Lecture 6 - Hip Biomechanics (part 1) Flashcards
What are the bones of the hip?
- Innominate bone
- Femur
What are the structures of the innominate bone?
- Acetabulum
- Labrum
What are the structures of the femur bone?
Head of the femur
What is the acetabulum formed by?
3 fused bones:
1. Ilium
2. Pubis
3. Ischium
What are the different surfaces of the acetabulum?
- Acetabular fossa (non articular depressed region on floor of acetabulum)
- Articular/lunate surface (makes contact with head of femur)
What is the orientation of the acetabulum?
Faces laterally and inferiorly
What is the labrum?
A fibrocartilaginous ring that helps…
1. Stabilize hip joint
2. Increase contact area
3. Decreases joint stress
What is the structure of the femur?
Femoral head: 2/3rds of a sphere
Articular cartilage: Makes more spherical
What improves joint congruence?
Cartilage
(Increase in congruence = Increase in stability)
What is the orientation of the femoral head and neck?
- Large head narrows abruptly into neck
- Neck enclosed by hip joint capsule
What does the orientation of the femoral head and neck influence?
- Hip motion and weight bearing
-> Frontal plane: 125 degree angle between neck and femur
-> Transverse plane: 15 degree angle between neck and femoral condyles
What is Wolff’s law?
- Form follows function
- Femoral neck sustains large bending moments and tensile compressive forces
- Neck reinforced by thickened cortical bone and trabecular bone
What is the important landmark of the femur?
Greater trochanter
- Insertion site of muscles
- Lengthens moment arm (improves mechanical advantage)
What do the landmarks of the femur help understand?
- Hip joint anatomy
- Muscle function
What type of joint is the hip joint?
Ball and socket joint
-> Synovial
-> Triaxial
-> 3 dof
What are the structures of the hip joint?
Joint capsule:
- Attached to bony rim of acetabulum and intertrochanteric crest
- Composed of multiple bands of fibers
- Encloses femoral neck and head
What reinforces the joint capsule?
Three ligaments…
Ligament of the head of the femur (one of them)
What is hip joint mobility?
The range of motion of the hip motion linked to motion of the low back and pelvis
What is the typical hip rom in the sagittal plane for flexion?
- 135 degrees
- Largest amplitude
What is the typical hip rom in the sagittal plane for extension?
- 45 degrees
- Limited by ligaments
What is the typical hip rom in the frontal plane for abduction?
- 45 degrees
- Can be improved by stretching
What is the typical hip rom in the frontal plane for adduction?
- 25 degrees
- Limited by contralateral limb
What is the typical hip rom in the transverse plane for internal rotation?
- 35 degrees
- Limited by ligaments
What is the typical hip rom in the transverse plane for external rotation?
- 45 degrees
- Limited by ligaments
What are the possible orientations of the pelvis in the sagittal plane?
a) Retroversion (posterior tilt - extends hip)
b) Neutral
c) Anteversion (anterior tilt - flexes hip)
What is the possible orientation of the pelvis in the frontal plane?
- Pelvic tilt (hike and drop) can occur
- Elevated side: hip adduction
- Dropped side: hip abduction
What is the orientation of the pelvis in the transverse plane?
a) Pelvic internal rotation (contralateral medial)
b) Pelvic external rotation (contralateral lateral)
What are spine-hip interactions?
- Patients/athletes compensate for lack of mobility with other joints
- Compensations occur in frontal/sagittal plane
What are the joint reaction forces of the articulating surfaces?
- JRF on femur are transmitted from the acetabulum to the femoral head
- JRF creates a torque on the neck of femur
- Wider femoral necks withstand torques better
- Men have wide necks than women
What is the alignment of the articulating surfaces in the frontal plane?
- Femoral neck and shaft: 125 degrees (optimal)
- Coxa valga > 125 degrees:
- JRF parallel to neck
- More compression
- Less bending
- Coxa vara < 125 degrees:
- Increased bending moment
Angle decreases with age
- Increased bending moment
What is the alignment of the articulating surfaces in the transverse plane?
Anteversion: 15 degrees
- Decreases during maturation
- Excessive anteversion places head of femur too anteriorly
Retroversion: less common
What is the alignment of the articulating surfaces in the transverse plane?
Medial rotation: compensates for excessive femoral anteversion
What causes lateral tibial torsion?
Excessive anteversion
What is cerebral palsy?
- Affects a persons ability to move and maintain balance/posture
- Can result in femoral anteversion
- Solution: femoral osteotomy (cut femur, realign head, stabilize)
What are the similarities/differences between the hip and shoulder joints?
Difference:
- Greater stability/less mobility in hip (greater boney congruence and support from ligament/capsule)
Similarities:
- Movement limited by ligaments and muscles
