J Oral Maxillofac 50:669-873.
Surg
1992
Creation of Disc Displacement in Human Temporomandibular Joint Autopsy Specimens LARS
DONALD
ERIKSSON, DDS, PHD,* PER-LENNART WESTESSON, MACHER, DMD,$ DAVID HICKS, MD,§ AND ROSS H.
DDS, PHD,t TALENTS, DDS”
The purpose of this study was to investigate the possibility of ,iatrogenically creating disc displacement in the human temporomandibular joint (TMJ). Fourteen fresh TMJ autopsy specimens with superior disc position were selected for the study. The upper and lower joint spaces were exposed via a preauricular incision and two to three superficial mediolateral incisions were made in the inferior surface of the posterior disc attachment (ie, retrodiscal tissue). After these incisions were made it was possible to manually displace the disc anteriorly. To maintain the disc in the anterior position the condyle was positioned against the posterior disc attachment in a manner corresponding to the closed mouth position. The joints were then fixed in this relationship and magnetic resonance imaging (MRI) was repeated using the same scanning plane and scanning parameters as before intervention. After imaging, the joints were cryosectioned to show the degree of disc displacement. Histologic analysis was made of the posterior disc attachment. Postoperative MR images and cryosections showed the disc to be displaced anteriorly in 12 of the 14 joints. Displacement of the disc was complete in eight joints (the entire mediolateral dimension of the joint) and partial (only in the lateral part of the joint) in four joints. The disc remained in a superior position in two joints. Cryosections and histologic analysis showed the incisions in the inferior aspect of the posterior disc attachment to be superficial. The results of this study suggest that the integrity of the inferior aspect of the posterior attachment of the disc to the condyle is essential for keeping the disc in its position superior to the condyle. Minor damage to this tissue layer could be one event that leads to disc displacement and internal derangement.
Disc displacement and arthrosis are the most common disorders affecting the temporomandibular joint (TMJ).‘” The etiology of disc displacement is unknown in the majority of cases, although trauma has been suggested as one possible etiologic factor for the development of disc displacement.“6 From an anatomic point of view, the lateral part of the posterior attachment of the disc to the condyle has a slightly different architecture than the more central and medial parts of the posterior disc attachment.7*8 Experience from TMJ surgery has suggested that when the inferior layer of the posterior and lateral attachment between the disc and the condyle is damaged it loses its firmness and becomes more elastic, allowing the disc to displace anteriorly or anteromedially. The hypothesis for this study was that superficial damage to the inferior layer of the posterior attachment between the disc and the condyle would permit disc displacement. To test this hypothesis
* Formerly, Visiting Professor, University of Rochester School of Medicine and Dentistry, Rochester, NY; currently, Associate Professor, Department of Oral Surgery, University Hospital, Lund. Sweden. t Associate Professor, Department of Radiology, University of Rochester School of Medicine and Dentistry, Rochester, NY. $ Instructor, Department of Orthodontics, Eastman Dental Center, Rochester, NY; Attending, Department of Oral and Maxillofacial Surgery, St Mary’s Hospital, Rochester, NY. § Assistant Professor, Department of Pathology, University of Rochester School of Medicine and Dentistry, Rochester, NY. ‘IAssistant Professor, Department of Clinical Dentistry, University of Rochester School of Medicine and Dentistry, Rochester, NY: Clinical Associate, Department of Orthodontics; Department of Prosthodontics, Eastman Dental Center, Rochester, NY. The study was supported by grants from the Torsten and Ragnar S&de&ergs Foundations, Stockholm, Sweden. Address correspondence and reprint requests to Dr Westesson: Department of Radiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 648, Rochester, NY 14642. 0 1992 American Association of Oral and Maxillofacial Surgeons 0278-2391/92/5008-0013$3.00/O
869
870
DISC DISPLACEMENT IN HUMAN TMJ AUTOPSY SPECIMENS
we obtained a series of fresh human TMJ autopsy specimens and studied them with magnetic resonance imaging (MRI). Those joints that had a superior disc position in the closed mouth position and no MR evidence of arthrosis were selected for further study. This article reports the results of creating superlicial damage to the inferior surface of the posterior attachment between the disc and the condyle. Material Fresh TMJ specimens were obtained in association with a routine autopsy examination that included autopsy of the brain. The specimens measured about 10 X 8 X 6 cm and were removed via the middle cranial fossa leaving the exterior of the cadaver intact. They were removed within 48 hours after death and kept deep-frozen until the study was undertaken. The mean age of individuals was 76 years, with a range from 62 to 82 years. No information regarding prior symptoms or treatment for possible TMJ disease was available. Initially, 23 specimens were obtained and imaged, but only the 14 with superior disc position and no MR evidence of arthrosis were included in this study. Methods After thawing the specimens to room temperature they were imaged on a 1.5 T MR scanner (Signa, General Electric, Milwaukee, WI) using a 6 X 8-cm surface coil. Sagittal and coronal images were obtained in planes that were parallel (coronal) and perpendicular (sag&al) to the long axis of the condyle.’ The scanning parameters were time of repetition = 2,000 milliseconds, time of echo = 25 and 80 milliseconds, field of view = 10 cm, slice thickness = 3 mm, number of excitations = 1, interslice gap = 0.5 mm. The MR images were obtained with the condyle located in the glenoid fossa corresponding to the closed mouth position. Following imaging, the joints were attached to a specifically designed holder” and opened in the same way as during clinical surgery,’ ’ exposing the upper and the lower joint spaces. Two to three superficial incisions were made mediolaterally in the inferior surface of the posterior attachment posterior to the disc itself. This area was termed the condylar part of the posterior disc attachment by Scapino. 7,8 The incisions were made with a no. 10 scalpel blade and were about 10 mm long in a mediolateral direction and less than 0.5 mm deep. The disc was then manually moved in an anterior direction and the condyle was pushed superiorly into the glenoid fossa behind the disc to maintain the disc in the anterior position. The top of the condyle now articulated against the inferior surface of the posterior disc attachment instead of the inferior surface of the disc. The joints were stabilized in this position with
the aid of a holding device.‘O The joint capsule was sutured and the specimens were stabilized in this position by attaching multiple layers of firm tape. The specimens were then removed from the holding device and the MR examination was repeated using the same scanning parameters and scanning planes as before. The laser lights on the MR scanner were used to assure that the positioning of the specimens was the same as before intervention. Following the second MR scan, the specimens were deep-frozen and embedded in acrylic material. The embedded specimens formed a rectangular box with the surfaces of the box parallel and perpendicular to the long axis of the condyle. The specimens were then cryosectioned in the sag&al plane as previously described.12 The cryosections were made at 3.5-mm increments parallel to the sagittal MR scans. The newly cut surface was photographed using a macro lens and high-resolution color slide film (Kodak K25, Kodak, Rochester, NY). The postsurgical MR images and cryosections were compared with the presurgical MR images and the degree of displacement was classified as partial or complete. Complete displacement implied that the disc was anteriorly displaced in the lateral, central, and medial parts of the joints. Partial displacement implied that the disc was anteriorly displaced in the lateral part of the joint only. Following the cryosectioning, the thin sections of the joints (approximately 2 mm thick) were fixed in 10% neutral buffered formalin and decalcified with a mixture of formalin and formic acid. Histologic sections (4 pm) were obtained and stained with hematoxylin and eosin, elastic, and Gomori connective tissue stains. The posterior attachment was evaluated for the extent of damage. Results After the joint compartments were opened, but before the incisions were made in the posterior disc attachment, it was not possible to displace the disc forward either by pushing the condyle up into the glenoid fossa or by manually pulling the disc forward. The posterior attachment appeared to hold the disc in place on top of the condyle. After the superficial incisions were made into the posterior disc attachment, this tissue became more elastic and lost its firmness. It was now possible to manually displace the disc forward. The posterior disc attachment was elastic, however, and the disc moved back to the top of the condyle. If the condyle was moved up into the glenoid fossa behind the disc, the disc remained in the anterior position. The superior part of the condyle now articulated against the posterior disc attachment and not against the disc itself.
ERIKSSON ET AL
FIGURE 1. Creation of disc displacement. A, Sag&alMR image before surgical intervention. The disc (arrow) is located with its posterior band superior to the condyle. B, Sagittal MR image after surgical intervention and creation of disc displacement. The disc (arrow) is displaced anterior to the condyle. C, Sagittal cryosection confirming disc displacement. The disc (white arrow) is anterior to the condyle and the posterior disc attachment (black arrows) is elongated.
The postoperative MR images showed that eight joints had complete anterior disc displacement (Fig I), four joints showed partial anterior disc displacement (Fig 2), and two joints showed normal superior disc position. The cryosections confirmed the observations of the MR images in all joints. Histologic evaluation showed that the damage to the posterior disc attachment was confined to the superficial, inferior layer of the posterior disc attachment (Fig 3). Elastic stains of the posterior disc attachment showed disorganization of the elastic and collagen fibers in the joints with disc displacement (Fig 3B). Diccussion This study has shown that it is possible to create anterior disc displacement in the human TMJ by making superficial incisions into the inferior layer of the posterior disc attachment and then pushing the condyle up into the glenoid fossa behind the disc. Normally the disc is firmly attached to the condyle,13 but after the incisions were made the posterior attachment became elastic and it was possible to manually move the
FIGURE 2. Partial anterior disc displacement. A. Cryosection from lateral part of joint showing the disc anterior to the condyle. The posterior band of the disc is indicated by an arrow. B, Cryosection from medial part of the same joint showing disc in superior position. The posterior band of the disc is indicated by an arrow.
disc forward. This phenomenon is similar to what is seen when the periosteum is incised in a mucoperiosteal flap for closure of an oroantral fistula. This observation suggests that weakness of the posterior attachment between the disc and the condyle might be one factor in the etiology of disc displacement. The study, however, does not provide any evidence to suggest the cause of the weakness of the posterior disc attachment. It only confirms that it is possible to displace the disc anteriorly after superficial incisions were made into the inferior surface of the posterior disc attachment. Because of the surgical opening in the lateral capsule wall, the significance of the lateral attachment could not be evaluated with our study design. The fact that we found several rotational disc displacements where the lateral part of the disc was anteriorly displaced but the medial part of the disc was still in a normal superior position may indicate that there is some significance to severance of the lateral disc attachment. It was, however, our impression from these experiments that it was usually not enough to cut the lateral disc attachment to displace the disc. The impression in these joints was that the incisions in the inferior surface of the posterior disc
872
DISC DISPLACEMENT IN HUMAN TMJ AUTOPSY SPECIMENS
FIGURE 3. Histologic sections of inferior surface of posterior disc attachment. A, Intact posterior disc attachment. The surface (arrows) of the attachment is intact. The collagen and elastic fibers are organized in a relatively parallel fashion (elastic stain). B, Damaged inferior surface of posterior disc attachment. Area of surgical intervention is indicated by arrows. The collagen and elastic fibem are disorganized (elastic stain).
attachment were essential to allow for the disc to be displaced. According to Rees, I4 the posterior attachment of the disc has two layers. The superior layer is attached to the squamotympanic fissure and the inferior layer is attached to the condyle. The superior layer consists of elastic fibers, while the inferior layer is more ligamentous in nature and its collagenous fibers exhibit a wavy appearance similar to the character of ligaments.15 These morphologic observations strongly support the importance of the inferior aspect of the posterior disc attachment for maintaining the disc position on top of the condyle. A comprehensive study of the collagen fiber organization in the posterior disc attachment was recently reported by Scapino. 738He described three groups of collagen fibers in the posterior attachment and these were termed the temporal part, the intermediate part, and the condylar part of the posterior attachment. The incisions made in this study were confined to the condylar part of the posterior disc attachment. The temporal and condylar fibers of the posterior disc attachment were found to be interwoven with a fanlike radiation into the posterior band of the disc. However, in the lateral part of the joint, where the posterior attachment as well as the posterior band of the disc tends to be thinner, the fibers connected the posterior attachment and the disc in a more parallel fashion.‘x8
One may speculate that this arrangement may be an anatomic weakness of the posterior attachment. It is supported by the clinical observation that anterior displacement of the disc is more commonly seen in the lateral part of the joint than in the medial part of the joint.“’ Our attempt to create disc displacement was unsuccessful in two joints. There are at least two possible explanations for this. First, the incision in the attachment might have been too superficial and the disc was not significantly displaced. The other explanation could be that the disc was displaced but the condyle did not sufficiently prevent the disc from moving back into its original position. This study has shown that relatively minimal surgical damage to the inferior surface of the posterior disc attachment in association with severance of the lateral joint capsule allows the disc to be anteriorly displaced. This suggests that damage to these tissues may play a role in the development of disc displacement in the human TMJ. References 1. Eriksson L, Westesson P-L: Clinical and radiological study of patients with anterior disc displacement of the temporomandibular joint. Swed Dent J 7:55, 1983 2. Westesson P-L: Double-contrast arthrotomography of the temporomandibular joint: Introduction of an arthrographic tech-
873
ERIKSSON ET AL
3.
4. 5.
6.
7.
8.
9.
nique for visualization of the disc and articular surfaces. J Oral Maxillofac Surg 41:163, 1983 Paesani D, Westesson P-L, Hatala M, et al: Prevalence of temporomandibular joint internal derangement in patients with craniomandibular disorders. Am J Orthod Dentofacial Orthop 101:41, 1992 Katzberg RW, Dolwick MF, Helms CA, et al: Arthrotomography of the temporomandibular joint. AJR 134:995, I980 Harkins SJ, Marteney JL: Extrinsic trauma: A significant precipitating factor in temporomandibular dysfunction. J Prosthet Dent 54271, 1985 Weinberg S. Lapointe H: Cervical extension-flexion injury (whiplash) and internal derangement of the temporomandibular joint. J Oral Maxillofac Surg 45:653, 1987 Scapino RP: The posterior attachment: Its structure, function, and appearance in TMJ imaging studies. Part 1. J Craniomandib Disord Facial Oral Pain 5:83, 199 1 Scapino RP: The posterior attachment: Its structure, function, and appearance in TMJ imaging studies. Part 2. J Craniomandib Disord Facial Oral Pain 5: 155, 199 1 Musgrave MT, Westesson P-L, Tallents RH, et al: Improved
10.
11.
12.
13.
14. 15.
magnetic resonance imaging of the temporomandibular joint by oblique scanning planes. Oral Surg Oral Med Oral Pathol 71:525, 1990 Westesson P-L, Omnell K-A, Rohlin M: Double-contrast tomography of the temporomandibular joint. A new technique based on autopsy specimen examinations. Acta Radio1 (Diagn) (Stockh) 21:777. 1980 Eriksson L: Diagnosis and surgical treatment of internal derangement of the temporomandibular joint. Thesis. University of Lund. Swed Dent J 25:6, 1985 (suppl IV) Westesson P-L, Bronstein SL, Liedberg J: Internal derangement of the temporomandibular joint: Morphologic description with correlation to joint function. Oral Surg Oral Med Oral Pathol 59:323, 1985 Griffin CJ, Hawthorn R. Harris R: Anatomy and histology of the human temporomandibular joint. Monogr Oral Sci 4: 1, 1975 Rees LA: The structure and function of the mandibular joint. Br Dent J 96:125, 1954 Griffin CJ, Sharpe CJ: The structure of the adult human temporomandibular meniscus. Aust Dent J 5: 190, 1960
Surg
1992
Creation of Disc Displacement in Human Temporomandibular Joint Autopsy Specimens LARS
DONALD
ERIKSSON, DDS, PHD,* PER-LENNART WESTESSON, MACHER, DMD,$ DAVID HICKS, MD,§ AND ROSS H.
DDS, PHD,t TALENTS, DDS”
The purpose of this study was to investigate the possibility of ,iatrogenically creating disc displacement in the human temporomandibular joint (TMJ). Fourteen fresh TMJ autopsy specimens with superior disc position were selected for the study. The upper and lower joint spaces were exposed via a preauricular incision and two to three superficial mediolateral incisions were made in the inferior surface of the posterior disc attachment (ie, retrodiscal tissue). After these incisions were made it was possible to manually displace the disc anteriorly. To maintain the disc in the anterior position the condyle was positioned against the posterior disc attachment in a manner corresponding to the closed mouth position. The joints were then fixed in this relationship and magnetic resonance imaging (MRI) was repeated using the same scanning plane and scanning parameters as before intervention. After imaging, the joints were cryosectioned to show the degree of disc displacement. Histologic analysis was made of the posterior disc attachment. Postoperative MR images and cryosections showed the disc to be displaced anteriorly in 12 of the 14 joints. Displacement of the disc was complete in eight joints (the entire mediolateral dimension of the joint) and partial (only in the lateral part of the joint) in four joints. The disc remained in a superior position in two joints. Cryosections and histologic analysis showed the incisions in the inferior aspect of the posterior disc attachment to be superficial. The results of this study suggest that the integrity of the inferior aspect of the posterior attachment of the disc to the condyle is essential for keeping the disc in its position superior to the condyle. Minor damage to this tissue layer could be one event that leads to disc displacement and internal derangement.
Disc displacement and arthrosis are the most common disorders affecting the temporomandibular joint (TMJ).‘” The etiology of disc displacement is unknown in the majority of cases, although trauma has been suggested as one possible etiologic factor for the development of disc displacement.“6 From an anatomic point of view, the lateral part of the posterior attachment of the disc to the condyle has a slightly different architecture than the more central and medial parts of the posterior disc attachment.7*8 Experience from TMJ surgery has suggested that when the inferior layer of the posterior and lateral attachment between the disc and the condyle is damaged it loses its firmness and becomes more elastic, allowing the disc to displace anteriorly or anteromedially. The hypothesis for this study was that superficial damage to the inferior layer of the posterior attachment between the disc and the condyle would permit disc displacement. To test this hypothesis
* Formerly, Visiting Professor, University of Rochester School of Medicine and Dentistry, Rochester, NY; currently, Associate Professor, Department of Oral Surgery, University Hospital, Lund. Sweden. t Associate Professor, Department of Radiology, University of Rochester School of Medicine and Dentistry, Rochester, NY. $ Instructor, Department of Orthodontics, Eastman Dental Center, Rochester, NY; Attending, Department of Oral and Maxillofacial Surgery, St Mary’s Hospital, Rochester, NY. § Assistant Professor, Department of Pathology, University of Rochester School of Medicine and Dentistry, Rochester, NY. ‘IAssistant Professor, Department of Clinical Dentistry, University of Rochester School of Medicine and Dentistry, Rochester, NY: Clinical Associate, Department of Orthodontics; Department of Prosthodontics, Eastman Dental Center, Rochester, NY. The study was supported by grants from the Torsten and Ragnar S&de&ergs Foundations, Stockholm, Sweden. Address correspondence and reprint requests to Dr Westesson: Department of Radiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 648, Rochester, NY 14642. 0 1992 American Association of Oral and Maxillofacial Surgeons 0278-2391/92/5008-0013$3.00/O
869
870
DISC DISPLACEMENT IN HUMAN TMJ AUTOPSY SPECIMENS
we obtained a series of fresh human TMJ autopsy specimens and studied them with magnetic resonance imaging (MRI). Those joints that had a superior disc position in the closed mouth position and no MR evidence of arthrosis were selected for further study. This article reports the results of creating superlicial damage to the inferior surface of the posterior attachment between the disc and the condyle. Material Fresh TMJ specimens were obtained in association with a routine autopsy examination that included autopsy of the brain. The specimens measured about 10 X 8 X 6 cm and were removed via the middle cranial fossa leaving the exterior of the cadaver intact. They were removed within 48 hours after death and kept deep-frozen until the study was undertaken. The mean age of individuals was 76 years, with a range from 62 to 82 years. No information regarding prior symptoms or treatment for possible TMJ disease was available. Initially, 23 specimens were obtained and imaged, but only the 14 with superior disc position and no MR evidence of arthrosis were included in this study. Methods After thawing the specimens to room temperature they were imaged on a 1.5 T MR scanner (Signa, General Electric, Milwaukee, WI) using a 6 X 8-cm surface coil. Sagittal and coronal images were obtained in planes that were parallel (coronal) and perpendicular (sag&al) to the long axis of the condyle.’ The scanning parameters were time of repetition = 2,000 milliseconds, time of echo = 25 and 80 milliseconds, field of view = 10 cm, slice thickness = 3 mm, number of excitations = 1, interslice gap = 0.5 mm. The MR images were obtained with the condyle located in the glenoid fossa corresponding to the closed mouth position. Following imaging, the joints were attached to a specifically designed holder” and opened in the same way as during clinical surgery,’ ’ exposing the upper and the lower joint spaces. Two to three superficial incisions were made mediolaterally in the inferior surface of the posterior attachment posterior to the disc itself. This area was termed the condylar part of the posterior disc attachment by Scapino. 7,8 The incisions were made with a no. 10 scalpel blade and were about 10 mm long in a mediolateral direction and less than 0.5 mm deep. The disc was then manually moved in an anterior direction and the condyle was pushed superiorly into the glenoid fossa behind the disc to maintain the disc in the anterior position. The top of the condyle now articulated against the inferior surface of the posterior disc attachment instead of the inferior surface of the disc. The joints were stabilized in this position with
the aid of a holding device.‘O The joint capsule was sutured and the specimens were stabilized in this position by attaching multiple layers of firm tape. The specimens were then removed from the holding device and the MR examination was repeated using the same scanning parameters and scanning planes as before. The laser lights on the MR scanner were used to assure that the positioning of the specimens was the same as before intervention. Following the second MR scan, the specimens were deep-frozen and embedded in acrylic material. The embedded specimens formed a rectangular box with the surfaces of the box parallel and perpendicular to the long axis of the condyle. The specimens were then cryosectioned in the sag&al plane as previously described.12 The cryosections were made at 3.5-mm increments parallel to the sagittal MR scans. The newly cut surface was photographed using a macro lens and high-resolution color slide film (Kodak K25, Kodak, Rochester, NY). The postsurgical MR images and cryosections were compared with the presurgical MR images and the degree of displacement was classified as partial or complete. Complete displacement implied that the disc was anteriorly displaced in the lateral, central, and medial parts of the joints. Partial displacement implied that the disc was anteriorly displaced in the lateral part of the joint only. Following the cryosectioning, the thin sections of the joints (approximately 2 mm thick) were fixed in 10% neutral buffered formalin and decalcified with a mixture of formalin and formic acid. Histologic sections (4 pm) were obtained and stained with hematoxylin and eosin, elastic, and Gomori connective tissue stains. The posterior attachment was evaluated for the extent of damage. Results After the joint compartments were opened, but before the incisions were made in the posterior disc attachment, it was not possible to displace the disc forward either by pushing the condyle up into the glenoid fossa or by manually pulling the disc forward. The posterior attachment appeared to hold the disc in place on top of the condyle. After the superficial incisions were made into the posterior disc attachment, this tissue became more elastic and lost its firmness. It was now possible to manually displace the disc forward. The posterior disc attachment was elastic, however, and the disc moved back to the top of the condyle. If the condyle was moved up into the glenoid fossa behind the disc, the disc remained in the anterior position. The superior part of the condyle now articulated against the posterior disc attachment and not against the disc itself.
ERIKSSON ET AL
FIGURE 1. Creation of disc displacement. A, Sag&alMR image before surgical intervention. The disc (arrow) is located with its posterior band superior to the condyle. B, Sagittal MR image after surgical intervention and creation of disc displacement. The disc (arrow) is displaced anterior to the condyle. C, Sagittal cryosection confirming disc displacement. The disc (white arrow) is anterior to the condyle and the posterior disc attachment (black arrows) is elongated.
The postoperative MR images showed that eight joints had complete anterior disc displacement (Fig I), four joints showed partial anterior disc displacement (Fig 2), and two joints showed normal superior disc position. The cryosections confirmed the observations of the MR images in all joints. Histologic evaluation showed that the damage to the posterior disc attachment was confined to the superficial, inferior layer of the posterior disc attachment (Fig 3). Elastic stains of the posterior disc attachment showed disorganization of the elastic and collagen fibers in the joints with disc displacement (Fig 3B). Diccussion This study has shown that it is possible to create anterior disc displacement in the human TMJ by making superficial incisions into the inferior layer of the posterior disc attachment and then pushing the condyle up into the glenoid fossa behind the disc. Normally the disc is firmly attached to the condyle,13 but after the incisions were made the posterior attachment became elastic and it was possible to manually move the
FIGURE 2. Partial anterior disc displacement. A. Cryosection from lateral part of joint showing the disc anterior to the condyle. The posterior band of the disc is indicated by an arrow. B, Cryosection from medial part of the same joint showing disc in superior position. The posterior band of the disc is indicated by an arrow.
disc forward. This phenomenon is similar to what is seen when the periosteum is incised in a mucoperiosteal flap for closure of an oroantral fistula. This observation suggests that weakness of the posterior attachment between the disc and the condyle might be one factor in the etiology of disc displacement. The study, however, does not provide any evidence to suggest the cause of the weakness of the posterior disc attachment. It only confirms that it is possible to displace the disc anteriorly after superficial incisions were made into the inferior surface of the posterior disc attachment. Because of the surgical opening in the lateral capsule wall, the significance of the lateral attachment could not be evaluated with our study design. The fact that we found several rotational disc displacements where the lateral part of the disc was anteriorly displaced but the medial part of the disc was still in a normal superior position may indicate that there is some significance to severance of the lateral disc attachment. It was, however, our impression from these experiments that it was usually not enough to cut the lateral disc attachment to displace the disc. The impression in these joints was that the incisions in the inferior surface of the posterior disc
872
DISC DISPLACEMENT IN HUMAN TMJ AUTOPSY SPECIMENS
FIGURE 3. Histologic sections of inferior surface of posterior disc attachment. A, Intact posterior disc attachment. The surface (arrows) of the attachment is intact. The collagen and elastic fibers are organized in a relatively parallel fashion (elastic stain). B, Damaged inferior surface of posterior disc attachment. Area of surgical intervention is indicated by arrows. The collagen and elastic fibem are disorganized (elastic stain).
attachment were essential to allow for the disc to be displaced. According to Rees, I4 the posterior attachment of the disc has two layers. The superior layer is attached to the squamotympanic fissure and the inferior layer is attached to the condyle. The superior layer consists of elastic fibers, while the inferior layer is more ligamentous in nature and its collagenous fibers exhibit a wavy appearance similar to the character of ligaments.15 These morphologic observations strongly support the importance of the inferior aspect of the posterior disc attachment for maintaining the disc position on top of the condyle. A comprehensive study of the collagen fiber organization in the posterior disc attachment was recently reported by Scapino. 738He described three groups of collagen fibers in the posterior attachment and these were termed the temporal part, the intermediate part, and the condylar part of the posterior attachment. The incisions made in this study were confined to the condylar part of the posterior disc attachment. The temporal and condylar fibers of the posterior disc attachment were found to be interwoven with a fanlike radiation into the posterior band of the disc. However, in the lateral part of the joint, where the posterior attachment as well as the posterior band of the disc tends to be thinner, the fibers connected the posterior attachment and the disc in a more parallel fashion.‘x8
One may speculate that this arrangement may be an anatomic weakness of the posterior attachment. It is supported by the clinical observation that anterior displacement of the disc is more commonly seen in the lateral part of the joint than in the medial part of the joint.“’ Our attempt to create disc displacement was unsuccessful in two joints. There are at least two possible explanations for this. First, the incision in the attachment might have been too superficial and the disc was not significantly displaced. The other explanation could be that the disc was displaced but the condyle did not sufficiently prevent the disc from moving back into its original position. This study has shown that relatively minimal surgical damage to the inferior surface of the posterior disc attachment in association with severance of the lateral joint capsule allows the disc to be anteriorly displaced. This suggests that damage to these tissues may play a role in the development of disc displacement in the human TMJ. References 1. Eriksson L, Westesson P-L: Clinical and radiological study of patients with anterior disc displacement of the temporomandibular joint. Swed Dent J 7:55, 1983 2. Westesson P-L: Double-contrast arthrotomography of the temporomandibular joint: Introduction of an arthrographic tech-
873
ERIKSSON ET AL
3.
4. 5.
6.
7.
8.
9.
nique for visualization of the disc and articular surfaces. J Oral Maxillofac Surg 41:163, 1983 Paesani D, Westesson P-L, Hatala M, et al: Prevalence of temporomandibular joint internal derangement in patients with craniomandibular disorders. Am J Orthod Dentofacial Orthop 101:41, 1992 Katzberg RW, Dolwick MF, Helms CA, et al: Arthrotomography of the temporomandibular joint. AJR 134:995, I980 Harkins SJ, Marteney JL: Extrinsic trauma: A significant precipitating factor in temporomandibular dysfunction. J Prosthet Dent 54271, 1985 Weinberg S. Lapointe H: Cervical extension-flexion injury (whiplash) and internal derangement of the temporomandibular joint. J Oral Maxillofac Surg 45:653, 1987 Scapino RP: The posterior attachment: Its structure, function, and appearance in TMJ imaging studies. Part 1. J Craniomandib Disord Facial Oral Pain 5:83, 199 1 Scapino RP: The posterior attachment: Its structure, function, and appearance in TMJ imaging studies. Part 2. J Craniomandib Disord Facial Oral Pain 5: 155, 199 1 Musgrave MT, Westesson P-L, Tallents RH, et al: Improved
10.
11.
12.
13.
14. 15.
magnetic resonance imaging of the temporomandibular joint by oblique scanning planes. Oral Surg Oral Med Oral Pathol 71:525, 1990 Westesson P-L, Omnell K-A, Rohlin M: Double-contrast tomography of the temporomandibular joint. A new technique based on autopsy specimen examinations. Acta Radio1 (Diagn) (Stockh) 21:777. 1980 Eriksson L: Diagnosis and surgical treatment of internal derangement of the temporomandibular joint. Thesis. University of Lund. Swed Dent J 25:6, 1985 (suppl IV) Westesson P-L, Bronstein SL, Liedberg J: Internal derangement of the temporomandibular joint: Morphologic description with correlation to joint function. Oral Surg Oral Med Oral Pathol 59:323, 1985 Griffin CJ, Hawthorn R. Harris R: Anatomy and histology of the human temporomandibular joint. Monogr Oral Sci 4: 1, 1975 Rees LA: The structure and function of the mandibular joint. Br Dent J 96:125, 1954 Griffin CJ, Sharpe CJ: The structure of the adult human temporomandibular meniscus. Aust Dent J 5: 190, 1960
