Jendrassik manoeure?
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Jendrassik manoeuvre mechanism reflex reinforcement neurology
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Here is a thorough answer synthesized from Harrison's, Ganong's, and Kelley's textbooks:
Jendrassik Manoeuvre
What It Is
The Jendrassik manoeuvre is a reflex reinforcement technique used during neurological examination to augment deep tendon reflexes (DTRs) that appear weak or absent on initial testing.
How It Is Performed
- The patient flexes the fingers of both hands into a hook-like form and interlocks them together.
- The patient then attempts to pull the hands apart isometrically (without actually separating them).
- While the patient maintains this isometric effort, the clinician elicits the desired reflex.
Variations:
- For lower limb reflexes (patellar/Achilles): the interlocked-hand pull-apart is the classic technique.
- For upper limb reflexes: voluntary teeth-clenching serves as the reinforcing manoeuvre instead.
Mechanism
The mechanism operates via increased gamma (γ)-motor neuron discharge:
- Afferent impulses from the hands (during the pulling effort) travel to the spinal cord.
- This increases γ-motor neuron activity via descending excitatory pathways.
- γ-motor neurons innervate the intrafusal fibers of muscle spindles - increasing their tension and sensitivity.
- This lowers the threshold of the stretch reflex arc, making Ia afferent firing easier to provoke.
- The result is a stronger monosynaptic reflex response when the tendon is tapped.
As stated in Ganong's: "Trying to pull the hands apart when the flexed fingers are hooked together facilitates the knee jerk reflex (Jendrassik manoeuvre), and this may also be due to increased γ-motor neuron discharge initiated by afferent impulses from the hands." - Ganong's Review of Medical Physiology, 26th Ed.
The rheumatology literature also notes it "creates a diversion to help relax the" tested limb - suggesting a cognitive distraction component that reduces voluntary muscle guarding as well.
Clinical Use
| Situation | Relevance |
|---|---|
| Diminished or absent reflexes on first testing | Allows re-testing with enhanced sensitivity before concluding true areflexia |
| Anxious or tense patients | Reduces voluntary guarding that suppresses reflexes |
| Screening in neurology | Part of standard DTR assessment - biceps (C5/C6), brachioradialis (C5/C6), triceps (C6/C7), patellar (L3/L4), Achilles (S1/S2) |
| Lower motor neuron disease (peripheral neuropathy, Guillain-Barré, etc.) | Helps confirm true hyporeflexia/areflexia |
Grading Context
After using Jendrassik reinforcement, reflexes are still graded on the standard scale:
| Grade | Meaning |
|---|---|
| 0 | Absent (even with reinforcement) |
| 1 | Present but diminished |
| 2 | Normal |
| 3 | Hyperactive |
| 4 | Clonus |
A reflex that is 0 even with Jendrassik reinforcement is considered truly absent and is more clinically significant than one that requires reinforcement to appear.
Key Teaching Points
- Always try Jendrassik before calling a reflex absent - a 0 without reinforcement may be a 1+ with it.
- The mechanism is primarily via γ-motor neuron sensitization of muscle spindles, not just patient relaxation.
- H-reflex (electrophysiological equivalent of the stretch reflex) studies confirm it enhances monosynaptic reflex arcs specifically.
- Named after Hungarian physician Ernő Jendrassik (1858-1921).
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