Ultrasound Depiction of the Optimal Window for Needle Placement for Electromyography of the Short Head of the Biceps Femoris.

INTRODUCTION/AIMS: Accurate needle electromyography (EMG) of the short head of the biceps femoris (SHBF) is often important to localize nerve damage when proximal to the fibular head. Techniques have been proposed for accurate SHBF EMG; however, needle placement accuracy is low and with the risk of inadvertent needle placement into the long head (LHBF) potentially resulting in false localization and inappropriate operative management. This study aimed to define the optimal window for accurate SHBF needle EMG placement through ultrasound (US) investigation of the anatomical relationships of the SHBF, LHBF, and common fibular nerve (CFN) in the distal posterolateral thigh.

METHODS: Forty lower limbs from 20 healthy adults were evaluated using US. Distances from the popliteal crease (PC) to the SHBF and LHBF myotendinous junctions and position of the CFN in the popliteal fossa were recorded. The "SHBF window" was defined as the region where the SHBF muscle body is present in the absence of the LHBF.

RESULTS: The SHBF was located anterolateral to the LHBF tendon/muscle and the CFN medial to the SHBF in all limbs. The average distances from the PC to SHBF and LHBF muscles were 0.6 and 6.4 cm, respectively. The optimal "SHBF window" was identified to be 3-4 cm (2-3 fingerbreadths) proximal to the PC, anterolateral to the LHBF tendon in the distal thigh.

DISCUSSION: SHBF examination within this optimized window results in increased accuracy of needle placement, aiding in the electrodiagnostic localization of fibular nerve lesions.