A 50-year-old woman has acute low back pain with radiation along the anterior and medial aspect of the right thigh and shin. She has weakness of knee extension, a depressed right knee jerk, and numbness over the medial leg. Straight leg raise is negative bilaterally. Which additional finding would support the diagnosis?

• A Loss of sensation over the lateral foot and sole
• B Reproduction of pain on dorsiflexion of the ankle during straight leg raise
• C Absent ankle jerk on the right
• D Reproduction of thigh pain on extension of the hip with the knee flexed ✓

Explanation

An L3-L4 disc prolapse compresses the L4 root, producing quadriceps weakness, a diminished knee jerk, and sensory loss over the medial leg and thigh. Because the L4 root is less tensed by the standard manoeuvre, the straight leg raise is often normal; the femoral nerve stretch test, hip extension with the knee flexed, reproduces the anterior thigh pain. An absent ankle jerk and lateral foot numbness point instead to an S1 root lesion from L5-S1 prolapse.

Reference: Apley's System of Orthopaedics and Fractures, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.