Proper Technique for Performing Biceps Jerk Reflex
The proper technique for performing a biceps jerk reflex involves striking the biceps tendon with the reflex hammer while the patient's arm is positioned in a midway (90°) position with the elbow partially flexed. 1
Patient Positioning and Preparation
- Position the patient with their arm relaxed, elbow partially flexed, and forearm in a neutral or midway position (approximately 90° between pronation and supination) 1
- Ensure the patient is comfortable and the biceps muscle is neither fully contracted nor fully stretched 1
- The patient should be sitting or lying with shoulders relaxed and arms hanging freely at the sides 2
Examiner Technique
- Stand to the side of the patient's arm being tested 2
- Locate and identify the biceps tendon in the antecubital fossa (front of the elbow) 1
- Place your non-dominant hand's thumb or index finger firmly over the biceps tendon to stabilize it 1
- Hold the reflex hammer in your dominant hand 1
Proper Striking Technique
- Strike the examiner's finger or thumb that is positioned over the biceps tendon (not directly on the tendon) 1
- Use a quick, firm tap with appropriate force - not too hard to cause pain, but sufficient to elicit the reflex 1
- The strike should be delivered in a perpendicular direction to the tendon 1
Assessment of Response
- A normal response is a brief contraction of the biceps muscle, causing slight flexion at the elbow 1, 3
- The response should be compared bilaterally for symmetry 3
- Grade the reflex on the standard scale (0 = absent, 1+ = diminished, 2+ = normal, 3+ = increased, 4+ = hyperactive with clonus) 3
Important Considerations
- Forearm position significantly affects the reflex response - supination may diminish or eliminate the biceps reflex in normal subjects 1
- In patients with upper motor neuron lesions (e.g., stroke), the biceps reflex may persist in supination, indicating hyperreflexia 1, 3
- Avoid having the patient perform a Jendrassik maneuver (interlocking fingers and pulling) unless the reflex is difficult to elicit 3
- Ensure the muscle is relaxed before testing, as voluntary contraction can interfere with reflex assessment 4
Common Pitfalls to Avoid
- Striking the tendon directly instead of striking your finger placed over the tendon 1
- Testing with the forearm in full supination or pronation, which can alter reflex responses 1
- Using inconsistent force when comparing sides 3
- Failing to recognize that asymmetric reflexes may indicate pathology 3
- Not considering that the "unaffected" side in hemiparetic patients may also show pathological reflex changes 3