Iliopsoas: a new electromyographic technique and normal motor unit action potential values

To describe a reliable technique of needle electrode examination and present the normal values of motor unit action potential (MUAP) parameters in iliopsoas muscle.

Thirty-one normal subjects underwent quantitative electromyographic (QEMG) examination of the iliopsoas muscle, following an ultrasonographically confirmed technique of needle electrode insertion and sampling. The leg under examination was flexed, abducted and externally rotated at the hip joint and also flexed at the knee joint. A slight flexion at the hip joint was used to uncover iliopsoas from the overlying sartorius. This provides enough space at the inguinal region between the sartorius and the femoral neurovascular bundle. Mean and outlier values of MUAP parameters and polyphasia were calculated.

Our technique was easy to perform and secure in sampling iliopsoas. The mean +/- SD values for MUAP duration, amplitude, area, area to amplitude ratio, phases and turns were 11.5 +/- 1.35 ms, 419 +/- 71.5 microV, 633 +/- 142.7 microV ms, 1.57 +/- 0.25, 3.1 +/- 0.32, and 2.9 +/- 0.44, respectively. Lower and upper outlier limits for duration, amplitude, area and area to amplitude ratio were 3.6/20.7 ms, 150/930 microV, 100/1567 microV ms, and 0.35/3.07. Mean polyphasia was 12.6% (range 0-30%).

The suggested EMG technique helped to distinguish iliopsoas from sartorius and at the same time increased the accessibility of its anterior surface. Normal values and outlier limits of the MUAP parameters of iliopsoas have been quantitatively established.

This new technique and the normal MUAP values might prove helpful for the examination of iliopsoas, important in the assessment of many neuropathic and, especially, myopathic processes.