This study is designed as a prospective cohort study evaluating the effect of temporomandibular joint arthrocentesis on articular capsular width using ultrasonography. The study is being conducted at the Faculty of Dentistry, Van Yuzuncu Yil University, Turkey, in accordance with the principles of the Declaration of Helsinki. Ethical approval has been obtained from the Van Yuzuncu Yil University Clinical Research Ethics Committee (approval no. 2025/02-07, dated February 28, 2025).

The study includes systemically healthy adult participants with unilateral intra-articular temporomandibular disorder who have not responded adequately to at least six months of conservative management, including medication, occlusal splint therapy, or physiotherapy. Exclusion criteria are systemic rheumatologic diseases, bony or fibrous ankylosis of the temporomandibular joint, previous open temporomandibular joint surgery, pregnancy or breastfeeding, and active infection.

All participants undergo unilateral temporomandibular joint arthrocentesis performed under local anesthesia by a single experienced oral and maxillofacial surgeon. A standard two-needle technique is used, and the upper joint compartment is irrigated with 150-200 mL of sterile Ringer's lactate solution. No pharmacological agents are injected after the lavage. The contralateral, asymptomatic joint serves as an untreated control.

Ultrasonographic and clinical assessments are performed at three time points: baseline before the procedure (T0), three months post-arthrocentesis (T1), and six months post-arthrocentesis (T2). The primary outcome is capsular width measured by ultrasonography. Secondary outcomes include pain intensity assessed using the visual analog scale, maximum incisal opening measured in millimeters, and lateral and protrusive mandibular movements.

All ultrasonographic evaluations and clinical measurements are performed by a single oral and maxillofacial radiologist who is independent of the surgical procedure and postoperative patient management, ensuring blinding and minimizing bias. Pain scores are self-reported by patients without investigator interpretation.

The sample size was calculated a priori using G*Power software. Based on previous morphometric data, a minimum of 26 participants was required, and 27 participants were enrolled to account for potential dropouts. Statistical analyses include the Wilcoxon signed-rank test, Friedman test, and Mann-Whitney U test, with a significance level set at p < 0.05.

This study is one of the first prospective clinical trials to evaluate longitudinal changes in temporomandibular joint capsular width using ultrasonography following arthrocentesis. The study has received no external funding, and the authors declare no competing interests.

Temporomandibular joint (TMJ) arthrocentesis is a minimally invasive procedure used to treat intra-articular temporomandibular disorders (TMD) that are unresponsive to conservative management. This prospective cohort study aims to evaluate the effect of TMJ arthrocentesis on articular capsular width using ultrasonography, while concurrently assessing clinical outcomes including pain, maximum incisal opening, and mandibular movements.

The study is conducted at Van Yuzuncu Yil University Faculty of Dentistry, Turkey. Ethical approval was obtained from the Van Yuzuncu Yil University Non-Interventional Clinical Research Ethics Committee (approval no. 2025/02-07, dated February 28, 2025). The study adheres to the principles of the Declaration of Helsinki and follows TREND reporting guidelines for quasi-experimental studies.

All participants undergo unilateral TMJ arthrocentesis performed under local anesthesia using a standard two-needle technique. The upper joint compartment is irrigated with 150-200 mL of sterile Ringer's lactate solution. No pharmacological agents are injected after lavage. The contralateral asymptomatic joint serves as an untreated control.

Ultrasonographic and clinical assessments are performed at three time points: baseline (T0, pre-treatment), three months post-arthrocentesis (T1), and six months post-arthrocentesis (T2). All ultrasonographic evaluations are performed by a single oral and maxillofacial radiologist with 12 years of experience, using a high-resolution ultrasound device with a 14-16 MHz linear transducer. Capsular width is measured as the linear distance between the hyperechoic capsular line and the hyperechoic cortical outline of the mandibular condyle.

Clinical assessments include pain intensity measured by visual analog scale (VAS, 0-10), maximum incisal opening (MIO) in millimeters, lateral mandibular movements (left and right), and protrusive mandibular movement. All clinical measurements are performed by the same blinded assessor.

Statistical analyses are performed using SPSS software. The Friedman test is used for repeated measurements across three time points, followed by post-hoc pairwise comparisons using the Wilcoxon signed-rank test with Bonferroni correction. Between-group comparisons (affected vs. non-affected side) are performed using the Wilcoxon signed-rank test. A p-value of less than 0.05 is considered statistically significant.

Sample size was determined a priori using G*Power software. Based on previous morphometric data, a minimum of 26 participants was required. To account for potential dropouts, 27 participants were enrolled. A post-hoc power analysis based on the observed effect size for the primary outcome (Cohen's d = 1.42) confirmed >99% statistical power.

The study has received no external funding. The datasets are available from the corresponding author upon reasonable request.

INCLUSION CRITERIA:

Systemically healthy adults with unilateral intra-articular TMD (disc displacement with or without reduction) for ≥6 months unresponsive to conservative treatment

EXCLUSION CRITERIA:

Rheumatologic diseases, TMJ ankylosis, previous open TMJ surgery, pregnancy/breastfeeding, active infection

DATA MAY BE AVAILABLE FROM THE CORRESPONDING AUTHOR UPON REASONABLE REQUEST.