K-line negative

Although posterior decompressive surgery is widely used to treat patients with cervical myelopathy and multilevel ossification of the posterior longitudinal ligament (OPLL), a poor outcome is anticipated if the sagittal alignment is kyphotic (or K-line negative).

Lateral radiograph showing the K-line (solid line) connecting the midpoints of the spinal canal at C2 and C7 (K-line [−]) (A). Lateral radiograph showing the ossification of the posterior longitudinal ligament not exceeding the K-line (K-line [+]) (B).