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Department
of Podiatry
Ankle
Equinus
Definition:
a sagittal plane deformity in which there is less than 10° of available
dorsiflexion at the ankle joint, when the subtalar joint is in its neutral
position and the midtarsal joint is fully locked
Two major
classifications
osseus
- due
to congenital morphology of ankle joint
muscular
- congenital
shortage
- acquired shortening of posterior leg muscles (various mechanisms)
- secondary to:
spastic paralysis
cerebral palsy
CVA
tonic spasm: 'guarding' mechanism to immobilize painful joints / structures
excessive pronation
decreased tension in posterior leg muscles leads to subsequent contracture
weak dorsiflexor musculature
tight hamstrings
limb length discrepancy
prolonged bed rest / high heels
Incidence:
present
in 96% of 176 male and female subjects with biomechanically induced
foot pain (Hill, 1995)
Functional
anatomy
gastrocnemius
- originates
above femoral condyles
- two heads, M>L
- inserts into tendo achilles
soleus
- deep
to gastrocnemius, originates from soleal line of tibia and upper third
of fibula
- inserts into tendo achilles
plantaris
- originates
close to lateral head of gastrocnemius
- obliquely crosses posterior aspect and inserts into medial side
of TA
- extremely variable, absent in 7%
tendo achilles
- thickest,
strongest human tendon
- variation in soleal and gastroc. components
To
review ankle joint muscular anatomy, click here
To
review ankle joint osseus anatomy, click here
Normal
AJ motion
- minimum
range of dorsiflexion required prior to heel lift = 10°
- no dorsiflexor muscle activity present
- after heel lift, AJ begins to plantarflex
- gastrocnemius
flexes KJ and plantarflexes AJ
3, not 2-joint muscle
assisted by plantaris
- soleus
plantarflexes AJ
2, not 1-joint muscle
Differential
Dx of limited ankle joint dorsiflexion
- test
AJ dorsiflexion with knee flexed and extended
- knee extended - gastrocnemius taut
- knee flexed - gastrocnemius lax
Therefore,
- insufficient dorsiflexion when knee extended and flexed: osseus
or soleal equinus
- insufficient dorsiflexion when knee extended, but sufficient when
flexed: gastrocnemius equinus
- only way to DDx between soleal and osseus equinus is the feel of
the end ROM
abrupt block - osseus
spongy - soleal
Pathomechanics
- inadequate
AJ dorsiflexion during stance phase
- needs dorsiflexion
- STJ pronation unlocks distal structures and allows DF of forefoot
on the rearfoot
uncompensated
- insufficient
STJ pronation
- heel cannot contact the ground, resulting in bouncy gait
- XS WB on forefoot: HK lesions and clawing of lesser digits
- achilles tendinitis
- secondary hamstring contracture
- GRFs cannot resist effect of supinator muscles, so supination contracture
may occur
- more proximal joints may attempt to compensate via genu recurvatum,
abducted angle of gait, excessive knee flexion, hip flexion
EQUIN
proximal compensation mechanisms
fully compensated
- STJ pronation provides required 10 degrees of DF
- excessive STJ pronation to achieve DF
- unlocking of distal structures
- sagittal plane PF of calcaneus and midtarsal joint collapse / break
- very destructive compensation
- leads to gross excessive pronation, and associated with all pronation-induced
pathologies
NB: if there is insufficient STJ ROM to bring heel to ground, a bouncy
gait with early heel lift may be observed (partial compensation)
Treatment
- orthoses
to control XS pronation
- gastrocnemius
stretching program
- heel lifts to reduce strain from achilles tendon
- surgery: achilles
tendon lengthening, gastrocnemius recession
Summary
- ankle
equinus - unable to obtain 10 degrees of dorsiflexion
- may be osseus or muscular
- compensated: STJ pronation to achieve DF
- uncompensated: insufficient STJ ROM, compensation may occur more
proximally
 References
Downey
MS (1987) Ankle equinus. In: McGlamry ED (ed.) Comprehensive textbook
of foot surgery. Vol 1. Williams and Wilkins, Baltimore, p. 368-402.
Lang L (1984) Ankle equinus. The Chiropodist Jan 4-7.
Rome K (1988) Equinus conditions affecting the feet. ACTUK journal
Spring 14-18.
Root ML, Orien WP and Weed JH (1971) Clinical biomechanics: normal
and abnormal function of the foot. Clinical Biomechanics Corp,
Los Angeles.
NB: Photo taken from the Queens University
of Belfast foot conditions web page.
Links to relevant web pages
Click
here for more information about ankle
joint equinus.
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