Postoperative K-line conversion from negative to positive is independently associated with a better surgical outcome after posterior decompression with instrumented fusion for K-line negative cervical ossification of the posterior ligament

Effectiveness of additional C2 decompression of the cervical spinal canal after cervical laminoplasty: a retrospective cohort study

PURPOSE

This study aimed to assess the effects of additional C2 decompression of the cervical spinal canal on the postoperative outcomes after cervical laminoplasty in patients with cervical stenosis caused by ossification of the posterior longitudinal ligament (OPLL).

MATERIALS AND METHODS

This retrospective cohort study included patients with cervical stenosis due to OPLL and treated between April 2014 and December 2015. The patients who underwent C2-7 (additional C2 decompression) and C3-7 posterior decompression were compared using the Japanese Orthopedic Association (JOA) scores, visual analog scale (VAS) scores, axial symptom scores, and intervals between the posterior margin of the vertebral body and the K-line.

RESULTS

There were 36 and 24 patients in the additional C2 decompression and control groups, respectively. The JOA scores were higher in the additional C2 decompression group than the controls at 1 and 3 years (p < 0.05). Upper extremity motor function after the operation and at 1 and 3 years and lower extremity motor function after operation were improved in the additional C2 decompression group (all p < 0.05 vs. controls). VAS scores were lower in the additional C2 decompression group than controls at 1 year (p < 0.05). Axial symptom scores in the additional C2 decompression group were decreased postoperatively but increased at 1 and 3 years (p < 0.05 vs. controls). Finally, the posterior shift of the K-line in the additional C2 decompression group was significant (from 0.98 to 1.68 cm, p < 0.05).

CONCLUSIONS

Additional C2 decompression might improve the effectiveness of cervical laminoplasty in patients with cervical stenosis caused by OPLL.

Risk Factors for Postoperative Loss of Lordosis, Cervical Kyphosis, and Sagittal Imbalance After Cervical Laminoplasty

OBJECTIVE

A retrospective cohort study was undertaken to elucidate the risk factors of loss of cervical lordosis (LCL), kyphotic deformity, and sagittal imbalance after cervical laminoplasty.

METHODS

A total of 108 patients who underwent laminoplasty to treat cervical myelopathy and were followed for ≥2 years were included. Logistic regression analysis and multiple regression analysis were performed to identify preoperative risk factors of LCL, kyphotic deformity (cervical lordosis <0°), and sagittal imbalance (sagittal vertical axis >40 mm) at postoperative 2 years.

RESULTS

Within multivariate multiple regression analysis, C2-C7 lordosis (P = 0.002), and C2-C7 extension capacity (P<0.001) showed significant association with LCL. Furthermore, age (P = 0.043) and C2-C7 lordosis (P = 0.038) were significantly associated with postoperative kyphosis. Receiver operating characteristic curve analysis for postoperative kyphosis showed that preoperative C2-C7 lordosis of 10.5° had a sensitivity and specificity of 81.3% and 82.4%, respectively. Preoperative K-line tilt (P = 0.034) showed a significant association with postoperative cervical sagittal imbalance at postoperative 2 years. Receiver operating characteristic curve analysis showed that a K-line tilt cutoff value of 12.5° had a sensitivity and specificity of 78.6% and 77.7%, respectively, for predicting postoperative sagittal imbalance.

CONCLUSIONS

Higher preoperative C2-C7 lordosis and less preoperative cervical extension capacity were risk factors of LCL. Small preoperative C2-C7 lordosis <10.5° and younger age were risk factors of postoperative kyphosis. Furthermore, a greater K-line tilt would increase the risk of postoperative sagittal imbalance, with a cutoff value of 12.5°.

Posterior Decompression and Fusion with Vertical Pressure Procedure in the Treatment of Multilevel Cervical OPLL with Kyphotic Deformity

Objective

To report the outcomes and feasibility of a new technique to change K‐line (−) to K‐line (+) via only a posterior approach to treat multilevel non‐continuous cervical ossification of the posterior longitudinal ligament (C‐OPLL) with kyphotic deformity.

Methods

In this study, 17 consecutive cases of patients who underwent vertical pressure procedure (VP) combined with posterior cervical single‐open‐door laminoplasty and instrumented fusion from January 1, 2017 to December 31, 2019 were enrolled. The following radiographic parameters: C2‐C7 Cobb angle, local Cobb angle, extent of OPLL, and the distance from OPLL to the K‐line(DK) were measured and analyzed. Clinically, the JOA score, VAS‐N and VAS‐A, NDI, and complications were collected from medical records to evaluate the clinical outcomes.

Results

All 17 cases shifted from K‐line (−) to K‐line (+).Comparing the preoperative images to the final follow‐up images, the mean C2‐7 Cobb angle changed from −6.94° ± 8.30° to 8.18° ± 4.43°, and the local Cobb angle altered from −9.12° ± 8.68° to 6.65° ± 6.11°. The mean DK increased from −2.64 ± 1.52 mm to 3.09 ± 2.19 mm. One patient showed C5 palsy and recovered within 3 months. The mean JOA score increased from 8.88 ± 2.11 to 14.71 ± 1.36. The average NDI decreased from 20.65 ± 7.80 to 8.94 ± 4.93. The mean VAS‐N and VAS‐A decreased from 3.44 ± 1.80 and 4.69 ± 1.97 to 1.25 ± 0.86 and 1.38 ± 1.16. All patients were followed up for at least 1 year.

Conclusion

A new technique added to posterior decompression and fusion (PDF), the vertical pressure procedure effectively corrects K‐line (−) to K‐line (+) and avoids the shortcomings of conventional anterior decompression and fusion (ADF) as well as PDF to provide a relatively safe and adequate decompression, cervical realignment. It pronounced satisfactory clinical outcome for extensive non‐continuous OPLL with kyphotic deformity even though OPLL remains ventral to the spinal cord.

Significance of Vertebral Body Sliding Osteotomy as a Surgical Strategy for the Treatment of Cervical Ossification of the Posterior Longitudinal Ligament

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

Vertebral body sliding osteotomy (VBSO) has previously been reported as a technique to decompress ossification of the posterior longitudinal ligament (OPLL) by translating the vertebral body anteriorly. This study aimed to evaluate the radiological and clinical efficacies of VBSO and clarify the surgical indications of VBSO for treating myelopathy caused by OPLL.

METHODS

Ninety-seven patients with symptomatic OPLL-induced cervical myelopathy treated with VBSO or laminoplasty who were followed up for more than 2 years were retrospectively reviewed. Cervical alignment, range of motion, fusion, modified K-line (mK-line) status, and minimum interval between ossified mass and mK-line (INT_(min)), and the Japanese Orthopaedic Association (JOA) score were assessed. Patients in the VBSO group were compared with those who underwent laminoplasty.

RESULTS

Cervical lordosis and INT_(min) significantly increased in the VBSO group. All patients in the VBSO group assessed as mK-line (-) preoperatively were assessed as mK-line (+) postoperatively. However, in the LMP group, the mK-line status changed from (+) preoperatively to (-) postoperatively in 3 patients. Final JOA score (p = 0.02) and JOA score improvement (p = 0.01) were significantly higher in the VBSO group. JOA recovery ratio (p = 0.03) and proportion of patients with a recovery rate ≥50% were significantly higher in the VBSO group (p < 0.01).

CONCLUSIONS

VBSO is an effective surgical option for OPLL-induced myelopathy, demonstrating favorable neurological recovery and lordosis restoration with low complication rates. It is best indicated for kyphotic alignment, OPLL with a high space-occupying ratio, and OPLL involving ≤3 segments.

The Kappa Line as a Regional Modification of the K-line: A Predictor of Neurological Outcome and Indicator of the Adequate Level of Decompression in Selective Laminoplasty

STUDY DESIGN

This is a retrospective cohort study.

OBJECTIVE

The aim was to introduce Kappa line (modification of K-line) for the prediction of postoperative neurological recovery after selective cervical laminoplasty (LMP) and use in determining the decompression level.

SUMMARY OF BACKGROUND DATA

The K-line is a radiographic marker that can predict prognosis and aid in surgical planning for patients undergoing LMP through C3 to C7. However, its efficacy in LMP involving limited segments is unclear. Furthermore, no specific radiographic marker to predict the prognosis of selective LMP has been reported.

MATERIALS AND METHODS

Fifty-one consecutive patients with a minimum 2-year follow-up after selective LMP for cervical myelopathy caused by ossification of posterior longitudinal ligament were retrospectively reviewed. The Kappa line was defined as a straight line connecting the midpoints of the spinal canal made by remaining bony structure after decompression procedures on a plain lateral radiograph in the neutral position. Patients were classified as K-line (+) or (-) and Kappa line (+) or (-) based on whether the ossified mass crossed the indicator line.

RESULTS

The Kappa line (+) group demonstrated significantly higher Japanese Orthopaedic Association (JOA) recovery rate (P=0.01), final JOA score (P<0.01), and dural sac diameter (P<0.01) postoperatively than the Kappa line (-) group. Cord compression grade was significantly lesser in the Kappa line (+) group. However, the K-line-based classification did not demonstrate significant difference in JOA recovery rate, final JOA score, and cord compression grade between the (+) and (-) groups; the dural sac diameter was significantly higher in the K-line (+) group (P<0.01).

CONCLUSIONS

The Kappa line showed better correlation with ossification of posterior longitudinal ligament size and cervical alignment, providing better prediction of neurological recovery and remaining cord compression following selective LMP. Therefore, the Kappa line can aid in determining the level of decompression in selective LMP.

Perioperative Complications in Posterior Surgeries for Cervical Ossification of the Posterior Longitudinal Ligament: A Prospective Nationwide Investigation

STUDY DESIGN

This was a prospective multicenter study.

OBJECTIVE

The aim of this study was to investigate the perioperative complications of posterior surgeries for the treatment of cervical ossification of the posterior longitudinal ligament (OPLL).

SUMMARY OF BACKGROUND DATA

Surgical treatment for cervical OPLL has a high risk of various complications. Laminoplasty (LAMP) and posterior decompression and instrumented fusion (PDF) are effective for multilevel cervical OPLL; however, few studies have focused on the surgical complications of these 2 procedures.

MATERIALS AND METHODS

We prospectively included 380 patients undergoing posterior surgeries for cervical OPLL (LAMP: 270 patients, PDF: 110 patients), and investigated the systemic and local complications, including neurological complications. We further evaluated risk factors related to the neurological complications.

RESULTS

Motor palsy was found in 40 patients (10.5%), and motor palsy in the upper extremity was most frequent (8.9%), especially in patients who received PDF (14.5%). Motor palsies involving the lower extremities was found in 6 patients (1.6%). Regarding local complications, dural tears (3.9%) and surgical site infections (2.6%) were common. In the univariate analysis, body mass index, preoperative cervical alignment, fusion surgery, and the number of operated segments were the factors related to motor palsy. Multivariate analysis revealed that fusion surgery and a small preoperative C2-C7 angle were the independent factors related to motor palsy. Motor palsy involving the lower extremities tended to be found at early time points after the surgery, and all the patients fully recovered. Motor palsy in the upper extremities occurred in a delayed manner, and 68.8% of patients with PDF showed good recovery, whereas 81.3% of patients with LAMP showed good recovery.

CONCLUSIONS

In posterior surgeries for cervical OPLL, segmental motor palsy in the upper extremity was most frequently observed, especially in patients who received PDF. Fusion and a small preoperative C2-C7 angle were the independent risk factors for motor palsy.

LEVEL OF EVIDENCE

Level III.

Fusion and subsidence rates of vertebral body sliding osteotomy: Comparison of 3 reconstructive techniques for multilevel cervical myelopathy

BACKGROUND CONTEXT

Vertebral body sliding osteotomy (VBSO) was previously reported as a technique to decompress spinal canal by translating the vertebral body anteriorly and is indicated for cervical myelopathy caused by spondylosis or ossification of the posterior longitudinal ligament. However, little is known about its fusion and subsidence rates.

PURPOSE

To compare the fusion and subsidence rates of VBSO, anterior cervical discectomy and fusion (ACDF), and anterior cervical corpectomy and fusion (ACCF).

STUDY DESIGN/SETTING

Retrospective cohort study PATIENT SAMPLE: One hundred sixty-eight patients who underwent VBSO, ACDF, or ACCF for the treatment of cervical myelopathy and were followed-up for more than 2 years were retrospectively reviewed.

OUTCOME MEASURES

Fusion and subsidence rates, visual analog scale (VAS) scores for neck pain, neck disability index (NDI), and Japanese Orthopaedic Association (JOA) scores were assessed.

METHODS

Results of the VBSO, ACDF, and ACCF groups were compared using Student's t-test and chi-square test.

RESULTS

The fusion rate at 1-year postoperatively and the final follow-up for VBSO was 92.9% (37/42). VBSO demonstrated a higher 1-year fusion rate than ACDF (77.9% [74/95], p=0.04) and ACCF (74.2% [23/31], p=0.04). However, the fusion rate at the final follow-up did not demonstrate significant difference. The mean amount of subsidence (ACDF group, 1.5±1.2 mm; VBSO group, 1.5±1.5 mm; p=1.00) and rate of significant subsidence of > 3 mm (ACDF group, 13.7% [13/95]; VBSO group, 14.3% [6/42]; p=1.00) were similar for ACDF and VBSO. Furthermore, the mean amount of subsidence in VBSO was significantly less than that in ACCF (1.5±1.5 mm vs 2.4±2.0 mm; p=0.04). Neck pain VAS, NDI, and JOA scores were not significantly different among the groups.

CONCLUSIONS

VBSO demonstrated faster solid union than ACDF and ACCF, although the fusion rates at the final follow-up were similar. VBSO resulted in less subsidence than ACCF at the 1-year follow-up. VBSO could be applied safely when the shape and/or location of the pathologic foci and sagittal alignment favor its application without much concern for pseudarthrosis or subsidence.

Mid-term Surgical Outcome of Posterior Decompression With Instrumented Fusion in Patients With K-line (-) Type Cervical Ossification of the Posterior Longitudinal Ligament With a 5-Year Minimum Follow-up

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

The objective of this study was to assess mid-term surgical outcomes after posterior decompression with instrumented fusion (PDF) in patients with K-line (-) type cervical ossification of the posterior longitudinal ligament (OPLL).

SUMMARY OF BACKGROUND DATA

The poor surgical outcome for K-line (-) type cervical OPLL can result from posterior decompression alone.

MATERIALS AND METHODS

We reviewed cases of K-line (-) type cervical OPLL in 24 patients who underwent PDF in our institute from 2002 to 2014. As a control, we used K-line (-) type cervical OPLL in 9 patients who underwent laminoplasty before 2002 (LMP group). The neurological status and radiographic findings were evaluated retrospectively.

RESULTS

The preoperative Japanese Orthopedic Association score was 7.9±2.4 points in the PDF group and 7.4±2.3 points in the LMP group (P=0.584). The postoperative Japanese Orthopedic Association score was 11.7±2.6 points in the PDF group and 9.2±2.0 points in the LMP group at a 5-year follow-up (P=0.008). The recovery rate on average was 39.0% in the PDF group and 14.9% in the LMP group at a 5-year follow-up (P=0.037). The range of motion postoperatively at the maximal spinal cord compression level decreased significantly in the PDF group. The C2-C7 angle was 2.7 degrees of kyphosis in the PDF group, whereas 5.5 degrees of kyphosis was found in the LMP group at a 5-year follow-up (P=0.303). The center of gravity of the head-C7 sagittal vertical axis was 40 mm in the PDF group and 43 mm in the LMP group (P=0.936).

CONCLUSIONS

The relatively good surgical outcome could be obtained by PDF for patients with K-line (-)-type cervical OPLL. The addition of posterior instrumented fusion eliminated the dynamic factor at the level of maximal spinal cord compression.

LEVEL OF EVIDENCE

Level IV.

The relationship between preoperative cervical sagittal balance and clinical outcome of laminoplasty treated cervical ossification of the posterior longitudinal ligament patients

BACKGROUND CONTEXT

Laminoplasty is a common surgical method used to treat patients with cervical ossification of the posterior longitudinal ligament (OPLL). Although laminoplasty is preferred over traditional laminectomy, the factors affecting the complications and outcomes are unclear. Recently, sagittal balance indexes have been revealed to be predictors of clinical outcomes in patients with cervical degenerative diseases, but their relationships with laminoplasty-treated OPLL outcomes remains unknown.

PURPOSE

The purpose of this study is to evaluate the relationship of preoperative cervical sagittal balance indexes and clinical outcome in laminoplasty treated OPLL patients.

STUDY DESIGN

This is a retrospective case study.

PATIENT POPULATION

Between January 2015 and January 2017, 181 consecutively included patients who underwent cervical laminoplasty for OPLL were enrolled (male:female ratio=126:75; mean age=60.2 years). Cervical spine lateral radiographs in neutral, flexion, and extension positions were taken before and 2 years after the surgery.

OUTCOME MEASURES

The C2-C7 Cobb angle, T1 slope, C1-C7 sagittal vertical axis (SVA), C2-C7 SVA, CGH (center of gravity of the head)-C7 SVA, cervical JOA (Japanese Orthopedic Association) score, and neck VAS (visual analogue scale) score were measured preoperatively and postoperatively at the 2-year follow-up.

METHODS

The patients were divided into two groups according to changes in the lordotic angle or the recovery rate of the JOA score. The relationships between the postoperative lordosis loss or the clinical outcome and the preoperative variables, including the patient's age, JOA score, C2-C7 Cobb angle, T1 slope, C1-C7 SVA, C2-C7 SVA, and CGH-C7 SVA, were investigated.

RESULTS

The patients were divided into two groups according to the postoperative change in the C2-C7 Cobb angle. There were no differences in the age, preoperative C2-C7 Cobb angle, C1-C7 SVA, or C2-C7 SVA; there was only a difference in the preoperative CGH-C7 SVA and T1 slope level (p=.038, p=.042). The postoperative JOA and JOA recovery rate were related to the postoperative lordosis loss in cervical alignment (p=.048, p=.031). We again divided the patients into two groups according to the JOA recovery rate and found that only the preoperative CGH-C7 SVA and C1-C7 SVA were related to the neurological outcome (p=.011, p=.047). According to the multivariate logistic regression analysis, higher preoperative CGH-C7 SVA levels were significantly associated with decreases in the lordosis angle postoperatively and the clinical outcome (p=.018, OR=1.225; p=.034, OR=1.654). The ROC (receiver operating characteristic) analysis revealed that the proper cutoff value of preoperative CGH-C7 SVA for predicting the postoperative loss of lordosis and clinical outcomes is 3.8 cm.

CONCLUSION

Preoperative cervical sagittal balance indexes are related to the outcomes of OPLL patients after laminoplasty. Patients with high preoperative CGH-C7 SVA levels have a high probability of developing sagittal imbalances and neurological symptoms of the cervical spine, and this measurement can be used as a predictor of outcomes in laminoplasty-treated cervical OPLL patients.

K-line (-) in the neck-flexed position affects surgical outcomes in patients with ossification of the posterior longitudinal ligament after muscle-preserving selective laminectomy

BACKGROUND

Posterior cervical decompression results in favorable outcomes for K-line (+) ossification of the posterior longitudinal ligament (OPLL) patients. However, even for patients with K-line (+) in the neck neutral position, K-line (-) in the neck-flexed position (flexion K-line (-)) may affect surgical outcomes. We investigated the influence of flexion K-line (-) on surgical outcomes after muscle-preserving selective laminectomy using multivariate analysis.

METHODS

This study involved 113 OPLL patients with K-line (+) in the neck neutral position who underwent muscle-preserving selective laminectomy. Patients were divided into flexion K-line (+) (n = 90) and flexion K-line (-) (n = 23) groups. We analyzed the influence of a flexion K-line (-) on radiological and surgical outcomes. We conducted a multivariate analysis to analyze the factors affecting surgical outcomes.

RESULTS

The patients with a flexion K-line (-) had a larger C2-C7 sagittal vertical axis (preoperatively, P = 0.042; postoperatively, P = 0.021), narrower postoperative clearance of the spinal cord (P = 0.003), a smaller proportion of segmental-type OPLL (P < 0.001), and a greater OPLL occupancy ratio (P < 0.001). The recovery rate measured by the Japanese Orthopedic Association (JOA) score was poorer in patients with a flexion K-line (-) (17.6 ± 32.2%) than in those with a flexion K-line (+) (35.3 ± 29.5%) (P = 0.013). Multiple linear regression analysis revealed that the flexion K-line (-) affected the recovery rate of the JOA score (β = -0.233, P = 0.013).

CONCLUSIONS

Even for patients with K-line (+) OPLL, the flexion K-line (-) affects surgical outcomes. The flexion K-line (-) is a useful predictor of poor surgical outcomes after posterior decompression surgery.

Effect of K-line on posterior cervical surgery in patients with posterior longitudinal ligament ossification

PURPOSE

To evaluate the effect of K-line on posterior single-door decompression with fusion fixation (PFF) and posterior single-door decompression with non-fusion fixation (PNF) for patients with ossification of posterior longitudinal ligament (OPLL).

METHODS

A total of 65 patients with OPLL were analyzed retrospectively. They consisted of 44 patients with positive K-line, designated as the K ( +) group, and 21 patients with negative K-line, designated as K (-). The patients were also divided into a PFF group (38 patients) and a PNF group (27 patients). The Japanese Orthopaedic Association (JOA) score, C2-C7 Cobb angle, improvement rate of JOA score, and complications were calculated and statistically analyzed between the groups.

RESULTS

In the K ( +) group, there were no significant differences in the incidence of C5 nerve root palsy and C2-C7 Cobb angle between the two groups of surgical patients, but there were significant differences in the improvement rate of JOA score and the incidence of axial pain. In the K (-) group, there were no significant differences in the incidence of axial pain, the incidence of C5 nerve root palsy, and preoperative C2-C7 Cobb angle between the two groups, but significant differences were observed in the improvement rate of JOA score and C2-C7 Cobb angle at the last follow-up.

CONCLUSION

In the K ( +) group, the improvement rate of JOA score was higher and the incidence of axial pain was lesser in the PNF group than in the PFF group. In the K (-) group, the improvement rate of JOA score was higher in the PFF group than in the PNF group, and there was significant loss of C2-C7 Cobb angle in the PNF group.

Outcomes of posterior cervical fusion and decompression: a systematic review and meta-analysis

BACKGROUND CONTEXT

Posterior cervical fusion (PCF) with decompression is a treatment option for patients with conditions such as spondylosis, spinal stenosis, and degenerative disc disorders that result in myelopathy or radiculopathy. The annual rate, number, and cost of PCF in the United States has increased. Far fewer studies have been published on PCF outcomes than on anterior cervical fusion (ACF) outcomes, most likely because far fewer PCFs than ACFs are performed.

PURPOSE

To evaluate the patient-reported and clinical outcomes of adult patients who underwent subaxial posterior cervical fusion with decompression.

STUDY DESIGN/SETTING

Systematic review and meta-analysis.

PATIENT SAMPLE

The total number of patients in the 31 articles reviewed and included in the meta-analysis was 1,238 (range 7-166).

OUTCOME MEASURES

Preoperative to postoperative change in patient-reported outcomes (visual analog scales for arm pain and neck pain, Neck Disability Index, Japanese Orthopaedic Association [JOA] score, modified JOA score, and Nurick pain scale) and rates of fusion, revision, and complications or adverse events.

METHODS

This study was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and a preapproved protocol. PubMed and Embase databases were searched for articles published from January 2001 through July 2018. Statistical analyses for patient-reported outcomes were performed on the outcomes' raw mean differences, calculated as postoperative value minus preoperative value from each study. Pooled rates of successful fusion, revision surgery, and complications or adverse events, and their 95% confidence intervals, were also calculated. Two subgroup analyses were performed: one for studies in which only myelopathy or radiculopathy (or both) were stated as surgical indications and the other for studies in which only myelopathy or ossification of the posterior longitudinal ligament (or both) were stated as surgical indications. This study was funded by Providence Medical Technology, Inc. ($32,000).

RESULTS

Thirty-three articles were included in the systematic review, and 31 articles were included in the meta-analysis. For all surgical indications and for the 2 subgroup analyses, every cumulative change in patient-reported outcome improved. Many of the reported changes in patient-reported outcome also exceeded the minimal clinically important differences. Pooled outcome rates with all surgical indications were 98.25% for successful fusion, 1.09% for revision, and 9.02% for complications or adverse events. Commonly reported complications or adverse events were axial pain, C5 palsy, transient neurological worsening, and wound infection.

CONCLUSIONS

Posterior cervical fusion with decompression resulted in significant clinical improvement, as indicated by the changes in patient-reported outcomes. Additionally, high fusion rates and low rates of revision and of complications and adverse events were found.