Difference between spasticity and rigidity

Pocket knife – more force has to be applied in the initial phase of opening – as in clasp knife spasticity

Spasticity and rigidity are 2 types of hypertonic states elicited when examining the tone of limbs. It is important to differentiate between them to arrive at a correct diagnosis.

Spasticity:

  • Seen in pyramidal tract lesions
  • Classically termed ‘Clasp knife spasticity’ – more tone during the initial part of movement – as in opening a pocket knife
  • It is velocity dependant – should be elicited by fast movement of the muscle groups involved

Rigidity:

  • Seen in extrapyramidal lesions – like parkinsonism
  • 2 subtypes
    • Cog wheel rigidity – Tremor superimposed on hypertonia – resulting in intermittent increase in tone during the movement – felt as jerks
    • Lead pipe rigidity – Uniform increase in tone
  • Velocity independent – does not vary with speed of movement of muscle groups involved
Image credits: Matěj Baťha
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