Front Matter

Chapter 11 Veterinary Orthotics and Prosthetics 269

also be reduced. Likewise, if the counter force
locations are applied closer to the corrective
force location (shorter lever arm), the magni­
tude of force at the corrective force location will
be increased (Figure 11.3).
An increase in lever arm length creates a
mechanical advantage and a reduction of force
required. Reduced force is important because
all forces are applied to the mechanical struc­
ture (skeleton) through the soft tissues, which
are vulnerable to shear and pressure injury. In
our example the ideal AF would be the proxi­
mal cranial antebrachium and the ideal CMF
would be the distal manus (Figure 11.2).

Modified three‐point corrective system

The M3PCS is similar to the 3PCS with a modi­
fication of the corrective force location. Rather
than presenting a single point of corrective
force to the affected joint, the M3PCS splits the

corrective force location into a proximal and a

distal component. This technique avoids bony

prominences or anatomic joints that restrict

desired contact with the limb. Furthermore, the

addition of a second corrective force location

distributes the total magnitude of force acting

on the limb over a larger surface area. Increasing

surface area decreases point pressure and soft

tissue trauma.

In our example of carpal hyperextension, the

accessory carpal bone interferes with direct

access to the carpus. To apply a cranially

directed corrective force to the carpus, the CRF

would be applied directly against the accessory

carpal bone. Pressing directly against the small

surface area of a bone with tendon attachments

is not desirable due to the increased risk of

pressure sores and patient discomfort. The cor­

rective force location is split into two points of

contact just proximal and just distal to the

accessory carpal bone (Figure 11.4).

CRF = AF + CMF

Decreased CRF force

AF

AF

CRF = kg

CRF = kg

CMF

(A) (B)

CMF

Increased CRF force

Figure 11.3 The length of a rigid lever arm determines the required magnitude of force applied to the lever arm to
create the desired moment at the pivot point. Longer rigid lever arms (A) lead to smaller CRF, and shorter rigid lever
arms to greater CRF (B). AF, anchor force; CMF, counter moment force; CRF, corrective force.