Hip and Pelvis Anatomy

Objectives of the Study

• Provide a description of the articular features and functions of the hip and pelvis region.
• Definition of the motions of the SI joint and their relationship with lumbopelvic movements.
• Discuss the factors that contribute to the stability of the SI joint.
• Describe passive stabilizing structures of the pelvic region.
• Identify the normal anatomical alignment of the hip and discuss the effects of alterations.
• Describe osteokinematic and arthrokinematic motions of the hip.
• Describe muscle activity and function of the hip.

Anatomy of the Pelvic Ring

• The pelvic ring comprises the sacrum and innominates.
• The Sacroiliac joints and pubic symphysis are included in the pelvic ring
• The pelvic ring transfers body weight between the trunk and femurs bidirectionally.
• The pubic symphysis is a cartilaginous joint.
• 2 ends of the pubic bones and a fibrocartilaginous disc join at the Pubic symphysis that is located between

Sacrum Anatomy

• A wedge-shaped sacrum is formed when five vertebrae fuse.
• The S1 section is the base.
• The S1section contains 2 facets face posteriorly to articulate with the L5 inferior facets.
• The S5 is the apex that articulates with the coccyx.

Sacroiliac (SI) Joint Anatomy

• The Sacroiliac Joint spans from S1 to S3.
• The Sacroiliac Joint is part synovial and part syndesmosis (fibrous).
• The Sacroiliac Joint’s synovial portion is "L" shaped but may be "C" shaped or "auricular."
• Sacral and ilial tuberosities articulate via Sacroiliac interosseous ligaments, establishing the joint's fibrous aspect.
• The size, shape, and roughness of joint surfaces greatly differ among individuals.
• The Sacroiliac Joint’s irregular shape helps it "lock in" to place

Sacroiliac Joint in Childhood vs Adulthood

• Younger individuals have more Sacroiliac joint mobility
• Joints in childhood are relatively mobile due to their flat, smooth surfaces.
• After individuals go through puberty, joint surfaces become rough and grooves & depressions start to form
• As one age, capsules become more fibrotic and less pliable.

Function of the Sacroiliac Joint

• Provides stability for load transfer between the axial skeleton & lower limbs.
• This joint also provides stress relief to the pelvic ring.
• The irregular articular surfaces and ligamentous support contributes to stability.
• Movement is very minimal with only around 1 - 2 mm of Gliding/translation and ~2 - 4° of Rotation
• Motion decreases as aging occurs.
• Joint movement is secondary to motion at adjacent joints
• No muscles act directly act at the Sacroiliac joint

Types of Pelvic Motion

• Anterior tilting
  • The ASISs move inferiorly & PSISs move superiorly.
  • Creates relative flexion of the hip. -Increases lumbar lordosis.
• Posterior tilting
  • The PSISs move inferiorly & ASISs move superiorly.
  • Creates relative extension of the hip
  • Flattens lumbar lordosis

Types of SI Joint Motions

• Nutation
  • A relative anterior tilt of the base (top) of the sacrum relative to the ilium.
• Counternutation -A relative posterior tilt of the base of the sacrum relative to the ilium.
• Nutation and counternutation to occur the sacrum or the ilium can move or a simultaneous motion of the 2

Nutation

• Nutation allows sacral locking of joint
• The most stable position of the Sacroiliac joint is when nutation occurs
• Nutation involves the forward motion of sacral base into the pelvis
• Nutation occurs with posterior pelvic tilt.
• During sacral nutation, the ilia move closer together and the Ischial tuberosities move farther apart.

Counternutation

• Counternutation allows sacral unlocking of the joint
• Counternutation has the opposite movement to nutation
• Counternutation involves posterior motion of the sacral base out of the pelvis
• Counternutation occurs with anterior pelvic tilt.
• During sacral counternutation, the iliac bones move farther apart the Ischial tuberosities move closer together

SI Joint Ligaments

• Iliolumbar ligament
  • This ligament stabilizes the lumbosacral joint
  • This ligament Reinforces the anterior aspect of the joint
• Interosseous ligament
  • The strongest ligament of the Sacroiliac joint
  • This ligament Rigidly binds the sacrum and ilium together
• Anterior sacroiliac ligaments
  • It is relatively thin compared to other Sacroiliac ligaments
  • Thickening of the anterior joint capsule that limits nutation

Posterior SI Joint Ligaments

• Long posterior sacroiliac ligament
  • Limit anterior pelvic rotation (tilt) or sacral counternutation
• Short posterior sacroiliac ligament
  • Limits all pelvic and sacral movement
• Sacrotuberous ligament & sacrospinous ligament
  • Limit nutation & posterior innominate rotation (tilt)
  • They provide vertical stability by resisting superior translation of the sacrum

Stress Relief in Pelvic Ring

• Motion at the SI joints and pubic symphysis dissipates stress in the pelvic ring
• Important with reciprocal motions like walking, running & stair climbing
• Walking is a reciprocal flexion and extension of LEs
• Each side of the pelvis rotates out of phase with the other.
• Tension in muscles & ligaments creates oppositely directed torsions through right & left iliac crests
• Most pronounced in the sagittal plane, but also in the transverse plane
• Intrapelvic torsions are greater with an increase in walking speed.

Associated Pelvis/Sacrum Motions with Lumbar Movement

• Flexion = Anterior Tilt + Counternutation
• Extension = Posterior Tilt + Nutation
• Rotation = Ipsilateral side is posterior tilt and nutation, Contralateral side is anterior tilt and counternutation
• Side bending = Ipsilateral side is anterior tilt and counternutation, Contralateral side is posterior tilt and nutation

Lumbopelvic Rhythm

• Trunk motion is achieved via a combination of the lumbar spine, pelvic and hip motion.
• The ratio of contribution from these areas is called a lumbopelvic rhythm.
• In healthy individuals, these motions occur simultaneously.

Variations in Lumbopelvic Rhythm

• "Normal" kinematic strategy is where there is around ~45°of lumbar flexion & ~60° of hip flexion
• Restricted hip flexion causes greater flexion in lower thoracic & lumbar regions to compensate
• Restricted lumbar mobility causes Greater hip flexion to compensate for the reduced flexion

Lumbopelvic Rhythm when Extending to Upright from Flexed Position

• Initial trunk extension phase
  • includes hip extension, via activation of hip extensors (glut max & hamstrings)
• Middle phase then occurs when
  • the trunk extension is via shared activation of hip and lumbar extensors
• In later phases
  • muscle activity largely is decreased once LOG shifts posterior to the hips

Stability of the SI Joint

• Form closure
  • Refers to a closed-packed position of the joint during nutation of the sacrum
  • Joint shape, coefficient of friction, and the impact of ligamentous integrity impact form closure
• Force closure
  • Is affected greatly by extrinsic factors and relies heavily on muscle action
  • stability is maintained as counternutation occurs.
• Motor control
  • It is dependent on the timing and coordination of muscles

The Hip Joint

• Is a Coxofemoral joint
• Is a Diarthrodial, triaxial joint.
• Proximal articular surface
  • Acetabulum which is a concave socket
• Distal articular surface
  • Convex femoral head
• Supports weight of the HAT (head, arms, and trunk)

Hip Structure

• There are 3 bones contributing to part of acetabulum: Ilium Ischium Pubis
• Ossification of the pelvis is achieved between ages 20-25 years.

Acetabulum

• Hyaline cartilage covers the periphery of the acetabulum (lunate surface)
• The horse-shoe-shaped area articulates with the femoral head
• The transverse acetabular ligament connects 2 ends of the lunate surface, by creating fibro-osseous tunnel, where blood vessels pass through into the acetabular fossa
• The acetabulum is deepened by a fibrocartilaginous labrum that surrounds periphery of acetabulum
• The acetabular fossa which is non-articular, contains fibroelastic fat covered with a synovial membrane
• It is positioned laterally with an inferior and anterior tilt
• Only the upper margin of the acetabulum has a true contour

Center Edge Angle of the Hip

• Angle of Wiberg
• It measures the depth of the acetabulum.
• Represents how much of the femoral head is covered by the acetabulum.
• Formed by originating at the center of the femoral head.
• A line extends vertically while the other extends to the lateral aspect of the acetabulum.

Abnormalities of the Center Edge Angle

• If there is definite dysplasia a measurement of less than < 16° Possible dysplasia is between 16° to 25°
• Normal is 25° - 40°
• Excessive acetabular coverage > 40°

Acetabular Labrum

• The labrum is a wedge-shaped fibrocartilage that that covers the periphery of the acetabulum by
  • deepening the socket increases concavity
  • Grasping the femoral head to maintain contact with the acetabulum
  • It acts as a seal to maintain negative intra-articular pressure and decreases force transmitted to articular cartilage
  • There are nerve endings located within labrum

Head of Femur

• Articular area forms ~ 2/3 of a sphere & is more circular than acetabulum
• The fovea of the femoral head is a small pit just inferior to the most medial portion.
  • It is not covered with articular cartilage
  • Attachment site for ligamentum teres

Positioning of Femoral Neck

• The femoral neck is about 5 cm long.
• Angled so femoral head faces medially, superiorly, & anteriorly with respect to femoral shaft & distal femoral condyles

Angle of Inclination

• A Frontal plane angle that's formed by a line through the femoral head/neck & the longitudinal axis of the femoral shaft.
• Normal angles are ~125° (a few degrees of variation b/w sides)

Angle of Inclination Variations

• If the Greater trochanter lies level with the center of the femoral head then the normal angle of inclination
• Variations of smaller inclination are located in females while larger are present in taller individuals
• At birth the angle ~ 150° at birth then Gradually declines to ~125° by skeletal maturity

Abnormal Angles of Inclination

• Normal Angles of Inclination angle that is pathologically > 125° is coxa valga
• Normal Angles of Inclination angle that is pathologically < 125° is coxa vara

Coxa Valga

• Is where the Femoral articular surface contact area with acetabulum decreases with joint stability
• Increases the Vertical Weight Bearing line as it shifts closer to shaft of femur
  • There is now a decreased distance between femoral head and greater trochanter increasing the MA of hip abductors
  • This increases the force demand to counterbalance the gravitational adduction moment at the hip (Single Leg Stance)
  • The Muscular force increases and Total JRF.
  • The patient may be functionally weakened because the abductors can't meet the increased demand

Coxa Vara

• In the Hip Joint of a patient: the Femoral head rests deeper in the acetabulum, improving congruence and MA of the hip abductor muscles increases.
  • This means increased force increases needed by abductors in Single Leg Stance and JRF.
• The femoral head & neck are more prone having Disadvantage: bending moment, and tensile stresses
• There is an increased in the density of trabeculae laterally in the upper and mid femur.
• The shear force along femoral neck will increase potentially leading to the fracture risk

Angle of Torsion Details

Transverse plane angle - The line starts to go through the head and neck - Also to the distal condyle Normally, femoral head & neck are offset anteriorly with respect to condyles by Averages 10° - 20° on a normal adult

Angle of Torsion Variations

• Newborns starts with a 30° and even 40° on other cases on average.
• All measurements starts to decrease as you aged to reach your skeletal maturity

Abnormalities of the Angle of Torsion

• Excessive Anteversion is indicated with pathological of increase in angle; Angle is > 15° to 20° - Associated with IR ROM of hip - ER ROM
• Reduces hip joint stability while Retroversion pathological is the opposite, and both is the decrease in the degree
• There will be labral damage that may occur.
• And also degenerative is another thing to happen in these types of diseases.

Common Compensation to Compensate Femoral Torsion

• Excessive of anteversion is where the patients may present as the -toe to help them improve alignment of articular region in their body
• Retroversion is where the other ones that may occur, where will be a excessive in outtoe as a stand to help improve alignment of the area

Negative Pressure & Hip Joint

• Negative pressure plays a large role to maintain in congruence
• When a joint is in pressure, that will have to must to “broken” to dislocate hip joint.
• Labrum is part of an important role to seal the maintainer of the integrity with the pressure.
• When the seal broke cause Labral to turn the hip to have more mobility than to do for support. Capsule:

Joint Capsule

• Is major contributor to Joint capsules and with greater support
• Also is a thicker at anterosuperiorly and Posteroinferior
• With the other zone that is relatively thin too.
• Zona orbicularis is a area that holds together to keep this type of structure a best quality.

The Ligaments of the Hip

• Consist of Ischiofemoral, Pubofemoral, Iliofemoral
  • Ligament that is mostly are found of this body. Has two side that makes the important area that mostly help joint to allow to functions with extension or other type of motion. With function also limit or posterior with this type of the hip joint this is all to help function.

Blood Supply to the Femoral Head & Lifespan Impact

• Ligamentum teres roles
• Are important with life spam as child: they have greater contribution to support because artery do not make though the cartilage With age their are not as reliant one because the arteries are now strong

Packing position

• In this placement of degree
  • 10 to 30 degrees as flex and with another to a abduction Also with a close is what allows you extend. To twist in these action to extend or contract. This is not ideal and with this being the problem.

Optimum is important

• With a neutral hip joints make the Cartilage to help or support, and is always best. Then make in this position around 90 degrees it helps you abduct.

Structural Adaptation

• In the help the joint do what needs to support it that helps
• In this part of the situation, it has the transfer help and support. In this with help make the hip and its structures do its propose to maintain and help body support.

Forces of Weightbearing Hip

• Makes them have strong force that helps keep the system and the structure support each other.
• Each part of the body is responsible with this action. Each of the section of the system support the leg structure for this body to maintain.

Motion at the Hip

• Normal motion is : 125 flexion and around 30 to -10 which will be normal extension (for the hip) To make these type of action work. When is it is done they help move a certain directions