The temporomandibular (TM) joint is unique in both structure and function. Structurally, the mandible is a horseshoe-shaped bone (Fig. 6–1) that articulates with the temporal bone at each posterior superior end and produces two distinct but highly interdependent articulations. Each TM joint contains a disc that separates the joint into upper and lower articulations. Functionally, mandibular movement involves concurrent movement in the four distinct joints, resulting in a complex structure that moves in all planes of motion to achieve normal function.
This chapter will introduce the TM joint. A discussion of the structure and function of the TM joint will allow you to appreciate and understand its unique features, its relationship with the cervical spine, and the impact of impairments and pathologies to the TM joint. A patient case scenario will provide the foundation for subsequent discussions. Although the purpose of this chapter is to discuss the normal function and structure of the TM joint, TM disorders are a common subgroup of orofacial pain disorders.1 This chapter will also introduce some of the common problems that involve deviations of normal structure.
Case 6-1: Patient Case
Jill Smith is a 32-year-old single mother with three children under the age of 6. She works as an office manager in a busy law firm. Recently she experienced the onset of frequent headaches and intermittent pain in her right ear as well as intermittent pain with occasional "popping" at her right jaw when she opens her mouth. She describes the headaches as a dull throb that starts at the back of her head and radiates over the top of her head to just behind her right eye. Jill reports edema on the right side of her face anterior to her ear. Jill is right-handed. Her medical history is unremarkable except for a history of allergies and a fall from her bicycle when she was 12 years old, hitting her chin on the handle bars on the way down. Radiographs taken at the time of the accident were negative for any fractures. Jill reports that she first noticed occasional, intermittent headaches after the bicycle accident. She indicates that the intensity and frequency of the headaches have gotten progressively worse. The symptoms anterior to her right ear are activated when she attempts to eat something chewy, hard, or large.
Jill's physical examination reveals a forward head posture, with rounded shoulders, winging scapulae, increased thoracic kyphosis, increased lumbar lordosis, hyperextended knees, and pronated feet. Her right shoulder is elevated slightly. Active movements of the mandible are restricted when performing mandibular depression, protrusion, and left lateral excursion. The mandible deflects to the right with mandibular depression. Active range of motion of the cervical spine is limited, especially in the upper levels. Passive mobility of the right TM joint reveals limitations with distraction, anterior ...