The nuchal, supraspinal, and interspinal ligaments lie in the midline and attach to the dorsal structures of the spine. Due to the common position, these ligaments also share the common biomechanical function – the prevention of the hyperflexion of the spine. Moreover, all these ligaments serve as an attachment point for multiple muscles and aponeuroses1–2.
The cervical spine with the ligamentum nuchae. The lateral view.
The nuchal ligament is an integral part of neck muscles, i.e., it is made by the aponeuroses of the trapezius, splenius capitis, rhomboideus minor, and serratus posterior superior muscles1. The strongest portion of the ligament – the so-called dorsal raphe – is the fibrous cord extending from the spinous process of C7 to the external occipital protuberance2.
There is growing evidence that the fibers of the nuchal ligament and the fibers of neck muscles joining the suboccipital portion of the nuchal ligament attach to the cervical dura mater via the atlantooccipital and atlantoaxial interspaces3–5. These fibers, therefore, may directly affect the shape of the spinal dura mater during the motion of the head and neck.
The lumbar spine with the supraspinal and interspinal ligaments. The lateral view.
The size of the supraspinal ligament decreases craniocaudally, and the ligament is rarely seen below the level of L41. This may be related to the need for an increased range of flexion in the lower lumbar spine that otherwise would be significantly restricted2.
In the lumbar spine, the ventral part of each interspinal ligament splits into the right and left lamina, which merges with the capsular ligaments of the zygapophyseal joints and yellow ligaments3,4.
The lumbar spine with the interspinal ligaments. The lateral view.
Please note the nearly horizontally directed path of collagen fibers of the interspinal ligament at the lumbar level1. This arrangement of ligament fibers reduces the resistance to the flexion of the lumbar spine compared to the longitudinally oriented ligaments of the spine2. The fibers of the interspinal ligament cranially from the lumbar level gradually become thinner, and fibers' orientation becomes less regular3. In the upper thoracic spine (T1–T5-6), the interspinal ligaments may not be present4.