9.1 Neurologic Examination: Reflex Testing
Key Takeaways
- Deep tendon reflex (DTR) grading uses the 0–4+ scale, with 2+ considered normal; compare sides and reinforce with the Jendrassik maneuver when reflexes appear absent.
- The patellar reflex tests the L2–L4 myotome (femoral nerve), while the Achilles reflex tests S1–S2 (tibial nerve); asymmetric loss localizes to the affected segment or nerve root.
- An extensor plantar response (positive Babinski sign) indicates an upper motor neuron (UMN) lesion above the L5–S1 level and is never a normal finding in adults.
- Hyperreflexia with clonus, spasticity, and a positive Babinski sign form the classic UMN pattern; hyporeflexia or areflexia with fasciculations suggests a lower motor neuron (LMN) or peripheral nerve lesion.
- Superficial reflexes (abdominal, cremasteric) are lost with UMN lesions and may be absent in normal elderly patients or after abdominal surgery; the plantar response remains the most clinically tested superficial reflex on board exams.
Why Reflex Testing Matters on Part II
Reflex examination is one of the fastest ways to distinguish upper motor neuron (UMN) pathology from lower motor neuron (LMN) or peripheral nerve disease — a distinction tested repeatedly on the National Board of Chiropractic Examiners (NBCE) Part II written examination. Reflex questions usually pair a brief vignette (weakness, gait change, trauma history) with a described reflex pattern and ask you to localize the lesion, name the segmental level, or choose the next appropriate test. Because reflexes are objective and difficult for patients to fake, they are high-yield clinical data points that also connect to diagnosis chapters on central and peripheral neurologic disorders.
Deep Tendon Reflexes (DTRs)
A deep tendon reflex is a monosynaptic stretch reflex: rapid muscle stretch activates muscle spindle Ia afferents, which synapse directly on alpha motor neurons in the spinal cord anterior horn, producing a brief contraction of the stretched muscle. DTRs are tested with the patient relaxed, the limb in a partially flexed position, and a reflex hammer delivering a sharp tap to the tendon — not the muscle belly.
Standard DTR Grading (0–4+)
| Grade | Description | Clinical Meaning |
|---|---|---|
| 0 | Absent — no contraction even with reinforcement | Areflexia; consider LMN lesion, peripheral neuropathy, or acute radiculopathy |
| 1+ | Trace — only a flicker, often requiring reinforcement | Hyporeflexia; may be normal variant or early pathology |
| 2+ | Normal — brisk, symmetric response | Expected finding in healthy adults |
| 3+ | Brisk — exaggerated but not sustained | May indicate UMN irritation; correlate with tone and Babinski |
| 4+ | Very brisk with clonus (rhythmic oscillations) | Strongly suggests UMN lesion |
Always compare right and left. A one-grade asymmetry is clinically significant when paired with weakness, sensory loss, or pathological reflexes.
Segmental Levels and Testing Technique
| Reflex | Tendon Struck | Segment / Nerve | Patient Position |
|---|---|---|---|
| Biceps | Biceps tendon in antecubital fossa | C5–C6 / musculocutaneous | Seated, forearm partially flexed and supinated |
| Brachioradialis | Distal radius (styloid process) | C5–C6 / radial | Seated, forearm neutral or slightly pronated |
| Triceps | Triceps tendon above olecranon | C7–C8 / radial | Seated or standing, arm supported, elbow flexed ~90° |
| Patellar (knee jerk) | Patellar tendon below patella | L2–L4 / femoral | Seated with knee flexed ~90° or supine with knee slightly flexed over examiner's hand |
| Achilles (ankle jerk) | Achilles tendon | S1–S2 / tibial | Supine or kneeling; dorsiflex ankle slightly and strike tendon |
Board trap: The patellar reflex is the classic L4 test, but its arc involves L2–L4 roots. Loss of the Achilles reflex with preserved patellar reflex points toward S1 radiculopathy (common in L5–S1 disc herniation affecting the S1 root).
Reinforcement: The Jendrassik Maneuver
When reflexes appear absent or diminished, ask the patient to clench the teeth, interlock fingers, and pull the hands apart (or plantar-flex the feet forcefully for lower-extremity testing). This distraction maneuver increases descending facilitatory input and can unmask a normal reflex that was suppressed by anxiety or incomplete relaxation. Failure to reinforce before documenting areflexia is a common clinical — and exam — error.
Superficial Reflexes
Superficial reflexes are polysynaptic responses to light stroking of the skin. They require intact peripheral nerves, spinal cord integration, and — unlike DTRs — an intact corticospinal (UMN) tract for normal expression.
| Reflex | Stimulus | Normal Response | Segment |
|---|---|---|---|
| Abdominal | Light stroke lateral to umbilicus toward midline | Ipsilateral umbilical deviation | T8–T10 (upper), T10–T12 (lower) |
| Cremasteric | Stroke inner thigh (male patients) | Ipsilateral testicular elevation | L1–L2 |
| Anal wink | Pinprick or stroke perianal skin | Anal sphincter contraction | S4–S5 |
| Plantar (Babinski test) | Firm stroke along lateral sole, curving medially across metatarsal heads | Flexion of great toe (normal adult) | L5–S1 (with UMN modulation) |
Abdominal reflexes may be absent bilaterally in obesity, multiparity, prior abdominal surgery, or advanced age without indicating pathology. Unilateral loss, however, suggests a contralateral UMN lesion at the corresponding thoracic level.
The plantar response is the single most tested superficial reflex. In adults, the normal response is plantar flexion of the great toe. Dorsiflexion of the great toe with fanning of the other toes is the positive Babinski sign — pathognomonic for UMN dysfunction above the segmental reflex arc (typically above L5–S1 in the spinal cord or brain).
Pathological Reflexes
Pathological reflexes are release phenomena: primitive reflexes that re-emerge when UMN inhibition is lost.
| Reflex | How to Elicit | Positive Finding | Localizing Value |
|---|---|---|---|
| Babinski | Plantar stroke as above | Great toe extension + toe fanning | UMN lesion (cord, brainstem, cortex) |
| Hoffman sign | Flick middle fingernail downward | Thumb flexion / index finger flexion | UMN lesion at C6–T1 or above |
| Clonus | Rapid dorsiflexion of foot (or patellar push) | ≥3 rhythmic beats of foot oscillation | UMN lesion; sustained clonus is always abnormal |
| Palmomental | Stroke thenar eminence | Ipsilateral chin twitch | Frontal lobe / corticobulbar pathway (non-specific) |
| Grasp reflex | Stroke palm | Involuntary finger flexion | Frontal lobe release (dementia, stroke) |
Hoffman sign in isolation may be seen in healthy patients with hypermobility or anxiety; on exams, pair it with other UMN findings (spasticity, hyperreflexia, Babinski) before localizing to the cervical cord.
Integrating Reflex Patterns: UMN vs LMN
| Finding | UMN Lesion | LMN Lesion |
|---|---|---|
| Tone | Spasticity (velocity-dependent) | Flaccidity |
| DTRs | Hyperreflexia (3+ to 4+) | Hyporeflexia / areflexia (0–1+) |
| Pathological reflexes | Babinski (+), Hoffman (+), clonus | Absent (fasciculations may be present) |
| Muscle bulk | Normal early; later atrophy from disuse | Early atrophy |
| Babinski | Positive (extensor plantar) | Negative (flexor plantar) |
Clinical vignette pattern: A patient with sudden unilateral weakness, increased tone, brisk reflexes, and a positive Babinski sign has an UMN lesion — think stroke, spinal cord compression, or demyelinating plaque. A patient with foot drop, absent ankle reflex, and thigh atrophy has an LMN pattern — think L5 radiculopathy, peroneal nerve palsy, or polyradiculopathy.
Practical Tips for the Chiropractic Setting
Reflex testing belongs in every neurologic screening when history suggests radiculopathy, myelopathy, or systemic neurologic disease. Document findings precisely (grade and side), reinforce before calling a reflex absent, and never interpret a single finding in isolation. When reflexes conflict with strength testing — for example, 5/5 strength with absent Achilles reflex — consider early radiculopathy, medication effect, or diabetes-related neuropathy, and correlate with dermatomal sensation and orthopedic provocative tests covered elsewhere in the NMS examination.
A 58-year-old patient reports progressive right leg stiffness and difficulty walking. Examination reveals 3+ patellar and Achilles reflexes on the right, sustained ankle clonus, and upgoing great toe on the right plantar stroke. Tone is increased in the right lower extremity. Where is the most likely lesion?
Which deep tendon reflex primarily evaluates the S1 spinal segment and tibial nerve function?
A reflex is graded 0 on initial testing in a anxious patient with otherwise normal neurologic findings. What is the most appropriate next step before documenting areflexia?
Unilateral absence of the upper abdominal reflex (umbilical deviation) with all other superficial reflexes intact on the same side most strongly suggests: