Sacroiliac Joint & Pelvic Complex

• The Sacroiliac (SI) Joint & Pelvic Complex explained

Objectives

• The objectives are to describe the features of the hip/pelvis, articular and functional
• Learn their relationship to lumbopelvic movements, and define motions of the SI joint
• Factors contributing to stability of the SI joint covered
• Understand its passive stabilizing structures
• Identify normal anatomic alignment of the hip & discuss the effects of alterations
• Describe osteokinematic & arthrokinematic motions of the hip
• Understand muscle activity and function at the hip

Pelvic Ring

• Sacrum & innominates comprise the pelvic ring
• Sacroiliac joints and the pubic symphysis included
• Transfers body weight bidirectionally between trunk and femurs
• A cartilaginous joint make up the pubic symphysis
• It's located between the two ends of the pubic bones
• Fibrocartilaginous disc which joins the pubic bones

Sacrum

• A wedge shaped sacrum is done from 5 fused vertebrae
• The base is S1
• Two facets face posteriorly to articulate with L5 inferior facets
• The apex is S5, it articulates with the coccyx

Anatomy of the Sacroiliac (SI) Joint

• The SI Joint spans from S1 to S3
• Part synovial, part syndesmosis (fibrous)
• Synovial portion is either “L”, “C” shaped or “auricular”
• Ilial tuberosities articulate with sacral tuberosities via Sl interosseous ligaments to form fibrous portion of the joint
• Size, shape, & roughness of joint surfaces vary greatly among individuals
• Irregular shape helps the joint “lock in” to place

Sacroiliac Joint

• SI joint mobility is greater in younger individuals
• The joint is relatively mobile with flat, smooth surfaces in childhood
• Joint surfaces become roughened between puberty & adulthood, grooves & depressions form
• The capsule becomes more fibrotic & less pliable with age

SI Joint Articulating Surfaces

• Includes the Iliac crest, iliac fossa, tuberosity of ilium, anterior / posterior superior iliac spine, body of ischium / pubis etc
• Includes Sacrum, articular surface, coccyx etc
• Dorsal interosseous ligament portion of the sacroiliac joint is fibrous
• The articular cartilage portion of the the joint is synovial and L Shaped

Function of SI Joint

• Stability provided for load transfer between axial skeleton & lower limbs
• Stress relief is provided for pelvic ring
• The joint is designed for stability, with ligamentous support and irregular articular surfaces
• Movement is typically very minimal
• Gliding/translation is about 1-2 mm
• Rotation is around 2-4 degrees
• Motion decreases with age
• No muscles directly act at SI joint, movement occurs secondary to motion at adjacent joints

Pelvic Motions

• Anterior tilting means the ASISs move inferiorly & PSISs move superiorly creating hip flexion and increases lumbar lordosis
• Posterior tilting means the PSISs move inferiorly & ASISs move superiorly creating hip extension and flattens the lumbar lordosis

Motions at the SI Joint

• Nutation is relative anterior tilt of the base (top) of the sacrum relative to the ilium
• Counternutation is relative posterior tilt of the base of the sacrum relative to the ilium
• Motion occur due to the:
• Sacrum on ilium
• Ilium on sacrum
• Simultaneous motion of the 2

Sacral Nutation: Sacral Flexion

• Nutation means sacral locking
• Most stable position of SI joint
• Includes forward motion of sacral base into pelvis (or backward rotation of ilium on sacrum)
• Occurs with posterior pelvic tilt
• The ilia move closer together
• Ischial tuberosities move farther apart

Sacral Counternutation: Sacral Extension

• Counternutation means sacral unlocking
• The opposite movement to nutation
• Includes posterior motion of sacral base out of pelvis (or anterior rotation of ilium on sacrum)
• Occurs with anterior pelvic tilt
• Iliac bones move farther apart
• Ischial tuberosities move closer together

Nutation / Counternutation

• The amount of motion in the video is exaggerated for the purpose of illustrating the directionality of the movements

Sl Joint Ligaments

• The Iliolumbar ligament stabilizes lumbosacral joint and reinforces anterior aspect
• The Interosseous ligament is the Strongest ligament of SI joint, rigidly binds sacrum & ilium
• Anterior sacroiliac ligaments are relatively thin compared to others
• Thickening of anterior joint capsule limits nutation
• Long posterior sacroiliac ligament limits anterior pelvic rotation or sacral counternutation
• Short posterior sacroiliac ligament limits all pelvic & sacral movement
• Sacrotuberous and sacrospinous ligament limit nutation & posterior innominate rotation and resist superior translation of sacrum

Stress Relief in the Pelvic Ring

• Motion at SI joints & pubic symphysis dissipates stress in pelvic ring
• Important with reciprocal motions
• e.g. Walking, running, or stair climbing
• Walking includes reciprocal flexion & extension of lower extremities
• Each side of pelvis rotates out of phase with the other
• Tension in muscles & ligaments creates oppositely directed torsions through right & left iliac crests
• More pronounced in sagittal plane, but also occurs in the transverse plane
• Intrapelvic torsions are greater with increasing walking speed

Associated Motions of the Pelvis and Sacrum Resulting from Lumbar Motions in Standing

• Flexion means anterior tilt and counternutation
• Extension means posterior tilt and nutation
• Rotation means Ipsilateral side is posterior tilt and nutation, Contralateral side: is anterior tilt/counternutation
• Side bending means Ipsilateral side is anterior tilt and counternutation, the Contralateral side: is posterior tilt and nutation

Lumbopelvic Rhythm

• Full trunk motion achieved via combo of L-spine, pelvic, & hip motion
• Ratio of contribution from these areas is called lumbopelvic rhythm
• Motions occur simultaneously in healthy individuals

Variations in Lumbopelvic Rhythm

• Normal kinematic strategy is ~45° of lumbar flexion and 60° of of hip flexion
• With restricted hip flexion, greater flexion in lower thoracic & lumbar regions is needed to compensate
• With restricted lumbar mobility, greater hip flexion is required to compensate

Lumbopelvic Rhythm: Extending to Upright from Flexed Position

• Initial trunk extension includes Hip extension, via activation of hip extensors
• Middle phase - trunk extension occurs via a shared activation of hip & lumbar extensors
• Muscle activity decreases once LOG shifts posterior to hips

Stability of the SI Joint

• Form closure is Refers to closed packed position of the joint (nutation of the sacrum)
• Joint shape, coefficient of friction and ligamentous integrity impact form closure
• External factors impact stability, relies heavily on muscular action
• As counternutation occurs, greater muscle activation is required to maintain stability
• Motor control is related to timing and coordination of muscles

The Hip Joint

• Also known as a Coxofemoral joint
• It's a diarthrodial, triaxial joint
• Proximal articular surface makes up the acetabulum which is a concave socket
• Distal articular surface is the convex femoral head
• The HAT weight is supported

Structure of the Hip

• 3 bones form the part that contributes to part to the acetabulum being the ilium, ischium, and pubis
• Full ossification of pelvis typically occurs between ages 20-25

Structure of the Hip: Acetabulum

• Hyaline cartilage covers periphery of acetabulum, which is the lunate surface that's horseshoe shaped and articulates with the femoral head
• Transverse acetabular ligament connects 2 ends of lunate surface
• This creates a fibro-osseous tunnel
• Blood vessels pass through into acetabular fossa
• The acetabulum is deepened by fibrocartilaginous labrum and surrounds periphery of acetabulum
• The acetabular fossa is non-articular where fibro-elastic fat covered with synovial membrane resides
• Positioned laterally with an inferior & anterior tilt
• Only the upper margin of the acetabulum has a true circular contour

Center Edge Angle

• It's a measure of acetabular depth which represent how much of the femoral head is covered by acetabulum
• Formed by 2 lines originating at center of femoral head
• One line extends vertically & other line extends to lateral aspect of acetabulum
• Definite dysplasia is when less than 16°
• Possible dysplasia is 16° to 25°
• Normal range is 25 - 40°
• Excessive acetabular coverage is any value exceeding 40°

Acetabular Labrum

• Wedge shaped fibrocartilage covering periphery of acetabulum
• Function explained
• Deepens socket & increases concavity
• Grasps the femoral head to maintain contact with acetabulum and an axis to maintain negative intra-articular pressure
• Decreases force transmitted to articular cartilage
• Nerve endings are located within labrum

Acetabular Labrum and related

• The Ilium includes the Iliofemoral ligament - note that Ischial/Pubis connects with the Ischiofemoral ligament, and the Acetabular labrum
• Blue highlighted areas represent regions of thickest articular cartilage

Head Of The Femur

• A Fairly rounded hyaline cartilage-covered surface
• Articular area forms around 2/3 of a sphere, more circular than acetabulum
• Fovea of femoral head
• Small pit just inferior to most medial portion
• Not covered with articular cartilage
• Attachment site for ligamentum teres
• The femoral neck measures around 5 cm long
• Angled femoral head faces medially, superiorly, & anteriorly with respect to the femoral shaft & distal femoral condyles

Angle of Inclination

• The Angle of inclination is the frontal plane angle where a line goes through femoral head/neck & longitudinal axis of femoral shaft
• Normal ranges ~125° +/- a few degrees
• Having a Greater trochanter lies level with center of femoral head
• Tends to smaller in females, and larger in taller individuals
• Changes across lifespan
• This is normally ~ 150° at birth
• Gradually declines to ~125° by skeletal maturity
• It May also slightly decrease further in the elderly
• Coxa valga is when pathologically greater than 125°, and Coxa vara is when pathologically less than 125°

###Coxa Valga

• Causes Femoral articular surface to move contact area with acetabulum
• Leads to decreased joint stability
• Vertical WBing line shifts closer to shaft of femur
• Leads to decreased MA of hip abductors, and T force demand
• Means that there's increased force needed to counterbalance gravitational adduction moment at hip during SLS
• Greater muscular force will increase total JRF
• If abductors can't meet the increased demand they will be functionally weakened

Coxa Vara

• Causes the Femoral head to rest deeper in acetabulum leading improved congruence
• If not caused by trauma, MA of hip abductor muscles will be
• Causes a decreased force needed by abductors in SLS & JRF
• Results in increased bending bending moment along femoral head & neck
• Density of trabeculae laterally found in the femur due to tensile stresses
• Resulting increased shear force along femoral neck increases fracture risk

Angle of Torsion

• Transverse plane, line through longitudinal axis formed when Femoral head & neck offset Anteriorly with respect to distal condyles
• Averages to 10° - 20° in normal adults, where newborns are 30-40°
• Angle decreases until skeletal maturity
• Excessive Anteversion is marked by a greater than 15-20° angle with the pathological increase in angle
• Causes an associated increase in IR ROM of hip, and decreases ER ROM and reduced hip joint stability
• Retroversion occurs as pathological decrease in angle of torsion with an Angle that´s less than 15° to 20°
• Characterized by ↑ ER ROM of hip and an decreased IR ROM

Compensation for Abnormal Femoral Torsion

• With excessive anteversion, the Patients may “in-toe" in standing or during gait to improve alignment of articular surfaces
• When retroversion occur, the Patients may present with an excessive "out-toe” in standing to improve articular alignment

Negative Pressure of the Hip Joint

• Negative pressure plays a large role in maintaining joint congruence
• Pressure within joint must be "broken" before hip can be dislocated
• Labrum acts as seal to maintain negative intra-articular pressure
• If the "seal" breaks with a labral tear, the Femoral head then has greater motion within acetabulum, increasing stress through the joint capsule

Joint Capsule

• A major contributor to joint stability
• Thicker anterosuperiorly compared to the Posteroinferior capsule which is relatively thin & lax
• Zona orbicularis has a Collar like structure around femoral neck plus an oblique fibers attachment to the fibrous capsule, and assists in preventing distraction of femoral head from acetabulum
• Key Hip Ligaments include Iliofemoral, Pubofemoral, and Ischiofemoral

Joint Capsule & Ligaments

• Hip joint, capsule & ligaments supports 2/3 of the body weight while standing
• When LOG falls posterior to hip joint axis:
• Passive structures support body weight in symmetrical bilateral stance with no need for active assistance from hip muscles

Ligaments of the Hip

• The Iliofemoral ("Y" ligament) proximally features the AIIS & iliac portion of acetabulum

• The distally thickened anterior & superior jt capsule attaches to the intertrochanteric line of femur

• Includes Hyperextension, superior limits adduction, and posterior pelvic tilt

• It´s superior portion limited adduction with lateral portion limiting some ER

• The Pubofemoral ligament

• Proximally, it is located at the pubis & anterior-medial or pubic portion of acetabular rim

• It´s Distal, characterized by a Thickens portion of that's thickened to the anterior & inferior capsule

• This attaches to anterior intertrochanteric fossa & neck of femur, posteriorly with Abduction, and ER, then Hip extension

• The Ischiofemoral proximally features the ischial portion of acetabular rim & labrum, posteriorly & Inferiorly

• This attaches to posterior femoral neck medial to apex of greater trochanter

• Can undergo Hip extension / Hyperflexion /IR with Superior fibers that limit extreme adduction

• The Ligamentum teres

  • Includes a Center of acetabular fossa It´s attachments • Supplies blood to femoral head / Serves as channel for branch of obturator artery

• Secondary function includes resisting extremes of combined ADD, flexion & ER or combined ADD,extension & IR

Blood Supply to Femoral Head

• The role of ligamentum teres for varies across lifespan
• The greater contribution occurs in a childhood setting since Retinacular arteries can't travel through avascular growth plates
• More is often vascular supply through ligamentum teres
• Vessels in ligamentum teres are often sclerosed in elderly
• Not a strong source of blood supply when the primary supply is disrupted
• Increases risk of avascular necrosis of femoral head following femoral neck trauma

Open and Close Packed Positions

• Open packed position is at 10 - 30° flexion, 10 - 30° abduction, & slight ER
• Close packed position is at Full extension, with slight abduction & IR
• Close-packed position of hip is NOT position of optimal contact between hip & articular cartilage
• In extension, the ligaments then twist around femoral head & neck, pulling femoral head into acetabulum

Position of Optimal Articular Contact

• Neutral hip joint features Articular cartilage of femoral head exposed anteriorly & superiorly
• Optimal articular cartilage to acetabulum contact achieved between ~90° flexion, abducted, the "frog-leg position"

Structural Adaptations to Weight-Bearing

• Trabeculae align up lines of stress
• Most weight bearing stresses in pelvis pass from Sl joints to acetabulum

Weight-Bearing Aspects

• With 2 Major trabeculator
• Compression on the medial aspect of the joint
• Greatest tensile resistance to forces exist where trabeculae cross at perpendicular angles
• The zone of weakness is caused by area in femoral neck
  • In this area the trabeculae are thin & don't cross one another
  • Causes weaker reinforcement meaning there's a greater potential fracture point here

Weight-Bearing Aspects and resistance

Most forces travel through femoral head

• Forcing the GRF to travel upwards over / through the shaft of the femur Forces then compress to create bending moments across a limited range of motion
• This can cause traction which makes it more more prone to inferior aspects
• The trabecular structure helps fight this

Weightbearing Forces

• A net effect of LOG associated with body mass and ground reaction force the effect a bending force through femoral shaft
  • The effect causes joint compression
• The front plane causes a downward traction at the side muscles
• The Saggital plane compresses inferior to superior
• As the weight bears it shifts
  • In more compression of the body at the posterior chain Less tensile force at all joint articulation

Motion at the Hip

• 125° average Flexion, 30° average Extension 45° average Adduction /Internal rotation and and 30° average Abduction/ External rotation
• Can be broken down by Femur on pelvis Flexion/extension / Abduction/adduction
• Internal/external /rotation And the Pelvis on femur can include
• Lateral tilt /All axis (all planes)
• Forward/backward tilt (Anterior/Posterior) Rotation (protraction/retraction)

Key Axis and Planes

• Frontal position (or Anterior/Posterior) includes a flex action meaning you need posterior to be fully used for stabilization
• If the hip is going to tilt more into the movement
• It requires and increased compression to stabilize the body during gait
• If the leg is not straight
• It could create potential lateral shift
• It pushes to have hip be moved closer together It has a similar effect if it does the opposite

Key Factors For Hip Muscles

• multiple are influenced the position being preformed
  • Their functional impact would be effected by angle/position
  • Consider the Adductor: it can flex when its neutral position is It is more beneficial to be an extensor if the hip is fully used If the hip is not it is far more beneficial it's in a flexed position
• Rotational and compression effects are effected by rotation and contraction
• As torsion shifts in a fully flexion
• It takes effect the action shifts, which limits force

Hip Flexors

• Primary flexors include the ilipsoas, rectus formoris, the TFL, and sartorius
• Secondary includes Peritoneus muscles

Iliopsoas

• Muscle group can flex hips or flex the Trunk - its comprised of the iIiacus muscle and psoas major
• It has active tension to pull up vertebra and prevent compression on vertebral discs
• Active Tension can cause an anterior tilt
• Critical for preventing hyper-extension (or the ability to tilt)
• Functions with the pelvis to lock body so the sacrum so it can function with extension in seated positions

Factors of the Rectus

• Spans both hip/knee
• Flex the hip- extends on Knee
• Limited to extending on the Knee -Flex hip
• Best for full range compression, but not torque

Factors of the Sutorius

• Spans across hip Abduction. ER of hip - flexion and IR of the knee
• Effects compression so its functional activity is only needed for simple activities

factors of the hip/TFL?

• Spans the hip (flexion/AB ER)
• Most use with stabilization of IT band - Tension that reduces amount of stress on femoral shaft
• Its muscle fibers attach distally into IT band, and function to contribute to hip joint stability
• Along with glut max, it helps maintain tension in ITB and relieves some tensile stresses imposed on femoral shaft in WBing

Hip Extensors

• It is a Primary mover including- Glut max and Hamstring muscle + Bicep / Long head / Semi-tend-tend
• It can secondarily use posterior muscles of the gluten medius and posterior muscles of the adduction

Gluteus Maximus

• Has the most torque production
• Used when resisted a strong activation of muscles at a 70 angle
• Allows ER of the Femur (requires balance / compression with the ilipsoas)
• With increased hip flexion with will start to decrease

Ham Strings

• Long Muscle of the Femurs + Tend
• Assist with Resistance of the hip or assisting in stabilizing the knee
• When the knee is extended in a more flex is created
• It increase and the hamstring force increases by 30 percent with extended.
• Combined hamstrings is far more effective in torque as it is< that glut max
• Its ability is impacted of hip functions impacts ability

Hip Abductors

Primary abductor that is a 3rd class lever when used as part of the gluten

• Assist when needed with TFL
• Assist in secondary movement/ when hip is being resisted
• This includes the periforms and sartorius