Motion analysis of normal patellar tendon reflex.

Background: Reflex assessment, an essential element in the investigation of the motor system, is currently assessed through qualitative description, which lacks of normal values in the healthy population. This study quantified the amplitude and latency of patellar tendon reflex in normal subjects using motion analysis to determine the factors affecting the reflex amplitude. Methods: 100 healthy volunteers were recruited for patellar tendon reflex assessments which were recorded using a motion analysis system. Different levels of input strength were exerted during the experiments. Results: A linear relationship was found between reflex input and reflex amplitude (r = 0.50, P < 0.001). The left knee was found to exhibit 26.3% higher reflex amplitude than the right (P < 0.001). The Jendrassik manoeuvre significantly increased reflex amplitude by 34.3% (P = 0.001); the effect was especially prominent in subjects with weak reflex response. Reflex latency normality data were established, which showed a gradual reduction with increasing input strength. Conclusion: The quantitative normality data and findings showed that the present method has great potential to objectively quantify deep tendon reflexes.