L3 - Biomechanics of the hip and pelvic girdle

Question 1

Name the parts of the pelvis.
What do these parts form?

Answer 1

• Ilium, ischium, pubis
• Make up acetabulum

See NDC p.3 for illustration

Question 2

Describe the hip joint.
- 2 parts
- type of joint
- degrees of freedom

Answer 2

• Proximal femur: Head is 2/3 of sphere + acetabulum
• Synovial, ball and socket (triaxial) joint
• 3 degrees of freedom

See NDC p.3 for illustration

Question 3

Describe the hip muscles.

Answer 3

Surrounding large, strong muscles

Question 4

Describe the ligaments of the hip joint.
- name
- location
- function (restricts…)

Answer 4

1. Iliofemoral: located at front of hip + strongest
   –> Hyperextension
2. Pubofemoral: anterior and inferior part of hip
   –> Abduction, External Rotation
3. Ischiofemoral: posterior part of hip
   –> Internal Rotation, Adduction, Extension

See NDC p.4 for illustration

Question 5

What is the function of the labrum of the hip?

Answer 5

Fibrocartilaginous ring that deepens acetabulum.

See NDC p.4 for illustration

Question 6

Describe the stability and mobility of the hip vs shoulder.
Why? (2)

Answer 6

Greater stability + less mobility (in hip vs. shoulder)
* Greater boney congruency (more contact)
* More support by ligament/capsule

Question 7

What causes movement restriction in the hip? (3)

Answer 7

• ligaments
• muscles
• combination

Question 8

Name the range of motion for movements in each plane.
- sagittal
- frontal
- transverse

Answer 8

Sagittal
- Flexion : 0~125°
- Extension: 0~15°

Frontal
- Abduction: 0~45°
- Adduction: 0~30°

Transverse
- External rotation: 0~45°
- Internal rotation: 0~45°

See NDC p.9 for illustration

Question 9

What are the minimum ranges of motion for common activities.
- flexion
- abduction
- external rotation

Answer 9

Hip flexion: at least 120°
Abduction: at least 20°
External rotation: at least 20°

See NDC p.10 for examples of range necessary for activities

Question 10

Describe the hip replacement.
- name
- reason

Answer 10

Hip replacement (arthroplasty) for:
- arthritis
- trauma

Question 11

What are the movement restrictions after a hip replacement? (3)
Why?
See NDC p.12 for examples of adaptive equipment.

Answer 11

Restricted ROM after hip replacement (posterior or
lateral approach)
- No hip flexion > 90°: sitting
- No extremes of rotation: leaving feet on ground and turning trunk
- No adduction past midline

Ensure hip does not dislocate

Question 12

Name the pelvis-hip interactions.

Answer 12

1. Hip hiking-pelvic drop
2. Forward/backward rotation
3. Anterior/posterior pelvic tilt

Question 13

Describe an anterior pelvic tilt VS posterior pelvic tilt.
- relative location of structures
- movement at hip

Answer 13

Anterior tilt: hip flexion
–> ASIS more anterior to pubic tubercle

Posterior: hip extension
–> ASIS more posterior to pubic tubercle

*ASIS = anterior superior iliac spine

See NDC p.14 for illustration

Question 14

Describe hip hiking-pelvic drop.
- movement happening at each hip

Answer 14

Lower side = hip abduction
Higher side = hip adduction

See NDC p.15 for illustration

Question 15

Describe forward/backward rotation.
- movement happening at each hip

Answer 15

Forward Innominate= hip external rotation
Back Innominate= hip internal rotation

See NDC p.16 for illustration

Question 16

Name the spine-hip interactions seen in hip extension and flexion.

Answer 16

Hip extension
- extending hip and lumbar spine
- anterior pelvic tilt

Hip flexion
- flexing hip and lumbar spine
- posterior pelvic tilt

See NDC p.17 for illustration

Question 17

Name the spine-hip interactions seen in hip abduction.

Answer 17

Hip abduction
- a lateral tilt of the trunk and pelvis

See NDC p.17 for illustration

Question 18

Why is it important to know the spine-hip interactions?

Answer 18

Joints work together
1. When stretching, compensation can stretch different parts that are not the goal
2. In lack of range, an athlete may compensate with spine = pain

Question 19

What “causes” hip flexion and extension during gait when the foot is on and off the ground?

Answer 19

When foot is in the air, flexion and extension of hip comes from the hip moving relative to the fixed pelvis.

When foot is on the ground, flexion and extension of hip comes from the trunk moving over the fixed femur.

See NDC p.18 for illustration

Question 20

What “causes” hip adduction and abduction during gait when the foot is on and off the ground?

Answer 20

When foot is on the ground, the hip is adducting (single leg stance) to avoid the pelvis from dropping too much.
–> the pelvis is higher on the side of the grounded leg

When foot is in the air, the hip is abducting because the pelvis is lower on the side of the floating leg.

*hip hiking-pelvic drop

See NDC p.19 for illustration

Question 21

What “causes” hip external and internal rotation during gait when the foot is on and off the ground?

Answer 21

When foot hits the ground, the hip is externally rotated
–> leg forward = pelvic rotates forward

As other leg swings, the grounded hip starts to internally rotate because the pelvic is rotating backward

When foot is about to go into air, other leg is extended
–> the pelvis on the grounded side is rotated backward = internal rotation of the hip

See NDC p.20 for illustration

Question 22

What femoroacetabular impingement?
Describe what happens.

Answer 22

A condition affecting gait

• Extra bone growth in hip = Irregular shape =Poor fit
• Bones rub = Joint damage (degeneration of cartilage + labrum)
• Pain + activity limitations

See NDC p.21 for illustration

Question 23

Name the 3 types of femoroacetabular impingement.

Answer 23

1. Pincer-extra acetabulum bone
   –> extra labrum over head
2. Cam-misshapen femoral head
   –> femoral head is mishappen
3. Combined-both

See NDC p.21-22 for illustration

Question 24

What can cause femoroacetabular impingement (FAI) in sports? (3)

Answer 24

1. Cam deformity: common in soccer, ice hockey
2. Overuse and excessive training (sport specialization*): loading leading to bone deformity
3. Increase physical activity (self-report) leads to greater risk of hip pain in adults (20-49 of age)

*speculative
IR = internal rotation

Question 25

What movements in soccer can cause problems (lead to femoroacetabular impingement (FAI)? (3)

Answer 25

1. Hip flexion 2. Adduction 3. IR with kicking *speculative IR = internal rotation

Question 26

What movements in hockey can cause problems (lead to femoroacetabular impingement (FAI)? (3)

Answer 26

Hockey* - Push off: Hip extension, abduction with skating - Recovery Hip flexion, adduction, IR with skating - Butterfly goalies: Hip flexion, IR *speculative IR = internal rotation See NDC p.24 for illustration

Question 27

What is the treatment for femoroacetabular impingement (FAI)? What are some of the outcomes? (2)

Answer 27

Surgery will remove extra bone and repair labrum (hip arthroscopy) Surgery can prevent hip degeneration/osteoarthritis (somewhat) (Hunsen 2023) Outcomes (research) 1. 78% of Swedish hockey players return to sport next season (96% for professional players). 2. Only 28% played same number of games as pre-surgery. (Lindman 2022)

Question 28

What is the impact of femoroacetabular impingement (FAI) on gait?

Answer 28

FAI may lead to decreased hip range of motion gait. No difference in hip angles during gait. See NDC p.26 for illustration

Question 29

What is the angle of inclination of the hip joint? What is a normal angle?

Answer 29

Angle between - line going thru femoral head/neck - line along the shaft of the femur Normal: About 125° See NDC p.27 for illustration

Question 30

What is coxa vara? Describe it. (3) - limb length - abductors - femoral neck

Answer 30

Coxa vara <125° 1. Limb is shortened 2. Abductors are more effective 3. More bending of femoral neck See NDC p.27 for illustration

Question 31

What is coxa valga? Describe it. (3) - limb length - abductors - hip - femoral neck - predicts...

Answer 31

Cox valga >125° 1. Lengthens the limb 2. Reduces effectiveness of abductors 3. Changes loading in the hip (moves lateral, less area) = increases risk for degeneration 4. Also-more compressive loads on neck, less bending force Maybe ish: it predicts the development of hip ostheoarthritis (degeneration) or severity See NDC p.27 for illustration

Question 32

Why are the abductor muscles less effective in coxa valga? What does this extra force cause?

Answer 32

Reduces effectiveness of abductors by reducing moment arm. The muscles need to do more work = greater joint reaction forces over less area. See NDC p.27 for illustration

Question 33

What is anteversion? What is the normal angle at the hip joint?

Answer 33

Anteversion= angle in transverse plane --> Neck-to-shaft angle Normal: 15° See NDC p.28 for illustration

Question 34

What is excessive anteversion? What is decreased anteversion?

Answer 34

Excessive anteversion: >15° Decreased anteversion: <15° See NDC p.29 for illustration

Question 35

What can we see if excessive anteversion isn't compensated for? What is the compensation of the body? How is it visible?

Answer 35

Without compensation: Femoral head will move anterior within the acetabulum - toes are pointing externally Compensation: hip internal rotation (to force femoral head back into the center of the acetabulum) - toed-in - patella facing inwards See NDC p.30-31 for illustration

Question 36

What is cerebral palsy? What is it caused by? What is seen in this condition?

Answer 36

Neurological condition Caused by damage to the developing brain during pregnancy or childbirth Spaticity: resistance of muscles to movement

Question 37

What can cerebral palsy cause? (2)

Answer 37

Can result in femoral anteversion: a condition where the femur (thigh bone) rotates outward (external rotation) 1. Hip subluxation/dislocation 2. Internally rotated hips during gait (to compensate for the external rotation, pushes hip back into socket)

Question 38

What is a treatment for femoral anteversion in cerebral palsy? Describe it. What are the benefits? (3)

Answer 38

Femoral osteotomy Cut proximal femur, realign femoral head in acetabulum, stabilize with pins/plates/rods Benefits: 1. Improve alignment 2. Prevent deterioration/pain 3. Improve gait

Question 39

Describe the forces acting on the hip when loading. (3)

Answer 39

1. Hip loading causes a twisting action on the hip = moment 2. Superior neck = tensile force 3. Inferior neck = compressive force See NDC p.37 for illustration

Question 40

What is Wolf's Law?

Answer 40

Bone will be organized to resisted applied loads ”Form follows function” --> if an astronaut spends a lot of time in space, they will lose bone mass " The trabecular system of the hip joint is the network of trabeculae, or bony struts, that make up the head and neck of the femur. The trabeculae grow in patterns that follow the lines of stress on the bone, with more trabeculae developing in areas of maximum stress." See NDC p.38 for illustration

Question 41

Name the static hip forces. (3)

Answer 41

1. Ground reaction force (Fw): wants to adduct the leg --> creates and adduction moment (torque) 2. Abduction muscle movement (torque): Abduction muscles counteract this adduction by abducting the leg 3. Hip joint reaction force = mathematical sum of everything we don't know (labrum, capsule, muscles) See NDC p.39 for illustration

Question 42

Name the hip joint forces for single leg stance. - abductor muscles forces - hip joint reaction forces

Answer 42

* Abductor muscle forces 1.5 to 2 times body weight * Hip joint reaction forces approximately 2.5 times body weight

Question 43

Why is the hip joint reaction force much bigger than the abductor muscle force?

Answer 43

Partly due to differences in lever arms (smaller for abductor muscle force than for ground reaction force)

Question 44

Can we change the lever arms for abductor muscle force and ground reaction force?

Answer 44

* Abductor muscle force – NO, attachment is fixed * Ground reaction force - YES --> changing our stance

Question 45

Describe the hip joint reaction forces when standing on two feet. --> how much weight can the hip joint withstand?

Answer 45

Standing on two feet - force = 30% of body weight (BW)

Question 46

Describe the hip joint reaction forces when standing on one foot. --> how much weight can the hip joint withstand? - standing - stairs - walking - running

Answer 46

Standing on one foot - force increases = 2.5 to 3X BW - stair climbing up to 3X BW - walking from 4 to 7X BW - running up to 10X BW

Question 47

What is the max weight the hip joint can withstand?

Answer 47

The hip joint can withstand 12 to 15X bw before fracture or breakdown in the osseus component will occur.

Question 48

What is the function of the hip abductor muscles in gait?

Answer 48

Hip abductor muscles (e.g. gluteus medius) balance the adduction moment (torque) --> it controls the pelvis over the femur

Question 49

What is trendelenburg gait/ gluteus medius lurch? What causes it? How is it recognizable?

Answer 49

Weakness in hip abductors (gluteus medius/minimus) Often due to pain in the hip from disease (hip osteoarthritis) Standing on affected leg, pelvis drops on unsupported side See NDC p.44-45 for illustration/video

Question 50

What is the compensation for trendelenburg gait / gluteus medius lurch? Why? (3)

Answer 50

Compensated by leaning upper body and trunk over affected leg (lateral trunk lean) - Decrease moment arm of the ground reaction force - Less adduction torque - Less hip abductor muscle force required See NDC p.44-46 for illustration/video