A possible etiology of the internal derangement of the temporomandibular joint based on the MRI observations of the lateral pterygoid muscle

Abstract

The purpose of this study was to evaluate the relationship of the temporomandibular joint (TMJ) internal derangement and lateral pterygoid muscle (LPM) by magnetic resonance imaging (MRI). In this study, 115 subjects with TMJ internal derangement (total 230 TMJs) and 21 subjects without clinical symptoms (total 42 TMJs) were included. TMJ disc position and LPM were evaluated using MRI. LPM attachments were categorized into two different types: type 1, where fibers of the superior head of the LPM (SLPM) were attached to the disc and fibers of the inferior head of the LPM (ILPM) were attached to condyle, and type 2, where fibers of the SLPM were attached to the disc and condyle, and fibers of the ILPM were attached to condyle. The presence of muscle atrophy and degeneration were also evaluated. LPM attachments were observed in two different parts. Disc displacements were common in the muscle attachments of both types. Type 1 muscle attachments were seen in 85.9% of all the anterior disc displacement without reduction (ADD) TMJs (total 64 TMJs). Atrophy was seen in a higher proportion (43.7%) in TMJs with ADD (28/64) than in TMJs with normal and anterior disc displacement with reduction (ADDR). Out of 74 TMJs with atrophy, 68 had type 1 muscle attachment. Four TMJs had atrophy in both superior and inferior heads of the lateral pterygoid. However, atrophy was not present only in the ILPM. It has been concluded that since the SLPM only attached to the disc in type 1, the disc may displace anteriorly very easily. Therefore, this situation will reduce the function of the SLPM. Reduced muscle function may cause muscle atrophy. The activity of the SLPM may be more reduced since the disc permanently dislocated in TMJs with ADD. Finally, spasm of the LPM causes disc displacement and atrophy and then the degeneration of the LPM may follow disc displacement.

Correlation between the lateral pterygoid muscle attachment type and temporomandibular joint disc position in magnetic resonance imaging

“…In contrast to our results, Taskaya-Yilmaz et al 10 and Omami et al 7 found only two heads of the LPM. However, their studies were based on samples smaller than that in our investigation, which may explain the different outcomes.…”

“…This finding stands in contrast to most of the studies investigating this relationship. Omami et al, 7 Taskaya-Yilmaz et al, 10 Imanimoghaddam et al 6 and Dergin et al 5 did not find a statistically significant relationship between these variables. This discrepancy can partly be explained by the fact that our study group was larger and that we used a different methodology for disc assessment.…”

“…5,6,10,14 Such an association, however, has not been established. [5][6][7]10 Nevertheless, studies investigating the correlation between the LPM attachment type and TMJ internal derangement analyzed the disc position only in the sagittal plane. Assessment of the disc in the sagittal plane is suitable for the diagnosis of anterior disc displacement, which is one of the most prevalent types.…”

Eminectomy for the Management of Closed Lock of Temporomandibular Joint

“…The decrease in size of the condyle increases joint space and thereby reduces pain. Taskaya et al [4 ], in a magnetic resonance imaging (MRI) study of 115 patients with TMJ ID and 21 subjects without clinical symptoms, found that spasm of lateral pterygoid muscle causes disc displacement and atrophy following degeneration of the lateral pterygoid muscle. A case of closed lock surgically corrected by performing eminectomy is being presented.…”

Pathologic Changes of the Lateral Pterygoid Muscle in Patients with Derangement of the Temporomandibular Joint Disk: Objective Measures at MR Imaging

“…1,2 There has been extensive investigation of the anatomic relationship of the LPM to the condylar head, disk, and capsule, as well as multiple electromyographic studies that demonstrate the patterns of contraction of the muscles of mastication during both rest and motion. [3][4][5][6][7] Wang et al 3 recently demonstrated maximal activity of the superior head of the lateral pterygoid muscle (SHLP) during clenching, with its major function as a stabilizer of the disk and condylar head.…”