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The Unknown Synovial Joint

Heuristic Short-Cut


The unknown synovial joint is the TMJ, even though its diagnosis is simple, it is poorly understood when compared to other synovial joints worked on by the medical professions. The investigational short-cut used to diagnosis TMJ takes 10 seconds of clinical time. Abnormalities of the TMJ are easily identified by briefly palpating with your finger (any finger) placed in the outer extent of the external auditory meatus and pushing forward when the patient’s jaw is opening and closing. The osseous tympanic plate that separates the deep medial one-third between the anterior wall of the ear and the deepest aspect of the TMJ will not hinder effective palpation. ENT physicians have long used this heuristic logic especially when their diagnostic schema reveals no ear pathology. When they have ruled out all ENT pathologies for patients whose initial complaint is ear pain, they palpate the anterior wall of the outer ear, push forward and ask the patient to open and close their mouth. Any noise or vibration felt at the finger tip, with or without pain or discomfort is sufficient to diagnosis the early signs of TMJ.


A normal TMJ makes no noise or vibration when the mandible is moving.


Abnormal noise or vibration originating from the TMJ is dysfunctional. Early diagnosis using this 10 second palpation test can lead to further investigation by a TMJ specialist, and help prevent further dysfunction and the beginning of jaw pain or discomfort. Remember to do both ears.



Pathophysiology


Any noise or vibration felt by palpation represents soft tissue weakness. The pathophysiology of the TMJ indicates that the weakest soft tissue element is the posterior ligament that originates on the external anterior wall of the external auditory meatus (including the deep anterior wall of the tympanic plate) and inserts on the posterior band of the TMJ meniscus. A healthy posterior ligament holds the meniscus in its proper position between the mandibular condyle and the articular eminence of the glenoid fossa. The TMJ meniscus held securely in its proper position effectively absorbs the forces of chewing. Another property of the meniscus is that it separates the osseous mandibular condyle from the osseous articular eminence, thus protecting the bones of TMJ articulation.


Soft tissue weakness in the posterior ligament allows the meniscus to slip forward resulting in compromise of the meniscus-evoked protection from chewing forces. In addition, the posterior ligament (while still attached to the posterior band of the meniscus) thins out as it stretches forward, thus weakening its insertional attachment to the posterior band of the meniscus.


Interestingly, as the posterior ligament abnormally stretches forward it occupies the location where the meniscus should normally be positioned. Such a forward position of the posterior ligament makes it vulnerable to normal chewing forces.


Histologically, the posterior ligament is highly innervated and highly vascularized. When the posterior band abnormally stretches forward into the area where the vector of chewing forces operate, what follows is mechanical stimulation of the nociceptors of the posterior ligament leading to hyperalgesia. In addition, vascular plasma extravasation occurs due, in part, to the compromise of the integrity of the endothelial “tight junctions”. Taken together, nociceptive activation and the vascular damage leads to inflammation, injury and, pain or discomfort, when the posterior ligament is abnormally stretched forward allowing it to become susceptible to injury by the power of mastication.



Discussion


Resultant injury of the posterior ligament can end up with a negative result or a positive result. Untreated, negative sequelae progress from a minor stretch of the posterior ligament to mechanical injury – the dense fibrous connective tissue of the posterior ligament (that normally is securely connected to the posterior band of the meniscus) will rupture, thus separating, either partially or completely, the ligament from the meniscus. At this stage of deterioration, bone on bone contact occurs. Arthritis of the TMJ begins.


With positive therapy, a favorable outcome is predictable. The TMJ can be saved from degenerative changes. Early treatment of early symptoms, i. e., painless noise or vibration can be appropriately treated in order to preserve the attachment of the posterior ligament to the meniscus. The initial inflammation and injury can be minimized and allowed to heal and maintain the posterior ligament-disc connection.


It is common medical knowledge that when inflamed dense fibrous connective tissue is allowed to heal, scar tissue forms. Scar tissue is primarily collagen, free of nociceptive innervation and thus free of pain or discomfort. If the healed posterior ligament remains between the mandibular condyle and articular eminence, its collagen base can serve painlessly as the meniscus. The collagen base represents an “extension pad” of collagen continuous with the meniscus. This unique repair process can only occur in the TMJ because the meniscus of the TMJ is composed of collagen. All other synovial joints containing menisci are composed of fibrocartilage.


The clinical relevance of the unique property of the TMJ that is composed of collagen, not fibrocartilage, is that early treatment of the posterior ligament allows healing with the goal of extending the collagenous meniscus to include more continuous solid collagen into the adjoining healed posterior ligament, thus replacing innervated and highly vascularized connective tissue. Mastication now functions on a solid painless collagenous support structure.


Brian D. Fuselier, DDS is a member of the International Association for the Study of Pain, and the American Pain Society.


Barry A. Loughner, DDS, MS, PhD is a member of the International Association for the Study of Pain, the American Pain Society, the American Dental Association, and the Ethics Committee of the American Association for the Study of Headache.


Dr. Fuselier and Dr. Loughner are actively practicing at Central Florida Oral and Maxillofacial Surgery. This practice is unique as they have both Oral Surgeons and Facial Pain Specialists practicing together. For more information visit www.cforalsurgery.com



 
 
 
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