Factors influencing muscle action

- position of tendinous insertion relative to joint axis - lever arm - variation in joint axis position (eg: medially deviated STJ axis) - position of adjacent joint (ie: AJ DF or PF affects muscle action at STJ) Subtalar joint moment arms Tibialis posterior -19.2 Flexor hallucis longus -7.8 Triceps surae -5.3 Tibialis anterior -3.8 Peroneus brevis 20.5 Peroneus longus 21.8 from Klein et al (1996) Clinical Biomechanics 29: 21-30.

 

Tibialis anterior

- origin: proximal 2/3 of anteriolateral surface of tibia and interosseus membrane - insertion: dorsal aspect of base of first ray - actions: dorsiflexes AJ supinates long. axis MTJ supinates STJ - function decelerates pronation and plantarflexion from HC toe clearance during swing phase - pathology · weak: foot drop, XS pronation · contracture: supinated foot

 

Tibialis posterior

- origin: posterior, proximal tibia - insertion: pl. surf. of all tarsal bones except the talus - actions: stabilizes midfoot major supinator / anti-pronator - function decelerates STJ pronation from HC supinates STJ during propulsion - pathology weak: XS pronation > pes planus contracture: supinated foot

 

Triceps surae

- consists of gastrocnemius and soleus - origin: gastrocs: above femoral condyles, soleus: soleal line of tibia and fibula - insertion: achilles tendon into posterior aspect of calcaneus - actions: plantarflexes AJ supinates a supinated STJ, pronates a pronated STJ - function active from FFL to TO for propulsion - pathology contracture: muscular equinus

 

Peroneals

- origin: lateral aspect of fibula - insertion:longus - base of first ray, brevis -styloid process of 5th met. - actions: PL: stabilises forefoot, plantarflexes first ray, pronates STJ PB: pronates STJ and OA MTJ - function stabilize forefoot prior to heel lift - pathology weak: overpowering of supinators > supination deformity contracture: pes planus

 

Digital musculature

long flexors / extensors insert into distal phalanx and produce motion at DIPJ
short flexors / extensors insert into intermediate phalanx and produce motion at PIPJ

interossei: dorsal and plantar layer, originate from met. shafts and insert into proximal phalanges
act to stabilise proximal phalanges in transverse and sagittal planes

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Manual muscle testing

- very useful, under-emphasized clinical technique
- clinical applications:
to determine muscles affected by neuromuscular conditions such as CP, polio
congenital shortening of muscle groups
post-surgical shortening
severing of tendons (eg: HAV)
post-traumatic weakness, eg: peroneal weakness post inversion ankle sprain
tibialis posterior dysfunction

Basic principles

- test position
one-joint muscles: end ROM position
two-joint muscles: half-way through ROM
- stabilise proximal structures
- apply resistance:
gradually, to let patient 'get set and hold', then uniformly
directly opposite to line of action of the muscle
always look for 'assistance' from other muscles

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For an excellent series of pictures outlining the technique of manual muscle testing of a number of muscles of the foot and leg, click here (this will link you to the University of Western Sydney's podiatry website).

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Grading system (as per Kendall)

Normal ++++
Good (+/-) +++
Fair (+/-) ++
Poor (+/-) +
Zero 0

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Summary

Need to remember:
- origin and insertion of lower limb muscles
- effect of contraction at AJ, STJ, MTJ, MPJs
- effects of contracture and weakness
- agonists and antagonists
- grading system

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References

Kendall FP, McCreary E, Provance PG. (1993) Muscles testing and function. (4th ed.) Williams and Wilkins, Baltimore.

(worthwhile text to purchase - about $45 at the LTU bookshop - make sure you check out the link above first, however)