Lecture Notes: Leg & Ankle

Leg & Ankle

Assigned Reading:		Moore & Auger: pp. 250-261, 274-280, or
		Jenkins: pp. 299-322.

N.B.	In your textbook structures associated with the lateral aspect of the crus are named using their Latin (fibula) rather than their Greek root (perone; as in Netter's Atlas), that is:
		common fibular nerve vs. common peroneal nerve
		fibularis longus muscle vs. peroneus longus muscle
	The latin root (fibular, fibularis) is anatomically correct (Nomina Anatomica, 1989) but historically the Greek roots have held sway and it is the Greek terms you will most likely hear in your clinical education. Both names are given in the outline below

I. Osteology

A. tibia - medial bone of leg; weight bearing
- 1. medial malleolus
- 2. interosseus membrane
B. fibula - lateral bone of the leg
- 1. head - articulates with tibia
- 2. neck - crossed by common fibular (peroneal) nerve
- 3. lateral malleolus
- 4. interosseus membrane
C. tarsus - comprised of 7 tarsals
- 1. talus - articulates with the tibia and fibula
- 2. calcaneus
  - a. tuber calcaneus - insertion of triceps surae and plantaris
  - b. sustenaculum tali
- 3. navicular
- 4. cuboid
- 5-7. cuneiforms (I,II and III) - articulate with metacarpals 1-3, respectively

II. Arthrology

A. interosseous membrane - interosseous ligament (syndesmosis) joining tibia and fibula along their common border; functions: (1) serves as area of muscle attachment; and (2) minimizes proximal/distal shifting of skeletal elements during loading
B. tibiofibular joints - allow minimal movement
- 1. proximal - synovial joint
- 2. distal - interosseous ligament (syndesmosis)
C. ankle joint - synovial joint between the talus and distal ends of the fibula and tibia; movement is limited by bones and ligaments to uniaxial hinge
- 1. ligaments
  - a. medial - group of 4 ligaments which prevent abduction and a/p translation; collectively known as the deltoid ligament
  - b. lateral - 3 distinct ligaments; most common site of sprain
    - i. anterior talofibular - lateral ligament preventing anterior translation of the foot relative to the crus
    - ii. posterior talofibular - lateral ligament preventing posterior translation of the foot relative to the crus
    - iii. calcaneofibular - lateral ligament preventing adduction
D. transverse tarsal joint - combined name for talonavicular and calcaneocuboid joints; functions in inversion and eversion of the foot
E. subtalar joint - combined name for the talocalcanear joints; also functions in inversion/eversion of the foot

III. Fascia

A. The deep fascia of the leg or crural fascia is continuous with the fascia lata (deep fascia of the thigh); its two (anterior and posterior) intermuscular septa along with the interosseus membrane divide the leg into 3 muscular compartments
B. extensor retinacula - two bands of deep fascia which bind the tendons of the anterior muscle group
- 1. superior extensor retinaculum lies above the ankle joint
- 2. inferior extensor retinaculum is a Y-shaped band below the ankle joint
C. flexor retinaculum - band of deep fascia which binds tendons of deep posterior muscle group
D. fibular (peroneal) retinacula - superior and inferior; bind tendons of lateral muscle compartment

IV. Myology, Neurology & Angiology

A. The leg is comprised of three muscular compartments separated by the anterior and posterior intermuscular septa and the interosseus membrane; each has its own nerve and blood supply
B. anterior compartment: four muscles innervated by deep fibular (peroneal) nerve and supplied by the anterior tibial artery; all four dorsiflex the foot while two invert and two evert
- 1. dorsiflexors and invertors
  - a. tibialis anterior
  - b. extensor hallucis longus
- 2. dorsiflexors and evertors
  - a. extensor digitorum longus
  - b. fibularis (peroneus) tertius
C. lateral compartment: two muscles innervated by the superficial fibular (peroneal) nerve and supplied by perorating branches from the fibular (peroneal) artery (a branch of the posterior tibial artery running within the posterior compartment); these muscle primarily evert and secondarily plantarflex the foot
- 1. fibularis (peroneus) brevis
- 2. fibularis (peroneus) longus
D. posterior compartment - six muscles innervated by the tibial n. and supplied by the posterior tibial artery and its fibular (peroneal) branch; the muscles can be divided functionally into 2 groups:
- 1. superficial plantarflexors
  - a. gastrocnemius
  - b. soleus
    - i. The two heads of gastrocnemius (medial and lateral) and soleus share a common tendon of insertion, the tendo calcaneus which attaches to the tuber calcaneus; these three muscles are collectively known as the triceps surae
  - c. plantaris - a small vestigial muscle (sometimes absent) whose tendon lies and inserts medial to the tendo calcaneus
- 2. deep plantarflexors and invertors
  - a. flexor hallucis longus - situated laterally
  - b. flexor digitorum longus - situated medially
  - c. tibialis posterior - located between FHL and FDL
E. Arterial anastomoses of the ankle and foot
- 1. The anastomoses of the ankle and foot are formed by branches of the (1) anterior tibial (and its continuation as the dorsalis pedis), (2) posterior tibial and (3) peroneal arteries; these anatstomoses are extensive and sufficient to sustain blockage of any of the 3 major vessels.
F. Muscle actions: The following figures may be helpful in understanding and learning the actions of the extrinsic foot muscles:
- Muscles of dorsiflexion/plantarflexion
- Muscles of inversion/eversion