Muscle Functions and Pathologies in Gait Mechanics

Swing Phase Muscles

Only muscles that are active during the swing phase are anterior group muscles.

Extensor Digitorum Brevis m.

Active from early midstance to late propulsion.

Mechanical Advantage Loss

Loses mechanical advantage before the end of the propulsion because of the lateral to medial loading.

Origin of Extensor Digitorum Brevis

Originates from dorsal and lateral surface of the calcaneus.

Insertion of Extensor Digitorum Brevis

Divides into tendon slips and inserts into the 2nd, 3rd, and 4th toes.

Function of Extensor Digitorum Brevis

Pronates about the OMTJ to stabilize the midtarsal joint in the early propulsive period.

Antagonist Function

Antagonist to the supination about the OMTJ that is normally occurring during propulsion.

Pronates

About the OMTJ to stabilize the midtarsal joint in the early propulsive period.

Antagonist to supination

Opposes the supination about the OMTJ that is normally occurring during propulsion.

Extensor Digitorum Brevis m. Function 1

Helps lumbricals and EDL muscles as they extend the 2nd, 3rd, 4th toes during propulsion.

Extensor Digitorum Brevis m. Function 2

Provides posterior stability for the 2nd, 3rd, and 4th metatarsals against the lesser tarsus.

Extensor Digitorum Brevis m. Function 3

Assists with posterior stability for the 2nd, 3rd, and 4th toes against the metatarsal heads and phalanges.

Extensor Hallucis Brevis m.

Functions from early midstance to late propulsion (same as EDL).

Extensor Hallucis Brevis m. Function

Functions later into the propulsive period because the hallux is the last one to come off the ground during the lateral to medial loading.

From early midstance to late propulsion

Functions later into the propulsive period because hallux is the last one to come off the ground during the lateral to medial loading.

Posterior stability for the first metatarsal against the lesser tarsus

Occurs during midstance and early propulsive period.

Posterior stability for the hallux against the first metatarsal

Provides stability during midstance and early propulsive period.

Assists in developing adduction stability of the hallux at the first MPJ during propulsion

Helps maintain proper alignment of the hallux.

Vertical axis of the first MPJ

Allows adduction stability.

Tendon is angulated so contraction places an adduction force on the hallux

No adduction motion, just an adduction force.

Feet are normally abducted during gait

EHB counters that force to keep normal alignment.

Transverse Axis

Perpendicular to the sagittal plane so motion occurs in the sagittal plane.

Vertical axis

Perpendicular to the transverse plane so motion occurs in the transverse plane.

Adduction stability

Assists in developing adduction stability of the hallux at the first MPJ during propulsion.

Tendon angulation

Tendon is angulated so contraction places an adduction force on the hallux.

Adduction force

No adduction motion, just an adduction force.

EHB function during gait

Feet are normally abducted during gait so EHB counters that force to keep normal alignment.

Adduction stability of the hallux

Assists in developing adduction stability of the hallux at the first MPJ during propulsion.

Lumbrical Muscles origin

Origin from the tendon slips of the FDL.

Lumbrical Muscles tendon passage

Tendon of each lumbrical passes beneath the transverse metatarsal ligament.

Lumbrical Muscles insertion

Tendon passes from plantar to dorsal and medial to lateral to insert onto the dorsal lateral shaft of the distal phalanx.

Lumbrical Muscles functions

Extend intermediate and distal interphalangeal joints during midstance and propulsive periods.

Lumbrical Muscles function during propulsion

Assists in plantarflexing the proximal phalanx during propulsive period.

Lumbrical Muscles stability function

Provide slight adduction stability of the proximal phalanx of lesser digits.

Lumbrical Muscles resistance

Can resist abduction forces of GRF and the oblique toe break during propulsion.

Hammer Digit syndrome

Normally, Lumbricals and EDB extend the interphalangeal joints to prevent buckling as the FDL contracts.

Effect of abnormal STJ pronation

Will cause FDL to work harder which disrupts the function of the Quadratus Plantae muscles.

Lumbrical Muscles dysfunction

End up flexing digits instead of their normal function to extend, causing hammer digit syndrome.

Theory of Lumbrical Muscles

May serve as antagonistic muscles to EDL during swing phase of gait.

Interossei Muscles timing

From late midstance to late propulsion.

Number of Interossei Muscles

There are seven interossei muscles.

Dorsal interossei

There are four dorsal interossei muscles.

Plantar interossei

There are three plantar interossei muscles.

1st dorsal interossei insertion

Inserts onto the medial side of the 2nd proximal phalanx.

2nd dorsal interossei insertion

Inserts onto the lateral side of the 2nd proximal phalanx.

3rd dorsal interossei insertion

Inserts onto the lateral side of the 3rd proximal phalanx.

4th dorsal interossei insertion

Inserts onto the lateral side of the 4th proximal phalanx.

1st plantar interossei insertion

Inserts onto the medial side of the 3rd proximal phalanx.

2nd plantar interossei insertion

Inserts onto the medial side of the 4th proximal phalanx.

3rd plantar interossei insertion

Inserts onto the medial side of the 5th proximal phalanx.

Plantar interossei 1st insertion

Inserts onto the medial side of the 3rd proximal phalanx.

Plantar interossei 2nd insertion

Inserts onto the medial side of the 4th proximal phalanx.

Plantar interossei 3rd insertion

Inserts onto the medial side of the 5th proximal phalanx.

Interossei Muscles Tendons

Insert onto the plantar plate.

Interossei Muscles Function - Posterior Stability

Provides stability for the bases of the lesser four proximal phalanges against the met heads.

Interossei Muscles Function - Transverse Stability

Provides stability of the bases of the proximal phalanxes.

Interossei Muscles Function - MPJ Stability

Provides adductor/abductor stability at the MPJ.

5th Digit Stabilization

Can only stabilize in an adduction capacity since it only has a medial insertion from the 3rd plantar interossei.

Lateral Force Cancellation

Helps to cancel out the lateral force at the 5th digit when loading from lateral to medial.

Interossei Muscles Function - Extensor Expansion

In some people, may assist in the function of the extensor expansion.

Interossei Muscles Function - Plantarflexing Force

Applies a plantarflexing force on the proximal phalanx (especially 2nd, 3rd, and 4th).

contracture of the digits

abnormal contracture of the digits due to the FDL working too hard.

weak resistance

the muscle can only exert a weak resistance against abnormal transverse plane pathology on the lesser digits.

Abductor Hallucis m.

though it's called abductor hallucis (toward the midline of the foot), it actually adducts the hallux toward the midline of the body.

Abductor Hallucis m. function timing

From late midstance to the end of propulsion.

Origin

Originates from the medial plantar tubercle of the calcaneus.

Conjoin Tendon

Forms a conjoin tendon with the medial tendon of the Flexor Hallucis Brevis m.

Encloses

Encloses the tibial sesamoid.

Insertion

Inserts into inferior medial side of the base of the proximal phalanx of the hallux.

Function - Stabilization

Stabilizes the hallux in adduction.

Function - Propulsion Stability

Assists with posterior stability of the proximal phalanx of the hallux during propulsion.

Function - Supination

Supinates forefoot about the OMTJ axis (normal motion).

Function - Plantarflexion

Plantarflexes the first ray and stabilizes the first met head during propulsion.

Stabilizes the hallux in

adduction

Assist with stability of the proximal phalanx of the hallux during

propulsion

Supinates forefoot about the

OMTJ axis (normal motion)

Plantarflexes the first ray and stabilizes the first met head during

propulsion

Extensor Digitorum Brevis

is the antagonist to normal supination

Pathology of Abductor Hallucis m.

Hypermobile first ray

Hypermobile first ray

A condition where the first ray of the foot exhibits excessive mobility.

Hallux Valgus

A deformity characterized by lateral deviation of the big toe.

Arch pain (especially medial arch pain)

Discomfort or pain experienced in the arch of the foot, particularly on the medial side.

Abnormal motion ? dorsiflexes instead of plantarflexing

A movement anomaly where the foot moves upward (dorsiflexion) instead of downward (plantarflexion) during certain activities.

Due to abnormal STJ pronation

A condition caused by excessive pronation at the subtalar joint.

Moves the abductor hallucis closer to the 1st ray axis

A biomechanical change that alters the position of the abductor hallucis muscle relative to the first ray.

Shortens the lever arm and diminishes ability to plantarflex the first met

A mechanical disadvantage that reduces the effectiveness of the abductor hallucis in plantarflexing the first metatarsal.

Abnormal STJ pronation lowers the medial longitudinal arch

A consequence of abnormal subtalar joint pronation that results in a decreased height of the medial longitudinal arch.

Lengthens the medial column which lengthens the abductor hallucis

An effect of altered biomechanics that increases the length of the medial column of the foot and the abductor hallucis muscle.

Decreases its mechanical advantage (because its longer than its normal physiological length)

A reduction in the effectiveness of the abductor hallucis due to its increased length compared to its normal physiological length.

Caused by an abducted gait

A gait pattern where the foot moves outward, leading to certain foot pathologies.

Person rolls medially off the hallux during propulsion

A movement pattern in which the individual shifts weight medially off the big toe while pushing off during walking or running.

GRF puts an abduction force on the hallux

Ground reaction forces that create a lateral force on the big toe, contributing to foot deformities.

Causes abductor hallucis to cramp

A result of abnormal forces acting on the abductor hallucis muscle, leading to muscle spasms.

Causes hallux valgus

A consequence of abnormal forces and muscle imbalances that lead to the development of hallux valgus.

Causes arch pain

A result of mechanical imbalances and stress on the foot structures, leading to discomfort in the arch.

Adductor Hallucis (Oblique head)

From late midstance to propulsion.

Fibular sesamoid

Covers fibular sesamoid.

Flexor Hallucis Brevis

From mid midstance to propulsion.

Flexor Digitorum Brevis

Active ONLY during propulsion.

Transverse Pedis Muscle

Active from late midstance to late propulsion.