Toxicity of Radiosurgery for Brainstem Metastases.

BACKGROUND: Although stereotactic radiosurgery (SRS) is an effective modality in the treatment of brainstem metastases (BSM), radiation-induced toxicity remains a critical concern. To better understand how severe or life-threatening toxicity is affected by the location of lesions treated in the brainstem, a review of all available studies reporting SRS treatment for BSM was performed. METHODS: Twenty-nine retrospective studies investigating SRS for BSM were reviewed. RESULTS: The rates of grade 3 or greater toxicity, based on the Common Terminology Criteria for Adverse Events, varied from 0 to 9.5% (mean 3.4 ± 2.9%). Overall, the median time to toxicity after SRS was 3 months, with 90% of toxicities occurring before 9 months. A total of 1243 cases had toxicity and location data available. Toxicity rates for lesions located in the medulla were 0.8% (1/131), compared with midbrain and pons, respectively, 2.8% (8/288) and 3.0% (24/811). CONCLUSIONS: Current data suggest that brainstem substructure location does not predict for toxicity and lesion volume within this cohort with median tumor volumes 0.04-2.8 cc does not predict for toxicity.

Impact of CyberKnife Radiosurgery on Overall Survival and Various Parameters of Patients with 1-3 versus ≥ 4 Brain Metastases.

Introduction This study's objective is to compare the overall survivals (OSs) and various parameters of patients with 1-3 versus ≥ 4 brain metastases post-CyberKnife radiosurgery (CKRS) (Accuray, Sunnyvale, California) alone. Methods Charts of 150 patients, from 2009-2014, treated with only CKRS for brain metastases were reviewed retrospectively for overall survival (OS) and patient, tumor, and imaging characteristics. Parameters included demographics, Eastern Cooperative Oncology Group (ECOG) performance scores, number and control of extracranial disease (ECD) sites, cause of death (COD), histology, tumor volume (TV), and post-CKRS whole brain radiotherapy (WBRT). The imaging characteristics assessed were time of complete response (CR), partial response (PR), stable imaging or local failure (LF), and distal brain failure (DBF). Patients and their data were divided into those with 1-3 (group 1) versus ≥ 4 brain metastases (group 2). For each CR and LF patient, absolute neutrophil count (ANC), absolute lymphocyte count (ALC)), and ANC/ALC ratio (NLR) were obtained, when available, at the time of CKRS. Results Both group 1 and group 2 had a median OS of 13 months. The patient median age for the 115 group 1 patients versus the 35 group 2 patients was 62 versus 56 years. Group 1 had slightly more males and group 2, females. The predominant ECOG score for each group was 1 and the number of ECD sites was one and two, respectively. Uncontrolled ECD occurred in the majority of both group 1 and group 2 patients. The main COD was ECD in both groups. The prevalent tumor histology for groups 1 and 2 was non-small cell lung carcinoma. Median TVs were 1.08 cc versus 1.42 cc for groups 1 and 2, respectively. The majority of patients in both groups did not undergo post-CKRS WBRT. Imaging outcomes were LC (CR, PR, or stable imaging) in 93 (80.9%) and 26 (74.3%) group 1 and 2 patients, of whom 32 (27.8%) and six (17.1%) had CR; 38 (33.0%) and 18 (51.4%), PR and 23 (20.0%) and two (5.7%), stable imaging; LF was the outcome in 22 (19.1%) and nine (25.7%) patients, and DBF occurred in 62 (53.9%) and 21 (60.0%), respectively. Uni- and multivariable analyses showed the independent parameters of a lower ECOG score, a greater number of ECD sites and uncontrolled ECD were significantly associated with greater mortality risk with and without accounting for other covariates. At CKRS, 19 group 1 and 2 CR patients had a mean ANC of 5.88 K/µL and a mean ALC of 1.31 K/µL and 13 (68%) of 19 had NLRs ≤ five, while 11 with LFs had a mean ANC of 5.22 K/µL and a mean ALC of 0.93 K/µL and seven (64%) had NLRs > five. An NLR ≤ five and high ALC was associated with a CR and an NLR > five and a low ALC with an LF. Conclusions Median OS post-CKRS was 13 months for both patients with 1-3 brain metastases and with ≥ 4. This is the only study in the literature to evaluate OS in patients with 1-3 and ≥ 4 brain metastases who were treated with CKRS alone. For groups 1 and 2 patients combined, 119 (79.3%) had LC and 38 (25.3%) had CR. The ANC, ALC, and NLR values are likely predictive of CR and LF outcomes.

Impact of CyberKnife Radiosurgery on Median Overall Survival of Various Parameters in Patients with 1-12 Brain Metastases.

Introduction This study's objective is to assess various patient, tumor and imaging characteristics and to compare median overall survival (OS) of 150 patients with 1-12 brain metastases post-CyberKnife radiosurgery (CKRS) (Accuray, Sunnyvale, California) alone. Methods Charts of 150 patients, from 2009-2014, treated with only CKRS for brain metastases were reviewed retrospectively for patient, tumor, and imaging characteristics. Parameters included demographics, Eastern Cooperative Oncology Group (ECOG) performance scores, number and control of extracranial disease (ECD) sites, cause of death (COD), histology, tumor volume (TV), and post-CKRS whole brain radiotherapy (WBRT). The imaging characteristics assessed were time of complete response (CR), partial response (PR), stable imaging or local failure (LF), and distal brain failure (DBF). The primary tumor Ki-67s of the breast carcinoma brain metastasis patients, who had the longest median OS of any group, were recorded when available. Results The predominant age group for the 150-patient cohort was the younger 17-65 years of age category, which was represented by 94 (62.7%). The 150-patient group had slightly more males, 79 (52.7%). The majority of 111 (74%) patients had an ECOG score of 1, 39 (26%) had 1 ECD site and uncontrolled ECD occurred in 112 (74.7%). The main COD was ECD in 106 (70.7%). The prevalent tumor histology was non-small cell lung carcinoma (88 of 150, 58.7%). The most common TV was 0-0.5 ccs (48 of 150, 32%). The majority of 125 (83.3%) patients did not undergo post-CKRS WBRT. Imaging outcomes were local control (LC) (CR, PR, or stable imaging) in 119 (79.3%), of whom 38 (25.3%) had CR, 56 (37.3%) PR and 25 (16.7%) stable imaging; LF was the outcome in 31 (20.7%) and DBF occured in 83 (55.3%). The median OS was 13 months. Patients 17-65 years of age had a median OS of 13 months, while those 66-88 years, had 12 months. Females versus males had median OS of 15 versus 12 months. The most prolonged median OS of 21.5 months occurred in those with an ECOG score of 0. Patients with two ECD sites had a median OS of 14.5 months, while those with controlled ECD, 20.5 months. Patients with breast cancer brain metastases had the longest median OS of 23 months. The median OS for each of three (0-0.5 ccs, 0.6-1.5 ccs, 1.6-4.0 ccs) of four CKRS TV quartiles was 13 months and for those with 4.1-28.5 ccs, 10 months. Median OS for patients with versus without post-CKRS WBRT was 23 versus 12 months. The longest median OS of 18.5 months for post-CKRS imaging outcomes was in patients with CR; those with LF had a median OS of 11.5 months. Of nine patients with breast carcinoma brain metastases with available Ki-67s from primary tumor resections, the Ki-67 values were ≥ 34% for four patients with CR, PR and stable imaging outcomes, and < 34% for five patients with LF. Conclusions An ECOG score of 0, ECD control, breast carcinoma brain metastasis histology. undergoing WBRT post-CKRS and CR imaging outcomes, each resulted in a longer median OS. The Ki-67 proliferation indices from primary breast carcinoma resection correlated well with the brain imaging outcomes in a small preliminary study in the present study's breast carcinoma patients with brain metastases.

CyberKnife radiosurgery for brainstem metastases: Management and outcomes and a review of the literature.

To our knowledge this paper is the first to use recursive partitioning analysis (RPA) for brainstem metastasis (BSM) patient outcomes, after CyberKnife radiosurgery (CKRS; Accuray, Sunnyvale, CA, USA); nine similar previous publications used mainly Gamma Knife radiosurgery (Elekta AB, Stockholm, Sweden). Retrospective chart reviews from 2006-2013 of 949 CKRS-treated brain metastasis patients showed 54 BSM patients (5.7%): 35 RPA Class II (65%) and 19 Class III (35%). There were 30 women (56%) and 24 men (44%). The median age was 59 years (range 36-80) and median follow-up was 5 months (range 1-52). Twenty-three patients (43%) had lung carcinoma BSM and 12 (22%) had breast cancer BSM. Fifty-four RPA Class II and III BSM patients had a median overall survival (OS) of 5 months, and for each Class 8 and 2 months, respectively. Of 36 RPA Class II and III patients with available symptoms (n=31) and findings (n=33), improvement/stability occurred in the majority for symptoms (86%) and findings (92%). Of 35 cases, 28 (80%) achieved BSM local control (LC); 13/14 with breast histology (93%) and 10/13 with lung histology (77%). All six RPA Class II and III patients with controlled extracranial systemic disease (ESD) experienced LC. Median tumor volume was 0.14 cm(3); of 34 RPA Class II and III cases, 26 LC patients had a 0,13 cm(3) median tumor volume while it was 0.27 cm(3) in the eight local failures. Of 35 cases, single session equivalent dosages less than the median (n=13), at the 17.9 Gy median (n=5) and greater than the median (n=17) had BSM LC in 10 (77%), four (80%) and 14 cases (82%), respectively. Univariate analysis showed Karnofsky Performance Score, RPA Class and ESD-control predicted OS. CKRS is useful for RPA Class II and III BSM patients with effective clinical and local BSM control.

Biomechanical Comparisons of Pull Out Strengths After Pedicle Screw Augmentation with Hydroxyapatite, Calcium Phosphate, or Polymethylmethacrylate in the Cadaveric Spine.

OBJECTIVE: In vertebrae with low bone mineral densities pull out strength is often poor, thus various substances have been used to fill screw holes before screw placement for corrective spine surgery. We performed biomechanical cadaveric studies to compare nonaugmented pedicle screws versus hydroxyapatite, calcium phosphate, or polymethylmethacrylate augmented pedicle screws for screw tightening torques and pull out strengths in spine procedures requiring bone screw insertion. METHODS: Seven human cadaveric T10-L1 spines with 28 vertebral bodies were examined by x-ray to exclude bony abnormalities. Dual-energy x-ray absorptiometry scans evaluated bone mineral densities. Twenty of 28 vertebrae underwent ipsilateral fluoroscopic placement of 6-mm holes augmented with hydroxyapatite, calcium phosphate, or polymethylmethacrylate, followed by transpedicular screw placements. Controls were pedicle screw placements in the contralateral hemivertebrae without augmentation. All groups were evaluated for axial pull out strength using a biomechanical loading frame. RESULTS: Mean pedicle screw axial pull out strength compared with controls increased by 12.5% in hydroxyapatite augmented hemivertebrae (P = 0.600) and by 14.9% in calcium phosphate augmented hemivertebrae (P = 0.234), but the increase was not significant for either method. Pull out strength of polymethylmethacrylate versus hydroxyapatite augmented pedicle screws was 60.8% higher (P = 0.028). CONCLUSIONS: Hydroxyapatite and calcium phosphate augmentation in osteoporotic vertebrae showed a trend toward increased pedicle screw pull out strength versus controls. Pedicle screw pull out force of polymethylmethacrylate in the insertion stage was higher than that of hydroxyapatite. However, hydroxyapatite is likely a better clinical alternative to polymethylmethacrylate, as hydroxyapatite augmentation, unlike polymethylmethacrylate augmentation, stimulates bone growth and can be revised.

Biomechanical comparison of cervical fixation via transarticular facet screws without rods versus lateral mass screws with rods.

OBJECTIVE: Transarticular facet screws restore biomechanical stability to the cervical spine when posterior cervical anatomy has been compromised. This study compares the more recent, less invasive, and briefer transarticular facet screw system without rods with the lateral mass screw system with rods. METHODS: For this study, 6 human cervical spines were obtained from cadavers. Transarticular facet screws without rods were inserted bilaterally into the inferior articular facets at the C5-C6 and C5-C6-C7 levels. Lateral mass screws with rods were inserted bilaterally at the same levels using Magerl's technique. All specimens underwent range of motion (ROM) testing by a material testing machine for flexion, extension, lateral bending, and axial rotation. RESULTS: Both fixation methods, transarticular facet screws without rods and lateral mass screws with rods, reduced all ROM measurements and increased spinal stiffness. No statistically significant differences between the 2 stabilization methods were found in ROM measurements for 1-level insertions. However, in 2-level insertions, ROM for the nonrod transarticular facet screw group was significantly increased for flexion-extension and lateral bending. CONCLUSIONS: Transarticular facet screws without rods and lateral mass screws with rods had similar biomechanical stability in single-level insertions. For 2-level insertions, transarticular facet screws without rods are a valid option in cervical spine repair.

Pituitary stalk Langerhans cell histiocytosis treated with CyberKnife radiosurgery.

OBJECTIVE: Langerhans cell histiocytosis (LCH) is a rare idiopathic disease that is characterized by clonal proliferation of Langerhans histiocytes in various parts of the body. These atypical cells have been found to infiltrate single or multiple organs, including bone, lungs, liver, spleen, lymph nodes, and skin. Central nervous system invasion in LCH patients has rarely been reported, especially in the adult population. METHODS AND RESULTS: We describe three histopathologically confirmed cases of adult LCH that involves both the pituitary stalk and hypothalamus, and report our limited experience of such cases in this location that has been treated with CyberKnife radio surgery. CONCLUSION: The treatment goal of controlling lesion growth is achieved by CyberKnife radiosurgery in this case series. All patients tolerated the treatment well without obvious complications.

A giant cell tumor of the cranial base treated by stereotactic radiosurgery.

Giant cell tumors (GCTs) developing from the cranial bones are rare. Occurrence of these tumors in the vicinity of eloquent areas precludes complete excision. Fractionated external beam radiotherapy (FEBRT) has been used for those cases, but with inconsistent outcomes. The authors report a case of a patient with a GCT involving the left occiput which was successfully treated by CyberKnife stereotactic radiosurgery (CK RS). There was improvement in the neurological deficit and occipital pain without adjunctive treatment. This is the first report of stereotactic radiosurgery (SRS) adopted as a primary treatment modality for a cranial GCT.

Lumbar disc rehydration postimplantation of a posterior dynamic stabilization system.

Biological attempts at disc regeneration are promising; however, disc degeneration is closely related to other predisposing factors such as alteration of disc height, intradiscal pressure, load distribution, and motion. The restoration of the physiological status of the affected spinal segment is thus necessary prior to attempts at disc regeneration. Dynamic stabilization systems now offer the potential of a mechanical approach to intervertebral disc regeneration. The authors used decompression and placement of the BioFlex dynamic stabilization device to treat a young male patient with disc degeneration. This patient underwent follow-up, and he was found to gradually improve both neurologically and radiographically. On MR imaging performed 1 year postoperatively, he had an increase in disc height and disc rehydration. This case and the concept of disc rehydration are presented in this paper.

Biomechanical comparison of single-level posterior versus transforaminal lumbar interbody fusions with bilateral pedicle screw fixation: segmental stability and the effects on adjacent motion segments.

OBJECT: Both posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) have been frequently undertaken for lumbar arthrodesis. These procedures use different approaches and cage designs, each of which could affect spine stability, even after the addition of posterior pedicle screw fixation. The objectives of this biomechanical study were to compare PLIF and TLIF, each accompanied by bilateral pedicle screw fixation, with regard to the stability of the fused and adjacent segments. METHODS: Fourteen human L2-S2 cadaveric spine specimens were tested for 6 different modes of motion: flexion, extension, right and left lateral bending, and right and left axial rotation using a load control protocol (LCP). The LCP for each mode of motion utilized moments up to 8.0 Nm at a rate of 0.5 Nm/second with the application of a constant compression follower preload of 400 N. All 14 specimens were tested in the intact state. The specimens were then divided equally into PLIF and TLIF conditions. In the PLIF Group, a bilateral L4-5 partial facetectomy was followed by discectomy and a single-level fusion procedure. In the TLIF Group, a unilateral L4-5 complete facetectomy was performed (and followed by the discectomy and single-level fusion procedure). In the TLIF Group, the implants were initially positioned inside the disc space posteriorly (TLIF-P) and the specimens were tested; the implants were then positioned anteriorly (TLIF-A) and the specimens were retested. All specimens were evaluated at the reconstructed and adjacent segments for range of motion (ROM) and at the adjacent segments for intradiscal pressure (IDP), and laminar strain. RESULTS: At the reconstructed segment, both the PLIF and the TLIF specimens had significantly lower ROMs compared with those for the intact state (p < 0.05). For lateral bending, the PLIF resulted in a marked decrease in ROM that was statistically significantly greater than that found after TLIF (p < 0.05). In flexion-extension and rotation, the PLIF Group also had less ROM, however, unlike the difference in lateral bending ROM, these differences in ROM values were not statistically significant. Variations in the position of the implants within the disc space were not associated with any significant differences in ROM values (p = 0.43). Analyses of ROM at the adjacent levels L2-3, L3-4, and L5-S1 showed that ROM was increased to some degree in all directions. When compared with that of intact specimens, the ROMs were increased to a statistically significant degree at all adjacent segments in flexion-extension loads (p < 0.05); however, the differences in values among the various operative procedures were not statistically significant. The IDP and facet contact force for the adjacent L3-4 and L5-S1 levels were also increased, but these values were not statistically significantly increased from those for the intact spine (p > 0.05). CONCLUSIONS: Regarding stability, PLIF provides a higher immediate stability compared with that of TLIF, especially in lateral bending. Based on our findings, however, PLIF and TLIF, each with posterolateral fusions, have similar biomechanical properties regarding ROM, IDP, and laminar strain at the adjacent segments.

Surgical strategies for managing foraminal nerve sheath tumors: the emerging role of CyberKnife ablation.

Sixteen Stanford University Medical Center (SUMC) patients with foraminal nerve sheath tumors had charts reviewed. CyberKnife radiosurgery was innovative in management. Parameters were evaluated for 16 foraminal nerve sheath tumors undergoing surgery, some with CyberKnife. Three neurofibromas had associated neurofibromatosis type 1 (NF1). Eleven patients had one resection; others had CyberKnife after one (two) and two (three) operations. The malignant peripheral nerve sheath tumor (MPNST) had prior field-radiation and adds another case. Approaches included laminotomy and laminectomies with partial (three) or total (two) facetectomies/fusions. Two cases each had supraclavicular, lateral extracavitary, retroperitoneal and Wiltze and costotransversectomy/thoracotomy procedures. Two underwent a laminectomy/partial facetectomy, then CyberKnife. Pre-CyberKnife, one of two others had a laminectomy/partial facetectomy, then total facetectomy/fusion and the other, two supraclavicular approaches. The MPNST had a hemi-laminotomy then laminectomy/total facetectomy/fusion, followed by CyberKnife. Roots were preserved, except in two. Of 11 single-operation-peripheral nerve sheath tumors, the asymptomatic case remained stable, nine (92%) improved and one (9%) worsened. Examinations remained intact in three (27%) and improved in seven (64%). Two having a single operation then CyberKnife had improvement after both. Of two undergoing two operations, one had symptom resolution post-operatively, worsened 4 years post-CyberKnife then has remained unchanged after re-operation. The other such patient improved post-operatively, had no change after re-operation and improved post-CyberKnife. The MPNST had presentation improvement after the first operation, worsened and after the second surgery \and CyberKnife, the patient expired from tumor spread. In conclusion, surgery is beneficial for pain relief and function preservation in foraminal nerve sheath tumors. Open surgery with CyberKnife is an innovation in these tumors' management.

Upper-extremity peripheral nerve injuries: a Louisiana State University Health Sciences Center literature review with comparison of the operative outcomes of 1837 Louisiana State University Health Sciences Center median, radial, and ulnar nerve lesions.

OBJECTIVE: Data from three Louisiana State University Health Sciences Center (LSUHSC) publications were summarized for median, radial, and ulnar nerve injuries. METHODS: Lesion types, repair techniques, and outcomes were compared for 1837 upper-extremity nerve lesions. RESULTS: Sharp laceration injury repair outcomes at various levels for median and radial nerves were equally good (91% each) and better than those for the ulnar nerve (73%). Secondary suture and graft repair outcomes were better for the median nerve (78% and 68%, respectively) than for the radial nerve (69% and 67%, respectively) and ulnar nerve (69% and 56%, respectively). In-continuity lesions with positive nerve action potentials during intraoperative testing underwent neurolysis with good results for the median (97%), radial (98%), and ulnar nerves (94%). For radial, median, and ulnar nerve in-continuity lesions with negative intraoperative nerve action potentials, good results occurred after suture repair in 88%, 86%, and 75% and after graft repair in 86%, 75% and 56%, respectively. CONCLUSION: Good outcomes after median and radial nerve repairs are attributable to the following factors: the median nerve's innervation of proximal, large finger, and thumb flexors; and the radial nerve's similar innervation of proximal muscles that do not perform delicate movements. This is contrary to the ulnar nerve's major nerve supply to the distal fine intrinsic hand muscles, which require more extensive innervation. The radial nerve also has a motor fiber predominance, reducing cross-motor/sensory reinnervation, and radial nerve-innervated muscles perform similar functions, decreasing the chance of innervation of muscles with opposite functions.

Lower-extremity peripheral nerve injuries: a Louisiana State University Health Sciences Center literature review with comparison of the operative outcomes of 806 Louisiana State University Health Sciences Center sciatic, common peroneal, and tibial nerve lesions.

OBJECTIVE: With the use of data from 3 Louisiana State University Health Sciences Center (LSUHSC) publications, various parameters for buttock/thigh-level sciatic nerve and tibial and common peroneal divisions/nerve injuries were summarized, and outcomes were compared. METHODS: Data from 806 buttock/thigh-level sciatic nerve and tibial and common peroneal division/nerve injury repairs were summarized. Lesion types, repair techniques, and outcomes were compared. RESULTS: Acute lacerations undergoing suture repair were best for the thigh-then-buttock-level tibial (93%/73%) and then same-level common peroneal divisions (69%/30%); at the knee level, tibial outcomes (100%) were better than those for the common peroneal nerve (CPN) (84%). Secondary graft repairs for lacerations had good outcomes for the thigh-then-buttock-level tibial (80%/62%), followed by common peroneal divisions at the same levels (45%/24%). The knee/leg-level tibial nerve (94%) did better than the CPN (40%) here. In-continuity lesions with positive intraoperative nerve action potentials underwent neurolysis with better results for the thigh-then-buttock-level tibial division (95%/86%) than for same-level CPN (78%/69%). The knee/leg-level tibial nerve did better than the CPN (95%/93%). CONCLUSION: Better recovery of buttock- and thigh-level tibial division/nerve occurs because: 1) the CPN is lateral and thus vulnerable to a more severe injury; 2) the tibial nerve is more elastic at impact owing to its singular-fixation site (the CPN has a dual fixation); 3) the tibial nerve has a better blood supply and regeneration; 4) the tibial nerve has a higher force-absorbing fascicle/connective tissue count than the CPN; and 5) the tibial nerve-innervated gastrocnemius soleus requires less reinnervation for functional contraction than deep peroneal branches, which innervate long, thin extensor muscles at multiple sites and require coordinated nerve input for effective contraction.

Imaging correlation of the degree of degenerative L4-5 spondylolisthesis with the corresponding amount of facet fluid.

OBJECT: The aim of this study was to correlate the degree of L4-5 spondylolisthesis on plain flexion-extension radiographs with the corresponding amount of L4-5 facet fluid visible on MR images. METHODS: Patients underwent evaluation at the Neurosurgical Spine Clinics of Stanford University Medical Center and National Health Insurance Medical Center (Goyang, South Korea) between January 2006 and December 2007. Only patients who were diagnosed with L4-5 degenerative spondylolisthesis (DS) and who had both lumbosacral flexion-extension radiographs and MR images available for review were eligible for this study. Each patient's dynamic motion index (DMI) was measured using the lateral lumbosacral plain radiograph and was the percentage of the degree of anterior slippage seen on flexion versus that seen on extension. Axial T2-weighted MR images of the L4-5 facet joints obtained in each patient was analyzed for the amount of facet fluid, using the image showing the widest portion of the facets. The facet fluid index was calculated from the ratio of the sum of the amounts of facet fluid found in the right plus left facets over the sum of the average widths of the right plus left facet joints. RESULTS: Fifty-four patients with L4-5 DS were included in this study. Of these 54 patients, facet fluid was noted on MR images in 29 patients (53.7%), and their mean DMI was 6.349 +/- 2.726. Patients who did not have facet fluid on MR imaging had a mean DMI of 1.542 +/- 0.820; this difference was statistically significant (p < 0.001). There was a positive linear association between the facet fluid index and the DMI in the group of patients who exhibited facet fluid on MR images (Pearson correlation coefficient 0.560, p < 0.01). In the subgroup of 29 patients with L4-5 DS who showed facet fluid on MR images, flexion-extension plain radiographs in 10 (34.5%) showed marked anterolisthesis, while the corresponding MR images did not. CONCLUSIONS: There is a linear correlation between the degree of segmental motion seen on flexion-extension plain radiography in patients with DS at L4-5 and the amount of L4-5 facet fluid on MR images. If L4-5 facet fluid in patients with DS is seen on MR images, a corresponding anterolisthesis on weight-bearing flexion-extension lateral radiographs should be anticipated. Obtaining plain radiographs will aid in the diagnosis of anterolisthesis caused by an L4-5 hypermobile segment, which may not always be evident on MR images obtained in supine patients.