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Ankle jerk ;Method of elicitation

It is an important deep tendon reflex of the lower limb
Other names of ankle jerk is Achilles reflex, as it is elicited by the blow on the Achilles tendon.
Being a deep tendon reflex, it is monosynaptic. It is also an example of  stretch reflex. It is an example of monosynaptic spinal segmental reflex. When it is  intact, integrity of the following is confirmed,cutaneous innervation, motor supply, and cortical input to the corresponding spinal segment.
Method of elicitation of ankle jerk
There are mainly 2 methods of elicitation of ankle jerk
Conventional method of elicitation of ankle jerk (patient in supine posture)
  • The patient is asked to lie  supine with the lower limb (to be examined) , flexed  at both hip     and knee and rotate it externally so that the lower leg rests across the opposite shin. The foot may rest on the opposite leg.
  • Then dorsiflex the foot at the ankle with the left hand and apply a sharp tap on tendo-achilles.
  • You can identify the Achilles tendon, a taut, discrete, cord-like structure running from the heel to the muscles of the calf. If you are unsure, ask the patient to plantar flex the foot which will result in  calf muscle contraction  and the Achilles to become taut.
  • Strike the tendon directly with your reflex hammer.
  • Make  sure that the calf if exposed so that you can see the muscle contraction.
  • A normal reflex will cause the foot to plantar flex (i.e. move into your supporting hand).
  • Watch and feel for plantar flexion at the ankle.
  • Note also the speed of relaxation after muscular contraction.
  • A positive result  is characterised by contraction of calf muscles with plantarflexion of foot.

If you are not able to elicit a response, a Jendrassikmaneuver can be tried
If the patient  cannot maintain this position, ask to lie supine, crossing one leg over the other in a figure 4.
The other alternative method is, arrange the legs in a frog-type position.
Ankle jerk in Sitting position
With the patient sitting, place one hand underneath the sole and dorsiflex the foot slightly. Then tap on the Achilles tendon just above its insertion on the calcaneus

Ankle jerk with patient in prone position
 Special method of elicitation of ankle jer
  •  Patient takes kneel-down position on a chair with both feet hanging out of the chair.
  • A sharp tap is applied on tendo-achilles (do not passively dorsiflex the foot).
  • Calf muscles contract and plantiflexion of foot occur .
  •  It is done specially in patients with myxoedema to elicit  the delayed relaxation time (myotonic reflex).
  •  Careful observation of delayed relaxation time in ankle jerk often clinches the diagnosis of myxoedema at the bedside.
 Myotonic reflex is classically demonstrated in ankle jerk

Ankle Jerk root value
This reflex is mediated by the S1 spinal segment of the spinal cord
Nerve involved is Sciatic Nerve

How to grade ankle reflex?
  • 4+   Very brisk, hyperactive, with clonus (rhythmic oscillations between flexion and extension)
  • 3+    Brisker than average; possibly but not necessarily indicative of disease
  • 2+    Average; normal
  • 1+    Somewhat diminished; low normal
  • 0      No response
Absent ankle jerk
  • The Achilles reflex checks if the S1 and S2nerve roots are intact and could be indicative of sciatic nerve pathology.
  • It is classically delayed in hypothyroidism.
  • This reflex is usually absent in disk herniations at the L5—S1 level.
  •  A reduction in the ankle jerk reflex may also be indicative of peripheral neuropathy.  
Causes of delayed relaxation of ankle jerk :
  • Myxoedcma (the contraction phase is delayed too)
  • Gross pedal oedema
  • Hypothermia
  • Obesity
  • Parkinsonism
  •  Diabetic polyneuropathy.