How do I examine deep tendon reflexes (biceps, triceps, knee, ankle) in a patient?

How to Examine Deep Tendon Reflexes

To properly examine deep tendon reflexes, position the patient comfortably with the limb relaxed and partially flexed, strike the tendon directly with a reflex hammer using consistent force, observe for muscle contraction, and grade the response using the standard 0-4+ scale while comparing both sides for symmetry. 1, 2

Standard Grading Scale

The deep tendon reflex grading system uses a uniform 0-4+ scale that applies to all reflexes 1:

• 0: Absent reflex
• 1+: Diminished or hypoactive (trace response, less than normal)
• 2+: Normal reflex
• 3+: Brisker than average (possibly but not necessarily pathologic)
• 4+: Hyperactive with clonus (definitively abnormal)

Asymmetry between sides is often more clinically significant than the absolute grade, as comparison bilaterally may indicate focal pathology even when both sides fall within the "normal" range. 1

Biceps Reflex (C5-C6)

Positioning: Have the patient's arm partially flexed at the elbow with the forearm supinated (palm up) and resting on the examiner's forearm or the patient's lap. 2

Technique: Place your thumb firmly on the biceps tendon in the antecubital fossa and strike your thumb with the reflex hammer. 2

Expected Response: Flexion of the elbow as the biceps contracts.

Triceps Reflex (C7-C8)

Positioning: The patient's arm should be flexed at approximately 90 degrees at the elbow, with the arm supported either by holding it or having it rest comfortably. 1

Technique: Strike the triceps tendon directly above the olecranon process (the bony prominence at the back of the elbow) with the reflex hammer. 1

Expected Response: Extension of the elbow as the triceps contracts. 1

Important Note: The triceps reflex can be technically difficult to elicit in some normal individuals and may be absent in up to 27% of normal limbs, making it less reliable than other reflexes. 3

Knee (Patellar) Reflex (L2-L4)

Positioning: Have the patient sit with legs dangling freely or lying supine with the knee slightly flexed and supported. 2, 4

Technique: Strike the patellar tendon just below the kneecap with the reflex hammer. 2

Expected Response: Extension of the knee as the quadriceps contracts.

Alternative Method for Difficult Cases: In elderly patients with paratonia or frontal rigidity, use the "superior patellar supine" method if the standard approach fails, as this was the best single alternative method in 42% of difficult cases. 4

Ankle (Achilles) Reflex (S1-S2)

Positioning: Have the patient kneel on a chair with feet hanging free, or position the patient supine with the hip and knee flexed and the foot dorsiflexed. 2, 4

Technique: Strike the Achilles tendon directly above its insertion on the calcaneus. 2

Expected Response: Plantar flexion of the foot as the gastrocnemius and soleus contract.

Alternative Methods for Difficult Cases:

• The "plantar strike method" (striking the sole of the foot) was best or equal best in 64% of difficult cases 4
• The "Achilles strike elevated" method was best or equal best in 71% of difficult cases 4
• The Achilles reflex is typically affected earlier and more severely than the patellar reflex in length-dependent neuropathies 5

Key Technical Considerations

Force Application: Clinicians typically use three ranges of peak tap force 6:

• 0-20 Newtons for testing hyperreflexia
• 21-50 Newtons for normoreflexia

• 50 Newtons for hyporeflexia

Hammer Selection: The Taylor hammer (small mass, short handle) has a ceiling effect in the hyporeflexic range and may not generate sufficient force. 6

Patient Relaxation: Ensure the patient is relaxed, as anxiety or muscle tension can artificially alter reflex responses. Document any factors affecting cooperation. 1

Bilateral Comparison: Always test both sides for comparison and symmetry, as this aids in identifying potential pathology. 1, 7

Clinical Interpretation

Diminished or Absent Reflexes (0-1+) indicate lower motor neuron dysfunction 1, 5:

• Peripheral neuropathy (especially diabetic neuropathy)
• Nerve root compression (L2-L4 radiculopathy affects patellar reflex; L5-S1 affects ankle reflex) 5
• Anterior horn cell disease
• Neuromuscular junction disorders
• Myopathies

Hyperactive Reflexes (3-4+) indicate upper motor neuron dysfunction 1, 5:

• Corticospinal tract lesions
• Spinal cord pathology
• Cerebral lesions affecting motor pathways

Specific Nerve Root Testing 1, 2:

• Biceps: C5-C6
• Triceps: C7-C8
• Knee: L2-L4
• Ankle: S1-S2

Common Pitfalls to Avoid

In elderly patients, standard methods may incorrectly suggest absent reflexes in up to 37% of knee jerks and 84% of ankle jerks due to paratonia. Using alternative positioning methods reduces these error rates to 19% and 21% respectively. 4

Left-right asymmetry of reflex amplitudes occurs frequently in normal individuals and these differences are reproducible on repeated measurements, so isolated asymmetry without other neurological signs may not be pathologic. 7

Reflex amplitude variability is significant both within and between subjects, and most reflex amplitudes diminish during repeated examination after a short interval, so serial measurements should be interpreted cautiously. 7