Correlation between disc-condyle relationship and the efficacy of conservative treatment in patients with anterior disc displacement without reduction

OBJECTIVE: To investigate the correlation between the positional relationship of the TMJ disc and condyle on MRI and the therapeutic efficacy of temporomandibular intra-articular injection in patients with Anterior Disc Displacement without Reduction(ADDWoR). MATERIALS AND METHODS: Retrospectively included 74 patients (74 joints) with ADDWoR who completed four temporomandibular intra-articular injections and underwent 3-month follow-up. On MRI images at closed-mouth and maximum-opening positions, measured the disc angle relative to the condyle before treatment(Angle), and the disc anterior displacement distance (Distance). Spearman’s rank correlation analysis assessed monotonic relationships between variables. Locally Estimated Scatterplot Smoothing(LOESS) fitted nonlinear trends, with statistical significance tested via the smoothing term in Generalized Additive Models (GAM). The R² value of the LOESS fit was calculated to quantify model explanatory power. Additionally, to determine the optimal cutoff value of the Angle metric for predicting treatment efficacy, ROC curve analysis was performed, and the optimal discriminative threshold was identified by maximizing the Youden index. RESULTS: Scatter plots reveal an S-shaped correlation between Angle and maximum mouth opening (MMO) before and after treatment, while Angle shows a W-shaped correlation with ∆MMO and ∆VAS. ROC curve analysis and determination of the optimal cutoff point by maximizing the Youden index indicate that the optimal cutoff is -20.65°. CONCLUSIONS: This study establishes an MRI based cutoff of -20.65° for the Angle as a preliminary indicator that may help clinicians rapidly identify ADDWoR patients(Patients with Angle < − 20.65°) unlikely to benefit from Sodium Hyaluronate injections(HA). CLINIC RELEVANCE: An MRI derived disc angle relative to the condyle of ≤ − 20.65° can serve as a preliminary indicaor of ADDWoR patients who are unlikely to benefit from temporomandibular intra-articular HA injections, thereby facilitating timely referral for other intervention and safeguarding the optimum window for osteoarthritic change management.