The medial capsule of the human temporomandibular joint

J Oral Maxillofac Surg 55:363-369. 1997

The Medial Capsule of the Human Temporomandibular Joint

BARRY A. LOUGHNER, DDS, MS, PHD,* HENRY A. GREMILLION, DDS,t PARKER E. MAHAN, DDS, PHD,$ AND RONALD E. WATSON, DDS§

Purpose: Attachments of the medial capsule of the temporomandibular joint (TMJ) to structures other than the medial fossa wall are thought to exist and to have functional significance. This study evaluated these relationships.

Materials and Methods: The anatomic relationships between the medial capsule and other medial structures, the sphenomandibular ligament, discomalleolar ligament, and auriculotemporal nerve, were examined in 14 cadaver heads.

Results: The results showed that the sphenomandibular ligament attaches separately from the medial capsule of the TMJ and therefore has no functional significance to the biomechanics of the joint. The discomalleolar ligament was found to be a continuation of the retrodiscal tissues and minimally associated with the medial capsule. The auriculotemporal nerve was not found to be in a relationship with the medial aspect of the condyle to the extent that mechanical irritation is possible during TMJ movement or disc displacement.

The medial capsule of the human temporomandibular joint (TMJ) is a fibrous attachment between the medial wall of the glenoid fossa and the neck of the mandibular condyle. The medial wall of the glenoid fossa consists of the anterior-inferior aspect of the petrous portion of the temporal bone. The medial wall is separated obliquely from the posterior wall by the petrotympanic fissure. The medial capsule is anatomi- cally associated with several structures in the vicinity of the petrotympanic fissure. The obvious structure that has clinical significance is the middle meningeal artery. TMJ surgeons tend to avoid the anterior-medial capsule of the joint for fear of damage to this vessel. Traumatic perforation of the anterior-medial capsule has been documented during arthroscopic surgery.’

Another structure associated with the medial capsule of the TMJ is the sphenomandibular ligament (SML),

Received from the Facial Pain Center, College of Dentistry, Uni- versity of Florida, Gainesville, FL.

* Director of Clinical Research, Midwest Center for Head Pain Management, Stouder Memorial Hospital, Troy, OH.

t Director, Parker Mahan Facial Pain Center. # Professor Emeritus, Department of Oral Biology. 8 Associate Professor, Department of Operative Dentistry. Address correspondence and reprint requests to Dr Loughner:

Midwest Center for Head Pain Management. Stouder Memorial Hos- pital, 920 Summit Ave, Troy, OH 45373.

0 1997 American Association of Oral and Maxillofacial Surgeons

0278-2391/97/5504-0007$3.00/O

a ligamentous connection between the lingula of the mandible and the spinous process of the sphenoid bone. The SML is classified as a ligament of the TMJ and is continuous with the pterygoid fascia.’ A portion of the SML continues into the petrotympanic fissure.3x” Another portion of the SML has been reported to be continuous with the medial capsule of the TMJ.3 The extent of this continuity between the SML and the medial capsule remains unclear. If the SML-medial capsule connection is extensive, a functional significance may be attributed to it; minimal continuity would most likely indicate no functional significance.

The discomalleolar ligament (DML) is another structure associated with the medial capsule. The DML has been reported, in adult human cadavers, to be a soft tissue connection between the TMJ and the malleus.3-5 The extent of the association of the DML and the medial capsule has not been adequately delineated.

The auriculotemporal nerve (AT) is also associated with the medial capsule. Arising from the posterior trunk of the mandibular nerve, the AT passes posteriorly along the medial side of the condylar neck. Histo- logic evidence of atypical positioning of the AT in the vicinity of the medial pole of the mandibular condyle has been reported.6 It has been speculated that compression of the nerve may occur because of the interpo- sition between the condyle and the medial wall of the glenoid fossa.

The purpose of this study was to investigate the

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364 MEDIAL CAPSULE OF TMJ

anatomic relationship between the medial aspect of the TMJ and the AT, as well as the SML and DML.

Materials and Methods

Dissections were performed on 14 adult cadaver heads having an average age of 72 years. No records of gender were available. Before dissection, all of the anatomic material was embalmed in formalin. The dissection was facilitated by using loupes of 3~ magnifi- cation.

The cadaver heads were sectioned sagittally in the midline and, then sectioned again parasagittally along the long axis of the petrous portion of the temporal bone. The floor of the middle cranial fossa (roof of the infratemporal fossa) was removed, which exposed the anterior trunk of the mandibular nerve, superior belly of the lateral pterygoid muscle superior cavity of the TMJ, medial fossa wall, medial capsule of the TMJ, and DML. The medial boundary of the infratemporal fossa, consisting of the eustachian tube, levator veli palatini muscle, and tensor veli palatini muscle, was removed. As a result, a medial view of the SML, superior and inferior bellies of the lateral pterygoid muscle, and the posterior trunk of the mandibular nerve, includ- ing the proximal course of the AT, was provided.

The SML was traced to its attachment at the spine of the sphenoid bone. At this point, the width of the SML was measured. The portion of the SML that attached to the spine and the portion that passed to the petrotympanic fissure was determined. The dissection was continued laterally to study the relationship between the medial capsule and the SML, AT, and DML.

Results

The average width of the SML measured at the spine of the sphenoid was 10.5 mm. The width of the SML attached to the spine was 6 mm. The remaining width of the SML attached at or in the petrotympanic fissure (Fig 1). The posterior aspect of the SML at the petrotympanic fissure was immediately adjacent to the medial capsule of the TMJ (Fig 2). There was no signifi- cant connection of the SML with the medial capsule. The medial capsule appeared to be composed of loose areolar connective tissue (Fig 3).

In one specimen, the petrotympanic fissure was enlarged and open (Fig 4). This opening was 8 mm in width. The SML was attached only to the lateral wall of the open fissure. The opening proceeded to narrow in a conelike fashion to the superior end of the fissure at the anterior malleolar ligament (AML). Despite the enlarged opening of the petrotympanic fissure, the medial capsule of the TMJ was not continuous with the

FIGURE 1. Medial view of infratemporal fossa. The anterior portion of the sphenomandibular ligament (SML) attaches to the spine of the sphenoid (open arrows). The posterior portion of the SML attaches at the petrotympanic fissure (closed UYYOWS). Auriculotem- poral nerve (AT); inferior alveolar nerve (IA); lingual nerve (L); lower belly of lateral pterygoid muscle (LLP); upper belly of lateral pterygoid muscle (ULP); buccal nerve (B).

AML through the fissure. Tension applied to the SML was not sufficient to move the malleus.

The posterior extent of the medial capsule continued to the retrodiscal tissues and attached to the medial fossa wall adjacent to the petrotympanic fissure. In one specimen the DML was extended from the retrodiscal tissues to the neck of the malleus (Fig 5). In this specimen, the small slip of tissue identified as the DML had minimal association with the medial capsule because the retrodiscal tissues were interposed. In another specimen, the DML was continuous with the AML. The remaining specimens contained no visible DML (Fig 6).

The AT was inferior to the medial capsule attachment on the medial fossa wall in all specimens (Fig 7). The AT was not observed to be in the proximity of the medial pole of the condyle.

LOUGHNER ET AL 365

Discussion

SPHENOMANDIBULAR LIGAMENT

The current study found no extensive anatomic connection between the medial capsules of the TMJ and the SML. This is in contrast to Yung et al’s7 report that the SML, along with the medial capsule, forms the medial wall of the upper compartment of the TMJ. Our observations suggest that the medial wall of the upper compartment is composed of the medial capsule and a bony landmark made up of the anterior-inferior aspect of the petrous portion of the temporal bone. This bony landmark is considered to be an articulating surface of the TMJ.* Whereas the medial capsule was observed to be immediately adjacent to the SML, it was not connected to the SML to the extent that a conjoined ligament existed (Fig 8). In addition, the portion of the SML that was not attached to the spine of

FIGURE 3. Anterior view of the medial aspect of the temporomandibular joint. Note that the medial capsule (MC), which includes the medial capsular ligament, is composed of loose areolar connective tissue. Also note the attachment of the MC to the medial wall (MW). Medial pole (MP).

FIGURE 2. Superior view of medial aspect of temporomandibular joint. Note the limited attachment (open arrows) of the sphenomandibular ligament @ML) with the medial capsule (MC). There is attachment (closed arrows) of the MC to the medial wall (MW). Medial pole (MP); posterior attachment tissues (PAT).

the sphenoid was found to attach in the petrotympanic fissure. The medial capsule of the TMJ was not continuous with the fibers of the SML that entered the petrotympanic fissure. Based on this evidence, the anatomic relationship between the medial capsule and the SML is minimal and, therefore, of no functional significance.

The loose areolar connective tissue of the TMJ that lies in the anterior-medial region of the joint forms a “capsule-like’ ’ structure.’ Our gross anatomic study indicates that the medial capsule also appears to consist of loose, areolar connective tissue (Fig 3). In contrast to dense fibrous connective tissue, such as that of the lateral temporomandibular ligament, loose areolar tissue is weak and loosely woven. Therefore, the medial capsule does not provide structural support to the TMJ as does the lateral temporomandibular ligament. The medial capsular ligament, which is the aspect of the medial capsule posterior to the crest of the articular eminence, is also composed of loose areolar connective tissue (Fig 3).


FIGURE 4. Medial view of the infratemporal fossa. Note enlarged and open petrotympanic fissure (open arrows). The sphenomandibular ligament (SML) continues into the petrotympanic fissure and is attached to the lateral wall. Auriculotemporal nerve (AT); inferior alveolar nerve (IA); lingual nerve (L); buccal nerve (B); medial pterygoid muscle (MP); external carotid artery (EC); maxillary artery (MA); middle meningeal artery (MM); spine of sphenoid bone (SS); styloid process (SP).

poral fossa, where it attaches to the spine of the sphenoid bone and in the petrotympanic fissure.

Does the SML have clinical significance other than its role as an accessory ligament of the TMJ? The SML may, in rare cases, influence the functional integrity of middle ear structures. Fibrous continuity between the SML and the AML has been shown histologically.4 Tension applied to the SML was reported to move the malleus in adult cadavers4%12 Could tension on the SML caused by either mandibular overclosure’ or inferior distraction of the mandible3 produce malleus movement-induced disruption of ossicle articulation? Based on the preponderance of evidence, the answer is no.13-16 Solberg et all7 reported that downward distraction of the TMJ was not possible in patients or in fresh autopsy specimens. Several clinical studies have concluded that arthroscopic surgery of the TMJ is not causally related to ear dysfunction or changes in hearing acuity. 14-16 Add to this evidence the observation in the current study that tension applied to the SML was not sufficient to move the malleus in the specimen possessing an open and unobstructed petrotympanic fissure (Fig 4). Only in cases of rare anatomic variation is the notion of SML-evoked malleus movement considered.4.‘x

Ear symptoms such as pain and ear sounds are often associated with TMJ dysfunction.‘9-2’ Neurologic substrates, not connective tissue, may be the underlying cause of TMJ-associated ear symptoms. Various structures of the masticatory system, such as the TMJ, may generate nociceptive input into the trigeminal nuclear complex as a result of tissue injury or inflammation. Nociceptive input also may target the motor nucleus of the trigeminal nerve and thus produce efferent im-

Together with the temporomandibular ligament, the SML provides structural support to the TMJ. Osborn” reported that the SML functions during normal conditions to help to maintain a “close-packed” position between the condyle and the glenoid fossa. Our study confirms this conclusion, suggesting that the SML acts as an accessory ligament of the TMJ,” although with- out substantial connection to the medial capsule. A confirmation of the limited SML-medial capsule association is found in the anatomy teaching laboratory. When the condyle-disc assembly is severed from the mandible at the neck of the condylar process and removed for demonstration purposes, the SML remains

FIGURE 5. Superior view of the posterior-medial aspect of the temporomandibular joint. Note that the discomalleolar ligament is a small slip of tissue (closed arrows) extending from the posterior attachment tissues (PAT) to the malleus (M). Also note the anterior

intact, undisturbed, and is clearly seen in the infratem- malleolar ligament (open arrows).

LOUGHNER ET AL 367

pulses sufficient to tonically activate the muscles of mastication and, perhaps, the tensor tympani muscle. Increases in masticatory muscle activity have been observed after exposure of the TMJ to proinflammatory agents.22’23 Moreover, the neural convergence theory of referred pain24 may explain ear pain associated with TMJ dysfunction. Projection neurons located in the subnucleus caudalis receive convergent input from the TMJ and other head and neck structures.25 However, no projection neurons have been found that respond exclusively to stimulation of the TMJ. Therefore, pain from the TMJ may be referred neurologically to adjacent structures such as the ear.

DISCOMALLEOLAR LIGAMENT

The DML has been reported to be continuous with the medial aspect of the retrodiscal tissues and the

FIGURE 7. Medial view of infratemporal fossa. Note the articular branches (a) of the auriculotemporal nerve (AT) (closed arrow) passing into the posterior attachment tissues (open arrows) on the medial side of the neck of the condylar process. Inferior alveolar nerve (IA); lingual nerve (L); medial pterygoid muscle (MP); external carotid artery (EC); maxillary artery (MA); spine of the sphenoid bone (SS); styloid process (SP); sphenomandibular ligament (SML); posterior border of ascending ramus of mandible (R).

FIGURE 6. Superior view of the posterior-medial aspect of the temporomandibular joint. Note the absence of the discomalleolar ligament. The posterior attachment tissues (PAT) comprise the soft tissue boundary of the posterior-medial aspect of the joint. Also note the anterior malleolar ligament (open arrows) as it continues to the malleus (M). Medial pole (MP); medial wall (MW).

medial capsule of the TMJ.4 The extent of the DML- medial capsule association found in this study was minimal. When present, nearly all of the DML was associated with the retrodiscal tissues. This observation is consistent with studies in fetal tissue that have de- scribed the DML as a tendon arising from the lateral pterygoid muscle, passing through the petrotympanic fissure, and connecting to malleolar tissue.26-28 Contin- uation of fetal tendinous tissue posteriorly from the superior belly of the lateral pterygoid muscle to retrodiscal tissues is presumably the embryologic ante- cedent to the disc and not the medial capsule. More- over, Kino et a129 have reported histologic evidence that shows that the most medial fibers of the retrodiscal tissues attach at one end to the area of the petrotym-


Petrotympanic \ II Fissure

FIGURE 8. Diagram of the temporomandibular joint (anterior view) showing the relationship between the medial capsule and the sphenomandibular ligament (SML). Note that the medial capsule has a limited connection with the SML and therefore has no functional significance to the dynamics of the SML.

panic fissure and at the other end to the most medial aspect of the posterior band of the disc. The suggestion that the DML is a possible cause of aural symptoms in patients with TMJ dysfunction3’ is unlikely ac- cording to the observations of this study and elsewhere4 that show minimal tissue connection with the malleus.

AURICULOTEMPORAL NERVE

In this study, the AT was not found to be interposed between the medial pole of the condyle and the medial wall of the glenoid fossa. By contrast, histologic evidence from human cadavers have shown the AT interposed between the medial pole of the mandibular condyle and an elongated wall of the fossa. Our small sample size may account for this difference.

The notion that the medial pole-medial wall area is a potential entrapment site is not new. The proximity of the medial aspect of the condyle to the petrotympanic fissure has been considered a potential risk for compression of the anterior tympanic artery as it enters the fissure.31 The medial pole-medial wall area together with the posterior slope of the articular eminence, is considered to be an articulating surface of the TMJ.’ This buttressing function, suggests that this area may be a potential entrapment site of soft tissue structures such as the AT.

References

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J Oral Maxillofac Surg 55:369-370, 1997

Discussion

The Medial Capsule of the Human Temporomandibular Joint

Norman D. Mohl, DOS, PhD State University of New York, Buffalo, New York

The report by Loughner et al provides an excellent review of the anatomy of the medial aspect of the human temporomandibular joint (TMJ). It is well written and includes clear and well labeled photographs of the dissections. Most impor- tantly, their conclusions appear to be consistent with their observations. Nonetheless, some of the interpretations associated with their conclusions deserve further discussion. These will be addressed in the same order as by the authors.

The authors report that the sphenomandibular ligament (SML) attaches separately from the medial capsule of the TMJ and therefore has no functional significance to the biomechanics of the joint. This conclusion is reasonable, given the fact that the petrotympanic fissure, at or in which the SML attaches, cannot be considered to be part of the TMJ because it is not within the anatomic and functional limits of the joint capsule. In this area, the capsule actually attaches to the squamous side of the more anteriorly placed petrosquamosal fissure, meaning that the petrotympanic fissure, along with its contents and attachments, are outside of the TMJ.’ In this regard, it would have been helpful if the authors had reported the relationship of the SML, if any, to the petrosquamosal fissure. It should also be noted that the authors’ reference to the medial wall of the glenoid fossa as consisting of the anterior-inferior aspect of the petrous portion of the temporal bone probably overstates the relevance of this small, finger-like, projection of the tegmen tympani to the TMJ. Although Zola’ did state that the medial wall of the mandibular fossa contains a facet for articulation with the medial pole of the condyle, he did not imply that the facet is located on the petrous portion of the temporal bone, as the authors (“this bony landmark”) contend.

The authors also state that their study confirms Osborn’s3 conclusion that the SML functions under normal conditions to help maintain a “close packed” position between the condyle and the glenoid fossa. This may require a more sophisticated biomechanical interpretation in view of Han- nam’? recent statement that “It is probably unwise to view the articulation as ‘close packed’, and perhaps better to con- sider the condyle as functioning in a physical milieu which

has variable viscoelasticity depending on the direction of its compressive loading.”

As for the authors’ observation that tension applied to the SML was not sufficient to move the malleus, this confirms the reports of others. Although the cranial attachment of the SML is continuous with the malleus and its anterior malleolar ligament in fetal life, all three being derived from Meckel’s cartilage, in the adult at least, movement between them is only possible in specimens that have been previously decalcified or fractured through the squamotympanic-petrotympanic fissures.’ Thus, we can agree with the authors’ conclusion that the preponderance of evidence does not support the claim that mandibular overclosure or inferior distraction of the mandible produces malleus movement-induced disruption of the auditory ossicles. Contentions to the con- trary must be viewed as highly speculative.

The authors’ statement that neurologic substrates, not connective tissue, may be the underlying cause of TMJ associated ear symptoms is probably correct in light of our current knowledge, especially with regard to referred pain. It is also a commonly held clinical belief that certain non-painful ear symptoms, eg, tinnitus, hearing loss, vertigo, and so on, are caused by, or at least associated with, disorders of the TMJ. Unfortunately, this premise has not been investigated in con- trolled clinical studies. Thus, until and unless it can be reli- ably shown that there is a higher incidence or prevalence of non-painful ear symptoms in temporomandibular disorder (TMD) patients than exist in a matched control group of non- TMD subjects, we must take the position that this presumed association remains anecdotal and purely speculative. For example, the article by Bernstein et al,’ which was cited by the authors as an example of a study linking ear symptoms with TMD, found that the hearing loss reported by the TMD patients was entirely subjective.

The authors report that the discomalleolar ligament (DML) is a continuation of the retrodiscal tissues and is minimally associated with the medial capsule. The lack of an overt attachment of the DML to the joint capsule is under- standable and consistent with observations that the articular disc also has separate and distinct attachments to the condyle. This may imply that “fused” or common ligamentous attachments within the TMJ impede condyle-discal movement or at least reduce the efficiency of such movement.

The DML, as correctly noted by the authors, is derived from fetal tissue arising from the superior belly of the lateral pterygoid muscle, and it extends posteriorly to the devel-

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The medial capsule of the human temporomandibular joint