MSK 9b: anterior and lateral leg

Question 1

Location of the anterior compartment

Answer 1

Anterior to interosseous membrane, between lateral surface of tibial shaft and medial surface of fibular shaft
Contains tibialis anterior, extensor digitorum longus, extensor hallucis longus and peroneus tertius

Question 2

General action of the anterior compartment muscles

Answer 2

Dorsiflexion of ankle

Question 3

Fascia

Answer 3

Bound anteriorly by deep fascia of the leg and skin:

• superiorly very dense so anterior leg susceptible to COMPARTMENT SYNDROME
• inferiorly, two band-like thickenings forming the RETINACULA to bind the tendons of the anterior compartment as they cross the ankle, preventing bowstringing during dorsiflexion

Question 4

Innervation of all anterior leg muscles

Answer 4

Deep peroneal/fibular nerve (L4, L5)

Question 5

Tibialis anterior

Answer 5

Lateral to bone when feeling shin; most medial and superficial
O: lateral tibial condyle and superior half of lateral surface
I: medial cuneiform and 1st metatarsal
A: dorsiflexion of ankle and inversion of foot

Test: dorsiflex ankle against resistance or stand on heels (if normal can see/palpate tendon)

Question 6

Extensor digitorum longus

Answer 6

Most lateral; deep to tibialis anterior
O: lateral condyle of tibia, medial surface of fibula and interosseous membrane
I: splits into 4 and inserts onto the middle cuneiform
A: dorsiflexion and extends the lateral 4 digits

Test: hand on dorsum, ask to extend/dorsiflex toes. Tendons should be visible and palpable

Question 7

Extensor hallucis longus

Answer 7

Thin, lies deeply between tibialis anterior and extensor digitorum longs
O: medial surface of fibula and interosseous membrane
I: dorsal aspect of base of distal phalanx of hallux
A: dorsiflexion of ankle and extension of great toe

Test: dorsiflex great toe against resistance; should see and be able to palpate tendon

Question 8

Peroneus tertius

Answer 8

Not always present. Separated part of EDL and shares its synovial sheath
O: inferior third of fibula and interosseous membrane
I: dorsum of base of 5th metatarsal
A: dorsiflexion of ankle and eversion

Question 9

Describe the lateral leg compartment

Answer 9

Smallest leg compartment, ends inferiorly at the superior fibular retinaculum. Bounded by the lateral surface of the fibula and the anterior/posterior inter muscular septum. Only contains 2 muscles: peroneus longus and braves

Question 10

What is the innervation of the lateral leg muscles?

Answer 10

Superficial peroneal nerve (L5, S1, S2)

Question 11

Peroneus/fibularis longus

Answer 11

Lateral and superficial, descends posterior to lateral malleolus under foot
O: superolateral two thirds of tibia and lateral tibial condyle
I: medial cuneiform and base of 1st metatarsal
A: eversion and weak plantar flexion. Helps to steady the leg when on one foot

Question 12

Peroneus/fibularis brevis

Answer 12

Fusiform muscle lies deep to fibularis longs. Passes over the calcaneus and cuboid bones
O: inferolateral two thirds of fibular shaft
I: dorsal surface of the tuberosity on the 5th metatarsal
A: everts foot and weakly plantar flexes the ankle

Question 13

What does the posterior tibialis artery supply and where can it be palpated?

Answer 13

Enters the tarsal tunnel to split into the lateral and medial plantar arteries, supplying the plantar aspect of the foot and contributing to the deep plantar arch.
Palpate posterior to the medial malleolus

Question 14

What does the dorsalis pedis artery supply and where can it be palpated?

Answer 14

Supplies tarsal bones and dorsal aspect of the metatarsals

Palpate on the dorsum of the foot, just lateral to the extensor hallucis longus tendon

Question 15

Describe the course of the small saphenous vein

Answer 15

Arises from merging of little toe vein and dorsal venous arch, travels inferior and posterior to the lateral malleolus, and runs with the sural nerve up the posterior leg until it terminates by drainage into the popliteal vein

Question 16

Describe the course of the great saphenous vein

Answer 16

Arises from merging of dorsal hallux vein and dorsal venous arch, travels anterior to medial malleolus, runs up medial side of leg, runs over posterior border of femoral medial epicondyle then moves anteriorly to lie on anterior thigh before saphenous opening where it joins to the femoral vein in the femoral triangle

Can be used as a coronary artery if stenting is not possible as small saphenous is sufficient drainage

Question 17

Describe the origin and distribution of the nerves of the leg

Answer 17

Saphenous-from femoral nerve, innervates skin on medial side of ankle and foot

Sural-From tibial branches and CPN. Innervates skin on posterior and lateral leg and lateral foot

Tibial-from sciatic nerve, innervates the posterior muscles of the leg and knee

Common peroneal-from sciatic, innervates skin on the lateral side of the posterior leg and the knee

Superficial peroneal: from CPN, innervates peroneus longs, peroneus brevis and the skin on the distal anterior 1/3 of the leg and dorsum of the foot

Deep peroneal: from CPN, innervates anterior leg and dorsal foot muscles

Question 18

What is the function of the extensor retinacula at the ankle?

Answer 18

Keeps the tendon of the leg muscles in place

Question 19

What are the signs of compartment syndrome and what are the consequences?

Answer 19

Raised pressure within an enclosed fascial space leading to localised tissue ischaemia; caused by intense exercise or trauma.
Signs: excessive pain worsened on passive stretching that is not relieved by analgesia. Neurovascular changes occur later

Tissue necrosis develops within about 12 hours, muscle necrosis causes Volkmann’s ischaemic contracture, nerve damage may be reversible but with long term infarction is damaged permanently

Question 20

Why might a patient who has undergone stripping of the long saphenous vein develop loss of sensation on the medial aspect of their foot?

Answer 20

Damage to the superficial peroneal nerve