Appendix A. Figures

Figure 1. MRI projections of TMJ are oriented on axial imaging. The upper part of the superior belly and running direction of the lateral pterygoid muscle (LPM) can be observed. (A) Axial MR images show orientation of orthogonal sagittal MRI scanning planes. Angle “á” indicates the LPM runs angularly with the scanning plane. (B) Axial MR images show orientation of oblique sagittal MRI scanning planes. Scanning plane is perpendicular to the long axis of the condyle. Angle “â” shows the angle between the main fibers’ running direction of the LPM and the scanning plane. Comparing (A) and (B), note that â < á. Oblique sagittal scanning planes are nearer to parallel to the long axis of the LPM than orthogonal sagittal scanning. (C) Axial MR images show orientation of condyle-lateral pterygoid muscle (CLPM) MRI scanning planes. The scanning planes are parallel to the main fibers’ running direction of the LPM. In CLPM projection the angle between the long axis of the LPM and scanning became zero. Note that when the angle between the long axis of the LPM and scanning plane becomes smaller, the trend of scanning plane is towards parallel to the long axis of the LPM, and more parts of the muscle can be scanned.

Figure 2. Visibility of the LPM in MRI. (A) Both bellies of the LPM can be observed clearly in MRI, classified as V2. Anterior gap (arrow) between the superior belly (SB) and inferior belly (IB) can be seen. (C = condyle) (B) Only one belly of the LPM can be observed in MRI, classified as V₁. In image B, only superior belly of the LPM (SB) is shown. (C = condyle) (C) Non-belly or only insertion part of the LPM can be observed in MRI, classified as V₀. In image C, anterior displaced disc with deformity is found (arrow), but the LPM cannot be observed. (C = condyle).

Figure 3. Normal imaging of the LPM obtained from volunteer and asymptomatic TMJs. (A) Mouth-closed, oblique sagittal, Proton Density (2000/20) (1.5-T magnet) left TMJ image of a 28-year-old male volunteer who had no suspicious clinical signs and symptoms of TMD. The normal LPM structures show as a fan-like muscle from the origins to the neck of the mandibular condyle or disc. A high signal layer of fat tissue separates the superior belly of the LPM (SB) form the inferior belly of the LPM (IB). A high-signal fat layer can be observed between the two bellies (arrow). Near the insertion part of the LPM the two bellies are fused with each other (C = condyle; D = disc). (B) Normal LPM find in mouth-closed oblique sagittal PD (3000/14) MRI image of left TMJ of a 65-year-old female who has experienced pain on jaw movement and clicking of right but no clinical symptoms on left side. On this image of the left TMJ, the disc is seen in normal position. The superior belly (SB) and inferior belly (IB) of the LPM appear normal. Vessels and fat layer can be observed between the two bellies (arrow) (C = condyle).

Figure 4. Hypertrophy of superior belly of the LMP shows in images of a 52-year-old female with chronic facial pain, jaw movement pain and TMJ pain on right side for nine years, symptoms released after splint treatment. Left TMJ recurrently painful and restricted in 3 months. Palpation pain of LPM and locking were detected on the left. Palpation pain of temporal muscles was found on both sides. Anterior disc displacement with non-reduction was found in TMJ on both sides in MRI (SB =  the superior belly; IB = inferior belly of the LPM; C = condyle). (A) In mouth-closed image (oblique sagittal, 3000/14, 1.5T, 3-mm-thick) of left TMJ, hypertrophy of the superior belly (SB) of the LPM is suggested by the evidently enlarged size of the belly (compare with the superior belly of the LPM of right TMJ in image B). Disc is anteriorly displaced and deformed (black arrow). Effusion can be found at bilaminar zone (white arrow). (B) The LPM shows as normal on mouth-closed image of right TMJ (oblique sagittal, 3000/14, 1.5T, 3-mm-thick). The disc shows anterior displacement (arrow). Osteoarthritic change of the condyle can be observed.

Figure 5. Atrophy of the superior belly of the LPM is found in TMJs either with disc in normal position or with disc displacement (C = condyle; D = disc; IB = inferior belly of the LPM). (A) Atrophy of the LPM superior belly (arrow) in a 42-year-old female who has had progressing pain in the TMJ, facial and temporal pain on the right side for five years. Palpation pain in the LPM and movement pain in both TMJs associate with painful clicking. The mouth-closed oblique sagittal PD (3000/15) (1,5-T magnet) MRI image of the right TMJ reveals atrophy and fatty replacement in superior belly of the LPM (arrow). Disc (D) appears in normal position. Condyle hypermobility was found in maximal mouth-open imaging of this joint. (B) Atrophy of the superior belly of the LPM (arrow) is revealed in a 35-year-old female who suffered pain on jaw movement, had difficult in mouth opening as well as facial pain on left TMJ for the past two years. The symptoms could not be improved by splint treatment. Painful locking and severe palpation pain on the LPM are detected on the left side. In mouth-closed, oblique sagittal image of the left TMJ (3000/14, 1.5-T magnet), atrophy of the superior belly of the LPM with large area high signal fatty replacement (arrow) is noted. The inferior belly appears normal. Anterior disc displacement (D) and osteophyte of the condyle (C) are found. The displaced disc cannot reduce in maximal mouth-open image.

Figure 6. Hypertrophy of the inferior belly combined with atrophy of the superior belly of the LPM has been diagnosed by side-to-side comparing in a 41-year-old female with long-term chronic pain on right TMJ for five years with recurrent subluxation. Movement pain, palpation pain of TMJ and masticatory muscles (temporal muscle and LPM) are found on the right side. The mandible is towards the left during mouth opening. No symptoms were found on the left side. Hypermobility of the condyle is found on both sides in maximal mouth open MRI (C = condyle; SB = superior belly; IB = inferior belly). (A) Normal LPM reveals on mouth-closed image of the left TMJ (oblique sagittal, 3000/20). Anterior gap between the two bellies can be clearly observed (arrow). Disc is in normal position. (B) Mouth-closed image of the right TMJ (oblique sagittal, 3000/20) shows hypertrophy of inferior belly combined with atrophy of superior belly (arrow) of the LPM. Atrophy shows as high signal fatty replacement in superior belly of the LPM (arrow). Hypertrophy of the inferior belly (IB) is shown as increased size of the belly (compare with the inferior belly of the LPM on the left side in image A). Note the anterior gap between the two bellies might have been occupied by hypertrophic muscular tissue of the inferior belly. The upper edges of the inferior belly become convex curves. Disc is in normal position.

Figure 7. Atrophy and contracture of the LPM is suspected in a 36-year-old female with occasional locking and chronic pain on both TMJs for 5 years, painful on the left side and restricted in jaw movements for 9 months. Symptoms show no evident improvement after splint and muscle exercising treatment. Severe palpation pain of the lateral pterygoid muscle (LPM) is found on both sides, painful on the left. In MRIs, the anterior displacements of disc are found on both sides. The displaced disc shows reducing on the left TMJ and non-reducing on the right. (A) Atrophy of the superior belly of the LPM is shown in the mouth-closed, oblique sagittal, proton dense image of the right TMJ (3000/14, 1.5-T magnet). High signal fatty replacement tissue can be observed inside the superior belly (white arrow). The inferior belly of the LPM (IB) shows as normal. Disc is anteriorly displaced (black arrow). (C = condyle). (B) In T2-weighted (3000/125, 1.5-T magnet) image mouth-closed oblique sagittal of right TMJ, the high signal fatty replacement in the superior belly of the LPM is observed more clearly (white arrow). The normal inferior belly shows isointense signals in either proton dense or T2-weighted image (compare image A and B). (C = condyle). (C) Atrophy of the superior belly combined with contracture of the inferior belly of the LPM is noticed in the mouth-closed, oblique sagittal, proton dense image of left TMJ (3000/14, 1.5-T magnet). The size of the inferior belly of the left LPM is evidently enlarged comparing to the right side (comparing with image A). Fatty replacement and fibrosis are found in both bellies (small arrows). Anterior disc displacement can be observed (big arrow). (D) T2-weighted (3000/125, 1.5-T magnet) mouth-closed oblique sagittal image of left TMJ, fatty replacement in both belly of the left LPM are evident (arrows).

Figure 8. Contracture and atrophy of the LMP find in a 46-year-old female with a long history of chronic facial pain and movement pain on both sides and occasional locking of left TMJ. Anterior disc displacement with non-reduction is found in the left TMJ in MRI (C = condyle). (A) Mouth-closed, oblique sagittal image of left TMJ (3000/14, 3-mm-thick), the atrophy of superior belly in the LPM shows as high-signal fatty replacement (white arrow). The contracture of the inferior belly shows fibrosis with lower signals (black arrow). The thickened disc is anteriorly displaced (white arrow head). (B) T2-weighted image (3000/125,3-mm-thick) of the TMJ in image A, the fatty replacement of the superior belly of the LPM (big white arrow) and the contracture of the inferior belly with lower signals fibrosis (black arrow) are more clearly observed. Effusion of the bilaminar zone (small white arrow) is suspected.

Figure 9. Disc position of temporomandibular joint (TMJ) is demonstrated by MRI (C = condyle, E = articular eminence) (A) Disc appears in normal position on mouth closed oblique sagittal PD (3000/14) (1,5-T magnet) MR image (arrow). The junction of bilaminar zone and posterior band of disc can be observed at 12 o’clock on the top of the condyle. (B) In the same TMJ of (A), reduction of the disc (arrow) is seen in maximal mouth open direct sagittal T1-weighted (400/12) (1,5-T magnet) MR image. (C) Anterior disc displacement (arrow) is seen in the mouth closed oblique sagittal PD (3000/15) (1,5-T magnet) MR image. (D) Maximal mouth open direct sagittal T1-weighted (400/12) (1,5-T magnet) MR image of TMJ in Fig. C shows reduction of the disc (arrow). Fig. C and D presents anterior disc displacement with reduction (ADDr). (E) Disc anterior displacement (arrow) with deformity is found in mouth-closed oblique sagittal (1,5-T magnet) MR image. Osteoarthritic change of the condyle can be noticed. (F) In the same TMJ of Fig. E, maximal mouth open direct sagittal T1-weighted (400/12) (1,5-T magnet) MR image shows that the disc is still blocked in front of the condyle (arrow) and anterior disc displacement with non-reduction (ADDnr) is considered.

Figure 10. Classifications of the condylar mobility: a horizontal tangential line of the top of the articular fossa and a vertical line through the top of articular eminence are made on sagittal or oblique sagittal image of TMJ. Two lines meet in point “O”. From the point “O”, making angles divide the articular eminence. The top of the articular fossa (TF) is on 0º and the top of the articular eminence (TE) on 90º. (C = condyle, E = articular eminence, TC = top of the condyle) (A) Hypomobility (limitation) of the condyle shows in maximal mouth open imaging. (B) Schematic representation of figure A, hypomobility of the condyle shows as the top of the condyle locates in 0º-90º ( < 90º). (C) Normal mobility of the condyle shows in maximal mouth-open imaging. (D) Schematic representation of figure C, normal motion shows as the top of the condyle located in 90º-120º of the eminence in maximal mouth opening. (E) Hypermobility of the condyle is found. Note that the hypermobilized condyle may put pressure on the anterior part of the disc (arrow). (F) Schematic representation of figure E, the condyle translates excessively, beyond and superior to the level of the articular eminence ( > 20º) in the images of mouth maximal opening.

Figure 11. Imaging abnormalities of the LPM can be found in TMJs with disc in normal position. The normal LPM may be observed in TMJs with severe osteoarthritic changes (C = condyle). (A) Atrophy of the LPM superior belly in a 36-year-old female who has had progressing pain in the TMJ, facial and temporal pain on the right side for five years. Palpation pain in the LPM and movement pain in both TMJs. The mouth-closed oblique sagittal PD (3000/15) (1,5-T magnet) MRI image of the right TMJ reveals atrophy and fatty replacement in superior belly of the LPM (arrow). Disc appears in normal position. In maximal mouth-open images bilateral TMJ hypermobility is found. (B) Normal image of the LPM is found in a 35-year-old male with painful locking, crepitating and movement pain in right TMJ, palpation pain of LPM and head-neck pain on both sides for three years. Pain symptoms have been released evidently after splint and psychical therapies, but mouth-opening limitation became worse. No palpation pain of the LPM and movement pain on both TMJs, slight palpated pain on right TMJ. The width of mouth opening is only 15mm. Mouth-closed oblique sagittal, PD image (3000/20, 3-mm-thick) of right TMJ shows severe erosion on the condyle (C). Disc becomes thinning (arrow). The LPM appears normal.