Correlation between the number and pattern of lateral pterygoid muscle attachments and pathologic changes of the temporomandibular joint according to Hegab stages based on MRI findings of 510 joints.

The correlation between the lateral pterygoid muscle attachment type to the disc-condyle complex and temporomandibular joint (TMJ) dysfunction has rarely been discussed and remains unclear. The study aimed to assess the correlation between the number and pattern of LPM attachment and the pathologic findings of the temporomandibular joint based on MR imaging findings. The study population comprised consecutive TMD patients. They were included if they had TMD requiring MRI examination for evaluation of internal derangement. Patients with either TMJ clicking, TMJ locking, restricted movement of the jaw, or pain in the TMJ region were included in the study. Patients with rheumatoid arthritis, condylar hyperplasia, and congenital craniofacial syndrome, and those who had undergone previous TMJ surgery were excluded from this study. Variations of the number of heads and the attachment pattern of the LPM to DCC was evaluated using MRI in the oblique sagittal and coronal images. The variation of the LPM heads and attachment patterns was correlated with pathologic changes of the TMJ. The sample size calculation was performed using G*Power version 3.1.9.2. The significance level was set at 0.05. The data were analysed using Instat statistical software (GraphPad Software, Inc., La Jolla, CA). A total of 255 patients (510 joints) were enrolled in the study. Of these, 52 (104 joints) were male and 203 (406 joints) were female, with ages ranging from 18 to 67 (mean age 32.05). Patients with internal derangement of TMJ were included. According to the data obtained from MRI examinations, LPM attachments to the disc condyle complex were categorized into four different types. The most common variation (type II-B) was shown to be two heads with the upper head attached to the disc and condyle, and the lower to the condyle. There was a statistical correlation between the type of LPM attachment and the pathological changes within the joint regarding disc displacement, osteoarthritis, joint effusion, disc degeneration, and condylar translation (P = 0.0003, r = -0.87, P < 0.0001& r = 0.29, P = 0.0002 & r = -0.93, P = 0.0061 & r = -0.98, and P = 0.0004, r = -0.54 respectively). The current study shows a statistically significant direct correlation between LPM attachment and TMJ osteoarthritis, while the disc-condyle relationship, joint effusion, disc degeneration, and condylar translation shown significant inverse correlations with LPM attachment patterns.