Preoperative Multifidus and Psoas Major Muscle Quality and Patient-Reported Outcomes After Anterolateral Lumbar Interbody Fusion: Predictors for Preoperative Disability and Back Pain Improvement.

Objective: To investigate associations between preoperative lumbar multifidus muscle (LMM) and psoas major muscle qualities and preoperative and postoperative patient-reported outcomes (PROs) after anterolateral lumbar interbody fusion (A-LLIF).

Methods: A retrospective review was conducted of patients with A-LLIF between L1 and S1 during 2017-2022 at a single institution who had at least approximately 1 year of follow-up and preoperative magnetic resonance imaging available. Preoperative magnetic resonance imaging was analyzed using 2 image analysis platforms (AMBRA and ImageJ). Parameters studied included cross-sectional area (CSA) and fat infiltration indices. Pearson correlation and multiple linear regression analyses were used to study relationships between muscle quality and preoperative and postoperative PROs. Subanalyses were performed for LMM CSA percentiles and stratification of previous surgery.

Results: One hundred patients met the inclusion criteria (mean [standard deviation] age, 65.3 [11.0] years; 57% women, 43% men) during a mean (standard deviation) follow-up period of 1.29 (0.20) years. In total, 207 surgical levels were analyzed. Smaller LMM CSA was significantly associated with greater preoperative disability and preoperative back pain (P < 0.04 [ImageJ]). There were no statistically significant confounding factors. Patients with greater LMM CSA and previous lumbar procedures (n = 42) had more improvement in visual analog scale for lower back pain delta scores (P = 0.02 [ImageJ]; P = 0.04 [AMBRA]). Neither LMM fat infiltration indices nor psoas major muscle morphology influenced PROs.

Conclusions: Significant associations were found between LMM CSA and preoperative disability and back pain. Compared to A-LLIF patients with larger LMM (CSA >12 cm), those with LMM CSA <5 cm had significantly greater preoperative disability and back pain.