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Department
of Podiatry
Subtalar
Joint
Anatomy
- comprised
of the articulations between the inferior aspect of the talus and
superior aspect of the calcaneus
- 4 distinct anatomical variations (Bruckner, 1987)
- 3 major ligaments: interosseus talocalcaneal, lateral talocalcaneal
/ cervical, posterior talocalcaneal
- motion occurs around a common axis
STJ variation
- three
facet, transitional two-facet, simple two facet, special two facet
(Bruckner,
1987)
STJ ligaments
1. talo-calcaneal
- limits inversion and eversion
2. cervical - limits inversion
3. posterior talocalcaneal - relatively insignificant
Axis of motion
- closely
related to AJ; often referred to as 'rearfoot complex'
- triplanar
- passes obliquely from posterolateral aspect of calcaneus through
the neck of the talus
- large variation in position of axis, between individuals, therefore
large variation in motion available
- 42° from transverse plane, 16° from sagittal plane (Manter,1941)
'Planal dominance'
- the
greater the angle formed between the axis and the plane of motion,
the more motion available in that plane
- eg: more vertical axis (increased angle between axis and transverse
plane), more transverse plane motion
- more horizontal axis (decreased angle between axis and transverse
plane), more frontal plane motion
- refer to Green and Carol (1984)
STJ motion
- still
not fully understood
- traditionally thought of as: functional hinge joint, triplanar
- triplanar STJ motion referred to as pronation and supination
- nature of STJ motion is dependant on whether the foot is non-
weightbearing (open chain) or weightbearing (closed chain)
Pronation
of the STJ
1.
Open chain: calcaneus free to move, talus locked in ankle mortise,
calcaneal abduction, eversion and dorsiflexion
2. Closed chain: calcaneus restricted by bodyweight, calcaneal eversion,
talar plantarflexion and adduction, foot abducts and dorsiflexes,
tibia internally rotates
Supination
of the STJ
1.
Open chain: calcaneal adduction, inversion and plantarflexion
2. Closed chain: calcaneal inversion, talar dorsiflexion and abduction,
foot adducts and plantarflexes, tibia externally rotates
NB:
motion is described in three planes but takes place simultaneously,
not stepwise
Subtalar
joint motion during gait
- ROM
is highly variable, and refers to frontal plane motion only
- approximately 30°, with 2:1 ratio (20° of inversion, 10°
of eversion)
- STJ motion required for normal gait has been reported as:
·
6° total STJ excursion (Wright et al, 1964)
· 4-6° of both inversion and eversion (Root et al, 1971)
- pronation
of the foot is necessary to:
·
adapt to uneven terrain
· absorb shock during initial contact
· absorb tibial rotation during the stance phase of gait
- supination
of the foot is necessary to:
·
create a rigid lever to enable normal propulsion during gait
- timing of STJ motion is still not fully understood
Subtalar joint compensation
- normal:
irregularities in terrain, changes in posture
- abnormal: to compensate for abnormal structure / function of lower
extremity or trunk
·
recurrent and persistent
· motion in other planes is excessive and leads to pathology
Summary
- STJ
motion occurs in all three plane simultaneously (triplanar)
- nature of STJ depends on whether the foot is WB or non-WB
- complex joint - still not fully understood
- pronation and supination are normal, necessary movements
- we can only clinically measure the frontal plane component
 References
Bruckner
J (1987) Variations in the human subtalar joint. Journal of Orthopedic
and Sports Physical Therapy 8: 489-494.
Green DR and Carol A (1984) Planal dominance. Journal of the American
Podiatric Medical Association 74: 98-103.
Kirby KA (1989) Rotational equilibirum across the subtalar joint axis.
Journal of the American Podiatric Medical Association 79(1):
1-14.
Michaud TC (1993) Foot orthoses and other forms of conservative
foot care. Williams and Wilkins, Baltimore, pp.9-14.
Root ML, Orien WP and Weed JH (1971) Clinical biomechanics: normal
and abnormal function of the foot. Clinical Biomechanics Corp,
Los Angeles, pp.26-62.
Valmassy RL (1996) Clinical biomechanics of the lower extremity.
CV Mosby, St. Lois, chapter 1.
NB: top graphic taken from web site of the American
Podiatric Medical Association.
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