YIJOM-3098; No of Pages 6
Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2015.02.004, available online at http://www.sciencedirect.com
Research Paper Trauma
The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study
D. Wua,b,1, X.-J. Yanga,1, P. Chenga, T.-G. Denga, X. Jianga, P. Liua, C.-K. Liua, F.-W. Mengc, K.-J. Hua, a State Key Laboratory of Military Stomatology, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, Xi’an, China; bDepartment of Stomatology, 152nd Hospital of the People’s Liberation Army, Pingdingshan, China; cDepartment of Stomatology, 359th Hospital of the People’s Liberation Army, Zhenjiang, China
D. Wu, X.-J. Yang, P. Cheng, T.-G. Deng, X. Jiang, P. Liu, C.-K. Liu, F.-W. Meng, K.-J. Hu: The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study. Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx. # 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The purpose of this study was to verify the role of the lateral pterygoid muscle in the reconstruction of the condyle shape during the sagittal fracture healing process by histological methods. Twenty-four adult sheep underwent an osteotomy to create a sagittal fracture of the left condyle; the sheep were then divided randomly into two groups. The lateral pterygoid muscles of the sheep in the experimental group were maintained on the internal poles of the condyles, and their functions remained stable. The lateral pterygoid muscles of the sheep in the control group were cut, and their functions were blocked. The shape, erosion, and calcification of the condyles were observed and measured after 4, 12, and 24 weeks of healing (n = 4 from each group). The condyles were then submitted to haematoxylin and eosin, Ponceau S, and Sirius red studies. The results of the histology studies showed increased bone formation in the experimental group in which the functions of the lateral pterygoid muscle remained the same. The results of this study suggest that the lateral pterygoid muscle affects the reconstruction of the condylar shape during the healing process of a sagittal fracture of the mandibular condyle, and may even be involved in the formation of ankylosis.
Ankylosis of the temporomandibular joint (TMJ) is a serious and disabling disease that severely restricts the movements of the mandible. It can cause problems with mastication, swallowing, digestion, speech, and breathing, and is even known to 0901-5027/000001+06
contribute to psychological disorders. When ankylosis of the TMJ occurs during childhood, it can retard mandibular development and lead to more serious maxillofacial deformities and dysfunction, such as facial asymmetry, micrognathia, and
Key words: lateral pterygoid muscle; temporomandibular joint; ankylosis; trauma. Accepted for publication 3 February 2015
malocclusion.1,2 Ankylosis of the TMJ is difficult to treat and its cause is quite complex. It can result from physical trauma, or 1 These authors contributed equally to this work.
# 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
2
Wu et al.
from local or systemic infections. Reankylosis is the most common complication after treatment,3 and the recurrence rate is 4–31%.4 An exploration of the pathogenesis of this disease might provide new avenues for the prevention and treatment of TMJ ankylosis. In previous reports, trauma has been considered the main cause of ankylosis.5 Both animal experiments and clinical observations have indicated that sagittal fracture of the mandibular condyle is more likely to lead to ankylosis than other types of condylar fracture.6,7 However, the specific mechanism by which ankylosis develops during the wound healing process remains the subject of controversy. Some researchers believe that the pathogenesis of traumatic TMJ ankylosis is the organization and ossification of an intracapsular haematoma after injury.5,6 Animal experiments, though, have shown that intracapsular haematoma alone does not cause ankylosis.8 Recently, some researchers have proposed that ankylosis of the TMJ is a progression, which like hypertrophic non-union, develops in long bone.9 Because of the way the mouth moves, these injuries cannot completely recover and eventually form bone adhesions.9 We hypothesized that distraction osteogenesis of the lateral pterygoid muscle may be an important factor in the genesis of traumatic TMJ ankylosis.10 Recent animal studies by our group further confirmed that the lateral pterygoid muscle plays an important role in the reconstruction of the condyle shape during the sagittal fracture healing process.11,12 Based on the research performed, we postulate that pathological osteogenesis may be caused by the traction of the lateral pterygoid muscle, which is crucial in the formation of traumatic ankylosis in the TMJ. The primary goal of this study was to substantiate the role of the lateral pterygoid muscle in the sagittal fracture healing process of the mandibular condyle, through histological methods. Materials and methods
The study protocol was approved by the ethics committee of the military medical university. All sheep were cared for in accordance with the guidelines for animal research set by the animal research centre laboratory of the military medical university. Twenty-four 1-year-old, healthy sheep were divided randomly into two groups of 12. All operations were done under satisfactory anaesthesia. After creating the fracture, the function of the lateral pterygoid muscle was cut off in
the control group, while the muscle was left unaltered in the experimental group.
assessed using the Student’s t-test; P < 0.05 was accepted as significant.
Operations
Results
The sheep were anaesthetized with xylazine hydrochloride (0.1 ml/kg) and their temporal regions were shaved and sterilized. We exposed the zygomatic arch and panniculus carnosus muscles at the surface of the capsule of the TMJ using a curved pre-auricular skin incision. A horizontal incision was then made through the capsule at the condylar neck in order to open the inferior joint space. The condylar head was then isolated and the superior joint space exposed. After pushing the disc inward, an oblique vertical osteotomy was made from the lateral pole of the condyle to the medial side of the condylar neck, using an ultrasound osteotome. The lateral pterygoid muscles of the sheep in the control group were separated and completely cut off, and the muscles of the sheep in the experimental group were maintained. The wound was closed in layers without suture of the capsule. After the operation, penicillin (20 mg/kg, twice a day) was given to each sheep to prevent infection, and this was continued for 3 days. Four sheep in each group were sacrificed at intervals of 4 weeks, 12 weeks, and 24 weeks after surgery. The TMJ was isolated, observed, and measured. Specimens were then examined histologically under a microscope.
Healing was uneventful following sagittal fracture in all 24 sheep. None of the sheep exhibited a clinical infection. Their skin exhibited only minor signs of inflammation during the first few weeks of healing. The animals were observed carefully and histological analyses were performed at 4 weeks, 12 weeks, and 24 weeks after the operation.
Observation
After the TMJ of the study animals had been isolated, we observed the shape, erosion, and calcification of the joint. The sizes of the condyles in both groups were measured using a Vernier caliper. Histological analysis
Specimens were fixed in a 4% formaldehyde solution for 2 weeks, and then decalcified in ethylenediaminetetraacetic acid (EDTA) for 3 months. Semi-serial sections measuring 5 mm in thickness were cut in the sagittal plane. The sections were stained with haematoxylin and eosin (H&E), Ponceau S, and Sirius red, as described previously.13,14 The sections were then subjected to histological analysis. Statistical analysis
SPSS version 16.0 software (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. The significance of the variations between the two groups was
4 weeks
In the biopsies obtained after 4 weeks, the surface roughness of the condyle was increased in both groups. The change was more apparent, with observable protuberances, in the experimental group (Fig. 1A and D). The size of the condyle was measured with a Vernier caliper. As shown in Table 1, the mediolateral size of the condyle in the experimental group was significantly larger than that of the control group (P < 0.05), while the anteroposterior size of the condyle showed no significant difference (P > 0.05). H&E examination showed the osteoblasts and chondrocytes to be actively growing in the fracture zone of both groups, but this was more distinct in the experimental group. Blood vessels were found in the fracture callus. Fresh bone formation was more vigorous in the experimental group than in the control group (Fig. 2A and D). Ponceau S examination showed a large amount of new bone in the fracture zone and the quantity of this was greater in the experimental group than in the control group (Fig. 3A and D). Sirius red examination showed the presence of collagen type I and III in both groups, while some thin collagen type II was found in the control group. Collagen type III appeared in larger amounts in the experimental group than in the control group (Fig. 4A and D).
12 weeks
After 12 weeks of healing, the volume of the condyle had increased in both groups. However, it was better defined in the experimental group, with larger and more obvious protuberances (Fig. 1B and E). Both the anteroposterior size and the mediolateral size of the condyle in the experimental group were significantly larger than those of the control group (P < 0.05; Table 1).
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
Lateral pterygoid muscle and fracture healing
3
Fig. 1. Changes in the condylar morphology after the operation. At 4, 12, and 24 weeks after the operation, changes were more obvious in the experimental group (A–C) than in the control group (D–F).
Table 1. Size of the condyle after the operation, measured by Vernier caliper (millimetres). Group Anteroposterior Muscle cut (Control) Muscle not cut Mediolateral Muscle cut (Control) Muscle not cut a
P < 0.05.
Postoperative week 4
12
24
14.5 (2.1) 15.1 (2.6)
15.4 (3.1) 16.8 (3.9)a
15.6 (3.1) 17.5 (4.3)a
22.6 (3.0) 23.3 (3.9)a
24.6 (4.0) 28.3 (5.4)a
24.8 (4.2) 29.6 (5.6)a
On H&E examination, osteoblasts around the mature trabecular bone, plus further deposition of new bone was seen in the experimental group, while bone structure close to maturity with osteoblasts was hardly seen at all in the control group (Fig. 2B and E). Ponceau S examination showed a mass of mature bone matrix to have appeared in the fracture zone. New bone was still forming slowly in the experimental group when compared to
Fig. 2. Histological sections showing that osteoblasts were more active in the experimental group at 4, 12, and 24 weeks after the operation (A–C) than in the control group (D–F) (haematoxylin and eosin stain, original magnification 100).
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
4
Wu et al.
Fig. 3. Histological sections showing that the amounts of newly generated bone were greater in the experimental group at 4, 12, and 24 weeks after the operation (A–C) than in the control group (D–F) (Ponceau S stain, original magnification 100).
Fig. 4. Histological sections showing that the type of collagen was different between the experimental group and the control group at 4 weeks after the operation (A and D), and that the collagen was thicker in the experimental group (B and C) than in the control group (E and F) at 12 and 24 weeks after the operation (Sirius red stain, original magnification 100).
the control group (Fig. 3B and E). Sirius red examination showed a large quantity of collagen type I and less collagen type III in the experimental group. Collagen type II
had disappeared completely in the control group, and the size of collagen type I was smaller than that of the experimental group (Fig. 4B and E).
24 weeks
At 24 weeks after the operation, the volume of the condyle had increased slightly
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
Lateral pterygoid muscle and fracture healing in both groups, and protuberances had morphed into apophysis in the experimental group (Fig. 1C and F). Both the anteroposterior size and the mediolateral size of the condyle in the experimental group were significantly larger than those of the control group (P < 0.05; Table 1). On H&E examination, osteoblasts existed only in the experimental group; mature trabecular bone was found in the experimental group compared with lamellar bone in control group (Fig. 2C and F). Ponceau S examination showed that new bone was mature in both groups. A small amount of the newly generated bone could be seen in the experimental group as compared to the control group (Fig. 3C and F). Sirius red examination showed that collagen type I was most common, whereas collagen type III was rarer in both groups (Fig. 4C and F). Discussion
It is well known that the general reason for traumatic ankylosis of the temporomandibular joint (TMJ) is a common ‘bone healing disorder’, which is affected by multiple factors. These factors include post-traumatic bleeding, fracture of the condyle, changes in condylar shape, shifting of the condyle, mismatching of the condyle and infratemporal fossa, shift of and trauma to the articular disc, trauma to the infratemporal fossa, and distraction osteogenesis of the lateral pterygoid muscle.5,15,16 These factors can cause excessive TMJ local bone hyperplasia and eventually ankylosis of the TMJ.17 In the presence of some or all of these factors, TMJ trauma may result in ankylosis. Many researchers believe that injury to the articular disc has a very important position in condylar fractures. Displacement of this disc can very easily lead to joint ankylosis.18 We also postulate that the articular disc between the condyle and articular fossa can act as a barrier that prevents the osseous adhesions, thereby preventing the occurrence of ankylosis. In this study, the discs were pushed inward, so the fracture region of the condyle was in direct contact with the articular fossa, causing internal migration of the articular disc once the fracture occurred. Our results showed that all the operation sites displayed the formation of new bone on the lateral condyle. However, there was a larger quantity of new bone formation in the experimental group, in which the lateral pterygoid muscle had remained. Compared to the control group, their osteogenesis was more dynamic; the osteoblasts and chondrocytes were
more active and the fracture callus was richer in the region of fracture. Of note, the arrangement of bone trabeculae in the new bone formation area in the experimental group showed a certain degree of directionality, which was similar to distraction osteogenesis.19 This may be caused by the repetitive motion of the lateral pterygoid muscle during movement of the mandible. Although they are not identical in appearance, we deduced that this may be because of the power of the lateral pterygoid muscle not sustaining itself or stabilizing. The Sirius red examination results revealed collagen type I and collagen type III to occupy the main position in the experimental group, and the amount of collagen type I increased over time. Collagen type I is the specific collagen produced by osteoblasts and accounts for more than 90% of a mineralized bone matrix. Also, collagen type I is the only type of collagen present in the mineralization of bone tissue. Fibroblasts can secrete types I and III collagen simultaneously, and increases in collagen type I indicate rapid new bone formation. Collagen type II is the specific collagen produced by chondrocytes, which are the main organic component of a cartilage matrix. Collagen type II was not visible in the experimental group, so we can deduce that the experimental group was more prone to intramembranous ossification, with no obvious endochondral ossification. In the experimental group, the condyle on the operation side had a strikingly changed morphology; although no obvious bony ankylosis was observed, osteoblasts were still active at 6 months and the formation of new bone was observed. Given an extended amount of time, this phenomenon is likely to form bony ankylosis. The formation of ankylosis is the result of multiple factors, but our results suggest that the tractive capability of the lateral pterygoid muscle may have an important influence on the occurrence of ankylosis. The purpose of surgical treatment of condylar fractures is to obtain anatomical repositioning to prevent ankylosis. Whether fractures of the condyle need to be fixed depends on many factors. These factors include the age of the patient, the classification of the fracture, the degree of displacement, the time of injury, and the experience and skill of the doctor. Although surgical treatment can slow the rate of ankylosis, the disease cannot be eliminated completely. Through our research, we assert that the power of internal fixation may sometimes be less than the
5
force of the lateral pterygoid muscle, causing traction of the muscle, which eventually leads to ankylosis. The achievement of open reduction and internal fixation of a condylar fracture is difficult because of its special anatomical location. There are many risks associated with surgical exposure, including injury to the facial nerve, scars after the operation, resorption of the condyle, and so on.20 Stricter standards with regard to the patient’s general condition are a requirement for surgery. This surgery is not recommended for paediatric patients, because their bodies are still developing at a rapid rate. Conservative treatment is non-invasive and simple, but in none of the studies included in a recent meta-analysis was conservative treatment shown to be superior to open reduction and internal fixation.20 Various surgical methods have been used in the treatment of joint ankylosis, such as gap arthroplasty, interpositional arthroplasties, and others.21,22 No single standard treatment protocol for TMJ joint ankylosis has been reported. The reankylosis rate remains high.23 If we could prevent the development of ankylosis with conservative treatment, the curative effect might be preferable to early surgical treatment and late reconstruction. Liu et al.24 used occlusal splints in the treatment of sagittal fractures of the mandibular condyle in children. The patient’s mouth was placed in a passive and slightly open position, in order to relax the lateral pterygoid muscle to some extent. The traction of the lateral pterygoid muscle was reduced, thereby avoiding ankylosis. Based on our animal experiments, we can begin to infer that the lateral pterygoid muscle plays a critical role in the reconstruction process of the condyle after sagittal fracture of the mandibular condyle. If we cannot block the traction of the lateral pterygoid muscle with proper intervening measures during the healing process of a fracture, active new bone formation will begin to take place, ultimately leading to ankylosis. It is therefore crucial to explore suitable methods to reduce the effect of the lateral pterygoid muscle after condylar fractures, in order to explore potential ways to prevent TMJ ankylosis. In summary, this study demonstrated that pathological osteogenesis, which is caused by the traction of the lateral pterygoid muscle, might play an important role in the formation of traumatic ankylosis of the TMJ. The study also indicates that the role of distraction osteogenesis of the lateral pterygoid muscle and its relation to ankylosis requires further study.
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
6
Wu et al.
Funding
This work was supported by the National Natural Science Foundation of China (No. 81271168). Competing interests
None declared. Ethical approval
This study was approved by the Ethics Committee, School of Stomatology, Fourth Military Medical University, and was performed in accordance with the recommendations of the Guide for the Care and Use of Laboratory Animals. Patient consent
Not required. References 1. Li J, Zhu S, Wang T, Luo E, Xiao L, Hu J. Staged treatment of temporomandibular joint ankylosis with micrognathia using mandibular osteodistraction and advancement genioplasty. J Oral Maxillofac Surg 2012;70:2884–92. 2. Zhu S, Wang D, Yin Q, Hu J. Treatment guidelines for temporomandibular joint ankylosis with secondary dentofacial deformities in adults. J Craniomaxillofac Surg 2013;41:e117–27. 3. Andrade NN, Kalra R, Shetye SP. New protocol to prevent TMJ reankylosis and potentially life threatening complications in triad patients. Int J Oral Maxillofac Surg 2012;41:1495–500. 4. Koslin MG, Indresano AT, Mercuri LG. Temporomandibular joint surgery. J Oral Maxillofac Surg 2012;70:e204–31. 5. Long X. The relationship between temporomandibular joint ankylosis and condylar fractures. Chin J Dent Res 2012;15:17–20. 6. He D, Ellis 3rd E, Zhang Y. Etiology of temporomandibular joint ankylosis secondary to condylar fractures: the role of concomitant mandibular fractures. J Oral Maxillofac Surg 2008;66:77–84.
7. Arakeri G, Brennan PA. The role of concomitant mandibular fractures in disc displacement and development of TMJ ankylosis secondary to sagittal fractures of the mandibular condyle. Int J Oral Maxillofac Surg 2011;40:1333–5. 8. Wang YL, Li XJ, Qin RF, Lei DL, Liu YP, Wu GY, et al. Matrix metalloproteinase and its inhibitor in temporomandibular joint osteoarthrosis after indirect trauma in young goats. Br J Oral Maxillofac Surg 2008;46: 192–7. 9. Yan YB, Duan DH, Zhang Y, Gan YH. The development of traumatic temporomandibular joint bony ankylosis: a course similar to the hypertrophic nonunion. Med Hypotheses 2012;78:273–6. 10. Meng FW, Zhao JL, Hu KJ, Liu YP. A new hypothesis of mechanisms of traumatic ankylosis of temporomandibular joint. Med Hypotheses 2009;73:92–3. 11. Liu CK, Liu P, Meng FW, Deng BL, Xue Y, Mao TQ, et al. The role of the lateral pterygoid muscle in the sagittal fracture of mandibular condyle (SFMC) healing process. Br J Oral Maxillofac Surg 2012;50: 356–60. 12. Meng F, Hu K, Kong L, Zhao Y, Liu Y, Zhou S. Veterinary and radiological evaluations of open and closed treatment of type B diacapitular (intracapsular) fractures of the mandibular condyle in sheep. Br J Oral Maxillofac Surg 2010;48:448–52. 13. Schmitt J, Roderfeld M, Sabrane K, Zhang P, Tian Y, Mertens JC, et al. Complement factor C5 deficiency significantly delays the progression of biliary fibrosis in bile duct-ligated mice. Biochem Biophys Res Commun 2012;418:445–50. 14. Drab T, Kracmerova J, Ticha I, Hanzlikova E, Ticha M, Ryslava H, et al. Native red electrophoresis—a new method suitable for separation of native proteins. Electrophoresis 2011;32:3597–9. 15. He D, Yang C, Chen M, Zhang X, Qiu Y, Yang X, et al. Traumatic temporomandibular joint ankylosis: our classification and treatment experience. J Oral Maxillofac Surg 2011;69:1600–7. 16. Kanatas AN, Re Worrall SF. Pathogenesis of post-traumatic ankylosis of the temporomandibular joint: a critical review. Br J Oral Maxillofac Surg 2012;50:90–1.
17. Kim SM, Park JM, Kim JH, Kwon KJ, Park YW, Lee JH, et al. Temporomandibular joint ankylosis caused by chondroid hyperplasia from the callus of condylar neck fracture. J Craniofac Surg 2009;20:240–2. 18. Zhang Y, He DM. Clinical investigation of early post-traumatic temporomandibular joint ankylosis and the role of repositioning discs in treatment. Int J Oral Maxillofac Surg 2006;35:1096–101. 19. Cakir-Ozkan N, Eyibilen A, Ozkan F, Ozyurt B, Aslan H. Stereologic analysis of bone produced by distraction osteogenesis or autogenous bone grafting in mandible. J Craniofac Surg 2010;21:735–40. 20. Kyzas PA, Saeed A, Tabbenor O. The treatment of mandibular condyle fractures: a meta-analysis. J Craniomaxillofac Surg 2012;40:e438–52. 21. Karamese M, Duymaz A, Seyhan N, Keskin M, Tosun Z. Management of temporomandibular joint ankylosis with temporalis fascia flap and fat graft. J Craniomaxillofac Surg 2013;41(8):789–93. 22. Nestal-Zibo H, Leibur E, Voog-Oras U, Tamme T. Use of the suture anchor in interpositional arthroplasty of temporomandibular joint ankylosis. Oral Maxillofac Surg 2012;16:157–62. 23. Sporniak-Tutak K, Janiszewska-Olszowska J, Kowalczyk R. Management of temporomandibular ankylosis – compromise or individualization – a literature review. Med Sci Monit 2011;17:RA111–6. 24. Liu CK, Meng FW, Tan XY, Xu J, Liu HW, Liu SX, et al. Clinical and radiological outcomes after treatment of sagittal fracture of mandibular condyle (SFMC) by using occlusal splint in children. Br J Oral Maxillofac Surg 2013;52:144–8.
Address: Kai-Jin Hu State Key Laboratory of Military Stomatology Department of Oral and Maxillofacial Surgery School of Stomatology The Fourth Military Medical University 145 West Changle Road Xi’an 710032 China Tel: +86 29 84776102; Fax: +86 29 84776102 E-mail: [email protected]
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2015.02.004, available online at http://www.sciencedirect.com
Research Paper Trauma
The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study
D. Wua,b,1, X.-J. Yanga,1, P. Chenga, T.-G. Denga, X. Jianga, P. Liua, C.-K. Liua, F.-W. Mengc, K.-J. Hua, a State Key Laboratory of Military Stomatology, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, Xi’an, China; bDepartment of Stomatology, 152nd Hospital of the People’s Liberation Army, Pingdingshan, China; cDepartment of Stomatology, 359th Hospital of the People’s Liberation Army, Zhenjiang, China
D. Wu, X.-J. Yang, P. Cheng, T.-G. Deng, X. Jiang, P. Liu, C.-K. Liu, F.-W. Meng, K.-J. Hu: The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study. Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx. # 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The purpose of this study was to verify the role of the lateral pterygoid muscle in the reconstruction of the condyle shape during the sagittal fracture healing process by histological methods. Twenty-four adult sheep underwent an osteotomy to create a sagittal fracture of the left condyle; the sheep were then divided randomly into two groups. The lateral pterygoid muscles of the sheep in the experimental group were maintained on the internal poles of the condyles, and their functions remained stable. The lateral pterygoid muscles of the sheep in the control group were cut, and their functions were blocked. The shape, erosion, and calcification of the condyles were observed and measured after 4, 12, and 24 weeks of healing (n = 4 from each group). The condyles were then submitted to haematoxylin and eosin, Ponceau S, and Sirius red studies. The results of the histology studies showed increased bone formation in the experimental group in which the functions of the lateral pterygoid muscle remained the same. The results of this study suggest that the lateral pterygoid muscle affects the reconstruction of the condylar shape during the healing process of a sagittal fracture of the mandibular condyle, and may even be involved in the formation of ankylosis.
Ankylosis of the temporomandibular joint (TMJ) is a serious and disabling disease that severely restricts the movements of the mandible. It can cause problems with mastication, swallowing, digestion, speech, and breathing, and is even known to 0901-5027/000001+06
contribute to psychological disorders. When ankylosis of the TMJ occurs during childhood, it can retard mandibular development and lead to more serious maxillofacial deformities and dysfunction, such as facial asymmetry, micrognathia, and
Key words: lateral pterygoid muscle; temporomandibular joint; ankylosis; trauma. Accepted for publication 3 February 2015
malocclusion.1,2 Ankylosis of the TMJ is difficult to treat and its cause is quite complex. It can result from physical trauma, or 1 These authors contributed equally to this work.
# 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
2
Wu et al.
from local or systemic infections. Reankylosis is the most common complication after treatment,3 and the recurrence rate is 4–31%.4 An exploration of the pathogenesis of this disease might provide new avenues for the prevention and treatment of TMJ ankylosis. In previous reports, trauma has been considered the main cause of ankylosis.5 Both animal experiments and clinical observations have indicated that sagittal fracture of the mandibular condyle is more likely to lead to ankylosis than other types of condylar fracture.6,7 However, the specific mechanism by which ankylosis develops during the wound healing process remains the subject of controversy. Some researchers believe that the pathogenesis of traumatic TMJ ankylosis is the organization and ossification of an intracapsular haematoma after injury.5,6 Animal experiments, though, have shown that intracapsular haematoma alone does not cause ankylosis.8 Recently, some researchers have proposed that ankylosis of the TMJ is a progression, which like hypertrophic non-union, develops in long bone.9 Because of the way the mouth moves, these injuries cannot completely recover and eventually form bone adhesions.9 We hypothesized that distraction osteogenesis of the lateral pterygoid muscle may be an important factor in the genesis of traumatic TMJ ankylosis.10 Recent animal studies by our group further confirmed that the lateral pterygoid muscle plays an important role in the reconstruction of the condyle shape during the sagittal fracture healing process.11,12 Based on the research performed, we postulate that pathological osteogenesis may be caused by the traction of the lateral pterygoid muscle, which is crucial in the formation of traumatic ankylosis in the TMJ. The primary goal of this study was to substantiate the role of the lateral pterygoid muscle in the sagittal fracture healing process of the mandibular condyle, through histological methods. Materials and methods
The study protocol was approved by the ethics committee of the military medical university. All sheep were cared for in accordance with the guidelines for animal research set by the animal research centre laboratory of the military medical university. Twenty-four 1-year-old, healthy sheep were divided randomly into two groups of 12. All operations were done under satisfactory anaesthesia. After creating the fracture, the function of the lateral pterygoid muscle was cut off in
the control group, while the muscle was left unaltered in the experimental group.
assessed using the Student’s t-test; P < 0.05 was accepted as significant.
Operations
Results
The sheep were anaesthetized with xylazine hydrochloride (0.1 ml/kg) and their temporal regions were shaved and sterilized. We exposed the zygomatic arch and panniculus carnosus muscles at the surface of the capsule of the TMJ using a curved pre-auricular skin incision. A horizontal incision was then made through the capsule at the condylar neck in order to open the inferior joint space. The condylar head was then isolated and the superior joint space exposed. After pushing the disc inward, an oblique vertical osteotomy was made from the lateral pole of the condyle to the medial side of the condylar neck, using an ultrasound osteotome. The lateral pterygoid muscles of the sheep in the control group were separated and completely cut off, and the muscles of the sheep in the experimental group were maintained. The wound was closed in layers without suture of the capsule. After the operation, penicillin (20 mg/kg, twice a day) was given to each sheep to prevent infection, and this was continued for 3 days. Four sheep in each group were sacrificed at intervals of 4 weeks, 12 weeks, and 24 weeks after surgery. The TMJ was isolated, observed, and measured. Specimens were then examined histologically under a microscope.
Healing was uneventful following sagittal fracture in all 24 sheep. None of the sheep exhibited a clinical infection. Their skin exhibited only minor signs of inflammation during the first few weeks of healing. The animals were observed carefully and histological analyses were performed at 4 weeks, 12 weeks, and 24 weeks after the operation.
Observation
After the TMJ of the study animals had been isolated, we observed the shape, erosion, and calcification of the joint. The sizes of the condyles in both groups were measured using a Vernier caliper. Histological analysis
Specimens were fixed in a 4% formaldehyde solution for 2 weeks, and then decalcified in ethylenediaminetetraacetic acid (EDTA) for 3 months. Semi-serial sections measuring 5 mm in thickness were cut in the sagittal plane. The sections were stained with haematoxylin and eosin (H&E), Ponceau S, and Sirius red, as described previously.13,14 The sections were then subjected to histological analysis. Statistical analysis
SPSS version 16.0 software (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. The significance of the variations between the two groups was
4 weeks
In the biopsies obtained after 4 weeks, the surface roughness of the condyle was increased in both groups. The change was more apparent, with observable protuberances, in the experimental group (Fig. 1A and D). The size of the condyle was measured with a Vernier caliper. As shown in Table 1, the mediolateral size of the condyle in the experimental group was significantly larger than that of the control group (P < 0.05), while the anteroposterior size of the condyle showed no significant difference (P > 0.05). H&E examination showed the osteoblasts and chondrocytes to be actively growing in the fracture zone of both groups, but this was more distinct in the experimental group. Blood vessels were found in the fracture callus. Fresh bone formation was more vigorous in the experimental group than in the control group (Fig. 2A and D). Ponceau S examination showed a large amount of new bone in the fracture zone and the quantity of this was greater in the experimental group than in the control group (Fig. 3A and D). Sirius red examination showed the presence of collagen type I and III in both groups, while some thin collagen type II was found in the control group. Collagen type III appeared in larger amounts in the experimental group than in the control group (Fig. 4A and D).
12 weeks
After 12 weeks of healing, the volume of the condyle had increased in both groups. However, it was better defined in the experimental group, with larger and more obvious protuberances (Fig. 1B and E). Both the anteroposterior size and the mediolateral size of the condyle in the experimental group were significantly larger than those of the control group (P < 0.05; Table 1).
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
Lateral pterygoid muscle and fracture healing
3
Fig. 1. Changes in the condylar morphology after the operation. At 4, 12, and 24 weeks after the operation, changes were more obvious in the experimental group (A–C) than in the control group (D–F).
Table 1. Size of the condyle after the operation, measured by Vernier caliper (millimetres). Group Anteroposterior Muscle cut (Control) Muscle not cut Mediolateral Muscle cut (Control) Muscle not cut a
P < 0.05.
Postoperative week 4
12
24
14.5 (2.1) 15.1 (2.6)
15.4 (3.1) 16.8 (3.9)a
15.6 (3.1) 17.5 (4.3)a
22.6 (3.0) 23.3 (3.9)a
24.6 (4.0) 28.3 (5.4)a
24.8 (4.2) 29.6 (5.6)a
On H&E examination, osteoblasts around the mature trabecular bone, plus further deposition of new bone was seen in the experimental group, while bone structure close to maturity with osteoblasts was hardly seen at all in the control group (Fig. 2B and E). Ponceau S examination showed a mass of mature bone matrix to have appeared in the fracture zone. New bone was still forming slowly in the experimental group when compared to
Fig. 2. Histological sections showing that osteoblasts were more active in the experimental group at 4, 12, and 24 weeks after the operation (A–C) than in the control group (D–F) (haematoxylin and eosin stain, original magnification 100).
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
4
Wu et al.
Fig. 3. Histological sections showing that the amounts of newly generated bone were greater in the experimental group at 4, 12, and 24 weeks after the operation (A–C) than in the control group (D–F) (Ponceau S stain, original magnification 100).
Fig. 4. Histological sections showing that the type of collagen was different between the experimental group and the control group at 4 weeks after the operation (A and D), and that the collagen was thicker in the experimental group (B and C) than in the control group (E and F) at 12 and 24 weeks after the operation (Sirius red stain, original magnification 100).
the control group (Fig. 3B and E). Sirius red examination showed a large quantity of collagen type I and less collagen type III in the experimental group. Collagen type II
had disappeared completely in the control group, and the size of collagen type I was smaller than that of the experimental group (Fig. 4B and E).
24 weeks
At 24 weeks after the operation, the volume of the condyle had increased slightly
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
Lateral pterygoid muscle and fracture healing in both groups, and protuberances had morphed into apophysis in the experimental group (Fig. 1C and F). Both the anteroposterior size and the mediolateral size of the condyle in the experimental group were significantly larger than those of the control group (P < 0.05; Table 1). On H&E examination, osteoblasts existed only in the experimental group; mature trabecular bone was found in the experimental group compared with lamellar bone in control group (Fig. 2C and F). Ponceau S examination showed that new bone was mature in both groups. A small amount of the newly generated bone could be seen in the experimental group as compared to the control group (Fig. 3C and F). Sirius red examination showed that collagen type I was most common, whereas collagen type III was rarer in both groups (Fig. 4C and F). Discussion
It is well known that the general reason for traumatic ankylosis of the temporomandibular joint (TMJ) is a common ‘bone healing disorder’, which is affected by multiple factors. These factors include post-traumatic bleeding, fracture of the condyle, changes in condylar shape, shifting of the condyle, mismatching of the condyle and infratemporal fossa, shift of and trauma to the articular disc, trauma to the infratemporal fossa, and distraction osteogenesis of the lateral pterygoid muscle.5,15,16 These factors can cause excessive TMJ local bone hyperplasia and eventually ankylosis of the TMJ.17 In the presence of some or all of these factors, TMJ trauma may result in ankylosis. Many researchers believe that injury to the articular disc has a very important position in condylar fractures. Displacement of this disc can very easily lead to joint ankylosis.18 We also postulate that the articular disc between the condyle and articular fossa can act as a barrier that prevents the osseous adhesions, thereby preventing the occurrence of ankylosis. In this study, the discs were pushed inward, so the fracture region of the condyle was in direct contact with the articular fossa, causing internal migration of the articular disc once the fracture occurred. Our results showed that all the operation sites displayed the formation of new bone on the lateral condyle. However, there was a larger quantity of new bone formation in the experimental group, in which the lateral pterygoid muscle had remained. Compared to the control group, their osteogenesis was more dynamic; the osteoblasts and chondrocytes were
more active and the fracture callus was richer in the region of fracture. Of note, the arrangement of bone trabeculae in the new bone formation area in the experimental group showed a certain degree of directionality, which was similar to distraction osteogenesis.19 This may be caused by the repetitive motion of the lateral pterygoid muscle during movement of the mandible. Although they are not identical in appearance, we deduced that this may be because of the power of the lateral pterygoid muscle not sustaining itself or stabilizing. The Sirius red examination results revealed collagen type I and collagen type III to occupy the main position in the experimental group, and the amount of collagen type I increased over time. Collagen type I is the specific collagen produced by osteoblasts and accounts for more than 90% of a mineralized bone matrix. Also, collagen type I is the only type of collagen present in the mineralization of bone tissue. Fibroblasts can secrete types I and III collagen simultaneously, and increases in collagen type I indicate rapid new bone formation. Collagen type II is the specific collagen produced by chondrocytes, which are the main organic component of a cartilage matrix. Collagen type II was not visible in the experimental group, so we can deduce that the experimental group was more prone to intramembranous ossification, with no obvious endochondral ossification. In the experimental group, the condyle on the operation side had a strikingly changed morphology; although no obvious bony ankylosis was observed, osteoblasts were still active at 6 months and the formation of new bone was observed. Given an extended amount of time, this phenomenon is likely to form bony ankylosis. The formation of ankylosis is the result of multiple factors, but our results suggest that the tractive capability of the lateral pterygoid muscle may have an important influence on the occurrence of ankylosis. The purpose of surgical treatment of condylar fractures is to obtain anatomical repositioning to prevent ankylosis. Whether fractures of the condyle need to be fixed depends on many factors. These factors include the age of the patient, the classification of the fracture, the degree of displacement, the time of injury, and the experience and skill of the doctor. Although surgical treatment can slow the rate of ankylosis, the disease cannot be eliminated completely. Through our research, we assert that the power of internal fixation may sometimes be less than the
5
force of the lateral pterygoid muscle, causing traction of the muscle, which eventually leads to ankylosis. The achievement of open reduction and internal fixation of a condylar fracture is difficult because of its special anatomical location. There are many risks associated with surgical exposure, including injury to the facial nerve, scars after the operation, resorption of the condyle, and so on.20 Stricter standards with regard to the patient’s general condition are a requirement for surgery. This surgery is not recommended for paediatric patients, because their bodies are still developing at a rapid rate. Conservative treatment is non-invasive and simple, but in none of the studies included in a recent meta-analysis was conservative treatment shown to be superior to open reduction and internal fixation.20 Various surgical methods have been used in the treatment of joint ankylosis, such as gap arthroplasty, interpositional arthroplasties, and others.21,22 No single standard treatment protocol for TMJ joint ankylosis has been reported. The reankylosis rate remains high.23 If we could prevent the development of ankylosis with conservative treatment, the curative effect might be preferable to early surgical treatment and late reconstruction. Liu et al.24 used occlusal splints in the treatment of sagittal fractures of the mandibular condyle in children. The patient’s mouth was placed in a passive and slightly open position, in order to relax the lateral pterygoid muscle to some extent. The traction of the lateral pterygoid muscle was reduced, thereby avoiding ankylosis. Based on our animal experiments, we can begin to infer that the lateral pterygoid muscle plays a critical role in the reconstruction process of the condyle after sagittal fracture of the mandibular condyle. If we cannot block the traction of the lateral pterygoid muscle with proper intervening measures during the healing process of a fracture, active new bone formation will begin to take place, ultimately leading to ankylosis. It is therefore crucial to explore suitable methods to reduce the effect of the lateral pterygoid muscle after condylar fractures, in order to explore potential ways to prevent TMJ ankylosis. In summary, this study demonstrated that pathological osteogenesis, which is caused by the traction of the lateral pterygoid muscle, might play an important role in the formation of traumatic ankylosis of the TMJ. The study also indicates that the role of distraction osteogenesis of the lateral pterygoid muscle and its relation to ankylosis requires further study.
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
YIJOM-3098; No of Pages 6
6
Wu et al.
Funding
This work was supported by the National Natural Science Foundation of China (No. 81271168). Competing interests
None declared. Ethical approval
This study was approved by the Ethics Committee, School of Stomatology, Fourth Military Medical University, and was performed in accordance with the recommendations of the Guide for the Care and Use of Laboratory Animals. Patient consent
Not required. References 1. Li J, Zhu S, Wang T, Luo E, Xiao L, Hu J. Staged treatment of temporomandibular joint ankylosis with micrognathia using mandibular osteodistraction and advancement genioplasty. J Oral Maxillofac Surg 2012;70:2884–92. 2. Zhu S, Wang D, Yin Q, Hu J. Treatment guidelines for temporomandibular joint ankylosis with secondary dentofacial deformities in adults. J Craniomaxillofac Surg 2013;41:e117–27. 3. Andrade NN, Kalra R, Shetye SP. New protocol to prevent TMJ reankylosis and potentially life threatening complications in triad patients. Int J Oral Maxillofac Surg 2012;41:1495–500. 4. Koslin MG, Indresano AT, Mercuri LG. Temporomandibular joint surgery. J Oral Maxillofac Surg 2012;70:e204–31. 5. Long X. The relationship between temporomandibular joint ankylosis and condylar fractures. Chin J Dent Res 2012;15:17–20. 6. He D, Ellis 3rd E, Zhang Y. Etiology of temporomandibular joint ankylosis secondary to condylar fractures: the role of concomitant mandibular fractures. J Oral Maxillofac Surg 2008;66:77–84.
7. Arakeri G, Brennan PA. The role of concomitant mandibular fractures in disc displacement and development of TMJ ankylosis secondary to sagittal fractures of the mandibular condyle. Int J Oral Maxillofac Surg 2011;40:1333–5. 8. Wang YL, Li XJ, Qin RF, Lei DL, Liu YP, Wu GY, et al. Matrix metalloproteinase and its inhibitor in temporomandibular joint osteoarthrosis after indirect trauma in young goats. Br J Oral Maxillofac Surg 2008;46: 192–7. 9. Yan YB, Duan DH, Zhang Y, Gan YH. The development of traumatic temporomandibular joint bony ankylosis: a course similar to the hypertrophic nonunion. Med Hypotheses 2012;78:273–6. 10. Meng FW, Zhao JL, Hu KJ, Liu YP. A new hypothesis of mechanisms of traumatic ankylosis of temporomandibular joint. Med Hypotheses 2009;73:92–3. 11. Liu CK, Liu P, Meng FW, Deng BL, Xue Y, Mao TQ, et al. The role of the lateral pterygoid muscle in the sagittal fracture of mandibular condyle (SFMC) healing process. Br J Oral Maxillofac Surg 2012;50: 356–60. 12. Meng F, Hu K, Kong L, Zhao Y, Liu Y, Zhou S. Veterinary and radiological evaluations of open and closed treatment of type B diacapitular (intracapsular) fractures of the mandibular condyle in sheep. Br J Oral Maxillofac Surg 2010;48:448–52. 13. Schmitt J, Roderfeld M, Sabrane K, Zhang P, Tian Y, Mertens JC, et al. Complement factor C5 deficiency significantly delays the progression of biliary fibrosis in bile duct-ligated mice. Biochem Biophys Res Commun 2012;418:445–50. 14. Drab T, Kracmerova J, Ticha I, Hanzlikova E, Ticha M, Ryslava H, et al. Native red electrophoresis—a new method suitable for separation of native proteins. Electrophoresis 2011;32:3597–9. 15. He D, Yang C, Chen M, Zhang X, Qiu Y, Yang X, et al. Traumatic temporomandibular joint ankylosis: our classification and treatment experience. J Oral Maxillofac Surg 2011;69:1600–7. 16. Kanatas AN, Re Worrall SF. Pathogenesis of post-traumatic ankylosis of the temporomandibular joint: a critical review. Br J Oral Maxillofac Surg 2012;50:90–1.
17. Kim SM, Park JM, Kim JH, Kwon KJ, Park YW, Lee JH, et al. Temporomandibular joint ankylosis caused by chondroid hyperplasia from the callus of condylar neck fracture. J Craniofac Surg 2009;20:240–2. 18. Zhang Y, He DM. Clinical investigation of early post-traumatic temporomandibular joint ankylosis and the role of repositioning discs in treatment. Int J Oral Maxillofac Surg 2006;35:1096–101. 19. Cakir-Ozkan N, Eyibilen A, Ozkan F, Ozyurt B, Aslan H. Stereologic analysis of bone produced by distraction osteogenesis or autogenous bone grafting in mandible. J Craniofac Surg 2010;21:735–40. 20. Kyzas PA, Saeed A, Tabbenor O. The treatment of mandibular condyle fractures: a meta-analysis. J Craniomaxillofac Surg 2012;40:e438–52. 21. Karamese M, Duymaz A, Seyhan N, Keskin M, Tosun Z. Management of temporomandibular joint ankylosis with temporalis fascia flap and fat graft. J Craniomaxillofac Surg 2013;41(8):789–93. 22. Nestal-Zibo H, Leibur E, Voog-Oras U, Tamme T. Use of the suture anchor in interpositional arthroplasty of temporomandibular joint ankylosis. Oral Maxillofac Surg 2012;16:157–62. 23. Sporniak-Tutak K, Janiszewska-Olszowska J, Kowalczyk R. Management of temporomandibular ankylosis – compromise or individualization – a literature review. Med Sci Monit 2011;17:RA111–6. 24. Liu CK, Meng FW, Tan XY, Xu J, Liu HW, Liu SX, et al. Clinical and radiological outcomes after treatment of sagittal fracture of mandibular condyle (SFMC) by using occlusal splint in children. Br J Oral Maxillofac Surg 2013;52:144–8.
Address: Kai-Jin Hu State Key Laboratory of Military Stomatology Department of Oral and Maxillofacial Surgery School of Stomatology The Fourth Military Medical University 145 West Changle Road Xi’an 710032 China Tel: +86 29 84776102; Fax: +86 29 84776102 E-mail: [email protected]
Please cite this article in press as: Wu D, et al. The lateral pterygoid muscle affects reconstruction of the condyle in the sagittal fracture healing process: a histological study, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.02.004
