20.1 Description of Internal Derangement of the Temporomandibular Joint

The term “internal derangement” implies an anatomical abnormality of the relationship of the disk–condyle components, with resulting changes in the smooth movement of the joint causing clicking, popping, locking, or momentary catching with or without associated pain and muscular disturbance.^1,2 When this term is used, it usually implies that these tissues have not yet undergone any degeneration and that when osteoarthrotic damage is visibly evident on a radiograph, then this diagnosis supercedes a diagnosis of internal derangement. Internal derangements of the temporomandibular joint (TMJ) can be differentiated into the following three clinically distinguishable problems: (1) disk displacement with reduction (DDWR), (2) disk displacement without reduction (DDNR), and (3) condyle open locking and dislocation.³ This chapter focuses on the differential diagnosis and treatment of these three conditions.

20.1.A Disk Displacement with Reduction (Also Known As Disk–Condyle Incoordination)

This condition is manifested clinically as a brief interference with the jaw opening movement which usually has an associated distinct brief joint sound or click. If the displacement is substantial, the patient may experience a momentary or intermittent restriction of condyle translation before the disk reduces to a normal position and full translation is achieved. Achieving full condyle translation after the click or lateral shift of the jaw joint occurs implies either a release or reduction of the momentarily jammed disk. This release allows the disk to continue its normal rotational movement about the condyle during opening. During closure, the disk will return to its original starting position relative to the condyle. Typically the opening click is loudest and this is thought to be due to the increased condyle pressure that is present during an opening motion. There is a much less noticeable reciprocal or closing click just before full intercuspation.⁴ In some patients, however, the opening movement produces a less noticeable click while the closing movement produces a severe jamming and loud click. The best explanation for a loud closing click is that the disk is more deformed and its shift back to an anterior position is more difficult, with more friction and more noise.

Since the most commonly observed anatomic abnormality is a physical displacement of the disk from its normal position, this clinical condition has been most frequently called a disk displacement with reduction (DDWR) disorder. The term “reduction” means that the disk is out of place in the closed mouth position and that during opening it returns, or reduces, to a normal position. To confirm that the patient’s complaints are related to a true DDWR, the TMJs are palpated bilaterally with very light pressure while the patient opens widely and closes several times. Any significant joint movement interference (especially if sound is produced) will be palpable. To document the problem, the timing of the joint movement interference relative to mouth opening is measured with a millimeter ruler. Many varied patterns of disk–condyle interference exist. Unfortunately, no definitive statement can be made regarding the severity, prognosis, or even the specific nature of the anatomic deformity based on these various patterns of joint sound or movement interference.⁵

20.1.B Disk Displacement with No Reduction (Also Known As Closed Locking)

This disk displacement with no reduction (DDNR) disorder is sometimes described as “closed locking.”⁶ The mechanism of this condylar movement restriction is also thought to be either disk perforation, condyle or disk deformation, disk–articular surface adhesion, or disk displacement without reduction. If the disk does not fully rotate from an anterior to a posterior position relative to the condyle during mandibular movement, a clear restriction of jaw opening will result; this is described as a nonreducing disk. To confirm that a true condylar restriction exists, maximum active mouth opening is measured with a millimeter ruler. Confirmation can also be obtained by palpating the lateral pole of the condyle during opening. Movement anterior to the crest of the articular eminence will not be felt if a restriction exists. Finally, a passive stretch manipulation of the jaw by the examiner will not produce normal opening. When associated pain occurs, it probably results either secondarily from a protective jaw closing muscle trismus or a muscle splinting response. This trismus response is an attempt to prevent either pinching or stretching of the disk tissue, or impingement on the vascular, highly innervated disk attachment tissues which are sometimes drawn into an area of articular loading. Of course, the pain could also be from a primary masticatory muscle disorder or any number of other orofacial pain conditions. Because full, friction-free movement of the disk does not occur, this condition can eventually lead either to a perforation of the disk or, more likely, to fibrosis of the disk-attachment tissues. In either case, there is usually a subsequent osseous remodeling (flattening) of the condyle and articular eminence.^7–9 These changes are essentially adaptive attempts to restore increased movement in a highly frictional joint. Neither the incoordination phase nor the restriction phase of an internal derangement is accompanied by obvious radiographic osseous change of the condyle or eminence.

20.1.C Open Condyle Locking and Open Dislocation

Although in most cases, when the jaw locks open, there really is not a dislocation of the condyle, even though the patient complains they cannot close their mouth. It would be better to simply call such cases an open locking until it is proven the condyle has traveled outside or beyond its normal range of travel. The mechanisms for open locking are several. First, there could be a simple jamming of the entire disk–condyle complex in a position anterior to the crest of the articular eminence due to jaw closing muscle trismus. The onset is often associated with extreme yawning or a dental treatment intervention where the jaw was open for an extended period of time. In the absence of ongoing pain, infrequent momentary open locking upon wide opening is not a serious clinical problem for most patients. The reason for this jamming is not because of any dislocation of the condyle beyond its normal open translation position, but simply because the friction in the joint is such that the condyle and disk are momentarily stuck anterior to the eminence. In the wide open jaw position the jaw closing muscles are maximally stretched which increases the friction forces between the eminence and the disk. In normal patients, this situation would not cause an open jamming, but if there is any increased stiffness in the jaw closing muscles or the intra-articular fluids are not lubricating the joint surface adequately, then once the condyle passes to the anterior of the eminence it may be more difficult to initiate the closing movement. It has been determined that the joint reaction forces during jaw opening are greatest in the open jaw position, and any increase in stiffness or any co-contraction of the jaw closers can magnify the joint reaction forces 3- to 10-fold in magnitude.¹⁰

Second, there are cases of true hyperextension of the disk–condyle complex well beyond its normal maximum translation. This condition is a true dislocation and fortunately it is rare. When it has been reported it has always been due to a traumatic insult to the jaw (e.g., intubation or surgery on the facial or jaw structures) and it is almost always in the frail elderly. Third, another form of “I can’t close my teeth together” is best described as a partial open locking situation where the patient is at least halfway closed or more, and it truly means they cannot get their teeth to come together. This clinical complaint is almost always a posterior disk jamming or folding problem which prevents the mandible from closing. In the last situation, the disk has difficulty returning to its usual more anterior position relative to the condyle on closure. Sometimes this derangement is momentary and therefore self-reducing; other times it may require manual manipulation of the mandible by the doctor to reduce the disk position abnormality.

20.2 Mechanism and Etiology of Internal Derangement

The above conditions have been accompanied by a list of probable mechanisms which might explain anatomically and functionally how a joint movement interference occurs, but mechanisms are not the same as etiology. A table of etiologies is provided (Table 20.1) and, with regard to mechanism, there are several proposed anatomic alterations that might produce a joint sound or a complete displacement of the disk and its associated brief movement disturbance. The most common mechanism is a simple displacement of the disk which produces a click or pop because the disk is jammed in front of the condyle as it moves and sound occurs once the jamming is released.¹¹ The most likely abnormality of anatomy that allows the TMJ disk to displace is an elongation of the lateral collateral ligament.^12,13 Other explanations are (1) disk and joint capsule and ligament hypermobility, (2) articular surface abnormality, such as flattening, erosion, or bony spur development,¹⁴ (3) disk–articular surface adherence due to altered (less lubricating) synovial fluids,¹⁵ and (4) disk perforation.¹⁶

Table 20.1 List of potential etiologies for internal derangement

TMJ, temporomandibular joint.

With regard to etiology and in common with general orthopedic problems, the etiology of a TMJ internal derangement is often multifactorial and difficult to determine clearly. Nevertheless, the major causes which can be considered as the most likely etiologies of a TMD are macrotrauma, parafunction–microtrauma, arthritic disease, hypermobility, and abnormal biomechanical loading. Each etiology is discussed in the following subsections.

20.2.A Macrotrauma to the Temporomandibular Apparatus

If a significant external-force trauma occurs from either impact or overstretching, the joint structures can be damaged.¹⁷ The predominant causes are blows to the jaw, iatrogenic stretching during dental and surgical treatment, or an impact to the jaw sustained during a motor vehicle accident. While trauma is not the most frequent cause of an internal derangement, patients complaining of a jaw function problem (e.g., clicking and locking) to a specialty clinic are more likely to have a history of major trauma (30%) than a nonpatient population of individuals with varying observed TMJ symptoms (13%).^18,19

20.2.B Parafunction

Repeated strain on the joint due to parafunctional activity is probably the most common cause of internal derangement and is sometimes thought of as microtrauma to the temporomandibular articulation. Parafunction includes any repetitive behaviors, such as tooth grinding (bruxism), chronic tooth clenching, or atypical chewing habits such as chronic gum chewing These behaviors can be highly injurious and produce painful TMJ and masticatory muscle disorders and joint dysfunction.^20–24 A more detailed discussion of bruxism and how this behavior is associated with TMJ clicking is presented in Chapter 19.

20.2.C Arthritic Disease As a Primary Cause of Disk Displacement

Many people consider that TMJ derangements are merely an early manifestation of an osteoarthritic process. The term “osteoarthrosis” implies the breakdown of the joint articular surfaces and probably synovial fluid alterations. These changes would predispose the disk to abnormal function.

20.2.D Joint Hypermobility of the Temporomandibular Joint

Joint hypermobility or joint laxity means excessive mobility of the mandible and it is caused by discal and joint ligament laxity. When present, these patients can exhibit associated symptoms such as disk–condyle incoordination or open condyle dislocation. The issue of whether joint tissue laxity is present in a high percentage of patients with temporomandibular dysfunction is dependent on the definition of joint laxity. When a conservative definition is used, the prevalence of polyjoint hypermobility is less than 3% of the population and certainly does not explain the majority of internal derangements.

20.2.E Abnormal Biomechanical Loading

This is defined as an unstable occlusion (e.g., severe open bite or loss of posterior tooth support). The evidence that dental occlusal abnormalities are related to disk displacement comes from a 1976 study where researchers placed a “high” gold onlay on the occlusal surface of a mandibular molar in 8 healthy subjects.²⁵ This interference was approximately 250 µm above the contacting plane, thus putting the tooth in supracontact. The experimental occlusal interference was in place for 14 days and the authors described via qualitative observations that the experimental occlusal interference produced noticeable changes in jaw muscle EMG symmetry during clenching. They described that these 6 subjects complained of TMJ tenderness and muscle tenderness as a result of the experimental occlusal interference. Finally, new spontaneous TMJ clicking was reported during mandibular opening bilaterally in 3 subjects during this experiment (these symptoms occurred at 7–14 days after insertion of the inlay). In one of these subjects there were still severe irregularities of the movement in both joints near maximal mandibular opening 1 week after the removal of the inlay. This symptom persisted for 9 months and abated after treatment with a stabilization splint. This theory has substantial merit in some cases when clicking is associated with new dental work or orthodontic care, but overall this association is weak at best and cannot explain many other cases of TMJ clicking or locking.

20.3 Diagnostic Tests for Temporomandibular Joint Internal Derangements

Even though the previously described TMJ internal derangements involve specific articular pathologic conditions, identifying the probable etiology of the problem is not always straightforward. This is especially true for intracapsular condyle restrictions, which are easily mimicked by jaw muscle pain and stiffness problems. Historical factors such as the onset, duration, character, and location of the jaw dysfunction and its relationship to pain in the region are of essential importance in the diagnostic process. When combined with physical signs such as joint noises, jaw movement patterns and restrictions, and the passive stretch and joint manipulation tests, they are of greater clinical importance than any other diagnostic test, including radiographs, in the differential diagnostic process.²⁶ A table of the various diagnostic procedures used for internal derangement is provided (Table 20.2). In spite of the many diagnostic instruments which are used for research which can also be applied clinically to document jaw motion or muscle activity levels, the TMJ internal derangement is still best discovered and documented with a thorough history and a clinical examination. The clinical examination items which are most important for this discovery process are (1) the passive stretch test and (2) the joint manipulation test (when indicated). Additional diagnostic tests (e.g., MRIs or tomograms) should only be ordered if they will either confirm or rule out specific recognized pathologic entities which are suspected from the clinical findings. Further, these tests should only be requested when they will definitely influence the diagnostic, prognostic, or treatment-decision process.

Table 20.2 Diagnostic tests and patterns helpful for internal derangement

CT, computed tomography; DDNR, disk displacement with no reduction; MRI, magnetic resonance imaging; TMJ, temporomandibular joint.

20.3.A Passive Stretch Test

The differentiation between a muscular cause of limited jaw movement versus a true intracapsular restriction may require two diagnostic tests, passive stretch and joint manipulation; this concept is presented in Chapter 10. The passive stretch test is performed by first rubbing the masseter and temporalis muscles with ice to help transiently block the protective muscle trismus response which prevents opening. The second step of this test is for the examiner to immediately stretch the jaw opening by applying a mild to moderate force between the maxillary and mandibular teeth with the fingers. If a muscular induced limitation is present, jaw opening will increase to a normal distance.²⁷

20.3.B Images and Radiographs

The primary purpose of this diagnostic procedure is to assess the degree (if any exists) of osteoarthrosis in the symptomatic joint.^28–30 Except when associated with osteoarthritis signs (e.g., joint tenderness and crepitation noises), most TMJ restrictions are usually free of overt radiographic signs. The most acceptable radiographs include panoramic films of the TMJ³¹ and cone beam computerized tomographic (CT) scans.³² Cone beam CT scans are preferred over the other radiographic films of the TMJ but, because of their cost, magnetic resonance images (MRIs) of the TMJ are an optional diagnostic procedure.³³ Except when associated with osteoarthrosis, TMJ internal derangements are usually free of overt radiographic signs. As previously mentioned, radiographs should be made only when indicated by the clinical examination. Clinical signs such as severe joint tenderness, repeatable joint noises on palpation, crepitation, or a progressive deterioration of TMJ movement indicate a need for radiographs of the TMJ. Cone beam CT procedures have great merit and have surplanted conventional tomographic radiographic techniques for hard-tissue imaging of the TMJ structures. Cone beam CTs provide clearly s/>