TMJ: Arthrokinematics and Pathology Review

The temporomandibular joint (TMJ) is one of the least commonly treated regions of the body in outpatient orthopaedics. Due to this infrequency, many will therapists simply refer out to specialists when these patients present. Many are unaware of the fact that the TMJ and cervical spine are connected by more than just proximity. The spinal nucleus of the trigeminal nerve travels down into the upper cervical spine. Because of this relation, dysfunction (even if non-painful) in one can contribute to dysfunction in another. For this reason, among others the TMJ should be considered in management of cervical conditions and vice versa. 

One general point to consider regarding TMJ arthrokinematics is that movement of the mandible requires motion in bilateral TMJ's. A restriction in one may force a relative hypermobility in the other. The arthrokinematics of the TMJ require both rotation and translation. Rotation occurs between the superior aspect of the mandibular condyle and the inferior articular disc. Translation occurs as the condyle and disc move on the mandibular fossa/articular eminence.

Protrusion/Retrusion: Relative anterior/posterior translation of disc and condyle on mandibular fossa/articular eminence. The mandible and condyle follow the slope of the articular eminence during the motion, so during protrusion, the mandible slide anteriorly and inferiorly. The opposite is true for retrusion.

Lateral Excursion: Side to side translation of the disc and condyle on the fossa. The ipsilateral condyle has minimal motion, while the contralateral condyle moves anteriorly and medially. The ipsilateral condyle almost acts as a pivot point.

Depression: Made up of two phases. During the early phase (35-50%), the condyle rolls posteriorly on the inferior surface of the disc with slight anterior translation. During the late phase (final 50-65%), it transitions to motion primarily consisting of condyle and disc translating anteriorly on the mandibular fossa and articular eminence. The roll and translation occur with varying degrees but the disc stays between the condyle and eminence to minimize stress between the structures. Protrusion and depression are limited by retrodiskal laminae being stretched by attachment to the disc.

Elevation: The opposite arthrokinematics  of depression. Elevation is initiated by tension in the retrodiskal laminae.

When you are assessing an individual referred for TMD and cervicalgia, your examination should include both (along with the rest of the upper quarter). Some standard examination techniques include are ROM, resisted isometrics, segmental mobility, palpation, listening for joint sounds (disc displacement), cotton roll test, and posture. ROM of the TMJ can reveal potential limitations of the capsule. Normal ROM is: 45 mm for depression, lateral excursion is 1/4 of depression, protrusion is 6-9 mm and retrusion is 3 mm (Ho, 2011). Lateral deviation to one side may signify capsular restrictions ipsilaterally, potential muscle dysfunction, or an anteriorly displaced disc without reduction ipsilaterally. This may be represented as a "C-curve" when opening (an "S-curve" is associated with hypermobility). Resisted isometrics can help you to identify a particular muscle that is not functioning properly. Segmental mobility of both the TMJ and upper cervical spine can potentially assist in identifying hyper- or hypomobility in a segment related to the abnormal mechanics. Palpation can be useful for assessing trigger points or tenderness in a capsule. The cotton roll test can help differentiate between muscular and joint involvement. If a patient complains of pain when chewing on one side of the mouth, have the patient bite down on a cotton roll. By doing so, this gaps the ipsilateral TMJ. Thus, if pain is decreased, it would appear the pain is joint related, but if it doesn't change or increases, the pain is muscular (it is still possible that the pain is related to the cervical spine as well). Also, we cannot forget about the cervical posture. Knowing the resting position of the teeth is important to understand the individual's TMJ mechanics and as previously mentioned the impact cervical posture can have on the TMJ. Finally, be sure to check for any poor habits such as bruxism, chewing on ice, grinding teeth, etc. that impact the TMJ.

There are three primary disorders of the temporomandibular joint. Anterior disc displacement with reduction occurs when the disc rests anterior to the condyle. During depression of the mandible, the disc slides into proper position throughout the motion, but as the mandible elevates it slides into its anterior position again. Both of these disc transitions typically are accompanied by a "click." Anterior disc displacement without reduction occurs when the disc rests anterior to the condyle but is unable to slide into proper position during jaw movements. There is typically no clicking occurring with this pathology and depression of the mandible is limited (blocking translation of the condyle). Posterior disc displacement occurs when the jaw has been held widely open for a prolonged period of time or extensive range and the disc gets "stuck" posterior to the condyle, blocking mandibular elevation. With reduction, a closing "click" may occur.

While this article by no means serves as a "how-to" with managing the temporomandibular joint, it will hopefully help to understand the biomechanics of the TMJ and some general concepts regarding TMJ pathology. It is essential to at least consider assessing the TMJ in cervical patients, particularly if their progress is limited. Unfortunately, the research for TMJ management is rather limited at this time.

​-Dr. Chris Fox, PT, DPT, OCS

---

Check out our Insider Access Page!

Learn from residency-trained, board-certified orthopaedic and sports physical therapists.​​With Insider Access, you gain access to advanced manual assessment and treatment techniques, exercise progressions, sports specific content, and more. Our goal is to facilitate your clinical and professional growth!