Week 7, Monday

Our next exam will be Cervical and SI Joint

Clinical Anatomy of the Sacroiliac Joints ppt.

The sacrum:

  • triangular shaped bone in the center of posterior pelvis

  • 5 fused segments

  • Primary curve (kyphosis)

  • Base is the superior

  • AP is the inferior

  • Faces anteriorly and inferiorly

    • Base is normally located anterior to the apex

  • Major function is to transmit the weight of the vertebral column and the pelvis

Sacroiliac joint is where the Ilium meets the Sacrum

Pelvic girdle:

  • sacrum

  • Pair of sacroiliac joint

  • Three bones of the hemipelvis (Os Coxa)

  • Pubis symphysis joint

Auricular surface:

  • shaped like a backwards C

  • Sacral surface is Covered with Hyaline cartilage 1-3mm thick

  • Iliac Surface is Covered by fibrocartilage-like hyaline cartilage

Sacral Auricular surface components

  • sacral groove

    • Longitudinal groove alone the center

  • Alar tuberosity

    • Superior to the sacral groove

  • Sacral tuberosity

    • Thick posterior rib of Groove

    • Sometimes forms an “accessory SI Joint”

Iliac Auricular surface components

  • Iliac ridge

    • Longitudinal ridge on the Auricular surface

    • PSIS at the inferior end

  • Iliac tuberosity

    • Aka iliac tubercle or Bonnaire’s tubercle

  • Iliac sulcus

    • Groove between iliac tuberosity and iliac ridge

Bony interlocking:

  • sacral groove → iliac ridge

  • Middle sacral fossa → Iliac tuberosity

  • Sacral tuberosity → sulcus between iliac ridge and the iliac tuberosity

  • Alar tuberosity → depression anterior and superior to the iliac tuberosity

Ligaments of the Sacroiliac Joints

  • Articular capsule

    • Only found on the anterior surface

    • Synovial fluid

    • Thick and tough

    • Innervated with Nocioceptive and Proprioception nerve endings

    • No capsule along position joint

  • Interosseous sacroiliac ligament

    • Receives the most stress of all SIJ ligaments

    • Connects the 3 sacral fossae to the iliac tuberosity and the area around the tuberosity

    • Keeps counterrotation from occurring (limits the SIJ from rotating posteriorly)

    • Consists of superficial and deep layers

  • Anterior sacroiliac ligament

    • Covers over and blends with the joint capsule

    • Fibers runs mostly horizontal and attach distant from the joint margins

    • Prevents diastasis (separation) of the anterior joint surfaces

  • Posterior Interosseous Sacroiliac Ligament

    • Attach the iliac tuberosity and surrounding area to the 3 sacral fossae

    • Short, thick wit densely packed fibers

    • Deep and superficial components

  • Short posterior sacroiliac ligament

    • Connects the sacral tubercles and articular porcecess of S1 and S2 to the iliac crest and iliac tuberosity

    • Runs in horizontal plane

    • Binds ilium to the sacrum and prevents diastatis of the joint

  • Long Posterior Sacroiliac Ligament

    • Connects S3 and S4 to the PSIS and inner lip of the iliac crest

    • Course vertically and blend inferiorly with the sacrotuberous lig.

    • Limits posterior tilting of the sacral base (counternutation)

    • Fascia of the glute max, erector spinae and thoracolumbar fascia attach on the LPSIL to help form this ligament

    • May be a source of pain during pregnancy in low back and pelvis

  • Accessory ligaments:

    • Sacrotuberous lig.

      • Found at the posterior inferior sacrum to Ischial tuberosity

        • Superficial fibers continuous with biceps femoris tendon

        • Strong ligament that creates the lesser sciatic foramen with the Sacrospinous lig.

    • Sacrospinous ligament

      • Anterior surface of the sacrum to the Ischial spine

      • Greater sciatic foramen located superior to this

    • Both ligaments function to limit anterior-inferior movement of the sacral as (nutation)

SI joint Motion:

  • stability and slight mobility

  • Weight bearing structure

  • Females have more movement than males

  • Primary movements are Nutation and Counternutation

SI Joint biomechanics

  • Receives all the longitudinal forces transmitted through eh spine

  • Part of the pelvic ring, which allows it to transmit forces through eh pelvis tote lower extremity

  • Forces from the lower extremity ca also be transmitted to the sacrum via the pelvis

Stress-relieving joint

  • Without it, there would be a solid ring of bone around the pelvis and we would walk more rigidly

  • We lose motion in this as we age, and that is necessary

  • Torsional stresses are normally buffered by the SI joint

  • When these forces are not buffered, insufficiency may develop

    • Commonly occurs in older individuals when the SI joint has to be ankylosed

SI joint:

  • Sacrum set obliquely between the ilia such that its anterior end leans forward

  • Under vertical loads the sacrum tends to tilt forwards and downwards, rotating around Bonnaire’s tubercle

Joint Stabilizing factors:

  • erector spinae muscles

  • Abdominal muscles

  • Gluteus and thigh muscles

  • The wedge shape of the sacrum all will not allow it to rotate forward

  • The wider posterior edge of the S1 segment will move inferiorly and will want to separate the ilia

  • The wider anterior end of the S3 segment will move upwards and will tend to separate the ilia

Biomechanics

  • ROM less than 1* of movement in most cases

  • Nutation is the anterior-inferior rotation of the SI joint

  • Counternutation in the Posterior-superior rotation of the SI joint

  • Instantaneous axis of rotation with hip flexion

  • Flexion: axis passes backwards from the pubic symphysis to the greater sciatic notch

  • Extension: axis passes from the pubic symphysis through the pelvis between the ischium and the coccyx

  • Hip flexion causes the ipsilateral ilium to glide beta wards and downwards across the sacrum and compresses against it, pivoting at the pubic symphysis

  • Hip extension causes the ilium to glide forward and flare away from the sacrum

  • Movements caused by axial loading of the sacrum and loads on the ilium caused by muscle contraction

  • These motions suggest that the SI joint is designed to relieve stress on the pelvic ring as it is distorted in 3D

Form closure:

  • the most stable the SI joint will be; no additional forces needed to maintain stability

  • If the sacrum would fit in the pelvis with perfect form closure, no lateral forces would be needed

Force closure:

  • a lateral force and friction are needed to withstand the impact of the vertical load on the pelvis

  • Muscles and ligaments also prevent shear forces by means of compression that can be adjusted to the specific loading situation

Facts:

  • Inherently stable

  • Designed for Load transfer and can safely transfer enormous compressive loading forces under normal conditions

  • Due to its anatomical make-up. intra articular displacements within the SI Joints are unlikely

  • Distortions of the pelvis observed clinically are likely to occur secondary to changes in pelvic and trunk muscle activity.

    • This results in directional strain and not positional changes within the SI Joints themselves

Causes of SI Joint Dysfunction:

  • Trauma

  • Disease of Bone

  • Arthropathies

  • other causes, such as Hyperparathyroidism, paraplegia, lower extremity disorders, activity-related, post-hip surgery, neoplasm, etc.

SI Joint Dysfunction and SI Joint pain are two distinct entities