Temporomandibular Joint

The temporomandibular joint (TMJ) is a complicated joint that can be classified as bilateral, diarthrodial, and ginglymoid. It allows both joint rotation and translation. The TMJ is unique in that movement in one joint is associated with movement in the contralateral joint. The TMJ is vulnerable to many pathologic conditions, including ankylosis and hypermobility.

Etiopathogenesis

Hypermobility

Hypermobility of the joint can be secondary to trauma, connective tissue disorders, or be idiopathic. The point at which excessive joint mobility becomes problematic is typically when it leads to recurrent joint dislocation. This is characterized by movement of the condyle past the articular eminence and into the infratemporal fossa. The latter may be associated with severe pain and loss of function. Subluxation also involves movement of the condyle past the articular eminence but differs from dislocation in that the condyle can spontaneously relocate to its normal position within the glenoid fossa. TMJ hypermobility may also be associated with an increased prevalence of internal derangement.

Ankylosis

Ankylosis of the TMJ may be defined as fibrous or bony. In either situation, the normal joint anatomy is progressively destroyed and replaced with dense fibrous tissue or bone with a concomitant reduction or loss of joint translation and, ultimately, rotation. Accordingly, the maximal incisal opening (MIO) and lateral excursive movements progressively decrease. The most common causes of ankylosis are trauma, infectious arthritis, autoimmune arthritis, and iatrogenic causes.

Pathologic Anatomy

Hypermobility

A complete understanding of normal joint anatomy is crucial to understanding joint pathology. Hypermobility is often associated with normal joint anatomy. However, the capsule, lateral TMJ ligament, and retrodiscal tissue may be lax and allow excessive condylar movement anterior to the articular eminence. This may result in subluxation or the more problematic dislocation. The one anatomic feature that is most readily identified in patients with subluxation and dislocation is a relatively small articular eminence. Internal derangement may also be associated with hypermobility, but the association between the two is not clearly understood.

Ankylosis

The joint anatomy associated with ankylosis is significantly different from that of a normal joint. Even though the joint capsule and extracapsular ligaments may be present and appear normal, the intra-articular structures are radically altered. This is the case for fibrous ankylosis, in which dense fibrous scar tissue extends from the articulating surface of the vestigial disc to the roof of the glenoid fossa and articular eminence of the temporal bone. Fibrous tissue may also extend from the inferior aspect of the disc to the articulating surface of the condyle. As the fibrosis progresses, the articular disc is typically replaced by fibrous tissue. Extra-articular structures and anatomy are usually unaffected. Bony ankylosis is different and particularly destructive. It often develops from long-standing fibrous ankylosis. Bone extends from the condyle to the glenoid fossa and articular eminence. The disc, retrodiscal tissue, and check ligaments are typically lost as they are replaced by bone. The ankylosis may be extensive and extend anteroposteriorly from the tympanic plate to the infratemporal fossa and mediolaterally from the zygomatic arch to the petrous portion of the temporal bone. The joint capsule is similarly replaced by the expanding bony mass. Extra-articular soft tissues, including nerves, blood vessels, and muscle attachments, may also be displaced.

Pathologic Anatomy

Hypermobility

A complete understanding of normal joint anatomy is crucial to understanding joint pathology. Hypermobility is often associated with normal joint anatomy. However, the capsule, lateral TMJ ligament, and retrodiscal tissue may be lax and allow excessive condylar movement anterior to the articular eminence. This may result in subluxation or the more problematic dislocation. The one anatomic feature that is most readily identified in patients with subluxation and dislocation is a relatively small articular eminence. Internal derangement may also be associated with hypermobility, but the association between the two is not clearly understood.

Ankylosis

The joint anatomy associated with ankylosis is significantly different from that of a normal joint. Even though the joint capsule and extracapsular ligaments may be present and appear normal, the intra-articular structures are radically altered. This is the case for fibrous ankylosis, in which dense fibrous scar tissue extends from the articulating surface of the vestigial disc to the roof of the glenoid fossa and articular eminence of the temporal bone. Fibrous tissue may also extend from the inferior aspect of the disc to the articulating surface of the condyle. As the fibrosis progresses, the articular disc is typically replaced by fibrous tissue. Extra-articular structures and anatomy are usually unaffected. Bony ankylosis is different and particularly destructive. It often develops from long-standing fibrous ankylosis. Bone extends from the condyle to the glenoid fossa and articular eminence. The disc, retrodiscal tissue, and check ligaments are typically lost as they are replaced by bone. The ankylosis may be extensive and extend anteroposteriorly from the tympanic plate to the infratemporal fossa and mediolaterally from the zygomatic arch to the petrous portion of the temporal bone. The joint capsule is similarly replaced by the expanding bony mass. Extra-articular soft tissues, including nerves, blood vessels, and muscle attachments, may also be displaced.

Diagnostic Studies

Hypermobility

Hypermobility is easily diagnosed with routine panoramic radiography. The image should demonstrate the condyle anterior to the articular eminence in the infratemporal fossa. Clinical evaluation of the patient should also reveal an anterior open bite of several centimeters and a palpable depression immediately in front of the tragus corresponding to an empty glenoid fossa. However, patients with long-standing TMJ dislocation may not have any appreciable anterior open bite. The same imaging modality can be used to confirm adequate reduction of the dislocation. In the absence of panoramic imaging, computed tomography (CT) can also readily illustrate a condyle that is anterior to the articular eminence. Magnetic resonance imaging (MRI) will provide soft tissue imaging that allows the magnitude of joint translation and disc position to be seen, but it has little to offer in the acute setting.

Ankylosis

Fibrous ankylosis is characterized clinically by limited MIO and, when unilateral, reduced lateral excursion toward the unaffected side. Radiographic features of fibrous ankylosis are conspicuous by their absence. Patients with bony ankylosis have no incisal opening or lateral excursions. Panoramic imaging of bony ankylosis will show heterotopic bone formation and no joint space. However, the ankylosis is best imaged with CT. Axial and coronal images are the most informative, although three-dimensional (3D) reconstructed images provide the most detail. For all but the most simple bony ankyloses, fabrication of a stereolithographic model from the CT scan allows the surgeon to assess the anatomy in detail, plan the surgery, and perform it first on the model. Closely related anatomic structures, including the middle ear, middle cranial fossa, foramen spinosum, jugular fossa, and carotid canal, should be clearly visualized.

Reconstructive Goals

Hypermobility

The primary objective is to decrease joint translation and prevent subluxation and dislocation. Normal rotation within the joint should be maintained, but excessive movement of the condyle anterior to the articular eminence must be prevented. When symptomatic internal derangement coexists with hypermobility, disc plication or discectomy can also be performed. Recurrent dislocation can be treated according to one of three basic philosophies. The first is to provide a mechanical barrier to joint translation through bony augmentation of the articular eminence or down-fracture of the root of the zygomatic bone (Dautrey procedure). The second philosophy also reduces joint translation but through plication, imbrication, or scarification of the capsule, ligaments, retrodiscal tissue, and disc. The third philosophy does not limit joint translation but rather eliminates the mechanical barrier to relocating the condyle when it translates past the articular eminence. This is achieved by performing an eminectomy.

Ankylosis

The primary objective is to create a functioning joint that allows some combination of joint rotation or translation. Joint-preserving procedures such as arthroplasty may be possible in patients with fibrous ankylosis if the fibrosis is minimal. If the fibrous ankylosis is more extensive or bony, joint preservation becomes challenging and gap arthroplasty may be needed. This can be combined with the use of interpositional autogenous tissue, alloplastic material, or total joint replacement. Total joint replacement would appear to be the most predictable, but in younger patients it will necessitate subsequent joint replacement over the lifetime of the patient. Total joint replacement is not approved by the Food and Drug Administration for pediatric and adolescent patients who are still growing. In these patients, autogenous tissue may be the preferred treatment because it potentially allows continued growth, although the likelihood of recurrent ankylosis may be increased.

Treatment

Hypermobility

Multiple different approaches to prevent recurrent dislocation have been described. Intra-articular injection of sclerosing agents such as sodium tetradecyl sulfate and sodium morrhuate have been used to create excessive fibrous tissue. Intra-articular injection of blood has also been recommended to promote intra-articular fibrosis. In addition, arthroscopic scarification of the capsule, retrodiscal tissue, and disc with the use of sclerosing agents, cautery, and laser has been reported. These techniques are difficult. The author prefers to manage recurrent TMJ dislocation with one of three surgical procedures, depending on the clinical situation.

The Dautrey procedure (Le Clerc) is a simple extra-articular surgical procedure. It is well suited to patients who have no symptoms of intra-articular pathology. The procedure has been criticized because of bone remodeling and the potential for recurrent dislocation. A standard preauricular incision is used to approach the TMJ capsule. The dissection should be carried forward in a subperiosteal plane to expose the lateral aspect of the articular eminence and root of the zygoma. A periosteal elevator is then used to elevate only the most inferior aspect of the temporalis muscle medial to the root of the zygoma. The same elevator is then passed deep to the root of the zygoma just into the infratemporal fossa to protect the soft tissues. A reciprocating saw is used to osteotomize the root of the zygoma in an oblique manner with the most superior aspect of the cut being posterior to the inferior aspect of the cut. The inferior aspect of the osteotomy should be just anterior to the apex of the articular eminence. The author prefers to displace the root of the zygoma inferiorly and medially with an orthognathic forked nasal septum osteotome. This typically results in a greenstick fracture of the zygomatic arch in a more anterior location ( Fig. 99-1 ). The displaced zygoma usually maintains its new position without any fixation. On rare occasion, the anterior fracture is not greenstick and too much mobility of the displaced zygoma is encountered, which necessitates rigid fixation to the lateral aspect of the eminence with a small bone plate. The condyle must not be able to translate past the apex of the articular eminence at the completion of this procedure.

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Jun 4, 2016 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Temporomandibular Joint
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