P138. Preoperative multifidus muscle quality is associated with patient-reported outcomes after lateral lumbar interbody fusion

Abstract

<h3>BACKGROUND CONTEXT</h3> Lateral lumbar interbody fusion (LLIF) is a commonly performed spinal surgery which involves a transpsoas approach. Despite the association between LLIF and postoperative iliopsoas weakness and iatrogenic neuropraxia of the lumbar plexus, no study has yet examined the effect of psoas or multifidus muscle quality on patient-reported outcomes (PROs). <h3>PURPOSE</h3> This study sought to investigate the effect of psoas and multifidus muscle quality on postoperative subjective patient-reported outcomes following LLIF. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort. <h3>PATIENT SAMPLE</h3> Patients who underwent LLIF with one of two senior surgeons at a single institution with 1-year minimum followup. <h3>OUTCOME MEASURES</h3> PROs evaluated included the Short Form 12-Item Health Survey (SF12), Veterans RAND 12-Item Health Survey (VR12), Oswestry Disability Index (ODI), and Visual Analog Scales (VAS) for Back and Leg pain. <h3>METHODS</h3> Preoperative psoas and multifidus muscle qualities were graded on magnetic resonance imaging (MRI) using two validated classification systems for muscle atrophy (Kader [KCS] and Goutallier [GCS]). Average psoas and multifidus muscle quality was calculated as the mean score from all levels (L1-2 through L5-S1). Univariate and multivariate statistics were utilized to investigate the relationship between psoas/multifidus muscle quality and preoperative, 6 weeks postoperative, and 1 year postoperative PROs. The variables adjusted for in the multivariate analysis included age, sex, BMI, smoking history, diabetes, concomitant posterior percutaneous instrumentation and history of prior open posterior lumbar surgery. <h3>RESULTS</h3> Seventy-four patients (110 levels) with a mean follow-up time of 18.71±8.02 months were included for analysis. Univariate analysis demonstrated that increased psoas atrophy was significantly associated with worse ODI scores (KCS: p=.018; GCS: p=.017). This became non-significant on multivariate analysis. Greater multifidus atrophy was associated with less improvement on ODI (KCS: p=.033; GCS: p=.019), SF12 (KCS: p=.005; GCS: p=.003) and VR12 (KCS: p=.003; GCS: p=.004) on univariate analysis. On multivariate analysis, a higher degree of multifidus atrophy independently predicted less improvement on SF12 (KCS, p=.023; GCS, p=.032) and VR12 (KCS, p=.016; GCS, p=.045). Patients with a history of prior lumbar surgery reported significantly worse pain and disability at all time points (p<.05), as well as less improvement in ODI (p=.043) and VAS Back (p=.028) from preoperatively to 1-year postoperatively. <h3>CONCLUSIONS</h3> Despite the direct manipulation of the psoas muscle inherent to LLIF, preoperative psoas muscle quality did not affect postoperative outcomes. Rather, the extent of preoperative multifidus fatty infiltration and atrophy was more likely to predict postoperative pain and disability. These findings suggest that multifidus atrophy may be more pertinent than psoas atrophy in its association with patient-reported outcome measures after LLIF. Our results also indicate that a history of prior lumbar surgery is associated with significantly less improvement in PROs after LLIF. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.