Normality

Root et al definition of normal structure of the osseous segments of the foot and leg at the middle of the stance phase:
• Calcaneus is vertical to supporting surface
• Forefoot lies on the same supporting plane as the calcaneus
• Subtalar joint is in it neutral postion
• Knee is fully extended
• Patella is in the frontal plane
• The 4th and 5th metatarsals are fully dorsiflexed
• Midtarsal joint is maximally pronated
• Bisection of the distal third of the tibia is parallel to the calcaneal bisection with the foot 90 degrees to the leg

Research has not supported the above criteria – if the criteria that the definition of normal is the mean + 2 standard deviation of an asymptomatic population.

In addition to the above for normality, Michaud (1997) lists the following:
• when the individual stands in his or her normal base of gait, the lower leg should be perpendicular to the ground (+2º)
• when the subtalar joint is maintained in its neutral position and the calcaneocuboid joint is locked in its close packed position, the vertical bisection of the calcaneus should parallel the vertical bisection of the distal tibia and fibula (+2º), the plantar forefoot should be perpendicular to the bisection of the calcaneus, and the plantar metatarsal heads should all rest on the same transverse plane.
• the distal extensions of the metatarsal heads should form a smooth parabolic curve.
• the lower extremities must be of equal length
• the various articulations of the lower extremity and pelvis should move through specific minimum ranges of motion
• neuromotor coordination must be intact, and periarticular tissues must provide ample proprioceptive information
• the supporting muscles must possess adequate strength, power and endurance
• the articular architecture should protect against excessive and/or abnormal motions
• ontogeny must allow for the formation of a relatively straight lower extremity and for the development of a functional medial longitudinal arch.

The criteria for normalcy, originally outlined by Root et al (1971) where based on theoretical constructs of what was assumed to be needed for normal function. Astrom & Arvidson (1995) found the following in 121 healthy subjects:
• tibial position – 6 (+2) degrees varus
• resting calcaneal position – 2 (+3) degrees everted
• forefoot to rearfoot relationship 6 (+4) degrees inverted

 
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