Sacrotuberous ligament

At a glance

English

Sacrotuberous ligament

Latin (TA2)

Ligamentum sacrotuberale

System

Ligament

Region

Abdomen

Side

Paired, left and right

About the sacrotuberous ligament

The sacrotuberous ligament, called the greater sacrosciatic ligament in older texts, is the larger of the two ligaments joining the sacrum to the ischium. It is flat and triangular, wide at its upper end, narrow in the middle and spreading out again below, rather like an hourglass seen from the side.

Its broad upper attachment runs along the posterior superior iliac spine and then over the back of the posterior sacro-iliac ligaments with which it blends, the lower transverse tubercles and lateral border of the sacrum and the side of the upper coccyx. From here the fibres pass downwards and outwards, twisting as they converge into a thick band, then widen again to fix on the medial edge of the ischial tuberosity. Some fibres carry on forwards over the ischial ramus, forming the falciform process, a curved fold that merges with the fascia lining the pudendal canal. This process is absent in some people.

The ligament lies behind the sacrospinous ligament and, with it, closes the lesser sciatic foramen. It also forms the back-and-side boundary of the perineum. Part of the lower gluteus maximus arises from its back surface, and in some people its lower edge is continuous with the tendon of the long head of biceps femoris, through which that muscle may help to steady the sacro-iliac joint. Twigs of the inferior gluteal artery heading for the coccyx pierce it, as do the perforating cutaneous nerve and small filaments of the coccygeal plexus.

The ligament tightens when the sacral base tilts forwards and so resists that movement, keeping the sacrum from tipping between the hip bones. The pudendal nerve can be compressed between it and the sacrospinous ligament, giving burning perineal pain on sitting; in severe cases surgeons divide the ligament to free the nerve.

Attachments and function

Attaches from

The posterior superior iliac spine and the surface of the posterior sacro-iliac ligaments, the lower transverse tubercles and lateral margin of the sacrum, and the upper coccyx.

Attaches to

The inner edge of the ischial tuberosity, continuing forwards on the ischial ramus as its falciform process.

Function

Resists forward tilting of the sacral base and backward rotation of its lower end, stabilising the sacro-iliac joint and helping enclose the lesser sciatic foramen.

Nerve supply

Twigs from the perforating cutaneous nerve and coccygeal plexus that pierce it.

Blood supply

The inferior gluteal artery sends twigs through it on their way to the coccyx.