1.Spasticity is an increased
resistance to the passive movement of a joint due to abnormally high muscle
tone (hypertonia) which varies with the amplitude and speed of displacement of
a joint.
1.Rigidity is an increased
resistance to the passive movement of a joint which is constant throughout the
range of joint displacement and not related to the speed of joint movement;
resistance is present in both agonist and antagonist muscles.
2.Spasticity is usually uni-directional,
and is velocity and amplitude dependent.
2.Rigidity is bi-directional, and
is non velocity or amplitude dependent.
When it Happens: The important of such
differentiation is that spasticity is typically caused by damaged to the
corticospinal tract, while rigidity is usually extra-pyramidal in origin.
How to Assess and Differentiate:
A simple way to assess spasticity
is by fast flexion or extension of selected joint, typically the elbow or knee,
to elicit a sudden increase in tone. This demonstrate the velocity dependent
nature of spasticity. Another phenomenon known as clasp-knife phenomenon,
describe a sudden release of tone after an initial hypertonia of selected joint
movement when the examiner passively move the joint to the extreme, this
demonstrate the amplitude nature.
To test for rigidity, passively
move the joint in both direction, a relatively uniform rigidity in both agonist
and antagonist muscle group is known as lead-pipe rigidity; if there is tremor
superimposed with background increase of tone – cogwheel rigidity. These
rigidity is commonly seen in Parkinson’s disease.