Log in with your email address username.

×

Attention doctorportal newsletter subscribers,

After December 2018, we will be moving elements from the doctorportal newsletter to MJA InSight newsletter and rebranding it to Insight+. If you’d like to continue to receive a newsletter covering the latest on research and perspectives in the medical industry, please subscribe to the Insight+ newsletter here.

As of January 2019, we will no longer be sending out the doctorportal email newsletter. The final issue of this newsletter will be distributed on 13 December 2018. Articles from this issue will be available to view online until 31 December 2018.

Ankles jerk — yes, but how?

- Featured Image

Eliciting an ankle jerk is not a trivial task. It requires the skills of an experienced bell-ringer, an expert golfer and a mechanical engineer. The experience of the examiner and the positioning of the patient are two factors contributing to the accuracy of reported findings.1,2 Accurate findings can provide invaluable clinical information.

When an ankle jerk is elicited, the response can be seen, felt and heard. When the response is present, the tendon produces an undamped oscillation heard as a “boing”, and when it is absent, the damped oscillation is heard as a dull “thud”.

Percussion on the Achilles tendon activates muscle spindles — specialised sensory receptors within the muscle that respond to stretch (lengthening) and vibration. Action potentials move centripetally via large diameter, myelinated, fast conducting fibres, and trigger responses in the spinal cord from α motor neurones that mediate muscle contraction. The magnitude and rapidity of the reflex response is modulated by both autonomic sympathetic tone and descending (upper motor neurone) inhibition.3

Reflex activation is faster and stronger when sympathetic nervous system tone is high. Patients who are anxious, thyrotoxic or withdrawing from alcohol will have stronger, brisker…

email