Femur Potpourri
Meniscus
Screw Home and Stabilizers
Case Study: Volleyball
Case Study: Soccer
100
What ligaments (2) are intracapsular? Extracapsular (2)?
Intra: ACL and PCL
Extra: MCL and LCL
100
Describe how the structure of menisci affect the functions.
Structure - fibrocartilage. Therefore, more PG/water/collagen
Functions:
Assist with stability by deepening contour of tibia
Shock and compressive load absorption (load per unit area)
Increase congruence
Reduce friction
Weight-bearing distribution
100
What are the anterior displacement stabilizers? What are the posterior displacement stabilizers?
Anterior displacement: ACL, hamstrings, glut max, soleus
Posterior displacement: PCL, quads, popliteus, gastro
100
A 16-year-old volleyball player has anterior right knee pain. Pain increases while playing volleyball, and pain stops after playing. Minor pain after stairs or prolonged walking. MRI showed healthy menisci and full integrity of all ligaments. You observe an increased Q angle (25 degrees), patella tracks mostly in the lateral aspect, and patellar crepitus.
Explain possible reasoning for why the patella tracks mostly in the lateral aspect.
First of all, the asymmetry of the condyles. Medial condyle is larger than lateral condyle. Lateral condyle is more anterior, aligns with shaft. Medial condyle is also more distal. So the patella is going to automatically go lateral because the axis is in the medial condyle.
Second, it could relate to the strength of dynamic stabilizers on either side. She may have a weak vastus medialis obliquus that cannot pull the patella into place medially. The vastus lateralis has increased strength from the IT band.
100
A 17-year-old student athlete injured her knee in a soccer game when someone collided with her trunk and threw her off balance. She felt a pop in her right knee, and her knee "giving away." Now she reports difficulty weight bearing due to pain and lack of muscle control.
What is the origin and insertion of the ACL? What is its function?
Origin: posteromedial aspect of lateral femoral condyle
Insertion: lateral/anterior aspect of the medial intercondylar tibial spine
Function: anterior translation (anterior shear) of the tibia on the femur
200
Explain how the structure of the condyles influences motion at the tibiofemoral joint.
The medial condyle is larger and more distal. The lateral condyle is aligned with the shaft and more anterior. This makes the planes of motion oblique and therefore combines movement for more motion at the joint.
200
Explain why there is a low chance of injury recovery in the White-White zone shown here on the meniscus. Additionally, what is the purpose of the white-white zone?
Low vascularity - begins once people become weight-bearing
White zone - diffusion of synovial fluid for nutrition, which depends on load/unload
200
What are the stabilizers for valgus? Varus?
Valgus stabilizers - MCL, ACL, PCL, pes anserinus, semimembranosus, medial gastroc
Varus stabilizers - LCL, ACL, PCL, IT band, biceps femoris, lateral gastroc
200
Describe patello-femoral tracking from full knee extension to full knee flexion.
Extension - no contact
10-20 degrees - inferior apex is first point of contact
20-90 degrees - area of contact increases distal to proximal and medial to lateral
At 90 degrees - all portions of patella have some contact
> 90 degrees - medial facet has contact and odd facet enters intercondylar notch
135 degrees - contact is on the odd facet and lateral facets, we have lost contact with medial
200
What signs and symptoms will you expect from an ACL injury? Correlate with arthrokinematics.
ACL becomes unable to resist extreme tibia anterior translation/gliding as well as torsional forces. It feels like it’s not there!
Arthrokinematics - usually in non-WB, when you glide the tibia anteriorly, it rolls anteriorly too. With ACL injury, it might very well just keep gliding and gliding because the ACL is too injured to stop it.
300
In lower extremity genus varum, there is a decrease in angle between Mechanical axis and the Longitudinal axis. This increases ____ forces on the lateral side and increases ____ forces on the medial side.
a. Compressive; tensile
b. tensile; compressive
b. tensile; compressive
300
How does meniscus tear lead to osteoarthrosis?
Every time the flap of the meniscus tear hits the cartilage on the femoral condyles, it erodes the cartilage → erodes the bone → OA
300
What is the origin and insertion of the PCL?
Origin - lateral aspect of medial femoral condyle
Insertion - posterior surface of tibia
300
Describe the patello-femoral compressive forces generated by the quadriceps at 0 degrees of extension vs. squatting at 40 degrees vs. squatting at 120 degrees.
0→ minimal stress at full extension because there are no oblique forces/resultant force thru the patella
Minimal stress until 90 degrees because contact area also increases
From 30 degrees to 70 degrees: patella has highest effect as pulley, increasing moment arm and decreasing quad force (compressive forces ↓↓)
120 degrees: contact area ↓↓, so pressure from compression ↑↑
Quads need to generate more force to overcome this large level arm of resistance
300
You want to check out the MCL and the medial menisci to make sure there’s no “unhappy triad.” Why? Compare the injuries of the MCL vs. LCL and medial vs. lateral menisci.
The knee is subject to extreme forces laterally, so any force coming laterally will affect the ACL, MCL, and medial meniscus. This is more common than medial forces.
LCL and lateral meniscus injuries would require extreme medial contact forces. And as we learned, the lateral meniscus is protected from distortion because it moves in relation with the Humphrey and Wrisberg ligaments.
400
Females tend to have wider hips due to evolutionary adaptations for childbirth. This gives females a physiological _____ of 7-10 degrees from the Mechanical Axis as opposed to males at 5-10 degrees. It also shifts the weight-bearing direction from ____ to ____.
a. Valgus; medial → lateral
b. Varus; medial → lateral
c. Valgus; lateral → medial
d. Varus; lateral → medial
a. valgus; medial --> lateral
400
What are the differences for rotation of the knee joint on the medial meniscus vs. the lateral meniscus? Why is the lateral meniscus relatively safe from rotational injury?
Medial meniscus - attachments to the anterior and posterior horns; distorted during rotation
Lateral meniscus - attachments to the Humphrey and Wrisberg ligaments handle the distortion
400
Explain the locking mechanism of the knee during an open kinetic chain.
Tibial plateau rotation on the femoral condyles
- tibia must EXTERNALLY ROTATE on femur during extension
- "locking" - evident during last 5 degrees of extension
- "unlocking" - any flexion force will automatically INTERNALLY ROTATE the tibia on the femoral condyles because of anatomy
** even if the popliteus muscle is removed, we can still "unlock"
400
You make an exercise program with OKC and CKC. Describe the effect of the forces when strengthening the quadriceps with a free weight leg extension machine from 30 → 0 degrees of extension. Compare to the effects of a CKC short squat from extension to 45 degrees of flexion.
OKC leg extension machine - the greatest compressive force of this movement will be at 30 degrees, and the level arm of the resistance increases as it approaches full extension. Therefore, quads must generate force to overcome the ↑ in level arm of resistance.
**ACL shear forces are greater in OKC!!
CKC short squat - we have co-contraction at 45 degrees of flexion between quads and hamstrings. There is increased contact area (not max contact) and has the highest effect as a pulley
400
Describe the synergistic and antagonistic dynamic stability of the ACL.
Synergists of ACL:
Hamstrings
Soleus
Glute max
IT band
Antagonists of ACL (PCL synergists):
Quads
Gastroc
Popliteus
500
We know that the Q-angle is the angle between ASIS to midpoint of patella, as well as the normal range in degrees (13.5 degrees, +/- 4.5 degrees). But there tend to be abnormalities, especially in women. What are risks that might explain an increase in Q-angle? (5)
Femoral anteversion
External tibial torsion
Coxa vara
Genu valgum
Laterally displaced tibial tuberosity
500
Why is it imperative that people do not sit in “w-sitting position,” especially children?
“W-sitting” is the position with the highest amount of tibial torsion and therefore highest distortion of the medial meniscus.
500
Explain the locking mechanism of the knee during a closed kinetic chain.
Rotational movement of femoral condyles on the tibia
- Lateral condyles rotate about the axis thru the medial condyles
- Lateral condyles do EXTERNAL ROTATION when dropping to a squat
- Condyles do INTERNAL ROTATION when coming back up
500
With the above question in mind, what kind of contractions/exercises should we do to reduce shear forces and strain on the ACL? Why?
Hamstrings increase posterior translation, so we should strengthen them to reduce forces on the ACL (soleus can also reduce forces when weight bearing).