Gait Analysis and Swing Phase

Swing Phase

• The swing phase is concerned with limb advancement, which involves foot clearance and preparation for initial contact.
• During initial swing and midswing, the limb flexes at the hip, knee, and ankle to shorten the limb for clearance.
• In terminal swing, knee extension lengthens the limb, increasing step length and preparing for stability at initial contact.

Gait Analysis

• Gait analysis classifies into kinematic and kinetic analysis.
• Kinematics studies positions, angles, velocities, and accelerations of body segments and joints during motion.
• Kinetic analysis studies the forces acting on the body during gait.

Kinematic Analysis

• Distance and time variables are classified as spatial parameters.
• Step length is the distance between initial contacts of opposite feet, averaging 64 cm for women, 73 cm for men, and 70.5 cm overall.
• Stride length is the distance between successive foot contacts of the same limb, averaging 128 cm for women, 146 cm for men, and 141 cm overall.
• Stride width is the horizontal distance between heel midpoints, typically 2.5 to 12.5 cm for adults, averaging 8 cm.

Head and Trunk During Gait

• Head and trunk move as a unit, with deviations in all three planes.
• Center of gravity (COG) displacement forms a sinusoidal curve, with upward deviations during midstance and late midswing, and downward deviations during loading response and preswing.

Shoulder Joint Motion During Gait

• Shoulder exhibits a sinusoidal movement pattern opposite the hip, flexing when the hip extends and vice versa.
• Shoulder reaches maximum extension at heel contact (25º) and maximum flexion at 50% of the gait cycle (10º).
• Amplitude of shoulder movement increases with gait speed.
• Arm swing balances rotational forces in the trunk and does not significantly affect energy expenditure during walking.

Elbow Joint Motion During Gait

• Elbow is at 20º of flexion during heel contact.
• It flexes to 45º during the first half of the gait cycle alongside shoulder flexion.
• It returns to 20º of flexion in the second half of the gait cycle with shoulder extension.

Kinetic Analysis of Gait

• Forces of gait include external forces (inertia, gravity, and ground reaction force) and internal forces (muscles, ligaments, tendons, joint capsules, and bony components).

Muscle Activity During Gait

• Terminal stance: Soleus and gastrocnemius contract eccentrically to control tibial advancement, prevent excessive dorsiflexion, and decelerate the tibia.
• Preswing: Plantar flexors contract concentrically to accelerate advancement of the unloaded limb.
• Initial swing and midswing: Tibialis anterior, extensor digitorum longus, and extensor hallucis longus contract concentrically to dorsiflex the ankle and isometrically to maintain neutral position.
• Terminal swing: Pretibial group muscles activate isometrically, with increasing activity of tibialis anterior to ensure neutral ankle positioning for heel contact.

Frontal Plane Analysis

• Hip joint experiences demands for lateral stability during early stance. This is provided by gluteus medius, gluteus maximus, and tensor fascia lata.
• Initial contact:
  • Adductor magnus contracts concentrically to counterbalance abduction moment from the laterally positioned GRFV.
  • Pelvis drops slightly.
• Loading response:
  • Gluteus medius, gluteus maximus, and tensor fascia lata contract eccentrically to control pelvic drop and counterbalance adduction moment.
• Midstance and terminal stance:
  • Hip abductors contract concentrically to counterbalance adduction moment and elevate the pelvis.
• Preswing:
  • Adductor magnus mainly contacts eccentrically to counterbalance abduction moment from the laterally positioned GRFV.
• Knee joint: Biceps femoris and gluteus maximus tension on the iliotibial band stabilize the knee against adduction torque.
• Subtalar joint:
  • Lateral GRFV during loading response continues subtalar eversion, allowing foot adaptation.
  • Inversion muscles (tibialis anterior, tibialis posterior, FHL, and soleus) contract eccentrically to counterbalance eversion moment.

Pathological Gait

• Gluteus Medius Weakness:
  • The pelvis drops laterally towards the opposite side during loading response and midstance due to inability of gluteus medius to counteract the adduction moment.
  • This creates a Trendelenburg gait.
  • Compensation involves leaning the trunk laterally towards the side of weakness.
• Unequal Leg Length:
  • Pelvis tilts downwards on the side of the shortened limb, creating a "stepping into a hole" appearance.
  • The tilt is accompanied by compensatory lateral trunk bending.

Functional Leg Length Discrepancy

• Four gait abnormalities (circumduction, hip hiking, steppage, and vaulting) aim to overcome functional discrepancies in leg length.
• Functional discrepancy occurs when one or both legs cannot adjust to the appropriate length for a gait cycle phase.
• Circumduction:
  • A swinging leg that is functionally too long is swung outward in a circular motion to avoid ground contact.
  • This usually occurs as a result of a neurological issue where a foot drop is accompanied by hip and knee extensor spasticity.