Sacroiliac Joint & Pelvic Complex

Sacroiliac Joint & Pelvic Complex

• Articular features and functions of the hip/pelvis are described
• Motions of the SI joint and its relationship to lumbopelvic movements are defined
• Factors contributing to the stability of the SI joint are discussed
• Passive stabilizing structures of the pelvic region are defined
• The normal anatomic alignment of the hip, and the effects of alterations are identified
• Osteokinematic and arthrokinematic motions of the hip are described
• Muscle activity and function at the hip are described

Pelvic Ring

• Composed of the sacrum and innominates
• Includes SI joints and the pubic symphysis
• Transfers body weight bidirectionally between the trunk and femurs
• The pubic symphysis is a cartilaginous joint
• Located between the two ends of the pubic bones
• A fibrocartilaginous disc joins the pubic bones

Sacrum

• Five vertebrae fuse to form a wedge-shaped sacrum
• S1 is the base of the sacrum
• Two facets face posteriorly to articulate with the L5 inferior facets
• S5 is the apex of the sacrum
• Articulates with the coccyx

Anatomy of the Sacroiliac (SI) Joint

• Spans from S1 to S3
• Consists of both synovial and syndesmosis (fibrous) parts
• The synovial portion is "L" shaped, and may be "C" shaped or "auricular"
• Ilial tuberosities articulate with sacral tuberosities via SI interosseous ligaments to form the fibrous portion of the joint
• The size, shape, and roughness of joint surfaces vary greatly among individuals
• The irregular shape helps the joint "lock in" to place

Sacroiliac Joint Mobility

• 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 and adulthood
• Grooves and depressions form
• The joint capsule becomes more fibrotic and less pliable with age

Function of SI Joint

• Provides stability for load transfer between the axial skeleton and lower limbs
• Provides stress relief to the pelvic ring
• Designed for stability through:
• Ligamentous support
• Irregular articular surfaces
• Movement is very minimal
• Gliding/translation at ~1-2 mm
• Rotation at ~2-4°
• Motion decreases with age
• No muscles directly act at the SI joint
• Movement occurs secondary to motion at adjacent joints

Pelvic Motions

• In anterior tilting, ASISs move inferiorly and PSISs move superiorly
• Creates relative flexion of the hip
• Increases lumbar lordosis
• In posterior tilting, PSISs move inferiorly and ASISs move superiorly
• Creates relative extension of the hip
• Flattens lumbar lordosis

Motions at the SI Joint

• Nutation
• The relative anterior tilt of the base (top) of the sacrum relative to the ilium
• Counternutation
• The relative posterior tilt of the base of the sacrum relative to the ilium
• Motions occur via the motion of:
• The sacrum on the ilium
• The ilium on the sacrum
• Simultaneous motion of the two

Sacral Nutation: Sacral Flexion

• Nutation is sacral locking
• The most stable position of the SI joint
• It is the forward motion of sacral base into the pelvis, or backward rotation of the ilium on the sacrum
• Occurs with posterior pelvic tilt
• Ilia move closer together
• Ischial tuberosities move farther apart

Sacral Counternutation: Sacral Extension

• Counternutation is sacral unlocking
• Opposite movement to nutation
• Is posterior motion of the sacral base out of the pelvis, or anterior rotation of the ilium on the sacrum
• It occurs with anterior pelvic tilt
• Iliac bones move farther apart
• Ischial tuberosities move closer together

SI Joint Ligaments

• The iliolumbar ligament
• Stabilizes the lumbosacral joint
• Reinforces the anterior aspect of the joint
• The interosseous ligament
• Is the strongest ligament of the SI joint
• Rigidly binds the sacrum and ilium
• The anterior sacroiliac ligaments
• Are relatively thin compared to other SI ligaments
• The thickening of the anterior joint capsule
• Limits nutation
• The long posterior sacroiliac ligament
• Limits anterior pelvic rotation (tilt) or sacral counternutation
• The short posterior sacroiliac ligament
• Limits all pelvic and sacral movement
• The sacrotuberous ligament and sacrospinous ligament
• Limit nutation and posterior innominate rotation (tilt)
• Provide vertical stability, resisting superior translation of the sacrum

Stress Relief in the Pelvic Ring

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

Associated Motions of the Pelvis and Sacrum

• With lumbar spine flexion is is anterior tilt of the innominate, and couternutation of the Sacrum
• With lumbar spine extension is is posterior tilt of the innominate, and nutation of the Sacrum
• With Rotation is is ipsilateral side: posterior tilt of the innominate, and nutation of sacrum and Contralateral side: anterior tilt of the innominate and counternutation of sacrum
• With Side bending is is ipsilateral side: anterior tilt of the innominate, and counternutation of sacrum and Contralateral side: posterior tilt of the innominate and nutation of sacrum

Lumbopelvic Rhythm

• Full trunk motion achieved via a combination of the L-spine, pelvis, and hip motion
• The ratio of contribution from these areas is called lumbopelvic rhythm
• In healthy individuals, these motions occur simultaneously

Variations in Lumbopelvic Rhythm

• "Normal" kinematic strategy = ~45° lumbar flexion and ~60° hip flexion
• With a restriction in hip flexion:
• Greater flexion in lower thoracic and lumbar regions is needed to compensate
• With restricted lumbar mobility:
• Greater hip flexion is required to compensate

Lumbopelvic Rhythm to Upright

• Initial trunk extension happens via hip extension, and activation of hip extensors (glut max and hamstrings)
• Middle phase trunk extension via shared activation of hip and lumbar extensors
• Muscle activity is largely decreased once the line of gravity shifts posterior to hips

Stability of the SI Joint

• Form closure
  • Refers to closed packed position of the joint (nutation of the sacrum)
  • Joint shape, coefficient of friction and ligamentous integrity impact form closure
• Force closure
  • Extrinsic factors impact stability
  • Relies heavily on muscle action
  • Greater muscle activation is required to maintain stability as counternutation occurs
• Motor control
  • Related to the timing and coordination of muscles

The Hip Joint

• It is a coxofemoral, diarthrodial, triaxial joint
• The proximal articular surface:
• Acetabulum which has a concave socket
• The distal articular surface:
• Convex femoral head
• The joint supports the weight of the HAT (head, arms, torso)

Structure of the Hip

• Three bones, the ilium, ischium and the pubis form, each contributing to part of acetabulum
• Full ossification of the pelvis occurs between ages 20-25 years

Structure of the Hip: Acetabulum

• Hyaline cartilage covers the periphery of acetabulum (lunate surface)
• Horseshoe shaped area
• Articulates with femoral head
• Transverse acetabular ligament connects 2 ends of lunate surface
• Creates a fibro-osseous tunnel
• Blood vessels pass through into acetabular fossa
• It is deepened by the fibrocartilaginous labrum
• The labrum surrounds the periphery of the acetabulum
• The acetabular fossa is non-articular
• Contains fibro-elastic fat covered with synovial membrane
• It has a lateral position with an inferior & anterior tilt
• Only the upper margin of the acetabulum has a true circular contour

Center Edge Angle

• Also known as the Angle of Wiberg
  • It measures of acetabular depth
• Represents how much of femoral head is covered by acetabulum
• Formed by 2 lines originating at the center of the femoral head
• One line extends vertically
• The other extends to the lateral aspect of the acetabulum
• Definite dysplasia is seen at an angle of less than 16°
• Possible dysplasia at 16° to 25°
• Normal range is 25° to 40°
• Excessive acetabular coverage is an angle greater than 40°

Acetabular Labrum

• Wedge shaped fibrocartilage covers the periphery of acetabulum
• Its functions are
• Deepens socket & increases concavity
• Maintains the femoral head in contact with the acetabulum
• Acts as a seal to maintain negative intra-articular pressure
• Decreases force transmitted to articular cartilage
• Nerve endings are located within the labrum

Head of the Femur

• Fairly rounded hyaline cartilage-covered surface
• The articular area forms ~ 2/3 of a sphere
• More circular than acetabulum
• Fovea of the femoral head is a small pit just inferior to most medial portion
• Not covered with articular cartilage
• Is the attachment site for the ligamentum teres
• The femoral neck is ~5 cm long
• Angled so femoral head faces medially, superiorly, & anteriorly with respect to the femoral shaft & distal femoral condyles

Angle of Inclination

• It is a Frontal plane angle
• Formed by line through the femoral head/neck & longitudinal axis of the femoral shaft
• Normal angles are ~125° in adults
• A few degrees of variation between sides
• A greater trochanter lies level with center of the femoral head in the normal angle of inclination
• Variations exist
• Smaller in females
• Larger in taller individuals
• The angle changes across lifespan
• ~150° at birth
• Gradually declines to ~125° by skeletal maturity
• May slightly decrease further in the elderly
• Coxa valga: pathologically an angle greater than 125°
• Coxa vara: pathologically an angle of less than 125°

Coxa Valga

• Decreases the amount of femoral articular surface contact area with acetabulum
• Decreases joint stability
• The vertical weight bearing line shifts closer to shaft of femur
• Decreases distance between femoral head & greater trochanter
• Decreases MA of hip abductors
• Increases force demand to counterbalance gravitational adduction moment at hip during SLS
• Greater muscular force results in a greater total Joint Reaction Force (JRF)
• Abductors will be functionally weakened if they cannot meet the increased demand

Coxa Vara

• Femoral head rests deeper in acetabulum, which results improved congruency
• If not caused by trauma, it increases the MA of hip abductor muscles
• Decreases force needed by abductors in SLS & JRF
• Disadvantages in that it increases the bending moment along the femoral head & neck
• Density of trabeculae increases laterally in femur due to tensile stresses
• Shear force increases along femoral neck which increases fracture risk

Angle of Torsion

• Transverse plane angle formed by a line through the longitudinal axis of the femoral head & neck and another through distal femoral condyles
• Normally, the femoral head & neck are offset anteriorly with respect to the condyles
• Averages 10° - 20° in normal adults
• Newborns: 30° - 40° on average
• The angle decreases until skeletal maturity

Torsion Abnormalities Compensations

• Excessive Anteversion is a pathological increase in angle
• The Angle is > 15° to 20°
• Associated with increased IR ROM of hip & decreased ER ROM
• Reduces hip joint stability
• Retroversion : pathological decrease in the angle of torsion
• Angle is less than 15° to 20°
• Associated with ER ROM of hip & decreased IR ROM
• Both excessive anteversion & retroversion can predispose an individual to labral tears or degenerative joint disease
• Excessive anteversion compensations include toeing-in, while retroversion compensations include toeing out

Negative Pressure of the Hip Joint

• Plays a large role in maintaining joint congruence
• Pressure within joint must be broken before hip can be dislocated
• The Labrum acts as a seal to maintain negative intra-articular pressure
• With labral tear the "seal" breaks increasing femoral head motion w/in acetabulum
  • Increases stress through the joint capsule

Joint Capsule

• The hip has a joint capsule is a major contributor to joint stability
• Thicker anterosuperiorly and posteroinferior capsule is relatively thin & lax
• The hip has a Zona orbicularis
• Collar like structure around femoral neck
• Attachment site for oblique fibers of fibrous capsule
• Assists in preventing distraction of femoral head from acetabulum
• In standing the hip joint, capsule & ligaments support 2/3 of the body weight
• When the line of gravity falls posterior to hip joint axis, passive structures of hip can support body weight in symmetrical bilateral stance w/o active assistance from hip muscles

Ligaments of the Hip

• Iliofemoral ("Y" ligament)
• Proximal Attachments- AIIS & iliac portion of acetabulum
• Distal Attachments- A thickening of anterior & superior jt capsule, attaches to intertrochanteric line of femur
• Motions Limited- Hyperextension, Superior portion limits adduction, Lateral portion limits some ER, Posterior pelvic tilt Pubofemoral
• Proximal Attachments- Pubis & anterior-medial or pubic portion of acetabular rim
• Thickening of anterior & inferior capsule, attaches to anterior intertrochanteric fossa & neck of femur, posteriorly
• Hip extension, Abduction, ER Ischiofemoral • Proximal Attachments- Ischial portion of acetabular rim & labrum, posteriorly & inferiorly Thickening of posterior & lateral capsule, attaches to posterior femoral neck medial to apex of greater trochanter
• Hip extension, IR, Hyperflexion, Superior fibers limit extreme adduction (esp. when hip is flexed) Ligamentum teres
• Center of acetabular fossa & Fovea of femoral head Functions- *Serves as channel for branch of obturator artery-Supplies blood to femoral head Resists extremes of combined ADD, flexion & ER or combined ADD, extension & IR

Blood Supply to Femoral Head

• The role of the ligamentum teres blood supply varies across lifespan and has a greater contribution in childhood
• Retinacular arteries can't travel through avascular growth plates; and are more dependent on vascular supply through ligamentum teres
• Vessels in the ligamentum teres often sclerosed in elderly which is not a good source if the primary retinacular supply is disrupted
• increases risk of avascular necrosis of femoral head following femoral neck trauma

Open and Close Packed Positions

• The open packed position, occurs in 10 - 30° of flexion, 10 - 30° of abduction, & slight ER
• The close packed position, occurs in full extension, with slight abduction & IR
• With extension, ligaments twist around femoral head & neck, pulling femoral head into acetabulum
• It isn't the position of optimal articular contact of the hip

Position of Optimal Articular Contact

• In the neutral hip joint:
• Articular cartilage on femoral head is exposed anteriorly & superiorly
• Includes a maximum articular contact of femoral head with acetabulum:
• ~90° flexion, abducted, & ER ("frog-leg position")

Structural Adaptations to Weight-Bearing

• Trabeculae line up along lines of stress
• Most weight bearing stresses in the pelvis pass from Sl joints to the acetabulum
• Two major trabecular systems, Medial compressive and Lateral tensile
• Greatest resistance to forces in areas where trabeculae cross at perpendicular angles
• Zone of weakness is area in femoral neck where trabeculae are thin & don't cross one other
• Less reinforcement and more potential for fracture
• In weight-bearing at least ½ the weight of HAT passes through the femoral head
• The GRF travels up the shaft of femur
• Combined forces create a bending moment across the femoral neck
• It has a tensile force on the superior aspect and compressive forces on the inferior aspect
• The trabecular system structure allows for resistance to these forces

Weightbearing Forces

• The net effect of the line of gravity associated with the HAT & GRF creates a bending force through the shaft of the femur: compressive forces medially & tensile forces laterally
• Sagittal plane compressive forces posteriorly & tensile forces anteriorly

Motion at the Hip

Normal ROM hip values are:

• Flexion: 125°
• Extension: 10 – 30°
• Abduction: 45°
• Adduction: 30°
• Internal rotation: 45°
• External rotation: 45°
• Includes Femur on pelvis:
• Flexion/extension, Abduction/adduction, Internal/external rotation
• Pelvis on femur (includes anterior/posterior pelvic tilt, Lateral tilt, Forward and Backward rotation
• Includes anterior tilting of the pelvis: Produces relative flexion of the hip and Increases lumbar lordosis
• Includes posterior tilting of the pelvis: Produces relative extension of the hip and Flattens lumbar lordosis

Pelvic -on-Femoral Motion: Frontal Plane

• Lateral pelvic tilt: named by motion occurring on Non-Weight Bearing (NWB) side
• Hip hiking results in elevation of the pelvis
• A Pelvic drop results in a drop of the pelvis
• Includes Right pelvic hike: hiking of pelvis around left hip joint, results in left hip abduction
• Includes Right pelvic drop:Dropping of pelvis around left hip joint, results in left hip adduction

Pelvic Motion on Frontal Plane

• Lateral shift: term used in bilateral stance Example: right lateral shift Right hip joint will be adducted Left hip jt will be abducted
• To return to neutral position, the right abductor & left adductor muscles work synergistically

Pelvic Motion

The reference for forward and backward rotation is the side opposite the supporting hip

• Forward rotation of pelvis around left hip results in IR of left hip j
• Neutral position of pelvis & left hip joint
• Backward rotation of pelvis around left hip results in ER of left hip joint

Arthrokinematics at the Hip

• The femur is moving on the acetabulum:
• Flexion is where the head of the femur primarily spins in place with a small posterior slide
• Extension is where the head of the femur primarily spins in place with a small anterior slide
• Abduction has the had of the femur rolling superiorly & slides inferiorly
• Internal Rotation happens as the head of the femur rolls anteriorly & slides posteriorly
• External Rotation happens as the head of the femur rolls posteriorly & slides anteriorly

Hip Musculature

• Multiple hip muscles are strongly influenced by joint position
• This means that function can vary depending upon angle/position of the joint
• Examples include:
• Adductor muscles, that assist with hip flexion when the hip starts in neutral or extended position and function as hip extensors when the hip joint starts flexed
• Internal rotators that are capable of greater torque production as hip flexion angle increases
• External rotators, have torque production decrease as hip flexion angle increases
• Piriformis positioned for ER at 0° of hip flexion, but for IR beyond 90° of hip flexion
• Hip muscles includes the primary flexors including:Psoas Iliacus, Rectus femoris, Tensor fascia latae and sartorius. The secondary flexors are Pectineus, Adductor longus, Adductor magnus, Gracilis as well as anterior fibers of glut medius
• Gluteus maximus exerts peak extensor moment at 70° hip flexion and has large capacity to ER femur, but this ability decreases with increased hip flexion
• There are several Lateral Rotators of the hip and provide compressive forces with both Weight-Bearing and Non-Weight-Bearing activities

Iliopsoas

• The iliacus muscle + psoas major
• Activity or passive tension can anteriorly tilt the pelvis (iliacus muscle) & pull lumbar vertebrae anteriorly (psoas major) In standing the iliopsoas keeps body aligned keeping head aligned with the sacrum
• The iliopsoas is critical for active hip flexion from seated position (or when hip is flexed 90°) Both segments of iliopsoas are active in various stages of hip flexion

Rectus Femoris

• Crosses both the hip & knee joints to Flexes the hip & extends the knee
• Limited as hip flexor when knee is extended (due to active insufficiency)
• Contributes more as hip flexor when knee is maintained in flexion

Sartorius

• Performs Hip flexion, abduction, and ER
• Performs Knee flexion & IR with functional significance during activities requiring simultaneous knee and it flexion
• Relatively unaffected by knee position

Tensor Fascia Latae

• Flexes, abducts, & IR’s the hip where abduction function depends on simultaneous flexion
• Muscle fibers attach distally into IT band and function with ITB to contribute to hip joint stability
• Along with glut max, the tensor fascia latae helps maintain tension in ITB and relieves some tensile stresses imposed on femoral shaft in WBing

Hip Extensors:

• Primary Muscles:
  • Hamstrings also Extend this hip with or without resistance, as well as flex the knee. The MA of combined hamstrings as hip extensors if less than Glute Max. If, the hip is extended and the knee is flexed of great than 90 degrees, the hip can contribute the hamstrings. The hip extension forces increase by 30% when the knee is extended. The primary Hip Extensors have a posterior Pelvic Tilt when the thigh is fixed
  • Gluteus Maximus
• Secondary Hip Extensors - Posterior Fibers of Gluteus Medius -Posterior Fibers of Adductor Magnus

Medial Hip Rotators

• No muscles have a primary function of IR
• It is a contributor to IR with Anterior portion of gluteus medius/minimus, TFL and the Adductor muscles (possible exception of gracilis)
• In general, there is 3x greater IR torque in a flexed hip than in extended hip Several hip muscles trend toward IR torques as the hip flexes

Hip Abductors

• Primary Hip Abductors: Gluteus medius,Gluteus minimus, and
• Secondary Movers- piriformis, sartorius, as well as inferior or superiorfibers of gluteus muscle or to the gluteus Maximus
• Gluteus medius and minibus abducts the femur or NWBing side, while it stabilizes the pelvis to Single Limb stance. There is always always that an offset production of torque from gravity against pelvic Drop from weighted side. Is significantly reduced and in neutral or abductive position. The function of its abductor’s is an Action of those abductors in the weight gain on single limb Exert which is a inferiorly directed force on the side ipsilateral, as well as counterbalances pelvi