991 p = 0.0271296; B0 = −0.5221894, p = 0.01585754; B1 = 0.992193, p = 0.03159398; OR = 2.697143 (1.093079; 6.655126). The general nonlinear regression model that includes all listed previously contributing factors has a predictive value of 78.33%, goodness of fit chi-square = 34.96233 p = 0.0000001. Conclusions Apparently, surgical intervention should be planned thoroughly avoiding destabilizing overextended decompression because this could be a significant contributing factor for the implant instability formation in future. Bone quality must be taken in view while planning spinal instrumentation. If necessary, augmentation with bone cement must be performed to prevent implant instability formation. The extension of fixation to the level S1 must be clearly justified as it was estimated that it is an additional considerable risk factor for pedicle screws loosening.

“Thickened” ligamentum flavum caused by laminectomy

ObjectiveThe purpose of this study was to evaluate the effect of a laminectomy on the adjacent ligamentum flavum (LF) by measuring LF thickness using magnetic resonance imaging (MRI). Materials and methodsA total of 78 patients (31 man, 47 woman) with laminectomy were included in our study. After determination of laminectomy level, measurements were done from the thickest parts of the bilateral LF at the upper level of the laminectomy where bilateral facet joints were evident at the slice. ResultsIpsilateral ligamentum flavum with laminectomy was significantly thicker than the contralateral ligamentum flavum with laminectomy. ConclusionLaminectomy cause thickening of ligamentum flavum. Therefore we assume that it should kept in mind that LFH may develop at the adjacent level to the laminectomy and careful clinical and radiological assessments’ should be done to exclude LFH in cases who complain about the recurrence of complaints during the post-operative period after laminectomy.

Effects on single segmental lumbar stability after graded facetectomy and laminectomy: a finite element study

To explore the effects on degenerative single segmental lumbar spinal stability after posterior graded laminectomy and facetectomy by a finite element method. A finite element model of L3-S1 segments with a single segmental degeneration at L4-5 level was established. Different models of L4-L5 segmental instability after posterior graded laminectomy and facetectomy were established. And interior 1/3, 1/2, 2/3 of laminar and bilateral facet joints were resected. Physical loads were applied to the models and the changes of range of motion (ROM) at L4-5 level in different models were recorded during flexion, extension, lateral bending and rotation. As compared to preoperative model, after resecting 1/3 bilateral facet joints at L4-5 level, L4-5 segmental ROM increased 18% during flexion, 27% during extension and 45% during torsion. And the increased degree of ROM became more obvious along with a greater resection range of bilateral facet joints. No significant difference existed in L4-5 segmental ROM during lateral bending in all models. Facet joints play vital roles in lumbar segmental stability. And segmental instability may occur when 1/3 bilateral facet joints are resected.

Outcomes of Extended Transforaminal Lumbar Interbody Fusion for Lumbar Spondylosis: A Retrospective Cohort Study

Objectives: The present study aims to assess the results of extended Transforaminal Lumbar Interbody Fusion (TLIF) for a two-surgeon, single institution series. Methods: 57 cases of extended TLIF with bilateral decompression were performed. Pain, ASIA scores, patient demographics, BMI, perioperative indices and radiographic measurements were recorded and analysed. Results: 57 operations were performed between February 2011 and January 2014, there were 38 female and 19 male patients. Mean patient age was 62.86 years, mean BMI was 30.31 kg/m2. In 49 patients spondylolisthesis was the primary indication. The mean intraoperative time was 284.65 min, this decreased as the series progressed. The median length of stay was 5 days, ranging from 2 to 9 days. The surgical complication rate was 22.8%. Two patients died from cardiopulmonary complications. 78.9% of the cohort had single-level TLIF, L4/5 was the most commonly fused level. Significant pain reduction was achieved from a mean Pre-operative VAS of 8.28 +/- 1.39 to post-op VAS of 1.50+/-1.05 at 12 months. No patients deteriorated neurologically. Spondylolisthesis was significantly corrected from a pre-operative mean of 6.82 mm to 2.80 mm post-operatively. There is a learning curve associated with the procedure. Discussion: TLIF with bilateral facet joint removal and decompression appeared to be a safe and effective alternative to other fusion techniques, and is comparable to other published case series. Stabilisation and correction of spinal deformity reduces pain, aids neurologic recovery and improves quality of life.

Gait abnormality due to spinal instability after lumbar facetectomy in the rat

Spinal instability of the lumbar spine causes various clinical symptoms. Among them, spinal instability is thought to contribute to low back pain, but the pathophysiological mechanisms are controversial. Although experimental animal models of spinal instability have been reported, it is unknown whether these models produce pain and whether spinal instability affects walking ability. We used the CatWalk system to investigate whether lumbar facetectomy causes gait abnormalities and low back pain. Thirty male Sprague-Dawley rats were divided into three experimental groups. In the sham group, only the bilateral L4-L5 facet joints were exposed. In the experimental group, rats underwent complete resection of the bilateral L4-L5 facet joints without neural tissue injury. The control group comprised naïve rats. The CatWalk system was used to analyze gait in postoperative weeks 3, 4.5, 6, and 7. Radiological and histological analyses were also performed. At 7 weeks postoperatively, the rats in the experimental group showed the gait abnormalities seen in low back pain and neuropathic pain models. Radiological examination of the same rats revealed spinal instability with histological evidence of intervertebral disc degeneration. These results suggest that spinal instability and/or intervertebral disc degeneration induce gait abnormalities and low back pain. This experimental model may be useful for elucidating the mechanisms underlying clinical symptoms, such as low back pain, in patients with spinal instability.

A Biomechanical Method for Reconstruction of Tumbling Trampoline- Associated Cervical Spine Injuries Using Human and Anthropometric Test Dummy Data

BackgroundRebound devices such as trampolines are associated with catastrophic spinal cord injuries. Cadaveric studies have reported thresholds for injuries that can be applied to the case of failed acrobatics such as backward somersaults. However, it remains unclear whether falls on rebound surfaces should be expected to cause neurological injuries in the majority of cases or only in unfortunate exceptions. The purpose of the current study is to demonstrate the risk of injury associated with a failed backflip performed on a rebound device such as a trampoline or tumbling trampoline.MethodsBackward somersault kinematic data was acquired using subjects fitted with a safety harness. This data was then applied to a testing rig designed to set a Hybrid III Anthropometric Test Dummy (ATD) in rotation and released at precise timing so as to reproduce failed backward somersaults. The ATD was instrumented to measure rotational rate, head acceleration as well as stresses in the lower cervical region.ResultsThe axial compression, shear force and flexion moment measured on average (SD) were respectively 1700 (470) N, 909 (667) N, and 360 (122) Nm while the threshold for bilateral facet joint dislocation (BFD) shown by previous cadaver studies showed a significantly lower threshold (p <0.001). Combined results have shown a likelihood of BFD for failed somersaults on tumbling trampolines ranging from 47 to 99%.ConclusionFailed backward somersaults causing BFD are also likely to cause neurological damage. Therefore, use of rebound devices requires the need for progressive skill achievement; supervision for beginners and the use of additional safety measures must be emphasized to prevent inverted vertical falls resulting in the specific combination of forces necessary to cause BFD.

Kissing Spine and the Retrodural Space of Okada: More Than Just a Kiss?

Baastrup (“kissing spine”) disease is characterized by contact by adjacent lumbar spinous processes and the presence of lumbar interspinous bursitis. The formation of an adventitious bursa within the interspinous region has been described previously in a retrospective review of routine lumbar magnetic resonance imaging in which the authors demonstrated the prevalence of interspinous bursitis in 8.2% of the study population [1]. These authors found an association between the formation of an interspinous bursa and the presence of associated degenerative changes such as central canal stenosis, disk bulging, and anterolisthesis. However, whether this bursa formation is the result of mechanical impingement from adjacent spinous processes or the result of degenerative conditions has not been fully characterized. Dr. Kikuzo Okada first described a communication pathway between single-level bilateral cervical facet joints in 1981 [2]. He described an extradural space dorsal to the ligamentum flavum that could connect the interlaminar region, interspinous region, and bilateral facet joints. This communication has been described in the lumbar spine, whereby interventional procedures in a single-sided facet joint have demonstrated flow of contrast material to the contralateral facet joint [3]. Usually “kissing spine” is thought to be caused by touching of approximating lumbar spinous processes during lumbar extension. This touching may create an adventitial bursa irritation within the interspinous ligament at the same level. However, we postulate that kissing spine disease may actually be an early sign of segmental instability. The anteroposterior shearing forces in persons with spondylolisthesis or early mid-range segmental instability may cause a friction moment, resulting in the interspinous formation of a bursa. Alternatively, excessive fluid within the facet joint caused by effusion may leak through the retrodural space of Okada to this region between the spinous processes and accumulate in the interspinous bursa. This bursa formation is different from a posterior facet joint synovial cyst in that the cyst has a contiguous relationship to the adjacent facet joint and is located in close proximity to the joint, whereas the adventitial bursa formation is more posterior within

Lumbar facet joint injection: feasibility as an alternative method in high-risk patients

To evaluate the effectiveness of therapeutic facet joint steroid injections for symptoms caused by lumbar spinal stenosis in patients who are at risk of bleeding. We analysed 134 patients who had previously undergone one-level bilateral facet joint steroid injections for lumbar radiculopathy caused by spinal stenosis from January 2011 to December 2012. All patients had a bleeding tendency due to several medical conditions. A retrospective chart review was conducted by one radiologist. Response was measured by using a five-point patient satisfaction scale. Evaluations of the relationship between possible outcome predictors were made using the chi-squared or Fisher's exact test, as appropriate. Among the 42 enrolled patients (male/female = 14/28; mean age, 58 years; range, 41-88 years), 25 patients (59.5 %) were classified to have received effective treatment; in 17 patients treatment was classified as ineffective. Eighteen (72 %) of the 25 patients with mild-to-moderate central canal stenosis had symptom relief, and 7 of the 17 (41.2 %) patients with severe central canal stenosis had symptom relief (P < 0.05). Other outcome predictors were not statistically significant. Therapeutic facet joint steroid injection is potentially effective for lumbar radiculopathy caused by spinal stenosis. This could be helpful in patients at risk of bleeding. • Epidural injection of steroids is a conventional treatment for lumbar radiculopathy. • Facet joint steroid injections showed similar therapeutic effects in lumbar spinal stenosis. • No serious complications, including bleeding, occurred with facet joint injections. • Facet joint steroid injection offers an alternative therapy in patients with bleeding risk.

Tubular surgery with the assistance of endoscopic surgery via midline approach for lumbar spinal canal stenosis: a technical note

We devised a tubular surgery with the assistance of endoscopic surgery via midline approach to the spinal canal to preserve the bilateral facet joints and the paravertebral muscles when treating lumbar spinal canal stenosis. We report details of this operative procedure. A 2-cm incision is made in the skin in the midline of the intervertebral level to be decompressed. The spinous process on the cranial side is partially excised, and incisions along the ligament fiber are made in the midline of the supraspinous and interspinous ligaments to expose the ligamentum flavum. After the lamina and the inferior parts of the bilateral facet joints are adequately excised, the microendoscopic discectomy system is inserted. With this procedure, no muscular tissue is seen in the surgical site. The portal approach is small, but if full advantage is taken of the spinal microendoscope's merits, the bilateral facet joints are preserved and wide decompression of deep parts is possible. The microendoscope is positioned above the spinal canal to provide a good symmetrical field of view to enable easy anatomical orientation. Bilateral intervertebral joints were satisfactorily preserved in ten patients who received this surgery. All became ambulatory on the day after surgery and the clinical results remained favorable 3 years after the operation. Tubular surgery with the assistance of endoscopic surgery via a midline approach is a minimally invasive surgical procedure with favorable results that enables preservation of paravertebral muscles and bilateral facet joints.

Delayed surgical treatment for a traumatic bilateral cervical facet joint dislocation using a posterior-anterior approach: a case report

IntroductionThere have been few reports of patients with bilateral cervical facet dislocations that remain untreated for eight weeks or more. We report the case of a 76-year-old man with an old bilateral cervical facet joint dislocation fracture that was treated by posterior-anterior reduction and fixation.Case presentationA 76-year-old Asian man was involved in a road traffic accident. He presented with neck pain and arm pain on his right side, but motor weakness and paralysis were not observed. He was treated conservatively; however, instability and spondylolisthesis at the C5 to C6 joint increased eight weeks after the injury. We performed a posterior-anterior reduction and fixation. After surgery, bony union was achieved, and his neck pain and arm pain disappeared.ConclusionWe recommend reduction and fixation surgery if a patient has an old bilateral facet joint dislocation fracture in the cervical spine.

Acute Paraplegia After Spinal Manipulation: A casereport

This is a case report about a 53-year-old female patient with a history of chronic back pain, suffered from complete paraplegia shortly after spinal manipulation. CT and MRI images consistently showed ossification of the ligamenta flava in conjunction with bilateral facet joints hypertrophy at the T10-11, T11-12 and L1-2 levels. Spinal cord injury with T12 paraplegia ASIA-A was thus diagnosed. Posterior laminectomy at the T10, T11, L1 and L2 levels and interbody fusion from T10 to L2 spines for fixation were performed. After rehabilitation, the patient regained some activities of daily living despite complete paraplegia. To raise public awareness, our report highlights the risk of acute paraplegia after forceful spinal manipulation. Furthermore, prompt evaluation and intervention is necessary when symptoms were worsen or neurological deficits were developed.

Posterior Epidural Migration of Sequestrated Lumbar Disc Fragments Into the Bilateral Facet Joints

Symptomatic lumbar disc herniation is common. Migration of a free disc fragment is usually found in rostral, caudal, or lateral directions. Posterior epidural migration is very rare. We report the first case with posterior epidural migration and sequestration into bilateral facet joints of a free disc fragment. A 78-year-old female presented with low back pain and right leg pain. Plain radiographs showed lumbar spondylolisthesis. Magnetic resonance imaging revealed a posterior epidural mass and intrafacet mass, which was hypointense on T1-weighted images and hyperintense on T2-weighted images. The lesion in the left L3-4 facet joint had rim enhancement, whereas the right one was not contrasted after gadolinium injection. Preoperative differential diagnosis included abscess, tumor, hematoma, or synovial cyst. An interbody cage fusion at L3-4 and L4-5 for spondylolisthesis was performed, and a hybrid technique was applied with the Dynesys flexible rod system at L3-S1 for multisegment degenerative disc disease. The lesion proved to be an epidural disc fragment with sequestration into bilateral facet joints. A free disc fragment should be considered in the differential diagnosis of posterior epidural lesions, and even in the facet joint.

Decompression via posterior-anterior approach and anterior fixation in treatment of fracturedislocation of the lower cervical spine with bilateral facet joints dislocation

Objective To evaluate the surgical strategy of decompression via posterior-anterior approach and anterior fixation in treatment fracture-dislocation of the lower cervical spine with bilateral facet joints dislocation. Methods This study retrospectively reviewed 37 cases of lower cervical spine fracture with bilateral joints dislocation. There were 21 males and 16 females with an average age of 42 years （19-58）. Distraction-flexion stage 3（DFS 3） were found in 24 cases and DFS 4 in 13 cases. All the cases were diagnosed by X-ray, CT and MRI and confirmed during the surgery. Decompression via posterior-anterior approach and anterior fixation had been adapted as the surgical strategy. The NASCIS and IMSOP standard were applied to definite the level of cervical spinal cord injury. The ASIA grading was used for evaluation the spinal cord function and the recovery rate. The X-ray and CT were used to observe reduction and bone fusion. Results The mean operative time was （4.5：±0.5） h, and the mean amount of blood loss was 360 ml （200-500 ml）. All the incision healed. The two segments fixation was used in 23 cases, 3 segments fixation in 13 cases, and 4 segments fixation in 1 case. The mean follow-up period was 32 months （16-45 months）.Postoperative X-ray and CT showed that bone fusion was achieved in all patients within 4-8 months, without graft displacement, or failure of implants. Spinal cord function did not aggravate, and sensory recovery ranged from 7 to 20 levels （averaged, 12.7）. The ASIA grade were improved with an average of one grade. Conclusion To treat fracture-dislocation of the lower cervical spine with bilateral facet joints dislocation, the posterlor-anterior approach and anterior fixation/fusion was benefit to preservation the cervical spinal cord function and reconstruction biomechanical stability of the cervical spine. Key words: Spinal fractures; Dislocations; Decompression, surgical; Fracture fixation

Spinal Facet Joint Biomechanics and Mechanotransduction in Normal, Injury and Degenerative Conditions

The facet joint is a crucial anatomic region of the spine owing to its biomechanical role in facilitating articulation of the vertebrae of the spinal column. It is a diarthrodial joint with opposing articular cartilage surfaces that provide a low friction environment and a ligamentous capsule that encloses the joint space. Together with the disc, the bilateral facet joints transfer loads and guide and constrain motions in the spine due to their geometry and mechanical function. Although a great deal of research has focused on defining the biomechanics of the spine and the form and function of the disc, the facet joint has only recently become the focus of experimental, computational and clinical studies. This mechanical behavior ensures the normal health and function of the spine during physiologic loading but can also lead to its dysfunction when the tissues of the facet joint are altered either by injury, degeneration or as a result of surgical modification of the spine. The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. Accordingly, this review summarizes the relevant anatomy and biomechanics of the facet joint and the individual tissues that comprise it. In order to better understand the physiological implications of tissue loading in all conditions, a review of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications. With this context, experimental studies are summarized as they relate to the most common modifications that alter the biomechanics and health of the spine-injury and degeneration. In addition, many computational and finite element models have been developed that enable more-detailed and specific investigations of the facet joint and its tissues than are provided by experimental approaches and also that expand their utility for the field of biomechanics. These are also reviewed to provide a more complete summary of the current knowledge of facet joint mechanics. Overall, the goal of this review is to present a comprehensive review of the breadth and depth of knowledge regarding the mechanical and adaptive responses of the facet joint and its tissues across a variety of relevant size scales.