What reflexes should be checked in a patient with sciatica?

Reflexes to Check in Sciatica

In a patient with sciatica, check the ankle reflex (Achilles tendon reflex) to assess for S1 nerve root involvement, and the knee reflex (patellar reflex) to evaluate L4 nerve root function. 1, 2

Primary Reflexes for Sciatica Assessment

Ankle Reflex (Achilles Tendon Reflex)

• The ankle jerk reflex is the most critical reflex to assess in sciatica, as it directly evaluates S1 nerve root function 2, 3
• L5-S1 disc lesions—the most common cause of sciatica—typically affect the ankle jerk reflex rather than the knee jerk 2
• The Achilles tendon reflex is more sensitive than the H-reflex for detecting S1 root compression syndromes 3
• An absent or diminished ankle reflex strongly suggests S1 nerve root compromise 3

Knee Reflex (Patellar Reflex)

• The knee jerk reflex is mediated primarily by L3-L4 nerve roots and helps evaluate upper lumbar pathology 2
• This reflex is not typically affected by L5-S1 disc lesions, which account for over 90% of symptomatic lumbar disc herniations 4
• Include knee reflex testing as part of a complete neurological evaluation to rule out higher lumbar nerve root involvement 1

Complete Neurological Testing Protocol

Beyond reflexes, guidelines recommend a comprehensive neurological assessment that includes: 1

• Temperature sensation - tests small fiber function 1
• Pinprick sensation - evaluates pain pathways 1
• Vibration perception (using 128-Hz tuning fork) - assesses large fiber function 1
• Pressure sensation (using 10-g monofilament) - identifies risk of foot ulcers 1
• Motor strength testing - particularly knee strength for L4 evaluation and foot dorsiflexion/plantar flexion for L5/S1 4, 2

Common Pitfalls to Avoid

• Do not assume a normal knee reflex rules out sciatica - most sciatica involves L5-S1 levels which do not affect the knee jerk 2
• Neither the H-reflex nor Achilles tendon reflex is useful for detecting L5 root compression - these tests specifically evaluate S1 function 3
• Reflexes may be normal in purely inflammatory nerve root conditions - palpation and other clinical tests may be needed when inflammation rather than mechanical compression predominates 5
• Absent reflexes alone do not confirm the diagnosis - correlation with dermatomal sensory loss and motor weakness is essential, as dermatomes can be unreliable 5

Clinical Context

The American College of Physicians emphasizes that physical examination findings, including reflexes, should correlate with imaging findings when present 1. Back pain with radiculopathy or clinical signs including absent lower limb reflexes suggests demonstrable nerve root compression 1. However, the natural history of lumbar disc herniation with radiculopathy shows improvement within the first 4 weeks in most patients regardless of reflex findings 1.