Hip Biomechanics Flashcards
What is the innominate bone a fusion of and when does it fuse?
The ilium, ischium, and pubis. At puberty.
Where do the right and left innominate bones connect and how do they contribute to a definition of the “pelvis”?
The right and left innominate bones connect at the pubic symphysis (anteriorly) and at the sacrum (posteriorly). The two bones + the sacrum makes up the whole pelvis.
What muscle attaches to the ASIS?
Sartorius
What muscle attaches to the pubic crest / tubercles?
The adductors (longus, brevis, magnus)
What muscles attach to the Ischial Tuberosity?
The hamstrings and adductor magnus.
In what direction does the proximal femur course and how does this affect gait?
Medially, which means it’ll lines up with the medial bias of the foot during gait for better overall efficiency.
What can we palpate on the proximal femur and what muscles attach here?
The greater trochanter, and the glute medius and minimus, and deep hip muscles (piriformis).
What is the angle of inclination @ the proximal femur? What are normal values and what are abnormal values called?
The angle of inclination is the angle of the femoral neck and femoral shaft when viewed in the frontal plane. Normal angles are 125 degrees. Coxa vara = anything less than 125 degrees. Coxa valgus = anything more than 125 degrees.
How does coxa vara vs. coxa valga affect femoral head loading? How about femoral neck loading? How is torque affected in either of these instances?
In coxa vara, the superior aspect of the head is overloaded. In coxa valga, the inferior aspect of the head is overloaded.
In coxa vara, the neck experiences more torsional stress. In valga, the neck experiences more compressive force.
In coxa vara, there is a longer moment arm so more of a mechanical advantage. In coxa valga, there is a shorter moment arm. Think weightlifters…
What is a SCFE?
A slipped capital femoral epiphysis. Often in teens and preteens, males, obese individuals - happens as a part of coxa vara. The head of femur falls off the neck and requires surgical stabilization.
How does coxa vara/valga affect the length of the limb? How does it affect joint contact force? How about hip stability?
Vara shortens the limb. Valga lengthens the limb.
People with valga have a higher joint contact force because the muscles have to pull harder to maintain the same torque.
You have more hip stability with vara. If valga goes into adduction it will be very unstable (because it has less coverage of the femoral head in the socket). It valga goes into abduction it’s more stable which is why it’s often set this way post-op.
What is a torsion angle of the femur? And what is considered normal, excessive, and retroversion?
It is the relative rotation between the shaft and the neck of the femur. Normal is 10-15 degrees. Excessive anteversion (the head is super anterior - the shaft is posterior) is greater than 15. Retroversion is less than 8 degrees.
What is excessive anteversion associated with?
Congenital dislocation.
Articular cartilage wear and tear.
Overtime you can lose ER and have to force IR to compensate - this means the tibia will ER… so the person will actually move the toe in to get more coverage of the head by the pelvis.
What is the “ACL and PCL” of the hip joint?
Ligamentum Teres
Where is the cartilage in the on the femoral head thickest?
“The lunate surface” - anterior and superior
Does the acetabular fossa contain any cartilage or have contact with the femoral head?
NO.
When in gait is the most joint reaction force from the hip required? How does the lunate surface respond to this?
Loading response to mid-stance. The lunate responds by widening to increase SA and reduce stress.
What is the acetabular labrum and what is its function?
It’s a fibrocartilage ring that acts as the meniscus of the hip. It’s chief role is stability which is creates by deepening the joint and increase the surface area gripping the femoral head.
What is the center-edge angle? How much is normal?
The angle that measures how much the acetabulum is covering the femoral head in the frontal plane. Normal is 35 degrees. The smaller this angle is the less stability you will have. There’s also more contact stress due to less contact area.
What is the acetabular anteversion angle? What is normal and risks does excessive anteversion impose?
How much the acetabulum surrounds the femoral head in a horizontal plane (looking down on it). Normal is 20 degrees. There is an anterior dislocation risk with this.
What are the 3 types of FAI?
CAM - which a bony growth on the head - more common in athletic males
PINCER - a bony growth on the acetabulum - more common in females
MIXED - is a bony growth on both sides
Which pelvic capsular ligament has the strongest tensile forces in the body? What motion does it limit? What role can it play in patients with SCI?
The Y ligament or iliofemoral ligament. It limits extension of the hip (and ER). In SCI patients it accounts for a lean back (they rely on their ligament to stabilize rather than their muscles.
Explain “hip close-packed position is not the position of maximal congruency”.
Hip close-packed position is full extension, with slight abduction and IR - congruency is 90 degrees of hip flexion, moderate abduction and ER.
