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Gait: A Complete Study Guide

The Gait Cycle - Foundation

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Gait Cycle Phases (Detailed)

Stance Phase (60%)

Swing Phase (40%)

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Temporal and Spatial Parameters

Spatial Parameters

Temporal Parameters

Key rule: As gait speed increases → stance phase % decreases → double support time decreases

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Six Determinants of Gait (Motion Patterns)

• Vertical: sinusoidal curve, amplitude 5 cm
• Lateral: sinusoidal curve, amplitude 6 cm
• CoM located 2 cm anterior to S2

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Kinetics and Kinematics of Gait

Kinematics (Joint Motion)

Kinetics (Forces and Moments)

• Ground Reaction Force (GRF): The mean load-bearing vector that changes in magnitude and direction throughout the cycle. It determines the rotational potential (moment/torque) on each joint, and therefore dictates muscle action requirements.
• Walking: GRF ≈ 1.5x body weight
• Running: GRF ≈ 3-4x body weight (due to the float phase impact)
• Knee forces (arthritis): 4-7x body weight; 70% of load through the medial compartment
• Hip forces: 2.6-3.0x body weight during single-limb stance

Major Muscle Actions

Most muscle activity during gait is eccentric - the muscle is active while lengthening, controlling joint motion rather than producing it. - Miller's Review of Orthopaedics, 9th Ed.

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Pathological Gait Patterns

1. Muscle weakness/paralysis - reduces ability to control joint movement
2. Neurologic conditions - weakness, spasticity, balance problems, incoordination
3. Pain - antalgic adaptations
4. Limb deformity - restricts ROM and alters mechanics
5. Joint disease - contracture, reduced ROM, pain

Gait Abnormalities by Phase and Joint (Summary Table)

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Running Gait

• During walking, up to 12% of the gait cycle is spent with both feet in stance (double support).
• In running, this is replaced by a float phase - a period when neither foot touches the ground.
• The increased GRF in running results from the greater impact after the float phase.
• As running speed increases, the float phase lengthens and the stance phase shortens further.

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Stair Climbing and Descent

• Knee joint forces: 4-7x body weight during level walking; even higher during stair climbing due to the greater knee flexion angle and increased quadriceps moment required.
• Stair ascent (step-over-step): Requires ~90-120° of knee flexion, active concentric quadriceps and hip extensor work (push-off from trailing limb), and plantarflexion power. The leading limb performs controlled eccentric loading.
• Stair descent: Even higher eccentric quadriceps demand (controlling knee flexion against gravity); greater patellofemoral joint loading.
• Patients with posterior-stabilized (PS) total knee replacements show decreased knee flexion during stair climbing and tend to lean forward in a quadriceps-sparing posture. - Campbell's Operative Orthopaedics, 15th Ed.
• The ankle requires adequate dorsiflexion range (plantar flexion to reach, dorsiflexion to clear the step and absorb loading).

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Assistive Devices and Gait Modification

• Cane (contralateral hand): Shifts CoG to the affected side, decreasing joint reaction force of the lower limb and reducing pain.
• Crutches: Provide two additional load points, increasing stability.

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Quick Reference: Key Numbers to Remember

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Q1. Kinetics & Kinematics of Gait [15 Marks]

Introduction

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KINEMATICS OF GAIT

1. Hip Kinematics

• Hip flexors advance the limb forward during swing.
• Hip extensors fine-tune limb trajectory during terminal swing (TSw) and before IC.
• Extensor activity dominates stance; flexor activity dominates swing.

2. Knee Kinematics

• The 15° knee flexion at loading response is the third determinant of gait - it dampens the shock of initial contact.
• Knee works in concert with foot and ankle to reduce unnecessary limb motion.

3. Ankle Kinematics

• The ankle follows the rocker mechanism - heel rocker → ankle rocker → forefoot rocker - enabling smooth forward progression.
• At foot flat, the hindfoot passively everts through the subtalar joint, absorbing energy.

4. Center of Mass (CoM) Motion

• CoM is located 2 cm anterior to S2.
• Vertical displacement: sinusoidal curve, amplitude = 5 cm (highest at midstance, lowest at double support).
• Lateral displacement: sinusoidal curve, amplitude = 6 cm.
• The six determinants of gait function to minimize these displacements, thereby reducing energy expenditure.

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KINETICS OF GAIT

1. Ground Reaction Force (GRF)

• During walking: GRF ≈ 1.5× body weight
• During running: GRF ≈ 3-4× body weight (due to impact after float phase)
• Stair climbing/arthritis: Knee forces ≈ 4-7× body weight

• First peak: at loading response (weight acceptance)
• Trough: at midstance (body vaulting over stance limb)
• Second peak: at terminal stance/push-off

• GRF anterior to hip in stance → external hip flexion moment → gluteus maximus activated
• GRF posterior to knee in stance → external knee extension moment → minimal quadriceps demand (passive stability)
• GRF anterior to ankle in stance → external dorsiflexion moment → gastrocnemius-soleus eccentrically resists

The GRF determines rotational potential (moment/torque) at each joint, which in turn dictates the muscle action required at that joint and across the entire locomotor chain. - Miller's Review of Orthopaedics, 9th Ed.

2. Joint Moments and Muscle Action

3. Types of Muscle Contraction in Gait

• Eccentric (most common): Muscle active while lengthening; controls deceleration of joint segments.
• Example: Quadriceps at LR (controls knee flexion), Tibialis anterior at IC (controls foot slap), Gastrocnemius-soleus through stance (controls dorsiflexion rate).
• Concentric: Muscle shortens to move a joint through space.
• Example: Iliopsoas in swing (hip flexion), Gastrocnemius at push-off, Tibialis anterior in swing (dorsiflexion for clearance).
• Isometric: Muscle length remains constant.
• Example: Gluteus medius in midstance (prevents pelvic drop).

4. Key Muscle Kinetics Summary

5. Energy Efficiency

• The combined kinematic and kinetic adaptations reduce excursion of the CoM, minimizing energy expenditure.
• Head, neck, trunk, and arms account for 70% of body weight; trunk CoG is anterior to T10, ~33 cm above the hip joints (average 184 cm individual).
• The gait pattern resembles a sinusoidal curve - analogous to an inverted pendulum during stance.
• Water walking significantly decreases joint moments and contact forces due to buoyancy.

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Q2. Pathological Gait [10 Marks]

Introduction

1. Muscle weakness or paralysis
2. Neurological conditions (spasticity, loss of coordination, proprioceptive loss)
3. Pain
4. Limb deformity (contractures, leg length discrepancy)
5. Joint disease (arthritis, reduced ROM)

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Major Pathological Gait Patterns

1. Antalgic Gait

• Cause: Pain in any part of the lower limb - most commonly degenerative joint disease (DJD/OA).
• Mechanism: The patient shortens the stance phase on the painful limb to minimize the time that limb bears load. The contralateral swing phase is correspondingly more rapid.
• Appearance: Asymmetric, limping gait with visibly shorter steps on the painful side. The upper body may tilt over the affected limb.
• Clinical note: Antalgic gait is the most common pathological gait pattern seen in orthopaedic practice.

2. Trendelenburg Gait (Abductor/Gluteus Medius Gait)

• Cause: Weakness of gluteus medius (hip abductor) on the weight-bearing (stance) side.
• Mechanism: During single-limb stance, the GRF passes medial to the hip joint, creating an external hip adduction moment. Normally, the gluteus medius generates an equal internal abduction moment to keep the pelvis level. When this muscle is weak, it fails to generate the necessary moment → contralateral pelvic drop (positive Trendelenburg sign).
• Appearance: Patient leans the trunk over the weak hip to shift CoM and reduce the adduction moment (compensated Trendelenburg). With bilateral weakness → waddling gait (side-to-side shoulder movement).
• Causes include: OA hip, DDH, fracture neck of femur, polio, after total hip arthroplasty.

3. Steppage Gait (High-Stepping Gait)

• Cause: Footdrop - weakness or paralysis of tibialis anterior / dorsiflexors.
• Mechanism: Loss of tibialis anterior function means the foot cannot be actively dorsiflexed during swing → foot drags on the ground. To compensate, the patient exaggerates hip and knee flexion to lift the foot higher for clearance.
• Appearance: Exaggerated knee and hip flexion during swing. At IC, foot slaps the ground loudly (loss of eccentric control by tibialis anterior).
• Causes: Common peroneal nerve palsy, L4/L5 radiculopathy, Charcot-Marie-Tooth disease, TA tendon rupture.

4. Scissor Gait

• Cause: Bilateral spastic hip adductors (spastic diplegia - cerebral palsy, upper motor neuron lesions).
• Mechanism: Overactive adductors draw both limbs medially; thighs rub or cross during swing.
• Appearance: Narrow/crossing base of support; legs move in a scissoring motion. May be accompanied by knee flexion from hamstring spasticity.

5. Equinus Gait (Toe Walking)

• Cause: Ankle equinus deformity (plantarflexion contracture) or plantarflexor spasticity.
• Mechanism: Plantarflexion prevents normal heel-toe sequence. During stance, the ankle cannot dorsiflex → patient walks on toes. Results in:
• Steppage gait in swing (exaggerated knee/hip flexion for clearance)
• Knee hyperextension moment during stance (genu recurvatum)
• Causes: Cerebral palsy, Achilles contracture, idiopathic toe walking.

6. Calcaneus Gait

• Cause: Triceps surae (gastrocnemius-soleus) weakness.
• Mechanism: Absent push-off at terminal stance. Increased ankle dorsiflexion during heel strike without ability to progress to heel rise.
• Appearance: Excessive heel contact throughout stance; absent push-off propulsion; shortened step length.

7. Crouch Gait

• Cause: Hamstring contracture, plantar flexor weakness, long limb, or a combination.
• Mechanism: Excessive knee and hip flexion throughout the gait cycle. Increased dorsiflexion moment at the ankle.
• Appearance: Crouched, bent-knee posture throughout stance and swing. Common in cerebral palsy.

8. Hemiplegic Gait

• Cause: Unilateral upper motor neuron lesion (stroke, TBI).
• Mechanism: Combination of spasticity, weakness, and balance impairment. The hemiplegic limb shows:
• Prolonged stance and double-limb support on the unaffected side
• Ankle equinus (plantarflexor spasticity)
• Limited knee flexion
• Increased hip flexion
• The patient may use circumduction to advance the stiff limb.
• Appearance: Stiff, circling gait; arm held in flexed posture; characteristic "circumduction" of the affected leg.

9. Waddling Gait

• Cause: Bilateral hip abductor weakness (bilateral gluteus medius weakness, muscular dystrophy, bilateral CDH).
• Appearance: Exaggerated lateral trunk sway to both sides alternately.

10. ACL-Deficient / Quadriceps-Avoidance Gait

• Cause: ACL-deficient knee.
• Mechanism: Decreased quadriceps activation moment during midstance to avoid anterior tibial shear. Compensated by forward trunk flexion, plantarflexion of the ankle, and sometimes manual hyperextension of the knee.

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Summary Table of Pathological Gaits

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🚶 GAIT - Everything in Simple Language

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PART 1: What IS Gait?

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PART 2: The Gait Cycle - "One Full Walk Step"

One gait cycle = from the moment your RIGHT heel hits the ground → to the next time your RIGHT heel hits the ground again.

🦶 Stance Phase (60% of the cycle)

🦵 Swing Phase (40% of the cycle)

⚡ Double Support

Key rule: The faster you walk → the shorter the double support time. When you RUN, double support disappears entirely and becomes a "float phase" where NEITHER foot touches the ground!

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PART 3: Gait Parameters - The Measurements

Spatial Parameters (Distance measurements)

Temporal Parameters (Time measurements)

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PART 4: The 6 Determinants of Gait - "How Your Body Saves Energy"

Walking is your body's way of moving forward as efficiently as possible - using the least energy.

• Up and down: 5 cm (like a gentle wave)
• Side to side: 6 cm

Trick 1: Pelvic Rotation

Trick 2: Pelvic Tilt (List)

Trick 3: Knee Flexion at Loading

Trick 4: Foot & Ankle Motion

• Heel rocker (heel strike to foot flat)
• Ankle rocker (foot flat through midstance)
• Forefoot rocker (heel rise to toe-off)

Trick 5: Knee Motion (working with ankle)

Trick 6: Lateral Pelvic Shift

Bottom line: All 6 determinants work together like a well-tuned machine to keep your head traveling in a smooth, nearly straight line - saving enormous energy over a day of walking.

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PART 5: Kinematics - "What Joints Are Doing"

Hip Joint Journey Through One Gait Cycle

• Gluteus maximus powers the hip from bent → straight (stance)
• Iliopsoas pulls the leg forward during swing

Knee Joint Journey

Ankle Joint Journey

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PART 6: Kinetics - "The Forces Behind the Motion"

Ground Reaction Force (GRF) - The Most Important Force

Think of it like this: When you push down on a trampoline, the trampoline pushes back up. That "push back" on your feet during walking is the GRF.

• Walking: GRF = 1.5× your body weight on each heel strike
• Running: GRF = 3-4× your body weight (much bigger because of the impact after the float phase)
• Stairs/Arthritis: Up to 4-7× body weight at the knee

• GRF passes in front of the hip → it tries to fold your hip forward → your gluteus maximus fires to stop this
• GRF passes behind the knee → it tries to straighten the knee → minimal quadriceps work needed (the joint is passively stable)
• GRF passes in front of the ankle → it tries to bend the ankle up → gastrocnemius-soleus fires to resist this and store energy for push-off

Joint Moments (Torques)

Types of Muscle Work in Gait

The KEY insight: Most of gait is ECCENTRIC work - your muscles are mostly acting as brakes and shock absorbers, not as engines. Walking is controlled falling!

Energy Flow in Gait

• In stance, your body vaults over your foot like an inverted pendulum - converting kinetic energy to potential energy and back.
• The muscles store and release energy efficiently (especially the Achilles tendon at push-off).
• The 6 determinants minimize the distance the CoM has to travel, so less energy is wasted.

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PART 7: Pathological Gait - "When Walking Goes Wrong"

1. 😣 Antalgic Gait - "Pain Walk"

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2. 🦁 Trendelenburg Gait - "Sailor's Walk" or "Waddling"

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3. 🦆 Steppage Gait (High-Stepping Gait) - "Footdrop Walk"

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4. ✂️ Scissor Gait - "Scissors Crossing"

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5. 🩰 Equinus Gait - "Toe Walking"

• During swing → foot too low → steppage gait develops to compensate (high knee lift)
• During stance → GRF is pushed forward → the knee tends to hyperextend backward (genu recurvatum)

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6. 🦶 Calcaneus Gait - "All Heel, No Push"

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7. 🙇 Crouch Gait - "Bent Knee Throughout"

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8. 🧠 Hemiplegic Gait - "Stroke Walk"

• Ankle equinus (foot pointing down)
• Knee doesn't bend in swing (knee stiffness/extension spasticity)
• Hip can't flex well in swing → circumduction to clear the floor
• Prolonged stance on the UNAFFECTED side (the good leg bears weight longer)

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9. 🦆 Waddling Gait

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10. ACL-Deficient (Quadriceps-Avoidance) Gait

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PART 8: Running Gait - "Walking's Faster Cousin"

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PART 9: Stair Climbing - "Gait Gone Uphill"

• Your knee must bend to 90-120° (much more than the 65° in normal swing)
• Your quadriceps must work very hard concentrically to lift your body weight against gravity
• Stair descent is even harder - quadriceps work eccentrically to control the lowering → very high patellofemoral joint forces

• Leading leg: controls eccentric loading → pulls body upward
• Trailing leg: pushes off concentrically (quads + calf)

• The leading leg must eccentrically control the knee bending against gravity - this requires MORE quadriceps force, not less
• Explains why people with knee OA struggle MORE with stairs down than stairs up

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Quick Memory Cheat Sheet

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