Gait Analysis

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Gait Cycle Basics - Stepping Stones

  • Gait Cycle: Heel strike (HS) of one foot to subsequent HS of the same foot.
  • Phases:
    • Stance Phase: 60%; foot contacts ground.
    • Swing Phase: 40%; foot airborne.
  • Double Support: ~20% of cycle (two periods, each ~10%); both feet on ground.
  • Key Metrics:
    • Cadence: Normal 90-120 steps/min.
    • Stride Length: Distance of one full gait cycle.
    • Step Length: HS of one foot to HS of contralateral foot.

⭐ Stance phase (60%) is significantly longer than swing phase (40%) in a normal walking gait.

Gait Cycle Phases and Percentages

Gait Kinematics - Motion Capture

  • Describes body segment motion (displacement, velocity $v$, acceleration $a$) and joint angles (e.g., flexion, extension, abduction, adduction, rotation) without considering forces.
  • Systems Used:
    • Optical (Gold Standard): Cameras (often infrared) track reflective markers on anatomical landmarks.
      • Passive markers: Reflect light.
      • Active markers: Emit light (e.g., LEDs).
    • Non-Optical: Inertial Measurement Units (IMUs), electromagnetic systems, mechanical goniometers.
  • Key Parameters Measured: Joint angular displacement ($\theta$), angular velocity ($\bar{\omega}$), stride length, cadence. ![Gait Analysis Setup](gait analysis setup)

Optical motion capture is the most common method for detailed 3D kinematic analysis, providing high accuracy for joint angles and segment trajectories during gait assessment for conditions like cerebral palsy or post-stroke recovery.

Gait Kinetics - Forceful Footsteps

  • Studies forces causing motion (GRF, JRF, muscle forces).
  • Ground Reaction Force (GRF): Force from ground.
    • Vertical: 1-1.5x body weight (walk), 2-3x (run); "M" shape.
    • A-P: Braking & propulsion.
    • M-L: Stability.
  • Moments (Torques): Rotational force. $M = F \times d$.
  • Power: Work rate. $P = M \times \omega$.
  • COP: GRF application point on foot. GRF, CoP, CoM, and VPP during gait

⭐ Vertical GRF's second peak (late stance) indicates propulsive force, mainly from ankle plantarflexors.

Determinants & Parameters - Gait's Guiding Stars

  • Determinants (Saunders): Minimize COM excursion & conserve energy.
    • Pelvic rotation ( total), pelvic tilt ( dip).
    • Stance phase knee flexion (~15-20°).
    • Foot & ankle rockers.
    • Lateral pelvic displacement (~2.5-5 cm).
  • Parameters:
    • Spatial: Step length (35-41 cm), stride length (1.4-1.6 m), step width (5-10 cm), foot angle (5-7°).
    • Temporal: Cadence (90-120 steps/min), velocity (~1.2-1.4 m/s).
    • Phases: Stance (~60%), Swing (~40%), Double support (~20%).

⭐ Double support time ↓ with ↑ speed; absent in running.

Pathological Gaits - Wobbles & Waddles

  • Antalgic Gait:
    • Cause: Pain.
    • ↓ Stance phase on affected side; shortened stride.
    • "Limp to get off the painful limb."
  • Trendelenburg Gait (Gluteus Medius Lurch):
    • Cause: Weak Gluteus Medius (hip abductor).
    • Pelvis drops on contralateral (swinging) side.
    • Trunk lurches to ipsilateral (stance) side.
    • Seen in: Superior gluteal nerve (L4, L5, S1) palsy.

    ⭐ Unilateral weakness of gluteus medius causes pelvic drop on the opposite side when lifting that foot (positive Trendelenburg sign).

  • Waddling Gait (Myopathic Gait):
    • Cause: Bilateral hip abductor weakness (e.g., muscular dystrophies, myopathies).
    • Broad-based, duck-like walk; exaggerated lateral trunk sway.
    • Often with Gluteus Maximus weakness (difficulty rising/climbing).
  • Short-Limb Gait:
    • Cause: True limb length discrepancy.
    • Pelvic dip to shorter side during its stance phase.
    • Compensation: Toe-walking (short side) or contralateral knee/hip flexion.

Trendelenburg vs Normal Gait: Pelvic Stability

High-Yield Points - ⚡ Biggest Takeaways

  • Gait cycle: Stance phase (60%) and Swing phase (40%) are fundamental.
  • Six determinants of gait (e.g., pelvic rotation, knee flexion) optimize energy efficiency.
  • Trendelenburg gait: Caused by gluteus medius weakness, results in contralateral pelvic drop.
  • Foot drop: Due to common peroneal nerve palsy (L4-L5), causes steppage gait.
  • Antalgic gait: Characterized by shortened stance phase on the affected painful side.
  • Double support phase: Present only in walking, crucial for stability, absent in running.

Practice Questions: Gait Analysis

Test your understanding with these related questions

In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?

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Flashcards: Gait Analysis

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When the knee is extended, the _____ bundle of ACL is tight, and the AM bundle is moderately lax.

TAP TO REVEAL ANSWER

When the knee is extended, the _____ bundle of ACL is tight, and the AM bundle is moderately lax.

PL

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