What reflexes should be checked during a motor assessment, particularly in an adult patient with potential neurological or musculoskeletal conditions?

Deep Tendon Reflexes in Motor Assessment: B T S K A

The standard deep tendon reflexes to check during motor assessment are: Biceps (C5-C6), Triceps (C7-C8), Supinator/Brachioradialis (C5-C6), Knee/Patellar (L2-L4), and Ankle/Achilles (S1-S2) - this mnemonic "B T S K A" represents the five essential myotatic reflexes that should be systematically evaluated in adult neurological examination 1.

Essential Reflex Assessment Components

Standard Deep Tendon Reflexes

• Biceps reflex (C5-C6): Assess with the forearm in midway position (90°), as forearm position significantly affects reflex response 2

• Triceps reflex (C7-C8): Test bilaterally to identify asymmetry, which occurs frequently and should be documented 3

• Supinator/Brachioradialis reflex (C5-C6): Can be elicited by tapping the radial bone, though response depends on forearm position 2

• Knee/Patellar reflex (L2-L4): Use standard method first, then employ "superior patellar supine" method if initial attempt is unsuccessful, particularly in elderly patients 4

• Ankle/Achilles reflex (S1-S2): Begin with "plantar strike method" and if unsuccessful, use "Achilles strike elevated" method to avoid false-negative results 4

Clinical Interpretation Framework

Reflex Grading and Significance

• Diminished or absent reflexes suggest lower motor neuron disorders, peripheral neuropathy, or muscle disease 1

• Increased reflexes with abnormal plantar reflex indicate upper motor neuron dysfunction 1

• Asymmetric reflexes are clinically significant and reproducible on repeated examination, requiring investigation for focal pathology 3

Critical Technical Considerations

• Elderly patients: Standard methods alone produce false-negative results in 37% of knee reflexes and 84% of ankle reflexes due to paratonia/frontal rigidity 4

• Alternative techniques reduce error rates to 19% for knee reflexes and 21% for ankle reflexes when standard methods fail 4

• Left-right asymmetry occurs frequently in normal subjects but is reproducible and should be documented for comparison 3

Common Pitfalls to Avoid

• Forearm position errors: The brachioradial reflex response disappears in 94% of patients when the forearm is supinated, potentially leading to false interpretations 2

• Inadequate technique in elderly: Relying solely on standard methods misses reflexes that are actually present, leading to diagnostic errors 4

• Single assessment method: Using only one technique per reflex increases false-negative rates, particularly for ankle reflexes 4

• Ignoring stimulus-response relationships: Reflex amplitude varies with stimulus strength, requiring consistent technique for meaningful comparison 3