Preoperative Back Pain Severity Influences Postoperative Clinical Outcomes and Trajectory in Patients Undergoing Lateral Lumbar Interbody Fusion

Abstract

Background The Visual Analog Scale (VAS) is a frequently used and validated instrument for assessing a patient’s self-perceived lower back and leg pain and is often employed to assess the efficacy of lumbar surgical intervention. Our study seeks to assess how preoperative severity of presenting lumbar back pain may influence postoperative clinical trajectory and patient-reported outcome measures (PROMs) following lateral lumbar interbody fusion (LLIF) Objective To compare perioperative and postoperative mean patient-reported outcome measures and minimum clinical important difference (MCID) achievement following LLIF in patients stratified by preoperative back pain. Methods A prospectively maintained surgical database was retrospectively reviewed for lumbar operations between June 2005 and December 2021. Inclusion criteria was set as primary, elective, single or multi-level LLIF procedures for degenerative lumbar spinal pathology. Patients undergoing a revision procedure, or surgery indicated for infectious, malignant, or traumatic etiologies were excluded. Additionally, patients who did not fill out a preoperative VAS back survey were excluded as well. Patient demographics, perioperative characteristics, and PROMs were collected. PROMs were administered at preoperative and 6-week, 12-week, 6-month, 1-year, and 2-year postoperative time-points and included Patient-Reported Outcomes Measurement Information System- Physical Function (PROMIS-PF), Visual Analogue Scale (VAS) for back and leg pain, Oswestry Disability Index (ODI), and 12-Item Short Form Physical Composite Score (SF-12 PCS). Postoperative complications were collected for each group as well. Patients were grouped into two cohorts, depending on whether a patient had a preoperative VAS back score of < (mild to moderate back pain cohort or VAS back score ≥ 7 (Severe back pain cohort). Demographic and perioperative characteristics were compared among groups using chi-square and Student’s t-test for categorical and continuous variables, respectively. Mean PROM scores were compared between cohorts at each time point utilizing a unpaired Student’s t-test. Postoperative improvement from preoperative baseline within each cohort was assessed with paired samples t-test. Achievement of Minimum Clinical Important Difference (MCID) was determined by comparing ΔPROM scores to previously established threshold values. MCID achievement rates were compared between groups with chi-squared analysis. Results Patient cohort consisted of 199 patients – 84 patients in VAS back preoperative <7 and 115 patients in the VAS back Preoperative ≥ 7 cohort (Table 1). Significant demographic differences between cohorts were noted for hypertensive status with VAS back Preoperative< 7 cohort having significantly higher rates of hypertension (p<0.029) (Table 1). The majority of patient cohort were male (51.8%), Caucasian (80.8%), non-smokers (81.6%), non-diabetic (85.9%) and utilizing private insurance(62.8%). Majority of patients in both cohorts had presenting spinal pathology of Degenerative Spondylolisthesis (50.8%) with concomitant central stenosis(86.9%) (Table 2). A significantly greater proportion of patients in VAS back preoperative < 7 cohort reported central and foraminal stenosis. No significant differences were noted between cohorts for operative duration, estimated blood loss, or postoperative day of discharge. Patients in the severe back pain cohort demonstrated significantly greater mean postoperative length of stay (53.9 hrs vs 40.6 hrs), greater postoperative VAS pain scores on POD0 and 1, and greater postoperative narcotic consumption on POD1 (p<0.049, all) (Table 2). Rate of postoperative complications did not differ between cohorts. Preoperative mean PROM scores were significantly different for all PROMs collected (Table 4). Cohorts demonstrated significant mean postoperative differences for the following PROMs at the following postoperative time points: VAS back at 6-weeks, 12-weeks, 6-months, and 2-years, VAS leg at 6-months, ODI at 6-weeks, 12-weeks. 6-months, and 2-years, SF-12 PCS at 6-months, and PROMIS-PF at 12-weeks, 6-months, and 1-year(p<0.049, all) (Table 4). Preop VAS back <7 patient cohort demonstrated improvement from preoperative baseline to the 2-year time point for all PROMs collected at all individual postoperative timepoints with the exception of VAS leg at 1-year, ODI at 6-weeks, SF-12 PCS at 6-weeks, and PROMIS-PF at 6-weeks. (Table 4). Preop VAS back ≥ 7 patient cohort demonstrated improvement from preoperative baseline to 2-year time point for all PROMs collected at all individual postoperative timepoints (Table 4). Patients in the VAS back ≥ 7 patient cohort demonstrated greater proportion achieving MCID for VAS back at 6-weeks, 12-weeks, 1-year, and overall as well as for VAS leg at 6-weeks (p <0.043, all) (Table 5). Conclusion Patients in both preoperative back pain severity cohorts demonstrated significant long term clinical improvement from their respective preoperative baselines at 2-years postoperatively for back pain, leg pain, physical function, and general disability. Patients with severe preoperative back pain (VAS >7), however, demonstrated significantly inferior short (6weeks-6months) and long term (2-year) mean outcome scores for back pain and general disability. 2-year mean outcome scores for leg pain and physical function were similar between cohorts. Results from our study may be used by surgeons to understand differing postoperative trajectories of patients undergoing LLIF stratified by back pain severity.