Posterior Ligamentous Complex Inflammatory Syndrome

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A tissue channel connecting the facet joints on opposite sides of the same spinal level was first identified in the cervical spine by Dr. Kikuzo Okada in 1981. In his studies, around 80% of cervical facets showed this link, which lies behind the ligamentum flavum on axial imaging and in the interlaminar space on coronal imaging. This connection is often seen during intra-articular injections of otherwise normal or mildly affected cervical facet joints.

In the lumbar spine, such a connection usually appears only with significant facet joint degeneration or in the presence of pars interarticularis defects. Here, the pathway can also link to an adventitial bursa in the interspinous ligament, as seen in Baastrup’s disease.

This space can act as a route for the spread of infection or, more commonly, inflammatory changes across joints and surrounding tissues. When inflammation or fluid is observed here in conjunction with back pain, this has been described as posterior ligamentous complex inflammatory syndrome. In people with lumbar pain and pars defects, the inflammation may extend to multiple facet joints, both pars defects, and the interspinous ligament, and can accommodate several millilitres of fluid.

This anatomical space can complicate epidural steroid injections, sometimes causing a false sense of loss of resistance or unexpected spread of injected contrast into facet joints or the interspinous ligament, rather than the intended epidural space. Similarly, during transforaminal injections in the cervical or lumbar spine, contrast may track from a facet joint into this retroligamentous space, imitating epidural flow.