Biomechanical principles
It is important to understand some basic
biomechanical and treatment principles
associated with orthotic intervention.
Essentially, orthoses are biomechanical
devices working on three-point force
systems i.e. to change the position of any
joint manually in a controlled manner
requires the application of three forces
(Charlton, 2009).
For example, a common condition in
stroke patients is dropped foot (when the
weight of the foot or abnormal activity
pulls the foot/ankle into plantar flexion).
To correct a dropped foot, force is
applied to three points on the patient’s
leg and foot. The three-point force
system is illustrated in Figure 1.
By understanding where force is
needed to correct the problem, the
orthotist can design the orthosis
appropriately, or select a prefabricated
one, if appropriate. The corrective forces
are applied either by the structure of the
device or by straps, which again are