Sunday, June 4, 2017

Clonus - A review.

Hello everybody!
Let's review Clonus breifly today.

So what is it?
It is a series of rhythmic involuntary muscular contractions induced by the sudden passive stretching of a muscle or tendon.

Clonus occurs most frequently at the ankle, knee, and wrist, occasionally elsewhere.

The important Clonus that we all frequently examine is the Ankle Clonus so let's see that in detail here.

Ankle clonus is a series of rhythmic alternating flexions and extensions of the ankle.

How to do it?
The leg and foot should be well relaxed, the knee and ankle in moderate flexion, and the foot slightly everted.
The examiner supports the leg, with one hand under the knee or the calf, grasps the foot from below with the other hand, and quickly dorsiflexes the foot while maintaining slight pressure on the sole at the end of the movement.
A single tap on the tendon to elicit the ankle jerk may occasionally provoke clonus.

Unsustained clonus fades away after a few beats; sustained clonus persists as long as the examiner continues to hold slight dorsiflexion pressure on the foot.

Unsustained (transient) symmetric ankle clonus may occur in normal individuals with physiologically fast Deep Tendon Reflexes. Nonorganic clonus occurs rarely. False clonus (pseudoclonus) in psychogenic disorders is poorly sustained and irregular in rate, rhythm, and excursion.

Sustained clonus is never normal. In severe spasticity, clonus may occur spontaneously or with the slightest stimulus. At the ankle, true clonus can usually be stopped by sharp passive plantar flexion  of the foot or the great toe; false clonus is not altered by such a maneuver

Mechanism:
Part one - For ankle clonus, the sudden stretch of the gastrosoleus muscle elicits a contraction essentially analogous to a stretch reflex that causes a contraction with resultant plantar flexion of the foot. The foot goes down. 
Part two - This contraction increases tension in the Golgi tendon organs in the gastrosoleus tendon, sending a volley of impulses via the Ib fibers that then inhibit the contraction of the gastrosoleus and facilitate contraction of its antagonist, the tibialis anterior muscle.  The foot goes up. 
This in turn passively stretches the gastrosoleus, and the cycle is repeated.

A simpler explanation is alternating stretch reflexes.

A few other Clonus' seen are :

1) Patellar clonus :
It consists of a series of rhythmic up-and-down movements of the patella. It may be elicited if the examiner grasps the patella between index finger and thumb and executes a sudden, sharp, downward thrust, holding downward pressure at the end of the movement. 

The leg should be extended and relaxed. Patellar clonus may appear when eliciting the patellar or suprapatellar reflex.

2) Wrist Clonus :
It is produced by a sudden passive extension of the wrist or fingers.

3) Jaw Clonus occurs occasionally.

So that's all about clonus.
Hope it was helpful!

Let's learn Together!
-Medha!



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