[Diagnostic value of symptomatic condylar angle for limited mouth opening in patients with temporomandibular disorders based on MRI].

Objective: To investigate the diagnostic value of MRI-measured symptomatic condylar movement angle in assessing limited mouth opening among temporomandibular disorder (TMD) patients. Methods: A retrospective cross-sectional study was conducted. Patients with unilateral TMD who underwent their first temporomandibular joint (TMJ) MRI examination at the TMJ specialty clinic of Beijing Friendship Hospital, Capital Medical University, between July 2017 and June 2024 were enrolled. All patients were categorized based on maximum pain-free opening (MMO) as limited opening (MMO<38 mm) or unrestricted opening (MMO≥38 mm). Age-based groups included adults (≥18 years) and minors (<18 years). The same patient's TMJ were further classified as symptomatic or asymptomatic sides. Bilateral condylar angles were measured on sagittal MRI images of the condyles in the open-mouth position. The angular difference and mean values were calculated. Diagnostic performance for limited mouth opening was evaluated using area under the receiver operating characteristic (ROC) curve (AUC), sensitivity, and specificity for each condylar angle metric. Differences in cut-off values between adult and minor groups were explored. Results: A total of 130 TMD patients aged [M(Q1, Q3)] 18.0 (15.0, 31.5) years were included, with 27 males (20.8%) and 103 females (79.2%). There were 59 cases (45.4%) who had limited mouth opening, while 71 cases (54.6%) did not have this symptom; 63 cases (48.5%) were minors, and 67 cases (51.5%) were adults. Among all patients, the AUC for diagnosing limited mouth opening using the symptomatic side condylar angle (0.880, 95%CI: 0.822-0.938) was higher than that using the asymptomatic side condylar angle (0.768, 95%CI: 0.687-0.848) and the bilateral condylar angle difference (0.727, 95%CI: 0.639-0.814) (both P<0.05). The condylar angle on the symptomatic side demonstrated a cut-off value of 89.0° for diagnosing limited mouth opening in the adult group, with a sensitivity of 96.7% and specificity of 83.8%; in the minor group, the cut-off value was 80.5°, with a sensitivity of 75.9% and specificity of 70.6%. The AUC for diagnosing limited mouth opening using the condylar angle on the symptomatic side in the adult group (0.968, 95%CI: 0.933-1.000) was significantly different from that in the minor group (0.779, 95%CI: 0.667-0.892) (P=0.002). Conclusions: The symptomatic condylar angle demonstrates high diagnostic efficacy for limited mouth opening in TMD patients. The cut-off value of the condylar angle differs between adult and minor patients.