Paraspinal Musculature and Adjacent Segment Disease After Lumbar Fusion: A systematic review and meta-analysis of fusion with and without posterior instrumentation.

Abstract

Adjacent segment disease (ASD) is the principal long-term complication following lumbar fusion, contributing to pain, disability, and the need for revision surgery. While biomechanical and patient-related factors have been proposed, iatrogenic injury to the paraspinal musculature during posterior exposure may also promote ASD. Minimally invasive anterior, oblique, and lateral approaches, which avoid posterior dissection, may mitigate this risk. To compare rates of radiographic (rASD) and symptomatic ASD, ASD-related reoperation, and secondary outcomes including fusion success, cage subsidence, and patient-reported outcomes between standalone anterior, oblique, or lateral lumbar interbody fusion (ALIF, OLIF, LLIF/XLIF) and fusion procedures involving posterior dissection and pedicle screw placement. Systematic review and Bayesian meta-analysis of comparative studies. Adults (≥18 years) undergoing lumbar fusion for degenerative pathologies including spondylolisthesis, stenosis, and degenerative disc disease. Primary outcomes were diagnosis of rASD, reoperation due to ASD and all cause reoperations. Secondary outcomes included fusion success, cage subsidence, perioperative complications, and patient-reported outcomes (Oswestry Disability Index, VAS back and leg). PubMed, Embase, and Scopus were searched (09/09/2025) without date restriction per PRISMA guidelines (PROSPERO CRD420251115394). Comparative studies of standalone versus posteriorly instrumented fusion were included. Data extraction and ROBINS-I bias assessment were performed independently by two reviewers. Bayesian random-effects models were used for all outcomes. Binary outcomes were analyzed with binomial models; continuous outcomes used normal likelihoods. Analyses were conducted in Python. Twenty-seven studies (4,388 patients: 1,877 no posterior instrumentation; 2,511 posterior instrumented) met inclusion criteria. All were rated at serious risk of bias. Standalone fusion was most commonly ALIF (8 studies), followed by OLIF (6) and LLIF/XLIF (4). Fusion without posterior instrumentation was associated with a significantly lower odds of rASD (OR 0.51, 95%CI 0.28-0.96) and reoperation for ASD (OR 0.58, 95%CI 0.33; 0.86). There was no difference in all-cause reoperation (OR 0.84, 95%CI 0.55-1.30), fusion success (OR 1.33, 95%CI 0.91; 1.98), or perioperative complications (OR 0.99, 95%CI 0.71-1.31). Standalone fusion had higher odds of cage subsidence (OR 1.99, 95%CI 1.22; 3.12). ODI scores were significantly lower (MD -1.37, 95%CI -2.76; -0.03), while VAS back and leg scores did not differ significantly between groups. Standalone anterior, oblique, and lateral lumbar fusions, which avoid posterior muscle dissection and pedicle screw fixation, were associated with reduced rates of ASD and ASD-related reoperation compared with posteriorly instrumented fusions. This is consistent with the hypothesis that preservation of the paraspinal musculature, particularly the multifidus, may be associated with less risk of adjacent segment degeneration. Although cage subsidence is more frequent, overall fusion success and functional outcomes appear comparable. Prospective randomized trials are warranted to confirm causality due to potential for bias among the included studies.