# Normal and Pathological Gait Analysis

## Introduction

**Gait analysis** is a fundamental skill in physical medicine and rehabilitation, enabling the identification of biomechanical deviations, diagnosis of underlying pathology, and prescription of appropriate interventions. Understanding the **normal gait cycle** is prerequisite to recognizing pathological patterns. Modern gait analysis combines observational assessment with instrumented techniques including motion capture, force plates, and electromyography to provide quantitative data for clinical decision-making.

## The Normal Gait Cycle

### Phases of Gait

One gait cycle extends from **initial contact** of one foot to the next initial contact of the same foot. **Stance phase** (60% of cycle): Foot is in contact with the ground. **Swing phase** (40% of cycle): Foot is off the ground, advancing forward. **Double limb support** (20% of cycle): Both feet on the ground; occurs at initial and terminal stance. Increased walking speed reduces double support time; running eliminates it entirely.

### Stance Phase Subdivisions

**Initial contact** (heel strike): Heel contacts the ground. **Loading response** (0-10%): Weight acceptance; opposite limb pushes off. **Midstance** (10-30%): Single limb support; body advances over the foot. **Terminal stance** (30-50%): Heel rises; body moves anterior to the support foot. **Pre-swing** (50-60%): Toe-off preparation; double support with opposite limb.

### Swing Phase Subdivisions

**Initial swing** (60-73%): Foot leaves the ground; hip and knee flex for clearance. **Midswing** (73-87%): Limb advances; foot clears the ground. **Terminal swing** (87-100%): Limb decelerates; knee extends in preparation for initial contact.

### Gait Determinants

**Pelvic rotation**: 4 degrees in transverse plane. **Pelvic tilt**: 5 degrees of pelvic drop on swing side (Trendelenburg mechanism). **Knee flexion in stance**: Approximately 15 degrees at loading response. **Ankle mechanisms**: Controlled dorsiflexion and plantarflexion.

**Lateral pelvic displacement**: Center of gravity oscillation minimized. These determinants reduce vertical and horizontal excursion of the center of gravity. ![Diagram of the normal gait cycle phases with stance and swing subdivisions](images/normal-gait-cycle-phases.png)

## Muscle Activity During Gait

### Key Muscle Groups

**Tibialis anterior**: Active at initial contact and swing (dorsiflexion, foot clearance). **Gastrocnemius-soleus**: Active mid-to-terminal stance (controlled forward progression, push-off). **Quadriceps**: Eccentric contraction in loading response (controlled knee flexion); concentric in terminal swing. **Hamstrings**: Decelerate swing limb in terminal swing; hip extension at initial contact.

**Gluteus medius**: Stabilizes pelvis in single limb support (prevents Trendelenburg drop). **Hip flexors (iliopsoas)**: Initiate swing phase.

| Muscle | Gait Phase Active | Function During Gait |
|--------|-------------------|---------------------|
| Tibialis anterior | Initial contact + swing | Dorsiflexion, foot clearance |
| Gastrocnemius-soleus | Mid-to-terminal stance | Controlled forward progression, push-off |
| Quadriceps | Loading response + terminal swing | Eccentric knee control; knee extension |
| Hamstrings | Terminal swing + initial contact | Decelerate swing limb; hip extension |
| Gluteus medius | Single limb support (stance) | Pelvic stabilization |
| Hip flexors (iliopsoas) | Pre-swing + initial swing | Initiate swing phase |

## Observational Gait Analysis

### Systematic Approach

Observe from **front, side, and behind**. Assess each body segment: trunk, pelvis, hip, knee, ankle, foot. Note symmetry, stride length, cadence, velocity, and base of support. Identify deviations in each phase of gait. Compare to contralateral limb. Assess with and without assistive devices/orthotics.

### Common Parameters

**Cadence**: Steps per minute (normal: 100-120). **Stride length**: Distance from one heel strike to next heel strike of same foot (normal: 1.2-1.5 m). **Step length**: Distance from heel strike of one foot to heel strike of opposite foot. **Walking velocity**: Normal comfortable speed approximately **1.2-1.4 m/s**. **Base of support**: Lateral distance between feet (normal: 5-10 cm).

## Pathological Gait Patterns

### Hemiplegic Gait (Circumduction Gait)

Characteristic of **upper motor neuron lesion** (stroke, TBI). Stiff knee with inadequate flexion during swing. **Circumduction**: Lateral arc of swing limb to clear foot. Equinovarus foot posture; toe-drag. Arm held in flexed, adducted posture. Reduced stance time on affected side.

### Diplegic/Crouch Gait

Common in **cerebral palsy** (spastic diplegia). Excessive hip flexion, knee flexion, and ankle dorsiflexion throughout stance. Short stride length; increased energy expenditure. Exaggerated anterior pelvic tilt. Scissoring pattern if hip adductor spasticity present.

### Parkinsonian Gait

**Short, shuffling** steps with reduced stride length. Festination: Progressive acceleration of steps. Reduced arm swing (often asymmetric initially). Difficulty initiating gait (start hesitation) and turning. Freezing episodes, especially in doorways and tight spaces. Flexed posture with retropulsion risk.

### Trendelenburg Gait

**Gluteus medius weakness**: Pelvis drops on the contralateral (swing) side. **Compensated Trendelenburg**: Trunk leans toward the affected side to shift center of gravity. Causes: Hip abductor weakness, hip arthroplasty, L5 radiculopathy, superior gluteal nerve injury.

### Steppage Gait

**Foot drop** from ankle dorsiflexor weakness (tibialis anterior). Excessive hip and knee flexion during swing to clear the foot. Foot slap at initial contact. Causes: Peroneal nerve palsy, L5 radiculopathy, peripheral neuropathy, CMT disease.

### Antalgic Gait

Shortened stance phase on the **painful limb**. Reduced loading and quick weight transfer. Causes: Any painful lower extremity condition (fracture, arthritis, soft tissue injury).

![Illustration comparing normal gait with hemiplegic, steppage, and Trendelenburg patterns](images/pathological-gait-patterns-comparison.png)

## Instrumented Gait Analysis

### Three-Dimensional Motion Analysis

Reflective markers placed on anatomic landmarks; tracked by infrared cameras. Generates joint kinematics (angles), kinetics (moments and powers), and spatiotemporal parameters. Gold standard for quantitative gait analysis. Primary applications: Cerebral palsy surgical planning, prosthetic alignment, research.

### Force Plates

Measure **ground reaction forces** in three dimensions. Calculate joint moments and powers when combined with kinematic data. Center of pressure analysis for balance assessment.

### Electromyography (EMG)

Surface or fine-wire EMG records muscle activation timing and intensity during gait. Identifies premature, prolonged, or absent muscle activity. Guides surgical and pharmacologic intervention (e.g., selective dorsal rhizotomy, BoNT injection targets).

## Clinical Applications

**Pre-surgical planning** in cerebral palsy (multi-level surgery decisions). Prosthetic and orthotic optimization. Assessment of treatment outcomes (BoNT, surgery, rehabilitation). Falls risk evaluation in elderly and neurologic populations. Sports medicine biomechanical assessment. Medicolegal documentation of functional impairment.

![Instrumented gait analysis setup showing motion capture cameras, force plates, and EMG sensors](images/instrumented-gait-analysis-setup.png)

## Key Clinical Pearls

1. The normal gait cycle consists of 60% stance and 40% swing, with double limb support comprising 20% of the cycle; increased double support time indicates instability or pathology. 2. Gluteus medius function is critical for pelvic stability during single limb support; weakness produces a Trendelenburg gait or compensated trunk lean that is often the earliest sign of hip pathology. 3. Circumduction gait in hemiplegia results from the combination of ankle equinovarus, stiff knee, and inadequate hip flexion during swing; each component may be addressed with targeted interventions. 4. Instrumented gait analysis with 3D motion capture is the gold standard for surgical planning in cerebral palsy, providing kinematic and kinetic data that guide multi-level surgical decisions.

## References

1. Perry J, Burnfield JM. *Gait Analysis: Normal and Pathological Function*. 2nd ed. Thorofare, NJ: SLACK Inc; 2010.
2. Gage JR, et al. *The Treatment of Gait Problems in Cerebral Palsy*. London: Mac Keith Press; 2009.
3. Kirtley C. *Clinical Gait Analysis: Theory and Practice*. Edinburgh: Elsevier; 2006. 4. Baker R. "Gait Analysis Methods in Rehabilitation." *J Neuroeng Rehabil*. 2006;3:4.