Chapter 6

Prosthetic Gait Analysis: Transtibial Amputation

Introduction

Understanding prosthetic gait deviations is essential for clinicians working with individuals who have undergone a lower extremity amputation. The ability to identify gait abnormalities and understand their underlying causes—whether patient-related or prosthetic in nature—allows for targeted interventions that can significantly improve a patient’s mobility and quality of life.

This chapter provides an overview of gait analysis for transtibial amputees, covering fundamental biomechanical concepts, sagittal and coronal plane deviations, and clinical approaches to problem-solving common gait abnormalities.

Fundamental Biomechanical Concepts

The Trochanter-Knee-Ankle (TKA) Line

Before understanding gait deviations in prosthetic users, clinicians must first grasp the concept of the trochanter-knee-ankle (TKA) line. This is an imaginary line drawn from the greater trochanter of the femur, through the center of the knee joint, and down through the ankle (approximately between the medial and lateral malleoli).

Figure 1: The Trochanter-Knee-Ankle (TKA) Line

When this line is extended through the ankle and into the prosthetic foot, it divides the foot into two functional components:

• Heel Lever: The posterior portion of the foot, behind the TKA line

• Toe Lever: The anterior portion of the foot, in front of the TKA line

Figure 2: The TKA line divides the prosthetic foot into the heel lever and toe lever

These lever arms play a critical role in determining knee stability and movement patterns during gait. The relative lengths of these levers can be modified through prosthetic alignment adjustments, which forms the foundation of prosthetic gait optimization.

Lever Arm Mechanics and Knee Control

The relationship between lever arms and knee motion follows predictable biomechanical principles:

• Longer heel lever → the knee sits relatively farther anterior to foot → GRF passes posterior to the knee → knee flexion moment

• Longer toe lever → the knee sits relatively farther posterior to foot → GRF passes anterior to the knee → knee extension moment

This relationship is fundamental to understanding how prosthetic modifications affect gait. When the ground reaction force moves anterior to the knee joint axis, it creates an extension moment; when it moves posterior, it creates a flexion moment.