Exploring the Link Between Temporomandibular Disorders and Sacroiliac Joint Kinematics

Temporomandibular disorders (TMDs) are a group of musculoskeletal conditions affecting the temporomandibular joint (TMJ), masticatory muscles, and associated structures. Symptoms such as clicking, pain, and limited range of motion can result from muscle tension, parafunctional habits, and psychosocial factors like stress or depression.

TMDs are classified into physical (Axis I) and psychological (Axis II) dimensions. Anterior disc displacement with reduction (ADDR) is the most common form, characterized by a clicking sound during jaw movements.

Biomechanically, the TMJ is linked to other body regions, including the cervical spine and pelvic girdle, through myofascial and dural connections. Some studies have proposed a cranium-to-sacrum transmission mechanism via the dura mater, potentially influencing posture and sacroiliac joint (SIJ) function. Despite these proposed links, dynamic studies evaluating the functional interaction between TMD and pelvic kinematics remain limited.

A study published in BMC Musculoskeletal Disorders aimed to assess pelvic girdle (SIJ) kinematics in individuals with chronic TMD (specifically ADDR) using a 3D motion analysis system and to examine any relationships between TMJ dysfunction and sacral movement during trunk flexion.

Methodology
Forty participants aged 20–40 were divided into two groups: 20 patients with chronic TMD (minimum 6 months of ADDR confirmed by DC/TMD) and 20 matched healthy controls. SIJ movement was recorded during forward trunk flexion using reflective markers and a 3D motion analysis system.

Participants performed three trunk flexions while SIJ translations and rotations were measured in three planes (sagittal, frontal, and transverse). The study controlled for potential confounders such as leg length discrepancy, spinal deformities, muscle tightness, and BMI.

Key Findings

• Baseline SIJ Differences: Significant differences were observed between groups at the starting position (standing). TMD patients showed greater linear sacral displacement in the sagittal plane and reduced angular sacral rotation around the frontal axis, suggesting altered sacral alignment compared to healthy individuals.
• No Dynamic Differences: During the forward flexion task, no significant between-group differences in sacral kinematics were found, indicating that dynamic movement might mask or normalize static positional discrepancies.
• TMD Severity and SIJ Alignment: The severity of TMD (but not TMJ pain or range of motion) was significantly correlated with sagittal plane sacral displacement and frontal axis rotation at rest. More severe TMD corresponded with greater sacral misalignment.
• No Link with TMJ ROM: There was no significant difference in TMJ range of motion between groups, and no relationship was found between TMJ mobility and SIJ movement, which aligns with the classification of ADDR as a non-restrictive form of TMD.

Clinical Implications
This study provides preliminary evidence that chronic TMD may be associated with altered static sacroiliac joint alignment, particularly in the sagittal plane. However, these changes do not persist or translate into altered movement during functional tasks, suggesting the possibility of postural compensation mechanisms or adaptation over time.

Therapists should consider:

• Screening for pelvic alignment issues in patients with chronic TMD.
• Integrating postural and biomechanical assessments beyond the cervical and craniofacial regions.
• Recognizing that TMD severity, not pain intensity, may better predict global postural or alignment deviations.

Limitations and Future Directions

• The study was limited by its small sample size and cross-sectional design, preventing causal inferences.

Conclusion
Chronic TMD—especially anterior disc displacement with reduction—is associated with subtle alterations in static sacroiliac joint positioning, but these differences are not evident during dynamic trunk movement. TMD severity, rather than pain or jaw mobility, appears linked to these changes. These findings support a biomechanical connection between the TMJ and pelvic girdle, reinforcing the importance of a whole-body approach in the assessment and treatment of patients with chronic musculoskeletal dysfunctions.