The sciatic nerve divides into the tibial and common peroneal nerves as it enters the popliteal fossa. The common peroneal nerve passes laterally winding around the neck of the fibula, whilst the tibial passes down the popliteal fossa lateral and superficial to the popliteal artery and vein.
Viewed with the patient prone, the probe is can be moved cranially and caudally. The two major divisions of the sciatic nerve can be seen diverging in the upper popliteal fossa and continuing distally.
The common peroneal gives sensory components to the knee, the sural nerve and the superficial and deep fibula (peroneal) nerves. This is the lateral lower leg and the dorsum of the foot. It supplies muscles that enable dorsiflexion of the ankle.
The tibial nerve sends sensory contributions to the ankle joint and the medial and lateral plantar nerves (sole of the foot). It supplies muscle of the calf enabling plantar flexion of the ankle and foot.
Sacha Schweikert with thanks to Graham Hocking and Tor Ercleve