Pelvic joints & ligaments

Question 1

What are the main joints and ligaments of the pelvis?

Answer 1

Joints:
* Sacroiliac
* Sacrococcygeal
* Pubic symphysis

Ligaments:
* Sacrotuberous
* Sacrospinous
* Iliolumbar

Question 2

Outline the sacroiliac joint.

Answer 2

• The sacroiliac joint is a synovial joint between the auricular surfaces of the ilium and sacrum.
• The articulating surfaces are jagged and there is very little movement.
• With increasing age fibrous adhesions and gradual obliteration of the joint cavity occur; earlier in males, after the menopause in females.
• The capsule is attached to the articular margins.
• Ligamentous bands surround the capsule. The anterior sacroiliac ligament is a flat band which joins the bones above and below the pelvic brim; stronger in the female, it indents a preauricular groove on the female ilium just below the pelvic brim.
• A mass of ligaments attaches the sacrum to the ilium behind the joint. * Most of them constitute the very strong interosseous sacroiliac ligament, whose fibres are attached to deep pits on the posterior surface of the lateral mass of the sacrum.
• The most superficial fibres form the posterior sacroiliac ligament.
• The posterior rami of the spinal nerves and vessels pass between the interosseous and posterior ligaments.
• The stability of the sacroiliac articulation depends entirely upon ligaments.
• Body weight transmitted through L5 vertebra tends to push the sacrum downwards and forwards towards the symphysis.
• Opposing any gliding movement of the joint surfaces are the interosseous sacroiliac ligament and the iliolumbar ligament, while opposing forward rotation of the sacral promontory are the sacrotuberous and sacrospinous ligaments.
• The sacroiliac ligaments soften towards the later months of pregnancy and permit some slight rotation of the sacrum during parturition.

Question 3

Outline the sacrotuberous ligament.

Answer 3

• The sacrotuberous ligament is a flat band of great strength.
• It is blended with the posterior sacroiliac ligament and is attached to the posterior border of the ilium and the posterior superior and posterior inferior iliac spines, to the transverse tubercles of the sacrum below the auricular surface, and to the upper part of the coccyx.
• From this wide area the ligament slopes down to the medial surface of the ischial tuberosity.
• The lower edge of the ischial attachment is prolonged forwards and attached to a curved ridge of bone. This prolongation is the falciform process; it lies just below the pudendal canal.
• The sacrotuberous ligament is narrower in the middle than at either end.
• Its gluteal surface gives origin to gluteus maximus.
• The ligament is said to be the phylogenetically degenerated tendon of origin of the long head of biceps femoris.
• It is pierced by the perforating cutaneous nerve and branches of the inferior gluteal vessels and coccygeal nerves.

Question 4

Outline the sacrospinous ligament.

Answer 4

• The sacrospinous ligament lies on the pelvic aspect of the sacrotuberous ligament.
• It has a broad base which is attached to the side of the lower part of the sacrum and the upper part of the coccyx. It narrows as it passes laterally, where its apex is attached to the spine of the ischium.
• The coccygeus muscle lies on the pelvic surface of the ligament.
• The ligament is the phylogenetically degenerated posterior surface of the coccygeus muscle.
• The sacrotuberous and sacrospinous ligaments, with the lesser sciatic notch of the ischium, enclose the lesser sciatic foramen, whose lateral part is occupied by the emerging obturator internus muscle and whose medial part leads forwards into the pudendal canal above the falciform process of the sacrotuberous ligament.

Question 5

Outline the iliolumbar ligament.

Answer 5

• The iliolumbar ligament is shaped like a V lying sideways, the apex of the V being attached to the transverse process of L5 vertebra, from which upper and lower bands fan outwards.
• The upper band passes to the iliac crest, giving partial origin to quadratus lumborum and becoming continuous with the anterior layer of the lumbar fascia.
• The lower band runs laterally and downwards to blend with the front of the anterior sacroiliac ligament.

Question 6

Outline the sacrococcygeal joint.

Answer 6

• The sacrococcygeal joint is a symphysis between the apex of the sacrum and the base of the coccyx, with an intervening disc of fibrocartilage.
• A short anterior sacrococcygeal ligament unites the bones at the front.
• Behind, there are two posterior sacrococcygeal ligaments: a short deep one uniting the adjacent bones and a superficial which closes over the sacral hiatus at the lower end of the sacral canal.
• At each side there is a lateral sacrococcygeal ligament running from the transverse process of the coccyx to the inferolateral angle of the sacrum, completing a foramen for the anterior ramus of the fifth sacral nerve.
• This ligament may become ossified.
• Slight flexion and extension are possible at this joint.

Question 7

Outline the pubic symphysis.

Answer 7

• The pubic symphysis as its name implies, is a secondary cartilaginous joint.
• The body surfaces of the pubes are each covered with a thin plate of hyaline cartilage and the two sides are connected by fibrocartilage forming an interpubic disc. Centrally a tissue-fluid space may develop, but it is never lined with synovial membrane.
• Ligamentous fibres forming the superior pubic ligament reinforce the symphysis above, and below it is strengthened by the arcuate pubic ligament.
• No perceptible movement occurs at the symphysis; some separation of the pubes may occur during parturition.