Lecture 9 - Biomechanics of the Knee (part 2) Flashcards
What are the main knee extensors?
Quadriceps femoris:
- rectus femoris
- vastus intermedius
- vastus lateralis
- vastus medialis
What kind of muscle is the rectus femoris?
multi-joint muscle
What effects of weakness does the rectus femoris have?
reduction in hip flexion/knee extension strength
What kind of joint knee extensor is the vastus intermedius?
single joint knee extensor
What effect of weakness does the vastus intermedius have?
decreased knee ext. strength
What effect of tightness does the vastus intermedius have?
decreased knee flexion ROM
Which is the largest of the quad muscles?
vastus lateralis
What is the dominant knee extensor?
vastus lateralis
What is the effect of weakness in the vastus lateralis?
reduced knee extension strength
What is the effect of weakness in the vastus lateralis?
limits knee flexion ROM
What % of knee extensor torque does the vastus medialis have?
10-12%
What does the vastus medialis balance?
the pull of the heads of the quads
What two knee extensors pull along the femur?
RF and VI
What knee extensor pulls lateral quad?
VL
Which muscle can balance with a medial pull?
only VM
What is the effect of weakness in the vastus medialis?
lateral shift in patellar movement
What is the effect of tightness in the vastus medialis?
contributes to decreased knee flexion ROM
Strength in what muscle may protect knee joint degeneration?
quadriceps femoris
What are the 5 main knee flexors?
hamstrings
popliteus
gracilis
sartorius
gastrocnemius
What are the 4 muscles part of the hamstrings?
- Bicep femoris longus (long head)
- Bicep femoris brevis (short head)
- Semitendinosus
- Semimembranosus
Which muscle of the hamstrings is the smallest but has the largest moment arm?
semitendinosus
Which muscle of the hamstrings is the largest?
semimembranosus
What do the hamstrings contribute to?
- medial/lateral rotation
- hip extension (not BF brevis)
- knee stability
What are the 2 effects of weakness in the hamstrings?
- Loss of knee flexion strength
- Produces little disability (control of knee flexion in everyday activities usually by eccentric contraction of quads)