Sacral and Pelvic Biomechanics Flashcards
What are the four common pain referral patterns of the SI joint?
i) bilateral SI region
ii) bilateral SI region and anterior hip
iii) lateral leg/buttock and anterior hip
iv) lateral leg/buttock
What are three possible MOIs for SI joint dysfunction?
i) trauma
ii) repetitive torsions
iii) postural abnormalities (ex. LLD)
What are the bony components of the pelvic ring?
i) R innominate
ii) L innominate
iii) sacrum (keystone - integrity depends on tight fit!)
iv) pubic symphysis
What is the function of the SI joint?
Transfer loads between lower limb and vertebrae while maintaining stability.
Describe the arthrology of the SI joint.
i) S1-3 vertebrae
ii) hyaline cartilage at sacrum, fibrocartilage at ilium
iii) C or L shaped
Describe how the arthrology of the SI joint changes with age.
i) diarthrodal -> symphhysis (fibrocartilage)
ii) smooth -> rough
iii) mobile -> immobile
iv) osteophytes and fibrotic fusion is later life
Describe the borders of the SI joint capsule.
i) superior - iliolumbar ligament extension
ii) inferior - blends with sacrospinous ligament
iii) posterior - interosseous ligament and long dorsal ligament
Describe the osteokinematic movements of the innominate at the SI joint.
i) anterior rotation (sagittal)
ii) posterior rotation (sagittal)
Describe the osteokinematic movements of the sacrum at the SI joint.
i) nutation (anterior rotation of base)
ii) counternutation (posterior rotation of base)
Under which conditions does the innominate rotate anteriorly on the sacrum?
i) thorax extension
ii) hip extension non-WBing
Describe the arthrokinematics of anterior rotation of the innominate on the sacrum.
Inferior, posterior slide of the innominate.
Under which conditions does the innominate rotate posteriorly on the sacrum?
i) thorax flexion
ii) hip flexion
iii) non WBing leg
Describe the arthrokinematics of posterior rotation of the innominate on the sacrum.
Superior, anterior slide of the innominate.
Describe the arthrokinematics of sacral nutation.
Inferior, posterior glide of the sacrum.
Describe the arthrokinematics of sacral counternutation.
Superior, anterior glide of sacrum.
What is the close packed position of the SI joint?
Sacral nutation.
How does sacral nutation contribute to stability at the SI joint?
i) increases compression and shear forces at joint surface
ii) base within column mechanically
Explain what is meant by sacral form closure.
Joint surfaces align to nutate the sacrum thereby increasing stability or self-locking the joint. No other forces are required to maintain stability.
Explain what is meant by sacral force closure.
Sacral stability and compression at the joint surfaces that is aided by external forces (ex muscles and ligaments).
Using the neutral zone model, what is the effect of form and force closure respectively?
i) form closure: is the shape of the bowl
ii) force closure: reduces the neutral zone of the bowl..
Under which conditions are form and force closure indicated?
i) form closure, or nutation torque from gravity and weightbearing, is adequate under SMALL and STATIC loading (ex. sitting, standing)
ii) force closure, or tensioning of ligaments and use of muscle to further nutate, is necessary for LARGER and DYNAMIC loads
Describe the sacral stabilizing effect of gravity in standing.
i) COM anterior to sacrum, therefore provides a nutation torque.
ii) femoral head compression in acetabulum provides a superiorly directed force causing the innominate to rotate posteriorly.
- The combined rotations locks the joint.
Describe the sacral stabilizing effect of ligaments.
i) nutation tightens the posterior ligaments (sacrotuberous, sacrospinous, interosseous) therefore increasing compression in the SI joint.
ii) Tension in the sacrotuberous ligament can be increased by posterior rotation of the innominate or contraction of muscles that attach to it (ex. biceps femoris)
Describe the effect of counternutation on sacral ligaments.
Counternutation tensions the long dorsal sacroiliac ligament. If this becomes static or regular posture, it can become a source for pain.
Contractile forces of muscle contribute to sacral stability by which mechanisms?
i) contribute to full sacral nutation
ii) pull on passive structures (ex. ligaments) that reinforce the joint
iii) generating active compression forces across the joint surface.
iv) produces slings of force that assist in load transfer.
Name the inner unit core muscles.
i) transversus abdominis
ii) pelvic floor
iii) multifidus
iv) diaphragm
What is the effect of multifidus contraction on the thoracolumbar fascia?
i) broadens TLF
ii) increases tension in TLF
Name the components of the posterior oblique sling.
i) contralateral latissimus dorsi
ii) glute max
iii) thoracolumbar fascia
Which outer unit sling contributes to force closure in rotation activities (ex. walking, golfing etc.)?
Posterior oblique sling.
Name the components of the deep longitudinal sling.
i) erector spinae
ii) multifidus attaching to sacrum
iii) deep lamina of TLF
iv) sacrotuberous ligament
v) biceps femoris
Name the components of the anterior oblique sling.
i) external oblique
ii) contralateral internal oblique
iii) contralateral adductors
iv) intervening anterior abdominal fascia
Name the components of the lateral sling system.
i) glute med/min
ii) tensor fascia lata
iii) contralateral adductors of the hip
- significant for pelvic girdle in standing and walking.
