Tremor is a rithmitic oscillation of a part of the body. Despite
we all have a small component of tremor, there are pathologies with
very disabling forms of tremor. Pathological tremor are the most
common movement disorder and in many cases are resistant to the
most common treatments (pharmacological or surgical). Orthotic
management of tremor an be a suitable alternative to current tremor
treatments when these failed or when users are reluctant.

In the design of orthoses for tremor suppression, besides the orthotic
principles currently established, other kind of factors, derived
from the intrinsic dynamical characteristics of tremor, must be taken
into account.

These factors has been summarized in three principles:

1. Restrict the relative displacement between supports of consecutive
body segments to increase the effective dynamic stiffness in
the contact orthosis–body segment.

2. Increase the pressure of contact in the support of the orthosis
(with respect to conventional orthoses) to increase the effective
dynamic stiffness in the contact orthosis–body segment.

3. Design orthosis supports to ensure the contact between the orthosis
and the body segment at least in three different points
non–aligned to warrant the alignment between the orthosis and
the body segment.

Besides, pathological tremor has been characterized to understand
how its dynamic characteristics are related with severity and for the
estimation of the joint loads associated to trembling movements.
Two orthoses for tremor suppression in the upper limbs have been
built taking into account this information. One of the orthoses is driven
by DC motors and controls the movements of elbow flexion–extension,
wrist flexion–extension and forearm pronation–supination. The other
orthosis is driven by a linear damper made of magnetorheological
fluids.

Both orthoses have been tested in real patients. The results show
an effective reduction of tremor for tremor power over a threshold that
depends on the characteristics of the orthosis.

Orthoses reduce its effectiveness for the more severe cases of tremor
when acting as viscous dampers. When the orthoses act as notch filters,
the effectiveness apparently increases with tremor severity.
Results show that the biomechanical principles obtained are effective
to design tremor–suppression orthosis. However the efficiency
of the orthosis depends on the physical characteristics of the active
element incorporated to the orthosis.