Normal Gait:
The gait (walking) pattern of every person, although slightly different from person to person, has various common phases and patterns. To be able to analyze and understand the reason for pathological gait we must first know normal gait. The following is a breakdown of the gait cycle (walking pattern) and important stages of that cycle. One cycle is from heel strike to heel strike of the same leg. (ie. right heel strike to right heel strike).
Observation of the walking pattern usually is done in the Saggital (side view) and Coronal
(front / back view) planes.
The gait cycle is divided into two sections, Stance and Swing.
Stance phase takes up 60% of the total cycle and is defined as the stage when the foot is in contact with the ground and some percentage of body weight is being taken through it.
Swing phase takes up 40% of the cycle and is defined as the stage when the foot is not in contact with the ground, resulting in forward progression of the leg.

The main purpose of everything that happens during the various stages of the gait cycle is to maximize efficiency of movement. This is done with a minimal amount of movement of the center of gravity. (C of G ) and energy cost. If these patterns are affected in any way the efficiency of walking decreases and more energy is required.
The role of the Orthotist is to help the patient walk as normal as possible with the least amount of energy used. If what is provided requires more energy to move and does not help smooth the gait pattern then it will most likely be rejected.


Stance Phase

The important stages are Heel strike, Foot flat, Mid stance, Heel off, Toe off.

Purpose
Shock absorption (heel strike – foot flat)
Body weight acceptance (mid – stance)
Forward propulsion of the limb (heel off – toe off)

Swing Phase

The important stages of swing are acceleration, mid swing, deceleration.
The foot is not in contact with the ground so that muscles are active against gravity and inertia of the leg. The changes in angle at each joint are to clear the limb from contact with the ground and to maximize step length.


Summary of Normal Gait

At the heel strike phase the GRF causes a hip flexion moment, a knee flexion moment and a plantar flexion moment. The moments are opposed by an isometric contraction of the hip extensor muscles, an eccentric contraction of the knee extensor muscles and an eccentric contraction of the dorsiflexion muscles. These actions stabilize the hip while causing a shock absorber action at the knee and ankle.
At mid stance phase in the frontal plane the hip abductors act eccentrically then concentrically to prevent excessive drop of the pelvis on the swing phase side. The concentric of the ankle invertors prepares the foot for push off. 
During the push off phase the moments created by the GRF are opposed by a concentric contraction of the hip flexors and a concentric contraction of the plantar flexors muscles. These actions propel the body forward.
The foot is not in contact with the ground during swing phase. The muscles act against gravity and inertia of the leg to allow clearance of the foot with the floor and forward acceleration of the leg. During initial swing the hip flexors act concentrically to accelerate the limb forward. The knee extensors act eccentrically to prevent excessive heel rise. The ankle dorsiflexion contract concentrically to allow toe clearance from the floor. During terminal swing phase the limb is decelerated by eccentric contraction of the hip extensors and knee flexors. The ankle dorsiflexors act isometrically to maintain the ankle in a neutral position.

Heel strike

Reaction:

Anterior to hip causing flexion moment.
Anterior to knee causing extension moment.
Posterior to ankle causing plantar flexion
moment.

Hip is flexed 250. The gluteus maximus and
hamstrings are active in preventing further flexion.    

Knee  is in full extension or heel strike. The
extension moment is overcome by action of the
hamstrings and the knee begins to flex.

Ankle  is in neutral position then begin to plantar
flex. This plantar flexion is controlled by action
of the pretibial muscles. 

Shortly after heel strike:

Reaction:

Anterior to hip causing flexion moment.
Posterior to knee causing flexion moment.
Posterior to ankle causing plantar flexion
moment.

Hip is held in 250 of flexion by action of             
gluteus maximus and the hamstrings.

Knee is in 5o of flexion and continues to flex.
The rate of flexion is controlled by action of
the quadriceps.

Ankle  is in 5o of plantar flexion and continues
to plantar flex under the control of pretibial
muscles.

Foot flat:

Reaction:

Anterior to hip causing flexion moment.                    
Posterior to knee causing flexion moment.                 
Posterior to ankle causing plantar flexion
moment.

Hip  is in 25o of flexion then begins to extend         
by action of gluteus maximus and the
hamstrings.

Knee reaches 15o of flexion and continues to
flex until it reaches 20o shortly after foot flat.
It then begins to extend. The quadriceps are
active in controlling the angle of flexion.


Ankle is in 10o of plantar flexion. The plantar flexion moment reduce as the reaction moves along the foot and the pretibial muscle activity falls off. As the ground reaction passes anterior to the ankle joint the segments of the supporting limb begin to
rotate over the flexed foot.
24 (b)

Mid Stance:

Reaction:
Passes through the hip joint, no moment.
Posterior to knee causing a flexion moment.
Anterior to ankle causing dorsiflexion moment.

Hip  is in 10o of flexion and begins to extend as the     
ground reaction moves posterior to the hip joint
shortly after mid stance.

Knee  reaches 10o of flexion and continues to extend.
Quadriceps action has fallen off and it is suspected
that the solves is active in controlling knee flexion.

Ankle 5o of dorsiflexion and continues to dorsiflex
due to ground reaction. The dorsiflexion is controlled
by calf group of muscles.

Heel off

Reaction:
Posterior to hip causing extension moment.
Anterior to knee causing extension moment.
Anterior to ankle causing dorsiflexion
moment.

Hip  reaches about 130 of extension then begins   
to flex. The ilocus and pesos major art active in
controlling extension and initial flexion.

Knee  is flexed to about 20 which is the moment of
extension reaches at this point in the gait cycle.
The gastrocnemius may be active in preventing
further extension.

Ankle  reaches 150 of dorsiflexion after which it
plantarflexed due to a powerful contraction of the
calf muscles which counteracts the dorsiflexion
moment and assists in propelling the body forward.

Toe off:

Reaction:
By toe – off the reaction has last most of its significance
as the majority of weight is borne by the other foot.

Hip is in 100 of extension and continues to flex due to
the plantar flexion of the foot and activity of the rectus femoris.

Knee is flexed to about 400 and continues to flex under the small   
ground reaction moment and plantar flexion of the foot.

Ankle has reached 200 of plantar flexion due to contraction of the
calf muscles. These muscles become inactive directly after toe off.


Acceleration

Hip  is in 100 extension and flexes as the hip flexors     
accelerate the limb forwards.

Knee is in 40o of flexion and continues to flex under      
pendulum action as the limb accelerates.

Ankle is in 20o of plantar flexion directly after toe off. 
It then begins to dorsiflex under action of the
pretibial group of muscles.

Mid swing

Hip is flexed about 200 and continues to flex.

Knee reaches about 65o of flexion then begins to       
extend under pendulum action.

Ankle has reached its neutral position and is held
there by slight activity of the pretibial muscles.


Deceleration

Hip reaches 25o of flexion and is restrained by gluteus maximus
and hamstrings.

Knee is in full extension and restrained by the hamstrings.

Ankle is still held in the neutral position by action of the pretibial muscles.     

The hip, knee and ankle are now positioned for the following heel strike. All the
muscles groups that are necessary to counteract the ground reaction force are
now active.