Evaluation of lateral pterygoid muscle in patients with temporomandibular joint anterior disk displacement using T1-weighted Dixon sequence: a retrospective study

Abstract

Background: Pathological alterations of lateral pterygoid muscle (LPM) are implicated in temporomandibular joint anterior disk displacement (ADD). However, quantification of the fatty infiltration of LPM and its correlation with ADD have rarely been reported. The aim of this study was to evaluate the fatty infiltration, morphological features and texture features of LPM in patients with ADD using T1-weighted Dixon sequence.

Methods: This retrospective study included patients who underwent temporomandibular joint MRI with T1-weighted Dixon sequence between December 2018 and August 2020. The temporomandibular joints of the included patients were divided into three groups according to the position of disk: Normal position disk (NP) group, Anterior disk displacement with reduction (ADDWR) group and Anterior disk displacement without reduction (ADDWOR) group. Fat fraction, morphological features (Length; Width; Thickness), and texture features (Angular second moment; Contrast; Correlation; Inverse different moment; Entropy) extracted from in-phase image of LPM were evaluated. One-way ANOVA, Welch's ANOVA, Kruskal-Wallis test, Spearman and Pearson correlation analysis were performed. Intra-class correlation coefficient was used to evaluate the reproducibility.

Results: A total of 53 patients with 106 temporomandibular joints were evaluated. Anterior disk displacement without reduction group showed higher fat fraction than normal position disk group (P = 0.024). Length of LPM was negatively correlated with fat fraction (r = -0.22, P = 0.026). Angular second moment (ρ = -0.32, P < 0.001), correlation (ρ = -0.28, P = 0.003) and inverse different moment (ρ = -0.27, P = 0.005) were negatively correlated with fat fraction, while positive correlation was found between entropy and fat fraction (ρ = 0.31, P = 0.001). The intra-class correlation coefficients for all values were ranged from 0.80 to 0.97.

Conclusions: Patients with ADDWOR present more fatty infiltration in the LPM compared to NP or ADDWR patients. Fatty infiltration of LPM was associated with more atrophic and higher intramuscular heterogeneity in patients with ADD. Fat fraction of LPM quantitatively and noninvasively evaluated by Dixon sequence may has utility as an imaging-based marker of the structural severity of ADD disease process, which could be clinical helpful for the early diagnose of ADD and predication of disease progression.

Keywords: Anterior disk displacement; Dixon sequence; Fatty infiltration; Lateral pterygoid muscle; Texture analysis.

Fig. 1

Flow chart of subject collection and exclusion criteria TMJ  Temporomandibular joint, PACS  Picture archiving and communication system, LPM, Lateral pterygoid muscle, NP, Normal position disk, ADDWR, Anterior disk displacement with reduction, ADDWOR, Anterior disk displacement without reduction

Fig. 2

Four phases of images obtained by coronal T1-weighted Dixon sequence. (A) In-phase image. (B) Opposed-phase image. (C) Fat image. (D) Water image

Fig. 3

Fat fraction of lateral pterygoid muscle (LPM) in normal position disk (NP) group, anterior disk displacement with reduction (ADDWR) group and anterior disk displacement without reduction (ADDWOR) group. Yellow dotted line shows the ROI in in-phase image (a) and fat fraction image (b). The LPM of NP group shows no obvious fatty infiltration in in-phase image (c) and fat fraction image (d). (e, f) Slight fatty infiltration (white arrow headed) showed in the white dotted line in the ADDWR group, (g, h) while obvious fatty infiltration (red arrow headed) showed in the ADDWOR group

Fig. 4

The morphological features of lateral pterygoid muscle (LPM) in normal position disk (NP) group, anterior disk displacement with reduction (ADDWR) group and anterior disk displacement without reduction (ADDWOR) group. The measurement of length (a), width (b) and thickness (c) of LPM. As the anterior disk displacement became more and more severe, (d, g, j) the length and (e, h, k) the width of LPM showed a tendency of decrease but the thickness of LPM (f, i, l) increased firstly and then decreased

Fig. 5

The Fat fraction and morphological features of lateral pterygoid muscle in normal position disk (NP) group, anterior disk displacement with reduction (ADDWR) group and anterior disk displacement without reduction (ADDWOR) group. (a) There is a significant difference of fat fraction between NP group and ADDWOR group. (b, c) There is no significant difference of length and width among three groups. (d) There is a significant difference of thickness between NP group and ADDWOR group, ADDWR group and ADDWOR group

Fig. 6

Relationship between fat fraction and age, and morphological features of lateral pterygoid muscle. NP, Normal position disk, ADDWOR, Anterior disk displacement without reduction. (a, c) There is a moderate positive correlation between fat fraction and age in NP group and ADDWOR group, (b) while no significant correlation is found in ADDWR group. (d) There is a weak negative correlation between fat fraction and length, (e, f) while fat fraction is not found significantly correlated with width and thickness

Fig. 7

Relationship between fat fraction and texture features extracted from in-phase image of T1-weighted Dixon sequence of lateral pterygoid muscle. ASM,  Angular second moment, CON , Contrast, COR , Correlation, IDM, Inverse different moment, ENT, Entropy. (a) Fat fraction was moderately negatively correlated with ASM, (c, d) and was weakly negatively correlated with COR and IDM. (e) Fat fraction was moderately positively correlated with ENT, (b) but not significantly correlated with CON