| Magnetic resonance imaging of the lateral pterygoid muscle in temporomandibular disorders | ||
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The relationship between LPM with normal or abnormal MRI findings and disc positions is presented in Table 7. Normal and abnormal MRI findings of the LPM exhibited no significant difference in TMJs with or without disc displacements (P = 0.082, Pearson’s Chi-square test, df = 2). Abnormal imaging of the LPM could be observed in TMJs with disc in normal position (66.7%, 142/213)(Fig. 11A) as well as in TMJs with ADDr (76.9%, 103/134) or ADDnr (74.8%, 92/123).
Table 7. MRI Findings of LPM and Disc Position in Patients with TMD
| NP | ADDr | ADDnr | Total | |
|---|---|---|---|---|
| LPMn | 71 | 31 | 31 | 133 |
| LPMan | 142 | 103 | 92 | 337 |
| Total | 213 | 134 | 123 | 470 |
| LPM = lateral pterygoid muscle, TMJ = Temporomandibular joint, NP=disc in normal position; ADDr = Anterior disc displacement with reduction, ADDnr = Anterior disc displacement with non-reduction, LPMn = the LPM shows normal in MRI, LPMan = the LPM shows abnormal in MRI, Pearson’s Chi-Square test, P=0.082 > 0.05 | ||||
Noticeable, normal imaging of the LPM could be found in 39.4% TMJs with disc displacement, even in some TMJs with severe osteoarthritic changes (Fig. 11B).
In order to analyze the possible reason which might lead to pathological changes of the LPM in TMJs with disc in normal position,-the relationship between disc position and condyle mobility in MRI was investigated. The results are presented in Table 8. Condyle hypermobility was mostly found in TMJs with disc in normal position (57.2%, 91/159). Condyle hypomobility was significantly more observed in TMJs with ADDnr (41.8%, 66/158)(P < 0.001, Pearson’s Chi-square test).
Table 8. Disc Position and Condyle Mobility in MRI in Patients with TMD
| NP | ADDr | ADDnr | Total | |
|---|---|---|---|---|
| Hypomobility | 50 | 42 | 66*** | 158 |
| Normal mobility | 72 | 36 | 45 | 153 |
| Hypermobility | 91*** | 56 | 12 | 159 |
| Total | 213 | 134 | 123 | 470 |
| LPM = lateral pterygoid muscle; TMJ = Temporomandibular joint, NP=disc in normal position; ADDr = Anterior disc displacement with reduction, ADDnr = Anterior disc displacement with non-reduction, Pearson’s Chi-Square test, ***P < 0.001 | ||||
The clinical symptoms and disc position of the patients with symptomatic TMJ hypermobility were studied in Paper IV. Clinical symptoms of TMD were found in TMJs either with disc in normal position or with disc displacement (Table 1 in Paper IV). Palpation pain of the LPM was significantly associated with the clinical symptoms in the TMJs without disc displacements (52.2%, 48/92) (P < 0.001, Pearson Chi-square test, Table 2 in Paper IV).