Lumbosacral joint

The lumbosacral joint articulates the fifth lumbar vertebra (L5) and the first sacral vertebra (S1).

Gross anatomy

Articulations

The lumbosacral joint has two significant articulations:

• formed by an intervertebral disc encapsulated between the L5 and S1 vertebral bodies and S1

• paired facet joints formed between the L5 inferior articular processes and the S1 superior articular processes

Attachments

Ligaments

• Iiolumbar ligament

  • major stabilizing ligament of the lumbosacral joints

  • starts from L5 transverse processes to extend inferolaterally to attach to the iliac crest inner surface

  • thought to be comprised of two major bands, an upper and lower band.

• lateral lumbosacral ligament: arises from transverse processes L5 to pass inferiorly to the ala of the sacrum

The anterior and posterior longitudinal ligaments, the ligamentum flavum, supraspinous ligaments, and the interspinous ligaments also support the lumbosacral joint.

Musculotendinous

• psoas major

• rectus abdominis

• external oblique

• internal oblique

• transversus abdominis

• multifidus

• longissimus lumborum

• iliocostalis lumborum

Movement

The major movements that occur are flexion and extension. Secondary movements can occur, such as lateral flexion.

Arterial supply

Iliolumbar and superior lateral sacral arteries are the major vascular contribuants of the lumbosacral joint.

Innervation

The lumbosacral joint is innervated by the fourth and fifth lumbar spinal nerves and its subsequent branches.

Variant anatomy

• Lumbosacral transitional vertebra