Consequences
Why your balance depends on your big toe
FHL shifts the center of gravity toward the back and the outer edge of the foot, and breaks the synchrony of the step. The result is measured in the clinic with a simple single-leg stance test, and shows up in real life as instability, falls and preventable accidents.
The cascade to balance
The body’s balance relies on a continuous stream of sensory information coming from the foot. When FHL disrupts this information and blocks the adjustments of the rearfoot, balance deteriorates in two complementary ways — in static posture and in movement.
The biomechanical chain involved
Static balance: displacement of the center of gravity
The clinical test is simple. The patient is asked to stand on one leg for a few seconds. The clinician observes the corrective sway and the position of the body. With FHL, the center of gravity shifts in a characteristic way toward the back and the outer edge of the foot.
Without FHL
Center of gravity well positioned
Center of gravity projected onto the middle of the foot, minimal corrective sway.
With FHL
Center of gravity displaced
Projection toward the back and outer edge of the foot, marked sway, instability.
This displacement can be objectively documented and quantified on a force plate or an instrumented treadmill. The Centre du pied has carried out this type of measurement on hundreds of patients as part of assessments before and after tenolysis of the flexor hallucis longus. The recovery of central positioning after surgery is one of the most telling markers of functional benefit.
Dynamic balance: the break in the step
Dynamic balance is even more telling than static balance. During the gait cycle, the foot performs alternating movements of pronation and supination. Pronation is a tilt inward, supination a tilt outward. The transition from one position to the other must occur smoothly, without any jolt.
Pronation–supination cycle
Normal transition vs FHL
Comparison between a normal (smooth) transition and a transition with FHL (a break) at the end of the stance phase.
Normal cycle
Smooth transition
Gradual shift from pronation to supination at the end of stance, without any jolt.
Cycle with FHL
A true break
Abrupt break at the end of stance, visible to the naked eye on video recordings.
The gait analysis work of the Centre du pied has revealed this abrupt break at the end of the stance phase in patients with FHL. The transition between pronation and supination, which should be fluid, becomes a jolt, sometimes visible to the naked eye on video recordings.
The body as an inverted pendulum
Walking is a synchronized movement that positions the body over the supporting foot, alternately left and right. The body passes over the foot along a pendulum-like path.
The teaching analogy
With every step, your body passes over the foot like an inverted pendulum
Each moment of this passage corresponds to a point of support under the foot that moves from back to front, all the way to propulsion. If pronation or supination is excessive or mistimed, the position of the body must adapt and compensate for the imbalance. This adaptation is not always possible, particularly for the knee, whose anatomy does not allow it to correct a rotational disturbance. The imbalance becomes chronic.
Two particularly affected populations
The practical consequences of the imbalance induced by FHL play out differently depending on the population. Two profiles are particularly exposed.
Athlete profile
Performance and injury risk
Dynamic imbalance disrupts performance and promotes acute injuries. Typical injuries: ACL tears, recurrent ankle sprains, meniscal tears from twisting, overload tendinopathies.
Senior profile
Fall risk and loss of independence
With age, the imbalance induced by FHL adds to the natural loss of proprioception. Consequences: falls at home and outdoors, femoral neck fracture, cautious walking, loss of confidence in movement.
Key takeaway
FHL is a modifiable biomechanical factor. Identifying and treating FHL in a senior at risk of falling, or in an athlete after a recurrent sprain, means acting on the cause rather than on the consequences.
Gait analysis, the reference diagnostic tool
The assessment of static and dynamic balance is done with two complementary tools in the clinic: the clinical single-leg stance test and gait analysis on an instrumented treadmill. The latter makes it possible to objectively document and quantify what the former only hints at.
Diagnostic tool
Instrumented treadmill
Gait analysis measures, in real time, the pressures under the foot, the displacement of the center of gravity, and the smoothness of the pronation–supination transitions. It is the reference tool for objectively documenting FHL in its dynamic expression and for tracking its progression under treatment.
« Balance is not an abstract faculty. It is a continuous dialogue between the foot and the brain, and when the foot no longer sends the right information, the entire body wavers. »
Dr Jacques Vallotton, Centre Orthopédique d’Ouchy
Understanding through video
Several video clips shed light on the role of podiatry and gait assessment in evaluating balance, from instrumented gait analysis to research work on FHL and locomotion.
A global therapeutic approach and the contributions of podiatry
The value of gait assessment and functional assessment
The child’s foot
The value of instrumented gait analysis
Research: FHL and Gait Analysis
Do you feel unsteady?
Assess your balance objectively
Whether you are an athlete or a senior, the mobility assessment with gait analysis at the Centre du pied makes it possible to objectively document any underlying FHL and its impact on your balance.
At a glance
Clinical test
single-leg stance
Displacement
backward and outward
Critical phase
end of stance
Measurement tool
instrumented treadmill
Athlete
acute injuries
Senior
fall risk
Going further
Other implications and useful pages
Ankle
The recurrent sprain, a direct consequence of dynamic instability at the end of the step.