TMJ Effusion and Anterior Disk Displacement: A Systematic Review and Meta-Analysis

Background: The objective of this study was to assess the association between joint effusion and anterior disk displacement. Specifically, it aimed to determine whether joint effusion is more associated with anterior disk displacement without reduction (ADDWOR) compared with displacement with reduction (ADDWR). Methods: The literature review for this study was conducted using PubMed, Scopus, SciELO, the Virtual Health Library (including LILACS), and The Cochrane Library (Trials and Reviews). Grey literature was also searched, specifically: ClinicalTrials.gov and the International Clinical Trials Registry Platform (ICTRP Search Portal, World Health Organization). The review was conducted according to the PRISMA 2020 statement, and the search strategy followed the PECO (Population, Exposure, Comparison, Outcome) protocol. Study quality was assessed with the Newcastle-Ottawa Scale (cohort studies) and the Joanna Briggs Institute critical appraisal tools (cross-sectional and case-control studies). All raw event counts were independently re-extracted and cross-checked against the original source tables for every included study, and a design-effect sensitivity analysis was performed to explore the potential impact of the non-independence of bilaterally assessed joints. Results: Seventeen studies were included, comprising 4254 temporomandibular joint (TMJ)-level observations (2256 ADDWOR joints, 1998 ADDWR joints) from approximately 2980 patients. The meta-analysis showed a statistically significant association between joint effusion and disc displacement, with a random-effects odds ratio (OR) of 1.70 (95% CI: 1.42-2.03; p < 0.0001; I² = 24.1%), consistent with the common-effect model (OR = 1.72; 95% CI: 1.50-1.97; p < 0.0001). The pooled estimate was not materially altered by the omission of any single study; Egger's test did not detect funnel-plot asymmetry (p = 0.94), although publication or small-study effects cannot be excluded; and an approximate design-effect sensitivity analysis for bilateral joints, under assumed intraclass correlation coefficients of 0-0.8, gave similar estimates. These results indicate an unadjusted joint-level association: joint effusion was more frequently observed in joints with anterior disc displacement without reduction (ADDWOR) than in joints with displacement with reduction (ADDWR). Conclusions: These findings indicate a significant unadjusted joint-level association between joint effusion and disc displacement without reduction. Because in all included studies disc position and effusion were assessed on a single MRI examination, this association should not be interpreted as evidence of causality; further prospective investigation is needed to confirm the association and clarify the underlying mechanisms.