Kissing Spine and the Retrodural Space of Okada: More Than Just a Kiss?

Abstract

Baastrup (“kissing spine”) disease is characterized by contact by adjacent lumbar spinous processes and the presence of lumbar interspinous bursitis. The formation of an adventitious bursa within the interspinous region has been described previously in a retrospective review of routine lumbar magnetic resonance imaging in which the authors demonstrated the prevalence of interspinous bursitis in 8.2% of the study population [1]. These authors found an association between the formation of an interspinous bursa and the presence of associated degenerative changes such as central canal stenosis, disk bulging, and anterolisthesis. However, whether this bursa formation is the result of mechanical impingement from adjacent spinous processes or the result of degenerative conditions has not been fully characterized. Dr. Kikuzo Okada first described a communication pathway between single-level bilateral cervical facet joints in 1981 [2]. He described an extradural space dorsal to the ligamentum flavum that could connect the interlaminar region, interspinous region, and bilateral facet joints. This communication has been described in the lumbar spine, whereby interventional procedures in a single-sided facet joint have demonstrated flow of contrast material to the contralateral facet joint [3]. Usually “kissing spine” is thought to be caused by touching of approximating lumbar spinous processes during lumbar extension. This touching may create an adventitial bursa irritation within the interspinous ligament at the same level. However, we postulate that kissing spine disease may actually be an early sign of segmental instability. The anteroposterior shearing forces in persons with spondylolisthesis or early mid-range segmental instability may cause a friction moment, resulting in the interspinous formation of a bursa. Alternatively, excessive fluid within the facet joint caused by effusion may leak through the retrodural space of Okada to this region between the spinous processes and accumulate in the interspinous bursa. This bursa formation is different from a posterior facet joint synovial cyst in that the cyst has a contiguous relationship to the adjacent facet joint and is located in close proximity to the joint, whereas the adventitial bursa formation is more posterior within