Page 47 - Canine Lameness

2.2 ­inetic Analysis 19

Body Weight Distribution (%BWD) – This is calculated from PVF and is expressed as a percent-
age (Table 2.1). It represents the percentage of total body weight placed on each limb. For most
dogs, normal %BWD is 60% in the front limbs (30% right; 30% left) and 40% in the pelvic limbs
(20% right; 20% left). Lame dogs will shift their weight to the non‐lame legs and have a reduced
%BWD in the affected limb. It is less common that FP software programs will automatically
calculate these values. Therefore, clinicians may need to manually calculate these values.

2.2.4 Pressure-sensitive Walkway Systems: The Basics

Kinetic analysis with PSW systems is based on pressure, specifically paw pressure, instead of force
(Figure 2.2). Pressure is measured by thousands of sensors embedded in the walkway. The main
clinical benefit of PSWs is in reporting stride characteristics with temporospatial variables (TSVs,
described below), the ability to record several consecutive foot strikes, semiautomated analysis, and
improved portability. Manufacturers producing pressure‐sensitive systems commonly used with
companion animals include Tekscan, Inc. (Walkway™; Tekscan, South Boston, Massachusetts, USA)
and CIR Systems, Inc. (GAIT4Dog®; CIR Systems, Franklin, New Jersey, USA). Systems can vary in
overall physical dimension, measurement capabilities, as well as the degree of computerized auto-
mation. It is important that clinicians consider their needs before purchasing any kinetic system:
Dimensions – PSW systems often have longer working lengths than individual FPs allowing for
recording of multiple footfalls in one pass over the walkway (Figure 2.1C). PSWs can be pur-
chased in varying length, depending on clinical need (i.e. size of patient population).
Ideal Animal Size – A wide range of animal sizes can be easily evaluated due to the longer record-
ing platform (compared to serially placed FPs). Some PSWs have sensors of varying degrees of
resolution and PSWs with higher‐resolution sensors are recommended for use with smaller
companion animals.

Table 2.1 Commonly used calculations for gait analysis parameters.

Variable Example formula

Body weight distribution (%BWD) PVFor Pressure froma single limb
%BWD 100
TotalPVF or Pressure froom all limbs
Body weight normalization (%BW) Force experted by a limb Newtons
PVFas a% BW 100
e
Total weight of the dog Newtons
Percent change (%Change) X 2 X 1
%Change 100
X 1
Symmetry index (SI)
SI X R X L 100
1
2 X R X L
Symmetry ratio (SR) SR X R 100
X L