214. MRI proxies for segmental instability in degenerative lumbar spondylolisthesis patients

Abstract

<h3>BACKGROUND CONTEXT</h3> Lumbar degenerative spondylolisthesis (LDS) has a heterogeneous nature. Some patients have a dynamic component of segmental instability associated with LDS which complicates the surgical treatment. The radiological diagnosis of instability has been based on dynamic radiographs. But studies have shown that magnetic resonance imaging (MRI) can show signs of instability. These MRI proxies (MRIPs) for instability involves disc height, facet joint angle and effusion. <h3>PURPOSE</h3> To investigate whether findings on MRI can be proxies for segmental instability in patients with degenerative lumbar spinal stenosis (LSS) and/or LDS. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> Patients with LSS or LDS at L4/L5 scheduled for decompressive surgery with or without fusion from 2010 to 2017, with preoperative standing lateral spine radiographs and supine lumbar MRI and enrolled in Danish national spine surgical database, DaneSpine, 2-year follow-up. <h3>OUTCOME MEASURES</h3> Radiograph: sagittal translation (slip, mm). MRIPs for instability: sagittal translation (slip, mm), facet joint angle (FJA, degree), facet joint effusion (mm), disc height index (DHI, %) and presence of vacuum phenomena. <h3>METHODS</h3> Instability was defined as slip of > 3 mm on standing lateral radiographs. Patients were divided into two groups based on presence of instability. Slips >3mm were considered unstable and slips 3 mm on radiograph as the dependent variable and MRIPs for instability as independent variables. <h3>RESULTS</h3> A total of 232 patients in the cohort divided into two groups: 47 in the stable group and 185 in the unstable group. The two groups were comparable with regard to baseline patient-reported outcome measures (PROMs). Cut points for MRIPs for instability: bilateral FJA = 46°(AUC: 0.644, 95 % CI: [0.566 – 0.722]); bilateral facet effusion = 1.5mm (AUC: 0.601, 95 % CI: [0.536 – 0.666]) and DHI = 13 % (AUC: 0.613, 95 % CI: [0.537 – 0.689]). Logistic regression showed statistically significant association with > 3mm slip on MRI (OR: 221.5; SE: 201.0; 95% CI [37.4 – 1311.5]; p<0.001), bilateral FJA = 46°(OR: 5.6; SE: 3.0; 95% CI [1.9 – 16.1]; p=0.002), bilateral facet effusion = 1.5 mm (OR: 4.5; SE: 2.5; 95% CI [1.5 – 13.7]; p=0.009) and DHI = 13 % (OR: 9.1; SE: 7.5; 95% CI [1.8 – 46.0]; p=0.007). ROC curve with an AUC 0.951. In the absence of slip on MRI logistic regression showed statistically significant association between instability on radiograph and the remaining MRIPs: bilateral FJA = 46°(OR: 3.1; SE: 1.4; 95% CI [1.3 – 7.3]; p=0.008), facet effusion = 1.5 mm(OR: 2.4; SE: 0.9; 95% CI [1.2 – 4.9]; p=0.017) and DHI = 13 % (OR: 12.7; SE: 13.1; 95% CI [1.7 – 96.1]; p=0.014). ROC curve with AUC 0.757. <h3>CONCLUSIONS</h3> Presence of MRIPs for instability defined as >3 mm slip on MRI, bilateral FJA = 46°, bilateral facet effusion = 1.5 mm and DHI = 13% showed statistically significant association with instability and excellent ability to predict instability on standing radiograph at L4/L5 in LSS and LDS patients. Even in the absence of slip on MRI the MRIPs had a good ability to discriminate presence of instability. Further studies will determine whether presences of MRIPs makes radiographs obsolete at diagnosing segmental instability. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.