bones and joints of pelvis

Question 1

Joints of the pelvis

Answer 1

• 2 x Sacroiliac joints
• 1 x pubic symphysis

Question 2

joints of the hip + knee

Answer 2

• hip joint
• tibiofemoral joint
• patellofemoral joint

Question 3

SACROILIAC JOINT - classification + info

Answer 3

• Largest axial joint, auricular-shaped
• has both synovial (Anterior) + fibrous (posterior) parts
• Wide variability in the adult SIJ (size, shape, and surface contour)
• may decrease in mobility with age

Movements
- Auricular surfaces are smooth at birth
- Once a child ambulates interlocking ridges & grooves on both auricular surfaces begin to develop
- These ridges increase with age (hence SIJ becomes less mobile)

Question 4

Pubic symphysis - classification + info

Answer 4

• Secondary cartilaginous joint
• Under the cartilage covering, the bony symphyseal surfaces have irregular ridges + grooves (increase with age)
• has a fibrocartilaginous disc (which is thicker in females)
• Small amount of motion normally - up to 2mm shift + 1° rotation

Question 5

Sacrococcygeal joint - classification + info

Answer 5

• Variable classification - symphysis, synovial or fused
• The first coccygeal vertebra articulates with the sacrum via a symphysial joint containing a thin intervertebral disc of fibrocartilage
• A small amount of flexion + extension occurs at the sacrococcygeal joint
• Usually the 4 coccygeal vertebrae (intercoccygeal joints) in adults are fused

Question 6

Movements at SIJ

Answer 6

Two main movements happen at the SIJ:
1. Nutation (‘nodding’)
2. Counter-nutation (opposite direction)
- Bilaterally, these movements occur around a transverse axis
- Approximately 1-4° of rotation range of motion with both legs fixed
- Limited by:
- interlocking bony ridges & grooves
- Ligaments
- muscles

Question 7

Sacral Nutation

Answer 7

• A small rotation of the sacral promontory in an anterior-inferior direction (i.e. forwards and towards the ground)
• Occurs as a result of the increase in load during standing
• Results in tensing all of the posterior SIJ ligaments (interosseous, posterior sacroiliac), hence compressing + further stabilising the SIJ
• get 1) pelvic inlet closure, 2) pelvic outlet opening

Question 8

Sacral counter-nutation

Answer 8

• A small rotation of the sacral promontory back in a posterior-superior direction.
• Results in reduced tension in the posterior SIJ ligaments
• These movts can occur differently on each side with pelvic rotation during gait.
• e.g. during walking one leg is in flexion + the other is in extension so there may be some degree of relative nutation on one side (stance leg) + counter-nutation on the other (swing leg)
• get 1) pelvic inlet opening, 2) pelvic outlet closure

Question 9

Pubic symphysis - more info

Answer 9

• Each pubic symphysis is covered by a thin layer of hyaline cartilage
• They are tightly bound together, but separated by a fibrocartilaginous disc that forms the symphysis.
• The disc has some mobility, about 2 mm, to allow some motion at the anterior pelvic ring
• In females this becomes more flexible during pregnancy (with effect of relaxin hormone)

Pubic symphysis – muscle attachment site
- Multiple muscles attach to the pubic symphysis
- Normally these can assist in providing dynamic stability
- Over-traction caused by these muscles can create damage to the pubic symphysis