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Biomechanics of si joint
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Biomechanics of si joint

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  • 1. Biomechanics Of Sacroiliac Joints 1
  • 2. • Introduction • Osteology • Articulating surfaces • Ligaments • Blood supply • Nerve supply • Factors promoting • Stability • Kinematics • Functional consideration • Clinical anatomy • SI Dysfunction FLOW OF THE LECTURE 2
  • 3. Sacroiliac (SI) Joint : • Articulations between Left and right articular surfaces on sacrum and left and right iliac bones INTRODUCTION 3
  • 4. • Plane synovial joint → modified amphiarthrodial joint • Stable, rigid; relatively immobile; allowing effective load transfer • Each of two SI joints are about 1-2 mm wide 4
  • 5. • Connects spine to pelvis • Absorbs vertical forces from spine and transmitting them to pelvis and lower extremities 5
  • 6. SACRUM • Large flattened triangular bone • Formed by fusion of five sacral verebrae • Forms postero-superior part of bony pelvis OSTEOLOGY 6
  • 7. • Upper part (base) of sacrum is massive • Supports body weight & transmits it to hip bones • Lower part (apex) is free from weight and therefore tapers rapidly • Sacrum has pelvic, dorsal, & right & left lateral surface 7
  • 8. 8
  • 9. ILIUM • Upper expanded plate like part of hip bone Parts: • Upper end called iliac crest • Lower end which is smaller & fused with pubis & ischium at acetabulum 9
  • 10. • Three borders: anterior, posterior & medial • Three surfaces: gluteal, iliac fossa & sacropelvic surface 10
  • 11. SACRUM: • Auricular (C)-shaped on sides of fused sacral vertebrae • Covered with hyaline cartilage • Thicker than iliac cartilage ILIA: • Covered with fibrocartilage • Type II collagen, typical of hyaline cartilage, has been identified ARTICULATING SURFACES 11
  • 12. • Flat and smooth in foetus • Postpubertal : marked by a central groove or surface depression • Rough irregular surface with many large ridges and depression • Form an interlocking mechanism with the ilium, fitting together like pieces of a puzzle 12
  • 13. • 6 times more resistant to lateral forces than lumbar spine • 1/20 resistance to forces in axial compression • 1/2 resistance to rotational forces compared to lumbar spine 13
  • 14. Primary Ligaments: Secondary Ligaments: a. Anterior sacroiliac a. Sacrotuberous b. Posterior sacroiliac b. Sacrospinous c. Interosseous LIGAMENTS 14
  • 15. 1. Anterior Sacroiliac Ligament • Iliac crests to tubercles of first four sacral vertebrae • Join ilia to sacrum • Thickening of part of capsule • Thin, not very strong 2. Interosseous SI ligament • Strong & massive • Superficial & Deep: Superior band Inferior band 15
  • 16. 3. Posterior Sacroiliac Ligament • Stronger than anterior ligament and connects sacrum to PSIS. • Categorized into two sets; - short (superior) posterior SI ligament; horizontal - long (inferior) posterior SI ligament; vertical • Short & long 16
  • 17. 4. Sacrospinous Ligament • Connects ischial spines to lateral borders of sacrum and coccyx • Forms inferior border of greater sciatic notch 5. Sacrotuberous Ligament • Connects the ischial tuberosities to posterior spines at ilia and lateral sacrum and coccyx • Forms inferior border of lesser sciatic notch. 17
  • 18. • Cartilaginous joint • Joins 2 ends of pubic bones • 3 ligaments associated are - superior pubic ligament - inferior pubic ligament - posterior ligament SYMPHYSIS PUBIS 18
  • 19. • Branches of posterior division of internal iliac artery : • Iliolumbar • Lateral sacral & • Superior gluteal arteries Blood supply 19
  • 20. • Superior gluteal nerve – Ventral rami & – Lateral branches of dorsal rami of first & second sacral nerve NERVE SUPPLY 20
  • 21. 21
  • 22. • Stability is primary requirment of joint • Maintained by: - Interlocking of articular surfaces - Thick & strong interosseous & posterior sacroiliac ligaments - Vertebropelvic ligaments - With advancing age partial synostosis of joint takes place which further reduces movements FACTORS PROVIDING STABILITY 22
  • 23. • Very slight motion is available • The SIJs are linked to symphysis pubis in a closed kinematic chain • Any motion at symphysis pubis is accompanied by motion at SIJs and vice versa • Rotational motion : 0.2 – 2⁰ KINEMATICS 23
  • 24. • Translation motion : 1 – 2 mm • Rom increase during pregnancy in which all ligaments of pelvis become loose under influence of hormones, to facilitate delivery of foetus 24
  • 25. NUTATION COUNTER NUTATION • Movement of sacral promontory anteriorly & inferiorly • Posterior ilium-on- sacrum rotation rotation • Anterior tip of sacral promontory moves posteriorly & superiorly • Anterior ilium-on- sacrum rotation 25
  • 26. • Coccyx moves posteriorly in relation to ilium • AP diameter of pelvic brim is ↓ • AP diameter of pelvic outlet is ↑ • Coccyx moves anteriorly in relation to ilium • AP diameter of pelvic brim is ↑ • AP diameter of pelvic outlet is ↓ 26
  • 27. • SIJs and symphysis pubis are closely linked functionally to hip joint • Affects and gets affected by movements of trunk and lower extremities Hip flexion in supine position Posterior tilting of ilium Nutation at SIJs ↑ diameter of pelvic outlet Facilitates delivery of Foetal head 27
  • 28. Hip flexion in supine Anterior tilting of ilium Counternutation at SIJs ↑ diameter of pelvic brim Descent of foetal head in pelvis 28
  • 29. • Hip extended position is favored early in birthing process to facilitate descent of fetal head into pelvis • Hip flexed position is used during delivery 29
  • 30. Movements of Ilium • Posterior Rotation • Anterior Rotation • Motion of innominate relative to sacrum occurs about a coronal axis 30
  • 31. Posterior Rotation • In Single leg standing: Both weight bearing and non weight bearing innominates, posteriorly rotates relative to sacrum which is relatively nutated • SIJ is thus in closed packed position 31
  • 32. • It is also associated with side flexion of pelvis. a) Non-weight-bearing innominate: antero- superior relative to the sacrum. b) Weight-bearing side: posterior and superior relative to the sacrum. 32
  • 33. Anterior Rotation • Occurs during extension of the freely swinging leg 33
  • 34. 2 main functions of SIJs: a. Stress relief in pelvic ring • During walking • During child birth b. Stable means for transfer of load between axial skeleton and lower extremities • SIJ plane is nearly vertical • Susceptible to slipping FUNCTIONAL CONSIDERATIONS 34
  • 35. • Nutation ↑ stability by increasing compression and frictional forces • Closed pack position = Full Nutation • Forces that create nutation torque include: - Gravity - Passive tension in stretched ligaments - Muscle tension 35
  • 36. Gravity 36
  • 37. Stretched Ligaments 37
  • 38. Muscles that reinforce and stabilize SIJ: • Erector Spinae • Lumbar multifidi • Abdominal muscles: External & Internal obliques Rectus abdominis Transversus abdominis • Hamstrings such as biceps femoris 38
  • 39. • Lumbosacral trunk & ventral ramus of s1 nerve crosses pelvic surface of joint & may involved in area of their distribution • During pregnancy pelvic joints & ligaments are relaxed, & locking mechanism becomes less efficient, it naturally puts greater strain on ligaments, the sacroiliac strain thus produced may persist even after pregnancy CLINICAL ANATOMY 39
  • 40. • After childbirth ligaments are tightned up again, so that locking mechanism returns to its original efficiency • Sometimes locking occurs in rotated position of hip bones adopted during pregnancy • This results in subluxation of joint, causing low backache due to strain on ligaments 40
  • 41. The systemic causes of sacroiliac dysfunction: – Inflammatory conditions • Ankylosying spodylitis, Rheumatoid Arthritis – Joint infections • Brucellosis, Tuberculosis – Metabolic disorders • Gout, Hyper parathyroidism – Miscellaneous • Osteitis condensans illi, Paget’s disease SACROILIAC DYSFUNCTION 41
  • 42. Doubts?? 42
  • 43. 43
  • 44. NUTATION COUNTER NUTATION 44
  • 45. 45

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