Alteration In Tmj

Dentomaxillofacial Radiology (2002) 31, 373 ± 378 ã 2002 Nature Publishing Group. All rights reserved 0250 ± 832X/02 $25.00 www.nature.com/dmfr

RESEARCH

Alteration of the horizontal mandibular condyle size associated with temporomandibular joint internal derangement in adult females H Kurita*,1, A Ohtsuka1, H Kobayashi1 and K Kurashina1 1

Department of Dentistry and Oral Surgery, Shinshu University School of Medicine, Matsumoto, Japan

Objectives: The purpose of this retrospective study was to analyse the relationship between horizontal size of the mandibular condyle and internal derangement (ID) of the temporomandibular joint (TMJ). Methods: One hundred and thirty-nine joints in 88 women aged over 18 years were included in this study. The horizontal condylar size was measured in the antero-posterior and medio-lateral (ML) dimensions using axial magnetic resonance (MR) images. Radiological ®ndings of ID were also assessed from MR imaging. Results: The condyles in the joints with permanent disk displacement were smaller than those in joints without displacement in both dimensions (Fisher's protected least signi®cant di€erence, P50.05). There were statistically signi®cant correlations between horizontal condylar size in the ML dimension and both disk morphology and radiological stage of ID (Spearman's correlation coecient by rank, P50.05). Conclusions: The results of this study suggest a possible relationship between horizontal condylar size and disk displacement. It is also suggested that the condyle becomes smaller in the ML dimension with advancement of ID. Dentomaxillofacial Radiology (2002) 31, 373 ± 378. doi:10.1038/sj.dmfr.4600727 Keywords: temporomandibular joint; condylar size; internal derangement Introduction A variety of condylar OA (osteoarthritis/osteoarthrosis) changes are observed in patients with internal derangement (ID) of the temporomandibular joint (TMJ).1 These morphological changes may lead to alteration of the size of the TMJ condyle. De Bont et al.2 have described a reduction in TMJ size in joints with disk displacement and perforation. However, a few other investigators have focused on the changes of the TMJ condylar size associated with ID.3,4 Experimentally-induced displacement of the TMJ disk induced shortening of the mandibular ramus on the ipsilateral side.5 It has also been reported that ID may be associated with disturbed facial skeleton growth such as retrognathia and mandibular asymmetry.6,7 These results suggest a possible relationship *Correspondence to: H Kurita, Department of Dentistry and Oral Surgery, Shinshu University School of Medicine, 3-1-1, Asahi, Matsumoto, 390-8621, Japan; E-mail: [email protected] Received 29 January 2002; revised 18 June 2002; accepted 12 August 2002

between disk displacement and changes in TMJ condylar size. The aim of this study was to analyse the relationship between disk displacement and the size in the anteroposterior (AP) and medio-lateral (ML) dimensions of the TMJ condyle. We also tested the hypothesis that the size of the TMJ condyle is altered with advancing ID, anticipating controversy over whether the change of the TMJ condylar size is a cause or a result of the TMJ ID. Materials and methods This study was based on examining selected subjects from among a consecutive series of 145 patients who underwent magnetic resonance (MR) imaging between 1994 and 2000. Patients under the age of 18 years were excluded from this study because their characteristic TMJ condyle pro®le has yet to be developed,8,9 and only women were included because of the speculation

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that there might be di€erences in the size of the TMJ condyle between sexes. Consequently, 139 joints in 88 women were included in this study. The mean age was 33.5 years (s.d. 14.3), with a range of 18 ± 80 years. An MR imaging study was performed with a 1.5tesla system (General Electric Medical System, Milwaukee, WI, USA) with a TMJ surface coil (6.0 mm in diameter). An initial axial localizer (TR 300 ms, TE 16 ms, FOV 24 cm, 5-mm slice thickness, 2566192 scanning matrix) that was nearly parallel to the Frankfort horizontal plane and could maximally visualize the lateral and medial poles of both condyles was obtained in the closed-mouth position. Five 3-mm slice thickness, oblique sagittal images of the TMJ (TR 500 ms, TE 15 ms, FOV 16 cm, 2566192 scanning matrix) were then obtained with the jaw in each of the closed- and open-mouth positions. Oblique sagittal MR images were assessed for disk displacement, degree of disk displacement, and disk morphology at a representative center depth of the TMJ (on a sagittal image that crossed the middle third of the condyle and where the disk was imaged the clearest). Disk displacement was de®ned as previously reported.10,11 The degree of disk displacement was classi®ed according to the criteria reported by Takase et al.12 Namely, in the sagittal images, disk displacement was classi®ed as slight if the posterior band of the anteriorly displaced disk touched the condyle in the closed-mouth projection, moderate if the posterior band was located within the posterior slope of the articular eminence, and severe if the posterior band was located under the articular eminence or more anterior. Disk morphology was classi®ed in the closedmouth projection in the sagittal plane and categorized as either biconcave, biplanar, biconvex, folded, or amorphous.13,14 Each MR image was separately evaluated by a trained radiologist and one of the authors (H Kurita). Any disagreements were discussed until consensus was reached. All joints were subsequently classi®ed into one of the ®ve radiological stages of ID described by Wilkes15 and Schellhas,16 as shown in Table 1. Because we had no data on the presence of perforation of the disk and/or the attachment, we could not di€erentiate stage 4 from stage 5. A method for describing the horizontal condyle size is illustrated in Figure 1. In the printed image of the

initial axial localizer (magni®cation: 0.4*1.1, mean 0.6 (s.d. 0.2)), a line was drawn through the medial (m) and lateral poles (l) of the condyle. A perpendicular line was drawn to bisect the line m ± l, and this intersected the anterior edge and the posterior edge of the condyle at points a and p, respectively. The distances of l ± m and a ± p were measured in half millimeters with a ruler. The horizontal sizes of the condyle in the AP and ML dimensions were obtained by computing the individual magni®cation in each patient as follows: (medio-lateral dimension)=(the distance of m ± l)/(magni®cation) and (antero-posterior dimension)=(the distance of a ± p)/(magni®cation). The measurements were taken two separate times by one of the authors (H Kurita) blinded to the results of the MRI study. The di€erence between the ®rst and second measurements was little (average, 70.06; standard deviation, 1.63; skewness, 71.01; kurtosis, 4.48; median, 0.00). The horizontal sizes were then obtained by calculating the mean value for each patient. Thereafter, the horizontal sizes of the condyles were compared among the joints with no disk displacement (NDD), with disk displacement with reduction (DDWR), and with disk displacement without reduction (DDWOR). Di€erences were tested using the posthoc test. Relationships between the horizontal size of the condyle and either degree of disk displacement, disk morphology, or the radiological stage of ID were analysed and tested by Spearman's correlation coefficient by rank. P50.05 was considered to indicate signi®cance. Results The results for the assessment of disk displacement, degree of disk displacement, and disk morphology are shown in Table 2. There was little disagreement in the assessments. Consequently, 30 joints had changes

Table 1 Radiological stages of internal derangement described by Wilkes15 and Schellhas16 Stage 1

Simple disk displacement without changes in the morphology of the disk or OA Stage 2 Reducible disk placement with mild-moderate deformity of the disk (usually associated with biplanar or biconvex disk) and/or OA Stage 3 Permanent disk displacement with mild-moderate deformity of the disk (usually associated with biplanar or biconvex disk) and/or OA Stages 4 Severe permanent displacement and deformity of the disk and 5 (usually associated with folded or amorphous disk) with OA Dentomaxillofacial Radiology

Figure 1 Measurement of the horizontal size of the TMJ condyle. A line was drawn through the medial (m) and lateral (l) poles of the condyle. A perpendicular line was drawn to bisect the line m ± l, and this intersected the anterior edge and the posterior edge of the condyle at points a and p, respectively. The distances m ± l and a ± p were measured in half millimeters

Condylar size and TMJ ID H Kurita et al

compatible with radiological stage 1, 31 stage 2, 20 stage 3, and 29 stages 4 or 5. Twenty nine joints were normal. The mean horizontal condylar size in the di€erent diagnoses of disk displacement is shown in Table 3. There were statistically signi®cant di€erences in the sizes of both the ML and AP dimension between the joints with NDD and those with DDWOR (Fisher's protected least signi®cant di€erence, P50.05). The condyle in the joints with DDWOR is smaller than that in the joints with NDD. There also was a signi®cant di€erence in the size of the AP dimension between the joints with NDD and those with DDWR (Fisher's protected least signi®cant di€erence, P50.05). The condyle in the joints with DDWR is smaller than that in the joints with NDD in the AP dimension (Fisher's protected least signi®cant di€erence, P50.05). The correlation between horizontal condylar size and degree of disk displacement is shown in Figure 2. In the ML dimension, the condyle tended to become smaller with advancement of disk displacement. On the other hand, in the AP dimension, the condyle was smallest in the joints with slight disk displacement and tended to become bigger with the advancement of disk displacement. However, there was no statistically signi®cant correlation between the degree of disk displacement and the horizontal condylar size (Spearman's correlation coecient by rank; P40.17 in the ML dimension and P40.55 in the AP dimension). The relationship between the horizontal condylar size and disk morphology is shown in Figure 3. There Table 2 Results of MR assessment of 139 joints in 88 patients with internal derangement of the TMJ Disk displacement None With reduction Without reduction Degree of disk displacement None Slight Moderate Severe Morphological changes in the displaced disk Biconcave Biplanar Biconvex Folded Amorphous

29 58 52 29 44 47 19 56 19 35 7 22

Table 3 Mean horizontal condyle size in joints with different diagnoses of disk placement Disk displacement (No. of joints) No displacement (29) Anterior displacement with reduction (58) Anterior displacement without reduction (52)

Horizontal condyle size medio-lateral antero-posterior dimension dimension 19.0+3.0 18.1+2.9 17.6+2.7

]

a

8.7+1.7 7.9+1.2 7.9+1.3

]

]

a

a There was a statistically signi®cant di€erence between the groups (Fisher's protected least signi®cant di€erent; P50.05). (Mean+ standard deviation, mm)

was a statistically signi®cant correlation between the condyle size in the ML dimension and disk morphology (Spearman's correlation coecient by rank, P50.05). The condyle became smaller in the ML dimension with morphological alteration of the disk. On the other hand, there was no signi®cant correlation between the condyle size in the AP dimension and disk morphology (Spearman's correlation coecient by rank, P40.67). The correlation between the horizontal size of the condyle and the radiological stage of ID is shown in Figure 4. The condyle became smaller in the ML dimension with advancement of ID, and the correlation between them was signi®cant (Spearman's correlation coecient by rank, P50.05). On the other hand, there was no signi®cant correlation between the condyle size in the AP dimension and radiological stage of ID (Spearman's correlation coecient by rank, P40.36). The condyle was biggest in the joints with the most advanced stages of ID in the AP dimension.

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Discussion This study was carried out to clarify the relationship between the horizontal TMJ condyle size and ID. For this purpose, MR images of an initial axial localizer were retrospectively used to measure the horizontal condyle size. There might be a concern that the axial image would not be representative of the entire condylar head. In this study, the axial image that was nearly parallel to the Frankfort horizontal plane and that could maximally visualize the lateral and medial poles of both condyles was obtained. We know that the lateral and medial poles of both condyles are not usually seen on an axial plane. However, we believe the use of this axial image is practical. In the measurements of the condyle size, we used printed ®lms with the mean magni®cation of 0.6. The single observer recorded little di€erence between the ®rst and second measurements. However, further studies that employ a more valid measurement method are needed. The results of this study showed that the TMJ condyle is smaller in joints where the TMJ disk is anteriorly displaced than in joints without a displaced disk in both the ML and AP dimension. Previously, Ohgushi et al.4 evaluated the relationship between anterior displacement and the size of the condyle using MR images. They reported that the size of the condyles with anterior disk displacement was signi®cantly smaller than that of condyles without anterior displacement. Kobayashi et al.3 measured the horizontal size of the TMJ condyle using axial images of X-ray computed tomography and found that the horizontal size of the condyle in joints with a displaced disk was smaller both in the long and short axis than in those without a displaced disk.3 Our results were compatible with theirs. These data suggest that there might be a relationship between the size of the TMJ condyle and disk displacement. Dentomaxillofacial Radiology

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Figure 2

Horizontal condyle size in relation to degree of TMJ disk displacement

Biconcave Biplanar Biconvex Folded Amorphous

Biconcave Biplanar Biconvex Folded Amorphous

Figure 3 Horizontal condyle size in relation to TMJ disk morphology. The correlation between the condyle size in the medio-lateral dimension and disk morphology is statistically signi®cant (Spearman's correlation coecient by rank, P50.05)

There may be some controversy as to whether joints with a small condyle might have a greater tendency for disk displacement or whether disk displacement might Dentomaxillofacial Radiology

result in a small condyle because of concurrent degenerative bony changes. In this study, the condyle size in the ML dimension decreased with advancing

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Figure 4 Horizontal condylar size in relation to radiological stage of TMJ internal derangement. The correlation between the condyle size in the medio-lateral dimension and ID stage is statistically signi®cant (Spearman's correlation coecient by rank, P50.05)

stage of ID. This result appears to support the latter possibility. It was experimentally shown that TMJ disk displacement could induce reduction of mandibular height and length,5 which implies that disk displacement may have an adverse e€ect on condyle growth. On the other hand, there was no correlation between the condyle size in the AP dimension and the radiological stage of ID. The mechanism of disk displacement is still unclear, and there remains a possibility that a small condyle in the AP dimension is one of the predictors for disk displacement. A possible relationship between the decreased condyle size in the ML dimension and disk morphology was suggested in this study. The condyle became smaller in the ML dimension as the disk was deformed. In addition, there was a tendency for the condylar ML dimension to decrease as the disk became more anteriorly displaced. Previously, de Leeuw et al.17 reported shortening of the condyle in the mediolateral direction (reduction of the oval projection) in patients with internal derangement and osteoarthrosis. This ®nding is compatible with our ®ndings. Previously, we reported that resorption of the lateral pole of the condyle occurred with advancing stage of ID.18 The TMJ disk is ®rmly ®xed at the medial and lateral poles to the corner region of the posterior aspect of the condyle.19,20 Anterior disk displacement would cause some pathological changes to the lateral disk-condyle attachment or to the area of the lateral part of the condyle. We think that regressive condylar remodeling

at the postero-lateral corner of the condyle may cause resorption, resulting in a decreased condyle size in the ML dimension. We think it is fair to speculate that more pronounced regressive changes occur in the joints where the disk is displaced far to the anterior and the disk is severely deformed. The results of this study showed that the TMJ condyle became bigger in the AP dimension in the joints with the most advanced stages of ID. In these joints, the TMJ disk is severely and permanently displaced and deformed and is sometimes associated with disk perforation.15,16 Rao et al.22 studied MR images of 276 TMJ and reported that the altered bony morphology (condylar remodeling, erosion, spurring, etc.) correlated with the severity of ID, that is, bony changes in the joints with an anterior closed lock were noted in 64% compared to 45% with reducible disk.22 It has also been reported that disk perforation could lead to osteoarthritis.21 We speculated that proliferative condylar degenerative changes including ¯attening, spurring, and eburnation might be responsible for lengthening of the condyle in the antero-posterior direction. Legrell et al.5 experimentally induced nonreducing disk displacement in rabbits and demonstrated a substantial regressive remodeling resulting in a change of condyle shape with forward/downward rotation of the enlarged articulating surface. This result is consistent with our speculation. In conclusion, our results suggested (1) a possible relationship between disk displacement and decreased Dentomaxillofacial Radiology

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size of the TMJ condyle, and (2) that the condyle became smaller in the ML dimension with advancement of ID. Further study that could clarify a relationship between condylar bony changes and condyle size is needed.

Acknowledgements We wish to thank the doctors in the Department of Radiology of Shinshu University School of Medicine for their assistance in the imaging study of TMJ.

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