Measurement of knee tendon reflex latencies in lumbar radicular syndromes.

The latency of the knee tendon reflex (KTR) in the vastus medialis muscle was measured by eliciting the reflex manually with a metal hammer. Normal values were obtained in a reference group of 35 subjects. The difference in right and left KTR was used as the parameter in the investigation of 20 patients with a proven L3 or L4 monoradicular syndrome; it was abnormal in 65% of the cases. In 10 patients an asymmetrical KTR was the only relevant abnormality in the combined electromyography and reflex study. Measurement of the KTR seems to be useful in the assessment of patients suspected of a lumbar radicular syndrome.