Zygapophyseal joints and articular dysfunction as a source of pain in TTH
Zygapophyseal joints have been long established as a source of pain. The facet joints connect the superior facet of a vertebra to the inferior facet of the adjacent vertebra and are typical loose synovial joints. The articular surfaces are covered with hyaline cartilage, thicker in the centre of the facet and thinner at the edges. A circumferential fibrous capsule joins the two facet surfaces. A fibroadipose vascular tissue may extend into the joint space from the capsule, in particular at the proximal and distal poles. This tissue is referred to as a joint meniscoid.
In the cervical spine the facet joint orientation is in the coronal plain, this changes, however, as one descends down the spine. This orientation in the coronal plane causes the facet joints to have a relatively diminished ability to resist flexion-extension, lateral bending and rotation.
The facet joints in the lower cervical spine (C4-C7) are innervated by the medial branch of the posterior dorsal rami of the cervical spinal nerves originating from one level cephalad and a level caudad to and at the same level of the joint. The first three vertebrae C1-C3 are believed to have multisegmental innervations due to communicating branches which connect the dorsal rami of C1, C2 and C3 and a communication from the posterior upper cervical plexus.