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Rotated subcondylar process fracture in the growing animal: An experimental study in rats
Int. J. Oral Maxillofac. Surg. 2001; 30: 545–549 doi:10.1054/ijom.2001.0147, available online at http://www.idealibrary.com on
Research paper: Trauma
Rotated subcondylar process fracture in the growing animal: An experimental study in rats
Joa˜o G. C. Luz, Vera C. de Arau´jo Departments of Oral and Maxillofacial Surgery and Oral Pathology, School of Dentistry, University of Sa˜o Paulo, Sa˜o Paulo, Brazil
Joa˜o G. C. Luz, Vera C. de Arau´jo: Rotated subcondylar process fracture in the growing animal: An experimental study in rats. Int. J. Oral Maxillofac. Surg. 2001; 30: 545–549. 2001 International Association of Oral and Maxillofacial Surgeons Abstract. Unilateral, rotated subcondylar fractures were surgically induced in young rats under general anaesthesia. A decrease in body weight was observed in the fractured animals, with recovery at the end of the experimental period. A tendency of deviation of the mandible to the fracture side was noticed on axial radiographs, but without significant difference between experimental and sham-operated animals. Histological data initially demonstrated acute inflammation along the articular capsule and adjacent muscle fibres. Within 2 weeks, exuberant callus formation occurred. Neither devitalized bone ends nor intra-articular granulation tissue were seen. After 1 month, the temporomandibular joint presented characteristics of normality, with the condylar process centralized into the temporal fossa, interposed by the articular disc. These results were preserved after 3 months. We concluded that rotational subcondylar fractures in young rats heal by callus formation, with simultaneous and prompt repositioning of the condyle.
Condylar process fractures are seen frequently in children and adolescents. In general they are unilateral, with medial deviation8,11,22. A favourable prognosis has been reported when these fractures are treated by closed methods8,16,20,24. However, sequelae subsequent to condylar fractures can occur in special bony ankylosis, mandibular asymmetric deformities, and functional disturbances15,17,19,23. Remodelling of the condylar process following closed treatment for displaced fractures has been demonstrated by radiographic studies4,12,18. Some understanding of the pathological changes within the temporomandibular joint (TMJ) has been obtained experimentally. Investigations have described the healing of condylar fractures without 0901-5027/01/060545+05 $35.00/0
deviation, giving emphasis to the role of bone remodelling21,28. Recently, healing by callus formation with simultaneous repositioning of the rotated fractured condylar process was demonstrated26. The purpose of the present study was to evaluate the associated mandibular deviation and the healing of rotated subcondylar process fractures in young rats. Materials and methods The study animals were 40 1-month-old Wistar rats, with a mean body weight of 78 g. They were distributed at random into experimental (n=25) and shamoperated (n=15) groups. The animals were subjected to surgery while under general anaesthesia, which was induced by intraperitoneal injection of ketamine.
Key words: mandibular condyle; condylar fracture; temporomandibular joint. Accepted for publication 10 July 2001 Published online 16 October 2001
All animals were fed an ordinary diet of rodent feed, administered in powder form for 2 weeks postoperatively, and in regular form in the remaining period. An approximate 10 mm pre-auricular incision was made on the right side. Blunt dissection was performed through the masseter muscle, just below the zygomatic arch, and the condylar process was exposed. Fracture was obtained by using mosquito (Halstead) forceps, and the condylar fragment was rotated in the medial direction. Care was taken so as not to damage the articular surfaces. The left TMJ of experimental animals was used as control. Sham-operated animals were submitted to the same procedure, limited to the exposition of the condylar process. The procedure was concluded with suture in layers with nylon. The
2001 International Association of Oral and Maxillofacial Surgeons
546
Luz and Arau´ jo Table 1. Body weight mean values (g), from experimental and sham-operated groups, at each period of the experiment Group Experimental
Sham-operated
Period
Mean
SE
Mean
SE
Significance
Initial 1 week 2 weeks 1 month 3 months
78.0 69.0 125.0 123.0 215.0
5.1 3.7 9.5 12.4 26.4
78.0 104.7 130.7 173.3 260.3
6.0 5.9 6.9 10.8 18.2
— Pc0.001 n.s. P=0.01 n.s.
n.s.: not significant.
specimens were decalcified in 20% formic acid; 7 m-thick semi-serial sections were cut in the coronal plane and stained with haematoxylin and eosin. Fracture and control sites were studied at the same magnification. Fig. 1. Radiogram of fixed skull and angle measurement. Radiopaque line: mandibular midline; TB: tympanic bulla. (H&E, 100)
experimental group animals were divided into five groups, with five rats in each, and were sacrificed after 24 h, 1 week, 2 weeks, 1 month and 3 months. Their body weights were then recorded. The body weights of the animals in the shamoperated group were obtained at the same periods of sacrifice as those of the experimental group, and they were sacrificed after 3 months postoperatively. Following 10% buffered formalin fixation for 1 week, axial (dorsal–ventral) projections of the skull of animals from experimental and sham-operated groups were obtained. Care was taken so as to mantain the horizontal plane. The skull was placed directly on a radiographic film, with the inferior border of the mandible as the horizontal plane reference. Radiograms were taken with a standard dental machine at 56 kV and 10 mA, with a 0.5 s exposure time. A constant 40 cm focus-to-film distance was mantained, and periapical films were used (Ektaspeed, Eastman Kodak Co., USA). Radiograms were subjected to computerized evaluation of the mandibular deviation. The radiographic image was digitized using an optical reader (Fotovix II, Tamron Co., Japan), and the measurements were obtained with Diracom3 software (LIDO, University of Sa˜ o Paulo, Sa˜ o Paulo, Brazil). Angular measurements of deviation of the mandible, with reference to a line between both tympanic bullae (angle ), were registered (Fig. 1). Right and left TMJs were removed from experimental animals. These
Results During the experimental period, the animals continued to grow and gain weight. Mean values of body weights of the animals from both groups, checked during the experiment, are shown in Table 1. There was a decrease in the experimental group after 1 week, deficiency until 1 month, and recovery in 3 months. To evaluate the significance of the difference between the mean values of both groups at each time period of the experiment, Student’s t-test was used and the level of significance set at P<0.05. Gross examination of the specimens revealed facial asymmetry, with deviation of the mandible to the right more intense in the experimental group. Angle mean values are shown in Table 2. There was a decrease in 1 week and recovering in 1 month. Kruskal–Wallis test among the mean values for the different periods in the experimental group revealed no significant difference (P>0.05). Student’s t-test between mean values at 3 months of experimental and sham-operated groups revealed no significant difference (P>0.05).
Histopathological findings
24 hours Fracture of the condylar process with medial rotation was verified, and the articular disc remained related to the condylar head. There was evidence of acute inflammation along the articular capsule and adjacent muscle fibres, as well as serofibrinous exudation into the joint space. The fracture ends exhibited viable bone (Figs 2 and 3). 1 week Cartilaginous proliferation and osteoblastic activity occurred on the external surfaces of the fracture site, while the fractured fragment was less rotated. There was evidence of chronic
Table 2. Angle mean values (degrees), from experimental and sham-operated groups, according to the period of the experiment Group Experimental
Sham-operated
Period
Mean
SE
Initial 1 week 2 weeks 1 month 3 months 3 months
89.8 86.9 85.9 86.3 87.2 87.7
1.0 0.8 0.7 0.6 1.0 1.0
Fig. 2. 24 hours. Medially rotated fracture of the condyle (C). The articular disc (D) remained attached, while serofibrinous exudate (arrows) is seen in upper and lower articular spaces (H & E, 25).
Rotated subcondylar process fracture in the growing animal
547
Fig. 3. 24 hours. Bone ends (BE) exhibiting viable bone. Intense inflammatory exudate is seen along the muscle fibres (H & E, 100). Fig. 5. 2 weeks. Exuberant callus formation is observed, with cartilaginous (*) and osseous (arrows) proliferation. The condylar fragment (C) has returned to its position (H & E, 25).
Fig. 4. 1 week. Bone ends (BE) with viable bone, and interposed by cartilaginous tissue (H & E, 100).
infiltration in the articular space and along the articular capsule. Fracture ends presented viable bone with interposition of cartilaginous tissue (Fig. 4). 2 weeks Thickening of the fracture area occurred because of proliferation of cartilaginous and osseous tissue. The fractured fragment was closer to the temporal fossa than observed after 1 week. Chronic infiltration along the articular capsule was present (Fig. 5).
1 month The TMJ with characteristics of normality was observed. The condylar process was centralized in the temporal fossa, and with interposition of the articular disc. The subcondylar region exhibited a discrete thickening but the fracture area was indistinct (Fig. 6). 3 months The characteristics of normality of the TMJ and condylar process were
Fig. 6. 1 month. Condylar process centralized in the temporal fossa, with interposition of the articular disc (H & E, 25).
preserved. The subcondylar region presented discrete signs of remodelling, with the presence of basophilic reversal lines (Fig. 7).
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Fig. 7. 3 months. Intra-articular area exhibiting normal articular surfaces and disc (H & E, 100).
Control None of the control sites showed changes in the articular or condylar process tissues.
Discussion The present study has shown that rotational subcondylar process fractures in young rats healed by callus formation, with simultaneous and prompt repositioning of the condyle. Thus, the final result was a TMJ presenting characteristics of normality, the condylar process centralized in the temporal fossa. In this model, we induced a unilateral, medially rotated fracture, which is the most frequent form of mandibular condyle fracture8,11,22. The experimental group presented a decrease in body weight when compared to the shamoperated group, from 1 week to 1 month, with recovery at the final period of the experiment. This indicates some influence of the condylar fracture on the eating ability of the growing animals, until the completion of reparative processes. This effect was not observed on adult rats when this kind of fracture was induced26. Deviation of the median line of the mandible toward the right side occurred in both groups, and the difference between them was not significant. Thus, this may be attributable to the surgical procedure and further studies on this matter are necessary. The possibility of a decrease in the growth of the condylar process caused by a periosteal lesion
should be considered9. Mandibular asymmetries have been related to condylar fractures in young individuals at variable rates7,15,17. Functional results of non-surgical and surgical treatment of condylar fracture6 are comparable8,25,27, although some degree of deviation can occur in the closed treated patient8,23. Histological sections initially demonstrated a medially rotated fracture of the condylar process. Neutrophilic and serofibrinous exudation around the fracture site occurred as part of the inflammatory process related to fractures2,3. Neutrophilic exudation and congested blood vessels along the articular capsule and adjacent muscle fibres, as well as fibrinous-haemorrhagic exudation into the articular space, are part of the inflammatory and circulatory processes associated with the type of injury studied13,26. There is some concern about the possibility of complications of intra-articular haemorrhage5, which may occur particularly in children. When a case of condylar fracture is treated closed, early mobilization could prevent intra-articular haemorrhage [to organize into a bony ankylosis]. On the other hand, arthroscopic examination of the TMJ, following acute trauma, has shown that hemarthrosis is common but spontaneously resolves in a few days5. Thus, the occurrence of lesions to the articular disc10,13 should be considered the main factor in the aetiology of ankylosis. Further steps in the process, between 1 and 2 weeks, included exuberant callus formation and a mild remodelling
process. Cartilaginous and osseous proliferation around the fracture site represent the initial phase of callus formation. Later, thickening of the fracture site by newly formed bone, with less cartilaginous content, indicates maturation of the callus2,3,6. Remodelling was represented by significant osteoblastic and discrete osteoclastic activities, which have been demonstrated in some types of experimental injuries to the TMJ1,13. Some studies on experimental fracture of the mandibular condyle, with or without rotation, have demonstrated healing and remodelling processes21,26,28. It is important to observe that devitalized areas were not verified on bone ends in any of the specimens. They are part of the healing process of fractures that are followed by resorption2,6,26. Furthermore, no intra-articular granulation tissue was seen. Absence of the latter finding is probably due to the young age of the experimental animals used in this study. The final result was a TMJ with characteristics of normality, verified at 1 month and preserved until 3 months postoperatively. Spontaneous condylar repositioning took less time than observed in adult rats when the same experimental model was used26. The articular disc was preserved, and this is an important factor in the healing of the TMJ10,13. The ability of the TMJ to remodel, which has been reported in the closed treatment of displaced condylar fractures, was confirmed by this study4,12,18,24. Adaptative changes of the TMJ in the growing rat have been described as a consequence to subcondylar osteotomy14. No adaptative changes were observed in our study, and the possibility that a rapid return of the rotated condyle would not allow such a response is suggested. Better results, both in tissular response and time demanded, were obtained in this study when compared to those obtained for adult rats26. Therefore, our study corroborates clinical observations indicating better results for closed treatment of displaced fractures of the mandibular condyle in young individuals7,16,20.
References 1. B P, M I. Condylotomy. A clinical and experimental appraisal of a surgical technique. J Maxillofac Surg 1975: 3: 170–181. 2. C DH. Ham’s histology. Philadelphia: J B Lippincott 1987.
Rotated subcondylar process fracture in the growing animal 3. C PD, M MM, P J, M FW. Experimental study of healing in fractures of membranous bone. Plast Reconstr Surg 1974: 53: 321–325. 4. F H, A-D J, R D. Long-term follow-up of subcondylar fractures in children by electronic computer-assisted recording of condylar movements. Int J Oral Maxillofac Surg 1992: 21: 70–76. 5. G AN, B AG. The arthroscopic appearance of acute temporomandibular joint trauma. J Oral Maxillofac Surg 1990: 48: 780–783. 6. G¨ G, N LP. Experimental mandibular fracture: studies on bone repair and remodellation. Scand J Plast Surg 1987: 21: 159–165. 7. H J, B G., S B. Long-term results of nonsurgical management of condylar fractures in children. Int J Oral Maxillofac Surg 1999: 28: 429–440. 8. J U, K J. Therapy of condylar neck fractures. Int J Oral Maxillofac Surg 1998: 27: 247–254. 9. K K, R¨ O. Condyle neck periostomy and the mitotic activity in the condylar tissues of the young rats. Swed Dent J 1982: 15: 109–113. 10. L DM. Role of the meniscus in the etiology of post-traumatic temporomandibular joint ankylosis. Int J Oral Surg 1978: 7: 340–345. 11. L C, S S, H T, S S. Maxillofacial fractures sustained by bicycle accidents. Int J Oral Maxillofac Surg 1986: 15: 12–18. 12. L JGC, C I. Remodelling of bilateral fractures of the mandibular condyle. Acta Stomatol Belg 1996: 93: 167–170. 13. L JGC, J RG, A´ VC, R JRV. The effect of indirect
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trauma on the rat temporomandibular joint. Int J Oral Maxillofac Surg 1991: 20: 48–52. M F, D E, N MJ, M C, D H JRA. Changes in temporomandibular joint after mandibular subcondylar osteotomy: an experimental study in rats. J Oral Maxillofac Surg 1993: 51: 1221–1234. N SE, K V, SP S, J AI. Pediatric condylar fractures: a long-term follow-up study of 55 patients. J Oral Maxillofac Surg 1993: 51: 1302–1310. P A, R H. Evaluation a long terme du traitement fonctionnel des fractures condyliennes mandibulaires. Rev Stomatd Chir Maxillofac 1993: 94: 1–8. P WR, V KWL, T TA. Early fracture of the mandibular condyles: frequently an unsuspected cause of growth disturbances. Am J Orthod 1980: 78: 1–24. S G, W E. Long-term results after childhood condylar fractures. A computer-tomographic study. Eur J Orthod 1989: 11: 154–160. S CP. Bony ankylosis of the temporomandibular joint: follow-up of 70 patients treated with arthroplasty and acrylic spacer interposition. Plast Reconstr Surg 1986: 77: 29–38. S KU, W A, G G, K G. Ergebnisse der funktionellen Behandlung von Kollumfrakturen in Wachstumsalter mit Aktivatoren. Dtsch Zahnarztl Z 1991: 46: 726–728. S M, O K, T A, K T, T, A, Y T. An experimental study on the healing of fracture of the condylar process of the
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mandible. Bull Osaka Med Sch 1987: 33: 164–178. S U, I T, L C, O K. Different patterns of condylar fractures: an analysis of 382 patients in a 3-year period. J Oral Maxillofac Surg 1992: 50: 1032–1037. S U, R AM, L C, O K. Occlusal and temporomandibular joint disorders in patients with unilateral condylar fracture. A prospective one-year study. Int J Oral Maxillofac Surg 1998: 27: 280–285. S DR. Postinjury condylar remodeling in children. Oral Surg 1982: 53: 340–341. T Y, I H, O M. Comparison of functional recovery after nonsurgical and surgical treatment of condylar fractures. J Oral Maxilloffac Surg 1990: 48: 1191–1195. T ACB, L JGC, A VC, A NS. Healing of the displaced condylar process fracture: an experimental study. J Craniomaxillofac Surg 1998: 26: 326–330. T M GS, E E III. Recovery of mandibular motion after closed and open treatment of unilateral mandibular condylar process fractures. Int J Oral Maxillofac Surg 2000: 29: 421–427. Y T, O N. Histomorphometric study of trabecular bone remodeling during condylar process fracture healing in the growing period: experimental study. J Oral Maxillofac Surg 1991: 49: 981–988.
Address: Professor Joa˜ o Gualberto C. Luz Rua Duarte de Azevedo 284, s.22, 02036-021 Sa˜ o Paulo SP, Brazil
Research paper: Trauma
Rotated subcondylar process fracture in the growing animal: An experimental study in rats
Joa˜o G. C. Luz, Vera C. de Arau´jo Departments of Oral and Maxillofacial Surgery and Oral Pathology, School of Dentistry, University of Sa˜o Paulo, Sa˜o Paulo, Brazil
Joa˜o G. C. Luz, Vera C. de Arau´jo: Rotated subcondylar process fracture in the growing animal: An experimental study in rats. Int. J. Oral Maxillofac. Surg. 2001; 30: 545–549. 2001 International Association of Oral and Maxillofacial Surgeons Abstract. Unilateral, rotated subcondylar fractures were surgically induced in young rats under general anaesthesia. A decrease in body weight was observed in the fractured animals, with recovery at the end of the experimental period. A tendency of deviation of the mandible to the fracture side was noticed on axial radiographs, but without significant difference between experimental and sham-operated animals. Histological data initially demonstrated acute inflammation along the articular capsule and adjacent muscle fibres. Within 2 weeks, exuberant callus formation occurred. Neither devitalized bone ends nor intra-articular granulation tissue were seen. After 1 month, the temporomandibular joint presented characteristics of normality, with the condylar process centralized into the temporal fossa, interposed by the articular disc. These results were preserved after 3 months. We concluded that rotational subcondylar fractures in young rats heal by callus formation, with simultaneous and prompt repositioning of the condyle.
Condylar process fractures are seen frequently in children and adolescents. In general they are unilateral, with medial deviation8,11,22. A favourable prognosis has been reported when these fractures are treated by closed methods8,16,20,24. However, sequelae subsequent to condylar fractures can occur in special bony ankylosis, mandibular asymmetric deformities, and functional disturbances15,17,19,23. Remodelling of the condylar process following closed treatment for displaced fractures has been demonstrated by radiographic studies4,12,18. Some understanding of the pathological changes within the temporomandibular joint (TMJ) has been obtained experimentally. Investigations have described the healing of condylar fractures without 0901-5027/01/060545+05 $35.00/0
deviation, giving emphasis to the role of bone remodelling21,28. Recently, healing by callus formation with simultaneous repositioning of the rotated fractured condylar process was demonstrated26. The purpose of the present study was to evaluate the associated mandibular deviation and the healing of rotated subcondylar process fractures in young rats. Materials and methods The study animals were 40 1-month-old Wistar rats, with a mean body weight of 78 g. They were distributed at random into experimental (n=25) and shamoperated (n=15) groups. The animals were subjected to surgery while under general anaesthesia, which was induced by intraperitoneal injection of ketamine.
Key words: mandibular condyle; condylar fracture; temporomandibular joint. Accepted for publication 10 July 2001 Published online 16 October 2001
All animals were fed an ordinary diet of rodent feed, administered in powder form for 2 weeks postoperatively, and in regular form in the remaining period. An approximate 10 mm pre-auricular incision was made on the right side. Blunt dissection was performed through the masseter muscle, just below the zygomatic arch, and the condylar process was exposed. Fracture was obtained by using mosquito (Halstead) forceps, and the condylar fragment was rotated in the medial direction. Care was taken so as not to damage the articular surfaces. The left TMJ of experimental animals was used as control. Sham-operated animals were submitted to the same procedure, limited to the exposition of the condylar process. The procedure was concluded with suture in layers with nylon. The
2001 International Association of Oral and Maxillofacial Surgeons
546
Luz and Arau´ jo Table 1. Body weight mean values (g), from experimental and sham-operated groups, at each period of the experiment Group Experimental
Sham-operated
Period
Mean
SE
Mean
SE
Significance
Initial 1 week 2 weeks 1 month 3 months
78.0 69.0 125.0 123.0 215.0
5.1 3.7 9.5 12.4 26.4
78.0 104.7 130.7 173.3 260.3
6.0 5.9 6.9 10.8 18.2
— Pc0.001 n.s. P=0.01 n.s.
n.s.: not significant.
specimens were decalcified in 20% formic acid; 7 m-thick semi-serial sections were cut in the coronal plane and stained with haematoxylin and eosin. Fracture and control sites were studied at the same magnification. Fig. 1. Radiogram of fixed skull and angle measurement. Radiopaque line: mandibular midline; TB: tympanic bulla. (H&E, 100)
experimental group animals were divided into five groups, with five rats in each, and were sacrificed after 24 h, 1 week, 2 weeks, 1 month and 3 months. Their body weights were then recorded. The body weights of the animals in the shamoperated group were obtained at the same periods of sacrifice as those of the experimental group, and they were sacrificed after 3 months postoperatively. Following 10% buffered formalin fixation for 1 week, axial (dorsal–ventral) projections of the skull of animals from experimental and sham-operated groups were obtained. Care was taken so as to mantain the horizontal plane. The skull was placed directly on a radiographic film, with the inferior border of the mandible as the horizontal plane reference. Radiograms were taken with a standard dental machine at 56 kV and 10 mA, with a 0.5 s exposure time. A constant 40 cm focus-to-film distance was mantained, and periapical films were used (Ektaspeed, Eastman Kodak Co., USA). Radiograms were subjected to computerized evaluation of the mandibular deviation. The radiographic image was digitized using an optical reader (Fotovix II, Tamron Co., Japan), and the measurements were obtained with Diracom3 software (LIDO, University of Sa˜ o Paulo, Sa˜ o Paulo, Brazil). Angular measurements of deviation of the mandible, with reference to a line between both tympanic bullae (angle ), were registered (Fig. 1). Right and left TMJs were removed from experimental animals. These
Results During the experimental period, the animals continued to grow and gain weight. Mean values of body weights of the animals from both groups, checked during the experiment, are shown in Table 1. There was a decrease in the experimental group after 1 week, deficiency until 1 month, and recovery in 3 months. To evaluate the significance of the difference between the mean values of both groups at each time period of the experiment, Student’s t-test was used and the level of significance set at P<0.05. Gross examination of the specimens revealed facial asymmetry, with deviation of the mandible to the right more intense in the experimental group. Angle mean values are shown in Table 2. There was a decrease in 1 week and recovering in 1 month. Kruskal–Wallis test among the mean values for the different periods in the experimental group revealed no significant difference (P>0.05). Student’s t-test between mean values at 3 months of experimental and sham-operated groups revealed no significant difference (P>0.05).
Histopathological findings
24 hours Fracture of the condylar process with medial rotation was verified, and the articular disc remained related to the condylar head. There was evidence of acute inflammation along the articular capsule and adjacent muscle fibres, as well as serofibrinous exudation into the joint space. The fracture ends exhibited viable bone (Figs 2 and 3). 1 week Cartilaginous proliferation and osteoblastic activity occurred on the external surfaces of the fracture site, while the fractured fragment was less rotated. There was evidence of chronic
Table 2. Angle mean values (degrees), from experimental and sham-operated groups, according to the period of the experiment Group Experimental
Sham-operated
Period
Mean
SE
Initial 1 week 2 weeks 1 month 3 months 3 months
89.8 86.9 85.9 86.3 87.2 87.7
1.0 0.8 0.7 0.6 1.0 1.0
Fig. 2. 24 hours. Medially rotated fracture of the condyle (C). The articular disc (D) remained attached, while serofibrinous exudate (arrows) is seen in upper and lower articular spaces (H & E, 25).
Rotated subcondylar process fracture in the growing animal
547
Fig. 3. 24 hours. Bone ends (BE) exhibiting viable bone. Intense inflammatory exudate is seen along the muscle fibres (H & E, 100). Fig. 5. 2 weeks. Exuberant callus formation is observed, with cartilaginous (*) and osseous (arrows) proliferation. The condylar fragment (C) has returned to its position (H & E, 25).
Fig. 4. 1 week. Bone ends (BE) with viable bone, and interposed by cartilaginous tissue (H & E, 100).
infiltration in the articular space and along the articular capsule. Fracture ends presented viable bone with interposition of cartilaginous tissue (Fig. 4). 2 weeks Thickening of the fracture area occurred because of proliferation of cartilaginous and osseous tissue. The fractured fragment was closer to the temporal fossa than observed after 1 week. Chronic infiltration along the articular capsule was present (Fig. 5).
1 month The TMJ with characteristics of normality was observed. The condylar process was centralized in the temporal fossa, and with interposition of the articular disc. The subcondylar region exhibited a discrete thickening but the fracture area was indistinct (Fig. 6). 3 months The characteristics of normality of the TMJ and condylar process were
Fig. 6. 1 month. Condylar process centralized in the temporal fossa, with interposition of the articular disc (H & E, 25).
preserved. The subcondylar region presented discrete signs of remodelling, with the presence of basophilic reversal lines (Fig. 7).
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Luz and Arau´ jo
Fig. 7. 3 months. Intra-articular area exhibiting normal articular surfaces and disc (H & E, 100).
Control None of the control sites showed changes in the articular or condylar process tissues.
Discussion The present study has shown that rotational subcondylar process fractures in young rats healed by callus formation, with simultaneous and prompt repositioning of the condyle. Thus, the final result was a TMJ presenting characteristics of normality, the condylar process centralized in the temporal fossa. In this model, we induced a unilateral, medially rotated fracture, which is the most frequent form of mandibular condyle fracture8,11,22. The experimental group presented a decrease in body weight when compared to the shamoperated group, from 1 week to 1 month, with recovery at the final period of the experiment. This indicates some influence of the condylar fracture on the eating ability of the growing animals, until the completion of reparative processes. This effect was not observed on adult rats when this kind of fracture was induced26. Deviation of the median line of the mandible toward the right side occurred in both groups, and the difference between them was not significant. Thus, this may be attributable to the surgical procedure and further studies on this matter are necessary. The possibility of a decrease in the growth of the condylar process caused by a periosteal lesion
should be considered9. Mandibular asymmetries have been related to condylar fractures in young individuals at variable rates7,15,17. Functional results of non-surgical and surgical treatment of condylar fracture6 are comparable8,25,27, although some degree of deviation can occur in the closed treated patient8,23. Histological sections initially demonstrated a medially rotated fracture of the condylar process. Neutrophilic and serofibrinous exudation around the fracture site occurred as part of the inflammatory process related to fractures2,3. Neutrophilic exudation and congested blood vessels along the articular capsule and adjacent muscle fibres, as well as fibrinous-haemorrhagic exudation into the articular space, are part of the inflammatory and circulatory processes associated with the type of injury studied13,26. There is some concern about the possibility of complications of intra-articular haemorrhage5, which may occur particularly in children. When a case of condylar fracture is treated closed, early mobilization could prevent intra-articular haemorrhage [to organize into a bony ankylosis]. On the other hand, arthroscopic examination of the TMJ, following acute trauma, has shown that hemarthrosis is common but spontaneously resolves in a few days5. Thus, the occurrence of lesions to the articular disc10,13 should be considered the main factor in the aetiology of ankylosis. Further steps in the process, between 1 and 2 weeks, included exuberant callus formation and a mild remodelling
process. Cartilaginous and osseous proliferation around the fracture site represent the initial phase of callus formation. Later, thickening of the fracture site by newly formed bone, with less cartilaginous content, indicates maturation of the callus2,3,6. Remodelling was represented by significant osteoblastic and discrete osteoclastic activities, which have been demonstrated in some types of experimental injuries to the TMJ1,13. Some studies on experimental fracture of the mandibular condyle, with or without rotation, have demonstrated healing and remodelling processes21,26,28. It is important to observe that devitalized areas were not verified on bone ends in any of the specimens. They are part of the healing process of fractures that are followed by resorption2,6,26. Furthermore, no intra-articular granulation tissue was seen. Absence of the latter finding is probably due to the young age of the experimental animals used in this study. The final result was a TMJ with characteristics of normality, verified at 1 month and preserved until 3 months postoperatively. Spontaneous condylar repositioning took less time than observed in adult rats when the same experimental model was used26. The articular disc was preserved, and this is an important factor in the healing of the TMJ10,13. The ability of the TMJ to remodel, which has been reported in the closed treatment of displaced condylar fractures, was confirmed by this study4,12,18,24. Adaptative changes of the TMJ in the growing rat have been described as a consequence to subcondylar osteotomy14. No adaptative changes were observed in our study, and the possibility that a rapid return of the rotated condyle would not allow such a response is suggested. Better results, both in tissular response and time demanded, were obtained in this study when compared to those obtained for adult rats26. Therefore, our study corroborates clinical observations indicating better results for closed treatment of displaced fractures of the mandibular condyle in young individuals7,16,20.
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