Gross Anatomy- Posterior Thigh

Question 1

Describe the Posterior Thigh

Answer 1

• Three of the four muscles of posterior compartment are hamstrings
o Have common origin
o Cross hip and knee joints
o Share common innervation
• Length of hamstrings vary, but can be changed with conditioning

Question 2

Describe the **Semitendinosu m. **

Answer 2

• Fusiform belly
• Distal part has long, cord-like tendon
• Is a pes anserinus m.
• O: Ischial tuberosity
** I:** Superior part medial surface of tibia (pes anserinus)
A: Extension of thigh and flexion of leg; MR (when knee is flexed); when thigh and leg
are flexed, extend the trunk
N: Tibial division of sciatic n. (L5, S1, S2)
B: Profunda femoris and posterior branches of obturator aa.

• MR is limited to about 10 degrees
o Synergists are gracilis, sartorius and popliteus mm.

Question 3

Describe the Semimembranosus m.

Answer 3

• Broad muscle
• Flattened, membranous proximal attachment
• Distal attachment divides into 3 parts:
o Direct attachment to tibial condyle
o Part that blends with popliteal fascia
o Reflected part that forms oblique popliteal l.
• O: Ischial tuberosity
I: Posterior part of medial epicondyle of tibia
A: Extension of thigh and flexion of leg; MR (when knee is flexed); when thigh and leg
are flexed, extend the trunk
N: Tibial division of sciatic n. (L5, S1, S2)
** B:** Profunda femoris and posterior branches of obturator aa.

• MR is limited to about 10 degrees
o Synergists are gracilis, sartorius and popliteus mm.

Question 4

Describe the Biceps Femoris m.

Answer 4

• Has long and short heads
o Share common insertion
• Workhorse of hip extension

• Long head protects sciatic n. as it descends through posterior thigh
o Common fibular n. continues running with biceps femoris t.
• Short head has different innervation than other hamstrings
• O: Long head – Ischial tuberosity
Short head – Linea aspera and lateral supracondylar line of femur
** I:** Lateral side head of fibula
A: Flexion of leg and LR when knee is flexed; extension of thigh
N: Long head – Tibial division of sciatic n. (L5, S1, S2)
Short head – Common fibular division of sciatic n. (L5, S1, S2)
B: Profunda femoris and posterior branches of obturator (long head only) aa.

• LR is limited to about 40 degrees

o Synergist is tensor fascia lata m.

Question 5

What two actions of the Hamstrings cannot be done maximally at the same time?

Answer 5

• Two actions of hamstrings cannot be performed maximally at same time
o Full flexion does not allow for extension
o Full extension does not allow for flexion

Question 6

Are the Hamstrings active under all conditions of thigh extension?

Answer 6

Yes, with the:

o Exception being full flexion of knee

Question 7

When are the extensors muscles of the thigh invovled mostly and what other posterior muscle is involved in this action and what action do the Hamstrings really play a roll in?

Answer 7

Extensor muscles are involved in walking mostly while the Gluteus m. is involved minimally.

The Hamstrings demostrate most of their activity in eccentric contraction (decelerating).

Question 8

How can the Hamstrings be tested?

Answer 8

• To test hamstrings:
o Flex leg against resistance
o Normally, tendons should be palpable on either side of popliteal fossa
o Tests integrity of sciatic n.

Question 9

Explain Hamstring Injuries

Answer 9

• Hamstring strains (pulled and/or torn hamstrings) common in those who:
o Run and/or kick hard
• Usually result from inadequate warm up
• Violent muscular extension required may avulse part of proximal tendinous part of hamstrings from ischial tuberosity
• Usually accompanied by bruising and tearing of muscle tissue
o Hematoma is contained by fascia lata
• Extremely painful
• Semimembranosus m. is most commonly torn
• Forcible flexion of hip with knee extended could result in avulsion of ischial tuberosity
o Proximal part of biceps femoris and semitendinosus mm.