Comparing saphenous nerve conduction study techniques at the knee and at the ankle and their relationship to body mass index.

OBJECTIVE

To evaluate the saphenous sensory response by 2 methods and the correlation of obtaining responses bilaterally with body mass index (BMI).

DESIGN

Twenty patients evaluated by 1 electromyographer and 10 patients evaluated by 2 blinded electromyographers.

SETTING

University electromyography laboratory.

PARTICIPANTS

Thirty healthy adult volunteers.

INTERVENTIONS

Saphenous sensory response with the recording electrode at the level of the medial malleolus, saphenous sensory response with the recording electrode at the level of the proximal tibia, and sural sensory response with the recording electrode posterior to the lateral malleolus.

MAIN OUTCOME MEASURES

Sensory-evoked amplitude and distal latency.

RESULTS

The saphenous sensory response was obtained bilaterally at the knee in 77% of subjects, whereas it was obtained bilaterally at the ankle in only 50% of subjects (P<.05). BMI of greater than 25 kg/m2 resulted in more difficulty in obtaining the saphenous sensory response at the ankle compared with the response at the knee (P<.05).

CONCLUSIONS

The saphenous sensory response at the knee is more consistently obtained than the saphenous sensory response at the ankle, and it is not affected by BMI.