Facet injury is one of the most common causes of pain following spinal hyperextension. During hyperextension the meniscoids may be forced against and pinched by the articular processes producing pain. In addition, the joint capsules may be torn resulting in pain. Joint pain may also result from thickening of the capsular ligaments.1,3,4
The capsular ligaments are thin and loose ligamentous sacs that surround the facet articulations. The capsular ligaments are lined internally and externally by synovial membrane which are highly vascular and innervated.5 With flexion-extension loading, the facet joint capsules and capsular ligaments are subjected to high degrees of strain and deformation. These tissues, being densely innervated with free nerve endings, create increased neural activity which may produce pain directly or cause contraction of the paraspinal muscles resulting in pain and spasm.1,6
Neck pain and possibly radiculopathy may result from referred facet pain via articular branches off the cervical dorsi rami that innervate the periarticular fibrous tissue.1,7
Trauma to the facet region, particularly when there are pre-existing degenerative changes present, may be the etiology of many of the symptoms following a hyperextension injury to the spine. Chronic or degenerative facet arthrosis can be visualized with plain films, CT and MRI imaging. However, acute inflammatory changes to the facet joint region are not well visualized by these diagnostic imaging modalities. Compressive orthopedic testing lacks objectivity and specificity.
Diagnostic ultrasound (DUS) provides a noninvasive, objective and joint specific means to diagnose acute facet area inflammation. DUS is a widely used diagnostic imaging procedure which transmits sound waves into the body and records the rate that the echoes are returned back to a receiver. The consensus is that ultrasonography of the musculoskeletal system is best used to evaluate muscles, tendons, ligaments and bursae.8
The normal sonographic appearances of muscular, ligamentous and tendinous tissues have been determined and correlation of sonographic and histologic findings in abnormal or pathologic states have been monitored over specific period of time.5,9
Reproducible studies focused on the measurement of the acoustic properties of a nerve-muscle preparation relative to its physiologic state, i.e. relaxed or contracted, active or passive have been successful.5,10,11,12 Acoustic parameters of tissues are definitely dependent on the current physiologic state of the tissue. In other words, acute or recent onset of an immuno-histologic response will alter the sound velocity as it travels through a visco-elastic medium differently than it would through a long-standing or fully resolved medium. This response is based on the density of the tissue.5,13
Osseous spinal landmarks have been successfully identified with DUS. The spinous process, transverse process, articular pillars, vertebral body and paraspinal muscles have been clearly identified.9,14,15,16
DUS of the spine is performed by placing a 5.0 MHz linear array transducer over the vertebrae in the transverse plane, aligned perpendicular to the segment being examined. The anechoic (black) shadowing of the spinous process, lamina, transverse process and vertebral body should be noted.
With DUS, soft tissue inflammation (fibrosis) appears hyperechoic (white) relative to the surrounding tissues. Acute injuries appear more echoic than resolving or chronic injuries. The degree of inflammation is directly related to the severity of the lesion.
In the transverse plane, hyperechoic signals in the area of the articular pillars are indicative of inflammation/fibrosis of the facet capsular ligament. Confirmation of these findings can be made in the longitudinal plane, through the lamina, by observing inflammatory changes at the articulation of the superior and inferior facets. The findings on the longitudinal image should have a similar depth when compared with the transverse image.
Conclusion
Acute facet area injury is a common cause of spinal pain. DUS offers a safe and objective method to diagnose acute inflammatory changes to the facet region, which are not well visualized by other diagnostic imaging procedures. DUS is a joint specific means to determine the vertebral levels involved, acuteness of the lesion, severity of the lesion, and progression of the lesion through the course of treatment. Once the lesion is visualized, the appropriate treatment plan can be directed toward the injury.
References
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James J. White, DC
Kendra Kaesberg-White, DC
Belleville, Illinois