Paraspinal Muscle Quality and Functional Outcomes Following Lumbar Fusion: A Systematic Review

Purpose Lumbar interbody fusion (LIF) procedures are associated with postoperative paraspinal muscle atrophy and fatty infiltration (FI), which may influence long‐term pain and functional recovery. However, the relationship between muscle quality, both pre‐ and postoperatively, and patient‐reported outcomes remains unclear for patients undergoing lumbar fusion. This correlation was compared between minimally invasive surgery (MIS) and conventional open surgery (COS) approaches to assess differences in postoperative muscle preservation and functional outcomes. Methods A systematic review, conducted following PRISMA guidelines and registered in PROSPERO (CRD420250650064), examined studies found in PubMed, Scopus, and Web of Science through February 2025. Studies were included if they assessed adult patients undergoing LIF with preoperative CT or MRI evaluation of the multifidus (MF) or erector spinae (ES) and reported postoperative cross‐sectional area (CSA), FI, or patient‐reported outcome measures (PROMs). Results Twenty studies met inclusion criteria; risk of bias was assessed with ROBINS‐I for 19 non‐randomized studies and RoB 2 for one randomized trial. Seven of nine COS intervention studies found significant pre‐ to postoperative muscle damage, including all three COS‐only studies, measured by CSA and FI. Two of twelve MIS intervention studies found significant pre‐ to postoperative muscle damage, with four of six direct comparisons found smaller declines in CSA, increases in FI, or both after MIS compared to COS in at least one muscle or setting. Higher preoperative muscle quality, particularly lower FI, and smaller pre‐ to postoperative muscle changes were associated with greater PROM improvements. Across the PROM‐focused studies, four of the five reported that higher preoperative CSA or lower FI predicted better postoperative improvements in functional outcomes, with one identifying that MF FI of 61% or greater as a threshold for failing to achieve clinically meaningful ODI improvements. Conclusion MIS techniques were associated with a decrease in pre‐ to postoperative FI compared with COS, although PROM improvement occurred across both approaches. While preoperative paraspinal muscle quality and size decreases are generally smaller with better functional outcomes following postoperative LIF, this relationship is not consistently observed across all studies or surgical techniques. These findings suggest that the current imaging‐based biomarkers may not fully capture the multifactorial nature of functional recovery and underscore the need for further research into additional predictors of muscle recovery.