Week 3: Sacroiliac Joints & Pubic Symphysis Flashcards
What are 4 similarities between sacroiliac joints and the pubic symphysis?
- Contribute to the bony pelvis
- Designed for stability - they also transmit body weight to the lower limbs (in standing) and absorb ground reaction forces in standing and sitting activities
- Minimal motion at both joints, but during pregnancy and childbirth there is likely to be an increase in movement (and possibly associated pain and dysfunction)
- No muscles act directly across either of these joints
Describe the difference of the articular surfaces of sacroiliac joints and the pubic symphysis:
SIJs: Left and right hip (innominate) bones and sacrum
Symphysis: Pubic portions of the right and left hip bones
What are the joint classifications of sacroiliac joints and the pubic symphysis?
SIJs: Ventrally - synovial, dorsally - fibrous (presence of strong interosseous ligament)
Symphysis: Cartilaginous
What are the ligaments of sacroiliac joints?
- Primary (directly associated with joint)
- Ventral sacroiliac ligament
- Interosseous sacroiliac ligament
- Dorsal sacroiliac ligaments (short and long) - Accessory (peripheral to joint but make important contributions to stability)
- Sacrospinous ligament
- Sacrotuberous ligament
- Iliolumbar
- Lumbosacral
What are the ligaments of the pubic symphysis?
- Superior pubic
- Inferior pubic (arcuate)
- Anterior pubic
- Posterior pubic
Describe the innervation of sacroiliac joints:
- Ventrally: Branches of the ventral primary rami L4-S3, superior gluteal and obturator nerves
- Dorsally: Branches from the dorsal primary rami L5-S2
Describe the innervation of the pubic symphysis:
Nerves penetrate the periphery of the disc only, and may be derived from branches of the pudendal and genitofemoral nerves, or branches of the iliohypogastric, ilioinguinal and genitofemoral nerves
Describe the movements of sacroiliac joints:
- Small rotatory movements of the sacrum (anteriorly and
posteriorly) - The lumbar spine and hip bones move as a unit - lumbopelvic rhythm
- SIJ motion is likely to increase during pregnancy and childbirth
Describe the movements of the pubic symphysis:
- Multidirectional and of small magnitude
- Slightly greater ranges may be possible in women who have given birth
- Likely to accompany SIJ motion
Which specific bony features articulate to form the ventral (anterior) and dorsal (posterior) aspects of the sacroiliac joint?
- Ventral: Iliac and sacral auricular surfaces
- Dorsal: Iliac and sacral tuberosities
Describe 3 functions of the sacroiliac joints:
- Act as stress relieving joints
- Unites the pelvic girdle to the axial skeleton
- Unite the two hip bones and the sacrum into the bony pelvis
The weight of the body reaches the sacrum anterior to the sacroiliac joint. What is the effect of this anteriorly directed force on the position of the sacrum?
Results in a turning or rotatory force on the sacrum so that the lower sacrum and coccyx tend to tilt backward and the sacral promontory tends to drop forward
Describe the bony features of the auricular surfaces of the sacrum and ilium (which form the ventral part of the joint):
Irregular contour marked by ridges, prominences, troughs and depressions these will match the auricular surface of the matching ilium
What is the functional significance of the bony features of the auricular surfaces of the sacrum and ilium?
Allow the bones to lock into one another
What is the function of the ligaments of the sacroiliac joint?
Bind the ilium to the sacrum
What are the attachment sites of the sacrotuberous ligament?
- PSIS, PIIS, lower margin sacrum and coccyx
- Ischial tuberosity
What are the attachment sites of the sacrospinous ligament?
- Lateral edge of sacrum below sacroiliac joint
- Ischial spine
What is the function of the sacrotuberous and sacrospinous ligaments at the sacroiliac joint?
Anchor the distal end of the sacrum - RESIST ROTATION of the sacrum between the hip bones
- Prevents lower sacrum and coccyx tilting backward and the sacral promontory dropping forward
Where is the greater sciatic foramen located?
Superior to the sacrospinous ligament & ischial spine
Where is the lesser sciatic foramen located?
Between the sacrospinous & sacrotuberous ligaments
What structures contribute to the formation of the greater and lesser sciatic foramen?
- Greater sciatic foramen: Sacrospinous ligament converts the greater sciatic notch
- Lesser sciatic foramen: Sacrospinous and sacrotuberous ligaments convert the lesser sciatic notch
What structures pass out of the pelvis through the greater sciatic foramen?
Piriformis muscle, sciatic nerve, superior and inferior gluteal nerves and vessels, (nerves to obturator internus and quadratus femoris)
Describe the general attachment sites of the iliolumbar ligament:
Transverse process of L5 to inner lip of the iliac crest
What is the function of the iliolumbar ligament?
Prevent forward sliding of L5 on the sacrum
What are the most important ligaments of the sacroiliac joint?
Interosseous sacroiliac ligaments
Describe the morphology of interosseous sacroiliac ligaments:
They are dense and strong, connecting the ligamentous portion of the sacrum with the ligamentous portion of the ilium
What is the function of the interosseous sacroiliac ligaments?
To bind the ilium strongly to the sacrum
What 3 mechanisms prevent the sacrum from rotating?
- Sacrotuberous and sacrospinous ligaments
- Interosseous sacroiliac ligaments
- Bony locking mechanism of the sacrum and ilium - prevent downward gliding of the sacrum under body weight
Are sacroiliac joints designed for a large range of motion? Why?
No, only a few degrees of motion are normally available due to the shape of the articular surfaces, size and density of ligamentous support
Is it easy to palpate the sacroiliac joints?
No, buried beneath the posterior aspect of the ilium and interosseous and posterior sacroiliac ligaments
What contributes to the formation of the pubic symphysis, and how is this joint classified?
Cartilaginous joint – formed by two pubic bones and intervening fibrocartilaginous disc
- Reinforced by pubic ligaments (the inferior or arcuate ligament is the strongest)
What are 2 functions of the pubic symphysis?
- To ensure that there is a strong union of the pubic bones in formation of the pelvic girdle
- The fibrocartilage disc also allows for shock absorption/slight give
How much movement is available at the pubic symphysis?
Very little (approx. 0.1-2mm) – may increase with injury and during late gestation and childbirth
What is osteokinematics?
The overall movements that may occur at a joint (e.g. flexion, extension, rotation)
What is arthrokinematics?
The motion occurring at the joint surface (e.g. roll, slide and spin)
At what joints of the lower limb do osteokinematic movements occur?
Hip joints, pelvis moving on stable femora
Describe the osteokinematic movements of the pelvis in the 3 different planes:
- Sagittal: Coronal axis - anterior & posterior pelvic tilt
- Coronal: Sagittal axis - lateral tilt
- Transverse: Longitudinal axis - anterior & posterior rotation
