Page 44 - Canine Lameness

16 2 Objective Gait Analysis

2.2.1 Force Plate Systems: The Basics
FPs measure force or more specifically ground reaction forces (GRF). Put simply, GRF are the equal
yet opposing force produced when an animal’s foot interacts with the ground. For example, when
we stand still on solid ground here on Earth, we are exerting a downward force on the ground that
is equal to the product of our mass and Earth’s gravity (F = m × g). The reason that we do not sink
into the ground is because the ground is exerting an equal and opposite upward force. This concept
was first described by Sir Isaac Newton and is known as Newton’s third law. When we move, as
compared to standing still, these forces are exerted in multiple directions, not just up and down.
These equal and opposite GRF produced when moving are the main focus of kinetic analysis with
FP systems.
FP systems are a staple in most modern veterinary gait laboratories (Figure 2.1A) and have long
been considered the gold standard in kinetic measurement of lame animals. However, there are
aspects of these systems that must be considered by clinicians:

Ideal Animal Size – FPs often have a shorter working length compared to PSW systems
(Figure 2.1B). Because of this, evaluating individual footfalls can be challenging in smaller ani-
mals or animals with shorter stride lengths. This makes typical FPs ideal for medium‐ to large‐
breed dogs. A method of adapting an FP for smaller animals has been described but is difficult
in a clinical setting (Kapatkin et al. 2014).

(A) (B)

(C) (D)

Figure 2.1 Kinetic and kinematic equipment: (A) modern veterinary gait laboratory; (B) dual (in‐line) force
plate system; (C) pressure‐sensitive walkway (PSW) system (Tekscan Walkway™); and (D) weight distribution
platform.