TEC1 - Semester 2: Pelvic biomechanics Flashcards
What are the bones of the pelvis?
Sacrum, Coccyx, Ilium, Pubis, Ischium
Describe the structure of the sacrum.
- triangular shaped
- part of the axial skeleton, but also helps completes pelvic ring
- 5 fused vertebrae
- articulates with L5 (S) and pelvic bones (L)
What are functions of the sacrum?
- strong foundation for pelvic girdle
- stable base for spine
- large area for attachment of muscles and ligaments
- protection of pelvic contents
What does the sacrum contain?
- encloses sacral canal
- contains cauda equina + spinal meninges
Describe the structure of the coccyx.
- is remnant of a tail
- triangular shaoed
- 3-5 fused vertebrae
Which bones form the “Innominate”?
ilium, pubis, ischium
Describe the ilium’s structure.
- fan shaped
- comprises superior 2/3 of the pelvic bone
- superior 2/5 of acetabulum
Which landmarks can one find on the ilium?
iliac crest, ASIS, AIIS, PSIS, PIIS
Describe the structure of the pubis.
- anterior part of pelvic bones
- has a body and 2 rami (S and I)
Which landmarks can one find on the pubis?
pubic tubercle, pubic crest, iliopubic ramus, ischipubic ramus
Describe the structure of the ischium.
- L-shaped
- has a body and one ramus
Which landmarks can one find on the ischium?
body, rami, ischial tuberosity, ischial spine
Describe the acetablulum.
- hemispherical cavity articulating with head of femur
- directed L, I and A
- stable joint due to deep concavity
What is the acetabulum formed by?
fusion of pubis, ischium and ilium
Pubis: A and I 1/5
Ischium: P and I 2/5
Ilium: remaining 2/5
What are the muscles of the pelvis?
tensor fascia latae, iliopsoas, gluteus max. med. & min.
What are the joints of the pelvis?
SI-joint, Symphysis pubis, Sacrococcygeal joint
Which joints are functional (=move)?
both SI Joints & pubic symphysis
Which types of joints can the SI joint be divided in?
- Fibrous syndesmotic joint
- Synovial plane gliding joint
Describe the fibrous syndesmosis.
amphiathrotic sacroiliac ligaments bind the tuberosities of the ilium to the sacrum
Describe the synovial sacroiliac joint.
alar surface of sacrum articulates with medial auricular surface of ilium
Does the SI joint have a self-locking mechanism?
yes
What does that mechanism serve for?
to reduce weight bearing efforts. helps with stability in push-off phase of gait
What is the closed-packed position?
= locked position
- maximal contact of articulating surfaces
- joint ligaments and capsule are tight
- no joint play
- very stable position
What is the loose-packed position?
- joint surfaces maximally separated
- joint capsule and ligaments relaxed
- a lot of joint play
- resting position
Describe the Symphysis pubis joint.
- cartilaginous symphysis joint
- amphiarthrodial
- lies between articular surfaces of the pubic bones
- resists tensile, shearing, compressive forces
Describe the Sacrococcygeal joint.
- cartilaginous joint
- amphiarthrodial
- slightly movable, but ossifies over time and becomes immovable
- between apex of surface and base of coccyx
What are the primary ligaments of the SIJ?
interosseous, posterior and anterior SI
Describe the interosseous sacroiliac ligament.
- connects posterior sacral auricular surface to the iliac tuberosity
- resists anterior and inferior motion of sacrum
- one of the strongest ligaments in the body
Describe the Posterior SI ligament.
- posterior to interosseous ligament
- stabilizes SIJ
- resists excessive counternutation
Describe the anterior SI ligament.
- strengthens anterior part of capsule/joint
- resists excessive nutation
What are the secondary ligaments of the SIJ?
iliolumbar, sacrospinous and sacrotuberous ligament
Describe the iliolumbar ligament.
- between iliac crest and TP of L5 (sometimes also L4)
- prevents anterior translation and excessive rotation of L5
Describe the sacrospinous ligament.
- between the lateral margin of lower sacral half and coccyx and the spine of the ischium
- anterior to sacrotuberous ligament
- resists sacral nutation during weight bearing
Describe the sacrotuberous ligament.
- proximal attachment: PSIS, PIIS, lower 1/2 of sacrum, lower 1/2 of sacral crest and coccyx
- distal attachment: ischial tuberosity
- stabilize sacral nutation and resist counternutation during weight bearing
What are the ligament of the symphysis pubis?
superior, inferior, anterior and posterior pubic ligament
What is the function of these ligaments?
to stabilize the pubic joint
What are the coccygeal ligaments?
anterior & posterior ligament, 3 lateral sacrococcygeal ligaments
What is the anterior ligament an extension of?
the ALL
What is the posterior ligament an extension of?
the PLL and ligamentum flavum
Describe the Sacrococcygeal ligaments
from lateral angles of sacrum to TP of coccyx
Which function do the ligaments perform?
stabilize the sacrococcygeal joint
What are the sacral motions?
nutation, counternutation and rotation
What happens in sacral nutation?
sacral base tilts anterior/inferior;
sacral apex moves posterior/superior
What happens in sacral counternutation?
sacral base tilts posterior/superior;
sacral apex moves anterior/inferior
Sacral rotation occurs along an oblique axis of rotation. Where is the right/left oblique axis?
Right: from right anterior base to left lower sacrum
Left: from left anterior base to right lower sacrum
what happens to the sacrum if the trunk laterally flexes?
torsion around ipsilateral oblique axis
(right lateral flexion = ROA; left lateral flexion = LOA)
what happens to the sacrum if the trunk rotates?
sacral torsion around contralateral axis
Which movements of the pelvis/innominates are possible?
anterior, posterior & lateral tilt, rotation
