MSK 8b: posterior thigh and popliteal fossa

Question 1

Biceps femoris

Answer 1

Most lateral, fusiform shape, two heads

O: ischial tuberosity (long head), linea aspera (short head)
I: tendon to head of fibula (lateral side)
N: tibial part of sciatic L5-S2 (long), common fibular part of sciatic L5-S2 (short)
A: flexion at knee, extension at hip, small amount of lat. rotation when knee flexed

Question 2

Semitend/mem muscle location

Answer 2

SemiMembranosus is on Medial side

SemiTendinosus is on Top

Question 3

Semitendinosus

Answer 3

Fusiform belly and tendon-like intersection; tendon about 2/3 way down thigh

O: ischial tuberosity
I: posterior-medial-superior tibia
N: tibial part of sciatic L5-S2
A: knee flexion, hip extension, some medial rotation when knee flexed

Question 4

Semimembranosus

Answer 4

Broad, flattened membranous form of proximal attachment

O: ischial tuberosity (most superior of all muscles attached)
I: medial tibial condyle
N: tibial part of sciatic L5-S2
A: flexion of knee, hip extension, some medial rotation

Question 5

Adductor magnus-hamstring portion

Answer 5

O: ischial tuberosity
I: adductor tubercle of the femur
N: tibial nerve
A: extends and adducts hip

Question 6

Hamstring strain

Answer 6

Common sports injury obtained in running or kicking: excess stretching or tearing of muscle fibres
Violent muscle movements may tear part of the proximal tendinous attachments to the ischial tuberosity

Question 7

Ischial tuberosity avulsion fracture

Answer 7

Hamstring tendons can tear a small piece of bone from the ischial tuberosity
Often in sports involving rapid contraction and relaxation, e.g. sprints
Difficult to heal, may need surgery

Question 8

Describe the course of the sciatic nerve

Answer 8

Lumbosacral plexus roots L4-S3
Leaves pelvis and emerges inferior to piriformis, then descends inferolaterally
Enters posterior thigh and passes deep to the long head of biceps femoris
Gives off branches to hamstrings
Terminates at apex of popliteal fossa: bifurcates into tibial and common fibular nerves

Question 9

Describe the arterial supply to the posterior thigh

Answer 9

Arise directly or indirectly from the internal iliac arteries

GLUTEAL ARTERIES: enter through greater sciatic foramen

• superior gluteal (largest); superficial and deep branches from IIA
• inferior gluteal: from IIA, before birth is main artery of posterior compartment
• internal pudendal: from IIA, anterior to IGA. Supplies the skin, external genitalia and muscles of perineal region

POSTERIOR THIGH: no major artery exclusive to it; receives blood from:

• inferior gluteal
• medial circumflex femoral
• popliteal
• perforating arteries (usually 4 of profuda femoris)

Continuous anastomotic arterial chain from gluteal to popliteal regions, gives rise to additional branches to muscles and sciatic nerve

Question 10

Describe the venous drainage of the posterior thigh

Answer 10

Tributaries of IIVs

SUPERIOR AND INFERIOR GLUTEAL VEINS: accompany corresponding arteries through greater sciatic foramen. Communicate with tributaries of femoral vein: alternative route for return if femoral vein occluded

INTERNAL PUDENDAL VEIN: accompany arteries, joints to form a single vein that enters the IIV. Drains blood from external genitalia

PERFORATING VEINS: accompany arteries to drain blood from posterior thigh into profunda femoris vein

Question 11

What is the popliteal fossa?

Answer 11

Diamond-shaped depression on posterior knee seen when knee is flexed. Mostly fat-filled; allows structures to leave the thigh and move into the leg

Question 12

Borders of popliteal fossa

Answer 12

Supero-medial: semimembranosus
Supero-lateral: biceps femoris
Infero-medial: medial head of gastrocnemius
Infero-lateral: lateral head of gastrocnemius and plantaris

Floor: knee joint casule and posterior surface of femur
Roof: popliteal fascia (continuous with fascia lata) and skin

Question 13

Contents of popliteal fossa

Answer 13

Termination of small saphenous vein then popliteal vein
Popliteal artery (deep)
Tibial and common fibular nerves (most superficial)

Question 14

Causes of swelling in the popliteal fossa

Answer 14

BAKER’S CYST:

• inflammation of the semimembranosus bursa; usually in conjunction with rheumatoid or osteo arthritis of knee
• usually self-resolves but can rupture, producing symptoms similar to DVT

POPLITEAL ANEURYSM

• abnormal dilation of popliteal artery. Roof is non-extensible so can cause problems with other contents
• tibial nerve likely to be damaged by compression by artery causing leg anaesthesia or loss of motor function
• can be detected by an obvious palpable pulsation in the popliteal fossa, with bruit

Rarer causes: DVT, adventitial cyst of popliteal artery, neoplasm