Q8-1. Anterior Compartment Flashcards
anterior compartment:
borders
- anterior intermuscular septum,
- lateral surface of the tibia, and the
- interosseous membrane
anterior compartment:
function and innervation
- dorsiflexors of the ankle and the digits
- innervated by deep fibular/ peroneal nerve
tibialis anterior:
key features
- origin is most medial
- insertion is on plantar foot
- strongest ankle dorsiflexor
- invertor
extensor digitorum longus:
key features
- origin is as proximal as TA & also arises from the lateral condyle fo the tibia
- no origin on the tibial shaft instead on the anterior/medial surface of fibular shaft
- weak evertor
extensor hallucis longus:
key features
- origin is more inferior/distal to the previous 2 (keep this in mind for when you begin to look as axial sections of the leg)
innervation of anterior muscular compartment of leg
deep fibular nerve (L4, L5)
tibialis anterior:
attachments and actions
- proximal: lateral condyle & superior half of lateral surface of tibia & interosseous membrane
- distal: medial & inferior surfaces of medial cuneiform and base of 1st metatarsal
- actions: dorsiflexes ankle & inverts foot
extensor digitorum longus:
attachments and actions
- proximal: lateral condyle of tibia & superior 3/4 of medial surface of fibula and interosseous membrane
- distal: middle and distal phalanges of lateral four digits
- main action: extends lateral 4 digits and dorsiflexes ankle
extensor hallucis longus:
attachments and actions
- proximal: middle part of anterior/medial surface of fibula and interosseous membrane
- distal: dorsal aspect of base of distal phalanx of great toe (hallux)
- main action: extends great toe and dorsiflexes
fibularis tertius:
attachments and actions
- proximal: inferior 1/3 of anterior/medial surface of fibula and interosseous membrane
- distal: dorsum of base of 5th metatarsal
- main action: dorsiflexes ankle and aids in eversion of foot & weak evertors
which common origin do all anterior muscular compartment muscles attach?
interosseous membrane
Which anterior compartment muscles are invertors? Which are weak evertors?
Invertors: tibialis anterior
Evertors: extensor digitorum longus, and fibularis tertius
what is the extensor hallucis capsularis?
tendinous slip coming off either the EHL (extensor hallucis longus) or TA (tibialis anterior), and inserts into the MTPJ 1 capsule;
may attach to the synovial membrane, where it acts as a retractor or it may insert into the fibrous layer of the capsule
peroneus tertius:
key features
- origin is most inferior/distal and often fused/continuous w/ EDL
- absent in 5-10% of subjects
- weak evertor
CC: If anterior compartment muscles are ONLY WEAK… when will major deficit occur?
at heel strike;
bc they can’t adequately control plantar flexion tendency of the ground reaction line and the forefoot will slap down hard
(results in foot slap)
extensor DIGITORUM brevis:
prox and distal attachments
- prox:
- calcaneus (floor of tarsal sinus);
- interosseous talocalcaneal ligament
- stem of IER (inferior extensor retinaculum)
- distal:
- extensor expansion of 3 medial digits (toes 2-4)
difference in action b/w the extensor digitorum brevis and extensor hallucis brevis muscles?
both extend/dorsiflex the toes
EDB extends the 4 medial toes at MTP and IP joints,
whereas EHB extends great toe at MTP joint
(*neither attach at 5th toe)
Although the pattern is variable, which are the superficial veins that can be found in the dorsum of the foot?
- great saphenous v
- small saphenous v
- lateral marginal v
- medial marginal v
- 1-4 dorsal MT v
- lateral dorsal digital vein of 5th toe
- medial dorsal digital vein of hallux
- dorsal digital veins
describe the general layout of the arterial supply to the dorsum of the foot?
(it is variable; what is a key variation?)
*in some cases, dorsalis pedis may be absent and instead is replaced by perforating fibular artery
- dorsalis pedis
- lateral tarsal artery
- medial tarsal artery (often 2)
- arcuate artery
- deep plantar artery
- first dorsal MT artery
- proper dorsal digital branch to medial side of hallux
- proper dorsal digital artery
- anterior perforating artery
- dorsal MT
- posterior perforating artery
- proper dorsal digital branch to lateral side of 5th toe
CC: how to take dorsalis pedis pulse
- fingertips b/w EHL and EDL and toward the 1st intermetatarsal space
- both pulses can be taken simultaneously
- some patients may not have palpable dorsalis pedis pulse b/c a larger perforating fibular compensates
describe termination of superficial fibular nerve
- travels w/in lateral compartment –>
- exits the deep fascia @ the inferior 1/3 of the leg and runs in the superficial fascia
- 2 terminal branches
which structures are deep to the course of the 2 terminal branches of superficial fibular nerve
- SFN starts at neck of the fibula, descending b/w fibularis muscles and the lateral side of the extensor digitorum longus
- Gives rise to motor branches –> supply the fibularis longus and brevis
- Continues to descend w/ ONLY cutaneous function, providing sensory innervation to the anterolateral aspect of the lower leg.
- In lower 1/3 of leg, SFN pierces the deep crural fascia and terminates by dividing into the medial and intermedial dorsal cutaneous nerves
- These nerves enter the foot to innervate the majority of its dorsal surface.
describe the branching of the Superficial Fibular nerve
- Superficial fibular nerve
- Intermediate dorsal cutaneous
- Common dorsal digital branch
- Proper dorsal digital branch
- Common dorsal digital branch
- Medial dorsal cutaneous
- Common dorsal digital branch
- Proper dorsal digital branch
- Proper dorsal digital branch to the medial side of the hallux
- Common dorsal digital branch
where does the deep fibular nerve contribute on the dermatome map?
very minimal contribution;
proper dorsal digital nerve from medial terminal branch
*just supplies medial aspect of 2nd MT, and lateral of MT 1
(aka the flip flop space)
describe course/ location of the lateral dorsal cutaneous nerve
branches from the sural nerve in posterior leg;
travels under lateral malleolus,
travels w/ sural
name the following nerve branches in the dorsum of the foot
