Level Of Spondylolisthesis Research Articles

Influence of postoperative sagittal balance and spinopelvic parameters on the outcome of patients surgically treated for degenerative lumbar spondylolisthesis.

OBJECTIVE The object of this study was to determine the association between postoperative sagittal spinopelvic alignment and patient-rated outcome measures following decompression and fusion for lumbar degenerative spondylolisthesis. METHODS The authors identified a consecutive series of patients who had undergone surgery for lumbar degenerative spondylolisthesis between 2008 and 2012, with an average follow-up of 3 years (range 1-6 years). Surgery was performed to address the clinical symptoms of spinal stenosis, not global sagittal alignment. Sagittal alignment was only assessed postoperatively. Patients were divided into 2 groups based on a postoperative sagittal vertical axis (SVA) < 50 mm (well aligned) or ≥ 50 mm (poorly aligned). Baseline demographic, procedure, and outcome measures were compared between the groups. Postoperative outcome measures and postoperative spinopelvic parameters were compared between groups using analysis of covariance. RESULTS Of the 84 patients included in this study, 46.4% had an SVA < 50 mm. Multiple levels of spondylolisthesis (p = 0.044), spondylolisthesis at the L3-4 level (p = 0.046), and multiple levels treated with fusion (p = 0.028) were more common among patients in the group with an SVA ≥ 50 mm. Patients with an SVA ≥ 50 mm had a worse SF-36 physical component summary (PCS) score (p = 0.018), a worse Oswestry Disability Index (ODI; p = 0.043), and more back pain (p = 0.039) than those with an SVA < 50 mm after controlling for multiple levels of spondylolisthesis and multilevel fusion. The spinopelvic parameters differing between the < 50-mm and ≥ 50-mm groups included lumbar lordosis (LL; 56.4° ± 4.7° vs 49.8° ± 4.3°, respectively, p = 0.040) and LL < pelvic incidence ± 9° (51% vs 23.1%, respectively, p = 0.013) after controlling for type of surgical procedure. CONCLUSIONS Data in this study revealed that patient-rated outcome is influenced by the overall postoperative sagittal balance as defined by the SVA.

Clinical Outcome of Cervical Laminoplasty and Postoperative Radiological Change for Cervical Myelopathy With Degenerative Spondylolisthesis.

A retrospective cohort study with prospectively collected data. The aim of this study was to investigate the clinical and radiological outcome of cervical laminoplasty for cervical myelopathy with degenerative spondylolisthesis. The presence of spondylolisthesis is thought to represent segmental instability in spine. Cervical laminoplasty is a common decompression surgery for cervical myelopathy, but its clinical result for cervical spondylolisthesis has not been well studied. One hundred seventeen patients who underwent cervical laminoplasty for degenerative cervical myelopathy were included. Japanese Orthopaedic Association score (JOA score) and visual analog scale of neck pain, upper arm pain and numbness were evaluated before surgery, and at scheduled time points after surgery. Spondylolisthesis was defined as more than 2 mm slip on plain radiograph, and the clinical results were compared between the patients with spondylolisthesis (group S) and without spondylolisthesis (group C). In the patients with spondylolisthesis, the slip distance and translational motion between flexion and extension was examined on plain lateral radiograph before surgery and 2 years after surgery. Degenerative cervical spondylolisthesis was found in 49 levels of 33 patients (28.2%), and the average age of group S was significantly higher than group C. JOA score and each VAS score was significantly improved after surgery in both groups. Average JOA score of group S was significantly lower than group C at every time points, but the recovery rate was similar between the two groups. In the level of spondylolisthesis, average slip distance did not changed, but average translational motion was significantly decreased in 2years after surgery. Cervical spondylolisthesis was common in elderly patients. The clinical outcome in group S was comparable with group C, and the level with spondylolisthesis has been stabilized after surgery. Thus, laminoplasty can be a treatment option even for cervical myelopathy with degenerative spondylolisthesis. 3.

Does spinal stenosis correlate with MRI findings and pain, psychologic factor and quality of life?

BackgroundTo investigate and analyze MRI findings in relation to visual analogue scale (VAS), Oswestry Disability Index (ODI), psychological-factor, sleep-quality, and Short-Form Health Survey (SF-36) scores among patients with central lumbar spinal stenosis (LSS) for the purpose of elucidating a correlation.MethodsFrom July 2013 to May 2014, 117 consecutive patients with central LSS were included in this study. All of the MRIs were evaluated by one of the authors, and the evaluated items were the dural sac cross-sectional area (DSCSA), the number of stenotic levels, and the presence and levels of spondylolisthesis. The ODI, VAS, 36-item SF-36, Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Pittsburgh Sleep Quality Index (PSQI) questionnaires were used to evaluate the participants.ResultsThere are no correlations between the ODI, VAS, BDI, BAI, PSQI, and SF-36 scores and the minimum DSCSA; however, a significant correlation was found between the ODI scores and multilevel LSS. The BDI, BAI, and PSQI scores are higher for multilevel LSS compared with single-level LSS, but the difference of this mean value is not statistically significant.ConclusionsA significant correlation was shown between those patients with multilevel LSS and the ODI scores; however, significant correlations were not found between the MRI findings and the psychological factors pertaining to sleep and life qualities.

Facet Joint Tropism and Degenerative Spondylolisthesis—A Study from the AOSAP Research Collaboration

Introduction Degenerative spondylolisthesis (dSpl) is translation of the vertebral body in relation to adjacent levels, mainly attributed to degenerative changes of the intervertebral disc and facet joint complexes, and primarily occurs at L4-L5. Studies have suggested that more sagittal oriented facet joints at L4-L5 are associated with dSpl. However, the role of facet joint tropism (i.e., asymmetry between facet joint orientations) in L4-L5 dSpl remains inconclusive, in particular, in an Asian population and possibly attributed to nonstandardized definitions of tropism. As such, the following study addressed the role of facet joint tropism in relation to L4-L5 dSpl in the Asia Pacific region. Materials and Methods A multinational, multiethnic cross-sectional image-based study was performed in 34 institutions in the Asia Pacific region. Lateral standing radiographs and axial MRIs and/or CT scans were obtained for patients diagnosed with lumbar dSpl. Imaging assessment consisted of the following: magnitude of slip displacement, level of spondylolisthesis, and left/right L4-L5 facet joint angulations were noted on image assessment. Patients with single level dSpl were included. Patients were further stratified into those presenting with (Group A) or without (Group B) L4-L5 dSpl. Facet joint tropism was defined as 7 degrees difference (Grogan et al 1997) between left and right facet joints and also assessed on receiver operating characteristics (ROC) curve analysis to identify critical values for multivariate analysis. Gender, age, weight/height (body mass index [BMI]), and ethnicity were also noted. Results The study included 351 patients (36.9% males and 63.1% females) with a mean age of 61.8 years (range: 24-90 years). The mean BMI was 25.6 kg/m2 (range: 15.4-43.9 kg/m2). There were 267 patients (76.1%) in Group A and 84 individuals (23.9%) in Group B (control). Sex type ( p = 0.295) and BMI ( p = 0.227) did not significantly differ between groups, but elevated age was more pronounced with L4-L5 dSpl ( p = 0.001). There was a statistically significant difference between right and left L4-L5 facet joint angulations between Group A (right mean: 57.5 degrees; left mean: 55.4 degrees) and Group B (right mean: 48.4 degrees; left mean: 46.5 degrees) ( p &lt; 0.001). Based on facet joint tropism of 7 degrees difference between facet angulations, there was no statistically significant difference between groups. ROC analysis identified high sensitivity and specificity of facet joint angulation difference of 15 degrees or greater associated with dSpl. Based on age-adjusted multivariate analysis, facet joint tropism with a critical value of 15 degrees or greater angulation difference noted an odds ratio of 2.34 (95% CI: 1.17-4.67; p = 0.016) associated with dSpl. Slippage was noted with increased facet joint tropism, but the effects could not be discerned. Conclusion Greater sagittal FJ orientation was associated with dSpl, as was joint tropism. A critical value of 15 degrees FJ angle difference produced a twofold increased likelihood of dSpl. Our study broadens the understanding of FJ morphology and its role in degenerative sagittal plane instability. Acknowledgments This study was funded by AOSpine Asia Pacific. Disclosure of Interest None declared

Analysis of Inadvertent Intradiscal Injections during Lumbar Transforaminal Epidural Injection.

BackgroundRecently, there have been several case reports and retrospective studies about the incidence of intradiscal (ID) injection during transforaminal epidural steroid injection (TFESI). Inadvertent ID injection is not a rare complication, and it carries the risk of developing diskitis, although there has been no report of diskitis after TFESI. We prospectively evaluated the incidence of inadvertent ID injection during lumbar TFESI and analyzed the contributing factors.MethodsTen patients received 2-level TFESI, and the remaining 229 patients received 1-level TFESI. When successful TFESI was performed, 2 ml of contrast dye was injected under real-time fluoroscopy to check for any inadvertent ID spread. A musculoskeletal radiologist analyzed all magnetic resonance images (MRIs) of patients who demonstrated inadvertent ID injection. When reviewing MRIs, the intervertebral foramen level where ID injection occurred was carefully examined, and any anatomical structure which narrowing the foramen was identified.ResultsAmong the 249 TFESI, we identified 6 ID injections; thus, there was an incidence of 2.4%. Four patients had isthmic spondylolisthesis, and the level of spondylolisthesis coincided with the level of ID injection. We further examined the right or left foramen of the spondylolisthesis level and identified the upward migrated disc material that was narrowing the foramen.ConclusionsInadvertent ID injection during TFESI is not infrequent, and pain physicians must pay close attention to the type and location of disc herniation.

C-5 palsy after cervical laminoplasty with instrumented posterior fusion

Postoperative C-5 palsy is known as a common complication after cervical laminoplasty. The authors of this article have encountered postoperative C-5 palsy more often when laminoplasty was combined with instrumented posterior spinal fusion than when it was performed alone. The purpose of this clinical study was to examine the incidence of fifth cervical nerve root palsy (C-5 palsy) and surgical results in patients with cervical myelopathy who had undergone laminoplasty with or without instrumented spinal fusion. The authors retrospectively studied patients with cervical myelopathy who had undergone laminoplasty with or without instrumented posterior spinal fusion. Clinical data on 58 patients were evaluated and analyzed. Preoperative diagnoses were cervical spondylotic myelopathy or ossification of the posterior longitudinal ligament of the cervical spine. Twenty-four patients with spondylolisthesis or kyphosis underwent laminoplasty combined with posterior spinal fusion using instrumented lateral mass fixation (fusion group), while the remaining 34 patients underwent laminoplasty without posterior spinal fusion (no-fusion group). In the fusion group, C-5 palsy developed in 6 patients; in the no-fusion group, it occurred in only 1 patient. There was a significant difference in the rate of this complication between the 2 groups. In the fusion group, local kyphosis and spondylolisthesis level were reduced at the fusion level, and all patients with C-5 palsy underwent C4-5 spinal fusion. The incidence of postoperative C-5 palsy is significantly higher after laminoplasty when it is combined with spinal fusion. Correction of kyphosis and spondylolisthesis using posterior instrumentation may be a risk factor for iatrogenic intervertebral foraminal stenosis leading to C-5 palsy.

THE CORRELATION DEPENDENCE OF THE CLINICAL AND MORPHOLOGICAL MANIFESTATIONS AND BIOMECHANICAL PARAMETERS IN PATIENTS WITH DEGENERATIVE SPONDYLOLISTHESIS L4 VERTEBRA

The study included 59 operated patients with spondylolisthesis L4 vertebra of I degree. All the patients were held clinical-anamnestic, neurological, radiological, radiopaque and biomechanical studies, MRI, CT, as well as puncture performed provocative tests. Revealed correlation of clinical manifestations of degenerative spondylolisthesis L4 and biomechanical parameters of the shape and orientation of the lumbar spine. The most pronounced clinical and morphological changes detected at the level of spondylolisthesis and adjacent segments in the group with hyperlordosis and excessive tilt angle of the chord forward, which is confirmed by MRI, CT, and carried out a disco-puncture provocative tests. A variety of pathological changes of the lumbar spine at L4 vertebra degenerative spondylolisthesis correlated with the biomechanical parameters violation of the shape and orientation of the spine in the sagittal plane.

Midterm outcome after a microsurgical unilateral approach for bilateral decompression of lumbar degenerative spondylolisthesis

The aim of this study was to evaluate the results and effectiveness of bilateral decompression via a unilateral approach in the treatment of lumbar degenerative spondylolisthesis (DS). Operations were performed in 84 selected patients (mean age 62.1 ± 10 years) with lumbar DS between the years 2001 and 2008. The selection criteria included lower back pain with or without sciatica, neurogenic claudication that had not improved after at least 6 months of conservative treatment, and a radiological diagnosis of Grade I DS and lumbar stenosis. Decompression was performed at 3 levels in 15.5%, 2 levels in 54.8%, and 1 level in 29.7% of the patients with 1 level of spondylolisthesis. All patients were followed up for at least 24 months. For clinical evaluations, a visual analog scale, Oswestry Disability Index (ODI), and Neurogenic Claudication Outcome Score (NCOS) were used. Spinal canal size and (neutral and dynamic) slip percentages were measured both pre- and postoperatively. Neutral and dynamic slip percentages did not significantly change after surgery (p = 0.67 and p = 0.63, respectively). Spinal canal size increased from 50.6 ± 5.9 to 102.8 ± 9.5 mm(2) (p < 0.001). The ODI decreased significantly in both the early and late follow-up evaluations, and good or excellent results were obtained in 64 cases (80%). The NCOS demonstrated significant improvement in the late follow-up results (p < 0.001). One patient (1.2%) required secondary fusion during the follow-up period. Postoperative clinical improvement and radiological findings clearly demonstrated that the unilateral approach for treating 1-level and multilevel lumbar spinal stenosis with DS is a safe, effective, and minimally invasive method in terms of reducing the need for stabilization.

Disc Height and Lumbar Index as Independent Predictors of Degenerative Spondylolisthesis in Middle-Aged Women With Low Back Pain

A age- and sex-matched case-control radiographic study. To identify the predisposing factors of degenerative spondylolisthesis (DS). None of the radiologic methods for predicting the development of DS are very reliable or readily accessible. The methods commonly used are computed tomography or magnetic resonance imaging. Data were gathered retrospectively on middle-aged women with degenerative lumbar spondylolisthesis. The most common slipped vertebra was L4 (63.64%) and the second was L5 (13.64%). Most parameters, including the disc height, body height, and angle measurements, for the case group tended to be lower than the control group, whereas the transverse process were larger than control group. The differences in disc height, lumbar index (LI), sacral inclination angle (SIA), sacral horizontal angle (SHA), and transverse process between the 2 groups were statistically significant (P < 0.05). Multivariate logistic regression analysis confirmed that anterior inferior disc height (DHIA) and LI were independent variables of predisposing factor to DS and both could explain a 50% variation of DS. Further analysis of the different levels of spondylolisthesis (L4 on L5 vs. L5 on S1 DS) revealed that there was a significant difference in the width of L5 transverse process in L4 on L5 spondylolisthesis (P = 0.03) but insignificant on disc height (P = 0.86). There are 2 independent predictors of DS, decreased anterior disc height and increased lumbar index. The iliolumbar ligament also contributes to the stability of lumbosacral junction, especially in L5 on S1 DS.

Significance of exact lateral roentgen documentation in Meyerding's grading of spondylolistheses

The treatment of spondylolisthesis-in particular the indication of operation-is based on clinical symptoms as well as radiological criteria. For radiological techniques, the lateral profile, especially in function tests, is of importance. As a basic requirement the grade of Meyerding should be evaluated on x-ray in the exact lateral profile. We have observed, that even a slight rotation of the spine leads to misjudging of the real degree of vertebral dislocation. In 30 patients with spondylolisthesis of the lumbar spine the x-rays, made in exact lateral position, were compared with x-rays in 10 degrees rotation of the spine. On the average we measured an increase of vertebral dislocation of 3-4 mm. The increase was independent of the grade of Meyerding or the level of spondylolisthesis. The results could be verified by a spine of a human corpse.

Treatment of symptomatic spondyloptosis in an adult previously treated with in situ fusion and instrumentation by L5 vertebrectomy and L4–S1 instrumented reduction

One traditional treatment for spondylolisthesis is fusion. However, for high-grade spondylolisthesis and spondyloptosis, posterior fusion has had high rates of nonunion, progression, and persistent physical deformity. Thus, some surgeons have recommended reduction and instrumentation. One such technique (Gaines procedure) entails a two-stage procedure: L5 vertebrectomy anteriorly, followed by resection of the L5 posterior elements and instrumented reduction of L4 onto S1. However, to our knowledge, there is no report of reversing the fusion and deformity reduction in a symptomatic patient with previous solid fusion of the spondyloptosis at L5-S1. To present the first reported revision via the Gaines procedure for failed fusion secondary to spondyloptosis. Patient report. A 24-year-old woman, who had undergone multiple procedures for L5-S1 spondylolisthesis and a final fusion and instrumentation attempt, presented with continued urinary retention, leg and back pain, and inability to stand. She subsequently underwent posterior hardware removal, followed by anterior L5 vertebral body resection. In the second stage, she had posterior osteotomy of the previous L5-S1 fusion, resection of the posterior elements of L5, and reduction and instrumentation of L4 to S1. At the 2-year follow-up, she had full resolution of symptoms, full return of motor strength, and resolution of urinary retention. The Gaines procedure has been performed successfully in patients without previous fusions at the level of spondylolisthesis or spondyloptosis. Patients for whom the traditional posterior fusion fails still may be candidates for this procedure, albeit at increased risk of neurologic injury.

Long-term Outcome After Posterolateral, Anterior, and Circumferential Fusion for High-Grade Isthmic Spondylolisthesis in Children and Adolescents

A cross-sectional study to evaluate the long-term result of posterolateral (PLF), anterior (AF), and circumferential fusion (CF) for isthmic spondylolisthesis. To assess the long-term effects of PLF, AF, or CF for high-grade isthmic spondylolisthesis on lumbar spine in children and adolescents by using MRI. Short- and mid-term clinical and plain radiographic results of isthmic spondylolisthesis and of PLF, AF, and CF in severe slip are well documented. The long-term effect of the fusion on soft tissues, on the intervertebral discs inside and above fusion in particular, is, however, unclear. Between 1977 and 1991, PLF (n = 21), AF (n = 22), or CF (n = 24) was performed on 67 patients (42 females, 25 males) with high-grade (slip > or =50%) isthmic spondylolisthesis. The average age of patients at the time of operation was 14.4 (range, 8.9-19.6) years. Clinical, spinal mobility and trunk strength in addition to MRI and plain radiograph examinations were performed on these patients after an average follow-up time of 17.3 years (range, 10.7-26.0 years). Three (14%) patients in the PLF and AF groups, but none in the CF group, reported back pain often or very often at rest. The mean Oswestry Disability Index (ODI) was 9.7 (range, 0-62) in the PLF, 8.1 (0-32) in the AF, and 2.3 (0-14) in the CF group (P < 0.05). The mean slip before surgery was 66% (range, 50%-100%) and at the last follow-up visit 66% (range, 26%-106%). Disc degeneration was most common in the PLF group (P = 0.0014) and inside the fusion and in the lowest moving intervertebral disc spaces in all subgroups. Only 1 patient had an asymptomatic prolapse. In MR images, none of the patients had lumbar central canal stenosis inside or above the fusion. In contrast, the spinal canal was wide at the spondylolysis and spondylolisthesis level in 23 (34%) patients. Of the patients, 19 (28%) patients (32 neural foramens) had severe narrowing of the neural foramen with impingement of the nerve root. No patients had clinically confirmed L5 nerve root symptoms. Muscle degeneration was found in 29 (43%) of patients. Longer fusion and muscle degeneration, but not disc degeneration, were associated with lower performance in spinal mobility and trunk-strength measurement tests. The clinical outcome was best in the CF group as measured by ODI. Degenerative changes were most commonly found at the level of the slip and above the fusion level. The prevalence of disc prolapses was low. Spinal fusion for isthmic spondylolysis is not associated with central canal stenosis above the fusion. Radiologic nerve root stenosis was common but asymptomatic. Mild muscle atrophy was common.

Surgical Treatment with Instrumentation for Severely Destructive Spondyloarthropathy of Cervical Spine

Nine patients with severely destructive spondyloarthropathy and marked neurologic deficits associated with dialysis-related amyloidosis underwent posterior decompression and fusion by means of instrumentation at our institute. All patients showed segmental kyphosis, six patients vertebral ankylosis, and eight patients spondylolisthesis. Spondylolisthesis at two levels was noted in three patients. Of the 11 levels of spondylolisthesis in all, 9 were proximally adjacent and 2 were distally adjacent to vertebral ankylosis. All patients underwent posterior decompression and multisegment fusion with autogenous iliac bone. From three to five spinal segments were fixed. Seven patients underwent posterior fusion by means of a pedicle or lateral mass screw between levels C3 and C7, one patient between C3 and C6, and one between C3 and T1. The clinical rate of improvement at the final follow-up was 74.3%. Though complete stability could not be achieved in three patients, the results were rated as good. No postoperative neurologic deterioration has been observed in this series, nor did any patients die immediately after surgery or during the postoperative follow-up period. As anterior long-span surgery might be too invasive for hemodialysis patients, we think that posterior decompression and fusion may well be a reasonable and effective strategy for severe hemodialysis-associated cervical spondyloarthropathy with neurologic deficits. To achieve complete stability, 360 degrees fusion with both anterior and posterior fixation with instrumentation may be required for these patients.

Posterior Epidural Fat on Sagittal MR Images: Can it Help in Distinguishing Between Isthmic and Degenerative Lumbar Spondylolisthesis?

Materials and Methods: The midline sagittal MR images of the lumbar spines were retrospectively studied for 50 patients without spondylolisthesis, for 78 patients with isthmic spondylolisthesis and for 43 patients with degenerative spondylolisthesis. The anteroposterior diameter of the posterior epidural fat (ADEF) was measured at each intervertebral disc level by two radiologists and these values were then compared between each group. To normalize for difference of body size, the posterior epidural fat ratio (PEFR) at each level of spondylolisthesis and at L1-2 were also determined for each level of spondylolisthesis, and the PERF was compared between each group. Statistical analysis was performed by the chi-square method. Results: For the patients with isthmic spondylolisthesis, the ADEFs at the spinal levels with spondylolisthesis were significantly greater than those ADEFs in the control group that were measured at the corresponding disc levels (p<0.05). For the patients with degenerative spondylolisthesis, the ADEFs at the spinal level with spondylolisthesis were significantly less than the ADEFs in the control group that were measured at the corresponding disc levels (p<0.05). The PEFRs obtained at L4-5 were 1.37±0.12 for the control group, 2.61±1.31 for the patients with isthmic spondylolisthesis, and 0.60±0.05 for the patients with degenerative spondylolisthesis. The PEFRs obtained at L5-S1 were 2.25±1.32 for the control group, 3.47±1.69 for the patients with isthmic spondylolisthesis and 1.65±0.18 for the patients with degenerative spondylolisthesis. At both levels, the PEFRs were greatest for the isthmic spondylolisthesis group and smallest for the degenerative spondylolisthesis group, and all the differences were statistically significant. Conclusion: The posterior epidural fat, which is easily seen structure on the midline sagittal MR image, is significantly increased in isthmic spondylolisthesis, but it is decreased in degenerative spondylolisthesis, and this could be useful in distinguishing isthmic spondylolisthesis from degenerative spondylolisthesis.

Effects of Slip Severity and Loading Directions on the Stability of Isthmic Spondylolisthesis: A Finite Element Model Study

Using a validated finite element model, the biomechanical effects of pars defect in a lumbar segment with and without different degrees of slip (up to 50% slip) were studied. To study the effects of slip severity and loading parameters on the stability of the lytic and adjacent motion segments. Better knowledge of the biomechanics of spondylolisthesis may help formulate treatment strategies such as bracing or spinal implants. Clinically, spondylolisthesis exists in varying grades of anterior slip, and the biomechanical stability of the motion segments at the lytic defect and adjacent level probably varies as well. In vitro studies of L4-L5 and L5-S1 isthmic spondylolisthesis slips have concluded that an L4-L5 pars defect is more unstable than an L5-S1 pars defect. Comparing the stability of lytic motion segments with different grades of spondylolisthesis is difficult to do experimentally and therefore has not been done. Further assessing the stresses in the bone and intervertebral discs at or adjacent to a lytic defect is also difficult to study experimentally, so no data are available. A finite element model of L4-S1 was validated with and without a pars defect at L5. The model was then revised to represent different degrees of slip at L5, and six different moment loadings were applied. The current study showed larger decrease in stiffness with increasing percent slip. The decrease in disc stiffness and increase in disc stresses with increasing percent slip were larger at the level of spondylolisthesis as compared to the changes in the adjacent segment. Lateral bending moment and torsion load showed the largest decrease in stiffness due to slip. At 50% slip, the maximum increase in motion (as compared to motion in an intact segment) was seen under lateral bending moment load (about 55% at L4/L5 and 250% at L5/S1). Lateral bending also produced the largest increase in stresses due to 50% slip in the anulus and endplates (300% increase in anular stress and 190% increase in endplate stress) at L5/S1. The stiffness of a spondylolisthetic motion segment decreases as the slip increases. Lateral bending and torsion are moment directions causing the greatest resulting motions.

Distinction between degenerative and isthmic spondylolisthesis on sagittal MR images: importance of increased anteroposterior diameter of the spinal canal ("wide canal sign").

The purpose of this study was to determine whether a visually apparent increase in the anteroposterior diameter of the spinal canal ("wide canal sign") can be used reliably to differentiate degenerative from isthmic spondylolisthesis on midline sagittal MR images. We hypothesized that the wide canal sign would be present only in isthmic spondylolisthesis, where the vertebral ring is disrupted by defects in the pars interarticularis. The midline sagittal MR images of 100 control subjects without spondylolysis or spondylolisthesis were analyzed to establish the normal range of sagittal canal diameters at the various lumbar levels. Midline sagittal MR images of the lumbar spine were reviewed in 53 patients in whom either isthmic (n = 35) or degenerative (n = 18) spondylolisthesis was confirmed with conventional radiography and/or CT. For each spinal level, the sagittal canal ratio, defined as the maximum anteroposterior diameter of the canal at that level divided by the diameter of the canal at L1, was calculated. From our analysis of the control subjects, a normal sagittal canal ratio was determined to be less than 1.25. A sagittal canal ratio of 1.25 or greater at the level of a spondylolisthesis was considered to represent an abnormally increased sagittal canal diameter (wide canal sign), indicating the presence of bilateral pars interarticularis defects. Using this sign alone, two neuroradiologists who had no knowledge of the true diagnosis classified the type of spondylolisthesis in a randomized subgroup of 34 age-matched adults (all more than 40 years old and with grade I isthmic or degenerative spondylolisthesis). In the 100 subjects without spondylolisthesis and in the 18 patients with degenerative spondylolisthesis, the sagittal canal ratio did not exceed 1.25 (mean values, 0.93-0.99) at any level of the lumbar spine. Conversely, the sagittal canal ratio at the level of isthmic spondylolisthesis exceeded 1.25 (mean value, 1.56) in 34 of 35 patients. In patients more than 40 years old, in whom degenerative spondylolisthesis is prevalent and misdiagnosis of isthmic spondylolisthesis is potentially more likely, both neuroradiologists were 100% accurate in correctly assigning the type of spondylolisthesis when using the wide canal sign alone. The wide canal sign on midline sagittal MR images (corresponding to an sagittal canal ratio > or = 1.25) is a reliable predictor of the presence of defects of the pars interarticularis at the level of a spondylolisthesis. This sign could be useful for distinguishing degenerative from isthmic spondylolisthesis when degenerative sclerosis in the pars interarticularis mimics spondylolysis, when direct axial imaging of the pars interarticularis has not been done, or when imaging is technically inadequate.

Myelography of nonmass lesions in the spinal canal

BNORMALITIES OF CURVATURE of the spinal canal whether congenital, acquired, or idiopathic show a similar myelographic appearance in regard to the position of the spinal cord. The cord takes the shortest path through the abnormally curved segment and will project as a straighter structure within the canal, always more closely apposed to the concave side of the curve (Fig. IA). A neurologic defect directly related to the abnormal curvature is rare, but when present, it is usually caused by an associated problem, such as herniated disk or vascular ischemia from crowding of the thorax. The curved portion of the cord is particularly susceptible to vascular changes due to diminished blood flow (Fig. 1B). In spondylolisthesis, the subarachnoid space and its contents are compressed as they become more and more confined to the dorsal aspect of the spinal canal. The myelographic picture (Fig. 2) is one of a bilaterally and dorsally constricted Pantopaque column containing crowded nerve roots. This may be further exaggerated by osteoarthritic changes laterally about the apophyseal joints. Ventrally, the epidural space is wider because of forward slippage of the vertebra. This may obscure a herniated disk. However, the incidence of herniated disk is greater above the level of spondylolisthesis. Congenital narrowing of the spinal canal is a potentially hazardous situation whether in the cervical or lumbar areas. Cord compression secondary to osteophytic spurs in a cervical canal with a narrowed anteroposterior diameter is well known. A similar situation associated with minor disk herniation in the lumbar area can cause a “cauda equina syndrome.“8 The plain film will show narrow interpedicular distances with failure to flair caudally. The myelogram most clearly depicts the narrowed anteroposterior diameter of the canal, the herniated disk defect, and the compressed cauda equina (Fig. 3). Details pertaining to dysrhaphia, arthritis, and degenerative changes of the spinal canal are presented elsewhere in this issue.