Biomechanics of si joint

1. Biomechanics Of Sacroiliac Joints Venus Pagare 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

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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: Anterior sacroiliac a. Sacrotuberous Posterior sacroiliac b. Sacrospinous Interosseous LIGAMENTS 14

15. 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

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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. Non-weight-bearing innominate : antero -superior relative to the sacrum. 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: 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

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44. NUTATION COUNTER NUTATION 44

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