OBJECTIVE: To identify the factors associated with a correction of the segmental angle (SA) with a total change greater than 10° in each level following minimally invasive oblique lumbar interbody fusion (MIS-OLIF).
METHODS: Patients with lumbar spinal stenosis who underwent single- or two-level MIS-OLIF were reviewed. Segments with adequate correction of the SA >10° after MIS-OLIF in immediate postoperative radiograph were categorized as discontinuous segments (D segments), whereas those without such improvement were assigned as continuous segments (C segments). Clinical and radiological parameters were compared, and multivariate logistic regression analysis was performed to identify factors associated with SA correction >10° after MIS-OLIF.
RESULTS: Of 211 segments included, 38 segments (18.0%) were classified as D segments. Compared with C segments, D segments demonstrated a significantly smaller preoperative SA (mean ± standard deviation [SD], - 1.1° ± 6.7° vs. 6.6° ± 6.3°, p < 0.001), larger change of SA (mean ± SD, 13.5° ± 3.4° vs. 3.1° ± 3.9°, p < 0.001), and a higher rate of presence of facet effusion (76.3% vs. 48.6%, p = 0.002). Logistic regression revealed preoperative SA (odds ratio (OR) [95% confidence interval (CI)]:0.733 [0.639-0.840], p < 0.001) and facet effusion (OR [95% CI]:14.054 [1.758-112.377], p = 0.027) as significant predictors for >10° SA correction after MIS-OLIF.
CONCLUSIONS: Preoperative kyphotic SA and facet effusion can predict SA correction >10° following MIS-OLIF. For patients with lordotic SA and no preoperative facet effusion, supplemental procedures, such as anterior column release or posterior osteotomy, should be prepared for additional lumbar lordosis correction required for remnant global sagittal imbalance after MIS-OLIF.

Spondylolisthesis is a common finding in middle-aged and older adults with back pain. The pathophysiology of degenerative spondylolisthesis is a subject of controversy regarding not only its etiology but also the mechanisms of its progression. It is theorized that degeneration of the facets and discs can lead to segmental instability, leading to displacement over time. Kirkaldy-Willis divided degenerative spondylolisthesis into three phases: dysfunction, instability, and finally, restabilization. There is a paucity of literature on the unification of the radiological hallmarks seen in spondylolisthesis within these phases. The radiographic features include (1) facet morphology/arthropathy, (2) facet effusion, (3) facet vacuum, (4) synovial cyst, (5) interspinous ligament bursitis, and (6) vacuum disc as markers of dysfunction, instability, and/or restabilization. We discuss these features, which can be seen on X-ray, CT, and MRI, with the intention of establishing a timeline upon which they present clinically. Spondylolisthesis is initiated as either degeneration of the intervertebral disc or facet joints. Early degeneration can be seen as facet vacuum without considerable arthropathy. As the vertebral segment becomes increasingly dynamic, fluid accumulates within the facet joint space. Further degeneration will lead to the advancement of facet arthropathy, degenerative disc disease, and posterior ligamentous complex pathology. Facet effusion can eventually be replaced with a vacuum in severe facet osteoarthritis. Intervertebral disc vacuum continues to accumulate with further cleft formation and degeneration. Ultimately, autofusion of the vertebra at the facets and endplates can be observed. With this review, we hope to increase awareness of these radiographical markers and their timeline, thus placing them within the framework of the currently accepted model of degenerative spondylolisthesis, to help guide future research and to help refine management guidelines.

BACKGROUND: Previous studies have identified various risk factors for adjacent segment disease (ASD) at the L5-S1 level after fusion surgery, including preoperative sagittal imbalance, longer fusion, and preoperative disc degeneration. However, only a few studies have explored the risk factors for ASD at the L5-S1 level after oblique lumbar interbody fusion (OLIF) at the L4-L5 level and above. This study aimed to identify the risk factors for symptomatic ASD at the L5-S1 level in patients with pre-existing degeneration after OLIF at L4-L5 and above.
METHODS: We retrospectively reviewed the data of patients who underwent OLIF at L4-L5 and above, with a minimum follow-up period of 2 years. Patients with central stenosis or Lee grade 2 or 3 foraminal stenosis at L5-S1 preoperatively were excluded. Patients were divided into ASD and non-ASD groups based on the occurrence of new-onset L5 or S1 radicular pain requiring epidural steroid injection (ESI). The clinical and radiological factors were analyzed. Logistic regression was used to identify the risk factors for ASD of L5-S1.
RESULTS: A total of 191 patients with a mean age ± standard deviation of 68.6 ± 8.3 years were included. Thirty-four (21.7%) patients underwent ESI at the L5 root after OLIF. In the logistic regression analyses, severe disc degeneration (OR (95% confidence interval (CI)): 2.65 (1.16-6.09)), the presence of facet effusion (OR (95% CI): 2.55 (1.05-6.23)), and severe paraspinal muscle fatty degeneration (OR (95% CI): 4.47 (1.53-13.05)) were significant risk factors for ASD in L5-S1.
CONCLUSIONS: In this study, the presence of facet effusion, severe disc degeneration, and severe paraspinal muscle fatty degeneration at the L5-S1 level were associated with the development of ASD at L5-S1 following OLIF at L4-L5 and above. For patients with these conditions, surgeons could consider including L5-S1 in the fusion when considering OLIF at the L4-L5 level and above.

Lumbar degenerative spondylolisthesis (LDS) is a common spinal disease. LDS has been differentiated into dynamic (unstable) and static (stable) spondylolisthesis. Standing flexion/extension lumbar spine radiographs are the best investigation to detect presence of dynamic spondylolisthesis. Magnetic resonance imaging is the investigation of choice to show lumbar canal stenosis and disc prolapse but it can miss dynamic LDS. Studies have shown good association between presence of facet fluid (FF) and dynamic spondylolisthesis.
A systematic review and meta-analysis were performed. All studies describing the relationship between FF and degenerative spondylolisthesis as measured on dynamic radiographs or kinematic magnetic resonance imaging were included.
Fourteen articles met the inclusion criteria. A total of 1065 patients were included in the meta-analysis. Of the patients with unstable spondylolisthesis, 71% had FF, whereas only 22% of the patients with stable spondylolisthesis had FF. The combined pooled odds ratio for unstable spondylolisthesis in the presence of FF was 7.55 (3.61-15.08; P <0.00001). The pooled standard mean difference in the FF size in the patients with unstable and stable spondylolisthesis was 0.97 mm (0.38-1.57; P = 0.001).
FF has positive correlation with the presence of dynamic LDS and the probability of dynamic LDS increases as the size of FF increases. The probability of having a dynamic spondylolisthesis in patients with FF >1 mm is 8 times that of patients with no FF. Standing flexion extension radiographs should be performed in patients with FF >1 mm.

BACKGROUND: Facet effusion represents a magnetic resonance imaging finding suggesting accumulation of fluid in the facet joint, potentially predictive of lumbar spondylolisthesis and low back pain. However, its prevalence and epidemiological characteristics in the general population remain unclear, because previous studies only included patients or volunteers. The aim of the present study was to investigate the prevalence of facet effusion in the general population and to describe its potential relationship with spondylolisthesis and low back pain.
METHODS: Our study enrolled 808 participants from the Wakayama Spine Study who underwent magnetic resonance imaging investigations in supine position. Facet effusion was defined as a measurable, curvilinear, high-intensity signal within the facet joint, closely matching that of cerebrospinal fluid on the axial T2 images. We used standing lateral radiographs to diagnose L4 spondylolisthesis.
RESULTS: We found that the prevalence of facet effusion in the lumbar spine was 34.3%, which did not differ significantly between men and women (p=0.13) and did not tend to increase with age, either in men (p=0.81) or in women (p=0.65). Additionally, we found no significant association between facet effusion and low back pain (odds ratio, 1.04-1.49; 95% confidence interval, 0.57-2.64; p=0.17-0.85), or between facet effusion and L4 spondylolisthesis (odds ratio, 1.55; 95% confidence interval, 0.80-2.86; p=0.17). In a subset of participants with L4 spondylolisthesis, we also noted that facet effusion was not significantly associated with low back pain (odds ratio, 1.26; 95% confidence interval, 0.37-4.27; p=0.70).
CONCLUSIONS: This is the first study of facet effusion employing a population-based cohort, and the findings are thus expected to accurately describe the relationship between facet effusion and low back pain in the general population. We are planning a follow-up survey of the Wakayama Spine Study cohort to clarify the natural history of facet effusion and its relationship with clinical symptoms.

METHODS: Retrospective cohort study.
OBJECTIVE: Lumbar segmental instability is a key factor determining whether decompression alone or decompression and fusion surgery is required to treat lumbar spinal stenosis (LSS). Some recent reports have suggested that facet joint effusion is correlated with spinal segmental instability. The aim of this study is to report the effect of facet effusion without radiographic segmental instability on the outcome of less-invasive decompression surgery for LSS.
METHODS: Seventy-nine patients with LSS (32 women, mean age: 69.1 ± 9.1 years) who had no segmental instability on dynamic radiographs before undergoing L4-L5 microsurgical decompression and who were followed for at least 2 years postoperatively were analyzed. They were divided into three groups on the basis of the existence and size of L4-L5 facet effusion using preoperative magnetic resonance imaging: grade 0 had no effusion (n = 31), grade 1 had measurable effusion (n = 35), and grade 2 had large effusion (n = 13). Japanese Orthopedics Association (JOA) score, visual analog scale (VAS), and the Short-Form (SF)-36 scores were recorded preoperatively and 12 and 24 months postoperatively.
RESULTS: JOA score; VAS of low back pain, leg pain, and numbness; and SF-36 (physical component summary and mental component summary) scores did not differ significantly between the three groups in every terms (p = 0.921, 0.996, 0.950, 0.693, 0.374, 0.304, and 0.624, respectively, at final follow-up).
CONCLUSIONS: In the absence of radiographic instability, facet joint effusion has no effect on the outcome of less-invasive decompression surgery.

BACKGROUND: Lumbar degenerative spondylolisthesis (LDS) is often diagnosed by conventional supine magnetic resonance imaging (MRI). Numerous studies have shown, however, that the degree of spondylolisthesis can be reduced or disappears when the patient is supine as compared with standing lateral and flexion-extension (SLFE) radiographs.
OBJECTIVE: To compare the sensitivity of supine MRI with SLFE radiographs in patients with L4-L5 LDS.
METHODS: A retrospective imaging study.
METHODS: Included patients diagnosed with L4-L5 LDS with both SLFE films and supine MRI.
METHODS: Lumbar degenerative spondylolisthesis was defined radiographically as a slip greater than 4.5 mm. Mobile LDS was defined as a difference of greater than 3% in slip percentage between lateral radiographs and sagittal MRIs. Additional measurements included L4-L5 facet effusion diameter on axial MRIs. Measurements were performed by two independent examiners. The kappa coefficient was used to assess the interobserver agreement.
RESULTS: Of 103 patients assessed, 68% were women and the average age was 66 years. Lumbar degenerative spondylolisthesis was seen on 101 (98%) lateral films and 80 (78%) MRIs. Average slip was 10.0 mm for lateral standing radiographs and 6.6 mm on MRI (p<.0001). Fifty (48%) patients were identified with mobile LDS. The positive predictive value of facet joint effusion for mobile LDS increased from 52% for effusions greater than 1 mm to 100% for effusions greater than 3.5 mm.
CONCLUSIONS: This study found that MRI had a sensitivity of 78% for detecting L4-L5 LDS compared with 98% for lateral standing films. We also identified facet effusion size as a marker to predict mobile LDS. These findings suggest that, particularly in the setting of facet effusions, the complete workup of patients in whom LDS is possible should include standing radiographs.