Articular facets

The most common type of injury due to combined tension and extension of the cervical spine is the whiplash syndrome. However, a large majority of such injuries involve the soft tissues of the neck, and the pain is believed to reside in the joint capsules of the articular facets of the cervical vertebrae [Wallis et al., 1997]. In severe cases, teardrop fractures of the anterosuperior aspect of the vertebral body can occur. Alternately, separation of the anterior aspect of the disk from the vertebral endplate is known to occur. More severe injuries occur when the chin impacts the instrument panel or when the forehead impacts the windshield. In both cases, the head rotates rearward and applies a tensile and bending load on the neck. In the case of windshield impact by the forehead, hangman s fracture of C2 can occur. Garfin and Rothman [1983] suggested that it is caused by spinal extension combined with compression on the lamina of C2, causing the pars to fracture. 

Therefore, the high compression loads at L5-S1 are borne primarily by the nucleus pulposus of the disc and the central end plate of the vertebral body. The high shear loads at L5-S1 are borne principally by peripheral structures, specifically the articular facets and the annulus fibrosus of the disc. 

The occipitoatlantal articulation consists of the superior articular facets of the atlas and the two occipital condyles. The superior facets of the atlas face backward, upward, and medially, and are concave in both anteroposterior and transverse diameters. The surfaces of the occipital condyles match the facets of the atlas, and the joint is best thought of as a sphere (the occiput) gliding on the articular surfaces of the atlas (Fig. 24-1). The freely movable occiput is limited by its muscular and ligamentous attachments, which make flexion-extension the primary motion, producing a smaii-amplitude nodding of the head. Flexion of the occiput on the atlas is accompanied by a posterior translatory slide of the occiput extension is accompanied by an anterior translatory slide. 

The atlantoaxial articulation is specially adapted for (nearly) pure rotation. In addition to the inferior articular facets of the atlas and the superior articular facets of the axis, movement other than rotation is limited by the anteriorly located odontoid process (dens) of the axis. The odontoid process is held close to the anterior arch of the atlas by the transverse ligament of the atlas, which allows only a slight amount of flexion of the atlas on the axis. 

There is no true lateral flexion at the atlantoaxial joint, only a wobble created by the articulation of the superior axial and inferior atlantal articular facets. Unlike most facets, these four facets are all convex in shape (Fig. 24-3). During rotation of the atlas on the axis to the right, the left articular facet of the atlas in effect slides uphill on the left articular facet of the axis, while on the right the atlas slides downhill on the axis. This wobble motion is not true lateral flexion. 

FIG. 24-5 Oriantation of articular facets of C3 and C4 vertebrae. SP, spinous process SF, superior facet IF, inferior facet VB, vertebral body AP, articular pillar TF, transverse foramina. 

The cervical vertebrae C3 to C7 move least in flexion-extension. In flexion the inferior articular facets of the upper vertebrae must slide up the superior articular facets of the lower vertebrae, up a 45-degree incline. The normal lordotic curve in this area places the cervical spine in partial extension the cervical spine has no neutral position. 

Although the thoracic spine has characteristic features that distinguish it from the cervical and lumbar spinal regions, it is mainly a transitional zone between the cervical and lumbar regions, as evidenced by the steady increase in height of the vertebral bodies from T1 to T12. Moreover, the inferior articular facets of T12 correspond to those in the lumbar area to allow proper articulation with LI. The different forms of articulation play a considerable role in the amplitude of various physiologic motions in the thoracic spine. 

The posterolateral comers of the snperior and inferior vertebral plateaus bear the costal articular facets. These facets are oval, set into the body at an oblique angle, and lined by cartilage. They articulate with the heads of the ribs. Of the thoracic vertebrae, only T12 has costal articular facets only at the superior plateau. 

The superior articular facets face backward, upward, and laterally. They are rotated approximately 60 degrees from the horizontal plane and 20 degrees from the frontal plane. In the transverse dimension, they are convex. 

The inferior articular facets face forward, downward, and medially. In the transverse dimension, they are concave. The inferior articular facets of T12 resemble those of a lumbar vertebra in that they face laterally and anteriorly and are convex transversely. 

The articular facets on the vertebral bodies are really demifacets (i.e., partial faeets). The entire facet consists in the demifacet on the superior... 

The superior articular facets of the lumbar vertebrae are concave and face primarily medially and backward. They are rotated 45 degrees... 

Many variations of articular facets occur in the lumbar region, notably at the lumbosacral articulation. These variations include sagittal plane rotations of 0 to 90 degrees, a horizontal planar orientation, and facet asymmetries. These variants contribute to low back instability, disk disease, and somatic dysfunction. 

The tenth rib is typical in every respect expect its costovertebral articulation. The single articular facet on the head forms a joint with the facet on the body of the TIO vertebra. 

The anterior talofibular ligament goes from the anterior margin of the lateral malleolus forward and medially to attach to the lateral aspect of the neck and the lateral articular facet of the talus. The posterior talofibular ligament runs from the lower part of the lateral malleolus to the lateral tubercle of the posterior process of the talus. The calcaneofibular ligament runs from the apex of the lateral malleolus downward and backward to the tubercle on the lateral surface of the calcaneus (Fig. 95-3). 

The primary motion of the occiput on the atlas is flexion-extension, with the occipital condyles convex and the superior articular facets of the atlas concave. 

The postorbital process of the Bearsden Stethacanthus bears a recessed articular facet for the palatoquadrate [79], flanked by a prominent crest. The anterior face of the postorbital process includes the opening for the trigeminofacialis chamber and jugular canal, enclosed ventrolaterally by an anteroposteriorly slender, lateral commissure [78]. 

Proximal articular facet of metapterygium directed anteriorly. Absent (0) present... 

Fig. 14.2a,b. Patella, a Posterior view of the patella reveals its posterior surface divided into medial (mf) and lateral (If) articular facets by a vertical ridge (arrows), b Longitudinal 12-5MHz US image over the patella (P) in a newborn. The immature bone is entirely cartilaginous and appears homogeneously hypoechoic at US. For that reason, its overall shape and the appearance of the underlying femoral trochlea can be nicely depicted. Note the attachments of the quadriceps (Qt) and the patellar (Pt) tendons... 

The patellofemoral joint is formed by the groove of the femoral trochlea and the V-shaped articular facet of the patella (Fig. 14.2a). The orientation of the articular surfaces of these bones varies from... 

The superior tibiofibular joint consists of the articulation between the medial articular facet of the fibular head and the corresponding facet of the tibia. It is a small joint located inferolateral to the femorotibial... 

Smith (1967) after the resection of the dens prepared a bed for the iliac graft which was inserted into the cavity and guaranteed good fixation. O Laoire and Thomas (1982), Fang et al. (1983) achieved good results with anterior fixation using bone chips placed between the articular facets of the lateral joints. 

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