The supraspinous ligament forms part of the posterior ligamentous system of the vertebral column. It is a strong fibrous cord that connects the tips of the spinous processes. It extends between C7 and L4 in 73% of adults. Anteriorly, the supraspinous ligament merges with the interspinous ligament. Posteriorly the supraspinous ligament blends with myofascial structures.
The most superficial fibers extend over three or four vertebrae, the deeper spans two or three vertebrae the deepest connect adjacent spinous processes.
Within the lumbar spine the supraspinous ligament is most easily distinguishable at L2-L3. It then gradually diminishes below this level.
The supraspinous ligament in the thoracic region is a thin membranous structure. It's only at the thoracolumbar junction does it become better defined.
The interspinous ligaments run between, to attach on to, consecutive spinous processes. It attaches to the ligamentum flavum anteriorly and supraspinous ligament posteriorly. The left and right ligaments are seperated by a potential cleft. Only the anterior part of the ligament is truly ligamentous. The posterior part of the ligament is formed from myofascial structures that dip into the interspinous space to attach to the superior edge of the spinous process rather than to its tip.
Collagen fiber orientation in the interspinous ligaments is:
Cervical region (Prestar et al 1985):
- Anterocranial direction: prevents flexion (i.e. the cervical lordosis from diminshing).
Thoracic region (Prestar et al 1985):
- Longitudinal bundles of fibres connect the tops of the spinous processes: prevents flexion (i.e. augmentation of the thoracic kyphosis).
The interspinous ligaments in the thoracic region is a thin membranous structure. It's absent in the upper thoracic spine being replaced by loose connective tissue between the two multifidus muscles. It’s only at the thoracolumbar junction does the interspinous ligament become better defined (Gillian and Zhang 2002).
Lumbar spine (Prestar et al 1985):
- L1-5: Heylings (1978) and Scapinelli et al (2006) found the collagen fibers to run in a posterocranial direction. They are divided into the anterior, middle and posterior sections. The anterior section is an extension of the ligamentunm flavum. The middle section has the largest volume and forms a thick italic S-shaped curve, which is believed to be the main component in resisting flexion. The posterior section inserts obliquely backwards blending into the supraspinous ligament.
- L5-S1: collagen fibers run in a posterocranial and posterocaudal direction. Mahato (2013) found these fibers to run a lot more vertical than those in the upper lumbar spine to resist flexion. These fibers interlace with the thoracolumbar fascia, whose fibres form, below L4, a scissor-latticed structure.
Changes in the interspinous ligament have been noted at L5-S1 due to the change in contribution from the aponeurosis of the longissimus thoracis in the lower lumbar spine and the supraspinous ligament being absent at this level. Because of this Heylings (1976) found fibres of the right and left lumbodorsal fascia were thickest at this level and decussated across the mid-line. He also found the most medial tendons of the erector spinae aponeurosis crossed the mid-line to gain attachment to the opposite side of the posterior edge of the L5-S1 spinous process.
The lumbar interspinous ligaments functions in:
- Resisting flexion: predominately in its middle part (Heyling 1978 and Scapinelli et al 2006).
- Resisting extension: Prester et al (1985) found the interspinous ligament to limit backwards-shifting of the cranial vertebra in extension.
- Transmitting tension from the thoracolumbar fascia to the spine (Aspden and Hukins 1987, Yahia et al 1990).
Characteristics of the supraspinous and interspinous ligaments at different levels
Johnson and Zhang (2002) analysed the supraspinous ligament at different levels.
Upper thoracic spine (T1–T5)
The dense connective tissue attaching to the spinous processes in the upper thoracic spine originates mainly from muscles and tendons.
Tendons of the trapezius and splenius cervicis blend together at the midline creating an impression of a fine ligament running longitudinally over the tips of the spinous processes.
Dense connective tissue fibers arising from the middle portion of trapezius meet in the midline, decussating prior to attaching to the tips of the T1–T4 spinous processes. They are joined by the tendons of the rhomboid major and splenius cervicis.
Willard et al (2012) found that although the posterior layer of the thoracolumbar fascia extended up to and fused with the trapezius and rhomboid muscles these muscles are positioned external to it. As such they are enveloped in their own epimysial fascia.
Standring (2016) found the supraspinous ligament is also formed from the tendonous attachments of the semispinalis thoracis.
The deep layer of the thoracolumbar fascia - overlying and connecting with the splenius cervicis, longissimus thoracis and iliocostalis - also attaches to the spinous processes.
The interspinous ligaments are absent throughout the upper thoracic spine. Instead, the interspinous compartment is occupied by a thin layer of loose connective tissue located between the bilateral multifidus muscles.
Lower thoracic spine (T6–T12)
At T6 the spinal attachments of the posterior layer of the thoracolumbar fascia becomes evident. This coincides with a marked transition in the midline connective tissue organization and the presence of the decussating fibers of trapezius.
This composite of fibers from the posterior layer of the thoracolumbar fascia, dense connective tissue and decussating fibers of trapezius attaches as a single layer of connective tissue directly to the lateral aspect of the T6–T9 spinous processes.
At T9 the lower portion of trapezius gives rise to a tendinous aponeurosis which spans the lower thoracic and upper lumbar spinous processes.
T9 also marks the commencement of fiber decussation of the thoracolumbar fascia. These fibers form small fibrous compartments around individual fibers running longitudinally within the lower tendinous portion of trapezius.
The interspinous ligament commences at T6 as an anterior extension of the thoracolumbar fascia. It forms a single sheet of dense connective tissue running between the spinous processes of adjacent vertebrae.
The posterior layer of the thoracolumbar fascia becomes progressively thicker below T10 and, correspondingly, the interspinous tissue becomes better defined and bilaminar in form.
Lumbar spine (L1–L5)
The principal connective tissue components of the supraspinous ligament in the lumbar spine is the midline attachments of the:
- Posterior layer of the thoracolumbar fascia: distinct bands of dense connective tissue fibers from the thoracolumbar fascia cross the midline to merge with the contralateral fibers to contribute to both the supraspinous and interspinous ligament. In the upper lumbar spine the tendonous aponeurosis from the trapezius intertwines with the midline attachments of the thoracolumbar fascia.
- Longissimus thoracis: with the multifidus contributes to supraspinous ligament formation in the mid and lower lumbar spine.
- Multifidus: Creze et al (2018) found the multifidus to be strongly attached to the erector spinae aponeurosis close to the midline. The multifidus with the longissimus thoracis contributes to the supraspinous ligament in the mid and lower lumbar spine.
At L5, the dense connective tissue becomes further modified to create a horizontal T-bar formation as the posterior layer of the thoracocolumbar fascia joins with the common erector spinae aponeurosis to attach onto the L5 spinous process.
Heylings (1976) found beyond the lower limit of the supraspinous ligament at L5-S1 fibres of the right and left lumbodorsal fascia were thickest and decussated across the mid-line.
Where the supraspinous ligament was present Heylibngs (1976) found the tendons of the erector spinae aponeurosis gained attachment to the lateral part of the posterior edge of the spinous process. At L5-S1, caudal to the termination of the ligament, the most medial tendons crossed the midline to gain attachment to the opposite side of the posterior edge of the L5-S1 spinous processes. More laterally placed tendons at this level remained attached to their own side of these spinous processes.
The absence of a supraspinous ligament at L5-S1 can be associated with the greater range of flexion in this region.
Connective tissue contributions to the interspinous ligament are from:
- Thoracolumbar fascia: distinct bands of dense connective tissue fibers from the thoracolumbar fascia cross the midline to merge with the contralateral fibers to contribute to both the interspinous and supraspinous ligaments.
- Longissimus thoracis aponeurosis.
- Multifidus tendons.
The interspinous ligament merges anteriorly with the posterior capsule of the zygoapophyseal joints.
The tendinous origins of the multifidus and erector spinae aponeurosis contribute to the midline dense connective tissue arrangement at this level. Caudal to S3, there is no contribution from the surrounding musculature and the fascia gradually diminishes at the level of the coccyx.
The thoracolumbar fascia: anatomy, function and clinical considerations (2012). F H Willard, A Vleeming, M D Schuenke, L Danneels and R Schleip
Regional differences within the human supraspinous and interspinous ligaments: a sheet plastination study (2002). Gillian M. Johnson Ming Zhang
Supraspinous and interspinous ligaments of the human lumbar spine (1976). D. J. A. HEYLINGS
Organization of the fascia and aponeurosis in the lumbar paraspinal compartment (2018). Creze M, Soubeyrand M, Nyangoh Timoh K, Ggey O
The lumbar interspinous ligaments in humans: anatomical study and review of the literature. (2006). Scapinelli R, Stecco C, Pozzuoli A, Porzionato A, Macchi V, De Caro R.
Ligamentous connections of the spinal processes (1985). Prestar FJ, Frick H, Putz R.
Anatomy of Lumbar Interspinous Ligaments: Attachment, Thickness, Fibre Orientation and Biomechanical Importance (2013). MAHATO, N. K.
Structure-function relationship of human spinal ligaments (1990). Yahia H, Drouin G, Newman N.
Collagen organisation in the interspinous ligament and its relationship to tissue function (1987). R. M. ASPDEN, N. H. BORNSTEIN AND D. W. L. HUKINS
Gray's Anatomy. The anatomical basis of clinical practice. 41st editon. (2016). Standring S